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Old 04-13-2021, 01:59 AM   #1
Low Elco
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TBI Info down on power

I just bought my 87 GMC 350/350 TBI back after 5 years. Still in good shape, but on the 120 mile run home, I noticed it being down on power. Still seems to run ok, but it had a lot more snap when I had it. Pulling up the hill to the house, I had my foot way into it, and Buuuuuuhhhhhh, no power. I'm assuming weak fuel pump/bad injector. Any other thoughts? Thanks!
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Old 04-13-2021, 12:57 PM   #2
mattfranklin
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Re: TBI Info down on power

Fuel filter(s) might be the quicker easier thing to check.

Then look at your spark plugs.
Then check compression.
And do your normal maintenance/tune-up things in between as you go.
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Old 04-13-2021, 03:09 PM   #3
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Re: TBI Info down on power

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Originally Posted by Low Elco View Post
I just bought my 87 GMC 350/350 TBI back after 5 years. Still in good shape, but on the 120 mile run home, I noticed it being down on power. Still seems to run ok, but it had a lot more snap when I had it. Pulling up the hill to the house, I had my foot way into it, and Buuuuuuhhhhhh, no power. I'm assuming weak fuel pump/bad injector. Any other thoughts? Thanks!

Like Matt said could be a plugged filter (fuel or air). I can't think what they had for filters. I guess it could be bad plugs or timing off too.

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Old 04-13-2021, 05:35 PM   #4
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Re: TBI Info down on power

This is all in the plan, Stacked up pretty tall for the next couple weeks, Has a filthy K&N on it now, and lord knows when the fuel filter was changed. Didn't seem to be misfiring. Has good Oil Pressure. They just put a cap on it and said it made a big difference. I might stick some plugs in it too. Planning on an LS this winter, so I just need it up to fun bombin' for the summer.
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Old 04-13-2021, 09:02 PM   #5
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Re: TBI Info down on power

Plugged muffler, catalytic convertor
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Old 04-13-2021, 11:04 PM   #6
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Re: TBI Info down on power

https://www.thirdgen.org/forums/tbi/
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Old 04-14-2021, 11:08 AM   #7
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Re: TBI Info down on power

A hundred years ago, I owned a '91 K2500 Suburban with a TBI 350 in it. Down on power and I checked or replaced everything I could think of. Fuel filter, fuel lines, fuel pump were all good. No trash in the tank, and everything else was pretty mechanically sound. Distributor and coil were good. New plugs and wires didn't help either. Total head scratcher.

Ended up being a faulty injector wire harness ($10 dollar part) where it plugs in to the injectors. Easy fix and made all the difference in the world.

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Old 04-14-2021, 10:04 PM   #8
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Re: TBI Info down on power

Hmm! Thanks for the tips, I'll give it a try!
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Old 04-14-2021, 10:17 PM   #9
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Re: TBI Info down on power

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Plugged muffler, catalytic convertor
Big ol Flowmaster, don't think it has a cat. I've had that before, feels like it's "huffing" into it.

This is more everything's opening, and nuthin's happening. Like it's waiting for something.
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Old 04-19-2021, 09:02 AM   #10
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Re: TBI Info down on power

Put a timing light on it. Retarded timing from the distributor slipping will present exactly how you describe. Don't forget to unplug the little wire when you check/adjust it.
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Old 04-24-2021, 07:53 AM   #11
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Re: TBI Info down on power

The tbi engines used flat tappets, and were notorious for wiping off the cam lobes. This could explain a lack of power.
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Old 05-03-2021, 07:22 PM   #12
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Re: TBI Info down on power

Finally got a bunch of boat stuff out of the way, hoping to take a look this weekend. Glad to see you around, Kevin!
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