TBI stumble when hot (1 Viewer)

[dallen341]

Need help!

I have a 1990 Chevy TBI 350 in my FJ40. When hot, and under hard acceleration, I get a bit of a stumble like it's either loading up or starving for fuel. Not sure where to start looking. Any thoughts out there?

plugs, wires, and distributor and cap are new.

Thanks...Don

 

[TLCSKULLS]

Sounds like fuel delivery. I'd check/replace fuel filter first. Could also be clogged injectors. Could also be a bad sensor. Change your fuel filter and check your ECM for error messages and go from there. Good luck.

 

[Fast Eddy]

Need help!

I have a 1990 Chevy TBI 350 in my FJ40. When hot, and under hard acceleration, I get a bit of a stumble like it's either loading up or starving for fuel. Not sure where to start looking. Any thoughts out there?

Post some pics of your fuel lines. You could be getting some fuel boiling.

Also describe your fuel pump(s). Old?

 

[Wayneraintree]

I had something like that happen on my 350 TBI... moved the igniter to the inner fender well and it stopped....theory was the ambient temp in the engine bay was goofing it up. HTH,

 

[dallen341]

I had something like that happen on my 350 TBI... moved the igniter to the inner fender well and it stopped....theory was the ambient temp in the engine bay was goofing it up. HTH,

Ignitor? wha dat?

 

[Wayneraintree]

oh, coil.... sorry.

 

[Bennett]

My theory:
Check your fuel pressure first. My dad always told me to check first fuel, spark then air

My guess is you are using a maximum 15psi pump (external ) for your tbi.. TBI does require a constant 15PSI ........but ....What happens when using a 15PSI pump.. under hard acceleration it drops down to 8-9 psi and you stumble.
I think you are starving for fuel under the heavy pedal.
Get a E2000 off a ford truck ( external mount) or a Bosch E8305 external re-test your fuel pressure under load..

got to the u-pull-it and buy a used unit for the test $15 and keep it as a spare.

link to specs and pics http://www.dune-buggy.com/buggytalk/index.cgi?read=240006

another good link shows the e 2000 pump
http://www.binderbulletin.org/forums/showthread.php?t=45292

 

[Wayneraintree]

I put a small fuel pressure guage in line near the back of the block, mounted to the frame rail, visible from the the fender well, just for the reason of verifying the pressure whenever I needed. I had trouble with pumps maintaining constant pressure and also overheating..... went with a Holley pump and I carry a spare.....

 

[dallen341]

I pulled codes today. I get a 42 (EST) Electronic Spark Timing. Anyone have a clue where I look from here?

Don

 

[TLCSKULLS]

PM me your e-mail and I'll send you the applicable pages from the manual.

Dan

 

[jblang]

I put a small fuel pressure guage in line near the back of the block, mounted to the frame rail, visible from the the fender well, just for the reason of verifying the pressure whenever I needed. I had trouble with pumps maintaining constant pressure and also overheating..... went with a Holley pump and I carry a spare.....

Do you run a fuel pressure regulator with your Holley blue and TBI or do you just run wide open?

Additionally, do TBI have internal regulators?

 

[Wayneraintree]

internal regulator on the back of the TBI......

 

['74 UA FJ]

Need help!

I have a 1990 Chevy TBI 350 in my FJ40. When hot, and under hard acceleration, I get a bit of a stumble like it's either loading up or starving for fuel. Not sure where to start looking. Any thoughts out there?

plugs, wires, and distributor and cap are new.

Thanks...Don

What distributor? HEI? What brand? Hard acceleration at around 2800 rpm and up? Could be your module/condenser. I think aftermarkets are putting in s*** ones these days. Find you a GM one and see if that solves the problem.

 

[Isotel]

Code 42 sucks.. it could be a lot of things, i was getting one in Moab..

At one point years ago i had my Spark plug wires ran too close to the Harness and that caused it.. This recent time i think it was my spark plug boots burn and arcing over to the ramshorn manifolds.. Could be ESC module, or pickup, or alot of things.. Best bet is to start with making sure your wires are all routed away from the harness and start exchaning out sensors..

 

[matt the sign]

I'd go with the fuel pressure not being great enough from the pump ... swapped mine over to a Range Rover fuel injection pump (I'm in the UK, we've got loads of Range Rovers ) and that cured it !

 

['74 UA FJ]

Everybody who is saying fuel: did you not read where he got a code 42--Electronic Spark Timing...

 

[matt the sign]

And that will definetly be the answer will it .....

 

['74 UA FJ]

And that will definetly be the answer will it .....

What are you saying?

GM computers normally point you in the right direction as far as trouble codes. If he is getting a code saying it is a spark problem then it most likely it is.

 

[matt the sign]

You could be right mate ... I'm sure he'll post up when its cured and let us know

 

[dallen341]

It may not be a code 42 after all. Apparently, code 42 will set when the timing connector is disconnected for timing. I had checked timing and did not clear the code. I have since connected a scan tool and no codes are set. Additionaly, all parameters appear normal. At this point, I'm leaning toward fuel delivery as a potential cause.

Don