: No pressure at fuel rails after sitting overnight



Poda
07-16-13, 03:30 PM
I've been trying to diagnose my hard start and stumbling issues, and while hunting down a fuel pressure tester (don't want to fork over $60 for a one-time, maybe two-time tool), I thought I'd just see if there was pressure at the shraeder valve after sitting overnight.

Nope, nada. I'd expect a drop in pressure, but not nothing. The car doesn't leak gas, so it's not escaping that way. Starting her up takes major cranking (I'm assuming as it re-pressurizes the rails), and there's an overwhelming smell of gas.

Fuel pump was done 6 months ago, but that was a whole cluster in and of itself (replacement pump fried, fried the harness, all had to be redone again), and it ran fine for a little bit.

The way I see it, my options are:

1) Re-do fuel pump (if I do, I'll upgrade to a lengthened racetronix harness a little later - $50 is cheap insurance for a brand new harness I know wasn't sourced from a wreckers). Pumps, strainers are cheap - it's just the labour although Cherie has convinced me that it's pretty damn easy ;)

2) Fuel pressure regulator - I have a spare used one kicking around - who knows what kind of shape it's in, it was on a set of spare fuel rails I got for dirt cheap.

3) Fuel filter - I don't think it was changed when the pump was done (grr), so it's possible gunk from the tank is gumming it up, but that doesn't explain the loss of pressure.

4) Leaking fuel injectors.

If it helps troubleshoot, it's not just hard starting. Partial throttle the car feels bogged down until something "clears" and a surge of power kicks in. Then it bogs down again. Hard acceleration it's the same thing, but the surge stays longer.. Idling is fine, with no real miss to speak of, and she doesn't stall (knock on wood). Turning the car off and back on is hit and miss - sometimes she fires right up, sometimes I have to crank a while. Every once in a while, it'll barely catch, lope, and the computer compensates by revving a couple of 100 rpms higher for 30 secs or so before it settles down.

This is driving me nuts, and I'm trying to avoid throwing parts at it. Anything else I should be looking at? I know there's the whole ignition system to look at too, but the lack of pressure is getting me focused on the fuel system first.

jayoldschool
07-16-13, 03:37 PM
Where's the smell of gas? That is your first clue. It will only smell if you have a leak. If under the hood, suspect connections, lines, regulator, injectors. If at the back, around the wheels, suspect sender. Did you do the sending unit when you did the pump? I would suspect the return line connection/hard line on the sender is rusted allowing pressure to leak.

turbojimmy
07-16-13, 03:43 PM
Wouldn't fuel rail pressure leak down to 0 overnight anyway?

Poda
07-16-13, 03:49 PM
Maybe - it's my understanding that there should still be some residual pressure though. If I'm barking up the wrong tree it's a start though.. I guess I should get clarification on that first.. :hmm:

turbojimmy
07-16-13, 04:09 PM
I thought after a few hours the pressure would bleed through the regulator and back into the tank via the return line. I may be recalling incorrectly, though. I wouldn't expect any pressure after sitting overnight. I think that's why there's a prime function when you turn the key on.

nebulosity
07-16-13, 05:28 PM
1) Re-do fuel pump (if I do, I'll upgrade to a lengthened racetronix harness a little later - $50 is cheap insurance for a brand new harness I know wasn't sourced from a wreckers). Pumps, strainers are cheap - it's just the labour although Cherie has convinced me that it's pretty damn easy ;)

;)

I'll reread your thread when I get back from lunch to see if I can contribute to the discussion.
:)

----------


. . .and while hunting down a fuel pressure tester (don't want to fork over $60 for a one-time, maybe two-time tool)

Option A: If you're looking for tools that you'll only use once or twice, you can usually rent these tools from O'Reilly (Kragen? Checker?), Auto Zone or other auto parts stores (e.g. My local Winchester Auto rents tools too).

Option B: Harbor Freight. Do you have a harbor freight in your area? Unfortunately it looks like their particular fuel pressure tester doesn't work for GM, and I'm really kinda surprised about that. ( http://www.harborfreight.com/fuel-injection-pump-tester-92699.html) But hey, I've bought 1/3 of my tools for the Caddy from harbor freight and they work well.



The car doesn't leak gas, so it's not escaping that way. Starting her up takes major cranking (I'm assuming as it re-pressurizes the rails), and there's an overwhelming smell of gas.

(Disclaimer: If I ask any stupid questions that you've already answered elsewhere, just let me know and I'll go back and read your previous threads..) Where are you smelling the gasoline? Inside the engine compartment, or just at the rear of the car? If you're smelling fuel, especially if it's in the engine compartment, part of me is inclined to say that your fuel pump is working. This is probably a stupid question, but have you watched the throttle body to see if you can see any fuel coming out of the fuel injectors? Here's a video of mine: http://www.youtube.com/watch?v=QzebUC49DIk#t=1m56s

I can't seem to remember properly, but how did you verify that the fuel pump is dead again? Have you checked to make sure the fuel isn't just collected on the top of the engine? When I was trying to start my caddy after replacing the fuel pump, I had forgotten to tighten down one of the fuel lines, and so when I cranked the engine, I smelled a LOT of gas, and I found that it just came out the fuel line and pooled on top of the engine, but it never overflowed onto the ground.



If it helps troubleshoot, it's not just hard starting. Partial throttle the car feels bogged down until something "clears" and a surge of power kicks in. Then it bogs down again. Hard acceleration it's the same thing, but the surge stays longer.. Idling is fine, with no real miss to speak of, and she doesn't stall (knock on wood). Turning the car off and back on is hit and miss - sometimes she fires right up, sometimes I have to crank a while. Every once in a while, it'll barely catch, lope, and the computer compensates by revving a couple of 100 rpms higher for 30 secs or so before it settles down.

This is driving me nuts, and I'm trying to avoid throwing parts at it. Anything else I should be looking at? I know there's the whole ignition system to look at too, but the lack of pressure is getting me focused on the fuel system first.

The more I re-read your post, the more I think I'm a little lost on the issue. Is your fuel pump dead, or are you worried it could die again?

outsider
07-16-13, 05:31 PM
I agree with Jim, the fuel pressure should be 0 or near 0 after sitting for a few hours. That is why the pump primes when you turn the key (or so I've come to believe)

On the fuel pressure tester I purchased the instructions actually stated something to the effect of "If the system holds pressure within 2 psi for 10 minutes after key is off then no leak. Pressure will decrease at this rate normally" or something like that, so I'd assume you'll get down to nearly 0 pressure with an overnight sitting.

turbojimmy
07-16-13, 06:16 PM
I assume you don't have any codes? I wouldn't automatically assume fuel delivery, particularly if it's intermittent. Could be TPS, MAF or MAP. If you have a strong smell of gas, it could be a bad FPR filling the vacuum lines.

Poda
07-16-13, 07:44 PM
Cherie - thanks for the input - The car runs, so fuel pump runs - I am worried about it crapping out, and regardless of whether it ends up being the problem or not I'll be switching it out along with the harness. I just don't trust the work done, especially with the vagueness of where the "new" harness was sourced from. Fuel is definitely not collecting anywhere. I pop the hood on a regular basis (once to twice a week) just to keep it clean under there.

Code wise I have two - 32 (EGR) which predates this by quite a bit, and and intermittent 44 (lean driver's side o2) which predates by a while too and caused by an exhaust leak at the driver's side y pipe manifold from the transmission swap last year. Now that I'm typing this out (doh!) - is it possible the racket coming from that exhaust leak is tripping up the knock sensor and causing it retard the timing? Still doesn't explain the hard-start issue, but it might explain the smell of gas and stumbling. Then again, it doesn't explain how I could be tripping these codes for 6 months with no driveability issues, and after a fuel pump and harness change the problems begin..

----------

Well, here's an update.. I just went back out to see if the valve would squirt some gas while I was letting the pooches out. I drove the car for about an hour about 3 hours ago.. nothing - just a hiss for a fraction of a second. Turned the key to "On" without starting to let the pump prime, back off, checked again, and it squirted fuel the way I remember from. Aside from a finger that reeks of gas, so far so good pump wise. Now to narrow down the rest..

jayoldschool
07-16-13, 11:04 PM
The left side could be getting very overfuelled if there is lots of gas being dumped in by the PCM commanding more gas to match the extra air read by that O2... and that would certainly explain stumbling.

turbojimmy
07-17-13, 08:51 AM
The left side could be getting very overfuelled if there is lots of gas being dumped in by the PCM commanding more gas to match the extra air read by that O2... and that would certainly explain stumbling.

Yep - I'd start by clearing up issues that are causing codes. O2 sensor could definitely cause stumbling and other driveability issues.

outsider
07-17-13, 09:30 AM
That's true. My 95 used to stumble and run rough (although threw no codes) and one day I discovered an 02 wire was corroded through. Spliced the wire and no problems ever since.

Poda
07-18-13, 10:11 PM
Weird. After yesterday, when I initially pressed on the shraeder valve and nothing, followed by priming the pump, pressing on the shraeder valve, hearing a bit of a hiss then fuel coming out, the car's been perfect.

Starts instantly every time, even after sitting overnight. No stumbling when driving either. I've taken 6 or 7 trips in the car today, and it's not exhibiting any of the symptoms. Only thing I can think of right now is that air got trapped in the system, but the way I understand it all to work if that was the case it should've been self-resolved months ago on its own. I'm skeptical that it's fixed permanently, but thought I'd give an update in case this changes anything (yes, I know I need to deal with my codes ;) )