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Bucking, going lean, falling on it's face, logs attached

 
Old 05-29-2019, 06:25 AM
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Question Bucking, going lean, falling on it's face, logs attached

Yesterday, decided to take the car out for a spin.

It is currently Speed Density Open Loop

Idle has been extremely "weird" the last few times car was driven.
One day my HOT IAC readings will be 45-60 counts, and some days mid 100's, for no apparent reason.
Car ran like absolute junk...bucking between shifts (automatic car)
I noticed in log, that I hit as high as 49.9% IDC, which is much higher than normal.
Even on Mustang Dyno, the highest I saw was only 40.7%, which is all it usually ever is at the dragstrip (I log every pass)
Also see, underhood gauge, that fuel pressure is only 56, and goes down 3-4 psi when revved, compared to what it "was", which was 62...FWIW, I couldn't ever get it any lower with the Aeromotive regulator.
Even when jumping out the secondary pump, I still see lower than normal fuel pressure

I "think" I have a split hose inside of the gas tank...
Reason I think that, is I have Racetronix hotwire kit w/dual 255 LPH pumps...one strictly for engine, and 2nd one triggered by relay if/when nitrous is activated.
Both pumps show the same FP readings, and same immediate fuel pressure drop when de-energized.
Car always kept well over 50psi of rail pressure for several minutes...now drops to 40 or so, as soon as key is turned off.

Anyway, while I beat my head against the wall at work today, jones-ing to fix this POS for this weekend's race, maybe a few of you can take a look at the driving, and idle logs attached, as well as the current tune, and see if you see something I simply am missing...

I already have the "trap door" mod, so that's the first thing I am doing after work...pulling the pump assemblies out and seeing if one of the fuel lines from either of the pumps, going to the "T", has split. Or clamp came loose, or something to that effect. I noticed just now, that pump seems very quiet, which it would, if it isn't dead-headed at the regulator like usual.

I already ordered a section of submersible efi fuel line

If not split or blowing out, I have a regulator diaphragm coming for it as well.

Tell me what you all think.
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Old 05-29-2019, 09:16 AM
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SD open loop, quite possibly the worst way to run a Gen3 PCM however if it's running like crap it's not from that. I doubt it's your fuel pressure either, if it dropped a few psi it's not going to make it run like crap and probably wouldn't even be noticeable under normal driving conditions even without it correcting via the fuel trims. I'm going to say, bad grounds. Check all grounds on the back of the head, block, etc. There isn't much else that can cause it to start bucking and doing weird random stuff.
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Old 05-29-2019, 09:54 AM
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Only reason I suspect fuel pressure is because of the sudden 8-10% injector duty cycle raise, I guessed, due to it trying to keep up.
It also has always maintained 55+# of fuel pressure when shut off, which it has stopped doing as well.

When it bucks, it goes dead lean, like as high as 18:1 AFR for a split second...then goes way rich...again, I guess due to PCM trying to do it's job?

I was able to get the pumps out this morning and see no issue with the lines, but am replacing them anyway, since it's all out.

I'd prefer to run MAF but originally thought I had a MAF problem, so flashed it back to SD.

Issue has gotten worse over the last 2 weeks

My buddy has a 6' line and giant FP gauge, I will try to use so I can actually monitor FP while driving.
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Old 05-29-2019, 11:46 AM
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How would the injector duty cycle raise that much on it's own? It's not like these older trucks have any sort of fuel pressure feedback like the newer ones do, plus it's in open loop both at part throttle and especially at WOT so it shouldn't be doing anything like that on it's own unless it's just compensating for temperature and air density but if it's higher it certainly shouldn't go lean. If it has a buck and goes dead lean that tells me you have an electrical issue somewhere. Tunes don't change but mechanical things do.
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Old 05-29-2019, 12:26 PM
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If it's trying to meet the commanded AFR, but has a lack of fuel supply, wouldn't the duty cycle raise, trying to compensate?

Asking, not debating.

That is what happened last summer when one of the hose clamps on the primary pump failed.
Under medium throttle, IDC went way up, for no apparent reason, yet wideband showed off the scale lean.

That was when car was turboed, but same everything else fuel-wise, even SD tuned (obviously not the same as it is today)

On a car that only makes 350+ RWHP on a Mustang Dyno, it doesn't make sense (at all, to me) for 60# injectors to be at near 50% duty cycle at 6000 rpm.
They've always been at 38-41% at absolute most.
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Old 05-29-2019, 12:34 PM
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Originally Posted by rel3rd View Post
If it's trying to meet the commanded AFR, but has a lack of fuel supply, wouldn't the duty cycle raise, trying to compensate?
That's the thing it's not trying to meet anything, it's not running in closed loop at WOT ever.

Originally Posted by rel3rd View Post
That is what happened last summer when one of the hose clamps on the primary pump failed.
Under medium throttle, IDC went way up, for no apparent reason, yet wideband showed off the scale lean.
That might have been a coincidence because if it's in open loop it has no feedback at all and will just run what it always runs regardless of fuel pressure, etc. If it was in closed loop at part throttle then yes that would make perfect sense because fuel pressure was low and it was compensating by just opening the injectors longer.

Originally Posted by rel3rd View Post
On a car that only makes 350+ RWHP on a Mustang Dyno, it doesn't make sense (at all, to me) for 60# injectors to be at near 50% duty cycle at 6000 rpm.
They've always been at 38-41% at absolute most.
Yeah, you definitely have a problem no doubt.
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Old 05-29-2019, 12:52 PM
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What's the build specs? Based on making 350 at the wheels seems like a lot of injector, I'm sure NicD could chime in more as he's defiantly the LS go to guy.
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Old 05-29-2019, 01:03 PM
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I first noticed a problem, on the dyno, maybe a month ago. (hardly drive it, the car is just a weekend toy)
I kept adding fuel, and couldn't get below 13:1 AFR at WOT, N/A, where it usually was 12.8:1
On a nitrous pull, I usually log 11.5-11.8:1, and saw 12:1...just figured it was due to different load on dyno, as compared to street/track.

Almost impossible that both pumps acted up at same time, and fuel lines IN the tank check out OK, but going to replace anyway.

I'm hoping the Aeromotive regulator is bypassing due to failed diaphragm...won't have that until Friday though.

Thanks for the replies.
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Old 05-29-2019, 01:29 PM
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Originally Posted by neblackshirts View Post
What's the build specs? Based on making 350 at the wheels seems like a lot of injector, I'm sure NicD could chime in more as he's defiantly the LS go to guy.
Yeah, they're definitely bigger than I need, but I had them already, and the 28#ers I tried were at 90% (@WOT), so I went with what I had...and they've been fine for a year now, so I haven't really worried about swapping to smaller ones.
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Old 05-30-2019, 03:53 PM
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Update...

Replaced both 2" long fuel lines that connect the pumps to the "Y", and also replaced the factory in-tank fuel pressure regulator. I still plan to replace the external Aeromotive regulator's diaphragm, since it had to be ordered...

Anyway, fuel pressure immediately spiked up to 65# with 2 key on/off cycles. After 1 hour, it still had 55#, like it used to...

Started car up and idle AFR was nearly a full point richer than the other day. No fluctuation on fuel pressure when revved thus far.

Couldnt drive it due to rain, but think it is "fixed"...

Will re-update once driven...hopefully tomorrow.
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