1991 4.0 wrangler has no spark ????

popcancherokee · Jul 29, 2011

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I have been trying to figure this out for 2 weeks now and no luck.So here is what I have done so far.Started with coil nothing.I went to change the crankshaft position sensor and the plug was cut out and hard wired.So I got a similar plug out of a Cherokee just different wire colors and found a diagram and wired it.Then changed all fuses and relays and cleaned every thing with electrical cleaner and nothing.So I changed computer and nothing.then I took cap and rotor off and checked the pick up and it was broke so got a different distributor and still nothing.
So is there any thing that would make it not get spark.I tested the cps wires and got 8volts 5volts and 0volts out of the wire from motor I get 12v at coil plug when I turn the key on then crank it and nothing I don't get no pulse with other wire in coil.The fuel pump comes on and runs for a few seconds.
I getting to the point I just want to sell it.But I have put a lot time and money into it in the last 4 months building it so it would trail ready and a daily driver.I'm laid off so no money to take it to a shop.So any help would be greatly appreciated.Thanks

fortric · Jul 29, 2011

Replace the cps. That is a common problem. I have even had one check good and was still bad

WA-Wheeler · Jul 29, 2011

The CPS was hardwired, no factory plug?? That seems like a botched fix. I would replace it all to OEM status, wire to plug then that plug to CPS. Do it right, do it once.

popcancherokee · Jul 29, 2011

fortric said:
Replace the cps. That is a common problem. I have even had one check good and was still bad

I have replaced it twice that was before I found that the pickup was broke.So should I try it agin ?

popcancherokee · Jul 29, 2011

WA-Wheeler said:
The CPS was hardwired, no factory plug?? That seems like a botched fix. I would replace it all to OEM status, wire to plug then that plug to CPS. Do it right, do it once.

I wish I could find the oem plug but it is connected to the main harness and these seem hard to find in wrecking yards.The xj plug looks the same as oem but the wire colors are different.If some how I coud double check the colors for each plug hole would make me fell better then going off a diagram I found on the computer.Thanks

fortric · Jul 29, 2011

Have you replaced it with a know good one for that year 4.0?

zukkev · Jul 29, 2011

As long as the splicing is good, and the positions of the wires are correct to the original equipment, should not be an issue...the chances of 2 CKP sensors being bad are slim to none...
Do you hear the 2second fuel pump prime when you first turn the key on??? I had a jeep kick me whent he pump was bad...not sure on 91, but if there's no pump, the ecm cuts spark on some models...:awesomework: hope this totally confuses you! :haha:
Also, have you cranked it over and tested for a signal from the CKP sensor??? Can be done with a voltmeter, but would be much clearer with a lab scope watching the waveform...

fortric · Jul 29, 2011

Did you buy it with this problem or is it something that just started

popcancherokee · Jul 29, 2011

fortric said:
Did you buy it with this problem or is it something that just started

I have been driving it for about 3 months off and on to work went to evens up the 311 a the upper one and got to top of the hill (im glad it made to the top) and it just died and would not start.We pulled off a coil off another jeep and got nothing put it back in his and his started.Called tow truck and had it towed home.Thanks

fortric · Jul 29, 2011

sounds like when the cps went out on my xj. was running great and just quit and wouldn't start back up. make sure you have the right cps for that year motor. one from a renix wont work in an HO and a HO wont work in a Renix.

JOOP · Jul 29, 2011

Pay to have a diagnostic and find out whats wrong with it instead of throwing parts at it.

junkyard jim · Aug 9, 2011

It sounds to me like either the CPS is for a '90 or older (it'll send a micro AC signal instead of DC switched signal) or the ignition switch **** the bed. There is a replacement harness from the computer to the CPS (or there was) available at the dealership.

popcancherokee · Aug 9, 2011

I got it running it was a broken pick up inside the distributor.And the crank position sensor wires were hooked up wrong I guess the wire diagram I got was wrong.
It runs and now.But it hesitates when I'm driving code scan said tps high or low voltage changed it and still the same any one have any ideas on this part.Thanks