Segond56

Hi, I am hoping to to get some help on this one. Some quick back ground, this is a C5 race car, highly modified, bored and stroked to 410CI made 536 RWHP. New motor this year, first event with the new motor. Dyno time and all running previous to today there were no issues with the car cutting out under power.

Today at Pocono 1st run out went great. 2nd run out about 2/3rds the way through the car started to cut in and out violently only under load. What would feel like hitting the REV limiter but harder. Once you lift and get back in the gas the car was fine. Once it did it the first time, it was repetitive and currently is. At one point it almost stalled. At this time I had just under 3/4 fuel level in the car. I though I was running out of fuel. Came in, and filled the tanks again, although only approx. 8 - 9 gallons went in. So the gas gauge must be off a little. However started the car after coasting in, fired right up and drove over to the trailer. Thought all was ok and that maybe one tank was not filling the other. Went out after lunch in my next run, only to make it 2 turns when under load it cut out again. Very frustrating, considering despite this fuel issue the car was running like a bat out of hell. I went the rest of the way around the track, and as long as I didn't get into the throttle past say 30% she ran fine. The moment you try any lay into it, bam, it cuts out. Higher RPM makes a difference as well, you need less throttle to make it cut out, compared to more throttle at a lower RPM.

I have a fuel pressure gauge in the car, it was bouncing all over the place when this would happen. It is normally set at a rock solid 60 PSI. A few notes on the car, it has the Racetronix C5 fuel pump kit, billet fuel rails and an Aeromotive adjustable fuel pressure regulator.

It seems electrical to me, not sure where to look, this is only my second event with this car, so still learning some things. Could the pump be bad? Do adjustable FPR's go bad? I guess the part that is troubling me is that it would idol fine, rev fine and if you drive it like your grandmother than your good. It is as soon as you get into it that there is a problem.

No PCM codes were generated during these issues or after I loaded it onto the trailer.

Segond56

Here are 2 videos, the first one is of me driving the car, probably only get to about 30% throttle and you can see the action going on with the fuel pressure...




This second video is to show while sitting in the garage the car has no problem with idol or revving. Quite smooth actually.



Any ideas after seeing the videos... I was hoping someone here has experianced this. Both videos were taken today when I took the car out this afternoon. The first video was driving it, and second was when I got back to the garage. Thanks in advance for some help.

Sam

0Anthony @ LGMotorsports

I still stick by what we talked about yesterday.

• check the regulator
• Possible hole or leak between the pump and the outside of the tank
• clogged inlet sock
• clogged fuel filter
• could have a bad connection at the pump?

Segond56

Anthony, thanks for the follow up and the help. Much appreciated that you took the time out. I won't be able to work on the car till Sat. this thing called work gets in the way. Once I get this fixed and figured out I will follow back on this thread to let you know what it was. Thanks again.


Sam

LoneStarFRC

I'm assuming you have already installed the Racetronix "hotwire" harness which connects fuel pump power directly to your alternator?

Segond56

yes, that is correct. The hotwire harness to the alternator is already installed.

LoneStarFRC

Anthony has already given you some very good things to examine.

I might also add (while you're checking the pump assembly inside the tank for a clogged/blocked screen) to examine the convoluted output hose and its crimp/clamp connections for any hole/damage or loose clamps which could cause the pump to "bypass" fuel internally back into the tank.

HTH

0Anthony @ LGMotorsports

One other thing too...since it does have a direct connection with the alternator....do you see any goofy voltage drops or spikes?

Segond56

@ lonestar, thanks for the other items to take a look at, I will certainly make that inspection.

@ Anthony, The voltage seemed to be stable above 13V the whole time, the range varied from 13.1 to 13.9 from what I can tell. I will make sure to make note of that tomorrow.

Tomorrow the game plan is to empty the fuel tanks, pull the pump, make the inspections. I did buy a new pump so if I don't see anything obvious from what I was directed to look into that will be my first step to put the new pump in. I also ordered a new FPR in case that is the culprit. Really appreicate the help and I will update tomorrow with the findings.

Sam

martysauto

I would bypass the relay and start wiggling the new harness while someone observes the gauge. Don't forget the ground. Check all connections. Maybe you have a connection problem where the connector plugs on the tank module.
Ever see a burnt blower motor or resistor connector? My money is on electrical, that agrees with the erratic gauge readings.

Segond56

OK, some intersting follow up. First off car is fixed. Bad fuel pump. New fuel pump in, she runs back to normal, full power and not more cut out.

Checked all the items that you all said to look at, from a visual inspection of the pump, sock, and wiring connections, there was nothing that I could tell was wrong so thats why we stuck the new pump in. However when removing the fuel from the tank, I hotwired the old pump to pump it out into my fuel jugs. When doing so it only pumped out the driver side tank. The passenger side tank was still full. When the tank was empty, fluid spitting out of the hose into my jug we started to unbolt the pump assembly. The only thing I will note was when we unbolted the pump assembly I would say about another gallon to half gallon of fuel spilled out which seem strange b.c the pump pick up is lower than the opening from the tank. Was this b.c that was some extra fuel that made it's way over from the passenger side tank, or just that the pump didn't get everything out of the tank. I would have throught that when I hot wired the pump to pull out all of the fuel it would have emptied out both tanks? Agreed or not correct?

If there is an issue with the transfer of the fuel from Tank to tank, what items can you do or check to see if the gas is moving into both tanks without the obvious test of seeing if the car runs out of gas from the driver side tank? How quickly does the fuel transfer from tank to tank? Was there potientially minimal transfer b.c I was pumping the fuel with no resistance?

My thoughts are that the pump was towards the end of its life, fuel was not transfering at all or fast enought when on track, ran out of fuel on track, again I remember the car just about stalling coming into the pits. Having the pump run dry pushed it over the edge so to speak and thus it began to fail. Just a thought. Help is always appreicated. I do have another event back up at Pocono this coming weekend so an easy fix at least for this coming weekend is don't let the driver side tank run dry! LOL. Please let me hear your thoughts and ideas! Thanks a bunch.

martysauto

Here's the way gm says it should work.
An electric high pressure fuel pump attaches to the fuel sender assembly inside the left fuel tank. The fuel pump pumps fuel to the fuel rail assembly at a specified flow and pressure. Excess fuel from the fuel pressure regulator, a part of the fuel filter, returns to the left fuel tank through the return pipe. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions and aggressive vehicle maneuvers. The PCM controls the electric fuel pump operation through a fuel pump relay.

The left tank fuel pump also supplies a small amount of pressurized fuel to the right fuel tank siphon jet pump through the fuel feed rear crossover pipe. The pressurized fuel creates a venturi action inside the siphon jet pump. The venturi action causes the fuel to be drawn out of the right fuel tank. Fuel is then transferred from the right fuel tank to the left fuel tank through the fuel sender fuel feed pipe.
Sounds like it's not transferring, that's why your gauge read 3/4 when you were able to add 8-9 gallons. If you open the circuit return for the right tank ( cut the gray wire), your gauge will read how much your pump has available from the left. You could splice a switch there and locate it where it's accessible for testing.

LoneStarFRC

Some residual fuel in the LH tank is normal, plus the fuel that was contained in the bucket surrounding the FP, which is designed to help keep the pump constantly submerged for not only maneuvering purposes but to help pump temperature control.
As to the RH tank remaining "full", if you were sucking fuel out of the LH tank, but not sending pressurized to the RH tank at the same time (as the system does when it operates normally), the siphon pump in the RH tank will not work and no fuel gets moved to the LH tank.
For now, I would try leaving the RH alone and driving the car after a complete fill-up, at least to the point where you know for sure you are well past the "halfway" point. I would carry a 2 gal gas can with me while I did this, just to be on the safe side.
If you experience problems (like running out of gas) and suspect the RH tank is not transferring properly, either remove and attempt to clean the orifice or better, replace the assembly. FWIW, as far as labor is concerned, the RH is much easier to swap out, so........

Segond56

@ Lonestar, great follow up and thanks for the good information.

We are planning to use the car this coming weekend up at Pocono and will try running it as is. Currently the car is topped off with fuel. Totally full. If we still have the problem of running the driver side tank dry then I will clean out the siphon pump on the passenger side tank to hopefully clear up the issue. Last resort would be to buy a new one. I read a really good thread from 2007 where MIKER had a great write up with the same issue and it seems it all stems back to that passenger side siphon pump getting clogged. I will update over the weekend and see where we sit.

As for the first issue thanks to all the chimed in and got me looking in the correct direction. Good to know there are some really knowledgeable people on the forum out there to lend a helping hand. Thanks so much!

Sam

0Anthony @ LGMotorsports

That explains a lot of things then. You never expect a brand new part to be the fault...but it sure explains it.

LoneStarFRC

That pump is manufactured by Walbro which, AFAIK, has a very good reputation for reliability. Mine has been solid for several years now.

@Segond: post up after your track outing and let everyone know the results (including if you take any trophies home ). It definitely helps the knowledge base for others going forward.

Segond56

Will do, thanks again guys!!!