Riley P
Jan 11, 2009
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Right now I am using.....or should I say, attempting the repair on a '91 GMC Sonoma. 4.3L Automatic 4x4.

Once the engine warms up, it dies when stepping on throttle. It starts out as a little bog, then keeps going, then the bog lasts longer until pressing on the gas simply kills the engine.

Parts replaced: Distributor and spark module, ignition coil, air idle control valve, map sensor, egr valve, some part that connects to the egr valve, and throttle body and injectors, fuel pump, fuel filter, replaced cat and muffler.

Yesterday I took the intake off and cleaned all the egr passages. The intake to head passage was 40% blocked. The passage from the egr valve to the intake where the air goes in was 100% blocked. Cleaned this and it helped but the truck still dies when hitting on the gas however it is more intermittent than before. Once it started acting up before it was done, now it can recover every once in a while and you can keep it going more easily but it definitely has the same issue.

We believe it is getting fuel while in the bog as we had it inside and could see fuel spraying into the intake as the engine was dying. But all thoughts are welcome! Quite stumped why this is happening.

One other clue.... We'll pull it in the shop right after it's been doing this, start it, most of the time it runs fine, revs, we can load the engine with it in gear, seems fine. Go outside, within a minute it's bogging and dying.....seems to only happen when driving and in a stop and go scenario.
 
Fuel tank was drained and so far about a liter of that fuel line antifreeze has gone in the tank. I was thinking that but I don't know why it would be so consistent, drive a minute or two and bog.

Something tells me that when the throttle gets pressed, something is cutting the spark but I don't know how it's connected. However, sometimes when stepping on the fuel, it just maintains speed or stumbles along and doesn't really die so could that even be spark? The tank was super dirty when the guy got the truck and the fuel looked like iced tea. He siphoned all the bad fuel out of it then vacuumed it out. However, I wonder if the pump is still getting clogged? Fuel filter partly clogged? But then once we bring it in the garage it rests for a bit and everything settles so it runs ok. Then you start driving it and flakes, debris gets back on the inlet for the pump? Would be nice to have a fuel pressure gauge.
 
a tank that was that bad should probably be replaced. sounds like there may have been a water issue for a long time and the inside of the tank is likely coated with rust. we see it quite often on metal outboard motor tanks and it plays havoc with the inlet needle in the carb. a throttle body would be pretty sensitive to debris.
 
Have you check fuel pressure? On vortec engine, a lost of 5psi of fuel pressure is enough to stall the engine. I know you have a new fuel pump but an electrical issue can give you a lower fuel pressure. I had a customer whit a c1500 pick up whit a 4.3 engine who had stalling and acceleration problem. After digging around, I checked the fuel pressure and it was border line. I took a seal beam and hooked it to the battery to see how bright it glow and took the voltage at the connection on the seal beam then did the same test at the connector of the fuel pump whit the key switch to run I had power for a few second, and it was enough time to see the voltage dropping 2 volts and the seal beam loosing brightness. I Finlay fixed corrosion problems in a connector closer to the cabin. Good luck

Give me more info on the truck like does it have a/c?, automatic?, 2wd/4wd?, and the engine code (8 digit of the serial #) and I will check on Identifix to see what where the fix for similar problems
 
Awesome, thanks guys! I questioned my friend on this as well. I know he said the injectors still had a nice spray pattern when it was bogging but was there still enough fuel to run? He is going to remove and clean the fuel pump, filter, and fittings and see if he can blow out all the lines today.

I will see if I can get the engine code.

Truck is a '91 automatic, 4x4, A/C, Cruise, TBI engine.
 
Even though there was a nice spray pattern, I figured it had to be fuel with ow it was acting and hearing that a decrease in fuel pressure can affect the CPI system so it makes sense it would affect the TBi as well.

The Fix!

There was a pin hole/crack in the pressure tube on the sending unit after the pump but inside the tank on the feed line to the TBI.

Truck drives like brand new now.
 
Good news, you wont have to put winter tires on the corvette or the mustang:rofl:

Hahaha. I'm not sure they make winter tires in the size I need for the Mustang.:D However, I think they do make them in sizes to fit the Corvette.:(

But it is funny. I was seriously considering why wouldn't I drive a Corvette in the winter? Active handling, traction control, heated seats, 50/50 weight bias, a big engine to throw lots of heat, and 95% of the time the streets are clear enough to drive on. If it snows, wait a day, no big deal.

now you don't need the C7 :)

I disagree! :D I need! I need!

Great to hear you got it fixed Riley. It's always the little things like that, to reach out and bite you at the end. Did you get a chance to squirt some OD on it?

Hmmm. Maybe. But I am not sure what OD is because I can't get the work Overdrive out of my head. :D

good job riley. it sure is satisfying to get to the root of these things before you go mental ain't it ? :D

Oh, man! I was seriously starting to fray around the edges. The thing is the guy I am helping.....or should I say, is helping me, knows these trucks inside out and upside down and I am doing my best to learn from him. So when he said the injectors are giving a nice spray pattern, I figured, ok, he knows his stuff, fuel is fine. But we changed every possible ignition/spark component and fueling component but the fact that it would die as soon as I hit the gas pedal confused me because I couldn't figure out what part that controlled spark would be absolutely fine in the garage but then would kill the ignition once the vehicle warms up and drives. So after thinking about it, it HAD to be fuel related but the catch was it would run great in the garage, rev up, do fine with load testing in gear but then die once it was driven. But logic still led me to it being a fuel issue and thank goodness he found that crack in the pressure line!
 
Hahaha. I'm not sure they make winter tires in the size I need for the Mustang.:D However, I think they do make them in sizes to fit the Corvette.:(

But it is funny. I was seriously considering why wouldn't I drive a Corvette in the winter? Active handling, traction control, heated seats, 50/50 weight bias, a big engine to throw lots of heat, and 95% of the time the streets are clear enough to drive on. If it snows, wait a day, no big deal.




I would like to see the face of the guy where you would bring the vette whit winter tires on and ask him for rustproof and a block heater :rofl:
 
OH Right! OD! No olive drab with this build. This is for the loaner truck that I am using. On my truck, since I am now replacing the cab, I figure I am just going to go back to black with my truck. :( The loaner truck is black and I really miss that color and think it looks sharp on the little trucks.......time to blend in with the masses I guess, although I will miss the look on kids faces as I drive by seeing them point and pulling on their parents arms to show them an "army" truck.
 
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