Mechanics

98 GRAND CHEROKEE FUEL PUMP???OR SOME

1998 Jeep Laredo

1998 Jeep Laredo 6 cyl Four Wheel Drive Automatic 130358 miles

ok I have been having problems with my grand cherokee laredo. At first it wouldnt start. Then we foind a cracked vacuum line and it started right up. A few days later as I was driving down the road at 55mph it started to buck and sputter and acted like and it was like it was trying to cut off on me. Well the CEL came on and I had the codes diagnosed it was a P138 (down oxygen sensor) and a P340 (camshaft pos sensor). We replaced the cam pos sensor. It turns out the reason the oxygen sensor code was thrown was that the wiring for the unit had been rubbing the drive shaft and it split one of the wires in two. Well after we fixed the wires it stopped for a few days. I had a mechanic drive it the last time it did it and naturally it did nothing so they couldnt help me. The day the mechanic drove it the bucking got worse and I could hear and feel a clicking near my gas pedal. I do have an exhaust leak that someone told me that could be throwing the oxygen sensor code also. But the actual sensor is not bad. Then last night I put a bottle of fuel injection cleaner in it and it started to shake violently and it was like it would rev up high then try to take off while my foot was on the brake. It did it till I cut it off and sat for a minute. I had my bf come and drive it and he said it did it once and when it did he could push the gas pedal all the way to the floor while it was only going 15 mph and doing the bucking and trying to go but just couldnt thing. He said he could feel it trying to go forward but it just wouldnt. The CEL light wont come on now but my bf said it seems like the fuel pump is going bad. I have had others tell me it could be the fuel filter but I thought that the filter was in the pump and you couldnt just replace the filter itself you have to do the whole pump. Is this true or is there reall ya filter somewhere? Is this what it sounds like a bad fuel pump? I am at a loss here. I dont know where to go next!
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Jlcca844
March 29, 2009.




Ok first of there may be a fuel filter depends on what jeep you have. If it is a grand cherokee then there is a filter just infront of the tank above the rear diff. If it is not a grand cherokee then no there is no filter. Now as for fuel pump depends. I would get a fuel pressure test first to see what it is then take it from there. Get back to me with what you find.

Racefan966
Mar 30, 2009.
Ok I will have someone check to see if there is a filter a lot of people have told me that the 98 grand cherokee is one whole assembly and I havent really been able to find just a filter thats sold seperately. But I will have a fuel pressure test done today and let you know what I find out. Thanks

Tiny
Jlcca844
Mar 30, 2009.
Ok just to let you know it will also depend on the production date. If it is an early model then it will not have a fuel filter if it is a later model then it will. If there is one this is what it will look like.


http://www.2carpros.com/forum/automotive_pictures/249564_783361_2.jpg


Racefan966
Mar 31, 2009.
Ok, I have the one the (98 laredo) that is the whole assembly inside the tank. I have had a fuel pressure test done and I had a friend drive it with a machine hooked up to it and they found nothing out of the ordinary. All the readings were normal. The throttle pos sensor and the o2 sensor didnt read off. Then he tested the fuel pressure and it didnt seem like it was off. Im completely stumped here. I would like to check the maf sensor and they suggested the ignition coil could these be possibilities? I changed the air filter myself when the problems first occured. I am going to have the exhuast leak fixed and see what happens. I dont know what else to try. If I have it looked at by someone who knows anything about cars it wont do anything so they cant fix a problem they cant see or hear. I hope I find some solution soon : -(

Tiny
Jlcca844
Mar 31, 2009.
OK I would like to test the MAP and the TPS as well as the coolant temp sensor manually. Meaning with a digital multi meter ok. First off unplug the temp sensor on the thermostat housing on the left (driver) side. Now set you meter on ohms and check the ohms of the sensor (not the wire harness) and do this when it is cold. Get me the reading and the temp at the time of the test.
Now the throttle position sensor ok. You will need a paper clip to use to back probe the reference wire and then you will set you meter on 20V scale and then hook up the meter + to the paper clip and - to a good ground and with key on engine off you should read.25 volts then slowly raise the throttle and it should steadly and gradually go up to 4.8 volts wide open. If there is any drops or glitches in it as you lift the throttle then it is bad replace it. Here is the wire you need to back probe (do not disconnect the sensor) the orange wire with the dark blue stripe.
If this all pans out then we will check the map sensor but you also need a vacuum pump so we can see what it is doing at different vacuum reading ok. So get back to me and we will take it from there.

Racefan966
Apr 1, 2009.
Ok im going to have those tested today. It stopped for a few days and it did it again last night. Now when it does the clicking in the gas pedal I can hear and feel worse now when the car acts like its out of gas. So im going to have a few things tested and I will let you know. Thanks!

Tiny
Jlcca844
Apr 2, 2009.
OK sounds great. Let me know what comes of it.

Racefan966
Apr 2, 2009.
I had the two parts tested that you suggested the map and the tps. They were both normal. Now my check engine light is back on and it is throwing the P138 code again it says there is a shortage on the downstream oxygen sensor. So now I am going to have to check on all the causes that would make it throw that code I had a friend pull up some things to check on alldata some of the options were the actual O2 sensor the fuel pressure regulator were my friends main concerns he is a mechanic granted he works mostly on big rig trucks but like he said you can't chase a ghost. He has driven it several times and it runs like a top for him but I'm gonna have a few of the problems alldata suggested checked out and I will get back to ya.

Tiny
Jlcca844
Apr 5, 2009.
According to my findings there is a short in the signal wire to from the o2 sensor to the computer. This wire is either tan with a white stipe or black with a pink stripe. What you need to do is do a test on that wire for voltage. So check voltage and let me know if it is more or less the 4.97 volts. This test can only be done after the car has been running for 5 minutes. As a mechanic it is true you can't chase a ghost but you should listen to what the car is trying to tell is wrong. Let me know what you find and decide to do.
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Racefan966
Apr 6, 2009.
Ok I had the pink/black wire voltage test done and it registered right at 3.89 volts. So this isnt too much less than the 4.97 voltage. Im not sure if I need to go ahead and change it or if its something else. Thanks.

Tiny
Jlcca844
Apr 7, 2009.

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