Dropping Fuel Psi

[TONY C]

HELLO GUYS. I've been having a fuel issue. no turbo. I am running EDIS, MSII. MS relay box, 14 gauge power and 2 grounds to pump, JSK fuel rail, supra 440 injectors w/ factory drop resisters, -6 braided lines all the way round trip, A1 70 micron filter, walbro 255 pump, sard regulator.

Out of the tank to the pump, to the filter, to rail, to reg, back to tank.

 

Car runs GREAT when cold and for the first 30 minutes of run time. Then fuel preasure starts to drop off drastically.

Hot wired the pump straight to the battery, with a fuse of corse. same prob.

Got to thinking that the sard was junk so I got an aeromotive reg. Same prob.

Swapped the Walbro for the stocker, Same prob.

Hot wired the pump to the bat. SAME PROB.

I drained and cleaned the tank, blew out all lines. All was clean. SAME PROB.

when hot, PSI gauge shows all is good at idle. Blip the throttle and psi increases slightly and then psi falls to "0" and then picks up again.

Let the car cool down for 30 min or so and go again.

ANY IDEAS WOULD BE GREAT.

Thanks. TC.

[BRAAP]

Just a few things come to mind…

 

1) Is your fuel tank vented? If not, try just cracking the filler cap to allow it to vent and retest.

 

 

2) You didn’t mention the fuel filter. (I’m assuming that you already checked that). You might also check to see if the fuel pump/s have an inlet screen in them and if so, verify the inlet screen is clear of debris.

 

 

3) Check to see if any of your fuel lines between the pump and fuel gauge are kinked, crimped, etc and that they are the at least 5/16” tubing, (plenty big enough for a hot N/A L-6).

[TONY C]

I did clean out the filter. all was good. very little to no dirt. the fuel gauge is on the JSK rail so no lines to kink.

Didn't think about the vent but I am running a stock tank w/ all stock parts.

I will try the filler cap but I suspect the same.

Thanks for the info. tc.

 

checked both pumps and both seem to be free of debris.

[TONY C]

WELL, I went for a ride with the gas cap removed an extra ground wire from the battery to the fp, Still no change.

 

also I have an lc1 o2 sensor. the car is Definately cutting fuel. o2 readings are great till the prob occures then lean real bad, let off the throttle, regains psi.

get out and check the psi gauge and it reads 35psi instead of the initial setting of 40psi. Rev and hold the motor and the gauge rises to 40 psi and then quickly falls to 0.

What Gives??? same situation with 2 different pumps, 2 regulators, hot wired or not, braided all the way around, checked for voltage drops to pump. What am I overlooking?

Is it posible that the regulator is getting too hot? I have it mounted high on the fire wall next to the bettery box, maybe 12" of hose connecting it to the rail.

I am running the boost/vac refference to it even though I am not using my turbo setup right now. Should I be running that?

I also thought it was weird that the psi raises when throttle is blipped even when running well. And I thought that was only supposed to happen under boost. Not sure though.

Could it be the charging system? Have not had any prior problems. Car starts every time and gauge always reads great. Battery is in the rear with all 2ot welding wire and a Moroso disconnect switch on the hot side. ground wire all the way to the starter to battery and from the battery to the chassis, all 2ot.

Thanks for any input. tc.

[BRAAP]

As for the kinked lines, I should’ve been more clear, sorry about that. I meant the ENTIRE fuel line between the fuel tank and the fuel rail. All the hard metal tubing lines AND the flexible rubber and/or braided lines that run under the car, either in the trans tunnel or along the frame rail, up the firewall, behind the differential, over the half shafts, etc.

 

Something else you might check is to run the fuel pumps, open at the outlet, (no hose, or at least a short piece of hose to direct fuel flow) into a bucket and verify that the pumps themselves are able to flow the appropriate volume of fuel. The pump you bought might have “free flow” volume rating. Verify that it is at least within 90% of the claimed rating. If the rating is given at specific pressure, then using one of your spare adjustable pressure regulators, do the same at the prescribed pressure. Fuel pressure is only part of the “adequate fuel supply” equation, without the volume, pressure means squat. This will at least help narrow down a faulty fuel pump or power issue. Maybe monitor voltage AND amperage AT the pump while performing the flow test, if you have an amp meter.

 

Also, being as you are using MS, you might try data logging with whatever data logging software you prefer, (I liked the data-log-viewer myself), and log the battery voltage as this situation happens. That will help identify voltage/alternator issues.

 

Let us know if you do find it….

[z-ya]

Yes, you need manifold pressure reference line connected to the regulator no matter if boosted or NA. This gives the regulator a reference as to what the manifold pressure is. The regulator will keep a constant pressure at the injector nozzle. When you blip the throttle, the manifold pressure rises, so the regulator will increase the fuel pressure to compensate.

 

Two, pumps, and two regulators, the same problem. This is a good one. You verified that the voltage to the pump is ok when the problem arises, correct?

[TONY C]

ok, just went for a ride with a digital volt meter hooked to the pump. holding 13.09 - 13 volts all the time even when the issues arise.

Have not checked the flow but when 2 pumps are doing the same thing.? However it seems that the stock pump actually deals with the problem better than the walbro, but only slightly.

Checked for kinks or excessive bends in the hoses/lines. all looks good. no sharp bends or potential areas.

Doesn't take as long for the prob to occure if the car has been warmed or driven earilier. Still wondering if a temp issue is at hand but what could it be effecting to cause this?

[z-ya]

How do you have your fuel lines routed? Could they be getting hot? Whatever the problem is, it is heat related.

[TONY C]

the lines are routed in the stock local. using most of the oe return line except under the hood. conection is made under the car on pass side. the feed line comes off the tank to a 90 -6an to the pump mounted in stock local. 90 off the pump to -6an this hose is the high psi kind of hose from a hydrolic shop that just pushes on to the fittings, no clamps or nothing. up to the a connect at the same place as the return and changes to ss braided, to filter to front of the rail, routed accross the top of the intake runners, out of rail 12" -6 to reg and then return.

Could the fuel be getting hot enough as it crosses over the runners and through the rail and back to the reg to make the reg open completely causing full return? Doesn't seem likely since everything is in almost the stock local. Also seems like fuel temps should not effect psi. I am so puzzled on this. I have checked everything 10 times but haven't found the prob.

I thought that maybe there is a wad of crap at the fuel feed outlet in the tank so i removed the hose after the problem occured. plenty of fuel. hook it back up and drive. still there.

pump never seems hot and never drops voltage.

I thought that maybe 1 of the lines was sucking shut but the only "sucking" line is 3" long from the tank to the pump and it is straight to a 90 fitting. So for the sake of finding the prob I removed it and the 90 and hooked it like the factory hose w/ clamps. no change.

Could it be that the vac feed line to the reg is hooked to the wrong place or too long or that I am also taping it to my vac/boost gauge. It is connected to the same place the factory connects the reg.

But to rule that out I have ran the reg with no vac connected and the hose plugged and still no luck.

Still seems temp related. or a supply hose sucking shut or ramble ramble....

my brain hurts on this 1

[TONY C]

charged the battery all night, wasn't low but anyway. hot wired positive and neg of pump straight to the battery. hooked up a volt meter to pump and drove. no change in volts. but the pump sounds different when the problem occures. more drone noise and when cold it is almost silient. I am still going crazy on it. PLEASE HELP. tc.

[z-ya]

Do you have the stock pump and regulator to try together?

[TONY C]

I have the stock pump installed right now and the aeromotive reg but all the hoses have been changed so hooking up the stock reg is a pain. I might have to go get some fuel hose and rerun everything just to test. I have ran out of ideas. tc.

[Pop N Wood]

I was thinking a fuel line might be sucking shut (they get softer if they are hot) or that something was floating around inside the tank. But sounds like you have covered those.

 

I don't understand what are you doing with 2 pumps. Are they running in series (the outlet of one feeding the other)? And you said you have replaced both pumps with different pumps with the same results? Niether pump has an internal pressure regulator that could be failing?

 

What ever it is, my guess is it will turn out to be something very simple and very stupid once you find it.

 

If you want to see if the regulator is sticking open, try splicing a see through fuel filter in the return line. Hopefully you will be able to see if there is flow through the line when the pressure drops. Another option would be to place pressure guages at the outputs of each pump. Might help you narrow down where the pressure loss occurs. Good thing is the problem is so repeatable.

[TONY C]

I am only running 1 pump on the car at a time. not 2. I keep thinking a hose might be sucking shut too. but, all but 3-5" is pushing psi not sucking psi.

I'm with you on the stupid simple part.

Seems like a sucked hose would be good for a minute or 2 if the car was shut off and then restarted allowing it to regain it's shape but this yields the same results.

Seems like heat is an issue.

Last night with the motor not running, I jumped power to the pump for 1 hour. pushing 55lbs psi. held constant psi and no problems. Then ran the car. About 20 - 30 mins drive time and the prob comes back.

I did this to see if it could be a hose sucking shut or if the pump running for a pieriod of time before the car was running would shorten the time before error, but it didn't.

Whatever it is, IT will kill me before I give up.

thanks for the ideas fellas. Keep them coming. I will try all of them. tc.

[Clifton]

When you wired the pump to battery did you do the negative side too or just postive? When your pressure drops below the set pressure on the fpr there shouldn't be any fuel coming out of the return if it is trying to keep it up to the set pressure. If you pinch the retun line off does the pressure stay low?

[TONY C]

Yeah, I wired both sides. Pinch the return and no change. Blew through the lines again, hot wired,and went for a ride. problem starts I come home. the pump is making aweful noises, growling. Gauge shows no psi. I leave the pump wired moter off. still no psi. So while pump is wired i removed the hose feed line from tank to pump. pump still growles and sings bad. Fuel pours out of tank fine. Hook up the hose and still no psi. disconnect power to pump momentarily, after I reconnect, psi jumps to 25lbs and then drops to 0. check volts all is good but no psi. pump feels hot. let it cool for 5. hook it up psi builds then noises from pump and no psi.

Think both pumps have gone bad? the stocker is about 3000 miles old and the walbro is maybe 500. I have run the tank low several times. Could this have hurt both the pumps in the same way?

I am going to reinstall the walbro after dinner and go again. tc.

oh yeah, when I turn the pump off the psi in the rail falls to 0 but when the pump/car is cold it will hold 20 psi when turned off. What's up with that?

[dot]

Can I put in a thought? I had issues like this at one point. My fuel lines ran parallel about 8†away from my exhaust. I moved them so they ran just under the door and through the fender well into the engine compartment. This solved my problems. I found I had a difficult time in spring because the gas stations up here were still running winter gas into the hot weather. Take gas with 10% ethanol churn it up with a high pressure pump and add a little heat and the stuff will boil. I could hear my pump oscillating erratically so I had a good idea what was going on.

[Clifton]

oh yeah, when I turn the pump off the psi in the rail falls to 0 but when the pump/car is cold it will hold 20 psi when turned off. What's up with that?

 

There is a check valve on the pump outlet. On Walbros you can see it in the end. It should hold pressure in the line for atleast a little while when it's off.

 

Is your 70m filter before or after the pump?

[BRAAP]

I'll throw this out here “just in case”. Are you plumbing the Fuel pressure regulators correctly? I.e. return comes out the “bottom” of the fuel pressure regulator, pressure “in” comes into the side of the regulator.

 

Either this or as has been mentioned many times, heat causing an issue some how, some way, to one aspect of the fuel/electrical system…

 

[TONY C]

ok I Reinstalled the walbro, set psi to 40 static at idle, went for a ride. got home psi was at 30-35 jumping and the pump was playing a tune to beat the band. sounded normal when I left but my ears hurt now. but it will hold psi for a while after shut down hot or cold. the stocker will not hold when hot.

 

The filter is after the pump. just like stock. I wanted to put 1 in front of the pump but with the pump in the stock local there is no room.

 

while the pump was singing, I jacked the car up and checked the lines. no issues that I can see, or feel. pinch the return and the psi does not change. like none is returning.

I have been thinking of welding a rear sump on the tank maybe now would be a good time. maybe something is clogging the line? I don't think so because I have cleaned it out a couple times recently, but if I cut a huge hole in it for the sump I can get it spotless for sure.

Just not fan of welding on a fuel tank because of leaks or BOOM!

oh yeah. I hot wired both pumps and fed the fuel line to a 5 gal gas can. Both pumps filled the can in under 10 mins. Not sure what they are supposed to flow and don't have a way to measure it anyway but they both are pumping great when cold anyway. And both are singing like he** after the ride. more testing tomorrow. Thanks for all the help. tc.