'97 Grand fuel pump relay killed fuel pump?

I have a '97 Grand Cherokee 4x4 that has had a myriad of ignition problems (well ... maybe one problem with a myriad of 'solutions'). I finally replaced the computer and the problems stopped for a couple of months. This week the engine died a couple of times while driving in hot weather and then would start again after a few minutes. It then began not starting when driven and then parked for about a half hour. It finally would not start again. No codes, no engine light. Towed to mechanic.

He says the fuel pump and the fuel pump relay are bad. It was replaced last year. The mechanic says the relay may have burnt out the fuel pump over time by creating spikes and low voltage. I don't know much about the system, but that sounds very strange for relays. Is this a likely diagnosis?

Thanks,

Joe M

Reply to
Joe_M
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I can tell you my fuel pump took out it's relay, it wouldn't stop running the pump with the ignition off. It ran another couple of months with a new relay and replaced culprit clogged filter. As a test it should run for a couple of seconds every time you turn on the ignition key on then shut off, if the engine is not started. But this really sounds like the Crankshaft Position Sensor:

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That's whyI asked you to test for the sound of fuel to confirm it's really notrunning. God Bless America, Bill O|||||||O mailto: snipped-for-privacy@aol.com
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Reply to
L.W. (Bill) Hughes III

You are still describing a code 12 issue I think.....

I would be making 'really' sure the body of the vehicle had full power.

To do this, I take a multimeter and read the volts at the battery posts with the engine running and the headlights and heater fan and wipers on. I then move the negative meter probe to the body with the positive still on the battery positive and compare the voltages.

If the voltages are different, your body ground path is bad.

Good luck!

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06
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Reply to
Mike Romain

Thanks Bill,

Already replaced the crank position sensor when previously chasing P0351 codes. Did not seem to have any impact, but I hear it often accounts for strange problems.

Reply to
Joe_M

Mike,

No codes on OBD II. I get codes 12 and 55 on the odometer and have for months. I was told previously that code 12 always shows and is not an indicator of a problem, even though it does not disappear after many start cycles. Was I told wrong?

I had cleaned and reseated both the negative to body ground and the negative to engine ground before the latest problem. I have not run the specific test you mention. I will when I next get access to the car.

Thanks,

Joe M

Reply to
Joe_M

Sometimes the cables can rot inside the clamps which is why the meter test is a good one just to make sure.

It wouldn't hurt to meter the engine block with the volt test also.

Code 55 should be the only one.

Mike

Joe_M wrote:

Reply to
Mike Romain

Fifty start cycles or scantool to reset.

Code 12 is only of consequence when it is surrounded by many other codes from all over the place. In that case it means the battery cable, terminal, or something inside the battery is not making good contact.

In my case the terminal popped off the battery when I was removing the positive cable to clean the connection. :/

Reply to
DougW

Grand back with new fuel pump and running.

I checked voltages with digital meter while engine idling with lights on, wipers on, and heater fan on. The reading was just over 13.5 volts across the battery terminals. About 2 to 4 hundredths of a volt higher with negative taken from bolt attaching coolant overflow reservoir to body. About

3 to 5 hundredths higher with negative taken where the coil attaches to the engine. I expect that a bad ground would create a much higher difference, but I don't know how big a difference it would be. I don't think most mechanics are going to be checking for differences measured in hundredths of volts.

I still get code 12. The battery had been disconnected in the shop. My OBD reader can reset OBD codes, but not the 12 code. Does it reset after 50 start cycles? Does start cycle mean starting the engine and then stopping it without any requirement to let if run for a while or get to closed loop?

Thanks,

Joe M

Reply to
Joe_M

Those volt readings are within any tolerances, when you start to see tenths, you have issues.

Could have just been a bad pump, it happens.

I believe the code will reset with a key start count like it counts to give you codes.

Mike

Joe_M wrote:

Reply to
Mike Romain

Joe_M proclaimed:

OK, it *could* happen, but I'd try a different mechanic.

Reply to
Lon

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