q for you efi guys - fuel pressure spikes at idle

[demonpixel]

hey guys, great forum you have here, some insanely great projects and beautiful cars.

i'm having a lil trouble with my project and was hoping some pro-touring efi guru could give me some suggestions...

i have a 72 firebird and i just installed a throttle body efi system on my pontiac 400. at cruise the car runs great, and fuel pressure psi is in the mid 40s. at idle however, no matter what idle i'm at, 700, 800, 900, and no matter if i'm in gear or not, the car will idle decently with the fuel pressure psi in the mid 40s, but then the fuel pressure will spike up to as much as 90+ psi. it does this only momentarily, and then the car idles fine again, then 7 to 9 seconds later, another momentary spike, then normal idle again, then 7 to 9 seconds later it spikes, then normal idle, then spike, etc etc

it is a returnless system. i've checked my alternator/battery voltage with the car on and it's at 14.6 so i think i'm good there. my vacuum at idle is -15 to -17.

has this happened to anyone? what sort of things would cause a spike in fuel pressure psi??

thanks to anyone willing to help me try and solve this weird issue!

[edl406]

Is the idle going up or down when the pressure goes high?

[demonpixel]

down, like the car wants to shut off.

[amx2334]

What system is it?
Saw your other post.

[demonpixel]

The system is the returnless style Retrotekspeed BossEFI system. www.retrotekspeed.com is their website.

What factors affect fuel pressure other than a return line and a fuel pressure regulator?

I noticed that ALL of the ports were plugged off on my fuel tank, including the return line. I thought I had a vented gas cap, but now I'm not sure. So what I did was I idled the car last night with the gas cap off but the fuel pressure psi spike issue didn't go away...

i don't know if removing the gas cap would give it proper ventilation. i'd think it would.

should i remove the cap from the return line?

[Fuelie Fan]

Have you called retrotek?

[amx2334]

Are you checking the pressure with a guage or on the display?
It appears they use a pulse width modulated fuel pump to maintain pressure via the sensor.
Measure the sensor output voltage and see if it corresponds to the increase in pressure.If your meter has a pwm feature check it at the pump.
As with any startup glitches- check the grounds and then check them again.

[demonpixel]

I've emailed Retrotek. They told me to unplug the stock return line that was plugged up with epoxy, and that would give it proper ventilation, and after that it should run fine. i'll do that tomorrow.

I'm checking the pressure on the display, not with a gauge amx. if the output voltage of the fuel pressure sensor corresponds with the psi spike, what does that mean? a bad ground, or something else?

i appreciate all the help and responses, thanks guys

[amx2334]

By checking with a guage you are verifying that the pressure really is rising. A bad sensor signal could tell the ecm the pressure is high and the ecm will respond by lowering the pump speed.Or the sensor could read low and the ecm will increase pump speed. It's a cause and effect thing.
What does the o2 read during the pressure spike? (make sure your warmed up and in open loop) Does it go rich or lean? This may tell if the actual psi is rising or falling.


I've emailed Retrotek. They told me to unplug the stock return line that was plugged up with epoxy, and that would give it proper ventilation, and after that it should run fine. i'll do that tomorrow.
By taking off the gas cap you have vented the tank and the condition still existed.Also if the venting was inadequate it would show up more so at higher speeds.
The fact it only happens at idle and has a constantly repeating cycle is really odd.This could be something in the ecm program. I recommend calling (not e-mailing) Retrotek and asking them. They may have seen it before and you might be fixed in no time. I am more than willing to help but I don't want to waste your time chasing something that could be a phone call away.If you don't get a reasonable response from them I am ready to help.Sound fair?
And if they do have the answer let us know. Otherwise it's gonna bug the heck out of me.

[demonpixel]

amx, thanks a ton for taking the time. I haven't had a chance to get to the car today because of work, but I did just get off the phone with Retrotek. He says that improper ventilation could cause a vapor lock in the system, and when that happens sometimes a little rubber check valve in the fuel pump can lodge itself and make the pump work extremely hard and eventually do damage. They ship the systems out now without a check valve in it.

He also said that if I took the gas cap off and I was still getting the psi spike, then ventilating wasn't the problem because it should have solved it. Same thing you said. I'm still going to uncap that stock return line tonight and use it as a vent. Then I'll knock out the check valve crap from inside the fuel pump and test it out.

He also mentioned that the sensor does not fail, and so I shouldn't worry about that part. And that the high pitched sound coming from the pump at the spike was the fuel pump trying extremely hard to suck fuel from the tank. If there's no air going into the tank to equalize with atmospheric pressure, then it WILL chug.

So a few things to try tonight, and I'll keep ya posted...

[MonzaRacer]

Put a pressure guage on it and also make sure your wiring to the sensor isnt running near any high voltage(re ignition) compnenets. It sounds like you actually are getting EMI spikes in the circuit and the ECM is misinterpeting it.
Ok to make you understand whats happening with this system I am pretty sure it is using a fuel pump control circuit to PWM (Pulse Width Modulate) the pressure pump.
By controling the voltage to the pump you control the speed/pressure of it, this also requires a pressure sensor to match the pressure to the PWM at the same time.
I have worked with some of this on Fords and pretty much all the new cars are going to it.
Its pretty simple if injector injects X fuel at X pressure then if you only need X fuel pressure at X rpm/load. It in simple terms is a second O2 circuit (as O2 sensors read the oxygen content in exhaust and the ECM adjusts the fuel accordingly to achieve 14.7 to 1 AFR or the AFR set by load/throttle opening) .
Not complicated just different. If you can get access to a graphing multimeter I would get a reading at the fuel pressure sensor.
anotherthing is that if you have a bifg hole in top of tank to vent it your gonna have fuel vapors all around the car.
I would use a new vapor canister hidden in the car, with a vent line to it and a line to the intake (use a small orrifice like a carb jet to limit the actual vaccuum bleed) and a simple vent solenoid that would cut the canister in to let the engine burn the fuel vapor and when the car is off let fuel vapors bleed into the canister .
I have a retrofit Evap system in prototype and so far its working well. I need to get better charcoal media for E85 as the one canister I used couldnt handle E85.
But if your reading from what the computer is seeing then you need to read what the sensor(s) are actually sending.
Also quadruple check ALL grounds for the system nad the engine as you need to make sure the engine and body are grounded together good.
Also all body parts around engine need grounded to each other.

[demonpixel]

well, i did exactly what they said, uninstalled the fuel pump, popped out the check valve that was in there, vented the gas tank, reinstalled the pump, and started the car.

it wouldn't start.
cranked it for 15 seconds and a short burst of flames came out of the throttle body.

tried cranking it after that and nada.

i don't think i'm getting fuel. is it possible that the fuel pump "burned up?"

[amx2334]

He also mentioned that the sensor does not fail, and so I shouldn't worry about that part. And that the high pitched sound coming from the pump at the spike was the fuel pump trying extremely hard to suck fuel from the tank. If there's no air going into the tank to equalize with atmospheric pressure, then it WILL chug.

I think the high pitched sound may be the pump trying to push upwards of 90psi. If the pump was having trouble sucking fuel the pressure would drop wouldn't it?
PWM signal is constant output voltage with a variable duty cycle. You will want a meter capable of reading duty-cycle(you can also use a dwell meter w/ 10meg ohm impedence).

[amx2334]

no fuel=no flames. do you smell fuel?

[demonpixel]

well, i am DEFINITELY not getting fuel. i just disconnected the fuel line right before the throttle body and put a coffee can underneath it. NO FUEL. faulty fuel pump is my guess

[demonpixel]

monza, thanks for the advice. here's a pic of my fuel pressure sensor:

http://bp2.blogger.com/_3iqjWGMxTPM/RvM7Y3EueoI/AAAAAAAAANg/Q5Hy23QrFis/s1600-h/tb5-FUEL-INJECTORS.jpg

do i just stick the sticks of a multimeter in those wires to get a reading? this is of course AFTER i get a new fuel pump, which retrotek is cool enough to send me.

and also, sorry for the dumb q but this is my first time doing a project of this magnitude...how exactly do you know if you have a good ground with a multimeter? is there a certain type of voltage that tells what good ground is?

[amx2334]

to check the pressure sensor put the red lead on the #1 terminal of the ecm(or the "A" terminal of the sensor connector) and the black lead on a good ground (preferably the ecm ground). The voltage should be between 0-5 vdc. It will change with pressure changes.
you can check grounds by putting one lead on the engine and the other on the frame. the voltage should read less than .1vdc. this is a voltage drop.you can do the same between any two objects.
could you post a picture of the check valve you removed along with the pump? I'm curious to see it.

[demonpixel]

ah ok never knew that amx, thanks man.

here's the pic

[demonpixel]

well, bench tested the fuel pump. had it going from a gas container to a coffee can. with a test battery, it pumped fuel into the coffee can just fine.

hooked it up to the gas tank, so it goes gas tank > fuel filter > fuel pump > coffee can. it did NOT pump fuel. i poured gas into the gas tank. eventually, fuel started coming out of the return line that comes out of my sending unit (comes out the top of the gas tank) that i uncapped for ventilation; remember this is a returnless system. i stop pouring gas into the tank, it stops spilling out the return line. i pour, it spills. but, fuel did NOT come out of the main fuel line though, even when i disconnected the fuel pump from the main fuel line, fuel still didn't come out.

maybe there's something blocking the main fuel line? what do you guys think??

today i'll try to remove the fuel filter from the equation...just run the fuel line to the fuel filter straiht from the tank, and see what happens.

i'll keep ya posted. i hope my sending unit isn't f'd up!!

[amx2334]

I would pull the filter. if there is no fuel there you probably have a problem with the pickup. murphys law now that the tank is full.
the strainer sock on the pickup may be the restriction.

[demonpixel]

oooookay, this is really embarassing but here's an update.

i connected a hose to the return hard line and made sure it was long enough to go above the fuel tank. that way if it spilled out then, then i definitely would have blockage in my main fuel line.

well, it didn't spill out there, but as i put more fuel into the tank, i saw fuel dropping onto the garage floor. took a look, and 3 out of 4 AN connections i have back at the tank/fuel filter are LEAKING. really weird because when i first installed everything and fired up the car weeks ago, i checked for leaks and didn't have any.

i'll tighten up those fittings after i'm back from lunch with the lady and see if i can get fuel to the pump.

this troubleshooting is making me nuts...

[demonpixel]

ok guys, sorry about getting back to you so late, as you can see by the pic i smashed my thumb in like crazy and had to wait a while before i could get a grip on fuel lines, fittings, fuel pumps, wrenches, etc. :hammer:

but a good friend of mine came over and really helped me out, and sure enough, the compression fitting was not seated far enough and the fitting wasn't sealed tight enough; this was causing a fuel leak and making the fuel pressure psi to spike (whining really high while it spiked, looking for fuel). once my buddy took care of that fitting, he also installed a new gasket that retrotek sent that was a little thicker to help with heatsoak issues. then i ran a 1/4 inch hose from the return line to above the tank to outside air, and that's being used as a vent. i also knocked out the check valve that was in the fuel pump (per retrotek's suggestion) and tested it to made sure fuel flowed freely through it, which it did.

did a little minor driving, and so far so good - no fuel pressure spikes at idle!! (knocking on some serious wood). need to renew my registration sticker so i can take it on the highway etc, but i'm sure it'll be fine.

thanks guys for helping me out along the way!

[DeltaT]

Very cool, keep us posted!

Jim