Car hesitating at WOT

I could try, but i'm hesitant to fill it up until i'm ABSOLUTELY SURE I won't have to drop it again. First time I dropped it it was full. Filled it to 1/4 tank to test and it made it much easier to drop the tank yesterday.

I also tried running it with the gas cap off to see if it was an issue of vacuum in the tank. Didn't fix it.

Based on internet searches, all that's left is electrical problem or crimped feed line. Feed line looks good all the way, filter is new, and I wouldn think a restricted line would cause the problem full time, not intermittantly like it is now.

I'll throw a relay at it and try to check some of the wiring out. Problem is that to really check the wiring I either have to drop the tank again or cut the hole in the floorboard that I should have cut in the first place.
 
I'm not a super-mechanic, but this clearly sounds like a bad MAP, MAF, Air Charge or TPS sensor (assuming the '93 had all those). I would start there with the sensors that detect load and are responsible for adjusting timing and fuel pressure.

My '93 F150 had the 300 L6 and did the exact same thing you are describing, If I floored it it would nearly stall, and since it was a stick, it would nearly break your neck. It idled rough occasionally, and would stutter under load sometimes. Oddly enough, there were no codes or check engine lights. And it was intermittent, which almost always means electrical.

Turned out to be primarily the MAP, and possibly the ECM, I replaced them at nearly the same time. After replacing the MAP changed it but didn't quite fix it, I opened up the ECM and there was a leaking capacitor. So I replaced the ECM, after that didn't fix it, I replaced the MAP again and that did the trick. Guess the first MAP was defective.
 
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I think I should try the full tank of fuel. This is a Bosch "premium" semi-universal fuel pump designed to "exceed the requirements of the stock pump" so I have no idea how much it really flows. I guess it's either not enough or way too much, right? I suppose it could just be an issue with the valve in the basket sticking too.

Calisonic... All that sounds reasonable, except I can see the fuel pressure dropping when it hesitates, and there is no electronic control of fuel pressure on this car outside of the relay turning the fuel pump on when the key is on and off when it's off. There could be some kind of solenoid controlling vacuum to the regulator, but I doubt it, and if there were, the most "vacuum" you can generate is 15 lbs and that only takes you down to the "idle" reading of 35-40 PSI fuel pressure. The pressure climbs over 50 when you hit the gas but drops to 20ish when it hesitates. No way a sensor or ECM error can do that because the sensor doesn't have that kind of control. If I still had fuel pressure when it was hesitating, that would indicate either a fuel injector issue, a fuel injector control issue, or some type of spark issue, and i'd definitely be looking at the sensors you mentioned.
 
I thought about it for a bit and I'm wondering - doesn't the return line dump the fuel into the "basket"? If so, you'd have to actually USE the fuel for this to be the problem, and however much fuel the new pump flows, i'm not burning any more than I was.

Anyway i'm going to go try filling it up with gas and seeing if that helps. If I have to drop the tank again, i'm going to be pissed at whoever suggested this!
 
Well what do you know, it worked. Put in another 11 gallons and it's nearly full, and it runs like it should. Or at least like it did. Good enough for me. I wonder how full i'm going to have to keep it to prevent this.
 
I was told not to let it get below 1/4, by someone?? I'm not sure if that is correct and I almost always do let it get lower than that before I refill.
 
I had 5 gallons in the tank and this was still an issue. With 1/8 tank it wasn't just WOT runs, it was any time I cracked the throttle. With a nearly full tank it seemed fine on a 2-3 mile test drive.

And this is not a 255 LPH pump, it's a stock replacement from advance auto parts.
 
Glad to hear it kinda solved your problem, Dave. I run a ford gt supercar pump and a kenne bell boost-a-pump, and I don't run it hard with less than a half tank of fuel. Launching hard, going up a hill, or a circle e-way on ramp will make The Mark starve for fuel.
 
1st gen cars do not have the baskets inside the tanks, thus that cannot be his issue.
Once and for all, the basket issue only happens with 97-98 mark viiis and higher than stock volume pumps. Don't clutter up the archives ;)

I would look inside that 1st gen tank though, as there is a channel that is supposed to keep the fuel around the pump as it sits on the bottom of the tank.
 
Even if the basket was there, it shouldn't cause this problem. With 1/8 tank (5 gallons after the first fuel pump swap minus test driving around the nieghborhood), if I backed out of my driveway, put the car in forward, and gave it any gas, it would fall on its face. I probably shouldn't have said "WOT" in the subject, but that is where it first surfaced. It did it seemingly randomly every time it was under load. Steady cruise was about all that was good.

Now it works though. It'll either fix itself by the time the tank gets low, or it won't and i'll keep it full of gas. To fix it "right" I should drop the tank and look at what restriction is there. That's not happening any time soon, if ever.
 
sleeper said:
It'll either fix itself by the time the tank gets low, or it won't and i'll keep it full of gas. To fix it "right" I should drop the tank and look at what restriction is there. That's not happening any time soon, if ever.
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True engineering approach :D
 
I have a Walbro 255 and have no fuel issues until the low fuel warning message comes on.

At the track, it has been known to have occasional WOT stuttering issues just before the low fuel warning.
 
Something is probably fubared in my tank then. It shouldn't be an issue of too much flow from the pump.

It hesitated on me for a moment yesterday, but the car had been sitting for two days then I romped on it cold. Might be unrelated, I was unable to replicate it afterward. It's down to about a half tank and still seems good.
 
Be2lose said:
I was told not to let it get below 1/4, by someone?? I'm not sure if that is correct and I almost always do let it get lower than that before I refill.
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I've heard not to let it get below a 1/4 tank because then the pump is not fully submerged and it does not get proper lubrication/cooling from the gas or something to that effect.
 
I presume you have checked the fuel line(s) for restriction. The most common place is the lower fender rail just behind the wheel well. It's has that stupid piece of plastic covering over the fuel line bundle. Sometimes all it does is hide the smashed line. ;)
 
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