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Discussion Starter · #1 ·
Well, I'm stumped! My 1993 6.5 diesel is surging only when the throttle is slightly pressed. I have no air intrusion and have 7-8 psi of fuel pressure at the engine.

Recent work: New fuel line pre-lift pump (old had air intrusion) and installed a Reman IP a few months ago to try to resolve a surging issue between 1500 and 1800 RPM. The new IP resolved that issue, but this new issue has taken its place. It is extremely frustrating, and the truck is basically not-usable in its current state. Yeah, the surge is THAT bad.

Since this problem has been around since I installed this IP, I'd say that is where my issue is, but I am curious if anyone else has had an issue similar, or if there is a fix other than "another IP."

Thanks!
 

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Well, I'm stumped! My 1993 6.5 diesel is surging only when the throttle is slightly pressed. I have no air intrusion and have 7-8 psi of fuel pressure at the engine.

Recent work: New fuel line pre-lift pump (old had air intrusion) and installed a Reman IP a few months ago to try to resolve a surging issue between 1500 and 1800 RPM. The new IP resolved that issue, but this new issue has taken its place. It is extremely frustrating, and the truck is basically not-usable in its current state. Yeah, the surge is THAT bad.

Since this problem has been around since I installed this IP, I'd say that is where my issue is, but I am curious if anyone else has had an issue similar, or if there is a fix other than "another IP."

Thanks!
I would install a piece of clear fuel line on the return side of the Injection pump and check your return fuel line going back to the tank for kinks, leaks, plugged up, etc
 
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Discussion Starter · #3 ·
I would install a piece of clear fuel line on the return side of the Injection pump and check your return fuel line going back to the tank for kinks, leaks, plugged up, etc
I currently have one on there and have no bubbles.
 

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Inspect or even better, replace the rubber fuel lines.
Crack open a injector and see if anything changes, also check if it's timing or high idle issues.
 

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93 C3500, 10k GVW, Crew, LB, Dually ,141 Block. Replaced much in 2020
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Well, I'm stumped! My 1993 6.5 diesel is surging only when the throttle is slightly pressed. I have no air intrusion and have 7-8 psi of fuel pressure at the engine.

Recent work: New fuel line pre-lift pump (old had air intrusion) and installed a Reman IP a few months ago to try to resolve a surging issue between 1500 and 1800 RPM. The new IP resolved that issue, but this new issue has taken its place. It is extremely frustrating, and the truck is basically not-usable in its current state. Yeah, the surge is THAT bad.

Since this problem has been around since I installed this IP, I'd say that is where my issue is, but I am curious if anyone else has had an issue similar, or if there is a fix other than "another IP."

Thanks!
Most unexpected surges or throttle runaway is the DB pump. I had one that did that and rebuild fixed it. One thing to try if you have cruise control, un-hook it from the pump linkage to rule it it malfunctioning. You might also disconnect the cold advance solenoid on the linkage too. I'm thinking the only thing then to raise RPM is more fuel, which would be the pump. Please let us know. Jim P
 
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Have you tried retarding the timing slightly?
 

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Discussion Starter · #7 ·
Inspect or even better, replace the rubber fuel lines.
Crack open a injector and see if anything changes, also check if it's timing or high idle issues.
I have gone through my rubber lines and replaced almost all of it. Everything on the truck is not leaking fuel or air. I would say this is more of a timing issue than a cold advance/high idle issue.

Most unexpected surges or throttle runaway is the DB pump. I had one that did that and rebuild fixed it. One thing to try if you have cruise control, un-hook it from the pump linkage to rule it it malfunctioning. You might also disconnect the cold advance solenoid on the linkage too. I'm thinking the only thing then to raise RPM is more fuel, which would be the pump. Please let us know. Jim P
That's what I would be thinking too. Odd thing is, this is a rebuilt pump. I would have though it would be good from the beginning.
I have not thought about that with the cruise control. I have not ruled that out. I have always had working cruise control, but it is certainly worth checking.

Have you tried retarding the timing slightly?
Initially, yes. Upon initial installation, I lined the marks up on the pump and the engine, and the truck would not start. I advanced it towards the driver's side and would start. As of now, I have it set almost as far towards that side as it will go. I wonder if the timing gear is misaligned? I did not remove the front cover when I did the job, I went through the oil fill hole.
 

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Discussion Starter · #8 ·
Finally got around to working on the truck some this morning. I made sure my IP timing was correct and checked all of my solenoids to be sure they are working. My marks are about 1/4 inch advanced towards the driver's side. Any less and the engine will not run, or will bellow white smoke while idling.

I drove around a good bit to test everything while I had time. I can make this truck start to surge on command now. Here is a video of what happens:

 

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Finally got around to working on the truck some this morning. I made sure my IP timing was correct and checked all of my solenoids to be sure they are working. My marks are about 1/4 inch advanced towards the driver's side. Any less and the engine will not run, or will bellow white smoke while idling.

I drove around a good bit to test everything while I had time. I can make this truck start to surge on command now. Here is a video of what happens:

Are you using any additive in your fuel?
 

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Discussion Starter · #10 ·
Are you using any additive in your fuel?
Yes, I have used DieselKleen cetane booster since I have owned the truck (January of 2019.)
 

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Discussion Starter · #12 ·
Tried running it with the fuel cap loose?
Not exactly, but I have done the mod where I drilled a hole in the underside of the fuel cap to bypass the faulty tank seal.
 
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