no start issues continued

OK, so here it goes:
it's a 94 XJ, manual transmission, and it has brand new crankshaft position sensor and camshaft position sensor. The symptoms are as follows:
1. No spark during no start
2. Sometimes it starts and then it seems to be working for a while. Just to see how it behaves (it started fine about a dozen times in a row) I took it for a test drive. While driving I have noticed that every so often the tach would spike or drop (no other sensors or indicators behaved badly at the same time eliminating potentially ground issues). This leads me back to it being CPS related as it is getting bad readings from it. So the question of the day is as follows:

Is the signal from the CPS going directly to the cluster or is it routed through the PCM always? Is there any way to test the CPS behaviour (even though it's a new one it does not do what it is supposed to do)? I have looked at wires beteween the CPS and the PCM and they appear to be all intact. I have cleaned the connection where the CPS plugs into the engine harness and it appears to be looking good....... so what next?

On the 93 and later models, connect an ohmmeter to the B & C terminals on the CPS connector and verify they read no continuity (open). If it reads otherwise, it is defective.

Jeremy89XJ said:

On the 93 and later models, connect an ohmmeter to the B & C terminals on the CPS connector and verify they read no continuity (open). If it reads otherwise, it is defective.

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well it has no continuity there but it still doesn't mean it's kind of bad Damn this is starting to piss me off.

That kind of sounds like a coil or the modual attached to the coil acting up. Do you have one you can snag and check it out?

Lincoln said:

That kind of sounds like a coil or the modual attached to the coil acting up. Do you have one you can snag and check it out?

Click to expand...

That is also new.... it was replaced when the whole thing started.

If you run out of things to check, check the voltage input to the cam position senor (or whatever they call it in a OBD 1) in the distributor.
I noticed when my CPS went out, that the input voltage to the cam position sensor was low. When I replaced the crank position sensor, the voltage returned to spec.
I also noticed my check engine light refused to work and I was unable to retrieve the Mil codes, until I put the new crank position sensor in.
My crank position sensor tested OK between the "B" and "C" pins, Which leads me to believe the problem was between the the "A" and "B" pins.

Yes double check the voltages. On my renix I had the harness go bad between the sensor and the computer. I don't know if the newer ones had the same problem but there was a repair harness for the CPS.

Other than that I would start at the coil checking voltages and work my way backwards. If the voltages are good going into the coil then it's the coil. Did you change the control for the coil at the same time? You dont' happen to have a spot in the harness that has been rubbed through? Look for any spots that look like they have been rubing and pull the loom and inspect them. I've seen where there was enough movement that the look rubbed the wire through.

Damn mofo of a ground on the far side of the block. When my dad swapped the engines out he put the ground on that bolt, started a nut which was a wrong size.... never tightened it (probably meant to come back? No clue, he doesn't remember now) and well... it was flopping around and sometimes it made better contact sometimes worse.......

MikeR thanks for showing up and catching it !!!!!!!!!!!!!!!!

I hate it when that happens.

For every sensor I've ever replaced in an XJ (I've had one or two in the driveway for near 20 years). I've found 3 or 4 to one, the trouble was something other than a faulty sensor. Loose connector, loose pin, corroded connector, corroded ground, rubbed or burnt through wire, a connector full of water or whatever. Sometimes it was a collection of most or all of the above.
I'm often astounded that the old XJ is still running at all, after I eventually find what was causing the fault. They are frequently tempermental, but often keep right on chugging.