7.3 Super Duty with Zero Off Idle Torque

[Petro]

I'm currently working on a 2000 F250 7.3 6 speed truck. A guy I know bought this truck with high miles knowing it needed some work. From the day he bought it, it has had absolutely zero off idle torque. Now when I say this, I mean when taking off in low or reverse you have to give it throttle to avoid killing it no matter what. When you begin to let out the clutch, it just dies. No trying to lug down and take off, just simply dies. It acts like a small block 302 but worse. Keep in mind this truck has 3:73 Gears and 285s for tires, so no tall gears and average tires. Anyway, Last fall it developed a dead miss, He assumed it was an injector due to the fact it didn't have any unusually high blow-by and used little to no oil. He ordered a set of Full Force AD injectors, installed them and the problem persisted. He brought it to me, I did a compression check and found low compression on multiple cylinders so he agreed to have me install an engine and we both assumed it would take care of his lack of off-idle torque. I installed a freshly machined .40 over longblock into the truck with the new injectors, new cam sensor, new ICP sensor, and new IPR. Also installed another used camshaft because the original was beginning to flake on one lobe. After All this, the truck runs well, drives pretty decent but still has absolutely ZERO off-idle torque. I tried another pcm out of another manual truck, no change and I tried another IDM with no change. The truck is throwing a lower-than-expected ICP code while driving, the pump is fairly weak but will make 2000 psi at WOT so I dont see that having any effect. Has around 500 psi at idle. If you ever so slightly begin to slip the clutch to pull the engine down (I mean VERY, VERY Slowly), ICP will spike to 700ish after about a second. It almost acts delayed, but it could be the rate at which the sensor is reading maybe? Other than that, it is code free. Does anyone have any idea what could be left? Has anyone seen this? I've scoured the internet and can't find any problem resembling this. Keep in mind, I've owned 10+ manual 7.3s and the owner has owned multiple also, so we know how they're supposed to drive. With its lack of grunt, it makes it a chore to drive empty in traffic, little lone towing. Does Anyone have any suggestions on what else to try? Can a throttle positioning sensor cause an issue like this? I may try a different HPOP but I'm skeptical. I'm open to all suggestions at this point.
Thanks
Dillon

 

[6.0 Tech]

I'm currently working on a 2000 F250 7.3 6 speed truck. A guy I know bought this truck with high miles knowing it needed some work. From the day he bought it, it has had absolutely zero off idle torque. Now when I say this, I mean when taking off in low or reverse you have to give it throttle to avoid killing it no matter what. When you begin to let out the clutch, it just dies. No trying to lug down and take off, just simply dies. It acts like a small block 302 but worse. Keep in mind this truck has 3:73 Gears and 285s for tires, so no tall gears and average tires. Anyway, Last fall it developed a dead miss, He assumed it was an injector due to the fact it didn't have any unusually high blow-by and used little to no oil. He ordered a set of Full Force AD injectors, installed them and the problem persisted. He brought it to me, I did a compression check and found low compression on multiple cylinders so he agreed to have me install an engine and we both assumed it would take care of his lack of off-idle torque. I installed a freshly machined .40 over longblock into the truck with the new injectors, new cam sensor, new ICP sensor, and new IPR. Also installed another used camshaft because the original was beginning to flake on one lobe. After All this, the truck runs well, drives pretty decent but still has absolutely ZERO off-idle torque. I tried another pcm out of another manual truck, no change and I tried another IDM with no change. The truck is throwing a lower-than-expected ICP code while driving, the pump is fairly weak but will make 2000 psi at WOT so I dont see that having any effect. Has around 500 psi at idle. If you ever so slightly begin to slip the clutch to pull the engine down (I mean VERY, VERY Slowly), ICP will spike to 700ish after about a second. It almost acts delayed, but it could be the rate at which the sensor is reading maybe? Other than that, it is code free. Does anyone have any idea what could be left? Has anyone seen this? I've scoured the internet and can't find any problem resembling this. Keep in mind, I've owned 10+ manual 7.3s and the owner has owned multiple also, so we know how they're supposed to drive. With its lack of grunt, it makes it a chore to drive empty in traffic, little lone towing. Does Anyone have any suggestions on what else to try? Can a throttle positioning sensor cause an issue like this? I may try a different HPOP but I'm skeptical. I'm open to all suggestions at this point.
Thanks
Dillon

What’s fuel pressure?


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[Petro]

What’s fuel pressure?


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Around middle 50s if I recall correctly.

 

[DEEZUZ]

Nothing is tight in the driveline I assume?

 

[Petro]

Nothing is tight in the driveline I assume?

Nope, literally can push it around by hand on pavement. Shifts fantastic and drives very nice. If you're rolling along in gear at idle with your foot off the throttle and slowly apply brakes, it will kind of slightly stumble, then you can hear the engine change tone and it lugs like it's supposed to. It's almost as if the reaction is delayed. Not sure how to describe it, it's very strange.

 

[Petro]

Another strange symptom is when you pull up to a stop light or stop sign. When you get to the light and step the clutch, the idle will drop below it's normal mark and kind of stumble before it returns to its normal 700ish mark.

 

[Powerstroke Cowboy]

It sounds like it could possibly be a weak hpop. Just a guess though. It should idle higher than 500 psi. Closer to 600 to 650 psi.

 

[DEEZUZ]

I see 430ish sometimes with no issue, keep in mind these are inferred values and should be going off voltage at such a specific complaint.

 

[DEEZUZ]

7.3 data stream is so slow its hard to tell sometimes what your at with like a 1.5 second delay on all data

 

[DEEZUZ]

I would do what your next thought was and try another hpop

 

[Petro]

7.3 data stream is so slow its hard to tell sometimes what your at with like a 1.5 second delay on all data

This was my thoughts. The computers are soo stupid, I figured the delay was probably normal. My thoughts were that, if the pump was super weak and struggling to hold pressure then the issue should show up more when the engine is hot as the oil would be thinner but even ice cold, it's exactly the same. Doesn't seem to matter one way or the other.

 

[DEEZUZ]

2k psi wot is fairly low. Glazed over that I guess

 

[Petro]

2k psi wot is fairly low. Glazed over that I guess

Yes, especially for a bone stock truck with absolutely no tuning. At idle with 140-degree oil temp, it's at like 480-500 psi with 7 to 9% IPR duty cycle. If you ever so slowly begin to lightly let out on the clutch and begin to pull it down duty cycle spikes from 12 to 18% and ICP spikes to 700 to 1200 depending on how aggressive you get. Everything seems to be working until you go to take off for real and it just dies like a gas engine.

 

[DEEZUZ]

Idle looks perfect, it's definitely lacking with enrichment.

 

[Petro]

Another fun fact, after you kill it and try to restart, it cranks for an extended amount of time before re-firing. ICP while cranking is 480+ but cranks for what seems like a few seconds before firing off. I'm pretty much at a loss anymore, on the verge of giving up.

 

[DEEZUZ]

Try pump.

 

[Petro]

Try pump.

Ill try that on Monday and report back on what I find. I think

 

[Powerstroke Cowboy]

Try pump.

Agree.

 

[houston88]

Sounds like the same issues that I had with me truck. Compression test caught mine. Hole 7 had 0 compression. Ring broken off. Which yours shouldn’t be as it’s a new long block. Wouldn’t hurt to compression it. Then you know the internals are good.


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[Petro]

Definitely not a compression issue on this truck, the issue was present before and after the new motor. I swapped in another new Ford IPR and that took care of most of the issue. Then threw in a new cnc fab stage one pump since the other was so weak. The truck is as close to normal as it's ever been, not great but can at least take off in low and reverse without slipping the clutch slowly. When trying to take off in any other steeper gear, it still doesn't seem 100% right, acts like it's reaction is delayed. I gave up, the customer is happy and I can't waste any more time on it.