fuel issue?

stock · Sep 13, 2014

The car is a 1996 GT, Ford crate PI engine w/ 15k. FRPP shorties, K&N, and dumped Flows. She sat for a few years (maybe 5 lol) and has been back on the road about 2 1/2 years now. Shortly after I got it back on the road, it started having fuel issues at anything more than 50% throttle, youd mash the petal and she would fall flat and almost stall out. Assuming dirty fuel lines from 5 years of bad gas sitting in it, I began to feed her a fairly constant dose of fuel system cleaners and regular fuel filter changes. The past 6 months, the problem had almost disappeared. Quick runs from stoplight to stoplight, 1st & second gear, accelerating to highway speeds, etc, she runs strong! But past that, I really don't drive her hard for any sustained amount of time.

Last night I finally made it out to the drag strip for the first time in maybe 10 years. Anyways, I was pretty disappointed. I only noticed it in the middle of scond gear a time or two, but third is bad. It begins a weak bucking feeling. It accelerates still, but not strong. And the bucking feeling isn't crazy strong, just small surges. But it go worse throughout the night. Seems not to happen at any certain rpm range, but maybe more at a certain length of time at WOT. I reproduced the same effect today on the highway doing an extended on ramp run.

My mind just keeps telling me its fuel related. The way it felt, the issues I ran into before, all my mind keeps telling me its fuel. The car is throwing no codes. The car really runs good under normal conditions, but the times I ran last night are driving me crazy and the fact that I have spent so much time trying to make this car 100% and then this! im just looking for outside opinions before I go dumping money into her. What would be a good way to clean the lines? The fuel pump is the 18 year old stock unit. Is this symptomatic of a pump going south? Or could there be something else that Im not thinking of??

D3VST8R96GT · Sep 13, 2014

Fuel pressure gauge and an a/f ratio gauge.

96blak54 · Sep 13, 2014

Sounds like a maf problem. Try unplugging the maf, then drive it. Youll know instantly if the maf is the culprit. Try clening the maf afterwards. The throttle position sensor could also be taking a dump, but they usually just fail causing a presistant high idle.

stock · Sep 14, 2014

OK, well I hooked up my scanner to look at the live data. Im not sure what the correct parameters are, but MAF seemed good. No erratic readings. I removed it and looked for any obvious grime or dirt, and honestly it looked nice and clean. I will try to clean it anyway, cant hurt. Will electrical parts cleaner be good? Or do I need something specific?

What is the best way to check the TPS? On the scanner the % readings seemed steady and didn't fluctuate while causing the surges. Which Ill add here, definitely got worse the more I replicated it. The last time, during a 2nd gear pull down the on ramp, the surging was truly bad and I noticed some pinging while it was doing it.

I did notice the LTFT for b2 was drasticly different than b1. b1 read a fluctuating range of +/- .8% while b2 is an almost constant reading of -4.7% and had changed it -6.3% by the end of the last ride. Not sure what that means entirely, but it is something I noticed.

The pinging makes me revert back to fuel. Im going to get a longer hose for my gauge tomorrow so I can watch it while I drive and while its occurring.

Any opinions on what I should use to make sure my lines are nice and clean? What about a factory option for a better fuel pump?

stock · Sep 14, 2014

And since Ive began so closely looking at everything going on in the car, Ive also noticed my voltage gauge can show quite a bit of fluctuation. It can go up to A or as low down as the beginning of the R, and the lights will begin to dim. The oil pressure gauge also seems to be readin oddly high lately, especially after a WOT run. Ive seen it at the A as well.

D3VST8R96GT · Sep 14, 2014

Hmmmm

stock · Sep 15, 2014

Fuel pressure at idle is 26psi. WOT with no load goes to 40psi. Haven't driven it yet with the gauge hooked up. What should the pressure be @ WOT??

Sprayed Coupe · Sep 17, 2014

Fuel pressure valve on the fuel tank. Mine did the same thing, stab the throttle or a hard pull through the gears and it would fall off then come back. Took mine completely off and it has never had an issue since. It does make the car a little tricky to start since fuel won't stay in the line (in the rails at the injectors) but you could always put in a new one.

stock · Sep 18, 2014

The problem is still kind of iffy, and im in the process of just replacing fuel system parts anyways. After replacing a VERY dirty filter AGAIN, and the car running awesome for about 2 days before acting up again, Ive decided to just replace the tank and pump at this point. Are you referring to the fuel tank vapor valve? Cant find anything referred to as a pressure valve on the tank, but im sure going to go ahead and replace it all while its out!

Sprayed Coupe · Sep 22, 2014

Can't remember the technical name for it but it's a plastic piece in the fuel pump assembly that keeps fuel from flowing back into the tank when the car is off.