Ye Ol' Cherokee

So I did a fuel pressure test on my 98 4.0 to try and diagnose my running problems, which includes intermittent bucking, stalling, etc.

I'm trying to find the correct fuel pressures according to spec.

First I pulled the relay and tried to start it to clear the lines. No start.

I then plugged up the testerms and got a reading of 10 psi. Started it up, let it run, and it stayed at a consistent 49 psi. I turned the jeep off, and the pressure gradually dropped over 10 minutes to 25 psi then I unhooked.

Do these numbers sound good? I know the 49 at idle is good, but the others, I'm not sure off.

I will be doing this test multiple times to try and catch the fuel pressure when it is exhibiting the running problems that I described.

I will soon provide the links to my other posts with more information

Thanks!

Ye Ol' Cherokee

Did the test again. This time, pressure with just the ignition on started at 32, then started dropping slowly.

At idle, it was still just below 50, but the needle was moving back and forth from like 47-51 range, as if it was wiggling super fast. Mean anything?

10 minutes after turning off, the psi went slowly down to 20

CCKen

That needle oscillation is the damper on the fuel rail working.


The idle pressure is okay.


The pressure drop is okay.


Spec is 49.2 psi +/- .5 psi.


Your intermittent bucking, stalling, etc., problem may be your upstream O2S.


Do you get a CHECK ENGINE light? Does the CEL bulb work?

Ye Ol' Cherokee

The upstream sensor and downstream was changed with oem ones about 3 months ago. I had a code for it, and once it was replaced, the code has stayed away.

I did over heat really badly tho. The engine has been checked and is fine. But could the heat have fried the o2 sensor? And wouldn't I get a code?

I do have a code 1282 and 0463. I swapped out the fuel pump relay with the elec. Fan to see if the relay is bad but it didn't fix problem and the relay code is there still

CCKen

P1282-FUEL PUMP RELAY CONTROL CIRCUIT


When Monitored: With the ignition on and battery voltage above10.4 volts.


Set Condition: An open or shorted condition is detected in thefuel pump relay control circuit.


POSSIBLECAUSES


FUEL PUMP RELAY WIRING HARNESS OBSERVABLE


FUSED IGNITION SWITCH OUTPUT CIRCUIT OPEN


FUEL PUMP RELAY


FUEL PUMP RELAY CONTROL CIRCUIT OPEN


FUEL PUMP RELAY CONTROL CIRCUIT SHORTED TO GROUND


FUEL PUMP RELAY WIRING HARNESS INTERMITTENT


POWERTRAINCONTROL MODULE





P0463-FUEL LEVEL SENDING UNIT VOLTS TOO HIGH


When Monitored: Ignition on and battery voltage above 10.4 volts.


Set Condition: The fuel level sensor signal voltage at the PCMgoes above 9.9 volts for more than 90 seconds.


POSSIBLE CAUSES


FUEL LEVEL SENSOR SIGNAL CIRCUIT OPEN


FUEL PUMP MODULE WIRING HARNESS INTERMITTENT


SENSOR GROUND CIRCUIT OPEN


FUEL LEVEL SENSOR


POWERTRAIN CONTROL MODULE


FUELLEVEL SENSOR SIGNAL CIRCUIT SHORTED TO SENSOR GROUND CIRCUIT

Ye Ol' Cherokee

So I see here that you said the the PCM is a possible cause for both codes.

When I changed my coolant temp sensor, the engine was hotter than I thought, and a volcano of coolant spewed in the direction that the coolant temp sensor points, which is right at the PCM.

I know the PCM got coolant on it, it had to. So could that have destroyed the pcm? Or at least cause it to short out? My problems are totally intermittent and only happen at random times, especially on the first start of the day

CCKen

I don't think so, but the connectors should be cleaned out with Electronic Cleaner.


Did the PDC take a bath as well? Worth a look inside.

Ye Ol' Cherokee

I forgot to mention, I did check the PDC, dry as a bone

Hellz

Did this issue ever get tracked down and fixed?

DFlintstone

Waz almost 4 years ago ya-know.........

Hellz

Yep, I'm having a similar issue. input?