Dies after 15-20 minutes

daveyboy43 · 03-30-2008, 08:48 PM

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.

70moparman · 03-30-2008, 08:51 PM

What was the problem that lead you to replace the fuel pressure regulator?

daveyboy43 · 03-30-2008, 09:37 PM

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.

impuresoul2k3 · 03-31-2008, 11:45 AM

Quick way to check is the smell of the FPR vacuum line

merlinTec · 03-31-2008, 03:49 PM

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

WJChris · 03-31-2008, 04:31 PM

Quote:

Originally Posted by merlinTec

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

BEST post this year.

makes huge sense.

impuresoul2k3 · 03-31-2008, 05:59 PM

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

daveyboy43 · 03-31-2008, 06:18 PM

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.

**ratmonkey** · 03-31-2008, 08:41 PM

the downstream fine tunes the mix further.

daveyboy43 · 04-01-2008, 06:14 AM

So is the rear o2 sensor the only thing I should try right now? What about the coolant tempature sensor suggestion?

impuresoul2k3 · 04-01-2008, 01:38 PM

Quote:

Originally Posted by ratmonkey

the downstream fine tunes the mix further.

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

impuresoul2k3 · 04-01-2008, 01:41 PM

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.

daveyboy43 · 04-01-2008, 02:15 PM

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.

merlinTec · 04-01-2008, 04:49 PM

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

daveyboy43 · 04-01-2008, 07:43 PM

I'll check that out,but it makes perfect sense to me. Does an oxygen sensor problem have to throw a code or not?

03-31-2008, 03:49 PM	#5
merlinTec Registered User Join Date: Jul 2007 Location: England Posts: 2,944 Profile Gallery Classifieds My Jeeps	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 __________________ UK Chrysler Jeep Master Tec.

04-01-2008, 04:49 PM	#14
merlinTec Registered User Join Date: Jul 2007 Location: England Posts: 2,944 Profile Gallery Classifieds My Jeeps	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 __________________ UK Chrysler Jeep Master Tec.

03-30-2008, 08:51 PM	#2
70moparman Registered User Join Date: Mar 2008 Location: South Jersey Posts: 10 Profile Gallery Classifieds My Jeeps	What was the problem that lead you to replace the fuel pressure regulator?

03-30-2008, 09:37 PM	#3
daveyboy43 Registered User Join Date: Jan 2007 Location: PITTSBURGH PA Posts: 138 Profile Gallery Classifieds My Jeeps	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.

03-31-2008, 06:18 PM	#8
daveyboy43 Registered User Join Date: Jan 2007 Location: PITTSBURGH PA Posts: 138 Profile Gallery Classifieds My Jeeps	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.

04-01-2008, 06:14 AM	#10
daveyboy43 Registered User Join Date: Jan 2007 Location: PITTSBURGH PA Posts: 138 Profile Gallery Classifieds My Jeeps	So is the rear o2 sensor the only thing I should try right now? What about the coolant tempature sensor suggestion?

04-01-2008, 02:15 PM	#13
daveyboy43 Registered User Join Date: Jan 2007 Location: PITTSBURGH PA Posts: 138 Profile Gallery Classifieds My Jeeps	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.

04-01-2008, 07:43 PM	#15
daveyboy43 Registered User Join Date: Jan 2007 Location: PITTSBURGH PA Posts: 138 Profile Gallery Classifieds My Jeeps	I'll check that out,but it makes perfect sense to me. Does an oxygen sensor problem have to throw a code or not?