Fluctuating Fuel Pressure
#1
Tech Contributor
Thread Starter
Fluctuating Fuel Pressure
Guys,
Need a little help diagnosing an issue.
I have a FAST EZ EFI 2.0 system running a HSR on my 383. I have the fancy regulator from Kirban, thinking it would solve my issue but it did not.
While running down the highway, I am seeing fuel pressure swings from 38-45 PSI, while at a constant throttle. It's making the car stumble a little bit under light throttle/cruise. Under WOT the pressure is rock solid. I believe the issue to be real because of the slight stumble, and also the wideband is showing a lean swing every time the fuel pressure is jumping around.
I have a wideband in each header - drivers side is feeding the ECU, the passenger side feeds a pillar gauge. The issue only seems to exist on the drivers side.
Do I have a bad injector? The system is batch fire.
Thoughts?
Jeremy
Need a little help diagnosing an issue.
I have a FAST EZ EFI 2.0 system running a HSR on my 383. I have the fancy regulator from Kirban, thinking it would solve my issue but it did not.
While running down the highway, I am seeing fuel pressure swings from 38-45 PSI, while at a constant throttle. It's making the car stumble a little bit under light throttle/cruise. Under WOT the pressure is rock solid. I believe the issue to be real because of the slight stumble, and also the wideband is showing a lean swing every time the fuel pressure is jumping around.
I have a wideband in each header - drivers side is feeding the ECU, the passenger side feeds a pillar gauge. The issue only seems to exist on the drivers side.
Do I have a bad injector? The system is batch fire.
Thoughts?
Jeremy
Last edited by Pwnage1337; 08-14-2018 at 05:56 PM.
#4
Tech Contributor
Thread Starter
I changed the fuel filter last year because that was my first thought. Do I need to have a special filter for a high flow pump? 255 lph
#5
Safety Car
Is the regulator vacuum referenced? Also can you data log the fast system to see what its own wideband is reading? I do not think the issue would only exist on the passanger side, I would assume this is related to both banks. Is the FAST controlling the timing, if so how is it being done?
Last edited by bjankuski; 06-13-2018 at 08:00 AM.
#6
Tech Contributor
Thread Starter
Is the regulator vacuum referenced? Also can you data log the fast system to see what its own wideband is reading? I do not think the issue would only exist on the passanger side, I would assume this is related to both banks. Is the FAST controlling the timing, if so how is it being done?
The FAST is controlling timing. There's two parts, the normal timing curve which is just an "initial timing" (at idle) and then a Max timing. You set an "all in RPM" that you want to achieve your max timing at. I'm currently 18 degrees at idle, 35 degrees Max, all in by 3000 RPM.
The second part of it is a vacuum advance based off the MAP sensor. Right now when this issue is happening the car is asking for about 35 degrees of timing under light load, about 8% TPS. 2000ish RPM
#7
Safety Car
Yes it's vacuum referenced, and it still does it with the vacuum disconnected . I'm unable to datalog this system which sucks, but had someone else drive the car while I watched both widebands. It could be that the passenger side just updates way faster?
The FAST is controlling timing. There's two parts, the normal timing curve which is just an "initial timing" (at idle) and then a Max timing. You set an "all in RPM" that you want to achieve your max timing at. I'm currently 18 degrees at idle, 35 degrees Max, all in by 3000 RPM.
The second part of it is a vacuum advance based off the MAP sensor. Right now when this issue is happening the car is asking for about 35 degrees of timing under light load, about 8% TPS. 2000ish RPM
The FAST is controlling timing. There's two parts, the normal timing curve which is just an "initial timing" (at idle) and then a Max timing. You set an "all in RPM" that you want to achieve your max timing at. I'm currently 18 degrees at idle, 35 degrees Max, all in by 3000 RPM.
The second part of it is a vacuum advance based off the MAP sensor. Right now when this issue is happening the car is asking for about 35 degrees of timing under light load, about 8% TPS. 2000ish RPM
#8
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My first question is what the vacuum is doing while the FP is moving.
When I had this problem it turned out to be the wiring on the sending unit in the tank though. Have you already upgraded that?
#9
Tech Contributor
Thread Starter
I got the hotwire kit, but not the upgraded in tank harness. Looks like I probably should have lol. With the vacuum reference disconnected, the fuel pressure should be solid, right?
#10
Safety Car
Yes, it should be stable. Maybe you have some sort of fuel tank cavitation problem. Is the discharge of the return line causing air bubles that cause cavitaion at low fuel usage and high return volume?
#11
Race Director
If the fuel pressure varies when the vacuum line is disconnected, it sounds like it could be the regulator.
#12
Tech Contributor
Thread Starter
#13
Tech Contributor
Thread Starter
It should be relatively stable either way, varying with vacuum, which is easy and my starting point, as it is the control. With stable control, a continued variance points downstream, like fuel supply or return line pressures.
That pump seems like overkill unless your engine is way more radical than what works well on my 550+HP 409.
Strange is the L/R difference, with the cross pipe connections. Assume there's no fuel odor anywhere?
That pump seems like overkill unless your engine is way more radical than what works well on my 550+HP 409.
Strange is the L/R difference, with the cross pipe connections. Assume there's no fuel odor anywhere?
I haven't given thought to the return filter on my car. There's a small filter on the return line... Don't know where I'd even get one
#14
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It is the in-tank stuff that will get fried at the connectors.
#15
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#16
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#17
Tech Contributor
Thread Starter
#18
Safety Car
How would I verify that? Add a hose to the return line in the tank that directs the flow away from the pump inlet and instead towards the driver side or passanger side of the tank.
One other question does this surging and fuel pressure issue change with fuel tank level?
One other note is I do not think you have a return line filter, I have never seen one and what would be the purpose?
One other question does this surging and fuel pressure issue change with fuel tank level?
One other note is I do not think you have a return line filter, I have never seen one and what would be the purpose?
Last edited by bjankuski; 06-14-2018 at 08:46 AM.
#19
Tech Contributor
Thread Starter
It appears that it's a dampner and not so much a filter. But it is there on my car.
Issue doesn't seem to be any different with tank level but I haven't paid it that much attention
https://www.corvetteforum.com/forums/c4-tech-performance/2532982-fuel-line-filter-in-return-line.html
Issue doesn't seem to be any different with tank level but I haven't paid it that much attention
https://www.corvetteforum.com/forums/c4-tech-performance/2532982-fuel-line-filter-in-return-line.html
#20
Tech Contributor
Thread Starter
The saga continues guys.
Car was off the road for about a month, blew a head gasket. That was my fault for beating on it in 100+ degree weather. I retarded my cam and ran a little thicker gasket to get my DCR into a more acceptable range since you can't buy 93 around here anymore, and you could when I built the engine. Also installed a 160* high flow T-Stat and a FlowKooler WP.
Initially my thought for the lean drivers side bank could have been the HG starting to let go. I was wrong. After putting the car back together, the issue persists. I've tried a couple things...
- Swapped injector harnesses, maybe a bad connection at an injector is causing one to not fire. - No Change
- One at a time, isolate vacuum to the FPR, climate control/cruise control, PCV system - No Change
-Pulled the plugs, and they all look pretty similar. Not like one is pure white while the others are nice and brown.
Thoughts of what I need to do/can do to diagnose:
-Move the fuel pump return in tank, what Bjankuski suggested.
-Check header primary temperature to see which cylinder could be running lean - ordered one of those thermal guns
-Swap injectors from bank to bank and see if the problem moves
-Swap the 02 sensors from bank to bank and see if the problem moves
Right now my order of business is:
Move the 02's - if the problem moves, I think i can be confident that i have a bad 02
Move the injectors - if the problem moves with the injectors, pretty safe bet that i have a plugged/faulty injector.
Burn the car to the ******* ground and start over
Other questions I have:
Is it possible for injectors to "partially fail" The car runs dead even at WOT, it's just under light throttle that the issue exists, and gets noticeably worse as the underhood heat gets up there.
Would an injector failing to fire cause any disruption in the fuel pressure and make it fluctuate? Doesn't seem likely but I'm not sure so that's why I'm asking. I could see maybe if the entire bank was failing to fire. If an entire bank was failing to fire i doubt the car would even run.
Edit: I haven't ruled out a Vacuum leak. I have tried finding one (for an hour straight) and can't find anything. Unless its pulling air from the lifter valley...
Thanks in advance
Jeremy
Car was off the road for about a month, blew a head gasket. That was my fault for beating on it in 100+ degree weather. I retarded my cam and ran a little thicker gasket to get my DCR into a more acceptable range since you can't buy 93 around here anymore, and you could when I built the engine. Also installed a 160* high flow T-Stat and a FlowKooler WP.
Initially my thought for the lean drivers side bank could have been the HG starting to let go. I was wrong. After putting the car back together, the issue persists. I've tried a couple things...
- Swapped injector harnesses, maybe a bad connection at an injector is causing one to not fire. - No Change
- One at a time, isolate vacuum to the FPR, climate control/cruise control, PCV system - No Change
-Pulled the plugs, and they all look pretty similar. Not like one is pure white while the others are nice and brown.
Thoughts of what I need to do/can do to diagnose:
-Move the fuel pump return in tank, what Bjankuski suggested.
-Check header primary temperature to see which cylinder could be running lean - ordered one of those thermal guns
-Swap injectors from bank to bank and see if the problem moves
-Swap the 02 sensors from bank to bank and see if the problem moves
Right now my order of business is:
Move the 02's - if the problem moves, I think i can be confident that i have a bad 02
Move the injectors - if the problem moves with the injectors, pretty safe bet that i have a plugged/faulty injector.
Burn the car to the ******* ground and start over
Other questions I have:
Is it possible for injectors to "partially fail" The car runs dead even at WOT, it's just under light throttle that the issue exists, and gets noticeably worse as the underhood heat gets up there.
Would an injector failing to fire cause any disruption in the fuel pressure and make it fluctuate? Doesn't seem likely but I'm not sure so that's why I'm asking. I could see maybe if the entire bank was failing to fire. If an entire bank was failing to fire i doubt the car would even run.
Edit: I haven't ruled out a Vacuum leak. I have tried finding one (for an hour straight) and can't find anything. Unless its pulling air from the lifter valley...
Thanks in advance
Jeremy
Last edited by Pwnage1337; 08-14-2018 at 07:46 PM.