Long story but here's the background
92 z28 5.0 camaro purchased from original owner 100k miles
he had a manual and a 5.7 swap done by someone who seemed like a backyard mechanic, found many things wrong. Vacume hoses routed from egr as a feed to the egr solenoid and nowhere else. The vacume reserve canister not even hooked up. Wrong trans fluid, no gaskets on the a/c hoses, theres so much more but you get the point.

It idled at 1200, so I went through, routed all the vacume lines correctly did a bunch of research and looked at the same year camaro of a friend's with same options etc. Found a broken vacume hard line in the firewall.

car ran mint after this but idles really low and stalls occasionally..
figured I would do a new tps / IAC.. tps ohm out a little out of spec. And figured the IAC never did anything because the vacume leak making it idle so high.

when doing the IAC reset procedure my dumb @ss though when it said jumper pins A and B I thought it meant the pins A and B on the harness side of the IAC connector :"(

Once I put it back together it ran so much worse, realized what I did, figured I fried a fuse or something, checked every fuse, even the ones not in fusebox, every fusible link, replaced the ECM but did not know it wouldn't come with a chip..

no trouble codes except 12 which is the ecm is normal code.. or whatever..
side note. Can not get a snapon OBD 1 solus scantool to communicate with my car.. but the paperclip produces code 12 as mentioned before.

do I replace the chip ? (Which was a "fast chip" made for a 5.7. TPI At least that's what the sticker says

or do I just head and carb swap it and do a mechanical distributor and fuel press. Reg with a return. Because it's gutless and I put 4.10 rear in it and having that wimpy small powerband kinda sucks.

problem is that I am broke right now. If I can just get it running normal I would be happy. But if I spend over 500 I would rather put that towards go fast heads and carb intake etc.

is anyone in or near Massachusetts a tpi guru? Please help

 

Where is the chip that was in the original ECM you replaced?

 

Installed in the new ecm

 

AutoZone/advance/O'Reilly "loan" a noid light set that includes a gm 4 pin iac tester. That will be the easiest way to determine if the ECM has been fried.

 

I'll check that tester out. The car also has a stumble / hesitation at low Throttle and coming from 0 Throttle to partial Throttle. And sometimes it's off like a r@pe date and sometimes it's normal. Sometimes lacking a but of power.. very unpredictable.
almost un-drive able below 2k rpm. Very frustrating

 

I would start with what you know could be an issue and work backwards. TPS voltage is smart to measure not only at idle, but in a slow sweep to WOT. It should be perfectly linear to a WOT voltage of close to 4.5v. any drops indicate a faulty sensor. Bad aftermarket sensors right ouf the box aren't unheard of.

 

roger..
I'll recheck that. I did check I believe from .7 volts to 4.5 at WOT. Ill.check again with the new one. Maybe shorting that IAC circuit ****ed with it.

 

It's possible. Typically TPS is 5v and iac uses switches 12v, but if something on the board popped it could take other things with it.

 

That's getting closer to the potential problem.

Shorting the "A" and "B" connections of the IAC connector (circuits 441-444 from ECM connector J3, Pins E3 - E6) effectively shorts the output of the IAC driver(s) and despite the current limiters provided internally could have damaged an output driver IC (smoked form overcurrent). If you open the ECM and inspect the board, look for an 9-pin SIP with the part number 16034993, also labeled on the board as "U7". Looks like this:



Since the ECM was replaced, the driver should be intact (unless the outputs were shorted again). If the IAC outputs are monitored with an oscilloscope, they can be verified as working or not. It would help immensely if you could connect a bi-directional scanner to the ECM, and I know that an older SnapOn MT2500 works just fine with mine. It can be used to control the IAC so the outputs can be monitored. Once that system is verified as operating, the diagnosis of the unstable idle can continue.

 

It would be easiest to diagnose if it had an original CALPAK and PROM, which should include the EST system for a '91 model. Anything non-stock is going to be complete unknown for function.

 

OK I understand mostly. I am unsure of how or where to connect a bi directional scanner to the ecm. Or what a bu directional scanner is or looks like.
could the snapon obd1 scanner not communicate because of the custom prom ?
would the scanner be able to do this if it could communicate ? Should I buy a new factory prom so I can scan it and get live data and command the iac?
I did not retry to Jump a and b on the iac connector after the new ecm. So that chip you mentioned should be intact and working..

 

do I need both calpak and prom ? I ordered the ecu for my car. Matching numbers. Wouldn't the calpak be right ? And just need a correct prom?
do I order a 5.0 automatic prom? Even though my car is now a 5.7 with all the original 5.0 intake and stuff. Except I believe he did the larger injectors to match the larger cubic inch

 

How old are you?

Have you ever had an auto shop class before? YouTube University doesn't count.

You said you had a Snap-on Solus that couldn't see the ECM. Who's Snap-on Solus was it? Does this guy know anything about working on cars and how to use the Snap-on Solus. Was this guy helping you when the IAC terminal got jumpered and things went south.

 

I'm old enough to know that your not here to help like the other men here trying to help me, I don't need you to demean me and pose as trying to help while stroking your ego. Thanks but no thanks

 

Good luck

 

Listen, the senior members of this board have earned their right to be a bit cantankerous when the moment arises. I promise, they all mean well. If you go back to his history, you'll see he has been around since the beginning. Hell, I have too, but you can't recover old "hotmail.com" email addresses anymore. So this is my new profile.

If youre a shop type, like lot of us old timers are, take it in stride and answer honestly. It's a hazing if you will.

You're already asking good questions, and you're responsive. You're just responding to someone that has dealt with a higher magnitude of questions by profiles that never return than you could ever expect.

 

Harbor freight has a noid light kit that includes a iac noid to help show command direction. A faulty ecm can give issues with scanner connection. A custom tune will still show target idle speed and iac could. Warm engine you want to see 20-25 steps and hopefully it will idle at 7-750 rpm.

 

understandable, I came for help and not hazing. Not what I would expect from a fellow camaro enthusiast. I was in auto shop in high school and worked at a used car dealer as a mechanic for a year or two before I decided to be a Welder and went to school for that.. so I can be a little hot headed myself.. I have always been mechanically inclined but never had any formal training in scantools and fuel injection (fuel infection to me)
I'm 33 years old. I'm not old enough to have never dealt with tpi ever before this. It's my 2nd camaro my last one I had since 2010 it was carburated. I did a 6 speed swap in 2011 before it was as popular and I'm not an ace mechanic when it comes to the computer side but also capable.

I borrowed the scantool from a friend that never really uses it. He's a self taught guy as well. He couldn't offer me much on why it wouldn't communicate. .
and yes. I jumpered the iac because the instructions for iac as posted here on this page said turn on key wait 30 sec. Unplug iac jumper pins a,b and then start and adjust idle to 450
never did it say where pins a,b were and so I saw the iac connector labeled a,b

my previous camaro the aldl might have well never existed to me so... you could see where my confusion sprouted from.

 

I hate to make you all wait but I'll try to get to a harbor freight this week and pick up the noid tester as well as the other stuff mentioned by other members

 

I dont really want to spend 200 + on it but is there another option besides hoping i can find one at camaro heaven ? Do i get the one labeled 350 or 305. My car started as 305 but is now a 350

 

my apologies for firing back. I've been fighting with this since about this time last year. At the end of my wits about it and super frustrated. Didn't mean to take it out on you but didn't have capacity to take the hazing after how long I've been at this.

 

No problems man. Looking over my reply to you again it does read kind of shitty. I didn't mean it in some kind of hazing the new guy way when I wrote it but it sure does read that way.

I'm sorry.

 

The Hypertech or aujp wouldn’t be the answer the 90-91 Vette was the closest tune but probably not ideal. Might have to read the chip or use a scanner to see target idle. This could be a cts issue as well as a misadjusted idle screw if iac steps are out of range.
https://www.harborfreight.com/11-pie...set-97959.html

 

it's all water under the bridge. Thanks for trying to help. Re-reading it I could have taken it better myself.

I'm just super bummed I made such a dumb mistake when doing the IAC / idle reset procedure

I bought the car off the original owner and it the nicest vehicle I've ever owned, so once I fixed the vacume leaks it ran sooo good until I ****ed up the IAC and now I can't even drive it. And it was drivable before :'(

Mines on the left. The one to the right is my friends with only 8k miles..

 

hmm I'll call that junkyard maybe I'll get lucky and find an exact match to mine.

 

I did replace the coolant temp sensor as well as the air charge temp sensor. Before messing with the IAC. I think I also did the map sensor and the fuel pressure reg.

 

Where are you located? Instead of buying one, I could send you mine to use and send back when you're done. I haven't used it in probably a decade and my new build has the four pin flat connector style (LT1 Throttle body)

 

I'm in sterling ma. I would pay for shipping and your time etc. Greatly appreciated

 

The image seems to show both a CALPAK and a piggyback style adapter for a custom PROM and header to plug the original CALPAK onto it as a backup. In the case of a 1991, the CALPAK also has a sub-board containing the EST setup. Those are all necessary for the ECM to function properly.

The customs I have done are basically conversions of the factory CALPAK with a PROM socket which allows a custom-burned PROM to be inserted.



The "ostrich" style adapters went even further, allowing the program to be loaded to a flash-ROM or EEPROM so that no more plugging/unplugging is necessary once the adapter is installed.

 

As for a recycled replacement, getting a CALPAK for a 350 would likely be best, especially if the 350 swap included 24 lb injectors. Unfortunately ,it would not be a surprise if you have a little difficulty finding something in a local wrecking yard since the newest vehicles using that ECM are from 30 years ago, and many yards purge older items like that on a regular basis.

Regarding the Solus scanner connection to OBD-1 systems, much like a MT-2500, a specific adapter, power supply, code/setup ("personality")key, and possibly a data update for the model(s) you are working with. Unlike OBD-II, it's not a straight plug-and-play without a lot of other configuration. The Solus is only slightly better than the MT-2500 in that regard, and may be slightly worse than the 2500 for capabilities with old ECMs, since the 2500 had complete interchangeable/updateable pug-in modules in lieu of downloaded software updates.

If you have the GM-1 to GM-3 interface module and appropriate power adapter/cable, and STILL cannot connect to the ECM, the ECM itself may have a firmware or hardware issue.

If you suspect the SnapOn hardware and paraphernalia, it can be more economical to download TunerPro and get an interface for that application to access live data.

 

I had similar problems when I bought my 89 Formula 350 last year. I got the vacuum leaks and idle corrected and still could not blink out codes or communicate with a Snap-on 2500 or an OTC 4000e. Also the check engine light only came on for a short time and went out without starting the engine. I followed the GM service manual for diagnostics which led me to replace the ecm which did not correct the problem. So it turned out someone reprogrammed the prom/memcal and eliminated all the diagnostic functions plus many other things. I purchased/installed a replacement prom/memcal from Brian at Tuned Performance and everything now works as it should.

 

I can’t remember the details of the tune was bad , I think yours was in limp home mode causing all kinds of running problems.

 

this sounds spot on. Fingers crossed the one being mailed out to me solves the issue for me. I'll have to find one to buy or have one made as it's a loaner. But that would be awesome

 

I've suspected limp mode but I'm not professional enough with the fuel injection and computer jazz to determine for myself 100%

 

The noid light came in yesterday and hoping soon the loaner prom arrives. I'll test the IAC for function and also try the new prom.

 

Have you tested the old ECM to confirm the iac circuits have failed?

 

no, that makes sense but I returned it for the core already

 

You are on the right track. I have a spare CALPAK and might have offered to lend it out for trial, but it is for a pre-1990 which does not include the EST on the carrier.

Whoever posted the comment that the diagnostics may have been disabled in code is completely correct, thus the suggestion to start with a bone-stock 350 CALPAK (carrier) and PROM. Your scanner should be able to communicate with the ECM unless there is a cabling or hardware problem.

I also need to give you my thanks for bringing this up, since it made me wonder about my MT-2500 since it doesn't get used very often any more. I pulled it out of its storage case and discovered the 9V backup battery had died, and in pulling the battery found it swollen but not yet leaking. You might have saved me on that - Thanks!

 

Ain't cheap but won't leak or swell up in your Snap-on MT-2500 either and holds its charge for up to 10 years.

 

I didn't have time this weekend to take a look at the iac noid test. I am still trying to track down a prom for the car.. I got a new ecm.. wouldn't that have a calpak in it ? It only came without the prom chip but had a calpak in it.. this is kind of confusing to me..

glad you pulled apart your scanner and addressed the battery issue before it became a problem !

 

Still trying to track down a factory prom/memcal but would this also work ?

 

Yes the aujp would work if you have a working vats system. Not perfect for your build but you could then check iac steps .

 

I don't think the vats is active. I'll have to see if I can find out if it is or not

 

I can tune out the vats and if your wanting to try the aujp can do a better deal off eBay since I wouldn’t be paying their fees. I can also post the target idle vs coolant temperature. I can change as well i think you stated its a manual ?

 

it's a 92 z28 converted to 5.7 and manual. It was a 5.0 and auto previously.. I did that lower temp switch for the fans already. Don't know if that changes anything.

 

I don’t mind helping by reading the ede wright chip and posting the target idle speed. A 350 aujp may or may not help diagnose but I’ll post the target idle vs cts. The fan sw is a separate circuit for secondary fan not associated with the ecm. A/c pressure switch effects fan operation iirc Vette $8d tunes are a different fan switch setting. The only benefit I see going with a 350 memcal is the right knock filter.

 

Aujp target idle a manual would be better at 700 warmed up engine

 

That's why I didn't offer a spare, and unless the EST is correct the system might never read a detonation event correctly, since I believe the 305 sensor circuit is a lot more sensitive. The "test knock" function wouldn't be very happy either.

 

I can get a whole ecm from a 91/92 with a 305 for 200 from my secret camaro junkyard. But I don't like what you're saying about the knock sensor
wouldn't it cause it to be constantly pulling timing out of the engine?

more and more I just want to find some jegs vortec heads and make the swap

 

The EST for the 305 has to contend with a smaller bore cylinder, and that leaves more cast iron and cooling jacket between the combustion chamber and the microphone (knock sensor) mounted to the lower flange of the block. The 305's smaller bore thus requires greater sensitivity to detect a potentially smaller knock, and that can be a bit over-sensitive for a 4" bore engine.

For the purposes of diagnosis, it will likely run the engine well enough, but the tune (all in the CALPAK) won't be suitable for the different injectors, different spark maps, different injector constant, and a host of other variations between the 305 and 350. Since the 1227730 ECM for the later ThirdGens incorporated the PROM, the resistor network for backup parameters, and added the EST all within the CALPAK/MEMCAL, the 350 version CALPAK with stock PROM installed is really best for the purpose. The ECMs themselves are the same for a Cavalier to a Corvette (not considering weatherproofing) but the CALPAK is the critical piece.