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I'm seeing a sporadic P1211 and only on heavy acceleration (which I do on long straight hills to give the engine a good workout). After a few minutes, the p1211 goes away on its own.
Just got another P1211 about 200 miles into a fresh oil change (always run T6 with OEM Motorcraft filter) and my oil level is showing full (and not a drop over). About 400 miles ago I did HPOP reservoir o-rings and used Motorcraft replacement parts from the Ford Dealer (i never buy anything labeled Motorcraft on amazon/ebay it's all counterfeit now).
So with mine, it's NOT:
oil level
oil quality
clogged screen (just replaced)
ICP sensor leak (oem motorcraft just replaced and no leak)
chip.. i don't run a chip it's 100% stock
Truck starts very easily in warm weather. It's started stumbling just after start in very cold (<40F) weather. I recently replaced the glow plug relay with the White unit, glow plugs were replaced not that many years ago with Ford Motorcraft parts I bought from the dealer.
That basically leaves weak HPOP? My truck has 404k on the odo, so if it's never been replaced I could certainly see that being an issue.
I have Forscan installed is there a PID to check function/health of the HPOP?
Last edited by queen of spades; Mar 18, 2026 at 12:36 PM.
More on the stumbling when starting issue. I had ForScan running this morning and captured the data in a csv file. Here's a screengrab below.
The data shows ICP building quickly to 2084psi, then the stumble happens and ICP drops to 321.2. The truck runs a bit ragged for a few moments then evens out to a steady ~900psi. Just changed oil with T6 and new filter about 400 miles ago. The stumble was happening prior to the oil change.
Thoughts, ideas?
Last edited by queen of spades; Mar 24, 2026 at 09:34 AM.
Also takes a bit of time for low pressure sensor to register pressure, I’d be interested to see an actual gauge put on the hpop reservoir to see what the pressure is doing there
Unknown if these are original. Here's a pic of them when I swapped in Motorcraft glow plugs and plug harness about 8 years ago. I've put about 50k on the truck since then.
Originally Posted by ESwift
Also takes a bit of time for low pressure sensor to register pressure, I’d be interested to see an actual gauge put on the hpop reservoir to see what the pressure is doing there
I do have a fuel pressure gauge. Do you know the port I'm hooking into, can also dig around youtube...
Last edited by queen of spades; Mar 27, 2026 at 08:56 AM.
Also takes a bit of time for low pressure sensor to register pressure, I’d be interested to see an actual gauge put on the hpop reservoir to see what the pressure is doing there
I found where to connect my fuel guage, but my gauge lead is only 12" long or so. Are you wanting me to check key on engine off fuel pressure, or engine on under heavy load fuel pressure?
If the latter, how can I do that with my test gauge?
If it still stumbles with the ICP sensor unplugged (rules out the wiring as well as the sensor), clean/reseal the IPR next.
Agree on getting a number on fuel pressure under load. Get a longer fuel hose so you can see the gauge from your windshield or driver's mirror. I did this with a harbor freight fuel pressure gauge kit and a 6ft length of hose.
A little update and background. I replaced the ICP + pigtail last November with OEM motorcraft ICP purchased from riffraff. The stumbling issue was happening prior to that replacement.
As of this past week, even on warm days with glow plug on for 1 minute, the truck is starting to die when it stumbles.
Also to clarify once the truck's been running for a couple minutes I can turn it back off (still cold) and it starts without the stumble/die condition. If it's warm, same thing.. starts fine without the stumble/die condition.
I had the folowing
bad injector orings
low fuel pressure
Baro was at 10k feet limiting fuel ( big change)
bad IDM did strange things but ran best when cold in winter and worse when driven in summer
leaking LPOP was introducing air into the oil (biggest change)
gunk in injectors cleaned with ATF in tank ( 2nd biggest change )
Now it starts up much better and smoother, still some sputter on coldest days but i have 300k on stock injectors
I had the folowing
bad injector orings
low fuel pressure
Baro was at 10k feet limiting fuel ( big change)
bad IDM did strange things but ran best when cold in winter and worse when driven in summer
leaking LPOP was introducing air into the oil (biggest change)
gunk in injectors cleaned with ATF in tank ( 2nd biggest change )
Now it starts up much better and smoother, still some sputter on coldest days but i have 300k on stock injectors
Just to rule these out in my chase:
Replaced all LPOP o-rings with Ford Motorcraft parts (riffraff) last fall
Everyday diesel treatment in every tank
Archoil oil treatment right after my last oil change (about 1k miles ago and long after the stumble started
Not sure of age of injectors, or whether they were replaced before I bought truck (with 325k miles at time of purchase, now 408k). Truck starts quickly outside of that very first startup each day. I have thick black smoke if I get on it real good, but I believe (correct me if wrong) this is normal for most any 7.3L
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