1989 YJ bogs down at interstate speeds - JeepForum.com
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post #1 of 25 Old 10-17-2011, 02:46 PM Thread Starter
usedsgm
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1989 YJ bogs down at interstate speeds

Hi guys, I bought an 89 wrangler last year and replaced the worn out 4.2 with a newly rebuilt 4.2 sporting a low torque RV cam. At the time of the swap I replaced all accessories except the distributor (fuel pump, starter, alternator, etc). It has a new Weber carb and holly fuel regulator. It runs great, however right after I got it out of the swap shop the jeep would not run past 70 mph (I think this thing should at least get 90mph if not better). I did the nutter and it improved some and then I did the TFI upgrade and the way it runs improved a little more, but it would still bog down at highway speed. It runs great all day in traffic and at 55mph but once you get on the interstate, accelarate to 65-70 mph it starts to immediately bog once you get to 70 and then rebels, bucks, spits and hesitates off to 50-60mph, if you depress the accelarator, it bogs even father (almost like the carb was loading up or it was choking for fuel). There are no smog components and the converter and muffler were removed/replaced this morning with new parts. I took it on a run up the interstate after the work and the same thing is happening. It does seem slow to crank at times. I am at my wits end in what to do, I am thinking of replacing the distributor with a HEI and even giving thought to replacing the carb and intake. The ignition module is also new. Any help would certainly be appreciated!

Thanks,

Mike

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post #2 of 25 Old 10-17-2011, 04:48 PM
jollyroger1
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When I bought my yj the p.o. said the regulator was set for about 70 mph,I havent tested that yet cause I dont do much interstate driving,but that could be your trouble
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post #3 of 25 Old 10-17-2011, 05:23 PM
wejeepinn
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Sounds to me like yours is starving for fuel.

My street jeep (1990) has a 258, Weber, and HEI. I had the same problem, thing would fall on it's face at 50-60 mph, and it turned out to be the fuel pressure regulator. I replaced it with one to the cheapie ones and it still happens from time to time. I've got it set for 3.5 lbs with a clear filter after it.

From time to time it will restrict and the filter runs dry. One twist of the knob and the pressure is released and it's back to normal for a while.

I guess I need to buy a real regulator.
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post #4 of 25 Old 10-17-2011, 06:00 PM Thread Starter
usedsgm
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Quote:
Originally Posted by wejeepinn View Post
Sounds to me like yours is starving for fuel.

My street jeep (1990) has a 258, Weber, and HEI. I had the same problem, thing would fall on it's face at 50-60 mph, and it turned out to be the fuel pressure regulator. I replaced it with one to the cheapie ones and it still happens from time to time. I've got it set for 3.5 lbs with a clear filter after it.

From time to time it will restrict and the filter runs dry. One twist of the knob and the pressure is released and it's back to normal for a while.

I guess I need to buy a real regulator.
It does sound like a fuel issue but I've checked the regulator and it is functioning correctly. I'm thinking about replacing the Weber and adding an HEI. Any suggestions on a simpler carb set up?
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post #5 of 25 Old 10-17-2011, 06:02 PM Thread Starter
usedsgm
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Quote:
Originally Posted by jollyroger1 View Post
When I bought my yj the p.o. said the regulator was set for about 70 mph,I havent tested that yet cause I dont do much interstate driving,but that could be your trouble
I've never heard that a regulator could be set for speed? I guess it could by the PSI delivery but could you still maintain a good idle pressure?
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post #6 of 25 Old 10-17-2011, 11:45 PM
MaddBones702
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for carb I'd go with the motorcraft 2100
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post #7 of 25 Old 10-18-2011, 05:23 AM
Karma
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HI,
90 MPH for a stock YJ? I think that is very optimistic. Further, high speed in ANY YJ would scare the hell out of me. This is not a road racer. It's a Jeep!!!

Sparky
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post #8 of 25 Old 10-18-2011, 05:51 AM
1998zj
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My stock 89 wouldn't run much over 80 mph when it was running good.

"Our lady of blessed acceleration don't fail me now"
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post #9 of 25 Old 10-18-2011, 07:22 AM
Karma
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Quote:
Originally Posted by 1998zj View Post
My stock 89 wouldn't run much over 80 mph when it was running good.
HI 19998zj,
Yes and you have a 4.0 engine. The op has a 4.2 which according to everything I have read came with 110 gigantic horses from the factory. I know my YJ, which has a Howell fuel injected '89 stock 4.2 would never even make 80 MPH. One thing is true for me is I live at roughly 5500 ft. That does make a difference. But still................

Sparky
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post #10 of 25 Old 10-18-2011, 07:48 AM
dtn8tr
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First off, as stated above, the Jeep with a 4.2 is NOT a race car. With 112hp you should be glad that it gets up to 70mph. That being said, I drive mine on the Interstate and drive 70-75 on the way up hunting often...I do have a problem maintaining that occasionally if there is a strong headwind like last weekend. 70 on the interstate should not be a problem depending on your setup. As I see in your profile, 4.2l with a Weber, BA-10/5 pos tranny and 31" BFG...same setup that I run...what is your gearing? I am running 3.55 but I could see you having problems if you are running the standard 3.07 because the slightest breeze is going to slow you down and make it hard to maintain speed. If you're running 3.55 or better then I would say that maybe you are running into a fuel issue and might have to make some adjustments. Which Weber are you running? With having the new motor with a slightly hotter cam in it, was the carb re-jetted? You might have to look at timing and re-adjust that slightly too. There are a lot of things to look into but wouldn't plan on a 90mph YJ even running perfect because you are driving something with the aerodynamics of a brick with flaws( a brick only has 6 surfaces).

1997 TJ, 5" IRO front with 4.5" HD IRO WJ rear, 35x12.5x15 Mickey Thompson MTZ, JKS disconnects
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post #11 of 25 Old 10-18-2011, 08:24 AM
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Quote:
Originally Posted by usedsgm View Post
....... the jeep would not run past 70 mph (I think this thing should at least get 90mph if not better). ....................... Any help would certainly be appreciated!

Thanks,

Mike
Mike,

Jeeps don't typically go much over 70mph. The near vertical windshield, vertical front clip, gearing, lack of wind tunnel commercials, and factory engine power... are all clues that it might not have been designed for interstate speeds.

You think it should go more than 90? plain and simple, you are wrong. what about your jeep would give you the idea it was build for higher speeds?

It should not be sputtering, but frankly when you are going over 70MPH in a jeep, I doubt you would even be able to tell the difference between the engine stumbling and you just trying to drive it too fast and it not wanting to go. Since the wind noise is too loud to hear the engine clearly, I am going to assume you just felt it not wanting to go any faster. That is normal.

If speeding and interstate speeds are your goals.... you need to look into buying a car.

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post #12 of 25 Old 10-18-2011, 09:26 AM
SirChiefton
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I have no pressure regulator, im 4.2, HEI, MC2100. I dont honestly know why you would need a pressure regulator on this setup. Is your float set correctly?

I have to agree with everyone else about high speeds in a Jeep. I can get mine to 70 but the pucker factor is way up there. I have 33's and 3.55's, 70mph is everything ole girl has.
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post #13 of 25 Old 10-19-2011, 05:26 AM
1998zj
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Hey Karma, since when did a stock 89 come with the 4.0? My 95 with a 2.5 rolling on 35's will go as fast as my 89 would go. It just doesn't have the torque down low like the 4.2.

"Our lady of blessed acceleration don't fail me now"
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post #14 of 25 Old 10-19-2011, 06:40 AM
dtn8tr
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Quote:
Originally Posted by Karma View Post
HI 19998zj,
Yes and you have a 4.0 engine. The op has a 4.2 which according to everything I have read came with 110 gigantic horses from the factory. I know my YJ, which has a Howell fuel injected '89 stock 4.2 would never even make 80 MPH. One thing is true for me is I live at roughly 5500 ft. That does make a difference. But still................

Sparky
My '88 carb'd 4.2 with 170,000 on it will make 80 and I need to re-jet it.

1997 TJ, 5" IRO front with 4.5" HD IRO WJ rear, 35x12.5x15 Mickey Thompson MTZ, JKS disconnects
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post #15 of 25 Old 10-19-2011, 08:28 AM
Tang87
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When I had my Jeep stock carb and everything I could get her up to 70 down hill lol. Now I rebuilt the motor (bored .060" over iirc) HEI and MC2100. The HEI is a huge dizzy, and I hear the vacuum advance is too much for the 258 and it's better If you leave it off and let the mechanical advance work. I could be wrong I'm still learning on my Jeep just wanted to toss in an idea. I will have to take mine on the interstate and see how fast she can go now that the motor is rebuilt.
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