Cutting Out At ~14 PSI Boost - Suspect Fuel Pump

[achalmersman]

Okay, I just checked, and it's 53 with the line off at the FPR (48 with the line on). I know that sounds high, but as I mentioned, I've been through the range, and have definitely had it at 43 with the line off before. I've taken the advice of others on the board to increase it to where it is now...during my troubleshooting attempts in the past. I'm open to bringing it down and do another run to confirm it won't improve anything. Of course, I don't know what the gauge will look like during the run, but I know it had the cutting out problem when I had it set at 43, line off.

But at this point, what's the concensus on my situation? Looks like I've got one confirmation that I've got a confirmed fuel pressure problem.

Dropping the base pressure isnt likely to fix the problem. Things to look for are filter condition, electric to the pump including ground, regulator condition? Fuel pump sock, kinked lines (wouldnt think it would be intermittent) in tank lines, and of course the pump itself.

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[Terbro]

I'll double confirm that Nick installed a new fuel filter - I think I already did a few months back. And I'll fully inspect the fuel lines front to back.

So...is anyone weird enough (stupid question, I'm sure there is) to cut a hatch in their trunk floor for easy access to the top of the fuel tank/fuel pump?

I do want to say that while in that run (that I filmed), I didn't officially experience cutting out), but there wasn't really a lot of power. One thing I've noticed - I have *more power* at less throttle, generally speaking. In other words, if you noticed, in that vid, I didn't even do a 2nd gear chirp. If I had done a run with 75-85% throttle, it would've pulled *much* harder. In fact, here's a vid I took in Dec., at probably 80% throttle. Watch the speedometer, and you can see the wheels (new Nitto DR's) not fully hooking, but by the time they do, I'm going 45. I pulled a lot harder w/less pedal:

 

[Chuck Leeper]

As mentioned BASE + BOOST = correct rise in FP.
Low psi vs boost and base can be several things, some of which are already mentioned.
1. Low voltage to the pump.
2. Partially plugged pump sock.
3. Split hanger to pump hose. [Also, loose clamps]
4. Pump going "south".
5. Poor tank venting. Canister vent line isn't plugged off, is it?
6. Lines over the rear axle kinked, liner coming loose.
7. BAD GROUNDS.
8. FPR is defective.

 

[Terbro]

As mentioned BASE + BOOST = correct rise in FP.
Low psi vs boost and base can be several things, some of which are already mentioned.
1. Low voltage to the pump.
2. Partially plugged pump sock.
3. Split hanger to pump hose. [Also, loose clamps]
4. Pump going "south".
5. Poor tank venting. Canister vent line isn't plugged off, is it?
6. Lines over the rear axle kinked, liner coming loose.
7. BAD GROUNDS.
8. FPR is defective.

Thank you Chuck, for all these things to look at. Re: #5...don't know. Where might that be? But that one's got me thinking...because of the fact it cut out less today than before (though as I mentioned, did flatten out a bit more later in the morning), I wonder if maybe it's because I didn't put the gas cap on as tight with last fuel fill. If checking the canister vent isn't an easy check, wouldn't just leaving the gas cap on loose or off (potentially sacrificing a bit o' fuel during the run during sloshing up) answer the question? If the problem disappears...ding, ding. Or...it just occurred to me...I have 2/3 a tank of fuel in it at the moment. I wonder if more/less fuel in the tank would affect the issue. Or...I could pull over immediately after a run and see if there's a vacuum at the cap. But if so, then there'd really be no ventilation!

Regarding BASE + BOOST...then if I'm at 48 with the line on at idle, at 15 psi boost, obviously I should be at 63 at WOT. So we've officially got PROBLEMS! I guess I'm encouraged though, knowing that once this issue is resolved, there's a lot more hp waiting. I've had it since last May, and it's about time I resolved this issue.

Really appreciate all your input so far guys!

Anyway...where is the canister vent line?

 

[achalmersman]

Thats a good idea to check as Chuck pointed out and I didnt think of it. Does the car have the factory canister in the front? A lot of guys just put a small engine fuel,filter on the end of the vent line above the rear axle where the steel line turs to rubber. Chuck is saying to check to see if somebody has capped that vent line on the tank side. If so remove cap and replace with a filter so it can breathe but debris not get into the tank. If the factory canister is hooked up then dont worry about this.

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[dynoman]

So...is anyone weird enough (stupid question, I'm sure there is) to cut a hatch in their trunk floor for easy access to the top of the fuel tank/fuel pump?

A few have . http://www.turbobuick.com/threads/fuel-pump-access-hole.407336/

 

[1986 Buick GX1]

Okay, I just checked, and it's 53 with the line off at the FPR (48 with the line on). I know that sounds high, but as I mentioned, I've been through the range, and have definitely had it at 43 with the line off before. I've taken the advice of others on the board to increase it to where it is now...during my troubleshooting attempts in the past. I'm open to bringing it down and do another run to confirm it won't improve anything. Of course, I don't know what the gauge will look like during the run, but I know it had the cutting out problem when I had it set at 43, line off.

But at this point, what's the concensus on my situation? Looks like I've got one confirmation that I've got a confirmed fuel pressure problem.

Your base fuel pressure is what you have with the vacuum line off, which looks like 53psi. Reconnect the vacuum line (the 48psi is irrelevant).
At 10psi boost, you should have 63psi fuel pressure (53 base + 10).
At 15psi boost, you should have 68psi fuel pressure (53 base +15).
At 20 psi boost, you should have 73psi fuel pressure (53 base + 20).
At 25 psi boost, you should have 78psi fuel pressure (53 base + 25).
And so on.
With a high base pressure you're fuel pump really has to work harder when the boost is on.

 

[Terbro]

*May* have found the problem. Don't have the canister (big K&N style filter in its place now ) anymore. Found the line...blew into it, and - fairly difficult to push air into. My first thought was - that's it. But then thinking about it, was wondering if it needed to be so free-flowing, being what it is. So talk to me!

Is there something that restricts this line, or should I be able to push air into relatively easily? If so, then because I can't, maybe that's my problem!

 

[Boost231]

There is a restriction at the hanger itself. It has a cover on the other side so it will never been free flowing.

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[Boost231]

How about the pinch test. Pinch off the return line and put power to the pump and see what the pressure goes to.

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[Boost231]

Also check to make sure your vaccum line going to the regulator is in perfect condition with no holes or cuts

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[TT/Ameasap]

To rule out any valve float. Put the car in second gear and do a no boost run to your max rpm range(whatever it is) and see if it still cuts out.

 

[achalmersman]

To rule out any valve float. Put the car in second gear and do a no boost run to your max rpm range(whatever it is) and see if it still cuts out.

That wouldnt rule out valve float as you would have no pressure on the backside of the valves due to boost and druve pressure. Non-conclusive test

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[TT/Ameasap]

Ok. Im out

 

[Terbro]

Figured seriously loosening the gas cap would answer the return line question (almost completely unscrewed). Went for a run...no improvement - down to 40 still. Curiously though, while the power wasn't all there, it didn't fall flat like it used to. It's almost as if the attached fuel pressure gauge has something to do with it. Just a yesterday or the day before, I raced an STI (killed him), but had to let off to 80-90% throttle, because it cut out like always. Probably unimportant info....just something I'm noticing.

Vacuum line to the FPR is new and looks great.

Inspected rubber fuel lines above axle (until they disappeared out of sight). They looked fine.

So...I'm looking at either bad wiring (either bad voltage, or ground to pump), bad pump, sock, FPR, split hanger to pump hose, or separated liner in lines above axle. Or a kink somewhere in lines I haven't seen yet.

I have a feeling I might be dropping the tank soon...

 

[Terbro]

BTW...off topic for a moment. Is anyone else having problems loading this website's pages? Time and time again, I can't load the page. And then sometimes I can, but once I'm on this thread, it'll freeze up when I try to reply or navigate anywhere else on the website.

 

[Boost231]

Do a pinch test. And for your sake stop beating on the car with a fuel pressure issue.

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[Terbro]

Do a pinch test. And for your sake stop beating on the car with a fuel pressure issue.

That line is pretty hard, so it's hard to pinch. So I capped it (screwed in a big bolt...very tight fit). I turned on the ignition/power to the pump, and it went to 52. I did it again a couple minutes later and it went to 53.

~But I just noticed something that might be important. When putting power to pump (ignition on), the instant the pump shut off, the fuel pressure dropped back down to almost 0 within a couple seconds. Is that normal?

I know, I'm concerned about low O2 MV's. I check the Scanmaster after every run. The lowest I've seen during these test runs is 789 (most are low 800s). Don't you think that's saying I'm not really anywhere near an engine damage danger zone?

 

[Terbro]

Do a pinch test. And for your sake stop beating on the car with a fuel pressure issue.

Say...forgot to ask - please explain what that reveals!

 

[dynoman]

Apply regulated pressure to the vac/pressure port of the fuel pressure regulator . Start at 10psi , turn on the pump with the prime wire with 0 air pressure , check base psi , apply 10psi & should go to base + 10 . Go on and increase air psi and FP should rise 1 for 1 up to at least 70 psi fuel pressure . No driving required . Sam