Hi there folks,

need some thoughts on a TBI problem that a friend of mine has with his '90 4.3 Astro. Yes I know it's not a thirdgen, but I do know that this board here is great and full of knowledgeable people willing to help
I've been looking at some threads but didn't find what I was looking for..

So far i've done some WinALDL logging and it seems the INT / BLM will always end up somewhere around the 110 mark when warm, after driving around for half an hour. Knock counter is around 30. CTS seems right, about 90ish °C. TPS, RPM and VSS signal also seem fine.

Idle is getting kinda rough when warm and also seems a little misfiring here and there, also could be a little higher rpm I think, but no wild sagging.
On acceleration, I got 2 lean intake backfires at around half throttle (by feel), when I get into it slowly it doesn't seem that bad but feels a little slow. WOT is generally not bad either.
I do get a rich O2 code, but to me it rather seems something's making it run lean? Thought about making a run with O2 unplugged and see if it clears up without the fueling adaption?

O2 (4 wire heated delco), plugs (some accels i don't like tho), rotor, cap and cables & EGR (type?) are rather new (2 years old but less than 1000 miles on them). Vehicle gets driven rarely (needs legal issues fixed before getting back on the street with regular tags).

Looking for a time-efficient way to troubleshoot this symptom.. Thanks in advance!

Greetz from Austria
Andi

 

Where is the initial timing?

What is the fuel pressure UNDER LOAD?

Any signs of catalytic converter plugging?

 

1) haven't checked, on the to do list
2) haven't checked but not sure it would make a difference if it runs ok cold and starts well in any condition
3) not to me anyways, what symptoms could be explained by that?
Thanks Schurkey!
Anyone else maybe?

 

Poor fuel pressure could cause a lean condition when the throttle is depressed. Just like you're complaining about.

Plugged converter could cause excess back-pressure, it would be worse with additional throttle opening. Just like you're complaining about.

 

ok i just want to understand the whole system and your thinking behind this, so got some more questions for you please bear with me.

@2: of course the lean condition makes sense coming from a low fuel pressure situation, but as said i only had two lean pops and otherwise the O2 shows a rich condition? like, it's pulling fuel, so i doubt the fuel pressure would be low?
@3: i understand about the back-pressure, but how would that produce the rich indication of the O2?

 

said friend just sent me results of an emissions test that thing failed last year. unfortunately the shop that did it was foolish enough to do it at about 25°C (80°F) oil temperature, so i was expecting to see lambda < 1. tests are not done on a roller, just in P/N.

first test "idle rpm" 770rpm, Toil = 23°C
Lambda 1.119 (16.5:1 AFR)
CO %vol 3.81
CO2 %vol 8.7
O2 %vol 5.2
HC ppmHEX 744

second test, 2640rpm, Toil = 25°C
Lambda 1.292 (wow, that converts to about 19:1 AFR!?!)
CO 0.24
CO2 11.0
O2 5.2
HC ppmHEX 408

gotta be some exhaust leak? that lean can't be right, it would barely run.
somewhat high HC i think is attributable to cat not being warmed up.. guess at these temperatures and high lambda you can't make any other statements anyways.

will progress with fuel pressure testing and initial timing check.

 

Fuel ratio that lean sounds like misfire to me. The entire cylinder's worth of O2 goes out the exhaust port without combining with the fuel. The excess O2 should throw lean codes, not rich codes.

A plugged catalytic converter will drop intake vacuum, the MAP sensor will direct the computer to add fuel thinking the engine is under load. This produces a conflict between the O2 sensor (low oxygen) and the ECM programming where the fuel trim is driven lean to compensate.

Your fuel trim is being driven lean. I'd open a hole in the exhaust pipe ahead of the converter, see if it runs better. Or, you could unbolt the converter and look inside--maybe you can see that it's plugged or melted.

 

Schurkey, thanks for detailling that!
The misfiring is a possibility but thinking this would also be reflected by the O2 content in the 4 gas test, no? I really think the values are not really good for indicating anything without establishing a tight exhaust path and normal operating temperature first.

I think for checking converter I might just unplug the O2 sensor and try open loop with a "pressure relief" in case the catcon produces too much backpressure.

About the intake vacuum/MAP value.. isn't the engine actually operating at higher load with the increased back pressure?

 

Yes.

Unless you're looking for problems during the warm-up.

If you're going to disconnect the O2 sensor, screw the thing out of the manifold--that accomplishes both goals. Open loop, and a hole for the exhaust to go out of. You'll want to pay attention to what the exhaust will be blowing on, as it rushes out of the hole.

Not in a meaningful way. More fuel and open throttle doesn't help, where more fuel and open throttle might work well to drag a trailer up a hill.

 

the way i see it, the O2 content on the 4 gas analysis doesn't show that much excess O2 like from a misfiring cylinder? however, that may also depend on how the resulting value is averaged/filtered when that cylinder is only dumping its unburnt A/F once per revolution..

good point on unscrewing the o2 while at it, and what it will be blowing on. however, i couldn't be sure what solved the problem if that works so i'd rather isolate the two approaches i guess.

more load not in a meaningful way in that it is not producing any increased motive power, yes, but it is still higher load (less vacuum) and therefore would be needed to be compensated by more fuel for my understanding?

thanks for your pointers.

 

A silicone poisoned O2 sensor will report rich. Driving the INT & BLM down to the point that the engine will cut out. BTDT.

RBob.

 

No. No amount of additional fuel and additional air will "compensate" for a plugged exhaust. Increased load (REAL "load") is readily compensated-for by more throttle opening, and spraying a bit more fuel--to the limit of the engine's torque curve.

Really good point, and one I should have been sensitive to.

Off-topic: What causes an O2 sensor to report false-lean conditions? I had an O2 sensor in my K1500 that would set lean codes at highway speed, but seemed to respond just fine at lower speed. I spent two years on-and-off trying to diagnose that. I finally just said "fukkit" and replaced the O2 sensor, because I couldn't find ANYTHING else wrong--poof, end of trouble codes at highway speed, and end of fuel trim numbers showing a rich-command.

This O2 sensor had something like 60--70 thousand miles on it, it was installed at the same time as a "crate engine" and complete exhaust system. Was never poisoned by coolant loss, oil consumption, or RTV silicone. The engine did spend a fair amount of time at 70+ mph and up. It came out in two pieces--but I can't guarantee that it didn't break as I was unthreading it.

Given the amount of time I wasted on that--and the number of times I re-set the Check Engine light...and the amount of fuel I wasted...I've become more open to the idea of replacing an O2 sensor if there's any question about it's performance.

 

Ok so i got some time to look into this again now.
Disconnected o2 sensor signal, very rough at idle, revving or under load. Would pop (not sure if rich or lean?) through TB under certain higher load situations. When connecting o2 again at idle it was hovering around 0.7volts and then slowly decreased to around 0.45-0.50v.
0.7 would indicate only slightly rich tho? I reset the PCM before trying this so INT/BLM were at 128.

Will borrow timing lamp on the weekend, already got TBI fuel pressure tester.

Also noticed that at warm idle MAP value in gear is roughly like 50..60kPa and 40..42 in P/Nif that helps with any diagnosis.

 

took another look at it yesterday. timing turned out to be at about 2° (should be 0° stock) and played with it a little, seemed to me it ran better at 4° (lower MAP at idle and less misfiring, felt like more torque throughout the band too). also checked and reseated spark plug wires. running it with connected o2 again, seems to get better after a while of driving around but still feels kind rough at idle and at low load, then seems it clears up at higher rpm/tps.
got winaldl to learn in some blm cells, some while ago it would always quit receiving valid frames for some reason.

anyone has an idea why the blms would be that much all over the place? see below. no more rich code but still rough/misfiring in some areas.

still need to check fuel pressure. looked at injector spray pattern and it didnt seem too bad to me, read sth about using the timing light connected to the coil wire to check that?

thanks for any and all inputs!

 

no one on these blms?

 

So my friend asked me to go look at the van again. He barely drives it but the last times he did to move some stuff around, it would stall out only after some minutes and wouldn't restart unless sitting for some time, and when it did it was kinda random.

I checked the following things...

-) Oil level ok and oil pressure gauge shows ok pressure. Unplugging the oil pressure switch with the engine running didn't change anything.
-) Fuel level ok, fuel pressure is ok
-) Timing is between the reported 0 and 2 degrees and i also tried with EST disconnected and it still stalled and wouldn't spray on restart attempt.
-) when it stalls, fuel pressure is also ok at key-on and cranking. when i spray with starter spray, it will chug and almost start, so that's telling me spark and ignition etc is kinda ok.

when it's sitting over night, it would always fire up and run for some minutes before stalling.
I'm thinking it could be the ignition module or fuel pump relay, which is not telling the ECM to fire the injectors or sth alike?

Thanks for any inputs.

 

1. What, in PSI, is "OK fuel pressure"?
2. If the engine has reasonable oil pressure, the fuel pump relay could be REMOVED and the engine will still run--because the oil pressure switch provides a redundant power source for the fuel pump.
3. If there is a problem with the distributor pickup coil, the computer does not get a proper sense that the engine is cranking--so it doesn't spray fuel. Failed magnets on the pickup coil are very common, leading to weak pickup coil signal to module. My own truck had a high-speed misfire that degraded into lower-speed stalling with (sometimes) difficult re-start. A replacement distributor mainshaft (or replacement distributor) fixed it.

 

Ownor

Check base timing. With EST plug open timing should be 0 to +2deg advanced. Idle speed will be low - around 575 to 625RPM. With EST plug connected and ECM controlling timing, at idle (650 to 700 RPM), fully warmed coolant temperature (CTS =85 to 90C) timing should be bouncing between 16 to 21 deg.

2x with Schurkey - distributor reluctor magnets are known to fall-off! Small hat dizzy is notorious for moisture condensation and reluctor ring is prone to rust. I would check state of the distributor before moving forward. Please note that with out distributor reference pulse (DRP) ECM will not fire injectors nor will it activate FP relay during cranking. This common no start condition when ICM fails or reluctor coil develops open. During cranking, while receiving DRP pulse, ECM will activate FP relay and pulse injectors. Oil pressure switch acts as back up (back up redundancy) to FP relay.

//RF

 

Thanks for your input guys!

@Schurkey:
1. OK fuel pressure = around 11 psi +-1 in all conditions I checked. IIRC TBI Service Range is 9-13 psi.
2. Thanks for the info, had that in backwards then about the FP Rel and the OPS. So then it can't be the fuel pump relay either that causes it to stall out (and the pump is running anyways, since I can see fuel pressure is present?)
3. see below

@RF
Checked timing as stated and it was somewhere between 0-2, no big problems here either. It wasn't warmed up at all though for the check, maybe 20°C CTS, but wouldn't stay running any longer so I left it at that. I haven't checked with EST connected, will do next week when I get there. Is there a big influence from idle speed here, with EST unconnected? Haven't checked it but was about normal.

It does have a small hat dizzy. I did pull dizzy out to check, but was more focused around gear condition and shaft play (marginal).
Yes, exactly, DRP.. I forgot that name. That was also my trace somehow.. Is there something I can do to nail that one down by multimeter use when it stalls out and won't restart?
I'm not 100% sure how it's designed here - the prone-to-fall-off magnets you are talking about here are on the distributor shaft, and the coil is the ring around that *picks up* revolutions by utilization of the hall effect, right? Which is afterwards amplified by the ignition module and creates the DRP for the ECM...? Something along these lines?

Edit: upon re-reading, I noticed that without a DRP the ECM might not fire the injectors, but since it did start chugging along with starting fluid, i can see that it actually triggers the spark plugs.. how is that possible if the pickup coil doesn't pick up the distributor revolutions correctly?

 

ownor

ICM - ignition control module (8 pin) performs a dual function. As rotor in the distributor turns reluctor coil produces a zero crossing AC voltage waveform. ICM takes that waveform and produces DRP signal and sends it to ECM. You'll need an oscilloscope to observe DRP pulse. A true RMS voltmeter may give you an indication that DRP signal is present. At the same time another portion of the ICM circuitry produces ignition primary coil charging current. Under 400 RPM ICM runs at a fixed timing to provide ignition coil control current. Above 400 RPM ECM control signal overrides ICM internal circuit. This way at engine speeds above 400 RPM ECM can control timing of the ignition.

You may be getting spark since this portion of ignition circuit is functional, but if the DRP signal does not reach ECM it, in turn, will not fire injectors. Using starting fluid is a substitute for injector firing - i.e. delivering fuel.
You can always put a test light on injector terminal to see if test light blinks - to determine if ECM is firing injectors. No blinky - no firing.

//RF

 

Yes, except it isn't Hall Effect. The distributor reluctor and pickup coil represents a specialized alternator of sorts. The amperage output of the pickup coil is microscopic, the voltage output is merely low. The shape of the waveform is also somewhat unusual, in that when going from - to +, the slope is relatively gentle, but going from + to - the slope is a dramatic plummet of the sort usually reserved for the first drop of a major roller-coaster. Well, steeper than that, actually. The module uses the plummeting voltage as it's trigger, because it's unmistakable. So RFMaster is correct about the zero-crossing being the trigger, but it's only the dramatic, plummeting zero crossing from positive to negative. The other zero-crossing--from negative to positive--is relatively mild, and is ignored by the module.

That's also the reason that GM has two "magnetic polarities" of pickup coil for the older HEI distributors. Because the pickup coil acts as an antenna for stray RFI, the pickup coil polarity is chosen so that the most-likely (or most-harmful) RFI is provided to the module as negative-to-positive polarity, so the module ignores it. A pickup coil with a yellow color code is build with a certain magnetic polarity, a pickup coil with a black, blue, or clear color code is the opposite magnetic polarity.

A Hall-Effect sensor produces a square wave; the pickup coil/reluctor produces a goofy, curvy triangle wave. Other manufacturer's ignition systems rely on Hall Effect, and some Delco HEIs have a Hall-effect sensor for specialized purposes--but the normal, everyday reluctor/pickup coil system isn't like that.

None of this matters in your situation. I'm just being picky.

 

Thanks for the pointer on measurement equipment and the dual function, makes sense. I remember reading about the timing control handover over 400 rpm back some years, when someone was stating a specific module had more timing builtin or sth like that.
That's kinda what I thought. So, supposing I have an Osci or true RMS voltmeter, on what terminal would I try to see DRP signal?
I also thought about checking signal at the inj terminals, but since usually sprays just fine and then at other times not at all, without big thermal influence, I decided it's not likely the injectors were the issue but more the ECM (not) commanding the injector signal.

Sounds almost like a sawtooth type signal?
I have never heard about the color codes of coils Interesting points with that and the stray RFI antenna part. Which models or years are you referring to when you say "older HEI" or which ones use the (seemingly) more rare version with the yellow color code coil?

Thanks all the same for your details on that

 

ownor

DRP signal is at Pin 'C' at the distributor 4 circuit plug. Typically it is a purple-white color wire, but wire colors may have been changed. At ECM back-probe Pin B5.

Make sure that you are getting +12 volts when ignition key is in run or cranking, at :
injectors - red wires
ECM A6 - pink black wire

//RF

 

Perhaps. If there's a standard for a sawtooth signal, this may or may not be it. However, yes, it it vaguely saw-tooth shaped. I can't find a good 'scope photo at the moment to show you.

I was thinking primarily of the '74--newer HEIs using the 4-pin modules. Some 5- and 7-pin module units would also be similarly color coded. On V-8 engines, they'd have the ignition coil built-into the distributor cap.

The yellow code isn't rare at all--most Chevys and Cadillacs got that one. What was the blue code evolved into the black code, used in Olds (except Toronado) and Buick. It has slightly longer wires than the yellow-coded one, because the connector has to be flipped upside-down to connect to the module. This reverses the magnetic polarity, while keeping the electrical polarity the same.

The clear code was just a black pickup coil with still-longer wires to fit Pontiac distributors.

http://www.chevelles.com/techref/ftecref5.html



Of course, the change in magnetic polarity of the pickup coil was accompanied with a change in magnetic polarity of the in-cap ignition coil. The in-cap coil with red and yellow wires (goes with the yellow-coded pickup coil) is reversed from the in-cap coil with red and white wires (goes with the blue, black, or clear pickup coil.) Separate (non-in-cap) ignition coils are not affected by this magnetic polarity, far as I know they're all the same.

 

Interesting "trivia" (if you want to trivialize that wealth of info there) on the pickup coil + ignition coil variants/codes and magnetic polarity
I will keep that in mind when working on the different HEI stuff especially BOPs ("ye be warned!").
However I guess in this case it is not relevant too much since it basically runs but dies at some point. Still interesting to discuss all the HEI backgrounds.

Anyhow, I will check DRP output since that seems to me the most promising check right now. Assuming DRP stops when it dies..where do I go on, ignition module or pickup coil? Would I find a pickup coil or magnet defect by just looking at the parts?

 

Broken magnets on the pickup coil are common. Weak magnets are somewhat common, but that doesn't show up on a visual exam. Both lead to a weak signal to the module.

Broken wire(s) between pickup coil and module are common especially on the older HEIs that have a vacuum advance. Often the conductor is broken inside the insulation, so again there's no visual clue.

The only common test of HEI modules that still work well enough for the engine to run, is to verify that the dwell varies with RPM. This is a common test because it's simple, not because it's a comprehensive test.

Here in the States, If I had any suspicion of a failed pickup coil on a small-cap HEI, I'd replace the distributor mainshaft, if not the entire distributor. I've got spares on the shelf of my garage, and I've seen this failure often. I understand that having to import replacement parts makes this more interesting and difficult.

Don't forget that the pickup coil and module could be perfectly serviceable, and the actual problem is in the wiring harness between module and ECM.

 

Ok thanks, still wasn't sure if the magnets where on the shaft or the pickup coil or sth. I do have extra stuff kicking around for quick replacement or troubleshooting, but I'm not sure V8 stuff would be suitable here albeit the 4.3 is just a V6 SBC. But my guess was sth would be different for the required part when it's got 2 cylinders less.
No vacuum advance here. I will make sure to check out the harness, grounds and pickup coil as well as try to verify DRP at dizzy as well as ECU today.
Thanks

 

Ok, update. Did some more troubleshooting today.
Findings:
12V to injectors 'A' with ignition on, no problems even when wiggling in connection A6.
Continuity also fine on 4-pin HEI connector terminal 'C' to B5, no contact problems.
Injector/Connectors get pulsed (grounded) just fine WHEN the car decides to start/run.
I noticed after stalling out sometimes it will command spraying during cranking, but then immediately dies at the run-to-start transition and I can even still hear starter freewheeling in this case, guess that's after it disengages from starter teeth ring on flywheel/flexplate.
Anyways, I also checked DRP pin 'C' at 4 pin HEI connector and found that sometimes it will randomly show 7V on the voltmeter when cranking, and that of course is also when it will randomly put out a spray with the injectors connected.
So I can definitely rule out wiring for injectors and DRP/HEI, but I'm not sure how to go on. Just change ignition module or do I want to go further with looking at pickup coil wiring, the pickup coil itself, magnets on the shaft, ...?

Also one more thing. I checked timing before doing all this and I noticed it's kinda all over the place even with the EST disconnected. Ok, that was at cold engine and it had some missing and hunting but still.. I could see it go about from -2° to 10° BTDC?

And on a sidenote.. For some reason the balancer on the crank has two grooves and I put the engine with dizzy pointing at cyl 1 on the dizzy cap, and verified which one was at about TDC on the timing tab pointer to make sure I was using the correct one.

 

Any chance you have a problem with the ignition switch intermittently failing to power
1. The injectors, or
2. The ECM, or
3. The HEI?

Do you still have spark even when the injectors don't get pulsed?

I'm leaning toward a faulty ignition switch that doesn't provide power to one or more of the three items above, although that wouldn't have to be the source of the problem. I suppose it could be an intermittent module, or intermittent pickup coil.

The pickup coil is semi-permanently mounted to the distributor shaft. I don't know of any source for the pickup coil separate from the shaft. Non-replaceable on it's own. Of course, you can still look for the broken ceramic magnets.

Let's see if that fixes itself when the intermittent non-spraying of fuel is repaired.

Two grooves: one narrow, one wide. The narrow one is for timing with a light, the wide one is for timing with a magnetic-sensor apparatus as was done at dealerships and probably at the factory. The timing pointer has a circular/cylindrical holder for the probe at the far (retarded) end of the scale.

 

To rule out the possibility of the ignition switch not supplying these, I guess I would just check the respective ignition switched +12V pins at the respective devices? i.e., at distributor 4 pin HEI connector, at the ECM supply pins, and at A6 and at injector A terminals.
I would need to check as for the spark thing when not spraying but as mentioned before it does want to start and begins chugging when I spray it with starter fluid when it doesn't pulse the injectors. Guess spark is a given then.
Last time I checked, the pickup coil can be changed? I'm pretty sure I did it on my Formula once. Need to push out the roll pin at the gears and disassemble the whole shaft and so forth, but still.. On the shaft rotating inside there's this star-like reluctor thing, maybe there's a problem with that? Is that where said magnets are located? Imho these are fixed to the shaft and non-replaceable without swapping the whole shaft.
I guess there's also some way to check the output of the pickup coil with a DVM tho? Haven't done research on that now but I'm sure that point is even in a Haynes book.

On a side note - now I think about it, I actually disassembled that Formula distributor twice already lol. Replaced pickup coil and managed to not tighten the dizzy hold down bolt enough, so it wiggled loose and wanted to come out top, stalling out on the test drive away from garage, not starting etc. Removing distributor at the side of the road, I found it had already started eating gears, so got some tools and gears from another "part out" distri I had, swapped distributor gears on the side of the road where the thing had stalled out, put it back in and off she went again Btw this was the only time that thing ever left me stranded *knock on wood*

 

Why isn't the engine RUNNING when you supply fuel?

 

Battery was drained tonight so needed to hook it up to a charger and will have a go again prolly tomorrow. Checked resistance of pickup coil anyways, 815 or so Ohm, seems to be fine static, but will check again when it's in no-spray state.

@the starter fluid thing, in the Astro the TB is not the most accessible thing in the world when you still have half the air cleaner lying on top of the engine, and the starter fluid can was close to empty so i didnt try longer than some chugging tbh. That was after some dry cranking so I'm sure there wasn't really any residue fuel.

 

Did a little research. easyautodiagnostics.com has a series of tests with good coverage on the whole problem, more specific pickup coil / ICM testing. For my situation, I think their Test #7/Page 6 should identify the issue I'm having http://easyautodiagnostics.com/gm/4....ed-icm-tests-6
Testing the pickup coil with DVM AC range setting while cranking.. Will try that tonight.
Also, here's a pic they had on the pickup coil's output signal on an osci (not the DRP tho):

 

Except that the signal is inverted. That will cause the spark advance to retard once under ECM control. So beware of the other information on that site.

RBob.

 

Thanks for the pointer Bob!

Anyways, a better inspection of the distributor inners revealed a couple of possible causes for the stalling and no DRP condition (to me anyways).
- Pickup coil connector having a wrong pin terminal, easy to get a bad connection here.
- one threaded hole to fix the ignition module to the distributor base for electrical and thermal contact is no more threaded, i could pull the small bolt out by hand
- To that bolt, a separate ground strap was attached, that goes through a hole in the distributor base and connects to the engine block.. Also quite strange and prolly jerry-rigged, too? What's the usual method to connect a ground here if there is one?

That said, pickup coil output with DVM checked out ok as per above site. Need to fix these "mechanical" issues first and i think that might already solve the stall issue?

 

Yup, that's the waveform...but as RBob said, it's upside-down.

Likely. I think you found it.

A longer screw, and a nut on the underside of the housing would work. A larger screw, and tapping the housing for the larger size might also work.

No need for the ground wire, although it wouldn't hurt.

Unless I misunderstand, you need a replacement pickup coil to get a satisfactory harness; and so far as I know the pickup coil is not offered without the entire distributor shaft.

Once you price the distributor shaft...one wonders if a replacement distributor isn't in order. I suspect you'll find that the distributor shaft new costs about the same as a rebuilt distributor, and more than a used distributor. Of course, your location may change that.

The distributor parts MUST be for the V-6.

 

http://www.rockauto.com/en/catalog/c...ckup+coil,7176
Btw, I was just checking out the parts compatability list and saw that many many GM HEI model can use a pickup coil like the ACDelco D1987.. also those that were only offered with a V8, so I'm thinking any pickup coil would be fine?

Thanks on your pointers for the 'mechanical' issues.
Will report back after achieving some progress.

 

Thanks for the link. Now I'm gonna have to figure out how the pickup coil comes off.

Since that style pickup coil doesn't include the timer teeth like the ones I posted earlier, cylinder count is unimportant.

One wonders how or if the magnets can be replaced. The magnets, wire coil, and outer timer teeth are an assembly on the earlier pickup coils. Not so with these.

 

Yes, that pickup coil is the correct one for the 4.3l engines. The 4.3l distributor is nearly identical to the SBC small cap distributor. Only difference is in the star wheel tooth count and the number of reluctor poles. The shaft with the magnetic star wheel is also available on RockAuto. If the magnet is falling apart or heavily cracked it would be worth replacing it too.

If the current ICM is an OEM unit at the least I would keep it. Even if replaced by another AC Delco ICM.

Note that the hole in the base plate that they passed the ground wire through is a locating hole for the cap. The cap has pins molded into it that fits those holes (one on each side), to accurately locate the cap on the distributor.

To get the shaft out of the distributor a carb gum cutter works wonders to cut through the varnish build up. Otherwise it can be impossible to very difficult to get the varnished areas of the shaft past the bushings. Berkebile 2+2 comes to mind.

RBob.

 

@Schurkey, as said there's a roll pin down there in the gears that you have to remove, if the shaft isn't all coked up with oil varnish it will come apart that way rather easily, if not it needs a little persuasion with a hammer or the like.
On the coil insides, I saw a video on youtube somewhere that shows how to disassemble a pickup coil with the parts you mention.
(Might have been this one here: )

@RBob, thought so on the SBC small cap similarities. So the shaft and magnetic star wheel would be different, read more expensive, for this V6 then, making a new/rebuild/etc distributor more cost efficient. Can I check for cracks in the mentioned star wheel and its magnets without unmounting shaft, pickup coil and the like?

Not sure if the ICM is an OEM one, how would I tell?
I'm planning to keep all components that don't need immediate replacement.

I was not aware of that hole being a cap locating hole/pin thing. However I did think the two screws on the cap would position and hold it down sufficiently. But then again I did see some timing jumps..any relevance here?

Good point on some aggressive carb cleaner thing spray for removing the shaft..

 

The shaft (pole piece) is listed at $91 on RockAuto. The part I don't like about reman distributors is that you aren't sure what you are going to get. And unless it was done by AC Delco you aren't going to get an AC Delco ICM.

Yes, I used a red arrow on your picture to show where the magnet is. It is clamped between the two pieces that are riveted together. It should also be visible around the shaft.

See if it has AC Delco or the numbers 466 molded into it.

Probably not related to the timing jumps, but the dowel pins do make sure that the rotor and cap terminals are properly aligned.

It makes it so easy to pull the shaft. Also good for getting varnished lifters out of the bores. Sure beats using a F*rd tool.

RBob.

 

The video posted is from an older, coil-in-cap V-8 HEI. While they "can" be disassembled, they shouldn't be, as it's somewhat difficult to get them re-aligned again--and--the replacement is sold as the complete assembly anyway. If the pickup coil or the magnet has problems, you're going to toss the housing, magnet, coil of wire, and pole piece in favor of a complete assembly.

Turning the magnet upside down causes problems, too.

I'm still looking for instructions for replacement of the pickup coil on the small-cap TBI distributors.

 

For the record, i fixed the pickup coil connector and cleaned the distri base plate, reapplied thermal paste and properly remounted the icm.
It would run a little longer that way but still stalls out with no spray condition after about 20 minutes.
Put an AC DVM to the pickup coil wires and it reads the voltage as described in that Test i linked to above. So ordered a new ICM now.
Seems legit I guess.