Engine hesitating and surging while cruising - need suggestions - JeepForum.com
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post #1 of 9 Old 07-07-2013, 01:59 PM Thread Starter
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1994 YJ Wrangler 
Join Date: Jul 2008
Location: Maryland
Posts: 57
Engine hesitating and surging while cruising - need suggestions

Hey so I started a thread about this last week but I figured I should start over with all of the details because I am still stuck. Any help you could give would be much appreciated.

94 Wrangler YJ 6 cylinder...~165k miles.

This problem started a week ago. I'll be cruising down the highway in 5th gear around 60-65 mph and then my engine will start to sputter a bit and looses power. It immediately regains power, but I often have to ease off of the accelerator because I don't want to push it. It rarely happens in 4th gear, but it does sometimes. I've noticed that the issue only occurs through the lower RPM range. When I am in high RPMs during fast acceleration there are no issues, and there are no issues with idling at all. It happens most when cruising at low RPMs. It also doesn't happen regularly. Sometimes I can drive with no problems and other times its very bad.

The other day I went to start the engine at night (after using the jeep for work and the store) and it would not start. The engine would turn over for a very long time and eventually fire up, but the RPMs were unusually low for idle and then the engine would choke out and die. The next day I came back and she fired right up with no problem and I was able to drive it.

I've been using my repair manual and searching through these seemingly endless online forums and I've done a bit of work and tests with no success:

I've tested my fuel pressure at the rail with and without the vacuum line connected, and I did the test where you turn the jeep off and let it sit for a while to see how your pressure changes. It passed all of these tests and everything seemed normal.

I used seafoam to clean out the engine, used fuel injector cleaner in my last tank of gas, used an oil additive within the last 2 weeks with an oil change. Took apart and cleaned my air filter system. Checked all of my vacuum lines. I also changed all of my spark plugs and inspected the spark plug wires and distributor cap. Everything normal.

Although I had recently changed my O2 sensor, I decided to buy a new one and put it in to see if it would help. It didn't, the problem remains. I also purchased a new TPS sensor, but I broke 3 torx bits trying to get the screws out of the throttle body to replace it. So I gave up attempting to replace that sensor. To me, it seems like if there was an issue with the TPS that I would have more consistent issues.

But right now my only leads are maybe the TPS sensor, maybe the ignition coil if it isn't giving the spark plugs the right power (but that would be weird since most of the time it works fine), maybe the fuel filter is still a possibility? Although all of the fuel pressure tests were fine.

If anyone can give any suggestions, I'm all ears. This is my daily driver and I need it for work. Thank you very much for your help.


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post #2 of 9 Old 07-07-2013, 07:09 PM
Joe Dillard
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1991 YJ Wrangler 
Join Date: May 2004
Location: Lexington Park
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Yep, I'd change the fuel filter. Its cheap & easy to do and could be overdue to have it changed. It might not be the problem, but if it is, it'll help save extra wear & tear on the pump if its partially clogged.
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post #3 of 9 Old 07-08-2013, 06:30 AM Thread Starter
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1994 YJ Wrangler 
Join Date: Jul 2008
Location: Maryland
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Yea I decided to go ahead and change the fuel filter. I did it and the problem is still around, and is actually much worse. I was driving today in 2nd gear on a back road and the jeep completely stalled on me. I had to pull over and it didn't start at all. The battery seems to be completely dead. No power at all when I turn the ignition. I can't even turn on my hazards.
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post #4 of 9 Old 07-08-2013, 08:58 AM
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1999 WJ 
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Location: Richmond, VA
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My WJ is having a similar problem. When I start it up sometimes and drive down the road within 20 feet of leaving my driveway it losses all acceleration power and I can floor the pedal and I get nothing. Then after about 50 feet or so all of a sudden I get power again. I'm not sure why its doing it but its been doing that randomly for a while. Just recently I started hearing a whining noise from the rear and I think it's coming from my fuel pump so I'm going to change that and see of its the problem. I changed my fuel filter a few months ago and that wasn't it. My battery also started dying last week and I tried to jump it with no results. Has to tap the starter a few times and it started. It's done that once or twice in the past week so I'm thinking their is a loose wire in the starter causing a short and draining my battery so I'm replacing that too.

99 WJ,4" Lift, 265/75/16 Treadwrights, RC wheel spacers, Sound System, CB, HID's with amberless headlights, Rola Rack...ect.ect. Money pit!
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post #5 of 9 Old 07-08-2013, 09:37 AM
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1990 CJ7 
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Check the connections and fuses at your PDC. Loose cable or burned contacts can do thst.

418 miles on 19 gallons of gas. Can't beat the BBD !
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post #6 of 9 Old 07-08-2013, 10:46 AM Thread Starter
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1994 YJ Wrangler 
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Location: Maryland
Posts: 57
I had to have it towed to a AAA repair center after the breakdown because I couldn't get it started again. I brought a new battery in and it would crank very fast and sounded great, but it wouldn't fire up. I checked to see if I had any fuel pressure at th rail and there was nothing. I feel like it has to be the fuel pump. I don't really understand it because all of the fuel pressures were completely fine during the testing that I did, but I'm not sure what else it could be. I'll keep everyone posted.
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post #7 of 9 Old 07-08-2013, 12:42 PM
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1991 YJ Wrangler 
Join Date: Apr 2011
Location: Nashville
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When it fails to start, does the fuel gauge peg to Full? If so, it might just be a bad ground for the fuel pump. I just went through a similar problem where it would stall randomly and sometimes start right but up and other times it would not. I did not notice the fuel gauge movement until I was about to drop the tank and replace the fuel pump for a second time in 2 years. Once I cleaned up the ground location and put a new terminal on some fresh copper, it has been working for the last two days (knock on wood).
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post #8 of 9 Old 07-08-2013, 08:29 PM
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1993 YJ Wrangler 
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I'm having a very similar problem with my 93 yj. When I first start it up, it will run fine, then after idling for a bit it craps out and runs low rpm's, then eventually it will stall. When driving in low rpm's it runs like crap, even stalling in second. If i let off my clutch and don't give it gas, it will stall completely. Now it doesn't even want to turn over when I try to start it. I've checked my fuses but I lost the cover to my pdc, so maybe a good chance that got wet and messed up. I also have check engine light on now. Running through all my friends to see who has a obd1 I can use to run the codes. This all started happening after a day of fun in the mud, though this is also my daily driver and I need it to run, starting a new job on wednesday! I've changed oil, oil filter, air filter, cap, rotor, wires, plugs, fuel filter. Going to try some of the other suggestions, if you find your answer keep us updated as I will do the same.

Last edited by SuprHpyFU2time; 07-08-2013 at 08:43 PM.
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post #9 of 9 Old 07-12-2013, 02:52 PM Thread Starter
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1994 YJ Wrangler 
Join Date: Jul 2008
Location: Maryland
Posts: 57
^^you don't need an obd1 to run any codes with your 93. just turn the ignition to the acc position (just before th engine cranks) on and off three times. then if you wait it will begin to blink a code. if you search for how to do it it will probably be better explained.

Anyway, I ended up taking my jeep to a AAA repair shop because I needed it back right away. They replaced the fuel pump and it has been running perfectly since. I can't believe it was the fuel pump even after I did all the testing on the fuel line. I guess it happened to be working perfectly when I tested. Oh well. 570 bucks later...
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accelerating , engine , hesitating , sensor , surging

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