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Sorry for all the posts


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I'm posting a lot because I don't know very much, but y'all's answers have really been helping me.

 

I'm trying to figure out why my truck is running so rough, now it is surging and bucking when I accelerate.

 

Here is what I've done:

 

1.  Rebuilt a '96 HO 4.0 I6 and replaced the existing '87 4.0 I6.

2. Deleted the EGR system

3. Changed up to a PCV open loop system.

4. Replaced the muffler and tail pipe.

5. After the muffler and tail pipe the truck briefly ran really good until the gas dropped down to about 1/8 a tank or a little less.

6. I thought it was the tank or the fuel pump, so we took the tank off and cleaned it out and replaced the pump.  We ended up having to patch a small hole in the tank, anyway.

 

This didn't fix the problem.

 

I've checked the indexing of the distributor, new 2x platinum plugs, etc.

 

Any ideas?

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13 hours ago, MancheKid86 said:

copper plugs for our trucks, not those fancy platinum plugs

 

have you checked the distributor bearing for wear?

 

have you done a leak down check?

 

what is your operating fuel pressure?

I didn't know there was anything wrong with using platinum plugs - that's what I used for years before I put this engine in here...

 

The distributor is new.

 

I don't know what a leak down check is, but I'll read up on it.

 

I won't know what the operating fuel pressure is or how to measure it, so I'll do some googling and  youtubing and get back to you eventually.

 

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I'm not positive what the reasoning is, but I've almost always understood it to be that the old Jeep engine was built to run with those old cooper spark plugs, so there's not much point in spending the extra money and putting in the fancy ones.

As far as running better on the old style plugs goes, I suspect the modern plugs will be designed to work very well in a specific set of conditions, but the older ones are more likely to do alright in a broader range of conditions. But because of other limiting factors from the less advanced engine technology, the extra performance in the specific set of conditions for the plugs isn't going to be very noticeable, if at all.

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I'm not positive what the reasoning is, but I've almost always understood it to be that the old Jeep engine was built to run with those old cooper spark plugs, so there's not much point in spending the extra money and putting in the fancy ones.
As far as running better on the old style plugs goes, I suspect the modern plugs will be designed to work very well in a specific set of conditions, but the older ones are more likely to do alright in a broader range of conditions. But because of other limiting factors from the less advanced engine technology, the extra performance in the specific set of conditions for the plugs isn't going to be very noticeable, if at all.


I’ve had 8 4.0s in different Jeeps. I tried the high end Bosch even split fires. They seamed to work great for a while then drop off within a year or less. The best overall preforming plug over the long haul I’ve found are NKG’s. I tried them on a recommendation about 11 years ago and haven’t looked back. Know I buy them for everything when possible. Well that’s my story and I’m sticking to it.


88 Pioneer 4x4 auto LB D30/D44
88 Eliminator 4x2 5sp SB D35
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6 minutes ago, jeeppapa said:

I’ve had 8 4.0s in different Jeeps. I tried the high end Bosch even split fires. They seamed to work great for a while then drop off within a year or less. The best overall preforming plug over the long haul I’ve found are NKG’s. I tried them on a recommendation about 11 years ago and haven’t looked back. Know I buy them for everything when possible. Well that’s my story and I’m sticking to it.

 

 

I have to agree with this. I've always run Champion copper cores for decades in my Jeeps and would never consider anything else. But one person on this forum raved about NGK's so much that I gave them a shot a few yeas ago. They performed about the same as the Champions, but where they really shine is at idle. Much smoother and steadier, even with the cam I have. Plus when I pulled them at 2K miles or so to re-gap they still look new, not eroded away as the Champions sometimes did. I'm an NGK convert....

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I have to agree with this. I've always run Champion copper cores for decades in my Jeeps and would never consider anything else. But one person on this forum raved about NGK's so much that I gave them a shot a few yeas ago. They performed about the same as the Champions, but where they really shine is at idle. Much smoother and steadier, even with the cam I have. Plus when I pulled them at 2K miles or so to re-gap they still look new, not eroded away as the Champions sometimes did. I'm an NGK convert....

Agree with that.


88 Pioneer 4x4 auto LB D30/D44
88 Eliminator 4x2 5sp SB D35
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  • 4 weeks later...
On 6/14/2018 at 10:30 AM, HOrnbrod said:

 

I have to agree with this. I've always run Champion copper cores for decades in my Jeeps and would never consider anything else. But one person on this forum raved about NGK's so much that I gave them a shot a few yeas ago. They performed about the same as the Champions, but where they really shine is at idle. Much smoother and steadier, even with the cam I have. Plus when I pulled them at 2K miles or so to re-gap they still look new, not eroded away as the Champions sometimes did. I'm an NGK convert....

Which NGKs are you running??

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