4.0 hesitation - JeepForum.com
 
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post #1 of 10 Old 03-14-2008, 03:50 PM Thread Starter
underpowered
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1998 ZJ 
 
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4.0 hesitation

my 1995 ZJ with 4.0 has a bad stumble to it. in park it revs fine, but under a load, if you tromp it, all it does is stumble and fall on its face. tried some fresh gas (who knows how old the other stuff was) with some fuel injector cleaner and it did not help. any other ideas on what i could do? probably gonna seafoam it this weekend and see what that does for it.


1998 ZJ-- lowered a touch

2005 GMC 2500HD 496 C.I.

Fat Amy-1989 K5 blazer. Linked, lifted, 38.5's on won tons. Big Girls can play in the woods too.
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post #2 of 10 Old 03-14-2008, 06:35 PM
_Kyle_
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I wouldn't advise using SeaFoam since it messes with the O2 sensors in Jeeps quite often. Try Mopar Combustion Chamber Cleaner from the dealership.

Sorry that's the only advice I have though.

-Kyle

1996 Grand Cherokee
2005 Wrangler Rocky Mountain Edition
RIP Troy (bigbluezj94)
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post #3 of 10 Old 03-14-2008, 06:38 PM
Windowsrookie
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I used Seafoam just fine. My dealership charges $38 for a can of Mopar CCC.

If you're really worried about it just dump the Seafoam in your gas.

2000 Grand Cherokee Laredo 4.7L V8 Quadra-Drive
1987 Wrangler 4.2L
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post #4 of 10 Old 03-14-2008, 06:38 PM
Vestjam
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Could be lots of things..... When was the last time the fuel filter was replaced or for that matter, the plugs, wires, cap/rotor?
Clean the throttle body also.

All things to look at...

2008 Jeep Wrangler X (Hard Top)
Incubus Off Road 511's with BFG 285/70-17

1998 Jeep Cherokee Sport
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post #5 of 10 Old 03-14-2008, 06:57 PM
_Kyle_
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Quote:
Originally Posted by Windowsrookie View Post
I used Seafoam just fine. My dealership charges $38 for a can of Mopar CCC.

If you're really worried about it just dump the Seafoam in your gas.
Good god, is it in a gold plated can? I paid $6 the other day, that was CHEAPER than any place had Seafoam, even on sale.

-Kyle

1996 Grand Cherokee
2005 Wrangler Rocky Mountain Edition
RIP Troy (bigbluezj94)
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post #6 of 10 Old 03-14-2008, 09:05 PM Thread Starter
underpowered
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this was discussed a while back,and the thread got closed. seafoam will not hurt it. the o2 in a jeep i smade of the same stuff as an o2 on a GM,ford, or any other make. no reason it would mess up on a jeep and not on anything else.


but back on topic, no idea on when the cap/rotor/wires/plugs/filter was all changed. i just bought it 2 months ago and have not evern messed with it till this past week, when i pulled out onto the road and tromped it to do a nice 4 wheel drift into the other driveway. it spun a little bit then fell flat on its face.

i will pull the plugs and see what they look like.

1998 ZJ-- lowered a touch

2005 GMC 2500HD 496 C.I.

Fat Amy-1989 K5 blazer. Linked, lifted, 38.5's on won tons. Big Girls can play in the woods too.
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post #7 of 10 Old 03-15-2008, 12:05 AM
my2monkeys
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Did you pull the plugs yet? My wifes 95 zj 4.0 auto, is doing the same thing. Been trouble shooting it for a couple weeks. I think I narrowed it down to the fuel pump. I put a fuel press. gauge on it, routed under the hood by the windshield so I could road test and check gauge when it stumbles. Couldnt get it to stumble(figures) yesterday, it had 1/4 tank. Wife drove it today, ran good. Went to pick up kid from school and it chugs and stalls with about 2 gals in tank now. I put $20 inthe tank (now its up to 1/4 tank again), put the press. gauge back on. yesterday the gauge read 40 psi consistently, today it would drop to below 20psi when I punched it and was chugging at 20psi then go back to 40psi when I let up alittle. Think I'll pull the pump tomorrow and see if its clogging up , seems to get bad with low fuel level.
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post #8 of 10 Old 03-15-2008, 03:19 AM
00gcl
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would check the plugs and wires first... I've had the same problems in other vehicles and it was always the wires, they may look good but if they're old they're not getting the spark to the plug, especially when the rpm's go up

2000 Grand Cherokee Laredo 4.0 I6
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post #9 of 10 Old 03-15-2008, 08:52 AM Thread Starter
underpowered
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its goin out on the trail today for a mud fest. i will see how it acts out there. for i all know it just needs blown out as it has not been actually driven for about 6 months now.

i will probably pull the plugs and wires tonight though.

1998 ZJ-- lowered a touch

2005 GMC 2500HD 496 C.I.

Fat Amy-1989 K5 blazer. Linked, lifted, 38.5's on won tons. Big Girls can play in the woods too.
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post #10 of 10 Old 12-21-2011, 11:35 AM
VAzj
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I have the same problem. The idle is fine after we put the new fuel pump in. It has a slight hesitation & surges around the 1800-2500 rpm range. IAC, MAP, TPS all are brand new. Was reading about the connector to the TPS, so I get my husband to check that.

Could it be the injectors? At 150k miles... they are pretty old.

I think the CAT is bad/old & I'll have that changed too later with the 02 sensors.
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