tbi fuel pressure too high??

[1tonyj]

Recently purchased a buggy with a ZZ3 Chevy crate motor fed by a Howell tbi kit. The motor starts easy, idles fine and revs up with no load perfectly. When u put the buggy in gear and hit the throttle the motor falls on its face...stumbles...and takes a bit to catch up. This is most noticeable in high gear. I changed fuel filter and noticed the in line electric pump is a 40 psi pump....I know tbi units only require 13 or so psi...could this pump be flooding my system?

 

[muddinmetal]

If there is no regulator, then absolutely, but I doubt it ever ran right if that was the case. What dis the previous owner say about how it ran?

 

[mrdrinksalil]

The GM TBI throttle body has the pressure regulator built into it. hook up a fuel pressure gauge and see if the pressure drops when the motor falls on its face. most are set around 12-16 and should never move from where its set. It also could be your MAP sensor isn't doing its job or isn't getting a good vaccum. This is what adjusts for more fuel under load in a TBI.

 

[1tonyj]

The buggy had been sitting for a long time...he didn't run it much in last two years. He did say it runs rich and burns a lot of fuel.

 

[mrdrinksalil]

I don't know much about the howell system but the factory computer is SO primitive it cant compensate much for anything without burning a new chip with changes to the fuel and timing tables. Its also very limited by how much air you can cram through that 2 barrel. I'd call howell and get them to hook you up with a way to log data and then have a new chip burned.

 

[1tonyj]

Yeah...that was gonna be my first call Monday morning. Thanks for the info guys.

 

[mrdrinksalil]

Id bet you aren't getting enough fuel for one reason or another. look in the TBI and verify both injectors have equal looking spray patterns, then fuel pressure check before doing anything. You've got a problem to fix before you can improve its performance and tune.

 

[muddinmetal]

I'd be real curious if the fuel filter is filthy

 

[1tonyj]

Filter actually wasn't bad.....and yes, I agree I gotta find out my actual fuel pressure. I'll let u guys know what I come up with.

 

[bgredjeep]

As long as you've got the return line hooked up it shouldn't be an over pressure issue. Honestly, it sounds just like what my 4.2 did when I installed a "stock" tune chip from Howell in my Jeep. I bought my efi second hand and it was tuned for a motor with a cam and headers that I didn't have. Their stock tune ran like total crap, loaded up, would flood horribly when cranking if I shut it off and let it sit for about 5 mins then tried to restart.

Best bet to get a good tune from Howell is to use a wideband o2 to map what it's doing now so they know what adjustments to try. They might be able to make a guess based on your motor setup. Also, have you checked for trouble codes yet?

 

[June dog]

The buggy had been sitting for a long time...he didn't run it much in last two years. He did say it runs rich and burns a lot of fuel.

There's a coolant sensor on the intake if it goes bad it will run like crap. Got a buddy who had the same problem they checked and changed everything on the engine and the last $12 sensor cured it. May not be your problem but it's a cheap sensor to change.

 

[johneddie]

There's a coolant sensor on the intake if it goes bad it will run like crap. Got a buddy who had the same problem they checked and changed everything on the engine and the last $12 sensor cured it. May not be your problem but it's a cheap sensor to change.

Whatcha talkin' bout Willis???.....Me?? :afro:
Fixed mine after motor had set for 6+ months. :****:

 

[bigsexy]

Had a buddy with a truck with similar symptoms but it would die. Only way it would start back was if you unplugged one injector then plug back in..it was having fuel pressure problems...way high...

 

[1tonyj]

Hey guys thanks for all the replys....i been working so much I havnt had time to mess with it till today. I guess I should have mentioned it is a 4 barrel TBI with 4 injectors. I checked and cleaned all vac lines, replaced the fuel filter again, and cleaned all my electronic connections. Now when i stab the throttle it has a pop (small back fire through the throttle body) a real short loss of power then she takes off like a champ, its better than it was but Im still not quite there. I talked to the previous owner again who assured me its not the tune as it ran great before, it just the buggy has been sitting for almost of a year... and I have no reason not to believe what hes saying. Going to hook it up tomorrow and see what codes its showing....will report back. Thxs again everyone.

 

[highrolrcustoms]

have someone sit inside and push the throttle while you are watching the injectors spray the fuel. mine sat for about a year and half and it did the same thing. it ended up being the injectors were gumed up

 

[1tonyj]

I did notice they were "spitting" ...more than a smooth spray