Fuel pressure issue

[TWISTER]

Fuel prssure is "jumping around" too much for my comfort. Let me supply you guys with all the info and see if anyone has a clue as to what is going on or can help me. I need to get this problem fixed!!!

The fuel pressure at idle is 9lbs. It sits there just fine in the pits or shop dead on 9lbs. Once on the track under acceleration it bounces all around from 6-9lbs(as best as the driver can tell its in that area) and every now and then the light comes on, with a 4 lb sensor,at the very very end of the straightaway. I have changed everything in the fuel system except the fuel filter canister(allstar brand torpedo style) and the braided line coming from the fuel log to the gauge. I can't see where either of those would be my issue but they are gonna be changed next. In the mean time I have tried with and without a regulator.2 different gauges,3 pumps(10-11 lb pumps), 2 regulators, new fuel line twice, all new fittings,2 different barry wright fuel cells, and 2 different carbs. None of those changes has fixed my issue. And yes the filter is in properly. We have changed the element in it and even took it out with no difference. I keep hearing that the issue is on the suction side of the pump but I don't know what else to do. I have had the push lok style fitting and hose on there and now I have the braided reinforced line. Fuel cell vent has been changed twice as well. Oh yeah, we have had 2 different motors in the car as well so the fuel pump rod can be ruled out. There are no obvious fuel leaks anywhere on the car that we can find. All fittings are teflon taped where applicable and others are good and tight. We have pulled the spark plugs and looked at them and they seem to be fine. Nice brown look to them. The motor is running great and we dont seem to have any issues but we have never had the fuel pressure to jump around like this before.

We are running all steel 362 limited motor.

This problem started when we got our new car. All of the original components in these scenarios were ran and proven to be just fine on our old car. We only saw this issue when we started with the new car and it has done it since the first night out in the car. However since the issue, as i have already stated, all components have been replaced except that 1 line and fuel filter canister.

ANY help on this would be appreciated!!!!

[bigk44]

What about the pick up? Has it been checked/ replaced?

[Brian Gray]

Is the fuel filter near a heat source. Close to header. Engine. Ect?

[Brian Gray]

Are you running a fuel return, what fuel pump.

[lazermod3]

Fuel prssure is "jumping around" too much for my comfort. Let me supply you guys with all the info and see if anyone has a clue as to what is going on or can help me. I need to get this problem fixed!!!

The fuel pressure at idle is 9lbs. It sits there just fine in the pits or shop dead on 9lbs. Once on the track under acceleration it bounces all around from 6-9lbs(as best as the driver can tell its in that area) and every now and then the light comes on, with a 4 lb sensor,at the very very end of the straightaway. I have changed everything in the fuel system except the fuel filter canister(allstar brand torpedo style) and the braided line coming from the fuel log to the gauge. I can't see where either of those would be my issue but they are gonna be changed next. In the mean time I have tried with and without a regulator.2 different gauges,3 pumps(10-11 lb pumps), 2 regulators, new fuel line twice, all new fittings,2 different barry wright fuel cells, and 2 different carbs. None of those changes has fixed my issue. And yes the filter is in properly. We have changed the element in it and even took it out with no difference. I keep hearing that the issue is on the suction side of the pump but I don't know what else to do. I have had the push lok style fitting and hose on there and now I have the braided reinforced line. Fuel cell vent has been changed twice as well. Oh yeah, we have had 2 different motors in the car as well so the fuel pump rod can be ruled out. There are no obvious fuel leaks anywhere on the car that we can find. All fittings are teflon taped where applicable and others are good and tight. We have pulled the spark plugs and looked at them and they seem to be fine. Nice brown look to them. The motor is running great and we dont seem to have any issues but we have never had the fuel pressure to jump around like this before.

We are running all steel 362 limited motor.

This problem started when we got our new car. All of the original components in these scenarios were ran and proven to be just fine on our old car. We only saw this issue when we started with the new car and it has done it since the first night out in the car. However since the issue, as i have already stated, all components have been replaced except that 1 line and fuel filter canister.

ANY help on this would be appreciated!!!!

Call Bloomquist!

[ric78]

Had a very similar issue earlier this year. If you are running a mechanical pump on the block check the pushrod length. Mine had worn, fuel pressure got real erratic change everything in the fuel system before I checked that.

[Bubstr]

No real answer, but I'd look at fuel line size, bouncing fuel gauge and the possibility of needing a large fuel log or small tank up front for fuel reserve. Or sticking spring on return circuit or pressure regulator if you have one.

Good guess is bouncing gauge or need reserve in the engine area, due to end of straight pressure loss.

Pumps pump well when slowing for corner, not so well when inertia is keeping fuel in the rear under acceleration. I've had this problem drag racing but put huge fuel lines on circle track apps. Sometimes a large fuel log to feed the double pumper is all the reserve you need before the easier pumping you get in shut down and corner. good luck

There is a difference between pressure and volume, if you don't have enough volume, your pressure drops.

[FlatTire]

What kind of pump? I'm assuming block mounted with those pressure settings. What kind of fuel? I never had very good luck running the edelbrock block mounted alky pumps. Always inconsistent fuel pressure.

Are all your fuel lines secured and not kinking or sucking shut?
Is the fuel tank vented? If it has a ball vent, is it installed properly?

[TWISTER]

I will try and answer everyones questions......
-Not only has the pick up been replaced, the whole fuel cell has been replaced.
-Fuel filter is approximately a foot from the header, but that is the exact same location it was on my other car where it worked perfectly fine.
-No fuel return and I have had 3 different CV2508 pumps on it. They are a 10-11 lb pump which i can adjust with the regulator and acheive the 11 lbs.. Has a holley regulator on it, and have tried 2 of those as well.
-The rod length will be checked but it has had the same problem on 2 different motors and these are the exact same motors that were in the old car and ran with no issues.
-Gauge is a mechanical quick car gauge. Gauge was brand new and is clean. Have used 2 different gauges with same problem.
-I am using #10 line from the tank to the pump and number 8 line from pump to carb which again is the exact same set up that was on the old car, and again with no issues. I have also replaced all this line, TWICE, with new fittings everytime. I have run this set up since I been racing and never had an issue.

I am going to try and vacuum test the system as much as possible to see if there is an air leak somewhere. As well as rebuilding my fuel pump to make sure that is at full capacity.

I am willing to try anything within reason guys, so please continue to help. Thanks for the suggestions. please, keep 'em coming. Thanks.

[TWISTER]

CV products, gas, block mounted pump. Yes all lines are secure and there are no extreme bends or kinks. Yes fuel tank is vented. 2 different fuel cells have been used.

[TWISTER]

I have been told that if you run a regulator that your fuel pressure should remain steady at your desired setting and not move around. However, if you remove the regulator that your fuel pressure is subject to drop a couple lbs when under hard acceleration. Just so im clear in my issue.......The fuel pressure is not dropping like a tire gauge when you are letting air out with a slow fall off, it is literally jumping around 9 to 6 to 8 to 7 to 5 to 9. Its giving the same action as a gauge does when all the gas has been drained out of the carb or fuel lines are empty and you crank the car back up and it has air in the line so it dances a bit before it levels out. Thats how the gauge is acting under acceleration on the track. That is what led me to look for an air leak and replace all fittings and lines. But to this point it has been wasted time and money because its no better.

[TWISTER]

No alky. VP gas.

[LimitedLM06]

I'm curious about the RPM's. You said at the end of the straight? Could the pump be floating?

[cjsracing]

every time I have had this happen I changed both the fuel pump and the rod and it fixes it. I used to happen the first night of the race season and then I started replacing the pump and rod right before the season and haven't had it happen since. It doesn't take much wear on the rod to make it to short.

[LimitedLM06]

I'm curious about the RPM's. You said at the end of the straight? Could the pump be floating?

[jedclampit]

Set pressure to 7 ~7.5#, reset float levels.

Fuel filter near header is just bad plumbing. Metal housings/frame mount will conduct heat to fuel very well.

Your leaving something on the table not running a return line system.

[TWISTER]

Jed,
We tried the pressure at 7.5 lbs and it dropped to 4. The fuel filter is mounted on the right side upper frame rail. I have ran it there for 8 years now and never an issue. I'm not saying its the best spot, I'm just saying that has been a constant without issue.

I do need to clear up something though. After talking to my driver tonight he told me that the needle on the gauge bounces back and forth from 9-6,9-6,9-6 not the way I originally understood it to be doing. He said it was just like bouncing a ball. Don't know if this changes anyone's thought pattern but just wanted to clear this up.

[jedclampit]

You need more volume to maintain the pressure. Why you lack the volume could be pump,restriction or vapor lock.

Not a fan of this mag, nor did I read the entire article, but you may find some useful info.

http://www.circletrack.com/enginetech/ctrp_1301_tech_engine_under_pressure/viewall.html

[Brian Gray]

i had problems with the filter near the header untill i ran a return with regulator on the return . also some regulators have an internal bleed look at the valve and see if it has a bypass . i was told by braswell 5 - 7 lbs on gas max. obviously if your maintaing pressure you have volume i'd check the regulator.

[hucktyson]

If your running a cv2508 / spin brand pump that is supposed to use a dead head style regulator. They don't produce enough volume to use a by pass regulator like gray is describing. The ideal situation would see you running a DSR belt driven pump off the back
Of your power steering with a bypass regulator because unlike the CV it won't run out of fuel at sustained high rpm . If you run 5 psi with a pushrod style cv pump like Brian suggests your going to melt pistons on a big hammer down track. With a pump like that you should have 7- 7.25 psi and with a dead head style regulator is your pressure is jumping around you have something wrong. I ran that set up for years and it was flawless. Although I was running a CV/Spin deadhead regulator not a Holley .

[TALON75]

Hmm, my cv pump does just fine with a return regulator. I used to run non regulated with a 9psi spring, no problems there either. What regulator are you using? Have you checked or replaced the line running to the guage?

[FlatTire]

I had a fuel hose fitting that had a pin hole leak causing the fuel pressure to drop when the float bowls ran out of fuel. The only way I found that leak was by opening up the dipstick cap on my fuel tank and pressuring up the fuel system with shop air. Just turn your shop air pressure down before you do this.

Maybe you could get this thing on a chassis dyno. You could measure the air-fuel ratio to see what's really going on. You might call your carburetor builder and pick his brain too.

[TWISTER]

Thanks for all the help everyone. I have been talking to my carb man(stealth) for 3-4 weeks about this as well as my engine builder(vic hill). The conclusion we have come to is to replace or rebuild my pump and replace the regulator with a better quality one. The regulator I am replacing it with has a place to mount a gauge on it. That way i can see if there is a descrepancy from that point to my gauge in the car. Also going to pressure test as much of my system as possible to check for a leak. In the off season we are going to convert over to the DSR pump on back of oil pump with return line system. Seems "no one" is having a problem there.

Talon, the line to my gauge is one piece that I have not replaced. Going to do that though. It seemed that the issue was being caused on the suction side of the pump but at this stage of the game who knows.
Again thanks to everyone for their input. I will let everyone know what I find so that it may possibly help someone else out in the future.

[powerslide]

http://www.youtube.com/watch?v=Kl2pa7pmES4

This is a big problem on dodge diesel trucks when you install a pressure gauge. Put a shutoff valve between the gauge and the fuel pressure line and adjust it so when you start the car it takes a brief moment for the pressure to come up. Search water hammer effects and you will find more solutions. I'm betting more cars do this but most drivers arent staring at the gauge, long as it runs, the plugs look good and the idiot light doesnt come on we dont care much.

[powerslide]

We had a car once that had a gauge screwed right into the fuel log. It would jump around like you describe at idle. If possible move the input where the gauge reads pressure further from the pump

[jasjenh]

I just went through the same problem on my brothers modified. it was the regulator. we run the same style regulator on a dead head system. we went through the whole system and even rebuilt the regulator twice before we found the area where the ball on the diaphragm seats was not sealing properly. I checked it by seating the diaphragm by hand and putting liquid in there and watching if it leaked past the ball. I fixed it by using valve grinding compound and lightly reseating the ball. It has more stable pressure now, then when the regulator was new. Everyone told us it was on the suction side to. good luck these types of problems suck

[fairlanechris70]

Had a similiar problem this year. one fitting on the fuel line wasn't completely snugged up and was sucking air.