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No spark after engine swap...

Should it start with a bad CPS?

Is there a cheap way to test the computer and ignition module?

Jared
 
To test the sync sensor do not unplug it. Back probe the plug with your meter on the 15 volt range. + into the blue wire terminal B, - into Gray/W terminal C.

With the key on you should read 5.0 volts +- 1 when you crank the engine the meter should swing back and forth.
 
Here's the deal -

I tested the sync sensor. It hovered at 5V with the key on. While cranking, the voltage drops to about 3V and stays pretty steady. Which should mean that it's bad. But I never get any spark whatsoever, and according to the info at hand it should run poorly at least with a bad sync sensor.

I did the same type of test on the CPS and did not see the needle move, but I don't think the needle could move fast enough to really show me anything definitive. I wish I had a lab scope to show a nice waveform or something. The CPS tested fine as per the tests listed in my Haynes Manual. It involved resistance across 2 terminals.

This is really driving me nuts! Should I just go to the junkyard and get a bunch of parts to start throwing at it? I hate fixing stuff by doing that.

Does anyone know how/what wires to test for power/grounds to the computer? I'm thinking that it HAS TO BE the computer or the CPS or some connection between the two.

Is there any hope?

Jared:tear:
 
I sometimes get to brain storming a problem so much, I get tunnel vision and brain lock.
No spark, listen to the injectors and see if you can hear them clacking, while it´s cranking (use a piece of tubing). If the injectors are clacking and the spark isn´t there, it narrows the probabilities down.
If you onplugged the C-101 connector and plugged it back up, without cleaning it really well, I´d do that. I disconnected one to clean the mud out, took me three tries to get it clean enough to work again. The die electric grease had gotten so thick and dirty over the years, it cut off most all power when smeared over the contacts again.
The MAP circuit will also shut you down. And many of the start and run circuits are seperate.
 
Is the C101 connector the one above the brake booster- or beside it? I have not unplugged it, but just curious.

Jared
 
DeadEyeJ said:
Here's the deal -

I tested the sync sensor. It hovered at 5V with the key on. While cranking, the voltage drops to about 3V and stays pretty steady. Which should mean that it's bad. But I never get any spark whatsoever, and according to the info at hand it should run poorly at least with a bad sync sensor.

I did the same type of test on the CPS and did not see the needle move, but I don't think the needle could move fast enough to really show me anything definitive. I wish I had a lab scope to show a nice waveform or something. The CPS tested fine as per the tests listed in my Haynes Manual. It involved resistance across 2 terminals.

This is really driving me nuts! Should I just go to the junkyard and get a bunch of parts to start throwing at it? I hate fixing stuff by doing that.

Does anyone know how/what wires to test for power/grounds to the computer? I'm thinking that it HAS TO BE the computer or the CPS or some connection between the two.

Is there any hope?

Jared:tear:
Click to expand...

Sounds like you could have a bad ground and the 12v is dropping too low while cranking. There are tons of ground wires on the right side of the engine block on the renix engines and they are all important. Also the braided strap going to the firewall can cause problems.

JoBo
 
OK - I replaced the CPS. It still has no spark. So then I retested the voltages coming into the ignition control module (ICM, attached to the coil). The larger gauge yellow wire has 12.5V with the key on, and the smaller gauge yellow wire shows only .5V. Neither pulses while cranking. If my thinking is correct, the smaller diameter yellow wire is the one coming from the ECU (computer) and should tell the ICM when to fire the coil.

.5V just sounds wrong to me. Could anyone verify the correct voltage found at the smaller diameter yellow wire coming into the ICM? It's the only wire in the 2-connector plug on the ICM.

Thanks,
Jared

If this voltage is wrong, what does it mean? I'd assume that it means: 1) a bad connection between the ECU and ICM 2) a bad connection between the CPS and ECU 3) a bad ECU.

Any thoughts?
 
Do you have color codes for those? Pulling the ECU to check which pin is what doesn't look too pretty.

And I'm reading your post as this -

Pin #6 = 5V supply.
Pin #7 = 8V supply.

Thanks

Also, what is the yellow AMC labeled plastic box directly below the steering column? Is the trans controller? It has a few adjustment screws on it.
 
DeadEyeJ said:
OK - I replaced the CPS. It still has no spark. So then I retested the voltages coming into the ignition control module (ICM, attached to the coil). The larger gauge yellow wire has 12.5V with the key on, and the smaller gauge yellow wire shows only .5V. Neither pulses while cranking. If my thinking is correct, the smaller diameter yellow wire is the one coming from the ECU (computer) and should tell the ICM when to fire the coil.

.5V just sounds wrong to me. Could anyone verify the correct voltage found at the smaller diameter yellow wire coming into the ICM? It's the only wire in the 2-connector plug on the ICM.

Thanks,
Jared

If this voltage is wrong, what does it mean? I'd assume that it means: 1) a bad connection between the ECU and ICM 2) a bad connection between the CPS and ECU 3) a bad ECU.

Any thoughts?
Click to expand...
That reading is correct, it should be very close to 0 vdc when running. Again I ask, are your injectors firing, thats where we need to go now.
You need to find out if the ECU is trying to start the engine or not.
If it's not the you need to look at what things tell it not to start the engine.
 
Last edited:
OK - I just stuck a very nice stethoscope onto 3 different fuel injectors while cranking. There was no clicking or ticking or anything of the sort. I put the scope directly against the metal housing of the injectors. Apparently, they're not firing.

Jared
 
I just realized that the fuel pump is never shutting off when the key is on. Either it's not building pressure, or the relay is not shutting it down when proper pressure is reached. I'll go test the pressure now.
 
DeadEyeJ said:
I just realized that the fuel pump is never shutting off when the key is on. Either it's not building pressure, or the relay is not shutting it down when proper pressure is reached. I'll go test the pressure now.
Click to expand...
Hmm.
It sounds then like your ECU is not running or something Or there's a ground off, the ECU has two grounds. One for Power to the ECU processor and one for the outputs.
 
The relay does not shut it down. The pump has its own pressure switch. If it keeps running, it is either the pump, the hose from the pump to the mounting bracket in the tank, or the pressure regulator. A If the pump keeps running and there is pressure, the pump has a problem, but that should not keep it from starting.
 
DeadEyeJ said:
I just realized that the fuel pump is never shutting off when the key is on. Either it's not building pressure, or the relay is not shutting it down when proper pressure is reached. I'll go test the pressure now.
Click to expand...
Check the pressure but pressure is not what shuts it off, the ECU has a three second timer that turns it off.
 
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