I'll state why I'm in the FPOP area after the following history recap. I hope I posted this in the right area, I'm still very green to how the site works.

I've restored a lot of things on this old engine including: rebuilt HEI distributor, of course plugs wires cap/rotor 02 sensor vac hoses egr system fine, pulling computers, exhaust manifold leak;shaved, intake manifold-upper/lower, fuel injection rebuild, water pump, timing chain and gears, dropping oil pan and starter to do that, , half a dozen sensors and/rotten connectors that crumbled in my fingers from age while testing or just "touching" them, ignition starter switch (had high resistance flakey connection), power brake booster, and reading an 8 inch thick service manual. Not in that order of course and many other restoration items, cleaning up things as I go.

Timing is dead-on at 6 degrees btdc. It took a while to get to this point, as a sloppy timing chain and gears seemed in order, as long as I was in there.

Now it runs great, starts better than it has since I bought it in 1990. Many trouble free years till about 5 years ago, and it just got old.

One day I filled it up for a nice test drive, and it stalled on deceleration; slow down to idle, stalled. Went around a corner, slowed down, stalled; hairy.
I fixed that I believed with the IAC connector and one valve according to the trouble chart; bad connector. Brake booster got RR-d in there too. Lots of trouble-tree-shooting, but it is intermittent now, and section B:intermittents don't really apply except for the engine grounds, which are fine. Probably replaced some good parts due to the intermittent nature; recreate it, test it, replace part, fixes it, problem comes back at random. Did that with engine grounds once too. Anyway, it's always fine. For a while.

Then another stall problem arose (or the same one I don't know for sure; just more chronic). Stalls in the driveway idling, revving, any rpm really. It will sit there running smoothly, and then just shut off like turning off the key. (Voltages at the distributor are fine, solid. They weren't for a bit till I found the battery was holding a charge and replaced it.)

I went back through the Distributor and double checked the ICM, pick-up coil, even found the four wire harness connector (don't ask how I found that). All fine. I eventually got it centered after re-stabbing so many times that now I can time it without hitting the plenum : ) Got good at that, turned the oil pump till she lined up. Went through and replaced dodgy relays with high contact resistance and was careful to get correct ones for FP, MAF sensor and MAF burn-off. MAF is new, as I buggered the screen on the old one which was still fine. (Unhook the MAF connector, and it still stalls.) FP relay connector still has ratty looking wires, but continuity is 0.0 ohms. I even cleaned old dielectric gunk off contacts to be sure. That helped I thought for sure, till it stalled again.

Runs fine, lots of power, revs fine; even power brakes; no shudders. Ready to drive. Stalls at random. 10 seconds, 5 minutes, 20-30, no pattern. (Now I have to fix a radiator heater hose bib that I must have leaned on, cuz it leaks when approaching fan-on temp, so trouble-shooting time is limited for now. Sigh.

I've watched the computer lines for ICM reference signal and ohmed out the four-wire many times. It runs without the 4 wire, which tells me it's not the pick-up coil, as the computer takes over without the ref signal when you do that. The ignition coil is new and the ground-strap goody there is fine. Checked engine grounds with DVM continuity and voltage drop testing. Less than or equal to 0.1 ohms and less 0.1 voltage drops, as far as meter allows for accuracy. The radio interference condenser replaced even thought the old one was good.

Back to the Fuel Pump Oil Pressure circuit. This seems to be the only other thing than the crank ref signal from dist, that would tell the computer to just shut off the engine like you turned off the key. The thing is, it works. I cleaned the contacts on FP relay for fun, and it ran for 30 minutes; another false positive.
The next day it stalled again. Did I mention it's usually a hot day when things seem to work. Seems like it, but I've been fooled by this intermittent over and over now.

Last night I pulled the FP relay out completely to see if it would start. It didn't. Cranked far past the oil pressure threshold. So it MUST be the switch right?
Came back ten minutes later, the relay is still disconnected, and it started right up! And it ran till I had to shut it off!

The FP relay should run the car, reading between the lines of a million half-*** descriptions in the Service Manual, and pulling it out would put the load solely on the switch, until maybe the switch falters, then somehow the computer senses that there is not enough oil pressure, of which it has plenty according to the separate gauge sending unit. (The 86 has both a gauge pressure sender, AND an FP-OPS.) That's the part that is fuzzy; how the redundant switch and relay contacts and failure of the oil pressure would signal the ECM to shut off.

I am about to change the OPS just because. Maybe THAT is the intermittent in this whole scenario. I'm familiar with the Senior Member's advice on here, been reading and learning this car for 5 years now and value their insight. Oh, my "scanner" is kinda useless, and can't afford another as I wasted money on an Ac***n which talks to ECM about 5% of the time, but the only codes I could ever get was a 42 when it died, and before shutting key off and paper clipping the aldl. No more codes anymore though.

Ask me some questions please, as I have done a lot more testing with the tools I do have. I am an old electronics tech with a limited attention span now, so it's hard to follow the relay logic in the schematics; are relay contacts shown activated, or in engine-off state for example. Circuit descriptions in the 86 manual are not comprehensive to say the least.

 

Guessing 86 tpi?
does the fuel psi drop while driving?
the oil psi switch is a backup incase relay dies.
If relay is bad and switch is good = long crank time to start. Until oil psi comes up.
As long as oil psi is good, it'll still run.
if relay is good and oil psi switch is bad, it won't stall out.

 

So, usually when that many words are in a single post, the answer is get a datalog.

 

x

 

x

 

TTOP, yes 86 tpi.

According to previous statement in third gen
@eseibel67
Supreme Member
15 Year Member"The OPSU is not a backup, it is the main power supply for the fuel pump. The fuel pump relay supplies power for prime and cranking only."

This is why I believed it may be a failing switch and replaced it today. The relay does not stay on per design.

Fuel pressure is fine, can't drive it though, as it is a random stall. Plenty of power otherwise.

Starts right back up after a key off, key on, wait 2 seconds as pump primes the fuel rail. Relay is new btw, wires look stretched/bare at connector, but ohm out fine.

If I pull the relay out completely, it IS a long crank and does start and run like you say. Then it eventually will just stop like the key was turned off. Maddening.

Also, the oil pressure is steady 30-60 I think, depending on rpm.

I replaced the switch today, no help. something is causing a glitch to the ECM. I was wondering if both were bad or intermittent, causing the stumble and ECM shutting things down. I don't think it is in this area anymore, but I really don't know what to look at anymore. I've been everywhere, twice or more. A remanned ECM a year ago with exact same symptoms. All coils and relays that could have damaged an ECM are fine and functioning.

 

To Komet;
Data log should be the next step I guess, but I don't have a laptop anymore. Just this Chrumbook and a phone. Is there a good solution for a Phone and an interface I could look into? I'm not that good in today's technology; my brain broke some years ago. I'm starting to be able to learn what's out there now. I have to dig into it, start over daily like Groundhog's Day movie without the gradual improvement. haha.

I looked at Boosted NW, but have so much to learn. Not sure where to start. Sorry, real tired now. Spent all day putting that switch in, it's so hard to get to.

This has become a long term project now, I have to be away with other stuff for week or two, but I'll check back in soon and keep reading what I can find.Last edited by johnster; Today at 12:04 AM.

 

barking up the wrong tree to solve your problems

 

Well, maybe if the comm link on these lb9 engines would work with what I have, I could have been up the right tree a long time ago.

What could I put together to be able to talk to the computer? I really need to do that, but I don't know whose product to use. Can you help?

Just a block diagram of what's needed. I can research each block from there and try to put it together. I just need a hand up. Thx

 

Yeah, you can get ALDLDroid for Android phones and the Xtreme ALDL (ALDU1 and CABL1) from https://shop.moates.net/ . That's what I do, I also needed a USB-A to USB-C adapter for the cable to attach it to my phone, got that off ebay. You can use the same cable with a laptop and TunerPro RT as well so it's nice to have.

 

might observe Vss and iac movement on decel if iac steps are correct at warm idle. Btw the ops like Anthony mentioned is back up for fp relay. Can observe a manual to see how it’s wired. No common lb9 tpi issue for stalling on decel. Doesn’t sound heat related either.

 

Thank you. That's a good roadmap to follow for me. I thought moates went away, but looks like they are back? I'll get on it.

 

Okay, thanks.
I've stared at that schematic and still have a hard time seeing how it works (my fast brain). Hard to visualize if those relays are shown with engine running (activated) or at rest. I'll look at relay specs to see what's n.o./n.c. That should settle it. But you're right, I was just looking up different branches hoping to get lucky.
Yeah, not heat related. Dies right away, or runs awhile then dies; completely random.
Oh yeah, it dies under open throttle so IAC should be out of the picture That was sorted out back in the intake rebuild phase, clean and shiny. Good connector.

 

still wouldn’t rule out fuel pressure loss, your first post indicates decel so 🤷‍♂️

 

May want to have a look at this video / channel, it may give you some incites into your issue.

 

When the car dies, what does the tach do? Do it drop to 0, or does it follow the engine RPM until the engine is no longer turning?

 

It falls to zero immediately when the engine shuts off. There is no rpm slow-down, it's just straight to off exactly like turning the key off.

It was jumping/pulsing a while back until I dressed the plug wires and got rid of some cross-fire. I was sure that was it. Fixed the tach jumping and some occasional code 42s, but the random stall eventually came back.

 

Thanks MaxpowerTA, That's a much easier schematic to read than my 86 serv. manual. Excellent circuit description too.

This is what I began to realize after back/forth ideas online about which was the primary voltage source to the pump; The Relay is on during Prime, Start-up AND Run.

Mine primes fine and starts easily if you turn on the key and wait the 2 seconds for the pump to stop before starting. I was suspecting a bad relay wire intermittent situation, which would then cause it to use the redundant pressure switch path. If that one was unreliable as well, dirty or failing, then the computer would see no oil pressure momentarily, and shut it all down. Unlikely, but possible.

I really don't think it's the Fuel Pump circuit anymore.

Until I get a reliable comm link to an analyzer, I'm going back to look at the engine grounds (again).

(BTW The relay was replaced to fix a poor contact long ago, but the wiring was all stretched out and bare at the connector. I was going to re-connector that, but it ohms out fine though since you can probe both wire input and contact.)

 

Sounds to me as though you're loosing your pick up signal, then.

 

Right, that's what I thought. But I unhooked the 4 wire harness to the ECM which takes the pick-up coil out of the picture. It should run then on an internal ECM fixed timing.
It runs for a while, and then It still stalls at random. Just shuts off. The only thing from the intermittent list in section B of Drivability is Engine Grounds.

Every other symptom involves, stumbling, bad idle, vacuum, fuel etc, but it runs perfectly, revs, idles down at warm-up to about 700 rpm like clockwork.

Then it stalls whenever it feels like it.

 

No it doesn't. The can CAN NOT RUN, w/o the pick up coil. The p/u coil is everything: it's your crank signal, your cam signal, your ignition, injection and fuel pump reference signal. It is the "now - now - now - now - now" that is absolutely required, for anything to happen, that makes an engine to run.



How? "Fixed timing" (no timing curve) is not the same as...."timing". How can the ECM possibly "know" when to fire plugs and injectors, if it has no reference pulse (from the pick up coil)? It can't.....it wouldn't even know that the crank shaft is turning, w/o that pulse.


IIWM, I'd be scrutinizing (diagnosing) the pick up coil. If the tach is dropping out instantly, when the engine dies, that tells me that you lost your p/u signal. Where/why did you lose it? That needs to be chased down. I would do that w/my scan tool, on data stream mode, if I were working on your car.

 

Embarrassing typo; I meant the Bypass connector. You are right of course about the ref signal, I was tired and not thinking clearly. (Was thinking of spark test chart I guess.)

I did replace the pickup coil, and it's resistance is around 700 ohms if I remember. It was really tough to get it centered so the pole piece didn't touch anywhere, but I got it. You could feel a gentle magnetic "thump" when spinning the shaft thru the 8 positions, and no mechanical interference.

The ICM tests out okay at the auto-parts store (that still has a tester) but that is a static one shot test I guess. And it stalls hot or cold, so it's not heat related.

Connections are rock solid, as I was able to find a 4-wire harness, the old one was crumbling, but the connection also seemed solid. So that wasn't it.

The connections to the ECM have been ohmed out 50 times. It should work. That's when I found the plug wires pulsing the tach, and fixed that, I thought, till it stalled again.

My scan tool is a worthless actron unit that won't communicate 95% of the time, so I'll have to put together a data-logger as mentioned above.

 

Yeah, sounds like that is what is needed to see what's going on. This is turning into a good'n.

 

"My scan tool is a worthless actron unit that won't communicate 95% of the time, so I'll have to put together a data-logger as mentioned above."
You know that is a trait of those 1227165 ECU's and not necessarily the scan tool right? They are notorious for connection issues. (That's why i hate them so much )

 

Yes, I came to that conclusion some time ago. And I hate them too.

I looked at the signal on a scope, and it is barely 2.4 volts out of 5. It probably won't even work with most comm ports as it is on the ragged edge. You can't trigger the scope either because it uses some stop-bit data stream, and it looks a mess. Even if they are functioning correctly, we can't talk to them half the time it seems. I wonder how the snap-on brick that techs used at the dealerships worked with them.

I thought of replacing it with a later model, I think it is a 19367537 that Rockauto says would fit, but would that be an improvement? Faster baud rate than the 160bps of the 165 I think.
But, they are unavailable now too. It looks like Cardone doesn't remanufacture them anymore. A year ago they were 125 dollars. They are 450 dollars on eBay now.

The Actron works fine on OBD2.
Funny thing, it worked better when I told it the car was an 87 Camaro, instead of an 86 T/A.
Then it didn't any more.
Electrons hate me.
I ordered the Moates today.

 

I would swap it to the speed density computer personally, that's what I've done with with every pre 90 third gen I've ever owned and helped some buddies convert theirs as well. i have an old snap on brick and that's actually the only tool I've ever found that connects to those 165's consistently

 

When upgrading to $6e mask in the 165 connection seems a lot better the 32 and 32b, solves issues with 86 aum tunes as well. Mt2500 seems to connect to all 3 165 masks. But i agree the 165 can be problematic to connect to.

 

Here is the resolution to this post. I was on another (hijacked by me) post, ("Bird keeps stalling and I’m lost".) and kept talking there about the same comm issues.
I had to go back to basics without the computer. It threw no codes, and wouldn't talk as you know. I copied my last post from the other to paste here.

Quote:
Originally Posted by TTOP350
Something just popped into my head from years and years ago with my 89 formula 350. It would randomly die and i dealt with this for several months.
Quote:
Originally Posted by TTOP350
one day i was under the car with key on engine off. I happened to bump a fusible link on starter. Noticed some things clicking an buzzing when I'd moved the wires.

Did a continuity/ wiggle test on them all and found a bad one. A few yrs later i found a 91 with same issue, it was killing power to part of fuse box.

maybe a quick test on those will help

Problem Solved: Johnster
Final update

Thanks to TTOP350 I was working with the fusible links. I had rerouted some draping plug wires away from the links in case of induced EMI into the ECM link. Seemed to help a little, but still stalled, maybe a little less often. Progress.

So then I tested the links by trying to find test points back through the ignition switch. Grounds are fine, so why not suspect the power right? (No end-to-end probe access on the link itself.)

Testing the links, I was especially concerned with the ECM power link. I 'ohmed' from the starter side to the next test point that I could put the probe on at splice 200 I think it was. The link was good. 0.0 ohms.

Then I found some varying resistance at the fuse block test point (ECM fuse), after it goes through the ignition switch when switching the key on and off (battery cable disconnected of course). I ended up taking the switch connectors off and douching them with an electronic cleaner and letting it dry. Somehow it got WAY worse, stalling immediately and throwing an unrelated BS code 15. I took them off again and pushed the spade connectors toward the connector wipes on the mating connector. That fixed that problem and code disappeared, but it still stalled. I then squirted inside the switch and left it overnight.

BTW, I replaced that switch some time ago because of wild resistance swings with the old switch. It fixed the resistance problem at the time, but not the stall.

The switch was made by Rocstra, the only one available back then for tilt wheel with an automatic transmission. Anyway, not the switch.
I stared at schematics, service manual tips for intermittents and the wall for awhile, and was pretty sure what it wasn’t by now.

So I went back to the 'EMI from plug wires' idea again, this time on the bat/tach side of the distributor, and the harnesses on the firewall where the plug wires make their way down the firewall to the lower wire comb off the head. I got them away from the firewall and the harness that had the Bat and Tach wires (and who knows what else), and dressed them so they were not cross-talking as best I could; lengths aren't what they should be. BIG improvement right away. But I got one stall after about 20 minutes. Dang.

I chose this time to replace my (unrepairable) radiator that sprung a leak at the top heater hose. Funkily, the stall increased just a little bit. That’s when I noticed the clamp on the MAF was askew. I pulled all that out (again), ancient warped plastic from ‘86, to rearrange and fix the clamp. The equally ancient O-ring inside broke, and I had to silicone it (black RTV). I also gave the connector a good clean with an electronic switch/contact cleaner.

Voila, no more stalling. Ran it up to temp, got the bubbles out of the new radiator and it just ran and ran for around a half hour or so. I put the steering column back up, and then ran it for a long time. Started and stopped about half a dozen times and not one stall. Fan comes on about 220 or so and cools back down as normal, and that was after running in the driveway for about 45 minutes off and on. Ran it up to temp and checked the timing. It was off too, which is weird, but not really.

The next day I was able to drive to a gas station and fill-er-up for the first time in a year. I put the ECM and dash back together. Then a buddy came over and we went on a long test drive, 25 or 30 miles, up and down Skyline Blvd, back down to cruise a super highway, stopped, had dinner, and started it back up and drove home. Never skipped a beat.

I’ve got a new O-ring on the way with the help of an impressively helpful Amazon robot after I gave my year car and the Delphi MAF I have, and the dimensions I measured; 80mm x 2.5 mm thick.

Thanks to all with the ‘Computer Comms 160 baud $32 / $6E’ solutions/education people. (You know who you are). I may someday be able to do all that with the $6E mask to fix the communication handshaking issue. (As I understand it, that will also get rid of the 9th injector).

But for now that is out of my reach. I've been learning about the PROM and data-logging world, and wonder if I can just get a PROM burned by someone with the basic $6E mask for the comms issue. My prom says AUM; is that the same thing as $32? (Or I may get the .adx file to work with droid. I’m not sure I did that right.)

One thing at a time I guess. I REALLY appreciate what you have taught me here, and all the research I had to do just to understand it.

Hope this helps someone down the road too.