'92 2.5 engine stuttering between 2,500 to 3,500K RPM - Jeep Wrangler Forum
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Old 05-24-2019, 07:29 AM
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Like the title says, I'm having issues with my YJ 2.5. When the engine is under normal operating temperature it stutters between the rpms mentioned. So far I've checked fuel pressure, although it was good, I replaced the fuel pump (in case the check valve was faulty and draining back to the tank), regulator, and fuel lines between the filter and tank, vapor lines and vent grommets which were rotted. The fuel lines were hard and collapsed. I also replaced vacuum fittings and brake boosted grommet to the air intake hose since it was rotted. Vacuum seems good now.

Spark plugs have normal color, the o2 sensor is a year old and so are the TPS, air intake temperature and engine coolant sensors and complete exhaust system including headers.

My YJ has 4.0 TB but I reused the 2.5 TPS and idle valve (which is old). The issue started several months after the TB swap so I don't think this is the issue.

When the stuttering occurs the idle trends to stay high and slowly drops.

The issue does not happen all the time. A few times it has happened before the engine warms up but most of the time after it is warmed up.

I'm wondering if the idle air valve or crank position sensor could be issue. I also heard that a worn distributor/pickup coil cause this problem.

I'm stumped. I'm planning on keeping this jeep so I want to fix the issue.

What do you guys/gals think? Crank sensor, distributor or something else.

Thanks for the help.

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'92 YJ Malibu Yellow, 2.5 L, 5 Speed, 4.88 gears, 3.5 inch lift, 33" BFGs, F&R Truetracs, Ten Factory rear axles, 4 Hole Injectors, headers, intake and 4.0 TB.
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Old 05-25-2019, 09:05 AM
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So yesterday after work I went I bought a crank position sensor and installed it. Turns out the issue is still there. I did notice something that I just didn't pay attention to before but the issue always started after revving the engine past 4k rpm in second or third gear. I also ordered the IAC to see if it help the high/erratic idle.

I'm still stumped.

Perhaps timing? Bad distributor/pickup coil? I'm buying one today and will install it right after.

This is driving me crazy.

Has anyone experienced this?

Could the 4.0 TB be the culprit?

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'92 YJ Malibu Yellow, 2.5 L, 5 Speed, 4.88 gears, 3.5 inch lift, 33" BFGs, F&R Truetracs, Ten Factory rear axles, 4 Hole Injectors, headers, intake and 4.0 TB.
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Old 05-25-2019, 10:28 AM   #3
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Just throwing this out there because I just went through it.....

check input and output voltage on TPS.

I installed a new one and it then started stuttering when under load about the same rpms you speak of. I ended up loosening the TPS and tweaking its position just a little. Tightened back up. Stuttering gone. Seems even if its in properly, there is a sweet spot to it.

Just my 2 cents
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Old 05-25-2019, 12:18 PM
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Quote:
Originally Posted by RI93YJ View Post
Just throwing this out there because I just went through it.....

check input and output voltage on TPS.

I installed a new one and it then started stuttering when under load about the same rpms you speak of. I ended up loosening the TPS and tweaking its position just a little. Tightened back up. Stuttering gone. Seems even if its in properly, there is a sweet spot to it.

Just my 2 cents
I just bought the distributor, spark plugs and coil. I may re-use the old TPS to see if the new (1 year old) was faulty.

If turns out it was just one sensor or what have you, at least most ancillary sensors, etc., are new so I wont have to worry for a long time. I just want the Jeep running good again.

Thanks,
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Old 05-25-2019, 04:50 PM
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So I just finished installing a new distributor, rotor, spark plugs, coil and new AIC. I fired it up and seems like timing was right on the mark. Phew, lucky me! I took it for a spin after it warmed up to operating temperature and accelerated the engine in 2nd and third to 5K RPM and the issue didn't appear as it usually did plus I didn't get any check engine light. I didn't feel any hesitation. I'm going to take it on a longer drive to see if it was fixed. Crossing my fingers.

The idle issue is still there. When slowing down it stays at around 1,200 RPM until it settles down to around 900RPM.

List of new parts:

Fuel Pump
Fuel hoses
Vapor line to tank
Tank vapor valve grommets
Crank position sensor
Idle Air Control Valve
Coil
Distributor
Rotor
Spark plugs
Vacuum fitting
brake booster grommet to air intake hose

Maybe the TPS is causing the idle issue or just the fact that the engine has a 4.0 TB could be culprit.
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Old 05-25-2019, 06:01 PM
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Forgot to mention that as a bonus, I discovered the lower steering shaft was loose right at the joint with the steering column. I tighten it up and now I no longer have the dead play on my steering wheel. It drives straight with one hand at 70 MPH. Now I get to return the steering box and shaft.
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Old 05-25-2019, 07:36 PM   #7
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I have a similar symptom, sort of a random stumble at idle, not enough to effect anything, but noticeable enough to feel.

I replaced much of the same components as you with no joy, I gave up years ago trying to figure it out
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Old 05-26-2019, 02:05 PM
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Been driving all day and issue hasn't come up. Still crossing my fingers.
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Old 05-26-2019, 08:22 PM   #9
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On TJ 2.5 a miss around 2-2.5 K rpm is common when injector harness to cylinder 3 and 4 are reversed

Something about the harness layout makes people put 3 on 4 and 4 on 3

Runs mostly fine as true fuel entry timing is intake valve not injector pulse but something about the 2.5 fuel map makes for a 2300 ish stumble when these two injector plugs are swapped

Check the wire colors to make sure right harness connector on right injector

Costs nothing and might help


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Old 05-26-2019, 08:25 PM
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Quote:
Originally Posted by Digger84 View Post
On TJ 2.5 a miss around 2-2.5 K rpm is common when injector harness to cylinder 3 and 4 are reversed

Something about the harness layout makes people put 3 on 4 and 4 on 3

Runs mostly fine as true fuel entry timing is intake valve not injector pulse but something about the 2.5 fuel map makes for a 2300 ish stumble when these two injector plugs are swapped

Check the wire colors to make sure right harness connector on right injector

Costs nothing and might help


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I tried that before I started buying and swapping parts. The it made much worse so I figured the connectors were where they were supposed to be. Thanks. It's been running awesome since I changed the distributor yesterday.

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