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97 cranks but wont fire

Anker26

NAXJA Forum User
Location
Knoxville Tn
My 97 4.0 cranks but does not fire. There is no power getting to the coil and none at the fuse. also the fuel pump is not kicking on. I have changed the relays, crankshaft sensor, checked the fuel pump and now I am stuck and on the verge of replacing the ecm. What am I missing? What else can I check to help narrow it down to the computer? Is the computer directly responsible for activating the relays and is there something else that will prevent them from switching on.:doh:
 
Might sound dumb but have you checked all fuses? I know you said relays, but I had a similar symptom. Turned out to be the fuel pump fuse under the hood was blown, and the fuel pump was so clogged it would blow the fuse within 30 seconds of running. New pump, new fuse, no problem. I thought it was the ecu too.
 
Grounds, check your grounds.
 
If the Crankshaft Position Sensor (CPS/CKP) is good, check all the fuses under the hood and on the inside.

I have fixed several no-start Cherokees. One was a mini fuse under the hood. One was a loose/dirty contacts relay above the passenger compartment fuse box. Test the Camshaft Pickup Sensor inside the distributor cap.
 
Find out why the fuel pump isn't kicking on - instead of replacing parts, buy a DMM (or find it) and do some measuring. This is where tracing wiring helps a lot... measure on the upstream side of the fuse that powers the fuel pump, then the downstream side, then the upstream side of the relay, then downstream side, etc till you find where you lose power. If it's at the relay, measure for voltage on both sides of the coil, keep tracing, etc. Eventually you will find a component that is getting all the right inputs and not doing its job.
 
What should the power be on the fuel pump relay, i had ground at one post and 10v at all others, is this right. Jeep ran yesterday, no start today, pump isn't primming. Maybe cps? What else should i check?
 
What should the power be on the fuel pump relay, i had ground at one post and 10v at all others, is this right. Jeep ran yesterday, no start today, pump isn't primming. Maybe cps? What else should i check?

PEOPLE, PEOPLE, PEOPLE--basics? Year/engine/etc.?

Describe your problem. You say you only have 10 volts to the fuel pump relay--how many volts in the battery, terminal-to-terminal?
 
If the Crankshaft Position Sensor (CPS/CKP) is good, check all the fuses under the hood and on the inside.

I have fixed several no-start Cherokees. One was a mini fuse under the hood. One was a loose/dirty contacts relay above the passenger compartment fuse box. Test the Camshaft Pickup Sensor inside the distributor cap.


I'd check that out first. Sometimes you can unplug it and plug it back in and if it starts then you need a new one.
 
PEOPLE, PEOPLE, PEOPLE--basics? Year/engine/etc.?

He said he had a 97 4.0



I will agree with joe, check your grounds. But I dealt with this EXACT same problem with my 98 cherokee sport just a few months ago. I had no power to the coil, no power to the fuel pump, voltage meter and fuel gauges weren't working, no spark, and maybe another thing or two that I'm forgetting. The Jeep did crank over.
After replacing some parts...Crankshaft position sensor, coil, ground straps, cleaning grounds, etc....I decided to say F it, and bought a computer. I plugged the new computer in and put the key to "on" position and my gauges that didn't worked before kicked on. Then I cranked her over and without hesitation she fired right up.

So if you feel you've gone through your Jeep thoroughly, I think you may want to think about the ECU. People say they don't go bad, but I've heard of many people that have had this problem. Wouldn't be a bad idea to find someone with the same jeep and swap their computer into yours to test it out. Good luck
 
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