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Sure could use some advice


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I've asked this question on several Cherokee / Comanche forums, and I haven't ever gotten a single suggestion......I KNOW some of you know these vehicles well enough to give me some advice: My '89 MJ cranks and runs fine (203,000 miles and doesn't smoke); however, just when I start to accelerate (right off of idle), it will sputter and die UNLESS I go ahead and give it a lot more throttle. Then it runs fine. Likewise, when driving and letting off the accelerator when coming up to a stop light, etc., it'll die almost every time. It'll crank right back up, but the damn thing just doesn't want to run right when normally accelerating from a stop and won't stay running when coming to a stop.

 

The CPS has been replaced. Cap, rotor, wires, and plugs have been recently replaced. I also just thoroughly cleaned both the throttle body and the IAC............any other suggestions would be greatly appreciated!

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Vac leak maybe. Check the vac line off the back side of the throttle body that runs up to the MAP/MAF on the firewall. Mine didn't fit tight at either end and caused the same symptons you describe. Possibility :dunno:
Thanks. I haven't tried that, but I'll give it a shot.
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I am pretty clueless about engines so remember that as you read this. But I experienced the exact same problem. I bought my truck new in '87 and sold it to my dad in 1995. He put only 10k miles on it in over 10 years. So obviously it didnt run as often as it should have.

 

I bought it back from him last summer. It ran ok but not like I remembered it. I replaced the rotor, plugs, wires, had the injectors & throttle body cleaned. I tried replacing the tps but that didnt help. It was better but still sputtered and sometimes died. I took it to the dealer last fall and they replaced the iac. It helped a little but still didnt run like I remembered it. It still stalled at times too. Stop lights were sometimes a challenge. On a couple of times, I had trouble starting it too.

 

I took it back this spring and asked for an old guy that has worked on the old 4.0 renix for a long time and they had a mechanic that owned one. He replaced the egr valve and solenoid. I could tell the moment I started the truck that he fixed it. It now runs like it did when I bought it new in '87.

 

Let me know if this helps.

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all good suggestions, i second the tps

 

:agree: ........But I'll 2X the EGR valve.

 

And like JT posted, do a fuel presser test first to see if your getting 39psi on the fuel rail.

 

Check this link out, about 1/2 way down is the "test" for the EGR valve-

 

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

 

I've been running my MJ for 3 years with the EGR vacuum line plugged with no bad results.

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EGR is definitley a possibility, but I am with JT on this one for the place to start...check the fuel pressure. Has the fuel filter been replaced in recent history?
You know, I had been wondering about the EGR. I used to have an Impala SS years ago, and they were bad about having slow speed running / idling problems when the EGR went bad......I'll be sure to check that. Question though: I haven't checked the fuel pressure, and I plan to do so; however, if I, in fact, had a clogged fuel filter, wouldn't it run fine at idle, but have problems as I ran at higher RPM's? The truck runs great at anything over about 1500 RPM........just curious
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EGR is definitley a possibility, but I am with JT on this one for the place to start...check the fuel pressure. Has the fuel filter been replaced in recent history?
You know, I had been wondering about the EGR. I used to have an Impala SS years ago, and they were bad about having slow speed running / idling problems when the EGR went bad......I'll be sure to check that. Question though: I haven't checked the fuel pressure, and I plan to do so; however, if I, in fact, had a clogged fuel filter, wouldn't it run fine at idle, but have problems as I ran at higher RPM's? The truck runs great at anything over about 1500 RPM........just curious

 

 

Not long ago I had my fuel pump hose pop off from being deteriorated, and it would idle ok, but would bump and sputter then regain power then sputter again...

After alot of money and parts later,, I pulled the pump and found the problem.. I should have pulled the pump to start with but I knew it was going to be a big PITA,,, but it was really a easy job to be honest...

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if I, in fact, had a clogged fuel filter, wouldn't it run fine at idle, but have problems as I ran at higher RPM's? The truck runs great at anything over about 1500 RPM........just curious

That would be the expected performance, yes, but these trucks--as I have found--do no do the expected with many things. If you are unsure of if/when the filter has been changed, then it's likely a good idea to change it as a preventative measure anyway.

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EGR is definitley a possibility, but I am with JT on this one for the place to start...check the fuel pressure. Has the fuel filter been replaced in recent history?
You know, I had been wondering about the EGR. I used to have an Impala SS years ago, and they were bad about having slow speed running / idling problems when the EGR went bad......I'll be sure to check that. Question though: I haven't checked the fuel pressure, and I plan to do so; however, if I, in fact, had a clogged fuel filter, wouldn't it run fine at idle, but have problems as I ran at higher RPM's? The truck runs great at anything over about 1500 RPM........just curious

 

 

It certainly could have the effect with a mostly clogged fuel filter. At idle there is enough fuel passing the filter to run fine. When you need more fuel not enough gets through and it starves the engine. If you can remember the last time you changed it. Its probably time to anyway.

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EGR is definitley a possibility, but I am with JT on this one for the place to start...check the fuel pressure. Has the fuel filter been replaced in recent history?
You know, I had been wondering about the EGR. I used to have an Impala SS years ago, and they were bad about having slow speed running / idling problems when the EGR went bad......I'll be sure to check that. Question though: I haven't checked the fuel pressure, and I plan to do so; however, if I, in fact, had a clogged fuel filter, wouldn't it run fine at idle, but have problems as I ran at higher RPM's? The truck runs great at anything over about 1500 RPM........just curious

 

 

It certainly could have the effect with a mostly clogged fuel filter. At idle there is enough fuel passing the filter to run fine. When you need more fuel not enough gets through and it starves the engine. If you can remember the last time you changed it. Its probably time to anyway.

Good point to all who have suggested the fuel filter change. That'll be the first place I start
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