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Help. I have a 90 4.0, it has a weird miss especially at cruise speed

Lusty

NAXJA Forum User
Location
Edmonton
I have recently got my intake gasket replaced, which fixed my old problem of high idle. But now an old miss i had is way worse and is very noticeable at highway speed, i just came back from x-mas trip and wanted to blow up my jeep(not really) cause this is very annoying. Loss of power and also wont kick down to passing gear when stepped on, anyone have this happen or similar? Please help me hopefully save a mechanic bill.(can everyone else with an older jeep like mine hear a sucking noise like vacuum all the time? i thought it was normal from my throttle body)I have also noticed that if i touch my last injector at the back my jeep will start to run rough, strange huh.
 
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I dont know about touching the injector doing anything, but have you thought about the TPS? Correct me if I'm wrong, but I'm pretty sure that a 90 has a throttle possition sensor, right? That sounds like it could be your problem, is it having trouble at idle? $55 at autozone, 2 torx screws to replace the old one. Worth a shot before you spend big bucks at a mechanic if you ask me.
 
I just had the TPS tested and adjusted at the mechanics. They said it is good to go. I also have a new 02sensor, egr valve, platinum plugs, wires, cap & rotor both chrysler, and a bunch of other goodies too. I am wondering if my fuel pump is buggered could it cause this effect. My jeep has over 300,000kms on it, and the pump is loud some days quiet others. Fuel filter is new.
 
please respond!!!

would like to bump this up because my fuel pump makes a humming sound on and off also, Does this mean it's bad,going bad or is this the norm? By the way it does start fine (except it really really needs a tune up.)Thanks for all replies....
 
you may try replacing the fuel filter. I had a similar problem with my 91 4.0 and it seemed to help. This may be a gradual problem though, not a sudden thing. It is cheap and probably needs to be done anyway.
 
I have replaced the fuel filter when i got the jeep, around 6-8 months ago(20,000kms) I was wondering if it could be my egr solenoid, because when u unplug them they are supposed to let vacuum through, abd this one does not. Theres good vacuum goin to it but none out the other side ,so i think its screwed.Dealer part im told.$$$$$$$.....

Earlier on i had a jerking missing type problem, my mechanics tested the tranny and found it was not locking up. Turns out there is a white plastic switch at the top of the brake pedal that lets the computer know when to downshift while braking, this being out a little made my tranny keep dropping out of overdrive thinking the brakes were on always. Something to check if anyone has this weird problem.
 
Re: please respond!!!

BADBOYXJ said:
would like to bump this up because my fuel pump makes a humming sound on and off also, Does this mean it's bad, going bad or is this the norm?

It's going bad. When it becomes loud all the time you can be sure that it'll soon call it quits.

Lusty said:
I have also noticed that if i touch my last injector at the back my jeep will start to run rough, strange huh.

Not really. That could be the reason why your engine's missing so you might wanna investigate that further.
 
well after i dont know how many dollars and tests and scans i finally believe my problem is over. I just went and bought a new egr solenoid and the highway miss is almost completely gone, 99% gone.WOOOOOHOOOO, i still got crappy fuel mileage though but whatever. 400km to a tank
 
I also have a '90 cherokee that has a miss at high speeds, ive changed multiple fuel, electrical parts so hopefully this will help my egr solenoid tests bad so its my next step many thanks.
 
Lusty if that injector is touched and the engine misses then the connection (electrical) is not good. Check that out further, to do two things for you. One it will probably completely cure your highway miss and secondly will improve your MPG which, if my math is correct, is terrible.
 
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