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Unread 01-10-2012, 11:54 AM   #1
Zombi
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1999 TJ Wrangler 
 
Join Date: Aug 2008
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Hesitation/surge?

Something weird is happening with the jeep these days but it doesn't happen at all times. It happens maybe once or twice when I drive it, accelerating at low speeds.

The best way I can describe it is that when you know you're on the gas at a steady rate the vehicle will slow down ever so slightly then surge back up to speed. This is noticeable without moving the pedal once it is depressed.

The fuel pump is new roughly 3-4000 miles on it.
The spark plugs were originally AP985's now Champion copper plugs. The plugs/wires/cap and rotor have less than 1000 miles on them.
I have also ran sea-foam/other fuel injector cleaners through the gas tank and once through the intake without any change in this issue.

I'm thinking this issue may be directly linked to my idle skip/flutter and may be caused by an injector going out.
What are your thoughts on this?

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Zombi's are in fact very unpleasant to be around, they smell, and bite--also, they eat babies.
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Unread 01-10-2012, 01:53 PM   #2
kevbz
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is it an auto or stick?
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Unread 01-10-2012, 02:57 PM   #3
JeffBowser
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You described a problem I have been chasing for 3 years now. Most recently I replaced my distributor, the whole thing, and the camshaft position sensor. Debugging over time, I've replaced the TPS, plugs, coil, wires, crankshaft position indicator, temp sensor, MAF sensor, and cleaned the TB (just off the top of my head). When my MAP sensor gets here Friday, I'll let you know if that has any impact.

1/17/2012 update:
Replaced my MAP sensor last night. No hesitation issues this morning, but it's not unusual for me to not encounter them everyday. I'll follow up again in a week.

Also - the MAF sensor I referenced above, I meant the IAT sensor.
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Unread 01-10-2012, 03:07 PM   #4
Junior166
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I had the exact same issue and its fixed but I can't say exactly what did it. I have been replacing tons of parts, not just for this issue but mostly cause I am anal.

At first I replaced the plugs/wires/filter/Dist cap and rotor/O2 sensor(along with the exhaust) which did nothing to fix it. Then I changed the TPS sensor on some advice from a friend and that didn't fix it.

This last round I replaced the MAP sensor, fuel sending unit, and clutch(and related clutch parts). The Surge (thats what I call it) is gone now.

So not sure that helps much but it had the issue up till that last batch of parts was replaced so i am assuming it was one of those.
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Unread 01-10-2012, 03:13 PM   #5
JeffBowser
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Tell me (Junior and OP) - if you let off the gas and got back into it, did (does) that clear it for the time?
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Unread 01-10-2012, 03:34 PM   #6
Junior166
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I don't really recall ever trying to leave off. I know it was exactly what was described and was something that didn't happen all the time. I would notice it mostly when accelerating at lower speeds but I did notice it a few times on the highway. The highway times can be confused with wind gusts though.
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Unread 01-11-2012, 09:49 AM   #7
srfnfly227
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I had this exact same problem almost 2 years ago. After a week or 2 of it happening, the Jeep finally stalled out in my parking spot. When I restarted, I had the engine code P0108 Manifold Absolute Pressure/Barometric Pressure Circuit High Input. I disconnected the battery, cleaned the battery terminals and cables, cleaned the sensor connections and hooked everything back up. I have never had the problem again.

Advice that I got on another site suggested that it may have been my battery going bad. Cleaning the connections solved it at the time, but 4 months later I ended up needing to replace my battery. Looking back at it now, it may have all been connected.
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Unread 01-11-2012, 09:54 AM   #8
JWebber
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Test your fuel pump pressure, should be around 49 to 52 psi at idle. I had the same problems my pump would go from 42 down to 36 psi during idle and driving. replace pump no more surge or slow take offs.
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Unread 01-11-2012, 09:57 AM   #9
JeffBowser
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There was also another thread up here not too long ago that described a very similar issue, and it turned out the guy had some bad wiring in the wire loom wad right there by the throttle body. Melted insulation, I believe, allowed some wires to intermittently touch. This is the issue I had with my CPS, but a bit further downstream.
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Unread 01-11-2012, 11:43 AM   #10
Zombi
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Oh boy, sounds like this one is going to be tough to track down.

The Jeep is a 5-speed, if that make a difference.

I will need to test fuel pressure at the rail to see if that is the culprit. I would be surprised though because it did this both before and after the fuel pump being replaced.

I cleaned the IAC a couple of times with no difference and the battery is less than 4 months old. It's a good one too, Diehard Platinum S2.

To answer your question Jeff, I haven't had to let off so I cant tell if that would have an impact.

Here is something I though about.
Recently (6 months ago) I replaced the entire exhaust on my 99' and went with a 2000+ 2-piece cast manifold. That required me to use a 2000 California only y-pipe. The bung for the O2 sensor on that down pipe is right before the location of the factory cat, much farther back on the pipe. Could that be causing issues?
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Quote:
Originally Posted by mrbates View Post
Zombi's are in fact very unpleasant to be around, they smell, and bite--also, they eat babies.
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Unread 01-11-2012, 01:07 PM   #11
JeffBowser
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I wouldn't think so. After all the debugging I did, I'm down to wires and the MAP sensor. After reading of Junior's debug, I'm hoping the MAP sensor. If that's not it, I'm cutting into that wiring mass and taking a close look.
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Unread 01-11-2012, 01:20 PM   #12
GunmetalX
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I have no specific ideas, sorry, however when the "hesitation" occurs do the engine RPM increase or decrease?

If they increase, I'd guess that it could be something mechanical (rather than electrical) whereby the load on the motor is removed causing the RPM to go up and the vehicle to slow down. In which case I'd probably start thinking about the clutch and maybe axles.
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Unread 01-12-2012, 06:26 AM   #13
Zombi
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The only thing the engine will do while it hesitates/surges is it wont rev as quickly as it does normally.

I cleaned the IAC last fall if that matters.
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Quote:
Originally Posted by mrbates View Post
Zombi's are in fact very unpleasant to be around, they smell, and bite--also, they eat babies.
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Unread 01-12-2012, 10:23 AM   #14
Dogbones
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having this exact problem too, happens right after clutch is released in a gear past 2nd, feels like its bogging down and the power disappears for 1 sec then returns..i'm not dogging it either...My friend recommended trying 93 octane to see if it would help and it seemed too but now its returned and happens intermittently once every 5 days i'd say...

Have you noticed it happening in a certain RPM range? mine seems to surge in 3-4th gear at almost exactly 2.8k RPMs...
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Unread 01-13-2012, 06:19 AM   #15
Zombi
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It only seems to happen (noticeably) at lower RPM under 2200.
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Quote:
Originally Posted by mrbates View Post
Zombi's are in fact very unpleasant to be around, they smell, and bite--also, they eat babies.
Zombi is offline   Reply With Quote Quick reply to this message
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