Computer Questions

XJdePlato · Mar 11, 2005

My XJ(92' 4.0L auto 4x4) turns on but will not start. No spark at spark plugs. No spark at coil wire. I also changed the spark plug wires and distributercap/rotor for percationary measures. I checked the coil and its fine, even double check with my trail spare. I'm thinking its the computer, what do you guys think? Also, is an ignition control unit the same thing as a computer? If not which should I change? Also I should add that the exhaust manifold has a real bad crack and I guess that could kill the O2 sensor. Could a shot O2 sensor keep the XJ from starting.

89xj · Mar 11, 2005

cps will cause a no start

XJdePlato · Mar 11, 2005

should I go to the junkyard and get a CPS first? How much should I expect to pay fro a new/used clutch position sensor?

casm · Mar 11, 2005

XJdePlato said:
How much should I expect to pay fro a new/used clutch position sensor?

$18,932.76 (sales tax at 8.25% applies if you're in CA). Please make checks/MOs out to cash, PM me for the address to send it to.

Seriously... What you're looking for is the crankshaft position sensor. Price varies from yard to yard, but a brand-new one for my 2000 is $122 from Kragen. Chances are yours will be considerably less.

XJdePlato · Mar 11, 2005

If it was just my crank position sensor would my OBD-II diagnostic system not work? I can't get the check engine light to flash any codes to me and I know how to do it(I do it all the time with my wrangler). I really can't afford to just throw parts at the problem right now going to school full time.

TBLimited · Mar 11, 2005

Yeah I hear ya I'm a full time student as well trying to get my heep going and its killin me. Mine was doing the same thing and I swapped the computer and I got spark at the plugs. The only problem is that mine still won't start.

MAP · Mar 11, 2005

Hey guys I have a 99XJ with a 4.0L.
At a little over the 100,000mile mark it wouldn't start. The computer seemed to be dead.

I got a response from a guy here that was a Jeep tech. It appears that the engine computers have short protection circuitry such that it there's a short on one of the sensors, the computer shuts down.

I couldn't get any trouble codes from the computer because it had shut down.

The problem ended up being the CPS that was shorted. Once I disconnected it the computer worked. Try disconnecting the CPS and then getting the trouble codes. If you can access the trouble codes, the CPS is probably shorted.
I believe it was about $60.

MAP

MAP · Mar 11, 2005

I guess the price went up. It's now $90 for my 99 XJ.

MAP

MAP · Mar 11, 2005

You're in luck. If the CPS is your problem, it's only $43 at Autozone.

MAP

Yucca-Man · Mar 11, 2005

Y'all are missing a good way to 'fix' the CPS - simply unplug it and reconnect it. It won't resurrect a truly dead CPS, but often the connector will corrode and cause problems. Reconnecting it will clear most of that corrosion although you may want to hit it with some contact cleaner too. That often gets you some more use out of the CPS

MAP · Mar 11, 2005

If it was a bad corroded connection, it would have high resistance(similar to an open) and shouldn't cause the computer to shut down.(as it appears to be in this case)

If he can't even get trouble codes to come up, I'd bet that the CPS is shorted.
A simple ohmeter check will tell you if it's shorted.

It would be nice if it was simply corrosion though.

MAP

JJacobs · Mar 11, 2005

If you're trying to use an OBD-II scanner on your 92 that's why you won't get any codes, if you could even hook one up- OBD-II started in 96.

XJdePlato · Mar 11, 2005

I don't have a ohmeter (yet) so I can't check the CPS to see if it is good. For the money I would spend on a ohmeter I could buy the CPS. If the CPS doesn't fix the problem I still replaced a weak link in the system anyways. As for the OBD-II , I was talking about the check engine light way of getting a code. The Haynes manual said my vehicle has an OBD-II system on it and that a bad CPS should come up as 11.

MAP · Mar 12, 2005

Try getting the codes after you disconnect the CPS.
If you can get the check engine light to flash, the CPS is the problem.
MAP

Eagle · Mar 12, 2005

XJdePlato said:
I don't have a ohmeter (yet) so I can't check the CPS to see if it is good. For the money I would spend on a ohmeter I could buy the CPS. If the CPS doesn't fix the problem I still replaced a weak link in the system anyways. As for the OBD-II , I was talking about the check engine light way of getting a code. The Haynes manual said my vehicle has an OBD-II system on it and that a bad CPS should come up as 11.

You can get a serviceable multi-meter from Harbor Freight Tools for $9.99 -- usually $3.99 if you catch a sale catalog. You can't touch a CPS for that price.

Do not waste time and money on a used CPS. What's the point? You pay half the price of a new one, and it might last a week.

And whatever you think you read in Haynes -- a 1992 XJ is not OBD-II.

rdx4me · Mar 13, 2005

Just bought a CPS for my 90 XJ 4.0 because I too stopped getting spark off the coil. Cost me $34 from Advance Auto. Will be putting it in tomorrow & will let you know if that was the problem. I have already replaced the coil, ICM, plug wires, dist & rotor.

XJdePlato · Mar 15, 2005

So did it work?

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