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Discussion Starter #1
Hi all I hope some one could help me with my engine swap. I had a 1994 LT1 being controlled by a OBD1 . I had to replace the motor
and I replaced it with a 1996 LT1. Now the Opti spark is different and the 1996 has a port for a crank position sensor . I was told to just
plug the Crank position sensor and I will be fine. Now when I run the engine it starts great runs fine until about 3800 RPM at full throttle
the engine stumbles and restarts. I get an error code 36.( This is either the mas air flow sensor or the crank position sensor ). Now I have
cleaned the Mas air flow sensor and the problem continues . If I continue to run the car with the error light on it seems to run fine even at full
throttle . Will not stumble again .
If I turn off the engine and restart the error is gone until I hit 3800 at full throttle again and the stumble happens again.


Is there any thing I need to change to get the OBD1 to work with the
Opti spark for a 1996 Engine? Am I looking at the wrong thing?
 

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DTC 36 on an opti spark car is the high resolution pulse missing. An oscilloscope will show both high & low res pulses. You can buy a pc based scope for around $70.

With the high res pulse missing or dropping out intermittently, engine will run, but not very well. As you have found out.

Use scope to make sure high res pulse is present and of the correct square wave, and it doesn't drop out at times.

A while back my 90 camaro dd quit running. A check of the 30 hertz fuel enable signal with my multi meter indicated the correct 30 hertz. But when I hooked car up to scope, the signal was all messed up and not the correct square wave needed to open fuel injectors.

I used this example to indicate the need of the oscilloscope for testing high & low resolution opti pulses. And how other tests can be inconclusive or wrong.

Crank position sensor is just for misfire detection. It does not affect running of engine and is not used in obd 1 computers.

You can buy a 95-97 opti pigtail. The 93-94 opti uses a different connector at opti end. Both types use same connector at intake manifold end.

And welcome to the forum.
 

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Discussion Starter #4
Thanks this helps.
Did more testing last night Re wired the Opti Spark . Still having engine cut out. The knock sensor could not be causing the
problem could it?
I do not have a scope to test the pulses:(
I am still using the OBD1 control so I believe I keep the same Knock sensor.
I have Tuner Cat cable and software and use Data Master to read the error
codes. I have noticed the knock sensor numbers change constantly . Is that normal?
 

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I am still using the OBD1 control so I believe I keep the same Knock sensor.
?
if you are running OBD1 you need to use the knock sensors from your original motor on the 96 motor. They are different. IDK the OBD1 just used the one on PS of block or both sides like OBD2.

Not talking about the "knock module" in the PCM (ECU)
 

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Discussion Starter #6
Well after replacing my opti spark (Durlast) all is running fine now.
Should have gone with the stock Gm Opti Spark from the start would have saved
me a bunch of work.
 

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So if I run the 95 to 97 optispark, timing chain cover and pig tail on my OBD1 1994 LT1 it should run correctly, but I would be able to use the vent system from the 95 to 97? I have to rebuild my motor and I hate the early opti with the vent holes. I have fitted the old opti with fittings that vent from above the engine and that keeps the water out. Unfortunately I am on my fourth opti between bearings and modules going out. Trying to decide if I should just scrap the Trans Am or restore it. I can't use it in the summer due to extreme overheating issues in the Arizona heat. The sad thing is no one around here can reprogram the ECU with better fan on/off points. Here if your temp gets above 200 degrees then you have lost it's ability to cool.
 

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The pc based tuning program called tunercat obd 1 tuner can easily reprogram you fan turn on temps. Go to the tunercat website to order. You can get a trial version of tunercat to use for 30 days for free. But to read your 94 pcm, you will have to spend 20 bucks for the proper definition file for 94-95. It's called the $EE definition file.

Also you will need a 12 pin GM aldl to usb cable to run the program. Get it at www.obd2allinone.com/aldl.asp

Now to the optispark. Your car came from the factory with the type 1 spline drive opti. If you want to run the pin drive 95-97 opti, besies the timing cover,pigtail, and the 95-97 cam timing sprocket.

This is because early cam sprocket doesn't have a big enough hole in the center for the pin drive type 2 opti to ride in. And you'll need a longer dowel pin on the camshaft.
 
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