Basslicks

Don't mind me... just lurkin' about to see how this turns out.

Cjjcalhoun

It is a no spark condition. Also don't have any injector voltage coming out of the ECM. So the engine turns over but will not start. I have traced it to a missing signal coming from the ECM but I have replaced the ECM twice.

I replaced the ignition switch but not the key lock. My theory behind this is that the switch was making bad contact when I was putting in the start position. Every once in a while when I turned the key off quickly the engine would "kick" just once. I also hotwired the switch and that did not work but, I have started to second guess everything I do so I changed the $15 switch.

XJeepCheep

Any updates?

Cjjcalhoun

I have refreshed the ground on the dipstick tube and have replaced the positive and negative battery cables/terminal connectors.

I have also cleaned all of the connectors. I am kinda pressed for Jeep time so I haven't got to the sensor ground connections although I don't see that as a determining factor of the no spark issue. I have to lean back towards the computer, again. It has the inputs required for spark (at least the ones I know about) and it doesn't have any output.

these are the inputs I believe to be required
CPS .35 VAC or higher. I have .5 at the computer
12VDC battery voltage
12VDC ACC Voltage

Is there a signal that would be required that I am missing? As far as I can tell there are no other signals that would keep the computer from creating the spark signal.

DFlintstone

CJ, Just to be doubly sure...that's .5 ACV which you can also measure at the the TWO wires from your CPS, correct?

Also I just learned, two screws and two minutes and you can check that that new coil has about one ohm through the primary.

Cjjcalhoun

Yes .5 VAC at the two pins on the ECM. I have checked, replaced and verified the new coil. I metered both the primary and secondary coils.

Thanks for the ideas. please keep them coming!

FYI, I just thought that I haven't checked the Park/Neutral safety switch. The next opportunity I get I will check the outputs of those pins and see if they are good. I am not sure exactly how this switch effects the spark but it has to be worth a try. If anyone has any information on this switch let me know.

Currently, I am at the Fire Department for an overnight shift (volunteer firefighter) so I wont be able to look at it until tomorrow.

cruiser54

Where are you checking for injector pulse?

There are 6 injector drivers....

Cjjcalhoun

So, let me start by saying that information on this vehicle is difficult to find and almost impossible to verify.

The information that I have found is that a positive D.C. Voltage is provided by the ECM and common amongst all of the injectors (one output voltage for all injectors). The injector drivers provide a ground that is individual to each injector (one wire for each). So when I say I am missing the injector signal I am missing the D.C. voltage. I assume that this is a 5v signal but I don't know that for sure.

cruiser54

Not on this system.

Cjjcalhoun

Thanks for the pin-outs. I have one but it is different, more like a wiring diagram. I will put my O-scope on those pins tomorrow and see what I get.

67 GMC

The NSS switch shouldn't have anything to do with this and as far as I know there's no impact on spark. The switch just keeps the starter from engaging if the shifter is in any other gear but park or neutral. If it cranks when the key is turned to start in P or N, but doesn't crank in D, then it's most likely ok. There is a signal back to the ECU, but my manual says it only impacts idle.
I'm going back to basics now. Focusing on what works. Do you have fuel pressure on the rail and the fuel pump is heard to prime when key is turned to RUN? MAP sensor tubing is good from throttle body to sensor? MAP sensor plugged in?

Also, do you have the "bible" on RENIX? Here's a link:
http://www.pirate4x4.com/tech/billav...ion_manual.pdf

freegdr

I haven't got to the sensor ground connections ....

Why not ???If sensor dont send correct signal to ecm maybe it cant send out a signal to fire....Cruiser ?

cruiser54

An excerpt from Tip 1:

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, failed emission tests, and wasted money replacing components unnecessarily.

All the components listed below ground at the dipstick tube stud:

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition Control Module, Fuel Injectors, ECU main ground (which other engine sensors ground through, including the Oxygen sensor, Knock Sensor, Cruise Control and Transmission Sync signal. All extremely important stuff.

freegdr

Did see any mention of Map Sensor testing or replacement or I missed it. I am getting up towards Major in the years...lol..

Cjjcalhoun

I do have fuel pressure and I do hear the pump turn on when I turn the key on. You're right about the P/N switch. It sounded good when I thought about it but it doesn't affect spark.

The map map sensor is plugged in and functioning properly. I put a vaccuum in it just to see if it was in range and it was.