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Started, died, and wont restart

IslanderOffRoad

IslanderOffRoad

NAXJA Forum User
NAXJA Member
Location
Houston, Tx
Great way to start my day at 4am!

Started up the Jeep to leave for work, backed up about a foot and it shut off on me. Cranks fine, battery is less than a year old. Just won't catch. The Jeep's been sitting all night, so its cold. Normally I'd jump to CPS, but I've only ever had CPS issues when the Jeep is hot. So is this more likely fuel pump?
 
Yank A Plug wire Jam A Flat Head In There Touch Ground And Turn The Key, Any Spark?

If Not Repeat The Process At The Coil Wire, If You Get It There But Not At A plug I'd Check Cap And rotor'
 
sidewaysstarion said:
anything odd being displayed on the cluster? checking the fuel pump is easy, just go poke the test port on the fuel rail and see if it has pressure.
Click to expand...

Nothing weird on the cluster
 
Not getting fuel
 
Took it to a shop. With my move at the end of the week, packing, and wrapping up my current job, no time to do it. Shop's driver thought fuel pump. We tested at the rail, no fuel.

Just got a call from them, CPS, as I thought. Getting that, an oil change, and my inspection done.
 
Follow up on this. Jeep seems harder to start with the new cps; has to crank much longer than I'm used to. Runs fine, just curious if anyone has had this happen with a new cps before
 
Year? If Renix, 87-90, Yes, the new CPS needs to be moved 1/16" closer to the flwx plate / flywheell to get up to the minimum cranking voltage output of .50 V

If HO, 91-01, the aftermarket CPS has been reported to be bad very often, most use the Jeep OEM CPS only on HO.
 
How did the no fuel story end?

IslanderOffRoad said:
Took it to a shop. With my move at the end of the week, packing, and wrapping up my current job, no time to do it. Shop's driver thought fuel pump. We tested at the rail, no fuel.

Just got a call from them, CPS, as I thought. Getting that, an oil change, and my inspection done.
Click to expand...
 
So that killed the fuel pump, is that what you are implying?

There should still be fuel pressure during the timer prime cycle!!!

Still wondering what year the rig is.

Digger87xj said:
CPS was bad

No signal from the CPS and the ECM won't activate the ASD or FPR.
Click to expand...
 
Ecomike said:
Year? If Renix, 87-90, Yes, the new CPS needs to be moved 1/16" closer to the flwx plate / flywheell to get up to the minimum cranking voltage output of .50 V

If HO, 91-01, the aftermarket CPS has been reported to be bad very often, most use the Jeep OEM CPS only on HO.
Click to expand...

98 4.0
 
IslanderOffRoad said:
with the shop replacing the CPS.
Click to expand...

I am still curious as to when it had no fuel pressure? Under what conditions? It should prime the fuel rail in the run position before you reach the start position, bad CPS or not. Once primed it should stay primed even with a dead cps!!!!
 
Ecomike said:
I am still curious as to when it had no fuel pressure? Under what conditions? It should prime the fuel rail in the run position before you reach the start position, bad CPS or not. Once primed it should stay primed even with a dead cps!!!!
Click to expand...

I dont know what to tell you. When I pressed the check valve, I got no fuel.

The only thing I can think is that because it started, let me back up, and then died, I may have ran what was in the line dry at the time? But that's just an uneducated guess.
 
IslanderOffRoad said:
I dont know what to tell you. When I pressed the check valve, I got no fuel.

The only thing I can think is that because it started, let me back up, and then died, I may have ran what was in the line dry at the time? But that's just an uneducated guess.
Click to expand...

Next time, cycle the ignition switch to run for 5 seconds, do not crank the engine, do that 2-3 times, and then recheck for fuel. If no fuel then, it can not be a bad CPS from what I think I know.

I had not fuel pressure on my 89, 2WD renix once, and all I did to fix it was clean the electrical connectors at the fuel pump to harness, near the gas tank. That was about 25,000 miles ago and 3 years ago on that rig.

Also, if it was running, it had to have a working CPS!!!! Thus if the CPS was working to supply spark (till it died), it had to be working to tell the pump it needed fuel. Therefore, it should not have run out of fuel, it should of had 39 psi of fuel the moment the CPS supposedly failed to deliver a signal for spark and fuel to operate via the PCM.

In other words, I don't buy that the CPS was the problem causing no fuel at the time it had no fuel?

Not saying the CPS did not suddenly go bad, it sounds like a miss diagnosis to me.

In fact I believe the no fuel with no spark, is no fuel injector signal to open fuel feed from the injector to the engine. I doubt it keeps the fuel pump from running while cranking, just because it does not see a CPS signal yet (but I am not sure of this).
 
Last edited:
The two issues could be related, or not. A failed check valve on the 97-01 fuel pump allows fuel pressure at the fuel rail to drop rapidly. This results in extended cranking before fuel pressure builds up.

A failed CPS causes the OBD PCM to not engaged the fuel pump after the initial 2-5 second ignition key ON prime, and causes the fuel injectors to not fire. If the fuel rail is drained, it may take 2-3 key on/off cycles to achieve any fuel pressure at the fuel rail, and the fuel vapors are not purged until the injectors fire, thus liquid fuel is blocked before reaching the fuel rail test valve.

The first thing to suspect when you have a "it cranks but won't start-up" situation is the CPS. Sudden failure of the CPS is common. "It started before and now it doesn't" is a common symptom CPS failure.
 
Last edited:
Ecomike said:
Next time, cycle the ignition switch to run for 5 seconds, do not crank the engine, do that 2-3 times, and then recheck for fuel. If no fuel then, it can not be a bad CPS from what I think I know.

I had not fuel pressure on my 89, 2WD renix once, and all I did to fix it was clean the electrical connectors at the fuel pump to harness, near the gas tank. That was about 25,000 miles ago and 3 years ago on that rig.

Also, if it was running, it had to have a working CPS!!!! Thus if the CPS was working to supply spark (till it died), it had to be working to tell the pump it needed fuel. Therefore, it should not have run out of fuel, it should of had 39 psi of fuel the moment the CPS supposedly failed to deliver a signal for spark and fuel to operate via the PCM.

In other words, I don't buy that the CPS was the problem causing no fuel at the time it had no fuel?

Not saying the CPS did not suddenly go bad, it sounds like a miss diagnosis to me.

In fact I believe the no fuel with no spark, is no fuel injector signal to open fuel feed from the injector to the engine. I doubt it keeps the fuel pump from running while cranking, just because it does not see a CPS signal yet (but I am not sure of this).
Click to expand...

good god man.
Really?
A failed CPS will cause a no fuel and no spark condition, just like the OP said were his symptoms.

It is quite common that when a CPS fail it draws down the 5v sensor feed line which effectively causes the ECM to go, what we techs call "Brain dead". There is no response from the ECM at all until the offending sensor is disconnected from the system.

In that situation there would be no fuel prime at all. Thusly no fuel pressure at the rail.

Another situation that would cause the same problem is a failing check ball at the fuel pump.
Regardless to what you might think, the check ball is not there to keep pressure in the rail but to keep VOLUME in the rail. The fuel rail simply needs to be full, not pressurized, for the prime function to work. In this situation, as soon as you push the schrader valve, the fuel starts draining back to the tank.

The fact of the matter is, the CPS fixed his no start. done and done.

I suspect that there is still the matter of fuel drain back as he now complains of an extended crank before startup.

done and done.
 
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