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TBI bogging?

X

xsmokey11499x

1/2 ton status
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Sep 29, 2010
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Location
lake elsinore California.
87 tbi setup the truck will start up and Idle. When I try and drive it will move if I am light on the throttle.
If I give it more than half throttle it seems like it's bogging out and won't accelerate.
I replaced cts. Egr valve. Fuel filter. Fuel line in tank.
I also swapped map sensor with no change.
Fuel pressure seems good. http://youtu.be/M69Gv4vyV-M
Im stumped..
 
Can't see your video, but what do you mean by "seems good" unless you've had a pressure gauge in line to see what it's doing at idle and under throttle, you won't know.
 
I'd suggest you stop shotgunning parts at it. That gets expensive quick!

Pop online and buy an ALDL cable and get some ALDL software. It's like 50 or 60 bucks and the software is free (winALDL is my favourite). Then you can see what the engine computer sees.

Start with the basics. Verify your timing is correct and steady.

Make sure your TPS reads properly and moves smoothly. Check that your MAP sensor reads about atmospheric key on engine off (~100kpa is average) and that the reading drops by the same amount of vaccum that the engine pulls (it's in absolute vs gauge pressure, check it with a gauge and minus the atm reading vs engine idling reading). Check that the IAC counts are normal around 15 or so at idle at full operating temp. Make sure the coolant temp sensor indication is believable too.

Your fuel pressure should be 12-15PSI. You need to check it on the supply side. This is a bit tricky with TBI, you need special adapters to do so. Make sure your injectors are both firing and that the spray pattern looks good, no dribbling.

Don't discount a mechanical problem too. Perhaps you have a vacuum leak? Blown intake gaskets? What about a sticky valve? Wiped cam lobe?

Do all your basic diagnostics first, don't shoot parts at it and pray for it to fix itself.
 
Russell said:
I'd suggest you stop shotgunning parts at it. That gets expensive quick!

Pop online and buy an ALDL cable and get some ALDL software. It's like 50 or 60 bucks and the software is free (winALDL is my favourite). Then you can see what the engine computer sees.

Start with the basics. Verify your timing is correct and steady.

Make sure your TPS reads properly and moves smoothly. Check that your MAP sensor reads about atmospheric key on engine off (~100kpa is average) and that the reading drops by the same amount of vaccum that the engine pulls (it's in absolute vs gauge pressure, check it with a gauge and minus the atm reading vs engine idling reading). Check that the IAC counts are normal around 15 or so at idle at full operating temp. Make sure the coolant temp sensor indication is believable too.

Your fuel pressure should be 12-15PSI. You need to check it on the supply side. This is a bit tricky with TBI, you need special adapters to do so. Make sure your injectors are both firing and that the spray pattern looks good, no dribbling.

Don't discount a mechanical problem too. Perhaps you have a vacuum leak? Blown intake gaskets? What about a sticky valve? Wiped cam lobe?

Do all your basic diagnostics first, don't shoot parts at it and pray for it to fix itself.
Click to expand...
Brand new intake gaskets. No sticky valve. This engine was running perfect before it was pulled out, it sat under a tarp for a month though. It then went into my k5
Also brand new distributor. (under warranty)
 
maybe I missed but, is this thing throwing any codes?

if not, I'd be looking at fuel...
 
ok, watched it... yeah, that shows ok, little low, but should run.....

how's the pattern?
 
I know the dizzy is new, but what's the ECM status? it might not be advancing right.. I think the guys are right, ya probably need an ALDL and start data logging..
 
Does it still have a catalitic converter?...might be plugging up...I've seen restricted exhaust pipes cause symptoms like this...some are double walled and can collapse and you'd never know it by looking at the outside...
 
diesel4me said:
Does it still have a catalitic converter?...might be plugging up...I've seen restricted exhaust pipes cause symptoms like this...some are double walled and can collapse and you'd never know it by looking at the outside...
Click to expand...


It does have a cat still.. Should I take the saw and cut my exhaust off.. Hah

But it does Rev up high in Park. Has a slow throttle response when revving up
But under a load it dies out
 
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Check the cat. I just had a 4.3L v6 in a Blazer with similar issues. No codes for the cat, low vacuum signal and while it started / ran fine it would not accelerate for anything.
 
I thought timing was quite a bit higher, like 20* at idle?

What is the *base* timing at? (IE, with EST bypass disconnected)
 
Sounds Like my blazer Right before the fuel pump went out. It ran but
Upon testing pressure It Was Only putting Out 4 psi. Tabu won't run correct under 9 minimum. Optimal is 12-15 psi. If it revs up at first and then slows it can be a clogged cat. Get a vacuum gauge on it. Should be pulling 18-22 at idle and go Down as you rev it Up. The map sensor uses the vacuum to change the advance on the dizzy. How does Spark look?
 
chulisohombre said:
Sounds Like my blazer Right before the fuel pump went out. It ran but
Upon testing pressure It Was Only putting Out 4 psi. Tabu won't run correct under 9 minimum. Optimal is 12-15 psi. If it revs up at first and then slows it can be a clogged cat. Get a vacuum gauge on it. Should be pulling 18-22 at idle and go Down as you rev it Up. The map sensor uses the vacuum to change the advance on the dizzy. How does Spark look?
Click to expand...
Spark is strong.
If I remember right, if I unplug the cts. It'll run ok.
I will test that here shortly. And If that's the case, Could I be losing fuel pressure under a load
 
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