HPFP dropping at WOT

gotovato

gotovato

Greenie N00B Member
Greenie Member
Hey everyone, strange issue here ive been chasing, and i think it is related to the P0300 i get on COLD START ONLY.

Im losing fuel pressure at wot. It seems pressure is dropping just randomly. It doesnt happen every time but when it does...it sucks lol.

last week i replaced my fprv as it failed the key on test. i pulled the fprv off my stock block and installed it. It passed the key on test no problem. 1800psi+.

after a 360mile cruise this weekend with many, many wot pulls in the 114f heat i noticed near the end of the cruise i was losing fuel pressure at wot. when i got home last night, i did the key on test and it failed, pressure did not rise. Is this fprv bad as well lol?

log is attached. Any suggestions on what i should service / replace? Keep in mind this car has NEVER seen e85 so it is not E related. Last summer mid season i rebuilt my hpfp with all new orings, and a cleaning in the redline fuel system cleaner. i was having similar fuel pressure issues at wot. after this clean up no issues. Are my internals just cooked maybe? worn out? tired of my shit?
 

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I've been trying to track down a similar issue on mine, but mine isn't dipping nearly as bad as that. Just curious, are you still on the factory ITFP? And what's your KOEO fuel pressure on a cold motor?

Might just be bad luck and another failed PRV though? I think if it was me, I'd also be pulling the HPFP and giving it a good inspection/cleaning no matter what though. I don't know which HPFP internals you installed, but when I did my CS internals, I noticed my stock HPFP spring was broken so I was glad the CS internals came with a replacement.
 
Kraze said:
I've been trying to track down a similar issue on mine, but mine isn't dipping nearly as bad as that. Just curious, are you still on the factory ITFP? And what's your KOEO fuel pressure on a cold motor?

Might just be bad luck and another failed PRV though? I think if it was me, I'd also be pulling the HPFP and giving it a good inspection/cleaning no matter what though. I don't know which HPFP internals you installed, but when I did my CS internals, I noticed my stock HPFP spring was broken so I was glad the CS internals came with a replacement.
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I’m going to pull my hpfp apart and service it again. Clean it and lube it. This was suggested to me by my tuner just now. I had an issue last summer. Same symptoms and it was from the internals sticking. After clean up there was no issue. Seems it’s happening again. It could also be a bad fprv again since that test failed.

I am still on stock itfp but koeo reads 61psi so it must be ok?
 
gotovato said:
I’m going to pull my hpfp apart and service it again. Clean it and lube it. This was suggested to me by my tuner just now. I had an issue last summer. Same symptoms and it was from the internals sticking. After clean up there was no issue. Seems it’s happening again. It could also be a bad fprv again since that test failed.

I am still on stock itfp but koeo reads 61psi so it must be ok?
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Yeah I think that's the move right now. I'm also tuning with Will and he told me the same thing, and I just recently saw Justin post that this happens quite often and he usually tells people to pull the HPFP and clean/lube then reinstall it as well. Give your spring a good once over when you pull it too, like I said, my stock one was broken. It was still working, but that can't be great for reliability lol.

And that's more than I get for KOEO and mine doesn't dip that bad, so that's probably not your issue. Mine has 200k miles so that's why I'm starting to suspect maybe my ITFP is on it's way out, or the sock is gummed up.
 
Kraze said:
Yeah I think that's the move right now. I'm also tuning with Will and he told me the same thing, and I just recently saw Justin post that this happens quite often and he usually tells people to pull the HPFP and clean/lube then reinstall it as well. Give your spring a good once over when you pull it too, like I said, my stock one was broken. It was still working, but that can't be great for reliability lol.

And that's more than I get for KOEO and mine doesn't dip that bad, so that's probably not your issue. Mine has 200k miles so that's why I'm starting to suspect maybe my ITFP is on it's way out, or the sock is gummed up.
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Definitely so the cleaning/servicing. Like I said that fixed the issue for me last year. Either that or you itfp might be bad but Will has mentioned to me the hpfp doesn’t require a TON of pressure to work properly. Unless your pump is like completely cutting out.

I’m thinking to swap my fprv again as well. The p0300 on cold start only has me thinking it’s bleeding off pressure or something.
 
Have you tried cleaning the spill valve? Your AFRs start out normal for WOT and then start to run lean as you go up in RPM which indicates a fuel supply problem. Looks like it's either that or your ITFP because your MAF readings look okay.

Also with the relief valve test you aren't always going to get to cracking pressure. You're mostly looking for it opening and start dumping pressure. If it was as bad as your log shows your fuel pressure would be behaving very erratically outside of WOT too.
 
broda said:
Have you tried cleaning the spill valve? Your AFRs start out normal for WOT and then start to run lean as you go up in RPM which indicates a fuel supply problem. Looks like it's either that or your ITFP because your MAF readings look okay.

Also with the relief valve test you aren't always going to get to cracking pressure. You're mostly looking for it opening and start dumping pressure. If it was as bad as your log shows your fuel pressure would be behaving very erratically outside of WOT too.
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When I meant my fprv failed the test lastnight I mean pressure did not build AT ALL. It was around 380 and just steady decreasing. Not rising. When I first installed the “new” fprv I did the test after a test drive and it climbed all the way to ~1800+.

i have not yet cleaned my spill valve. That I’ll give a go tomorrow. It might be the problem but I think the fprv might be bad again? Unlikely though.

my afrs and fuel pressure are always great at wot. Until the hpfp pressure drops which you can see in the log. Pressure drops and car goes dead lean.
 
Ok y’all. Spill valve serviced. It was coated in some crap for sure. Cleaned it up real good, reinstalled. First start still got my stupid p0300 code. Still don’t know what’s cause that shit.

fprv test is now passing. I started the car up for maybe 2 minutes. Shut it off. Key on, and my rail pressure is steadily climbing so that’s good right?

still not sure wtf is causing my p0300 on cold start but I believe it has something to do with vtcs delete and the cold start process.

I had a local buy my PNP stock manifold. He recently installed it and he is also getting p0300 on cold starts only. Gotta be related to vtcs right ?

anyways need to log and see if my hpfp is working proper now. On the weekend I may pull the pump apart just to clean it up anyways
 
Do you still have the little black box for the flappers?
 
Try bypassing the cold start by pushing the throttle slightly while starting and see if you still get the code.
 
broda said:
Try bypassing the cold start by pushing the throttle slightly while starting and see if you still get the code.
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I’ll try this again. I tried it once before but couldn’t get the car to bypass cold start(think I was pressing too far down on the pedal)
 
Removing it throws a code I'm not sure which one. If it's not turned off in your tune you can trick it by plugging in the box. It's doesn't have to connect to the brake manifold but as long as the ECU sees the box it thinks it's working
 
Easter Bunny said:
Removing it throws a code I'm not sure which one. If it's not turned off in your tune you can trick it by plugging in the box. It's doesn't have to connect to the brake manifold but as long as the ECU sees the box it thinks it's working
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im gonna give this a shot for sure. hopefully it works lol. i can tell my local buddy to do the same. i gotta try to bypass the cold start too maybe first
 
Plugging the box in will only address the code. Your going to have to figure out just how much to press the gas to bypass the cold start.

I remember papa Smurf on the old forum battled the rough start for a while to the point he didn't want to start the gar first thing in the morning for the sake of his neighbors but pressing the gas cleared it up
 
Easter Bunny said:
Plugging the box in will only address the code. Your going to have to figure out just how much to press the gas to bypass the cold start.

I remember papa Smurf on the old forum battled the rough start for a while to the point he didn't want to start the gar first thing in the morning for the sake of his neighbors but pressing the gas cleared it up
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I really just don’t want that stupid p0300 code. The loud ugly start up is whatever it’s just that damn code that’s annoying. Will try plugging the box back in
 
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