LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

FPR leaking, time to replace, which best adjustable?

Old 03-18-2019, 09:23 AM
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Re: FPR leaking, time to replace, which best adjustable?

Originally Posted by canbaufo View Post

Idle FP with AFPR vacuum line pulled from vacuum source (lower intake manifold port) with the port plugged = 45 PSI
Ideally it should be 43.5....
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Old 03-18-2019, 10:50 AM
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Re: FPR leaking, time to replace, which best adjustable?

Originally Posted by Chimera96 View Post
Ideally it should be 43.5....
He's tuning the engine, open loop, using fuel pressure adjustments. I've suggested there may be a better way to do this, and offered to set him up with a very accomplished LT1 tuner, but he isn't interested. He feels his own tuning is the best.
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Old 03-19-2019, 12:29 AM
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Post Re: FPR leaking, time to replace, which best adjustable?

Originally Posted by Chimera96 View Post
Ideally it should be 43.5....
Yes, I'm aware, thanks. 41 - 47 is normal to see according to most. I just wanted to report what the FP was "out of the box" for the Borg Warner unit discussed, so someone else could possibly benefit from the info via search later on.

Originally Posted by Injuneer View Post
He's tuning the engine, open loop, using fuel pressure adjustments. I've suggested there may be a better way to do this, and offered to set him up with a very accomplished LT1 tuner, but he isn't interested. He feels his own tuning is the best.
LOL hardly, as the only "tuning" I can do now is via AFPR adjustments (laptop and backups gone). To clarify something, in response to your "...hoping you can somehow duplicate an unknown adjustment some tuner made for you many years ago" (comment in #14 above); that "adjustment" went with an old tune (stock engine with blower) and is only relevant to the current tune in the car because the current tune was also dialed in at whatever that FP was (memory says about 37-38 at idle which is what I'm now seeing anyway). I believe with the former stock engine / blower tune the tuner simply installed the Aeromotive AFPR without making an adjustment (it was likely set to stock FP out of the box anyway, like the Borg Warner seems to be). He was "chasing" an issue and "trying things" so he probably just thought my stock regulator might be iffy and decided to try the Aeromotive since he could make adjustments with it if he needed to for some reason. In the end, the issue back then was with weak stock valve springs causing valve float.

I'm selling the car anyway, only need the state of tune "close enough", no need for perfection. The tune in it now is the one that's been in it for years (in the past I tweaked it many times but it's been the same flash for many years now). The engine / blower is the same setup as well. Shoot, it even ran great with or without the blower (just a low-boost setup) on that last flash from years back. The only variable that has now likely changed (but probably only slightly) is fuel pressure, which I can adjust in small increments to get back to approximately where I was before. I don't believe the pressure is meaningfully different than before anyway, from memory of having a fuel pressure gauge mounted in the car in the past, it's very close anyway.

I have a wideband and a Scanmaster and know roughly what to expect to see. If drivability is good, wideband readings are within range under boost, and no knock retard is present, that will suffice. The tune I tweaked years ago that became the "permanent tune" for years now had been verified on a dyno and I was pleased with the results. I went to great lengths to dial out cam surge at low loads and found that disabling closed loop (I set enable parameters that were impossible to reach) by far had the most positive outcome. So I don't want to spend more money on a mail order tune that may or may not hit desired wideband readings, and I don't like closed loop. O2 sensor feedback / fuel trims aren't particularly efficient with aftermarket cams due to the valve overlap. You've likely seen info about it, it's not unique to my situation. Hopefully my hesitation for a mail order tune makes a little more sense now, but nothing is out of the question of course.

The caveat will be if for some reason I can't get it running like it used to with mere fuel pressure adjustments. Should that be the case (and I would be surprised if so) I'd prefer to just take it to a dyno tuner. But oh boy did I have a rough experience with one of those in the past lol. Just hoping to get by on what I have. Fred, I assume you saw recent posts in my huge thread? Thanks again so much!

Last edited by canbaufo; 03-19-2019 at 01:24 AM.
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