Intermittent bogging while driving...

[Ole Bessie]

Have an issue that has me stumped. 91 TBI 350 with 240k miles. Truck starts up, runs, and drives great. No rough idle, no bogging off the line, but once I am moving and hit the gas to accelerate and pass someone or speed up the engine will bog down and backfire. If I let off the gas then slowly get back into it it will be fine. It started doing this a couple months ago and because of that I had to leave the truck in Maryland at my moms while I moved out to Utah. I had the truck shipped to me and have had it back for almost 2 weeks and it I'm still having the issues.

Replaced spring last year:
Distributor cap/rotor
Coil
Plugs
Wires
Air filter

I have a fuel filter but haven't put it in yet since it will start up and run just fine (most of the time)

I haven't tried to jump the OBD1 port to see if any lights flash on the dash, but I can't figure out what the issue is. I feel like it might be the throttle position sensor is losing voltage once everything gets nice and warm, but I'm not positive and don't want to throw parts at it. I have thought about just getting a reman L05 from Autozone with a new TBI unit and such just so it's got a fresh motor.

Any ideas what it might be?

 

[scott2093]

I'm not positive and don't want to throw parts at it.

Trying to get codes would be a cheap date... If you can borrow a scanner, even better..

Manuals for your truck are here..

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

Fuel filter is usually a good idea regardless...

 

[GoToGuy]

You can plenty of fuel for idle, no great demand, but applying a load , and having insufficient pressure or volume , you can guess how performance would be crap. You have a filter , use it. What if you filter flows ok at idle but under higher demand slows down ? Easy, quick. Would more accurate if you get to a scanner for checking.
Did you test the TPS ? Have tested the actual health of your engine?

 

[Drunkcanuk]

I had basically the same symptoms on my 91. After a shot with the parts cannon, it turned out to be the little rubber hose that connects the fuel pump to the fuel lines, in the tank. It was full of holes, the new ethanol gas eats those old lines. So if your pumps original, it's a suspect.
So I would verify fuel pressure at idle and under load.
And take the 5 minutes to change the filter!

 

[Ole Bessie]

Slight update: swapped the new fuel filter in and jumped the OBD1 port with a wire and didn't get any codes (I'm wondering if the check engine light even works) The bogging got better for a few days but today on the freeway at 70 mph it just didn't like it. Engine cut out a couple times and restarted fine. When it started bogging around 70 mph it wouldn't work right if I slowly got back on the gas until I got to around 50 mph. After doing some more googling I'm wondering if it's the ICM on the distributor. I'm sure a new fuel pump wouldn't hurt and replacing any old fuel hoses but I really don't want to drop the tank to check the hoses like drunkcanuk mentioned since it's pretty full.

 

[WICruiser-97]

Continue to drive it until the tank gets low enough that you can drop it to change the fuel pump.
If your check engine light does not illuminate for a short time when you turn on the key the bulb may be out.

 

[Scooterwrench]

Continue to drive it until the tank gets low enough that you can drop it to change the fuel pump.

Or break out a siphoning hose,AKA Georgia credit card. It definitely sounds like a fuel starvation issue. Another culprit could be catalytic converter. A good check for that is to get someone to sit inside and floor it while you feel the amount of exhaust coming out of the tail pipe. Should blow pretty hard.

 

[movietvet]

I am a little confused. You are willing to install a whole different motor, and you have replaced the fuel filter and IT GOT BETTER and you have yet to get a fuel pressure reading, at idle and while driving. A clogged fuel filter likely over worked the fuel pump and when you changed the filter, that pump breathed for a while and then the problem popped up again. 10 motors later, you still have the same old fuel delivery. I would rather drop a tank and install a fuel pump than swap out a motor, unless of course the motor is actually needed.

C'mon man. Get the fuel pressure readings and post here. That fuel pump change dread is because of the rust, right?

By the way, welcome to the forum from Oregon. By the way, move from Maryland to Utah was smart.

 

[Drunkcanuk]

You can use the ODB port to jump the fuel pump, you don't have to siphon it out.
Unhook the fuel line at the filter, attach a hose and pump it into Jerry cans.

Slight update: swapped the new fuel filter in and jumped the OBD1 port with a wire and didn't get any codes (I'm wondering if the check engine light even works) The bogging got better for a few days but today on the freeway at 70 mph it just didn't like it. Engine cut out a couple times and restarted fine. When it started bogging around 70 mph it wouldn't work right if I slowly got back on the gas until I got to around 50 mph. After doing some more googling I'm wondering if it's the ICM on the distributor. I'm sure a new fuel pump wouldn't hurt and replacing any old fuel hoses but I really don't want to drop the tank to check the hoses like drunkcanuk mentioned since it's pretty full.

 

[PlayingWithTBI]

Remove all the bed bolts except 1, loosen it. Disconnect the fill and tail lights, tilt the bed so you can get to the top of the tank, and prop it up with a 2X4 or something.