Previous thread I started looked real long, so gonna try to make this shorter, but please view previous thread if you have time to read more details)

Looking for people who might have had these symptoms and what their problem was.

Symptoms: 1 yr ago it used to run "good" for 30 minutes but then start running bad\rough\ like its missing, sounds & runs retarted, has only 1/2 the power.
But over time as we tried replacing parts like plug wires, plugs, rotor, cap, COIL, Mass air flow, fuel filter, -- it no longer runs good for that 1st 30 minutes anymore. Difficulty starting.

Minor symptoms car always had: engine light would come on if outside temperature ever got below 60 degrees. And if you cut engine off after been driving for awhile, it won't restart unless you let car sit for 5 minutes.

Previous years fixes:
-replacing the COIL did fix it before.
-replacing the Mass Air Flow sensor did fix things before.

But now replacing those things did not work. And we replaced other things like plugs, plug wires, fuel filter, and not working.

Probably going to try these next:
Coolant temperature sensor, air intake temp sensor, electronic spark control module, ignition control module.

Thanks for any feedback and your time
--
James N Jenell

 

By simply plugging in a datalogger you can do a ton of troubleshooting in a relatively short time, - relative to your sensor outputs & function.

If you have already determined sensors to be fine, then have you tried replacing the ignition pick-up module or the distributor?

 

Hi. I'm not familiar with a datalogger? Are they expensive?

On 12/27/2011 we replaced distributor, MAF sensor, Coil, Spark Plugs & Wires.(Yeah car has been doing alot of sitting)

I think next we will try ignition pick-up(control) module if I find out we haven't already. Possibly a "electronic spark control module", and maybe some temp sensors.

Thanks for the input.

I'm hopeful its going to be the ignition control module based on what you said, and when i looked it up on autozone/advance auto parts.com it seems to be a common item. VS the 'electronic spark control module' looks to be harder to get special order.

 

Have you tryed check what is the code when engine light comes on? You might also try fuel pressure (40.5-47 psi ) Have notice any louder sound from the fuel pump?I have experienced with a bad fuel pump after running car was surging,wont run and some other issues,replaced sending unit,fuel filter and fuel pump,fuel presure is good now and back on road

 

hi. i actually thought this was a different thread.
thanks for your input.
yeah we checked fuel pressure
and it had 40. glad to hear it was your fix.

we r now thinking about replacing the computer
ecu.
i am hearing some examples
where that fixed their problem.

 

The most common causes of your symptoms are ignition control module(the one in the distributor), pick up coil(also in distributor), or injectors. Unlikely that your ECM is causing this. Sounds like you've replaced alot of parts. Would have almost been better to have had it diagnosed professionally.
As an auto technician, I make a practice of testing and verifying a part has failed before I replace it. Otherwise I wouldn't have a job for long. I would recommend you spend some time testing before you buy anymore parts. Several members of this forum are well versed in methods for testing the above components and we'd be happy to help if you ask.

 

very greatful for your input.

how can we test the ecu? and injectors?

any special way to test those?

 

many years ago i had the ecu go bad on mine caused some of the same symptoms you have, then years after had same issue but found out the hypertech chip i installed went bad an was frying the ecu..

 

wow! thanks for your input.

 

Minor symptoms car always had: engine light would come on if outside temperature ever got below 60 degrees. You have yet to tell what codes you got?

 

that was an old symtom
from 1 yr ago. ive had car for maybe 10 yrs and it always had trouble running when weather is cold
<60. when i check code now it only gives 12 code meaning no real code.
i believe when light comes on and goes away that means computer corrected itself.

 

When light comes and goes away it means there is a soft code. You need a scan tool to monitor the system and see what soft code is causing the light to come on. It may be a clue.

I tried twice to reply yesterday. I was having trouble sending my replies. I always seem to write novels. Ill try to be more brief.

Test injectors for resistance. Test them cold and again hot. They should read 12-17 ohms and should read higher when hot. Look for any that read lower when hot. Any that read less than 12 are bad and need to be replaced.

Its best to test them with a lab scope where we can see the signal pattern. This reveals a great deal about the health of the entire circuit and even possible mechanical faults in the injector. What cannot be seen any way but on a test bench is the spray pattern. A clogged or restricted nozzle can cause fuel to stick to the port wall rather than atomize and lead to a misfire. If there is any question, remove the injectors and take them to an injector service for cleaning testing and replacement as needed.

 

Thanks for your input. Go ahead right a novel, I will read it! And I have same problem.
Umm.. the CEL light hasn't gone off in a long time, when I last checked it only gives the 12 code.
Thanks for the how to test injectors.
And S*** I accidentally clicked on the "Unsubscribe to this thread link" so I hope by replying now it will resubscribe me. I also hope I did not click on the "Unsubscribe to all threads" link.

 

Verify spark KV using an inexpensive adjustable spark tester from any parts store. Set the tester at 40KV. GM HEI should easily fire 40KV. If not, try 30, if no good try 20. If you get 20 or 30 and not 40, check the plug wires for breaks or arcing to ground. Try the test at the coil wire. If you get 40KV at the coil and not at the plugs, think about replacing plug wires, cap and rotor. Verify 40KV at atleast several plug wires.

As far as ECM failure goes. In 20 years as a GM and Chrysler FI specialist, I've replaced a hand full of ECMs/PCMs. Two that I remember very well were replaced in error because I missed a mechanical or other failure in my diagnosis. ECMs, aside from user error or physical damage, rarely fail. But we get frustrated not being able to find anything else wrong so we go for the ECM. One thing I will concede is that these cars are getting older and even solid state components are subject to internal failure from years of hot-cold cycling and being inside a moving vehicle.

We can check ECM health by monitoring data and looking for anything that's off. Test the circuit and sensor and verify that it's okay. If the sensor and circuit are okay but data is weird, then you may have a bad ECM. Actuator circuits are the same, especially injector or IAC circuits since they can be stressed by a shorted actuator or wiring. Verify that the actuator is okay by checking resistance. Verify the circuit is okay by checking continuity and for shorts to power or ground. If the circuit and actuator are okay and the ECM doesn't control it as it should according to ECM data, then you likely have a bad ECM.

 

Code 12 is also a failure code. We forget this because were used to thinking of it as an indication that the self diag system is functioning normally. But the reason we get code 12 is because the engine isn't running and producing a crank reference pulse. Code 12 means "no crank reference pulse received by ECM" and may be a clue to a problem in the distributor or circuit. The purple wire from the 4 wire dist connector to the ECM carries the crank ref signal. Its a 5V square wave and should look like 2.5 volts on a volt meter with the engine running.
Never assume thayt because a part is new, it's okay. Especially Cardone distributors. I've seen too many of these be bad right out of the box. Verify the crank signal and check circuits if the signal's not there.

 

Man its been 15+ years since i took my car to a GM garage only things i remember the tech guy telling me is that they changed out the ecu an the new one blew out right away then they replaced two relays an the ecu again then it was all fixed up..

 

I bet that tech had a very bad day when his boss had to pay for an ECM. One of the main things they hammer us on is checking all powers, grounds and actuator circuits before installing any ECU. The most common cause of ECU failure is poor power or ground connections or a shorted actuator circuit.

GM dealer techs today know less about these early cars than many of the members on this forum. Dealer techs are focused on vehicles built in the last 15 years, especially those still under warranty. You may get lucky and find an old timer who grew up on these like I did. If he hasn't forgotten most of what he ever knew, like I have. LOL

BTW, some vocabulary: ECU means electronic control unit and can define any solid state control device. ECM means engine control module and identifies the ECU that controls the engine. PCM means powertrain control module and defines a module that controls both the engine and electronic transmission.

 

hmm, dont remember what 2 relays they were talking about do you?

 

Hey so replacing our computer didnt fix it.

My question to you is how can we test the distributor to make sure it is ok? You might have just told me above and I'm not picking up on it. I told my dad that maybe we should pull the distributor and at least get the ignition module in it tested at autozone(I know they can do that much), but how do I know if the distributor itself is bad? Please let me know if you already told me how to test Dist in the quoted above. Appreciate your help.

-Also what was strange after we replaced the computer, the car started "bumped off" real strong, whereas just yesterday we couldn't hardly get the car to start. So immediately we thought we had it fixed... the engine seemed to be running smoothly....then minutes after idling it kinda went back to it's old ways running bad and engine/car shaky.
Some guy here mentioned that he replaced his computer, the computer went bad immediately, then they had to replace 2 relays, replaced the computer after that, then it was fixed. I wonder what 2 relays he was talking about.

 

As stated earlier, I would highly recommend checking the injectors. Check them with an ohmmeter for proper resistance (12-17ohms) when cold and hot.

Check fuel pressure when car is not running to see if they are leaking. The pressure should stay up ~43psi forever (or at least minutes), it if decreases, the fuel pressure reagulator or injectors are suspect.

 

Check the ECM connectors/wires for bare spots, burns..Make sure the PROM is seated properly.

It is VERY unlikely (as mentioned before) that this is an ECM issue.

 

It was the Injectors!