P1211 on hard acceleration
Logistics Pro
Joined: Mar 2007
Posts: 4,580
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From: knoxville, tn
I wonder if you might have some injector orings that are aging. Warm them up and add some oil and they seal up better. If you don’t know their age, then they are suspect. It could also contribute to your code on long pulls.
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Laughing Gas
Joined: Jul 2013
Posts: 1,056
Likes: 67
just for diagnostics and troubleshooting purposes, the black smoke clears out once I've got on it pretty good like going up and up ramp to an expressway. Or if I'm pulling heavy equipment, it doesn't really do it much then
Oddly enough, when I went out to start the truck today using my usual 60 seconds of glow plug It started up and did not stumble..
Oddly enough, when I went out to start the truck today using my usual 60 seconds of glow plug It started up and did not stumble..
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Laughing Gas
Joined: Jul 2013
Posts: 1,056
Likes: 67
Still having the ongoing stumble on first start issue.
Here is the section of the cold-start log where it almost died this morning.
4.507s - RPM 734 - ICP 762 psi - IPR 16.80%
5.081s - RPM 720 - ICP 500 psi - IPR 17.19%
5.395s - RPM 602 - ICP 366 psi - IPR 19.14%
5.566s - RPM 534 - ICP 336 psi - IPR 23.44%
5.744s - RPM 460 - ICP 305 psi - IPR 31.64%
5.864s - RPM 386 - ICP 329 psi - IPR 39.45%
5.928s - RPM 348 - ICP 340 psi - IPR 40.23%
6.040s - RPM 429 - ICP 363 psi - IPR 41.41%
6.347s - RPM 625 - ICP 425 psi - IPR 43.36%
6.526s - RPM 854 - ICP 605 psi - IPR 44.92%
Note how ICP first drops into the 300s, followed immediately by RPM drop (stumble). IPR picks up, then the ICP corrects itself and RPM stablizes.
Every start the rest of the day is fine, no stumble even if the engine is cold from sitting 12hrs.
Bosch fuel pump was replaced about 6-7 years ago, and the Hutch/Harpoon mods were done at the same time.
Unsure when IPR and/or HPOP was last serviced or replaced (I bought the truck with 325k in 2015, it has 408k as of today)
Here is the section of the cold-start log where it almost died this morning.
4.507s - RPM 734 - ICP 762 psi - IPR 16.80%
5.081s - RPM 720 - ICP 500 psi - IPR 17.19%
5.395s - RPM 602 - ICP 366 psi - IPR 19.14%
5.566s - RPM 534 - ICP 336 psi - IPR 23.44%
5.744s - RPM 460 - ICP 305 psi - IPR 31.64%
5.864s - RPM 386 - ICP 329 psi - IPR 39.45%
5.928s - RPM 348 - ICP 340 psi - IPR 40.23%
6.040s - RPM 429 - ICP 363 psi - IPR 41.41%
6.347s - RPM 625 - ICP 425 psi - IPR 43.36%
6.526s - RPM 854 - ICP 605 psi - IPR 44.92%
Note how ICP first drops into the 300s, followed immediately by RPM drop (stumble). IPR picks up, then the ICP corrects itself and RPM stablizes.
Every start the rest of the day is fine, no stumble even if the engine is cold from sitting 12hrs.
Bosch fuel pump was replaced about 6-7 years ago, and the Hutch/Harpoon mods were done at the same time.
Unsure when IPR and/or HPOP was last serviced or replaced (I bought the truck with 325k in 2015, it has 408k as of today)
Last edited by queen of spades; Apr 27, 2026 at 12:28 PM.
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Laughing Gas
Joined: Jul 2013
Posts: 1,056
Likes: 67
Also apologies that I seem to have two issues in the same thread. The bigger issue is the stumbling, but I cannot edit the title. Perhaps the two are related, but bear with me as I continue to work through troubleshooting!
Anyone have the part numbers for connecting a fuel pressure guague to the fuel bowl? Would like to have the correct size and pitch threads and fittings on hand since this is my only vehicle atm.
Anyone have the part numbers for connecting a fuel pressure guague to the fuel bowl? Would like to have the correct size and pitch threads and fittings on hand since this is my only vehicle atm.
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Laughing Gas
Joined: Jul 2013
Posts: 1,056
Likes: 67
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Laughing Gas
Joined: Jul 2013
Posts: 1,056
Likes: 67
More background:
The LPOP seals were replaced about 1000 miles ago with genuine Motorcraft parts from Riffraff. The ICP sensor and ICP pigtail were replaced at the same time, also with genuine Motorcraft parts from RiffRaff.
The cold-start stumble was happening before that work and is still happening afterward, so I do not think the LPOP reseal, ICP sensor, or ICP pigtail caused it.
The LPOP seals were replaced about 1000 miles ago with genuine Motorcraft parts from Riffraff. The ICP sensor and ICP pigtail were replaced at the same time, also with genuine Motorcraft parts from RiffRaff.
The cold-start stumble was happening before that work and is still happening afterward, so I do not think the LPOP reseal, ICP sensor, or ICP pigtail caused it.
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Lead Driver
Joined: Jun 2004
Posts: 6,340
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From: Amarillo, TEXAS!
It smacks of IPR valve hanging. You can remove it, disassemble and clean it and reinstall it. If it resolves the issue, well, then there you have it. There are instructions and links to videos here and all over the web.
Lead Driver
Joined: Aug 2022
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From: Oologah, OK
After you hit Edit, click on "Go Advanced", then change title.
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