Intermittent hard start/stalling

[CTeunuch]

I have a '99 XJ, 4.0, AW4, 158k. Recently I've been having an intermittent hard/no start, then stalling. If I hold the accelerator down, it fires up and runs fine, then dies when I let off. After I keep it running for a minute or so, it will stay running fine. Other times it will fire right up, and drive for days without issue. I have good spark, and hear the fuel pump turn on, any ideas?

I did some reading about the check valve in the tank, seems like this could be the cause, you guys agree? Or a possible bad injector?

 

[Ecomike]

Run and OBD-II scan for pending codes first. Then get an ohm-volt meter and test the sensors. Could be a spark coil going bad (they seem to be rare), or the CPS going bad (common), or dirty-loose battery clamps......on and on. The IAC valve in the throttle body may be sticking, and good electrical solvent cleaning and light machine oil will solve that. Also the TPS may be going bad.

Does not sound like a fuel problem or injector problem.

 

[Talyn]

Clean the IAC and check fuel pressure while cranking. Being that if you hold the accelerator down indicates a malfunctioning IAC.

 

[kastein]

try the poor mans prime - ignition to RUN, wait till the pump shuts off, cycle back to off then run again, repeat 2-3x. If you do this every time you start it for a while and it doesn't give you any problems, it is probably the check valve.

Holding the throttle down may be fixing it because it's going into flood clear mode, allowing the fuel pump to catch up and pressurize the rail before the injectors start firing.

I have to do this basically every time I start my red turd.

 

[Ecomike]

Clean the IAC and check fuel pressure while cranking. Being that if you hold the accelerator down indicates a malfunctioning IAC.

I agree. Is there a timer relay on the IAC in 99 like the B+ relay on renix?

 

[Talyn]

I don't think there is. FWIW I had this exact problem on my 97 ZJ 5.2L. IAC was the problem, being that it ran with the pedal depressed I went straight to the IAC. I would have checked the fuel pressure first, but the silly thing doesn't have a check port.

 

[CTeunuch]

I had been thinking it was the IAC, but I don't have a CEL, so I was trying to think of any other possibilities. I'll hook it up tomorrow at work and see if there are any pending codes. Worst case I'll start swapping in sensors off the parts Jeep until it goes away. Thanks for the help guys.

 

[Talyn]

Flooring the throttle goes into flood clear mode, not part throttle.

 

[CTeunuch]

Flooring the throttle goes into flood clear mode, not part throttle.

I don't have to go WOT, just partially open to get it to fire, then hold it so it doesn't die.

 

[kastein]

oh, I thought you had to floor it for some reason. Yeah, I'd put my money on the IAC.

 

[ktwalker01]

My 99XJ did this right after I got it for a good 3 months. Everything tested out fine plugs, o2 etc no vacuum leaks etc. It would stumble after starting up but if i gave it gas it would come to life just fine. Sometimes it would flat out stall. I pulled the fuel rail off and replaced all 12 injector orings and it was a fixed. 6$ fix. Might be worth the shot.

Also how old is your battery, these things run terribly after starting on a weak battery if the alternator cant put out enough power at the low idle.

 

[jimmy96xj]

If theres no code I would check the cps

 

[adrnalinlovr]

Cps (ckp) have ultimate control of injectors, when they fail they FAIL, I'm blaming iac/tps

 

[Talyn]

The CKP is not the same thing as the CPS. CKP = cam sensor, CPS = crank sensor. CKP feeds the injectors, CPS feeds the timing.

 

[gradon]

psss: CMP=caM and CKP & CPS=cranK, though sometimes people/threads will call the CMP a CPS.

 

[Ecomike]

psss: CMP=caM and CKP & CPS=cranK, though sometimes people/threads will call the CMP a CPS.

I started to mention that myself. IIRC CPS is also used for Cam Position Sensor, by some people, vehicles, groups. I don't recall seeing the CMP before, interesting, but it is rarely discussed and rarely goes bad in my Renix circles.

My favorite is the air manifold temp sensor, it seems to have at least 3 know acronyms, LOL.

 

[adrnalinlovr]

Ckp= crank Cmp= cam cps = nothing

 

[Ecomike]

LOL, this is going to get fun, pop corn, peanuts....

 

[Ecomike]

http://en.wikipedia.org/wiki/CPS

Automotive

• Cam Profile Switching (CPS), a variable valve timing technology by Malaysian carmaker Proton.

They list about 50 other choices too, LOL


This shows both Cap and Crank using CPS as the name-acronym.


https://www.google.com/search?q=aut...s=org.mozilla:en-US:official&client=firefox-a

 

[adrnalinlovr]

Say cps and you won't find a part