Question about Jeep Grand Cherokee

3 Answers

While driving (mostly high speeds but has happened at low speed- my JEEP 'bumps"down to 30-35 and pops right back up to 65-70. It is random and sometimes the fuel gauge goes right down to empty and the light goes on then the gauge goes right back to normal.It feels like it's almost 'bucking' (like I'm puttig on brakes)rather then stalling and I don't actually lose power. The check engine light does not come on and no codes either. We have replaced PCM, alternator, voltage regulatoir, spark plugs and fuel filter with still no resolution.

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  • ddeyton Jul 15, 2009

    This could possibly still be the case even though this has been going on for 5-6 months? Just wanted to clarify it was not something that's just happend in the last week or two...

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3 Answers

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  • Jeep Master
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Based on what you have said, I would first make sure that body and engine grounds (including any ground leads at the computer) are clean and secure. I would definitely check the ignition switch ...Reason that will not set a code is that turning on and off from the switch is a normal activity...The computer cannot tell if you are turning the switch on and off or the switch is disconnecting by itself. It will not set a code, otherwise every time you turn the car on or off, a code would be set.
I'm going to throw a bunch of ideas out here because sometimes after I close, I can't get back in with another idea...It is possible that your fuel pump may be in the initial stages of failure. when this happens the motor intermittently binds up which would not cause a stall but will cause symptoms like a bad filter. A poor ground at the pump can also mimic this. Again...no codes for pump, and testing while working will not usually show anything. This could also have something to do with fuel gauge problem as both operate off the same ground wire. Not to be denied, the old wiggle the wires test may also be helpful. Though not high tech, it often helps isolate a problem area. Another item to give a look to is the map sensor. If its not working correctly it changes ignition timing and fuel mixture...but I don't see any relationship to fuel gauge there. But, there may be two separate problems that can't be tied together...you can have a leak in a tire and a bad alternator at the same time...fixing one will not help the other, but for now, assume your problems are somewhat related. If I remember anything else, I'll try to get back in...Hope I haven't given you too much info and confused you. Generally I keep this stuff in my head and work on each idea till it can be proven incorrect then move to next idea.Its only a machine and parts do fail...finding them is fun isn't it?.

Posted on Jul 28, 2009

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  • Jeep Master
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Hi

Given that you have already carried out significant work to your Jeep - first check the main engine earth strap is not disconnected or poorly grounded to the chassis to eliminate a poor or intermittent earthing issue. The other issue is that you may have an intermittent short somewhere in the wiring harness. Check harness particulary at stress points e.g. where it enters the bulkhead for evidence that it is compromised.

Check for any shorts on the power supply to the coil that may be touching the frame and creating problems or the coils themselves which can play up intermittently. The fact that you are having this erratic behaviour with the fuel guage makes me wonder also about an intermittent short possibly at the ignition switch which would be effecting both driveability and instrument operation like this.

The fact that no codes are being stored is unusual to say the least. This will be a process of elimination I am afraid.

Hope this helps. Please remember to rate my answer. Many Thanks.

Posted on Jul 16, 2009

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  • Master
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Hi,
Sounds like there is an air lock in the fuel lines, disconnect the fuel line at the engine and pump the accelerator pedal or try turn the engine until the airlock is out, fill the tank again and pump the pedal until it just pumps fuel out. When you reconnect the line use the manual fuel pump to flood the engine. Be careful not leave any air in the lines and do it in a safe place away from naked flames.



Regards.

Posted on Jul 14, 2009

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