Hello,
over a year ago, I changed my L98 motor and bought a zz4 crate motor. Installed a new custome prom chip for the ECM and was good to go. Car ran great until one of my fuel injectors grounded itself out and fried my ECM.

I changed out the ECM with a rebuilt computer, replaced the fuel injector and installed my old prom chip. The car would smoke like crazy and would hardly run. Removed the prom chip and the car would run better. Not 100%, but better. Took it to the GM dealership to shoot the computer, only to find out that they could not read the computer. They jumped the ALDL and the code 12 appeared but no data available.

Question,
do I buy another $350+ prom chip? Or is the problem my rebuilt ECM? And shouldn't my prom chip (programed for original ECM) work with the rebuilt ECM???

Any help greatly appreciated,
JB90vette

 

So you had no prom in the ECM?
$350 is way too much to be paying for a tune
Even PCM for less only charge $200 for custom tunes

 

I agree 100%.....and that is not for tuning. That is only the cost for the prom chip, which seems not to work properly in the rebuilt ECM.

Do you know if GM performance division would build/program an ECM for me?

 

A grounded injected isn't going to harm the ECM and I'd guess you either have a harness problem or it dumped so much fuel into the cylinder that it's blown the head gasket or bent a rod. Pull that plug so that you can get a clue; check compression.

 

The wierd thing is that when I unplug the battery from the car and then plug the battery back in.......the car runs good (with eprom and Memcal installed correctly)......for about 20-30 min. After that, the car goes back to barely running at idle and bad throttle response.

So I do not think it is an engine problem. Just ECM, chips, and/or the harness as you suggested.

What else am I missing??

 

You need to check your O2 Sensor and be sure it is working when in closed loop. Sounds like it goes bad at that point. Dave

 

Thanks. I will replace the O2 sensor. How do I check if/when it is in closed loop? I will check the service manuals.

 

You can check the signal voltage from the sensor prior to the ECM and verify that the the voltage jumps up and down from say 200mv to 800mv and it should cycle regularly back and forth. When you first start the car prior to closed loop, the ecm just tells the engine to hold 14.7 volts as it warms up. At a specified point (time and temp) for your ecm it will go to closed loop and you will notice the voltage on a digital volt meter jumping up and down. The cold open loop at idle 14.7 setting should be near about 550mv and steady without changing any throttle settings. After warm up it will begin jumping up and down. Good luck. Dave

 

Mailed in my eprom (that I had made to run the zz4 motor with tpi system) today to get it tested.

Do any of you know where I can send my ECM to get it tested.....to make sure it is good?? I had GM shop try and check the system with a Tech1, however, he was not able to read anything from the ECM. I'm not sure if this is because of the eprom that I installed. He could read code 12, but that is it, nothing else.

Other than that, I've removed/replaced the O2 sensor with the same results (motor will idle with 100rpm hesitation and will hesitate as I press the accelerator smoothly up toward 2000-3000rpm). If I press the accelerator down quickly, the motor jumps as it should, for the most part.

I've checked the wiring....not in best shape, but I've made repairs, nothing open.

Kinda at a loss here........I would love to remove/replace all my wiring in the engine bay. Any thoughts?!

Thanks,

 

Trying to think of ways to fix this car in stages........

1. Is there a way that I could tune the motor without the ECM....or the GM shop?? Just making sure the motor (without electrics) works properly. The motor was replaced Nov. 08' and needs to be tuned anyway (under 2,000 miles on it).

2. Then if it is not something mechanical, where and whom do I get to look at the electrical side....GM shop not useful because thier Tech1 isn't able to communicate.

Any thoughts?!

 

Only if you were to put a carb on it

 

Try these folks. http://www.ecmdepot.com/ecmlist.php?page=4&cat_id=5. They carry/rebuild GM ECMs also. Mstrs 2

 

Sounds to me like it's still dropping the Driver which could be a bum ECM or the harness is inconveniently shorting out on something. You might just check it when it occurs; ie, does it flash a NOID on either side once it's crapped out. If not, I'd suspect it's grounded and the ECM shuts off the Driver to keep it from washing/wiping out the motor.

 

Could you elaborate on the "flash NOID?" The mechanic told me that he wasn't able to communicate with the ECM....(only read code 12).....is this something that should flash on the Tech1? The mechanic didn't tell me anything else.

Also, the car would run ok (some hesitation at idle 1000-2000rpm). However, after about 15-20 min., the car would die at idle and would not start.

I plugged in my fuel gauge at the rail and it reads 40psi with engine off and 34psi (consistent - changed out the fuel pump last Oct.) while the engine is running. I'm thinking this might be a fuel injector problem.........I havn't changed out the injectors since I bought the car. They could be 20 years old.

What do you guys think before I spend the money???

 

Noid light or tester goes onto the Injector harness and simply flashes as the ECM pulses/drives the Injector. Your's is Batch Fire so it doesn't matter what injector you pick to test - It should flash on each side - left and right harness - so test one injector on one side and then on the other. The ECM shuts down the driver if it senses a short. That's important. If it kept giving it fuel it would easily flood the engine and ruin it.

 

Have you checked the resistance of your fuel injectors with an ohm meter? If not, check them with the engine cold then check them hot. Are they the original multitech injectors?

 

Question:
Fuel pressure at the rail when key "on" engine "off" is around 40psi. I would take around 10-20min shooting some wires (looking at service manual) and would look back at the fuel pressure gauge and see that it would bleed off to 20-30psi. Is this a problem?? The fuel has to be going somewhere and I don't see any fuel leaks. Does the fuel pressure bleed back into the fuel tank or is it leaking out of the fuel regulator and/or fuel injectors into the engine??? Hopefully, its not leaking into the engine.

Second question:
Sounds weird but if I unplug the battery and let the car sit for a day it will start up usually with no problems. It will run ok for about 15-20min at idle and then start to stumble and die. It will not start again.

Does this sound like an ignition problem - distributor?? Hooked up a timing light and the timing looks normal....although I didn't have it hooked up when it started to die.

I ran though the "Diagnostic Circuit Check" and again jumped ALDL terminal "B" to "A" and only flashed a code 12, nothing else. When it asks if the "scan" tool displays ECM data......which I don't have, only going from what the GM tech told me from the Tech1 (I selected no). The troubleshooting tree says use chart A-2. This chart says to check serial data CKT800A or 800B for open or short to ground between ECM and ALDL connector. How do I properly do this?? Because if this connection is good, the check list says it's a faulty ECM or Mem-cal (would suck if its my memcal).

 

I'll do that today and I would be guessing if they are the original multitech injectors. I assume they are (except for 1 that I replaced last Oct.)

I think I will order up a new fuel filter and 8 (flow matched) Bosch genIII. At fuelinjectorconnection.com they have the set and o-rings for around $200. Otherwise I might replace the distributor.

After that (and the car still will not run properly) I guess I will replace the engine wire harness and THEN the ECM. This is becoming a very expensive hobbie!!

Anything that I'm missing??

 

Checked all the fuel injectors with a meter.......all but the one I replaced last october were reading between 5-8ohms. Does this mean that the fuel injectors are "heat soaked." The new fuel injector read 17ohms!

 

I think you found your problem. They should all read close to 17 Ohms.