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Longer video was taken after truck sat for 3hrs or so was driven this morning. Shorter video was taken right after the first.. Couldn’t get videos to upload here, but here are links:
The first longer video it looks like fuel pressure is lower - 20s instead of 30 in second video. If you listen to audio can hear it start. And this isn’t taking that long because was driven earlier
I haven’t seen the videos, but 20-30 is way lower than earlier screen shots. And is lower than t should be. warrants further research if you are really in that range.
I haven’t seen the videos, but 20-30 is way lower than earlier screen shots. And is lower than t should be. warrants further research if you are really in that range.
at KOEO it should be (from memory) 45 ish
Once running, it should stay within 38-40ish.
Here’s a screenshot from the video. This is key on engine off after the truck sat for about 3hrs since driven:
And here are the specs from service manual for my 4.6:
So the key on engine off should never dip below 35ish and I was getting a reading of 21… so what I’m not understanding is when I turn the key much as I can without cranking engine - shouldn’t it be priming the fuel system?
if the fuel pressure is bleeding off with time, then I thought it would prime the system turning key like that…
Here’s a screenshot from the video. This is key on engine off after the truck sat for about 3hrs since driven:
And here are the specs from service manual for my 4.6:
So the key on engine off should never dip below 35ish and I was getting a reading of 21… so what I’m not understanding is when I turn the key much as I can without cranking engine - shouldn’t it be priming the fuel system?
if the fuel pressure is bleeding off with time, then I thought it would prime the system turning key like that…
I have an 08 4.6, assume they would be same or close to same, but I don’t know. I have an edge gauge with fuel psi displayed at all times.
koeo, primes to mid forties (I’d have to look again for exact). If you sit there without starting it, it will slowly bleed down. From memory I’m guess 1 psi every few seconds or something like that.
Once I start it, it pretty much stays at 39 (38-40h.
I have an 08 4.6, assume they would be same or close to same, but I don’t know. I have an edge gauge with fuel psi displayed at all times.
koeo, primes to mid forties (I’d have to look again for exact). If you sit there without starting it, it will slowly bleed down. From memory I’m guess 1 psi every few seconds or something like that.
Once I start it, it pretty much stays at 39 (38-40h.
I don’t have time to rescan thread right now to figure out what’s been done. But just knowing where you are at now, I would:
- triple check ground at fpdm and at fuse box in cab. If any doubt check resistance.
- check plug connection at fpdm for good solid connection
If no improvement:
- read up on “jumping” power to fuel pump at fodm connector, this will temp you of fuel pump can reach proper psi (don’t leave jumpered after completing test)
if fuel pump and grounds check out, and there is any doubt in fpdm, consider replacing.,.. it’s 40-60$ for a part that frequently gives intermittent issues and never hurts to carry a spare.
—/———
Here’s a screenshot from the video. This is key on engine off after the truck sat for about 3hrs since driven:
And here are the specs from service manual for my 4.6:
So the key on engine off should never dip below 35ish and I was getting a reading of 21… so what I’m not understanding is when I turn the key much as I can without cranking engine - shouldn’t it be priming the fuel system?
if the fuel pressure is bleeding off with time, then I thought it would prime the system turning key like that…
See where it says fuel pump %75. My understanding is that if the DC is displaying 75% then the PCM is not commanding the pump to do anything.
I , like you, also thought that if you turn the key to the "on" position it was supposed to turn the pump on for 1 second and then back off again if it doesnt sense engine rotation.
This is one of the areas that's fuzzy because it seems like they don't cover it at all in the service manual, it says to see the PCEM manual. But the PC/EM manuals have sort of vague or not necessarily model specific info from what I have looked up regarding the fuel pump control scheme.
Perhaps if the pressure is already over some lower threshold, say 20psi it doesn't "prime" the pump.
I have never paid that much attention to on my pressure other than every time I have thought to check it reads right around 40psi.
Last edited by needsmoarturbo; 06-23-2024 at 09:37 PM.
This quote is from a website that I lost the address to, here goes
"If the FPDM outputs a 75% duty cycle, it means that the FPDM has detected an open or short on the fuel pump control circuit. The PCM sets a P1237 DTC."
couple days ago, when i had the spare down to test fpdm ground, i decided to warranty the fpdm i replaced about 4yrs ago, and it didnt cost me anything - absolutely no change same long crank hard start. so i believe we can rule out fpdm as two parts doing exact same extremely unlikely.
i'll look into jumping the pump, and im also curious about the 75% scanner reading.. someone mentioned the ground for the fuse box, anyone have pic or know where it is? i'll look in service manual should be able to find
sorry about delay in getting back to you all, thanks very much for the input-replies below
Originally Posted by laterongc
I have an 08 4.6, assume they would be same or close to same, but I don’t know. I have an edge gauge with fuel psi displayed at all times.
koeo, primes to mid forties (I’d have to look again for exact). If you sit there without starting it, it will slowly bleed down. From memory I’m guess 1 psi every few seconds or something like that.
Once I start it, it pretty much stays at 39 (38-40h.
with my truck sitting key on engine off, it does the same thing and pressure drops with time. the pic i posted of 21 psi my truck must've been sitting with key on prior.
Originally Posted by laterongc
I don’t have time to rescan thread right now to figure out what’s been done. But just knowing where you are at now, I would:
- triple check ground at fpdm and at fuse box in cab. If any doubt check resistance.
- check plug connection at fpdm for good solid connection
If no improvement:
- read up on “jumping” power to fuel pump at fodm connector, this will temp you of fuel pump can reach proper psi (don’t leave jumpered after completing test)
if fuel pump and grounds check out, and there is any doubt in fpdm, consider replacing.,.. it’s 40-60$ for a part that frequently gives intermittent issues and never hurts to carry a spare.
—/———
see what Jim has to say/recommend
i triple checked and tested the ground on the fpdm and ground is good. - the connector looks fine also. i will look into jumping the fuel
Originally Posted by needsmoarturbo
See where it says fuel pump %75. My understanding is that if the DC is displaying 75% then the PCM is not commanding the pump to do anything.
I , like you, also thought that if you turn the key to the "on" position it was supposed to turn the pump on for 1 second and then back off again if it doesnt sense engine rotation.
This is one of the areas that's fuzzy because it seems like they don't cover it at all in the service manual, it says to see the PCEM manual. But the PC/EM manuals have sort of vague or not necessarily model specific info from what I have looked up regarding the fuel pump control scheme.
Perhaps if the pressure is already over some lower threshold, say 20psi it doesn't "prime" the pump.
I have never paid that much attention to on my pressure other than every time I have thought to check it reads right around 40psi.
thats very interesting info, i wasn't aware
Originally Posted by Jimboy
This quote is from a website that I lost the address to, here goes
"If the FPDM outputs a 75% duty cycle, it means that the FPDM has detected an open or short on the fuel pump control circuit. The PCM sets a P1237 DTC."
Did you get a P1237?
ive gotten zero codes and this long crank hard start has been happening for 2 months or so.. no pending codes, all monitors are set
I don’t have time to rescan thread right now to figure out what’s been done. But just knowing where you are at now, I would:
- triple check ground at fpdm and at fuse box in cab. If any doubt check resistance.
- check plug connection at fpdm for good solid connection
If no improvement:
- read up on “jumping” power to fuel pump at fodm connector, this will temp you of fuel pump can reach proper psi (don’t leave jumpered after completing test)
if fuel pump and grounds check out, and there is any doubt in fpdm, consider replacing.,.. it’s 40-60$ for a part that frequently gives intermittent issues and never hurts to carry a spare.
—/———
The location of the grounds that you asked about are right next to the fuse box (Central Junction Box). The fuse box is located behind the plastic kick panel by the passengers foot well and the panel has to be removed to gain access.
06-23-2024, 03:20 PM
