TBI Hesitation at WOT

[midog]

I will try and be as short and complete as possible.

Motor 5.7 L TBI out of a 1993.

Problem- After warm up if I punch the throttle I get major hesitation and can visibly see the injectors struggling to increase fuel spray. I should say this issue seems to be intermittent and does not happen all the time.

What I've replaced and fixed-

1. New walbro fuel pump GLS 395 rated at 10-15 psi (my gauge reads between 7 and 13). I replaced the old one (walbro 393 rated at 30psi becuse it was only producing 7-13 psi as well), new pump is the same.
2. 2 new fuel filters 1 before and one after the pump.
3. I swapped out the computer for one I had in my garage, no change.
4. I put a new fuel pressure regulator in my TBI, no change.
5. Swapped the coil for fun, no change
6. I took the cap off the fuel cell to make sure I didn't have a back pressure issue from the rollover valve being stuck, no change.
7. Swapped out the TPS from another one I had in the garage, no change.
8. I check for vacuum leaks and nothing.
9. New O2 sensor

That is where Im at, any help or suggestions would be great.

 

[Tacoma]

Have you checked your fuel pressure to see what its fluctuating to and from? There are a couple things that can cause your symptoms... Let me check a few manuals.

 

[lewis]

This is driving me crazy. Need to hurry and fix it so I can get it out of my head.

 

[midog]

This is driving me crazy. Need to hurry and fix it so I can get it out of my head.

Did that vid come threw on your phone? If so how hard would it be to throw it on youtube?

Its driving me crazy as well!

 

[midog]

Have you checked your fuel pressure to see what its fluctuating to and from? There are a couple things that can cause your symptoms... Let me check a few manuals.

It seems different each time, I start it and then stays at that pressure (it does not rise and fall during acceleration).

Its between 7 and 12 psi.

Today one start it ran at 12psi, then it was at about 7psi and the other it was at about 9psi.

Any ideas would be appreciated!

 

[Tacoma]

well... that's too low. Pressure should be 9-13psi, or you're going to have problems. I had some issues where it would idle fine, and not run worth a damn above that-- turned out to be the short piece of rubber hose included w/my new fuel pump, it was garbage and not fuel-rated at all, and fell apart. Not something I would think to check. So check that.
Also make SURE you have a good ground. That also causes some funky issues.

After that, you may want to test your IAC, which I will detail in a bit, manual is in my wife's car, and she's not here.

Fuel pressure is a good place to start and rule out problems. Yours is low, and needs to be dealt with one way or the other.

 

[Tacoma]

FWIW, my stock pump wouldn't keep the truck running at 7psi, but idles at 9 now that I fixed the hose issue. 2psi doesn't sound like much, but it's enough.

 

[midog]

well... that's too low. Pressure should be 9-13psi, or you're going to have problems. I had some issues where it would idle fine, and not run worth a damn above that-- turned out to be the short piece of rubber hose included w/my new fuel pump, it was garbage and not fuel-rated at all, and fell apart. Not something I would think to check. So check that.
Also make SURE you have a good ground. That also causes some funky issues.

After that, you may want to test your IAC, which I will detail in a bit, manual is in my wife's car, and she's not here.

Fuel pressure is a good place to start and rule out problems. Yours is low, and needs to be dealt with one way or the other.

I agree with the fuel pressure issue. My old pump was an inline pump (out of the tank) rated at 30psi, I only would read 7-11psi with that pump, so I thought OK I know what the problem is- bad pump, and ordered a new pump (also inline) this on is rated up to 16-17 psi (designed for use with TBI systems). I hooked it up and it read 12psi right off the bat, I warmed up the engine then stopped it. Came back and started it again a few minutes later and only got 7 psi. This made me think maybe the filters are clogged so I put in some new filters and that took the pressure up to 9-10 psi. I don't know why I would not get better pressure with a new pump and a new fuel pressure regulator in the throttle body?

Checked the ground on the pump and its tight and solid.

I'll look forward to the IAC info

Thanks for your help!

 

[Tacoma]

Since the filters are after the pump, any restriction BEFORE the pump should show up on say, the 2nd start up. you'll have enough gas in the lines to read good pressure for a bit if that hose is messed up. I went through the same thing, because I had a brand-new pump in there, and a recent rebuild on the TBI unit... I would NEVER have guessed that the 2" of fake fuel hose was a possible culprit.

IAC info as soon as I get my manual back.

 

[lewis]

So what filters you using? Maybe give it a go without any filter to see if the pressure problem is fixed.

 

[Tacoma]

... also make SURE they're installed with the right flow direction. SOmetimes it's somethign dumb.

 

[midog]

So what filters you using? Maybe give it a go without any filter to see if the pressure problem is fixed.

I got them at auto zone (rated for fuel injection) I have one before (Part #FF3419) and after (part#FF756) the pump.

Wonder if I should only run one filter? If so, before or after the pump/ (I thought I read those pumps are good pushers but bad pullers)?


The fuel hose is the blue goodyear 3/8 id rubber hose from EVCO (rated for fuel and oil). Ran from the tank to the TBI and back.

 

[midog]

... also make SURE they're installed with the right flow direction. SOmetimes it's somethign dumb.

Checked and Checked!

 

[Tacoma]

Hmmm I wonder if that hose is collapsing? the factory uses nearly entirely hard line, with only short sections of braided flexible lines from the tank to the framerail, and from the framerails up to the TBI unit. Two filters is also outside factory parameters.. could be causing problems.

Just thinking out loud for now.

 

[midog]

Hmmm I wonder if that hose is collapsing? the factory uses nearly entirely hard line, with only short sections of braided flexible lines from the tank to the framerail, and from the framerails up to the TBI unit. Two filters is also outside factory parameters.. could be causing problems.

Just thinking out loud for now.

This time around I used a less restrictive (carb) fuel filter before the pump, then used the regular filter after the pump.

I will check the hose to see if I have a strange kink or bend some place.


I should also say that I ran it at Moab for 8 hrs or so and it ran great! Started to have problems when I went to unload it off the trailer after running poison spider and ran crappy ever since.

 

[shellez]

My friend had this problem, the pins on back of the dist. where it plugs in were dirty. We used a paperclip and cleaned the female side and now it works great. I believe the dist. sents the injector pulse to you injectors telling them when to fire and how much fuel to use Just a thought

 

[midog]

My friend had this problem, the pins on back of the dist. where it plugs in were dirty. We used a paperclip and cleaned the female side and now it works great. I believe the dist. sents the injector pulse to you injectors telling them when to fire and how much fuel to use Just a thought

Thats a great idea! I will try it. I never thought about the distributer (thought is was a fuel issue) I took off the cap and the rotor looks bad. I will clean the pjns and put a new cap and rotor on and hopefully that fixes the problem!

 

[eatrocks]

The injectors get a Tach signal from the disturber this tell the system it base number of the RPM The fuel regular does get a vacuum signal lean the system out when the vacuum goes high. Such as decal and then it goes richer under load and should go to 13 to 13.5 at wot. If the regulator, it’s in the top of the TBI is not working or the diaphragm has a hole this would happen

 

[midog]

The injectors get a Tach signal from the disturber this tell the system it base number of the RPM The fuel regular does get a vacuum signal lean the system out when the vacuum goes high. Such as decal and then it goes richer under load and should go to 13 to 13.5 at wot. If the regulator, it’s in the top of the TBI is not working or the diaphragm has a hole this would happen

Put a new regulator in, tomorrow I will put this the new cap and rotor and let you all know what happens!

 

[midog]

OK.... Update- I put in the new Cap and rotor in and it roared back to life! I had great fuel pressure (13PSI) and it does not bog down when I "punch it"

I spent a bit of money to get to this point but now I guess I have some spare parts.

Thanks everyone with your help (otherwise I would have never thought it was the distributer)!!!