I'm just finishing the rebuild on my '86 IROC..

I've had a helluva time trying to get it to run, today we put new AC spark plug wires on it and fired it up, it ran HORRIBLE, wouldn't hold an idle, was pinging etc..

I went and disconnected the EST and started the car, it ran like a damn top.. WTF?!?!?!

the only thing I can think of is that the ECM took a dump and when it's forced to run off the MemCAL it defaults to the stock timing curve and runs good..

do I have a dead ECM? I also noticed when I took it out for a drive that over 50% throttle the car would seriously choke and want to shut off..

the TPS is fine, I set it to within .01 volts of spec..

I have an '89 ECM here, can I put that in as-is or should I put the '89 ECM in with the '86 MemCal..

thanks

Colin
Webmaster: www.IROC-Z.org

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Webmaster: www.IROC-Z.org

 

Don't think the ECM swap is waht you need at the moment. What was the base timing with the EST bypass disconnected? Could be you're just too far advanced.

 

base timing is 6 degrees, the motor is 100% stock...

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Webmaster: www.IROC-Z.org

 

I *think* that when the EST bypass connector is unplugged, the only advance given to the ignition, is through the ICM. (I hope I'm not confusing this with another car I have) and the ICM allows for 5-10* of advance.

So with the EST line disconnected, the ECM is no longer controlling the advance through the EPROM spark curves.

I guess you could have a bad ECM, but just as easily (and more likely) the ECM is getting an input from something else telling it to add more timing.

Is this TPI or TBI?

Any codes set?

I'm guessing that since you were able to rebuild the engine yourself, you got all the plug wires routed correctly?

 

i just put brand new plug wires on, 8mm AC Delcos, for the '86 305TPI specifically..

plug wire routings are correct, doublechecked.. with the EST disconnected the car runs really good, perfect, unless you stomp on the gas hard it'll choke and want to shut off..

the car has new:
<ul>[*]ignition module, cap, rotor, plugs, wires[*]Knock sensor[*]EGR[*]MAT[*]Coolant Temp Sensor[*]Oxygen sensor[*]IAT sensor[*]PCV valve[*]timing chain (including crank and cam sprockets)[*]new vacuum tubing all the way around[/list]
it's throwing the EGR, but only when the EST is set, it also throws a lean code, only when the EST is set..

the car has a 305TPI, bone stock, for now..

it's impossible to even idle the car with the EST connected, it runs so bad that the car starts choking, sputtering, refusing to idle, missing horribly, and fouls plugs..

disconnect the EST and the car purrs like a kitten, tends to knock a bit under hard acceleration (if i slowly ramp up the throttle) but will choke if i mash the gas.. tends to be a bit sluggish off the line but I think it's due to the EST not being connected..

the changes in idle are so drastic that there HAS to be something wrong with the ECM.. it's night and day..

thanks for the help, bro
Colin

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Webmaster: www.IROC-Z.org

 

FYI the ECM for an 86 TPI and an 89 TPI are the same, something like 1227165.

I think the problem is one of those simple but overlooked things that crop up during an engine R&R. No vacuum leaks or vacuum hose that fell off or got put on the wrong thing?

James

 

nopes..

all vacuum hoses have been checked and rechecked..

i'm positive it's a TPI problem as as soon as I turn off the car and disconnect the EST the car magically runs like a top, turn off the car and reconnect it, car runs absolutely horrible..

it 'has' to be EST related..

the car also tends to choke anytime, whether the EST is on or off, under WOT..

then again, when the EST is connected the car runs so bad 'period' that it's almost impossible to tell what's going on..

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Webmaster: www.IROC-Z.org

 

How about the ESC module? Is it functioning normally? Also the 89' ECM's eprom has VATS so you are going to have to swap EPROM's, but I don't really think that is your problem just yet. HTH!

 

Sounds to me like you are WAAAY too far advanced OR your distributor's ignition module is shot, which is probably the case if you used a timing light to check your initial advance setting with the bypass disconnected....

 

you actually set the timing with the EST disconnected so that the computer can't adjust the timing...

i set it at 6BTDC with the EST disconnected, 6 degrees advance..

 

you're right, the '89 has VATS..

it hasn't thrown a code for the ESC yet, only thing I thought that did was retard the timing if it experiences major ping.. i don't know much about it, just that with my '87 IROC when my knock sensor came unplugged it would throw that code constantly..

 

i'm still leaning towards the computer itself having issues, last night it started this surging BS..

i took it out for a drive with my GF so we could goto supper, at the lights in drive the car would cycle slowly back and forth from 600-1000rpm, kinda surging.. my GF thought it was playing around i was like, nooo it's surging..

this is new.

ideas?

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Webmaster: www.IROC-Z.org

 

Re: The ESC module, I think you're correct Collin, the ESC just interpets the signal from the knock sensor, and send the info to the ECM to retard timing.

Are you able to get an approximate read on the timing at idle w/EST bypass connected?

The EGR codes and lean exhaust could be an area to look at also, if you're getting EGR at idle, the ECM most likely does not have an avenue to adjust for that, and you should get lean readings. EGR open at idle can/will cause a difficult starting problem and very diffcult to idle, but how it relates to the EST, I've no idea. I'll look through the EGR diag in my book and see if speaks of any EST relation.

 

It's the pickup coil. Had the EXACT same symptoms. $10 part. You may just elect to replace the whole distributor with a better one.

Two auto shops swapped the ECM in my car before I figured out what the problem was.

 

'86 has a pickup coil?

how exactly does the pickup coil work?

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Webmaster: www.IROC-Z.org

 

Sure. You pickup coil is located inside the cap, around the shaft, by the module. You have to disassemble the ditributor to get it out. Mine was 11 years old so I decided to just go ahead and replace the whole distributor. You can make sure by measuring the resistance in the coil. Most manuals will tell you how. Even Haynes.

Check this out: http://www.autoweb.com/garage/subsys/09-05d.htm

If you're not getting any magetic field from the pickup coil, you're module/ECM won't know what in the hell to do. Check your timing mark as the EST BP connector is connected. Look at the mark. It'll jump around like no tomorrow.

 

Allan,

that was my problem exactly..

i changed the pickup coil in my '87, i guess i should have done it in the '86 when I was rebuilding it..

when the EST is bypassed (disconnected) does the ECM then disregard info from the pickup coil to advance/retard the timing?

if so, that's my problem then... everything else is new, everything... the only sensor that isn't new is the MAF, and i'll be changing that soon, too..

thanks for the heads up, i'm actually excited about pulling the distributor out tomorrow and replacing the pickup coil

thanks man!
Colin

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Webmaster: www.IROC-Z.org

 

I suggest pulling out your distributor first and check the overall condition. Try pulling off the pu coil. That way, if you break something (like the points), you'll just get a new distributor. When you pull the plug, you're essentially, disabling advance. Advance is, in part, determined electronically via the pu coil/module and relaying that info to the ECM along with other readings throughout. Essentially, yes, the ECM ignores the reading with the plug disconnected. Erroneous or not.

Good luck, let us know how you fare!

Allan

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IROC-Zone
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'88 Camaro IROC-Z 350 TPI

"Yea, though I walk through the valley of rice,
I shall fear no Turbo; for Torque art with me."
- Cullan Hooley

[This message has been edited by Allan (edited July 12, 2001).]

 

Any luck, Colin?

 

actually I was just about to post

I changed the pickup coil today with one from AutoZone. The original one was pretty greasy, the motor had cratered pretty bad and alot of oil was going up the plenum.

Regardless, I cleaned up the whole distributor with gasoline (my favorite solvent, thank God I don't smoke!) and assembled it.

I put the distributor in and fired the car up, at 8 degrees advance, not bad for the old "line-em up the way they came out" approach.

With the EST disconnected the car is now dead on 6 BTDC. It doesn't waver even half a degree, must be the new timing chain doing it's job

With the EST connected it instantly advanced the timing to about 20 BTDC and holds it there. The car idles roughly, misses occasionally, and is hard starting.

With the EST disconnected it's hard to notice that it's just running off the base timing. It still hiccups if you get on it WOT but not quite as bad as before. I can pretty much stomp it off the line and board it up to 60mph. This is new. In fact, it actually runs pretty damn good.

I went and got gas. While I was there I reconnected the EST. The car started and died on me. I hit the key again and kept on the gas. It fired up and held a fairly high idle, about 1700. I dropped it into gear and drove off. I got on the street and tapped the gas about 3/4 and INSTANTLY had to let off. It was missing horribly and hesitating like there was no tomorrow.

I continued driving it around to test different throttle angles, downshifts, part-throttle acceleration. The car seems like it runs on 8 cylindres for awhile and then peters out, running on 7 for a few seconds and then back on 8. Weird.

I stopped off at Kragen, disconnected the EST and drove off. The drivability is now back, the car runs good and is hardly missing, only the occasional.

Alright, now that I've changed every sensor except for the MAF I'm starting to wonder if possibly the ECM didn't take a dump after all. The change in the car is unbelievable when the EST is connected/disconnected.

It's better than before, especially with the EST connected, but not much. At least with the EST connected I can drive around town if I 'really' pussyfoot it. One thing I don't understand is that it doesn't matter whether the EST is connected or disconnected the car will still surge sporadically at idle. It will cycle from about 600-1100, but not everytime I come to a stop. Sometimes it's fine, other times it will surge. There's been quite a few times that I will drive down the block, stop and it's fine, hit the next light and it's surging, hit the next light after that surge, next light nothing and then it'll be fine for the rest of the day.

Ideas?

Thanks so much for the help man, I appreciate it!!

Colin

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Webmaster: www.IROC-Z.org

[This message has been edited by ColinOpseth (edited July 13, 2001).]

 

Man, I'm scratching my head on this one. The only other time I had surging, it wasn't that bad. Ended up being a bad EGR valve. But I hate throwing crap out at you to try. I suppose it would be a good idea to try and get an ECM to at least try as well. Have you messed with the ECM at all? Maybe the contacts for the PROM are dirty and could use reseating?

 

honestly, i haven't even touched the ECM..

i'm thinking that i need to pick one up, could i use the '89 VATS-equipped ECM if i put the '86 PROM in it?

i thought VATS was only on the PROM not in the ECM itself.. if that's so I'll try to change the ECM tomorrow and go from there..

it's got to be something sensor-related because of the change in how it runs with the EST disconnected and connected..

and you think you're confused? imagine me, lolol..

thanks for your help man I'll keep you posted, i'll look up the ECM numbers tonight and see what gives..

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Webmaster: www.IROC-Z.org

 

Back from the dead baby!! Can't believe I didnt find this post earlier. I'm having this exact same problem, car runs OK with the EST bypass disconnected, connect it and it runs like crap, stalls out. Car is throwing no codes. So far I've replaced IAC, TPS, Plugs, Cap, Rotor, Ignition Module, ECM, Knock Sensor, and its still doing it! Looks like I'll be replacing the Pickup Coil tomorrow. Hope this fixes it. I'm about ready to set this car on fire.

 

Even though you replaced the pickup coil, the distributor itself could be worn out.


This is small cap HEI, correct?


I would try a reman distributor.

 

my friend had the same problem with his 91 v6. replaced ecm, memcal, ign coil, pickup coil, cap, rotor, mostly all sensors and we never solved the problem. will someone find the answer to this mystery. the v8 swap will though. LOL

 

I'm having this same problem.
Let us know what you found/find out.

 

OK...I've been coming across this same problem a lot on this board lately so I decided to check the schematics. All the VIN's I checked for the 1991 model year (3.1L VIN T, 5.0L VIN E, 5.0L VIN F & 5.7L VIN 8) have remarkedly similar ignition circuits. Almost identical in all cases. I came up with the following list of possible causes (excluding an actual part's defect/damage):

1.) Any one or combination of the following distributor wires feeding from the ECM to the distributor may have an intermittent short/open:
·Ignition Module Bypass Control (TAN-BLACK)
·EST Output (WHITE)
·Distributor Reference Pulse HI (PPL-WHITE)
·Distributor Reference Pulse LO (BLK-RED)
As a quick test, you could run some jumpers from right at the distributor to the ECM directly, take the car around the block and see how she runs. If it's much better, remove one wire at a time until the problem comes back -- then you'll know what line was bad.

2.) Something which really has me wondering is if the Tach itself in the instrument cluster is causing a problem here such as sinking too much current and drawing power away from the ICM. It should be easy enough to pull the instrument cluster, start the car and see, but GM has made it a bit more difficult at least on my LO3. When I start the car with the cluster pulled, it acts a little strange. I haven't bothered firguring out why, but chances are it will do the same thing to all engine types of that year, at least. You could snip the WHITE tach wire as a test, but a lot of these ICMs use two white wires: one which feeds a TECH signal to the cluster and one momentarily sunk to ground to fire the coil. If the car doesn't fire -- you know you snipped the wrong one. hehehe...Just make sure you leave enough room to reattach the TACH line when you're finished.

 

Here's two of the ignition circuits (VIN E & VIN 8)

 

And here's VIN T & VIN F. Note that for VIN T, it looks like there's a schematic error with the PINK & WHITE wires running between the ICM & the coil -- they look as though they've been swapped. As it is now, everytime the coil fired, there would be a direct short to ground. To be safe, assume this schematic has an error for this harness.

 

Some have had similar problems due to cross connecting the secondary fan, or high temp over-ride switch with the knock sensor. The connectors are the same. Won't hurt to check.

 

You did say that your getting an egr code correct? I would correct that problem before changing anything. Better yet scan it with a good quality scanner that you can drive the car with and watch whats going on. This might cost you a few bucks for a shop to do but its cheaper than replacing parts on a guess!

 

I had the problem with the surging..replaced tps, iac, egr, egr selenoid, O2 sensor, ....come to find out I had a bad intake manifold gasket leak...replaced it car runs like brand new...except now it wont run in gear at idle...disconnect the est and it runs like a champ but will tend to run hot if a lot of stop n go intown...get a little wind under it and the temp will drop all the way ....
hope that helps someone ....and if anyone knows why my car wont stay running with the est connected but runs great with it disconnected please let me know

 

I'm having same issue in my 86 Firebird. It originally had the 305 5.0L fuel injected but my cousin blew it up. Had 96k now my pap has had a garage put a 350 5.7L in the car it's from a 88 or that year engine gm bc it was at a 88 I found the correct valve cover gaskets, he has gotten to old to work on it so I inherited the car . But has an hei on the tpi system and I've done wires, plugs n checked over everything. All the forums. And it's Def ran way better with the est wire unplugged. But horrible with it plugged in. No codes at all only when the wire is unplugged the engine light comes on..