Thread: fuel pump's fauiling on me??

Yea I ran with the 3.4” and noticed fuel pressure dropping off going thru 2nd gear but I get no KR. Max boost with the 3.4” was ~9.85#

i would do a few runs and then check the wires to see if maybe they are getting warm if so id say that you wires may be to thin. just a thought

Thats weird to be sure. It seems like it could be the fuel pump, but the whole thing is not sitting well with me. It would think if it were a fuel pump issue then you would see it no matter what unless the pump is just not able to handle higher loads.

Your IPW's are horrendous, your timing not good, and your O2s show a lean condition. Is your KR occurring during this point, when your O2's go low? Do you have a model GP that has the fuel resistor? If so, I wonder if forcing it into high speed mode would reveal anything.

Im wondering now, what kind of 'race' pump it was that Ed sold you.

i bend tab 85 to enable the fuel pump to run only in hi-speed, stil no good, KR grew as my O2s got lower/leaner and WB got higher/leaner. I did one run with the 3.2” up to 3rd gear shift, even though I was getting KR as much as 8* I still floored it(not the best method I understand), a second or 2 after it shifted into 3rd I noticed the KR died off but went back up to 1-2* of KR b4 the road ended with O2s lean of course.

Originally Posted by fst

i bend tab 85 to enable the fuel pump to run only in hi-speed, stil no good, KR grew as my O2s got lower/leaner and WB got higher/leaner. I did one run with the 3.2” up to 3rd gear shift, even though I was getting KR as much as 8* I still floored it(not the best method I understand), a second or 2 after it shifted into 3rd I noticed the KR died off but went back up to 1-2* of KR b4 the road ended with O2s lean of course.

See, thats just weird. Everything you said up to 'a second or 2 after it shifted into 3rd' would have led me to believe it is the fuel pump, but if the pump is bad (and I cannot conclusively rule it out) why would it not continue to starve the engine for fuel and thus maintain the high level of KR?

The only thing that comes to mind at the moment is that perhaps the computer is re-assessing the situation and adjusting timing or maybe at the shift the load was reduced enough from the rpm drop that the fuel pump was able to supply the motor sufficiently for a few moments.

Its just strange, everything seemingly points to the fuel pump, but somethings are not lining up in my mind.

believe me im confused as well. maybe I said something not specifically or clearly, since I do have scans, but havent able to upload them since im somewhat forgetful and lazy. However FWIW I did in the past had a similar issue where I was running lean up top at WOT well b4 the cam swap and rockers i believe. it ended up going away while i was moving the fuel lines and checking them from the engine bay to the fuel pump. back then i was confused and currently today im still confused. maybe i have a kink line somewhere that reappared itself that i just cant figure out. maybe it isnt a kink line, but everything points to the fuel pump loosing pressure at higher load/speed.

Yeah, I would tend to agree with you. I am a troubleshooter by trade (not specifically automotive but system flow is system flow and the mentality is the same whether its a car or a network or a computer) and it seems to point to the fuel pump as an issue. But not all you are stating as symptoms falls in line with a bad fuel pump.

However, it has been said that if you eliminate all the logical possibilities then what remains, no matter how improbable must be the solution. And right now, everything predominantly points to the fuel pump or at a minimum something in that system.

Is it possible the sock on the pump is collapsing or something like that at high pump volumes and restricting flow. Just kinda thinking out loud.

Ive had a bad fuel pump before, not in the GP but in my last vehicle. But it showed up weeks prior to it actually failing in my fuel mileage. You seeing anything like that. I keep meticulous fuel mileage records and I could clearly see abut three weeks in advance from my mileage that my fuel pump was on the fritz. So if you keep good fuel mileage records, any thing there thats showing a sudden and drastic drop off in fuel economy?

the ONLY thing i noticed oddly that im aware of with the fuel pump i bought from ed was the fact that when i fill up at the gas station when i have the fuel gauge light come on and if i fill it to approximately 7-7.5 gallons the needle on the fuel gauge level is just about 3/4 filled? now i hardly ever filled it o full but i just found that odd about the needle. maybe i installed the fuel lever arm wrong or bent it installing the pump into the tank, i dont recall. my fuel mileage i basically look off the DIC and it seems 'normal'. i tested the MPG on the DIC a few times where i would drive on the highway for like 15miles at a steady pace and speed at 70mph at ~2000RPMs and the DIC showed i was getting 30mpg.

FWIW I calculate my mileage by hand. I think I have nearly every fuel receipt for the GP unless I have lost one or two, but I have them.

If you couple what you just said with the fact you Ed stated your pump was a 'race' pump, that brings to mind an issue with the Walbro pumps I believe it was where they were not picking up fuel properly or you were not able to scavenge fuel completely or something like that. Maybe someone can step in and speak to that but I remember there being a issue of some sort. Its just been a while since Ive seen any talk of it.

hmm interesting point. ed didnt kno what kind of pump it was other than it was working off a junked L67 so i took his word that it worked nonetheless >_>

edit-i did a few WOT b4 the cam swap and didnt really have issues with the fueling up top. maybe the occasional 2-3* but since it appeared i was running rich on both WB and O2 it was because of that. maybe it wasnt because i was rich but loosing fuel pressure and the added vs cam magnified everything?

A cam would I believe as it is going to increase your air flow some which should in turn increase your fuel requirements.

well im researhing anything on the walbro if thats what i have.....^_^;

edit- i forgot another point, whenever im close to empty of the light comes on for low fuel, if i go WOT or even hit PE i start to get KR whereas if it was anything above 1/4 tank i wont FWIW

Yeah, that may be whats making this seem odd, that variable right there. If you had a completely stock pump available to you, I would try that and see if the situation changes.

well i still have my oem one but thats been around alot of dust and debris so I don’t know if that’s still useable….

Well that sucks. Any chance you could clean it sufficiently just to run a test with it?

Originally Posted by archemedes

have you by chance run a fuel pressure test?

define fuel pressure test please

i did....idle it was steady at 41-42psi....going WOT it maxxed at 61-62psi and midway thru 2nd it was dropping and b4 i let off due to the road ending it was at 55psi

just got back from a few test runs. i had a friend of mine sit in the back seat and had a voltage meter reading the voltage off the fuel pump. at idle it was reading ~14.5v which looks normal. i did 2 WOT runs on the highway with the 4-2 downshift. honestly both runs he said the voltage stayed at the 14.5v as well as i scanned both runs and my O2s were in the average range of 960-945 and WB was at a conservative 10.1-10.6. this was with the 3.4 pulley and alky turned off. i was running 14-15* of timing and blips of KR.
this makes me even MORE confused. every other runs i tested b4 today i was getting KR and O2s and WB were dropping/leaning. im thinking my fuel pump's going out already damnit.....
i am awaiting a race tronix fuel pump and kit from a member on CGP. for now im gonna run the 3.4 and prolly disconnect the BBV wire and limit boost to 4#. god its gonna suck on the road