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Old June 28th, 2011, 07:56 AM   #1
Tranny Tom
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1989 K3500 454 TBI running issues

This truck has had this intermittent issue of bogging, missing at anything over 1/2 throttle. It has progressively gotten worse. The truck came to me recently barley running with the gas tank hanging on by 1/4 of a strap. I pulled the tank replaced the pump (since I had the tank down anyway), filter, and straps then reinstalled the tank. Then I put new premium tune up parts on it. Test drove it to find the bogging issue. Called the owner he said it has been doing this for a while. It had a code 13, 42, and 44.

Things I changed trying to figure out the problem:
Map sensor is newer (was replaced a year ago)
TBI unit
Ignition module w/ known good one
Coil w/known good one
reset the timing.
cleaned all computer grounds
New O2 sensor.
Fuel pump and filter

I cleared the codes and they have not come back yet.

Doing all of this didn't change bogging missing at over 1/2 throttle at all. My next thing I'm going to do is pull the EGR off and block it off. Does anyone have any ideas? Owner says he is fine with picking up the truck the way it is because he used to it running this way but I can't let it go if it isn't 100%.

Last edited by Tranny Tom; June 28th, 2011 at 09:06 AM.
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Old June 30th, 2011, 12:00 PM   #2
in2deep
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bad pick up in dist
coolant sensor
spark plugs
does it do it all the time or just when hot
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Old June 30th, 2011, 12:05 PM   #3
kevinr839
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I had a truck doing similar things but was more rpm related. ended up being broken and weak valve springs.
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Old June 30th, 2011, 12:08 PM   #4
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Quote:
Originally Posted by in2deep View Post
bad pick up in dist
coolant sensor
spark plugs
does it do it all the time or just when hot
temp sensor reads ok on scanner and ohm checks good
newer plugs
all the time. It only breaks up under load.
I'm going to swap the dizzy tonight.
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Old June 30th, 2011, 12:55 PM   #5
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Quote:
Originally Posted by kevinr839 View Post
I had a truck doing similar things but was more rpm related. ended up being broken and weak valve springs.
I too was wondering if it didn't fit the criteria for something like a bunch of bad valve guides or worn springs? the other thing that would noticed is hard starting cold if its guides. they tend to prevent the valves falling center on the opening and make for a weak vacuum signal.
as for checks while you running I would add a large vacuum canister in the fender somewhere. a gallon size can hooked to manifold vacuum could be enough back up vacuum that it will help compensate when you do your tip in at part throttle. use about a 3/8" hose to get a stable signal fast to the intake.
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Old June 30th, 2011, 07:23 PM   #6
Disturban
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Have you checked the TPS sensor? Does it bog and misfire in both open loop and closed loop? I would also check the distributor drive gear they are known for going bad and causing issues like you described and make sure the timing advance mechanism inside the distributor is functioning correctly and not binding/froze.

ps: Another thing to check is the injectors, if they are dirty and not flowing 100% it will run good at part throttle but when you get on the gas it cannot supply enough fuel, shine a timing light on the fuel coming out and it should have a nice cone pattern to it.

Last edited by Disturban; June 30th, 2011 at 07:32 PM.
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Old June 30th, 2011, 07:43 PM   #7
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I was gonna say the gears are getting worn on the dist shaft, would make sense if it's does it under throttle
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Old July 4th, 2011, 01:20 PM   #8
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also check fuel filter i had a truck doing this to me getting plenty if fuel until about 30 mph then it would just bog down and die
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Old July 6th, 2011, 07:54 PM   #9
Tranny Tom
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I FISSED IT!!!!! Thanks for all the responses and ideas guys! I swapped the temp sensor (the lead fell out of it) and found a broken computer ground so it was at least one of those if not both.
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