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david craig
david craig, Auto Mechanic
Category: Jeep
Satisfied Customers: 3783
Experience:  owner/mechanic at 3D Automotive
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1997 jeep grand cherokee 5.2L I have a problem with the

Customer Question

1997 jeep grand cherokee 5.2L I have a problem with the RMP's jumping at highway speeds i have replaced plugs, wires, distributer ,tps, fuel pump, just baffled with this issue.
JA: Have you ever replaced the fuel pump, or is this the original?
Customer: New fuel pump
JA: Are you fixing your Grand Cherokee yourself? What have you tried so far?
Customer: yes
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
Submitted: 1 year ago.
Category: Jeep
Expert:  david craig replied 1 year ago.

Hi Im David, thanks for using the site. is the check engine light on, or does it comes on when experiencing this problem?

Customer: replied 1 year ago.
No check engine light
Expert:  david craig replied 1 year ago.

ok. let me look up sometihng for your vehicle. thanks

Expert:  david craig replied 1 year ago.

are you performing any tests on the components that you replaced? it seems to me you are wasting your money and hoping something fixes it. i dont work that way, so i hope you are ready to do some tests. do you have a scan tool and a multi meter?

Customer: replied 1 year ago.
Expert:  david craig replied 1 year ago.

ok. good

Expert:  david craig replied 1 year ago.

first thing you'll need to do is access the vehicle speed sensor so we can test it.

Expert:  david craig replied 1 year ago.

you also may be having a torque converter issue. The RPM is going up when it unlocks and then down when it re locks. A common cause of this is a bad brake switch. The only way to 100 percent verify this though is with a scan tool while driving the vehicle and watching what the brake switch input is doing. Besides the brake switch the other common concern is the torque converter it self. I would start with a brake switch though if you dont have access to a scan tool that has a data display. If that dosent correct it you will need to take it to a mechanic for further diagnosis

Expert:  david craig replied 1 year ago.

does your scan tool have live data and transmission capabilities?

Customer: replied 1 year ago.
I switched out the brake switch already
Expert:  david craig replied 1 year ago.

ok. if your scan tool can reading vehicle speed then taking the vss out isnt necessary. you can just drive it and monitor its output. also to check the torque converter lock up you can drive it and when goin up a small grade on the highway, tap the brake pedal and the transmission should drop a gear.

Customer: replied 1 year ago.
Will do, thanks
Expert:  david craig replied 1 year ago.

you're welcome. please accept the answer and leave me a 5 star rating if you were satisfied with my help.after you rate me, i will keep this open if you'd like. thank you. have a good night

Customer: replied 1 year ago.
A loose connection was the culprit for the rpm issue. The scanner says all cylinders are misfiring but runs very smooth??????
Expert:  david craig replied 1 year ago.

erase the codes

Customer: replied 1 year ago.
I cleared the codes then they reappeared
Customer: replied 1 year ago.
No check engine light
Expert:  david craig replied 1 year ago.

take the car for a drive

Expert:  david craig replied 1 year ago.

before you do that disconnect the battery cables, both of them. touch them together for 10 seconds, then reconnect and check for codes again

Customer: replied 1 year ago.
Will do
Expert:  david craig replied 1 year ago.

any news?

Expert:  david craig replied 1 year ago.

do you still need assistance?