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#1057579 - 06/01/18 09:39 PM ecm fried?  
Joined: Mar 2016
Posts: 17
newb'65 Offline
Junior Member
newb'65  Offline
Junior Member

Joined: Mar 2016
Posts: 17
Holland, MI
Well, I'm about fit to be be tied....

History;
3 weeks ago; engine light comes on intermittently car running a little rougher. Check codes and get a 13, 24, 41 and 45. Just to be sure nothing weird is going on, I clear he ecm by disconnecting battery for an hour. After starting the car and driving around a few days, check engine light comes on intermittently, i check the codes but now only get code 13.

Although my o2 sensor is only a couple of years old i bought a new bosch sensor and was going to replace it as a way to eliminate that component in my diagnostic quest. Well today before I had a chance to replace the o2 sensor I was driving and my check engine light started rapidly flashing and the car ran like crap. Its definitely running rich by the way the exhaust smells and the car is running like it did when my ecu crapped out last fall.

So this afternoon i thought that before I spend a lot of time chasing diagnostics I would check codes again. When I attempted to pull codes using the jumper method, i get nothing, not even the 12 code. So i pulled the ecm and cleaned up the terminals to make sure good connection and contacts were being made-- no difference.

other weirdness; while the car still runs (poorly) it is hard to start, tach is jumpy, and idle is up and down. I also just noticed that some relay (fast idle relay?) located next to the spark control module sometimes is rapidly cycling with the MCC with the key in the 'on' position but not yet started. Perhaps it always has done this, but I just noticed this sound today. I also have been hearing some ticking coming through the radio in the last week making me think ignition issues.

Stuff I have replaced;
TPS (good quality NAPA unit) last fall, lubed the barrel and stretched the spring. Good voltage readings after replacement.
ECM new used unit last fall.
Set timing (verified tdc) at 6 degrees btdc.
Rebuilt entire carb with deluxe kit from Cliff last fall along with re-bushing the primary shafts.
new plug wires, but I have never replaced cap, rotor or coil.

Car ran well after the work/parts above until about 3 weeks ago when the check engine light started coming on. engine is otherwise stock. Any advice?


--Steve--
1st Father-Son project 1985 SS
#1057591 - 06/02/18 05:22 AM Re: ecm fried? [Re: newb'65]  
Joined: May 2007
Posts: 5,026
Buick Runner Offline
10+ Year
Buick Runner  Offline
10+ Year
Member

Joined: May 2007
Posts: 5,026
Dharma station 1 the Hydra
It would be highly unlikely two ECMs would go bad likd that. Do you have a dwell meter for checking the fuel mixture dwell? I kind of suspect you may have a vacuum leak causing a lean mixture, which smells worse than a rich mixture. Other thing is that your wiring harness may have a short to ground somewhere or your alternator is overcharging.


SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes, and Jmod.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1057595 - 06/02/18 04:16 PM Re: ecm fried? [Re: newb'65]  
Joined: Dec 1999
Posts: 11,898
86ttop Offline
20+ Year
86ttop  Offline
20+ Year
Member

Joined: Dec 1999
Posts: 11,898
Brooksville, Fl
Sometimes when the ECM is suspected, it will set codes in the 50's, having said that, it doesn't necessarily mean that 50's codes will be set every time the ECM is suspected. The ECM is a very durable device and many times when it is the suspect, it is in fact another problem such as poor grounds or sensors out of range. Can you get it scanned??


Leo Paugh
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POW*MIA
You are not forgotten
If things improve with age, I must be approaching magnificent. thumbs
#1057611 - 06/03/18 03:56 PM Re: ecm fried? [Re: newb'65]  
Joined: Jun 2016
Posts: 360
ChasUno Offline
Member
ChasUno  Offline
Member

Joined: Jun 2016
Posts: 360
Bradenton, FL
The MCS is the only thing I recall that rapidly "ticks" with ignition on and engine not started.

Also, from what I have heard, ECM's either work or they don't. The fact that your car still runs, albeit poorly, suggests that the issue lies elsewhere. Faults with sensors can cause the ECM to get confused as it won't be receiving the correct values to work with. Sometimes it will default to a limp mode, though intermittent faults can cause running issues that you describe.

Have you checked ground points? It could be a poor connection causing issues. Also check that fast idle solenoid near the throttle quadrant lever isn't behaving oddly.

I also agree with Buick and 86 above, check for vacuum leaks and wiring shorts along with vehicle ground points.

Last edited by ChasUno; 06/03/18 03:57 PM.

1986 Monte Carlo SS

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#1057615 - 06/04/18 12:48 PM Re: ecm fried? [Re: Buick Runner]  
Joined: Mar 2016
Posts: 17
newb'65 Offline
Junior Member
newb'65  Offline
Junior Member

Joined: Mar 2016
Posts: 17
Holland, MI
thanks for the advice. I will go through the grounds and vacuum circuits and check those. It also looks like the cap/rotor/coil may be original, so I going to replace those to rule out any ignition/ coil problems. I am going to buy a dwell meter as the service manual calls for this tool in a number of diagnostics.

One item nobody has commented on is the rapidly flashing check engine light. This flashes constantly when the engine is running and does not reset even after I clear the ECM by disconnecting the battery for an hour. The shop manual doesn't mention this condition.

any thoughts here?


--Steve--
1st Father-Son project 1985 SS
#1057626 - 06/04/18 03:44 PM Re: ecm fried? [Re: newb'65]  
Joined: Jul 2003
Posts: 9,208
SickSpeedMonte Offline
15+ Year
SickSpeedMonte  Offline
15+ Year
Member

Joined: Jul 2003
Posts: 9,208
MD
http://www.winaldl.joby.se/

I made the cable described on this page and downloaded the software. It allows you to read sensor values and engine codes with a laptop. It was very helpful diagnosing my TCC issue, which turned out to be the ECM. So the car can still run and have an ECM problem.

To enter in to the mode that allows the ALDL port to output serial data to the laptop, you insert a 10k ohm resistor across pins A and D (pretty sure... its the same pins you short to read on the CEL). That causes the CEL to flash very rapidly, I guess reflecting the 1's and 0's going to the serial cable at 160 Hz.

#1057640 - 06/05/18 08:41 AM Re: ecm fried? [Re: newb'65]  
Joined: Jun 2003
Posts: 187
stew'86MCSS396 Offline
Member
stew'86MCSS396  Offline
Member

Joined: Jun 2003
Posts: 187
Honolulu
Rapidly flashing cel is normally attributed to a bad PROM chip but it also may mean it's not seated all the way into the ECM, too.

#1058220 - 07/11/18 06:27 PM Re: ecm fried? [Re: stew'86MCSS396]  
Joined: Mar 2016
Posts: 17
newb'65 Offline
Junior Member
newb'65  Offline
Junior Member

Joined: Mar 2016
Posts: 17
Holland, MI
Thanks to all for your input. I've been out of town for a few weeks and finally have been able to chase down the problem. Since I could not pull any codes due to the wacky behavior of CEL, I switch out the ECM and the problem was solved. Also had a faulty o2 sensor which I replaced and no CEL now. Not sure if switching the ECU fixed an ECU or PROM problem, but it was the easiest as I had an extra ECU laying around.


--Steve--
1st Father-Son project 1985 SS

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