Mustang and Ford Performance Forums banner
1 - 15 of 15 Posts

·
Registered
Joined
·
587 Posts
Discussion Starter · #1 ·
Gentlemen I need some help. Background on my car: Fore hat with twin 255 Walbros, Trick Flow inline fuel filter, Fore rails, RC 75lb fuel injectors, Aeromotive A1000 regulator, a -8 feed line and a -6 return line. I have relays running to each fuel pump.

This car ran fine previously. Jon Lund tuned it, and the car has made pulls to 6000+ RPM plenty of times.

My car is losing fuel pressure around 4500 RPM. We strapped it down on the dyno, and the fuel pressure spikes up to 60, stays there for a split second, then starts rapidly dropping. As it drops, my AFR obviously spikes up and we cut the run off.

Put air pressure to the regulator port with the key on engine off and it increases the fuel pressure properly and stays there. Data logged the battery voltage and it drops a bit to 13.0/12.9 volts from 13.8 but drops no further than that. Both fuel pumps are getting voltage and are running. Everything on the data log looks normal.

I need suggestions on why the fuel pressure would drop rapidly even though it does raise the fuel pressure properly upon the intial boost.

Thanks!
 

·
Registered
Joined
·
889 Posts
Check Fuel Filters, Thats A Classic Sign Of Clogged Filters.
 

·
Registered
Joined
·
587 Posts
Discussion Starter · #3 ·
Check Fuel Filters, Thats A Classic Sign Of Clogged Filters.
Thanks. That's the first thing on our list tomorrow. I thought we had found the problem with the regulator so I spent time on that. The wiring was suspect from the start and something I wanted to replace anyhow.

But would a clogged fuel filter really allow the pressure to spike up and then drop at the same area each time?
 

·
Registered
Joined
·
889 Posts
Thanks. That's the first thing on our list tomorrow. I thought we had found the problem with the regulator so I spent time on that. The wiring was suspect from the start and something I wanted to replace anyhow.

But would a clogged fuel filter really allow the pressure to spike up and then drop at the same area each time?[/quote

FIRST, I HAD THIS EXACT PROBLEM. NOT SAYING FOR SURE IT IS YOURS BUT MINE DID THE SAME THING. PUT ALL NEW FUEL SYSTEM IN. 100%NEW PARTS. RAN THE PUMP SET UP FOR 2 WEEKS. PUT ON DYNO AND TRIED TO TUNE. AS SOON AS HALF THROTTLE WAS ACHIEVED ( ME GOING FROM 40MPH AND FLOORING IT) IT PINGED. SAME ISSUE. THE HIT IS FINE BECAUSE FUEL IS MOVING, SLOW BUT MOVING. WHEN THE REG CLOSES THE PRESSURE INCREASES BECAUSE FUEL IS MOVING. WHEN THE INJECTORS NOW START TO OPEN ALOT, THE PRESSURE GOES DOWN BECAUSE OF THE CLOGGED FILTERS NOT ALLOWING THE VOLUME TO BE THERE AND PRESSURE DROPS BECAUSE OF THIS. I FOUND WITH AN AIR COMPRESSOR HOOKED TO THE FILTER BACKWARDS DID NOT LET AIR TO PASS, IT WAS THAT CLOGGED. I.E. I GOT A SUMP WELDED TO THE BOTTOM OF THE NEW TANK, THE PERSON WHO WELDED IT DID NOT TAKE ALL THE EXTERIOR PAINT OFF THE NOW EXPOSED INSIDE OF THE TANK. CLOGGED MY 40 MICRON FILTER INSTANTLY. HAD PROBLEMS FROM THE START. I GUESS THE FUEL ATE THE PAINT AND TURNED IT INTO SLUDGE. JUST CHECK THEM, EVEN FOR FUNNIES.
 

·
Registered
Joined
·
587 Posts
Discussion Starter · #6 ·
You have the wire upgrade and 2 relays to fire pumps separately right?
Yes sir. I'm pretty certain it's either a clogged filter or a dying/dead pump. I know both pumps are running at idle, but who knows if they're staying on during a pull. I'm gonna increase the backpressure and measure their flow, if the problem isn't the fuel filter.

I'll get it straightened out today and post back the results.
 

·
Registered
Joined
·
5,237 Posts
Yes sir. I'm pretty certain it's either a clogged filter or a dying/dead pump. I know both pumps are running at idle, but who knows if they're staying on during a pull. I'm gonna increase the backpressure and measure their flow, if the problem isn't the fuel filter.

I'll get it straightened out today and post back the results.
You have them on seperate relays and individual fuses right Carlo? Just pop the fuse for one pump and see how it flows. Do the same for the others. I have mine all fused up individually for this reason.
 

·
Registered
Joined
·
587 Posts
Discussion Starter · #8 ·
You have them on seperate relays and individual fuses right Carlo? Just pop the fuse for one pump and see how it flows. Do the same for the others. I have mine all fused up individually for this reason.
Yea. That's the plan after we check out the fuel filter. Gonna pop off the return line and measure the flow of each pump separately and then both pumps together. Bump up the pressure to 65 and make sure they're still flowing up there. Stopwatch and a 5 gallon jug, low tech engineering!

Justin @ Fore Precision got in touch with me last night (At 9pm on a Saturday night!) to help me trouble shoot the problem. I can't express how much that meant, as we all know my top hat and fuel rails aren't what would cause this problem. Good vendors make this hobby much more enjoyable.

I'll make some pulls on the dyno later and post up the results.
 

·
Registered
Joined
·
215 Posts
Personally I think your voltage is too low. I had a bad alt on my car and hurt my engine from it. The car drove like nothing was wrong. It was a mystery to me what happened. Until I one day at work I put our charging system tester on it and found I had excessive diode ripple. With all ecectrical loads off at idle I was at normal B+ voltage 13.8v-14.2v. But with the radio on, lights on, a/c blower motor on, foot on the brake I was only seeing 12.0-12.2v. As soon as I bumped up the rpm it would go over 13v.

I'm not saying that's your problem, but I don't think you should be going under 13.8v. If you don't have access to a charging system tester stop by autozone or napa they will test it for free. Just for piece of mind if anything. Then you can rule it out of your equation.

Dan
 

·
Registered
Joined
·
1,658 Posts
Personally I think your voltage is too low. I had a bad alt on my car and hurt my engine from it. The car drove like nothing was wrong. It was a mystery to me what happened. Until I one day at work I put our charging system tester on it and found I had excessive diode ripple. With all ecectrical loads off at idle I was at normal B+ voltage 13.8v-14.2v. But with the radio on, lights on, a/c blower motor on, foot on the brake I was only seeing 12.0-12.2v. As soon as I bumped up the rpm it would go over 13v.

I'm not saying that's your problem, but I don't think you should be going under 13.8v. If you don't have access to a charging system tester stop by autozone or napa they will test it for free. Just for piece of mind if anything. Then you can rule it out of your equation.

Dan
I think his voltage is fine. I agree it is probably the fuel filters. I had the same problem even with a new tank. There's a lot of junk that needs to get washed away in the new tank and lines. Mine also occurred after about 2 weeks. My pump relays would get hot and voltage would drop along with fuel pressure. My voltage drop was worse an the pumps got loud.
 

·
Registered
Joined
·
587 Posts
Discussion Starter · #11 ·
Verdict is in, one of the Walbros was near death. Checked the fuel filter, it looked fine, took it out and measured the flow of each pump. One was barely moving fluid.

Taking the tank out now.
 

·
Registered
Joined
·
4,670 Posts
We had a few go bad, I do not like the in tank Walbro anymore, when they go bad they start to scream at idle, a annoying him that gets louder.
 

·
Registered
Joined
·
587 Posts
Discussion Starter · #13 ·
Tillman Speed had the pump in stock today for cheap! Picked it up, put the car back together, and proceeded to make 665/621 on pump gas.

Turned the timing up two degrees, spiked the tank and made 690/636. Still running that massive upper pulley for low boost.

Uncorrected numbers were over 725! Love this cold weather, hate the snow/ice.

I have the DRF files and will make a new post in the 3.4L Whipple Users thread regarding the info. Logged boost and A/F, as well as all the SCT parameters.
 

·
Registered
Joined
·
5,237 Posts
Tillman Speed had the pump in stock today for cheap! Picked it up, put the car back together, and proceeded to make 665/621 on pump gas.

Turned the timing up two degrees, spiked the tank and made 690/636. Still running that massive upper pulley for low boost.

Uncorrected numbers were over 725! Love this cold weather, hate the snow/ice.

I have the DRF files and will make a new post in the 3.4L Whipple Users thread regarding the info. Logged boost and A/F, as well as all the SCT parameters.
Awesome man, its awesome to see them pick up like that with timing. This blower is going to pump once we turn them up a little more.

I am going to flow check each one of my pumps for the hell of it this spring before I come out. My pressure was never dropping on the dyno last year, but good to check.
 

·
Registered
Joined
·
587 Posts
Discussion Starter · #15 ·
Awesome man, its awesome to see them pick up like that with timing. This blower is going to pump once we turn them up a little more.

I am going to flow check each one of my pumps for the hell of it this spring before I come out. My pressure was never dropping on the dyno last year, but good to check.
It's so easy to check, a caveman could do it. Alright corny joke, but I had a good day fixing the car.

Timing is still conservative. I'm still 4 degrees below the max spark on that tune.

It's still on the dyno, maybe later this week I'll get in touch with Jon and bump it up over that 700 mark on SAE.
 
1 - 15 of 15 Posts
Top