Fuel flow help

[Luc]

What to do next?

To solve a hesitating engine I changed my fuel filter with a Napa unit. Cured my problem for a week.

I removed the skid plate and drained a liter of gas yesterday and it's nice and clean. Do I need to drain more or the whole tank ?

Did I just get a crappy filter? Is there a screen somewhere I should check?

Help ! Luc

[mazdab2600]

if the fuel pumps in the tank the pick- up screen on the pump maybe plugged.
just went through this as well. the filler neck rotteded out allowing road grim from the wheel spray to get into the tank.out of sight out of mind.

[Luc]

OK, thanks, I'll check it out.

[Luc]

if the fuel pumps in the tank the pick- up screen on the pump maybe plugged.
just went through this as well. the filler neck rotteded out allowing road grim from the wheel spray to get into the tank.out of sight out of mind.

Filler neck is in good shape.

I'm going to change the fuel filter again, maybe I got a bad tank of gas.

[boyota]

Is it still hesitating around 2000rpm? The cheaper fix was tried. You may have problems with your TPS. If your TPS is faulty it's sending the wrong message to your ECU and injectors. check this link out. http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml hope it helps.....

[slacker]

are you sure your fuel pump is "up to snuff" .. there real common !!

I'd say check your fuel pressure first !

[Luc]

Yah, back to the hesitation around 2000 rpm's and lower now, when engaging the clutch.

The engine pulls strong above.

Driving around today i was thinking that it has to be fuel pressure. The hesitation is most pronounced when pulling away from a stop.

That means it could be the fuel pressure regulator, fuel pump or the fuel pressure vsv or cold start injector.

To troubleshoot, I unplugged the cold start and drove around, but, no change.

Why would it all go away when a new fuel filter is installed, only to come back, less then a week later??? Too low fuel pressure makes sense. But how do we figure out what's causing it?

[83LB]

You might as well rule out the pressure reg. They don't fail

[slacker]

initally a failing fuel pump can be intermittent ... best to check with a pressure guage , @ idle I believe it should run ~ 45lbs , but check the manual .

[boyota]

Granted checking your fuel pressure is a good idea. But if your pump can feed the engine at high RPM, and not low RPM it doesn't make a whole lot of sense to me. I'd lean stronger towards the throttle positioning sensor. Think of it this way.... Your ECU needs to know how much jam you're giving it to control the fuel injectors. It needs info from your AFM, 02sensor and other sh*t as well. Your AFM is good or broke no in between really. same as 02sensor. If your engine runs smooth at certain RPM I'd say those things are fine. But if your TPS is sending the wrong signal to your ECU than you could have a lean or rich fuel mixture, at the same time your timing could be advanced or retarded by this bad signal. It's one of the overlooked parts because most people are stuck thinking the EFI throttle body is a simple carb. When it's obviously not. If your ECU gets the wrong message from your TPS at anytime it would totally f*ck up how it drives until the ECU gets the right info. Take it to toyota and have them do a pressure test and check the TPS. Does this make sense?

[Luc]

OK, the pump is most likely 16 years old now, could be failing.

What's the best way to check the pressure output? I have a fuel pressure gauge that I can install, but, where? Just before the regulator, after it? Will need to get a T fitting.

A Toyota pump will be very expensive, any recomendations for a replacement brand and source?

Could be the TPS as well. I've checked it before, I'll check it again.

[Luc]

update;

I jumped the fuel pump from the testing plug (forget the real name) and it seams to work fine.

With a volt meter I tested the voltage from the O2 sensor and the voltage jumps around no matter what RPM the engine is at. So I got a new one from Lordco and will install it when the exhaust is a little cooler.

While I was at Lordco, I got all the fittings I needed to hook up a fuel pressure gauge. Hooked it all up and it doesn't work. It's an Autometer with a fuel line connection and a black and white wire. I hooked up the fuel line to the fuel line just prior to the regulator with a T fitting. The white wire to the positive of the battery and the black to the negative. Did I do it right???

Will also test my TPS using Roger Brown's info and report back.

Thanks for all your helps guys !

Luc

[Matt16]

update;

I jumped the fuel pump from the testing plug (forget the real name) and it seams to work fine.

With a volt meter I tested the voltage from the O2 sensor and the voltage jumps around no matter what RPM the engine is at. So I got a new one from Lordco and will install it when the exhaust is a little cooler.

While I was at Lordco, I got all the fittings I needed to hook up a fuel pressure gauge. Hooked it all up and it doesn't work. It's an Autometer with a fuel line connection and a black and white wire. I hooked up the fuel line to the fuel line just prior to the regulator with a T fitting. The white wire to the positive of the battery and the black to the negative. Did I do it right???

Will also test my TPS using Roger Brown's info and report back.

Thanks for all your helps guys !

Luc

Luc, did it do this before the '82 Supra AFM install? Just curious, how if changing the fuel filter changes the problem how the AFM would be the problem. I found a '82 AFM in a New York, and I'm having it shipped.

Do you notice that it only does this at certain amount of fuel in the tank? If it only did this at near empty, one might think that some water/ rust/ sediment was being stirred up by the sloshing around and plugging the inlet screen on the pump.

[Luc]

Hey Matt,

It was doing this before new afm, just not as bad. The engine runs awesome at wide open throttle, misses bad when pulling away from a stop, especially when cold.

After I changed the fuel filter, it ran perfect for about 5 days, then it slowly started up again. Now it's more at low rpm pulling away from a stop, runs better around 2000 rpm's. Runs strong above 2500 and goes very nicely to 4300. Not sure above that, I chicken out, but, I`m sure it would keep going.

I haven`t had time to check my tps, but it does make sense, at idle and at wot it runs well, it`s in between that I get the missing, hesitation.

Feel free to comment, all ideas are considered.

Luc

[GeoffC]

I have had hesitation problems that I swore up and down were fuel related. To the extent of rebuilding carbs on older cars, and doing all the same checks as others are suggesting, TPS, pump, etc on EFI vehicles.... Where it runs fine at certain Rpm's and barely runs at others.

Only to find that it was a spark plug wire. If you have an ohmmeter, check continuity on all the wires. As your checking, move wire around as they can be a bit intermittent.

It could be any of the other problems too, but it usually is the simple things.

Hope this helps