It's a little murky in my head how things work in the Renix engine but I'm curious. I'm getting 0.0 AC Volts on my CPS when cranking and I'm getting no spark at the spark plugs.

Questions:
1. How are these 2 related?
2. If there is 0.0 volts at CPS, is it because there is no spark?

I've gone through 2 or 3 CPS now, they each show good resistance but 0 volts when cranking. I dug deeper and no spark at the plugs so curious if they are related?

 

If the ecu doesnt see a crank signal it won't fire the coil. Does the crank sensor have power, ground, and continuity back to the ecu?

 

Bookmark Cruiser's Renix tips. Your answer is likely within.

https://www.cherokeeforum.com/f51/cr...x-tips-153657/

 

So back probing sensor wires between CPS connector and ECU, right?

 

On Renix, the CPS is also the Engine Speed Sensor. It not only reports where the crankshaft is in it's rotation, but also how fast the crank is turning. The engine speed must be 300 RPMs or higher to trigger the ECU to begin fuel injection.

You also have 3 other threads going on this topic (essentially, Crank, no start) Which one do you want us to use and respond?

 

This one since it's the most recent one. Sorry for creating more threads, I'm kind of flying blind here and have a constant list of things to check. I'm doing some voltage, ground, continuity tests on this one. Given it's a magnet sensor (as I understand it) and it connects straight to the ECU, is the procedure to pull out the ECU and back probe those cables for the CPS there to at least ensure continuity? I want to at least make sure there is no shorting from the CPS connector back to the ECU.

 

You would first disconnect it at the CPS and probe for AC voltage while the engine cranks. Cruiser's tips has the details for the test. If that works, it time to swim upstream. You'd then check for continuity/short from the CPS connector to the C101 connector. Then the C101 connector to the ECU.

Another of Cruiser's tips is the cleaning of the C101 connector. You may want to do this while you have it open. He also has one about eliminating the C101. Personally I have not done this to my '88. A good cleaning was all it needed.

 

I thoroughly cleaned out the C101 yesterday, still nothing. The CPS gives me correct resistance reading but always 0.0v AC. I'm also wondering if the little plastic cover that's around the CPS on the bell housing may be interfering with the distance to the flywheel at all. I even made the mounting holes of the CPS larger per Cruiser's tips, still nothing when engine cranks.
Would you agree that I have 2 main points to check here?
1. CPS cable continuity to ECU.
2. Removing plastic tab/protector from bell housing to see if distance to fly wheel improves.

 

You have to check that the sensor is getting power from the ecu. Need a multi meter to check for proper voltage.

 

I just checked voltages... i'm getting 3.41 volts on both sides of the connector for the CPS. I think this should be 5 volts. I checked the TPS and it said ~10.5V, I think this should also be 5 Volts as reference. is the ECU toast?

 

I answered another person on the thread but getting ~3.4v on both sides of the CPS connector. Then I'm seeing 10.5 volts for the TPS. This is when just turning the key so I can get the reference volts which I think on the 87 should be 5 volts. Do you think it's the ECU?

 

Disconnect the CPS. Set your meter to AC, not DC. Connect the meter probes to the CPS pins (sensor side). Have someone crank the engine (it won't start with CPS disconnected). Note the reading. You should see about .5v ac (that's 1/2 volt). Verify the CPS voltage is correct.

https://cruiser54.com/?p=50

As for the TPS, you're correct. Reference voltage should be 5 V DC. In reality, you may see slightly less than 5. Make sure you're one the correct connector and keep the TPS connected while you back probe it.

https://cruiser54.com/?p=54

Verify the sensor is generating the right signal. If so, then trace the wires back to the ECU (sadly it's under the dash).

 

Yeah I've done these, with voltage on DC AC and I get 0.0 volts with all the new CPS, same result. I just stopped for tonight and I'm pretty much getting 12 volts on all sensors when just the key is in. I spent a long time back probing.

This might be a silly question but is there a chance this could be a faulty starter relay? I haven't seen that mentioned anywhere but just want to check.

Tomorrow I'm going to try taking the plastic protector thing from the CPS, maybe that's obstructing something since it has to sit very close to the flywheel.

Otherwise I'm just lost as to what to do, that's why I keep posting new findings in the hopes that something will stand out. Not sure at this point if it's the ECU for some reason.

 

I'm sorry I miss typed.... I meant to say I've done this with voltage in AC.

 

Ah OK. I would pull the inspection cover off the trans and check the flex plate as well. Make sure the "ring" (part that gets close to the CPS is OK).

The CPS test is completely independent of any other issue since it's disconnected from everything else. It only needs the ring on the Flex plate to pass close enough to induce the voltage. When the gap passes, the mag field collapses If you're getting Zero volts A/C disconnected with the engine cranking, that can only mean if the sensor is bad, or the gap is too large.

If you can crank the engine (which you can), the solenoid is OK. You can check the fusible links which feed power to the rest of the vehicle.