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TBI rich stumble on acceleration

BGKYK5

BGKYK5

3/4 ton status
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My truck (in sig) just developed a bad stumble on acceleration. Unless I accelerate very slowly, it coughs and stumbles and wants to die. It's OK at steady speed, but not great. The TBI and engine are stock. I ran a datalog with WinALDL and the only thing that stood out to me were a bunch of rich flags. No codes were set (other than 12). The O2 reading is switching from 0.1 to 0.9 normally.

I did have the steering column out just before it started acting up, and now the brake light is on (and no, the e-brake isn't on, I don't have one). Could I have knocked something loose that would cause the stumble?

Also, I've noticed the fuel pump running for up to 30 seconds or so after I shut off the truck (key out). I assume it runs to keep pressure in the lines for the next start. The pump is running noticeably longer than it used to. Could I have leaky injectors or something?

I'll probably borrow Kjunky5's fuel pressure gage next weekend to see if that shows anything interesting.

Any other ideas?
 
check your spray pattern.... I was expecting an EGR code, that's notorious bad EGR symptoms...
 
I think something went wrong in the steering coulmn wiring and switches below?

Pump should not run after key is off?

Pump should run a couple seconds key on before start...
 
It was doing that prior to pulling the column. The fuel pump is not supposed to run after key off? Sticky fuel pump relay?

I'll check the spray pattern when it's not snowing. :D
 
I just read this again and you say rich stumble?

Well rich does not cause stumble like your describing, you are describing hesitation which is usually a lean issue. I think because you saw the rich flag in WinALDL you are thinking it is rich/bad! It is supposed to go rich/lean constantly.

With your fuel pump running after you turn key off, and this hesitation, it really points to a fuel issue. Checking fuel pressure is a must! :D

I've never had to deal with fuel pump running after key off (on a stock TBI truck) so when you say sticky relay? That is a possibility? I have dealt with it on TBI conversions and it was a wiring issue. That is why I pointed to steering column change...
 
Yes it is switching from rich to lean constantly (O2 from 0.1 to 0.9), and yes I am guessing that the rich flags correspond to the stumble, but that could be wrong.

If the pump is not supposed to run after key off, then i will definitely look into that issue. It may (or may not) be related. It has been doing that longer than the stumble issue though (before the column was out).

The only other changes at the time the stumble started were the replacement of the ignition switch (which is why the column was out), replacement of the fusible link from the starter solenoid to power distribution block (temporarily with 10 awg wire), and removal and reinstallation of the starter.
 
Supposed to go rich/Lean constantly. It's cross counts to O2 sensor to keep it at 14.7 to 1. So that's good!

Nothing else you said points me in any direction of what you did, caused the problem. I think it is unrelated to what you did...

I've never heard of or seen a sticky relay? But that would sure cause your fuel pump run on issue. When key goes off so does power to relay, why it waits 30 seconds I do not know?

Fuel Pressure reading for hesitation first! :waytogo:
 
Too rich will stumble. Mine will do this when cold, in open loop. If I mash the throttle it will just fall on it's face - wide band O2 shows 8:1 range.
 
I borrowed a fuel pressure gage from KJunky5, but there is no easy place to connect it. It looks like I need the adapter in the upper left of this pic.

gage.JPG

I know CFM Tech and some others have adapters to hard mount a gage, but I'm looking for something with a schrader valve because my head doesn't fit under the hood very well while driving. I guess I could buy the whole thing - but I'd rather not spend the money right now.

gage.JPG
 
Normally it does not come with the adapter for feed line on TBI. It goes in after fuel filter under truck.
 
Maybe? There is one made to go inline at TBI as well... the ones I have seen with gauge go inline at fuel filter.
 
I made an adapter that goes after the fuel filter and then allows an electric fuel pressure sending unit to screw in and sends the pressure to a guage in the cab. I got tired of testing the pressure at idle and not being able to see what it's doing going down the road.

In the picture the fuel guage is on the far right. Hey this is the first time I got to show it off!!! Cool

IMG00149-20111230-1552.jpg
 
That is what I should do long term. Short term, i think i'm gonna bite the bullet and buy the gage with the TBI adapter in the picture in post #10.
 
BGKYK5 said:
That is what I should do long term. Short term, i think i'm gonna bite the bullet and buy the gage with the TBI adapter in the picture in post #10.
Click to expand...
Do you have an autozone near you? You can "borrow" their fuel pressure guage for free and it comes with the adapter. If you don't have an autozone you might check some of your local parts dealers. They might have a similiar tool you can borrow.
 
I bit the bullet and bought one with the right adapter. I haven't got a chance to use it yet - I spent the weekend working on my DD. Maybe next weekend if the weather isn't horrible...
 
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