Chicago TDP

iTrader: (3)

OK, so I have been searching/reading posts and googling till I can't see straight....
I am having a rough time tuning my car now and am seeing a fuel pressure issue on my HPtuner logs.
The symptom is when I run the car from a dead stop, go WOT, the car takes off, hits 4K RPM, lays over, then starts to pick back up again at 4.5K
Right around 5.5K, it lays over AGAIN but then runs hard till 6k+

What I see on my logs is the fuel pressure dips around these areas and the AFR leans up a bit. Not a bad lean but it does make a blip on the graph.

Fuel system is as follows: 400LPH Walbro, brand new, main pump with a 255 LPH that comes on at 1 PSI. They Y together outside the stock tank with has them sitting in a bucket. They feed a -8 that then y's at the rail. At the end of the rails is a Maganfuel FPR that returns to tank via -6.

I just put a new 10AWG ground wire to the fuel pump hat and did not see much of a difference. Tonight I will hard-wire the pumps straight to the battery in the trunk so see if that helps.

What I see is that the fuel pressure log increases from 47 base up to 64 base vial boost ref. line to the FPR. But at WOT, I loose pressure down to 40ish. The log corresponds to when I feel the motor lay over for a split second and then it picks back up, hits a wall again and then finishes strong until redline.

JoeNova

Voltage at the dips?
Running a check valve?

Have you tried disabling the 2nd pump and running on just the 450 to see if you have this issue?

Chicago TDP

iTrader: (3)

1st - OKAY, how do I log voltage ( I feel like that is a VERY DUMB QUESTION!, lol)
2nd - I pulled the pumps last night, put them in water as to not blow myself up and then turned on the main pump connected to the secondary, then visa-versa - they were good at making 80 PSI dead-headed and no leaking of their stock check-valves

Tonight I will unplug the 2nd pump just to see if it is taking away precious voltage or causing an anomaly - good idea!

JoeNova

Voltage is one of the parameters you can log in HPT. You'll just have to find it in there somewhere.
I can't remember if its labeled as battery voltage or ECU voltage. If your alternator is losing charge (like many of them do at higher RPM), it'll show there.

Chicago TDP

iTrader: (3)

ok, logging voltage...says 12.5 all the time basically, little dips to 12.3 at WOT

WITH the two pumps hard wired DIRECTLY to the battery in the trunk, the pressure still drops from 58 base to high 30's.

Ran just the 400LPH walbro, same thing...pressure drops...had that run off the standard relay wire as well as directly wired to the battery

I went ahead and bumped up the base pressure as well from 45 to 58 and the same time.

So, at this point I am lost

Tramminc

Almost sounds like your injectors are to big.

Chicago TDP

iTrader: (3)

Right not, the injectors are at 65% at WOT redline. When the PSI starts to drop, the duty cycle is about 30%? 3,500 rpm?

80 lb SD injectors

Richard62

I have exactly the same symptoms. This was a new build/conversion. Used a corvette tank and filter/regulator from Tanks, Inc. I connected the filter/regulator according to the diagram on their website. It is wrong. The fuel feed and the return are reversed on the drawing. So I hooked the 2 lines from the tank backwards. Tried to start it and - no start. Swapped the lines and got a good start. My fault for being a DA. It would run fine under normal conditions. During hard pulls while tuning, the issue showed up. The tuner guy said he had seen this before. So applying feed pressure to the return nipple must damage the regulator internally. It runs fine other than WOT on a hard pull. Haven't yet changed the filter/regulator - can't find my removal tool. I'll get it swapped tomorrow.

truckdoug

iTrader: (25)

you gonna need like 14v @ 50A at the pumps. thats a lot of current. what size wire you run and how long of a run?

you might be overspeeding your alternator too. they quit at about 18,000 rotor rpm. good thread in the FI forum about it.

stevieturbo

That voltage sounds low...but if it's consistent at that...not the cause of this problem. But it is still a problem.

If fuel pressure is dropping...that too is a problem. Is there plenty of fuel in the tank available to the pumps ? The tank can breathe ok ?

Chicago TDP

iTrader: (3)

Well, think I fixed it. I went ahead and rewired the pumps with industrial fine strand 10 gauge wire for each of the pumps. I hooked them up to 75 amp relays (overkill but I wanted to use big terminal rings on the 10 gauge) which are tripped by the small relays. The new relays are in the trunk with the battery which is where the new 10 gauge wires are hooked to. So far, with the new setup, the car is PERFECT and pulls like it should, which is AWESOME!

I have flat fuel pressure at 10 PSI of boost sustained in 2nd gear at WOT. So that is good. the Boost re FPR rises right up like it should and sits solid.

I did just install a new larger pulley on the alternator because I still see the voltage drop over 5000 rpm. I need a longer belt now so I will get that tonight and test it out.

But, for now, the car no longer stumbles, good fuel pressure and I am a happy name!

truckdoug

iTrader: (25)

nice man. glad it worked it. i was having the same issues last year. a bigger pulley and a HD brush kit kept my rotor revs under 18k and the brushes from floating