Javier87z28

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hello guys im new to this forum im looking for some help. Ive been having intermittent troubles on my 87 z28 305 tpi with code 42 some days it will run perfect and some days it will start off fine then after reaching operating temperature check engine light goes on and it drives in backup mode which is sluggish. It always starts out fine then once reaching operating temperature check engine light will come on but sometimes it drives without any issues even when reaching operating temp. I was advised that code 42 is a short somewhere in the est lines going into ignition module or bad ignition module or bad ecm, ive changed ignition module with no luck ive looked over wires to not find a short and im at a dead end? anyone have any feedback or had this occur to them? Any advice would be appreaciated

Tuned Performance

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http://www.chevythunder.com/est_code_42.htm

Javier87z28

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when initially turning the car on and just on idle ses light will not come on its only after ive been driving about 15-20 minutes and sometimes it wont even turn on and drive perfectly fine

Tuned Performance

iTrader: (92)

sounds heat related but since you already replaced the icm that should be ruled out. It could still be the ecm or ecm ground behind the pass cylinderhead

Javier87z28

iTrader: (1)

would you happen to have a pics of where exactly the ground is? and yeah i was almos sure it was the ignition module having that it would only do it when reaching operating temp only to replace it and no luck, one other thing when this all started happening my brother was in the passenger side seat and slammed the door while i was driving almost immediately it stalled idk if it might be relevant?

Tuned Performance

iTrader: (92)

The ecm is on the passenger side under the dash, Tell him to buy you a new one lol. The 1227165 ecm has been known to have issues with the circuit board flexing over time. This sounds silly but drop down the ecm and start the car and tap on the ecm case with the end of a screw driver handle it the car stalls and starts running rough get a new ecm. Sorry dont have a picture of the ground. I believe there are 3 wires on a stud on the back of the cylinder head. Not real easy to get to. There should also be a ground strap from that to the bulkhead.

Javier87z28

iTrader: (1)

hmmm i have a service manual so ill look it up lol and geez ever since then its been a pain!!! how exaclty do you take off the ecm? are there bolts or screws?

Tuned Performance

iTrader: (92)

disconnect your battery first. The ecm is in a plastic holder under the dash. You will need a 7mm nut driver . there are 2 screws that hold the plastic bracket to the dash frame. drop the ecm down aways and you will need to unplug the ecm connectors. There is a blue tab on the top of each connector push and hold them down and pull and wiggle the connectors back. drop out the ecm and plug it back in and lay it on the passenger side floor. reconnect your battery and fire up the engine. lightly rap on the ecm case and see if the car starts running rough or stalls.

Javier87z28

iTrader: (1)

Thanks ill give that a try today...ill let you know how it goes! And ill give my brother a slap upside his head lol

Javier87z28

iTrader: (1)

one other question ive also heard that this code could be a result of a prom or cal pack not seated correctly where is this located?

Tuned Performance

iTrader: (92)

the memcal is inside of the ecm and is not related to this error code. If this is a bad ecm tell your bro he owes you a ecm and a icm and a large pizza

Javier87z28

iTrader: (1)

lol so i would have to replace the icm again? i just changed it maybe a month ago? and is there any additional way of testing ecm? and that doesnt sound too bad right about now lol

Tuned Performance

iTrader: (92)

I was just saying have your brother pay you back for the icm you bought was all. No other way I know of testing the ecm

Javier87z28

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lol okay ill try it out and let you know how it goes thanks

Tuned Performance

iTrader: (92)

Just remember I didn't say to hit it with a sledge hammer

Javier87z28

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so I took off the ecm and no luck but I have been trying something usually when I'm coming a stop or at a stop that when the car will idle real low then stall and throw code 42 so when coming to a stop I will just keep the engine revved above 750 and voila it didn't throw the code for two days now any ideas? I have already put in New iac valve?

Javier87z28

iTrader: (1)

and in get no pizza double hammer!

Tuned Performance

iTrader: (92)

are you sure its not maybe a code 24 than ?
My wife got us pizza last night I was thinking about you lol

Javier87z28

iTrader: (1)

lol must've been nice and I actually am eating pizza but my brother didn't buy it but yeah it's code 42 4blinks pause 2 blinks but it's weird if I just don't let the idle drop it doesn't throw the code I'm at a standstill

Tuned Performance

iTrader: (92)

That is really odd, Im leaning towards ecm, hate to tell you to spend money in the wrong area though. You might set your min idle speed adjustment.

Javier87z28

iTrader: (1)

at park it usually idles at about 750 and drive about 550 to 600 sometimes a bit lower is this correct?

Tuned Performance

iTrader: (92)

Thats a good rpm range if it drops to 400 the emgine will die way to low and the injectors will shut off.

Javier87z28

iTrader: (1)

hmmm wish there was someone I could swap ecms with not a lot gens out here

Tuned Performance

iTrader: (92)

post a ad in the classifieds with your location, maybe some one close would let you borrow theres for a day

Javier87z28

iTrader: (1)

good idea I'll see if I have any luck if you come across anything let me know

Tuned Performance

iTrader: (92)

I do have one you can borrow but shipping to you would maybe be 12 and then 12 back to me.

Javier87z28

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thatd be great if you could!!

Tuned Performance

iTrader: (92)

I will send you a personal message with my paypal and will ship it in the morning

Tuned Performance

iTrader: (92)

did you still want to try the ecm ?

Javier87z28

iTrader: (1)

yeah did you get the $12 i sent you a pm

Tuned Performance

iTrader: (92)

your usps tracking is 9405509699939532880166

oddscrounger

did you fix this issue? I went with an OEM replacement ICM and it fixed the problem. I also ensured that my chip was seated correctly in the ECM...

Javier87z28

iTrader: (1)

Yeah checked both with no luck it still throws code 42, just when having driven for about 30 mins and car reaches operating temperature

oddscrounger

I had a code 42 for the longest time and when the car was cold it would sputter/pop/hesitate on takeoff and usually run better as the car warmed up, so sounds like I had the opposite problem. Could be the wiring that goes to the ECM from the ICM...

TUNEDPERFORMANCE supplied me with that chart and I fooled around long enough until I finally put back in an OEM ICM (mine was an aftermarket) and the SES light went away. My SES light would come up right at startup even after I cleared codes.

oddscrounger

did you ever check out the ECM and see if there was an aftermarket chip in there?

Javier87z28

iTrader: (1)

Yeah he actually gave lent me a ecm to swap out and no luck my ecm and prom are stock im thinking might be the wiring to the icm was a little rough and thats what mine is doing running rough on startup

oddscrounger

All I know is the ICM controls spark timing during crank and after that it's the ECM/PROM once the car is running... and these commands run through the wires that connect to the ICM so I would check all of those... that chart should help..

Javier87z28

iTrader: (1)

So i rewired the maf and viooola no check engine light so im driving and its driving good and im at a stop and boom it stalls, so there is no check engine light seems like the rewire took care of that but now it stalls at stops???

oddscrounger

IAC motor needs to be cleaned and minimum idle air speed needs to be checked... also check to make sure correct voltage at TPS and that there is no vacuum leaks

ASE doc

The MAF has nothing to do with code 42. If repairing the MAF wiring caused code 42 not to return, that's a coincidence. The stalling that you're having now is likely due to the same problem that was causing code 42. The ECM harness runs behind the intake manifold and is subjected to very high underhood temps. It's not uncommon for wiring inside the harness to fuse through the insulation. Check MAF voltage with a DVOM. It should read about 1.6 volts at idle. Try wiggling the harness at the rear of the intake while the engine is running and look for a change in the idle.

I would connect a scan tool and look for anything on datastream that looks off.

Javier87z28

iTrader: (1)

Well the re wiring of the maf got rid of code 34 and 36 but code 42 comes on ocassionally after it has reached operating temperature not always though it us intermittent

ASE doc

That makes sense. The thread doesn't state that you also had codes 34 and 36. The intermittent code 42 is almost certainly faulty wiring inside the loom of the ECM harness. The most common trouble area for this harness is right at the rear of the intake where it sees the most heat. Try opening up the loom in this area and visually inspecting the wiring. Look for the wires to be fused together. When you find the damaged wiring, you can go the easy route of separating the wires and wrapping them with tape, or you can do it the right way and rebuild the harness, replacing the damaged portions of wire with new and splicing them with solder and heat shrink tubing.

Javier87z28

iTrader: (1)

Thats what i was thinking but its a pain seeing anything behind the intake, would i have to remove the plenum to get a good view, and sorry about the miscommunication but i think the stalling was more than likely due to the maf codes.

ASE doc

I thought you said that the car was stalling after the MAF circuit repair.

The wiring behind the intake is hard to get at. You might try removing the dist cover from the back of the plenum and the dist cap for better access. I haven't had to remove the plenum to do basic repairs on this part of the harness but if the damage is extensive, you may need to clear a larger path. What I generally do with a suspect harness is disconnect both ends, which would mean disconnecting the ECM and the dist. Then do a continuity and short circuit test. You can do this a few different ways. I have done it by applying power to one circuit and looking for solid power on the other end using a test light, or better yet using a tail light bulb with test leads connected, while wiggling the harness, then look for power on any of the other wires in the disconnected harness that shouldn't have power. Another method is just to use an ohmmeter to test for continuity from end to end of each circuit and between circuits. The difference is that the light bulb or even the test light places a load on the circuit and will point out a weak circuit. Applying power to each circuit while looking for that power on the other circuits is also a more definite way of finding shorts.

Javier87z28

iTrader: (1)

It was stalling consistently prior to me adressing the maf wiring now it only does it every other week once a week, i inspected that area visually but couldnt see anything but yeah a test is my next step also the pickup coil wiring to the icm is a little questionable to me Im not sure if that could cause the issue as well doubt it

ASE doc

You can hardly touch the little connector from the pick up coil to the back of the ICM , on an older small cap HEI without it crumbling. Generally though, as long as the terminal contact is good, this doesn't affect performance. The recurring code 42 along with the stalling makes me think of a short to ground in the white wire. More likely what's happening is that the white wire and the black and red wire are fusing together. This will cause the engine to stall and set code 42.

Javier87z28

iTrader: (1)

Thanks man I'm going to look into it this weekend ill check back to tell you all how it went

Javier87z28

iTrader: (1)

Wiring between pickup coil and icm was a bit questionable so i replaced pickup coil, and car starts better idle is constant right about 550-650 and have not experienced any trouble for the past week so im guessing that is what was causing it no intermittent code 42 anymore

oddscrounger

it always makes me happy to see someone tackle a code 42 problem...

Javier87z28

iTrader: (1)

Biggest PITA trouble code ive experienced yet, but thanks guys this forum is awesome alot of very useful information!!! Maybe this can help someone out