ECM Heat Soak?
Thread Starter
Drifting
Joined: Mar 2008
Posts: 1,801
Likes: 426
From: Denver CO
ECM Heat Soak?
Recently bought a low mi 84 and thought I had worked out all the gremlins.Runs great until it gets up to operating temps about 30 min. into a drive then falls down and pops out the TB.Let it cool down and it runs fine again.The reason I'm leaning towards ECM is for the first time this season I used the heater and within 5 min it acted up. Hot air blowing in the cockpit where its located? Ive done a complete tune up. Cap /rotor/coil/Control module /plugs/wires and a new Cat. No SEL and throwing no codes. Just passed emissions w/flying colors.This computer controlled sh## is frustrating.I'm loving my 76 more every day. Help!
Last edited by gjohnson; Oct 20, 2015 at 11:47 AM.
Melting Slicks
Joined: Jan 2008
Posts: 2,054
Likes: 120
From: AZ
I'll be real surprised if it makes a difference. I think you have something else going on, unless there is a real problem with an old ECM. Lots of old school guys blame the mysterious silver box, when it is fairly rare, though they do, fail.
The basics are as before; just accomplished a bit differently.
The basics are as before; just accomplished a bit differently.
Race Director
Joined: Mar 2015
Posts: 15,926
Likes: 579
I'll be real surprised if it makes a difference. I think you have something else going on, unless there is a real problem with an old ECM. Lots of old school guys blame the mysterious silver box, when it is fairly rare, though they do, fail.
The basics are as before; just accomplished a bit differently.
The basics are as before; just accomplished a bit differently.
I am thinking icm or lack of thermal paste or evan the coil going bad. 
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Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
Your issue sounds electrical on the firing side to me. There is another coil inside the distributor who's name escapes me right now. Its located under the rotor on the base of the distributor. Easily tested with a DVM. Check an FSM for more details. Sorry I couldnt be more help with names but just speaking from my own experience.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
That is the "pick up coil" and if he has injector pulse, then the pick up coil is working. He never said that he did, so that would be a good and easy thing to check when it dies. Especially easy, on an '84.
Melting Slicks
Joined: Nov 2010
Posts: 2,216
Likes: 112
From: Michigan
I read some of the oem ecm's had an issue were they would crack, then when warm they'd act up. My car was running rough after running for about 30-40 mins, so I swapped the ecm with a remain I had left over form my TA and it went away.
Thread Starter
Drifting
Joined: Mar 2008
Posts: 1,801
Likes: 426
From: Denver CO
Acted up once again like clockwork so I pulled over and pulled the air cleaner cover to see whats goin on. Injectors in unison are spitin and sputtering. What all sends info to the ECM back to the injectors. Besides complete ignition tune up I have replaced O2 sensor/Cat. Replacing the ECM coolant sensor next.Still No SEL or codes when it acts up . I'm quickly finding out that C-4's have tons of problems by looking at all the treads on this forum.Are C-4's lemons? My C-3 has performed mechanically flawless for the 25yrs I've owned it. I'm still leaning towards bad ECM or PROM.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Acted up once again like clockwork so I pulled over and pulled the air cleaner cover to see whats goin on. Injectors in unison are spitin and sputtering. What all sends info to the ECM back to the injectors. Besides complete ignition tune up I have replaced O2 sensor/Cat. Replacing the ECM coolant sensor next.Still No SEL or codes when it acts up . I'm quickly finding out that C-4's have tons of problems by looking at all the treads on this forum.Are C-4's lemons? My C-3 has performed mechanically flawless for the 25yrs I've owned it. I'm still leaning towards bad ECM or PROM.Now back to reality. The primary inputs for the injectors are:
*Coolant temp sensor
*MAP sensor
*Pick up Coil
*ECM receives and drives it all...
*...and fuel pump and regulator ensure an even amount of fuel pressure.
None of those devices are typically affected by heat. We need to get back to some basics here. Go drive the car until it dies w/the proper tools to do the following: When it dies, what is missing? SPARK or FUEL? For fuel, you need to install a fuel pressure gauge. From this:
Injectors in unison are spitin and sputtering.
..I'm thinking a fuel pressure issue, which is fairly common on CFI cars -a lot more common that over heating ECM's. Test those basics...report back. I'm sorry for your frustrations, but computer controlled cars are easily diagnosable -if you follow a procedure.
Race Director
Joined: Mar 2015
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Acted up once again like clockwork so I pulled over and pulled the air cleaner cover to see whats goin on. Injectors in unison are spitin and sputtering. What all sends info to the ECM back to the injectors. Besides complete ignition tune up I have replaced O2 sensor/Cat. Replacing the ECM coolant sensor next.Still No SEL or codes when it acts up . I'm quickly finding out that C-4's have tons of problems by looking at all the treads on this forum.Are C-4's lemons? My C-3 has performed mechanically flawless for the 25yrs I've owned it. I'm still leaning towards bad ECM or PROM.ok just saw it's not a lt1 so don't know but would look into it.
I would test the coil and icm too they can be bad from new and drive you nuts.
Last edited by antfarmer2; Oct 23, 2015 at 06:28 PM.
Thread Starter
Drifting
Joined: Mar 2008
Posts: 1,801
Likes: 426
From: Denver CO
Havent done the coolant sensor yet,its due to arrive tomorrow from vendor.How much coolant will come out w/change out?. Its the one on the front of manifold.I did test the coil and it checked out,(ohms). One thing was the ground wire was loose on the coil.That would be great if that was it. I did put back in the old coil that I replaced,in case that caused an issue w/the new coil.Thanks for the replys!
Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
Cold engine:
Loosen sensor, loosen rad cap, squeeze upper rad hose flat, tighten rad cap, change sensor quickly = minimum loss of coolant.
Suggest checking fuel pressure the pump could be headed south after 30 min run time.
Loosen sensor, loosen rad cap, squeeze upper rad hose flat, tighten rad cap, change sensor quickly = minimum loss of coolant.
Suggest checking fuel pressure the pump could be headed south after 30 min run time.
Race Director
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Race Director
Joined: Apr 2002
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From: Anaheim CA
Thread Starter
Drifting
Joined: Mar 2008
Posts: 1,801
Likes: 426
From: Denver CO
BUT.......
The reason I said that is the because of the difference between the C-3 problem threads and C-4 problem threads.BIG numbers diff.Being a C-3 owner for 25 yrs I noticed. I will figure this "glitch"out.