98 XJ, new fuel pump - knocking !!
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Newbie
Joined: Mar 2010
Posts: 11
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From: Mesa Arizona
Year: 1998
Model: Cherokee
Engine: 4.0
98 XJ, new fuel pump - knocking !!
Well this is pretty weird... I finally broke down & replaced the in tank 'fuel module' because of a faulty check valve (& pressure was a little low (5psi). After going through the major pain of getting the old one out, and the new one back in (plus skid plate), it fired up & showed 49 psi, which is right on the money - and pressure holds after shutting it off. BUT ... after about 15 seconds of running there's a loud knocking coming from underneath that sounds like a piece of sheet metal rattling against the exhaust pipe, or something similar - but it's coming from the fuel tank ! I can get underneath it & actually feel the knocking coming from the tank, and it's LOUD - loud enough to hear over the engine running.
I called the manufacturer of the pump - they have a tech support line - and they've never heard of this. He just said 'you'll have to take it out again & check it'......
I'm thinking maybe it's some kind of air lock situation, as I've read about this problem with other vehicles . . . I don't know. Looks like I'm going to be tearing it out again I guess
. . . any ... ideas ???
I called the manufacturer of the pump - they have a tech support line - and they've never heard of this. He just said 'you'll have to take it out again & check it'......
I'm thinking maybe it's some kind of air lock situation, as I've read about this problem with other vehicles . . . I don't know. Looks like I'm going to be tearing it out again I guess
. . . any ... ideas ???
Thread Starter
Newbie
Joined: Mar 2010
Posts: 11
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From: Mesa Arizona
Year: 1998
Model: Cherokee
Engine: 4.0
CF Veteran
Joined: Sep 2009
Posts: 8,567
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From: ☼ Blackhole Sun
Year: My Jeep is a GMC
It's got to be either the fuel tank or skid plate. The fuel pump can't airlock and supply fuel to the engine at the same time. As far as the pump itself peeps don't seem to have the best luck with Airtex pumps.
CF Veteran
Joined: Nov 2010
Posts: 5,841
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From: In the middle of Minnesota!
Year: 1999
Model: Cherokee
Engine: 4.0
Take it back.
See if you can find either a Bosch or a Carter. The Bosch are expensive but are the best in the business. Carter is okay too. Jeep is good, but expensive.
I won't install anything but the above. Way too many problems.
See if you can find either a Bosch or a Carter. The Bosch are expensive but are the best in the business. Carter is okay too. Jeep is good, but expensive.
I won't install anything but the above. Way too many problems.
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Thread Starter
Newbie
Joined: Mar 2010
Posts: 11
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From: Mesa Arizona
Year: 1998
Model: Cherokee
Engine: 4.0
I'll still try to get a Bosch ...
Thread Starter
Newbie
Joined: Mar 2010
Posts: 11
Likes: 0
From: Mesa Arizona
Year: 1998
Model: Cherokee
Engine: 4.0
I found a Bosch pump assy on Amazon for $240, which is the cheapest. (I paid $200)
Before I took it out again I tried something: I depressurized the fuel rail & discoed the line from the tank (the pump) and routed it into a 5 gallon gas can. I then took the pump connector apart and inserted wires to power the pump externally via a car battery.
When I hooked up the 12 volts, it pumped quietly and worked fine - I pumped about a gallon & half with no noise. So . . . . . this meant it only made noise when the engine was running & that most likely meant SOMETHING was rattling or vibrating within the tank or at least on it...
I found that an exhaust pipe clamp was within 1/8" of the tank's skid plate - even though I couldn't move it into contact. I repositioned the clamp and jacked up the pipe so it sits higher now.
So . . . after I fired it up it seemed OK - no noise. I still can't believe the knocking in the tank was from the exhaust pipe, but I'll bet when it was misfiring, it vibrated enough to hit it intermittently... maybe.
The next problem - which is significant - is the fuel level sensor. I put 5 gallons into the clean dry tank & it said it was almost half full. (the book says it's a 20 gal. tank) So I put exactly 10 gallons in & it says 7/8 of a tank. ****. I may have to replace it again after all . . .
Before I took it out again I tried something: I depressurized the fuel rail & discoed the line from the tank (the pump) and routed it into a 5 gallon gas can. I then took the pump connector apart and inserted wires to power the pump externally via a car battery.
When I hooked up the 12 volts, it pumped quietly and worked fine - I pumped about a gallon & half with no noise. So . . . . . this meant it only made noise when the engine was running & that most likely meant SOMETHING was rattling or vibrating within the tank or at least on it...
I found that an exhaust pipe clamp was within 1/8" of the tank's skid plate - even though I couldn't move it into contact. I repositioned the clamp and jacked up the pipe so it sits higher now.
So . . . after I fired it up it seemed OK - no noise. I still can't believe the knocking in the tank was from the exhaust pipe, but I'll bet when it was misfiring, it vibrated enough to hit it intermittently... maybe.
The next problem - which is significant - is the fuel level sensor. I put 5 gallons into the clean dry tank & it said it was almost half full. (the book says it's a 20 gal. tank) So I put exactly 10 gallons in & it says 7/8 of a tank. ****. I may have to replace it again after all . . .
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