bizarre fuel pressure issue... at wits end - Third Generation F-Body Message Boards

thunder85 · 09-11-2009, 10:20 PM

Hi all,

ok, here's the symptoms: afr reads in the 20-22 range (LC-1), fuel pressure (with vacuum line removed) reads 25-30 psi. I have completely taken the system apart twice... lines are clean, rail is clean, injectors are clean. injectors are 1 year old bosche type 3, holley afpr is 1 year old. The diaphragm on the holley looks good, i've taken it apart and inspected all parts. no leaks. i have replaced my fuel pump with a walbro 255. the problem will not go away.

i'm tempted to just throw a standard replacement fpr on just to see if it is my regulator. do any of you have any ideas on what to try?? i'm confused as to how a relatively new afpr with no visible issues can be bad after a year, but i guess stranger crap has happened.

please let me know what you all think... i'm a day late leaving for my vacation to florida because i can't get this problem worked out.

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aliceempire · 09-11-2009, 10:24 PM

Did you try to readjust the regulator? I'm guessing you did, so I'll ask this too, what happened when you tried new adjustments.

thunder85 · 09-11-2009, 10:26 PM

screwing it in all the way is what gets me to the 25-30 psi. as you would expect, backing the adjuster out gets me lower and lower pressure.

Glenno · 09-11-2009, 10:28 PM

Quote:

Originally Posted by thunder85

Hi all,

ok, here's the symptoms: afr reads in the 20-22 range (LC-1), fuel pressure (with vacuum line removed) reads 25-30 psi. I have completely taken the system apart twice... lines are clean, rail is clean, injectors are clean. injectors are 1 year old bosche type 3, holley afpr is 1 year old. The diaphragm on the holley looks good, i've taken it apart and inspected all parts. no leaks. i have replaced my fuel pump with a walbro 255. the problem will not go away.

i'm tempted to just throw a standard replacement fpr on just to see if it is my regulator. do any of you have any ideas on what to try?? i'm confused as to how a relatively new afpr with no visible issues can be bad after a year, but i guess stranger crap has happened.

please let me know what you all think... i'm a day late leaving for my vacation to florida because i can't get this problem worked out.

So what your saying is the fuel pressure is to low? If that's the case and all other things look good I would swap out the FPR and try another one. It sounds like you tried everything else.

aliceempire · 09-11-2009, 10:30 PM

My rough guess. (and I mean rough) The spring on the regulator got weak or the Walbro is losing it. Just to be on the free side check if the pump is getting a full 12V and ground.

thunder85 · 09-12-2009, 10:10 AM

allright.. i'm going to go buy the factory diaphragm and spring from a parts store... worse case scenerio i can throw my original case back on, but i hope i don't have to.

the walbro is new... and this problem is what motivated me to install it as i was seeing the same issue with my old fuel pump. I checked the wiring when i installed the pump.. its seeing full 12v and has a clean ground.

thunder85 · 09-12-2009, 02:30 PM

ok... i've replaced it with a factory regulator and diaphragm... freakin pressure is LOWER??? i'm at a loss here. i have a new fuel filter, new fuel pump, new everything except fuel rail and it still won't work right. any thoughts??

aliceempire · 09-12-2009, 02:39 PM

when you shut off the engine does the fuel pressure drop to zero or does it hold pressure still?

thunder85 · 09-12-2009, 02:48 PM

with the holley afpr it holds and very slowly drops.. takes about 30 minutes to drop to 0. the factory fpr is dropping immediately to 0

aliceempire · 09-12-2009, 02:55 PM

I feel like I'm drawing at straws but maybe a clogged or pinched line. Past those possibilities I'm out of ideas. You tried everything else and if you had a leak somewhere it would drop right away with either regulator. Good luck to you.

BigBadLou · 09-12-2009, 04:31 PM

Before you start throwing money and parts at the problem, have you tried gradually pinching the return hose to see whether the pump can develop higher pressure with enough blockage? If you pinch the return hose all the way and you still get 30psi, that would point to the pump as it takes the regulator completely out of the circuit.

Hope this helps.
Lou

thunder85 · 09-12-2009, 08:14 PM

well, i was able to get my fuel pressure up by inserting a spacer disk in the holley afpr to see if it was just that disk flexing under the pressure... sure enough i'm now right up where i need to be for fuel pressure.

now my issue is a surging idle. i cannot freaking win with this thing. my afr goes from 8 to 22 and back, surging idle, intermittant stalling at the low rpm of the surge. when it warms up, it won't start without a little help on the gas. after that, it runs for a while (still surging)

i've tested for vacuum leaks by pressurizing the plenum... nothing. i have healthy vacuum around -20 at idle. tps is .51 at low, 4.65 at top.

any ideas?? i'm going to go log the data with tunerproRT and see if i can see what value is out of range (if any).

thank you all for your help so far!

BigBadLou · 09-12-2009, 08:51 PM

I'd bump the fuel pressure even more, to be on the safe side before you start running it. Do you have a lopey cam in it or just the stock L98?

TunerPro is a good move, you want to know what is causing your fluctuating idle.

Lou

thunder85 · 09-12-2009, 09:19 PM

fuel pressure is set at around 45 (vacuum line off). i'm running the stock bottom end (3 year old acdelco reman engine), and i just picked up some 083 casting heads that were worked over with 2.02 and 1.6 valves and some porting. the problem existed before i rebuilt everything, but i now have a new distributer (reman from autozone), the better heads, accell 300+, new wires, new plugs, injectors are 1 year old bosche type III, etc. i'm running out of stuff to replace.

thunder85 · 09-12-2009, 09:45 PM

now i have a code 42 that won't go away. lovely

BigBadLou · 09-12-2009, 10:25 PM

Code 42, I believe, means bad ignition module. It could be a problem in your reman distributor.

Lou

thunder85 · 09-12-2009, 11:05 PM

just replaced it.. and realized after it wouldn't start that i left the freaking rotor sitting on the firewall. i've been working on this thing too long.. lol. man i need a drink

will update after i put the rotor back on

transam85dudeman · 09-13-2009, 12:12 AM

sorry dude

irocuroc · 09-13-2009, 12:26 AM

did you check the cold start valve to see if its leaking.. just pull it out and presure up the rail.. see if it squirts,

thunder85 · 09-13-2009, 02:20 AM

deleted my cold start... can't be leaking.

thunder85 · 09-13-2009, 10:18 AM

ok... here's the update. i broke my pressure gauge doing the pressure test (squeezing the return line) as it spiked the needle so i know the fuel pump is good. after changing ignition module i'm still seeing the surging idle, but the code 42 is gone. afr is slamming between 8 and 22 while the idle is surging. blm is at about 153, tps is normal, cts is reading correctly, iat is correct. what else should i be looking for while logging this??

video coming soon.

thunder85 · 09-13-2009, 12:01 PM

allright.. here's some video so that it will be easier to diagnose (i hope)

first video is just watching it surge from the engine, second video is after a stall, showing the gauges (vacuum and afr) I need to hook up my internal fp gauge as I broke the other one.

MTXaudioSYSTM · 09-13-2009, 05:54 PM

possible bad ecm, or vacuum leak?

bad *** steering wheel. stock?

z-villejw · 09-14-2009, 07:32 AM

After watching your video, Try putting the rest of your duct work on the end of your MAF. I found this out when we had mine on the dyno. To much air turulance going past end of MAF. Hope this helps.

thunder85 · 09-14-2009, 10:19 AM

ecm doesn't appear bad... plus the problem follows me from the factory ecm to my megasquirt and back, so i'm confident its not ecm based. steering wheel is stock GTA.

i will try the ductwork and see if that alleviates the issue.

Beggins · 09-14-2009, 11:02 AM

No tears or holes in the Ducting.. According to the GM repair manual that will cause surging and stalling.

BigBadLou · 09-14-2009, 11:10 AM

Did you try cleaning the IAC? Also, you can reset it to make sure it's in the right position. There's a procedure writeup here on TGO.

But if your BLM's are at 230, I don't know what to think, that sounds like it's running VERY VERY VERY lean. To the point of blowing a hole in a piston. If you trust the BLM numbers, I'd bump the fuel pressure to bring them down to 128 or below 128 and tune it from there.

Lou