CPS Follow Up. Bad Computer? Im lost.

JeepDrivr93 · 11-11-2008, 08:45 PM

So I posted up that I was under the impression my CPS (crank position sensor was bad). Well I tested it and tested the new one and infact it was bad. Well the Jeep still just cranks over.

I had my mechanic friend come over with this really cool Snap-On SOLUS computer and plugged it into the jeep. We tested alot of "stuff" but still no spark. I just replaced the "pick-up coil" and still nothing. We tested the coil and think its good, could be wrong. Now im wondering if the computer is bad. The fuel pump does come on when the ignition is turned on. I really dont feel like buying more sensors to find out its not the problem.

Any other suggestions or tests that you could recommend that would be greatly appreciated. Other wise I will be forced to take it into a mechanic to further diagnose it (unfortunately my friend has limited tools outside of work and his work is strict about bringing in cars that are not his after hours.).

It just kills me that I cant figure it out, what else could it be?

-Nick

XJ4oh · 11-11-2008, 10:05 PM

If the fuel pump is kicking on, chances are the ECU (computer) is fine.

Here is what happened to me...

My crank position sensor AND my computer went at the same time.

It would turn over, but had no fuel and no spark. The gas gauge didn't read, and the fuel pump didn't prime. That was the indicator that the computer was gone.

The CPS cuts spark I beleive, as we couldn't even get it to cough when spraying some starter fluid down the intake.

That was an expensive repair... but it doesn't sound like that is your problem.

How are you verifying it is getting no spark?

JeepDrivr93 · 11-11-2008, 10:11 PM

We took the spark plug out while still connected to the wire and grounded a 12 gauge wire to the negative battery terminal and the plug and then touched it to metal in the engine compartment.

XJ4oh · 11-11-2008, 10:15 PM

Oke doke...

Well, not sure what to suggest. Don't want to say something out of the blue just to have $ wasted on it.

JeepDrivr93 · 11-11-2008, 10:34 PM

haha well suggest it b/c i may just check it out or look into it. Could it be something else in the distributor?

**filluptrk** · 11-11-2008, 11:20 PM

I have the 00, no dist. But there should be something in your FSM that shows how to check for input voltage to your dist. I don't know if you have any type of module on dist like my old Ford Ranger, they go out all the time. But the manual should show you the voltage path, through sensors etc to get spark. I would start at the connector at the dist and see which pin in the connector you get voltage to the dist, and go from there. But if you have voltage to the dist, then I would suspect the dist.
However, sometimes it is cheaper to go to the dealer.
Or you could go to a junkyard and find a 98 that doesn't look like it was beaten to death and get all the spare stuff you can and take a chance by swapping it out one bit at a time and see if it works out. Probably not the best way, but I would do this because I hate the thought of someone else working on anything I own. Phil

Shane01638 · 11-12-2008, 06:40 AM

I am by no means a mechanic, but did you check the rotor? maybe it's broken or not turning because of another distributor problem. I would pull the cap off and check.

dert · 11-12-2008, 07:45 AM

Cant remember where I saw this but the average lifespan of a Jeep computer is 9-11 years.Had the CPS and comp.go bad th the same time.Over 1100.00 total incl labor for all.Doubled the MPG and runs great.You can get a rebuilt comp.for 250.00.The site is somewhere in these forums.

**tjwalker** · 11-12-2008, 07:47 AM

Inspect crankshaft position sensor wiring harness all the way into the engine bay. Sometimes wiring becomes burnt and or damaged and prevents the signal from making it to the computer. Unplug the connector for the crank sensor by the #6 injector/firewall, clean and reseat. What do you mean by "you think the coil is good but could be wrong? Did your coil specs match up with the good specs from the factory? Replace cap/rotor if not already done.

JeepDrivr93 · 11-12-2008, 01:10 PM

All i have is a half@$$ chiltons manual so i dont have the luxury of a FSM. I have checked the CPS wiring and it all checks out.

I am not sure what the coil specs are so thats why Im not 100% sure its not the problem. The rotor seems to be in one piece but i will check and see if it is turning.

So can the computer be bad even if I hear the fuel up come on and the gas gauge works?

If anyone one has time to look in their FSM and tell me the coil specs for voltage that would help alot.

XJ4oh · 11-12-2008, 01:44 PM

Quote:

Originally Posted by JeepDrivr93

So can the computer be bad even if I hear the fuel up come on and the gas gauge works?

If anyone one has time to look in their FSM and tell me the coil specs for voltage that would help alot.

I wish I had the answer for that. When mine went, everything went and I don't know anyone else that had the same problem as me.

I know you said you didn't get spark, but I suggest spraying some starter fluid in the intake while cranking the Jeep over and see if it catches or coughs like it may be getting some spark.

Even if the pump is priming, there may be a problem somewhere down the line.

It's kind of a longshot, but it may be possible the computer is bad... the fuel pump is priming, but the injectors aren't cycling because the comp. is burnt out.

**tjwalker** · 11-12-2008, 02:23 PM

I assume this problem is with your 98.

For coils manufactured by Diamond, the primary resistance at 70-80 degrees farenheit should be 0.97-1.18 ohms and the secondary resistance should be 11,300-15,300 ohms.

Coils built by Toyodenso should exhibit a primary resistance of 0.95-1.20 ohms and a secondary resistance of 11,300-13,300 ohms.

Replace any coil with a new one if it does not meet these specifications.

JeepDrivr93 · 11-13-2008, 09:47 AM

Thanks everyone for the additional tips. I am going to re-test the coil with those numbers (thanks tjwalker for those). If it tests ok then I will re-check the distributor and its components. If it all checks out then i will have to buy a computer from a junk yard.

Next question if i take out the computer and take it up to the Jeep stealership can they test it? And maybe not charge me a ton of money to do that.

I talked to my friend (mechanic who helped me) last night and he seems to think it is a good possibility the computer is bad.