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1998 Jeep Laredo 98 Jeep Grand Cherokee fuel pump?Or some

Tiny
JLCCA844
  • MEMBER
  • 1998 JEEP GRAND CHEROKEE LAREDO
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 130,358 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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Sunday, March 29th, 2009 AT 12:44 PM

17 Replies

Tiny
RACEFAN966
  • MECHANIC
  • 5,029 POSTS
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.
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Monday, March 30th, 2009 AT 9:50 AM
Tiny
JLCCA844
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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
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Monday, March 30th, 2009 AT 10:04 AM
Tiny
RACEFAN966
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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.


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

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Tuesday, March 31st, 2009 AT 10:09 AM
Tiny
JLCCA844
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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 :-(
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Tuesday, March 31st, 2009 AT 1:05 PM
Tiny
RACEFAN966
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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.
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Wednesday, April 1st, 2009 AT 10:02 AM
Tiny
JLCCA844
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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!
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Thursday, April 2nd, 2009 AT 9:37 AM
Tiny
RACEFAN966
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OK sounds great. Let me know what comes of it.
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Thursday, April 2nd, 2009 AT 10:31 AM
Tiny
JLCCA844
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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.
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Sunday, April 5th, 2009 AT 9:30 PM
Tiny
RACEFAN966
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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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Monday, April 6th, 2009 AT 9:44 PM
Tiny
JLCCA844
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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.
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Tuesday, April 7th, 2009 AT 2:59 PM
Tiny
RACEFAN966
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OK now on that same wire I need you to start the Jeep and let it warm for about 5 minutes and then while it is idling wiggle the wire harnes of the O2 sensor and see if the voltage will increase. Get back to me with what you find and if it increases let me know how much the increase was ok.
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Wednesday, April 8th, 2009 AT 10:29 AM
Tiny
JLCCA844
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Ok we tested it and it seems that there is a short in the same damaged wire as before that I had repaired. We are going to solder it and the mechanic said that this should fix the problem. And he doesnt see anything else that would cause it. He has tested all the sensors that would cause the problems that I am having. I hope this is it. Thanks for all of your help. I couldn't have done it without you.
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Thursday, April 9th, 2009 AT 9:23 AM
Tiny
RACEFAN966
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Great found something that alway's helps to know that there is something causing it. Now let me know how it goes and if there is anything more needed then just ask. Thanks and have a Great Day.
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Thursday, April 9th, 2009 AT 11:02 AM
Tiny
JLCCA844
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Ok there is really something wrong with it now. We havent soldered the wires yet but my friend the mechanic went to start it today and nothing. No electrical whatsoever. No dash lights no sounds zip. He tried about 10 times to get it to do anything, jiggled the ignition switch, the gear shift, but you could hear a clicking noise that sounds like a blinker coming from my passenger side under the glovebox. Finally he got it to start by pushing down on the throttle and it ran for a minute, and drove 1/4 mile then died twice the only way it will run is by keeping the throttle pushed down. And when it runs by itself, it is very weak. He messed with the throttle under the hood (the thing you push to give it gas with the wire) and it would run for a minute then go back down to running very weak.
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Friday, April 10th, 2009 AT 12:47 PM
Tiny
RACEFAN966
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There is a few relay's behind the right kick panel so you would have to remove that kick panel and see which relay is clicking. Also check the auto shut down relay next to the fuel pump relay that is in the power distribution box near the battery. Let me know what you find.
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Friday, April 10th, 2009 AT 9:19 PM
Tiny
JLCCA844
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We have taken out the relays and tried to duplicate the problem and got nothing. Could it possibly be the pcm? I did find that one of the covers to the grey plug(far left) on the pcm the cover is not on all the way and some of the wires are showing. I tried to close it and when I did I couldnt get it but I saw a lot of dirt come out of the bottom of the plug so I stopped messing with it. They did notice that my battery cable was a little loose and tightened it up. So I guess I will see what happens now.
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Monday, April 13th, 2009 AT 8:30 AM
Tiny
RACEFAN966
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Ok on that connecter I would like you to get some electricl connector cleaner at your local parts store. Then unplug it and clean it really good and plug it back in and lets see what happens. Yes it could be the pcm and we can do some pin tests once we know that the connection is clean ok. Get back to me and we go there next.
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Monday, April 13th, 2009 AT 6:32 PM

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