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Dies after 15-20 minutes

1K views 14 replies 6 participants last post by  daveyboy43 
#1 ·
99 G.C. with 4.7 liter engine. Yesterday I replaced the fuel pressure regulator to correct a problem that had many stumped for quite awhile. Last night the Jeep ran fine and then after 15 or 20 minutes it started to stumble like it was choking and then it stalled. I had to wait a few minutes and then it started but acted up again. I parked it for a few hours and then drove home about 10 minutes away with no issues. This morning it started right up and was running like a champ while I had it idling in the driveway and just like last night after 15-20 minutes the engine stalled and I had to wait a few minutes to get it started again. It's like something is happening after the engine warms up and I'm puzzled with this. Please help.
 
#3 ·
Running rough,bad idle,black smoke and nasty smell coming from exhaust. Turned out the diaphram in the pressure regulator which operates on a vacuum went bad and it was sucking raw fuel back into the manifold. Thus the bad running condition plus black smoke and smell from exhaust,all of which went away with new part replacement. Also cleared all codes after replacement and there are no new codes being thrown since this new problem developed.
 
#5 ·
Hi
I would be looking at the rear o2 lambda sensors have gone down due to it running so rich. 15 to 20 minutes it’s when it goes from open loop (cold engine) to close loop (worm engine) so o2 sensors then control the mixture.
Regards,
Merlin
 
#7 ·
rear sensors don't control the mixture ;) Also you might want to check the coolant temp sensor, I know mine is bad and will start acting up after the jeep warms up(sputtering, missing, terrible gas mileage) but I have mine on a switch resister now. Also I lose overdrive if I let the sensor do its thing
 
#8 ·
I didn't think the downsteam o2 sensor had anything to do with the fuel air ratio,that it was the upstream sensor. Also wouldn't that trip a code. Also the tempature gauge does seem to move up quicker than it has in the past. I also just noticed that the cooling fans aren't running.
 
#11 ·
No it doesn't, it tells the ecu weather the cat is working or not, why do you think it throws a code if you remove the cat? Also an O2 will not always throw a code
 
#12 ·
For the CTS sensor problem, you can stick a resistor in the harness plug just to simulate a CTS reading around 180-200 degrees so you don't have to swap sensors just to find out that wasn't it. Plus the resistor is cheaper, to get it started you might have to take it out so it defaults then once its started you can put it back in.
 
#13 ·
I'll try that. Do you think the cooling fans not coming on are related to this?
So the upstream O2 sensor could be malfunctioning but not throwing a code
correct? With the problem with the fuel pressure regulator and how rich it was running it's quite possible the O2 sensor is now bad.
 
#14 ·
Hi
The rear sensors will take control over the front sensors. yes, normal operation the front sensors adjust the mixture the rear sensor test the efficiency of the cat but I have had it a number of time (I admit mostly on 4.0l) where the rear sensor goes down and reads high so the ECU weakens off the mixture so it just splutters and dies. This will only happen when it goes into closed loop control (normal temp). Going by the fault you had before I am positive it’s an o2 sensor fault or related fault as to if it’s just the rears or all four as they don’t like being soaked in fuel couldn’t say without DRB plugged in then could tell you in 5 minutes. Could be an idea to get a tester to read the o2 sensor voltages to pick out what ones are down it’s going to be more then one or it would only affect one bank.
Regards,
Merlin
 
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