1990 K1500 Runs... Kinda

MrSony

Geezer
Nov 15, 2014
6,494
113
Des Moines, Iowa
I'm back with my tbi sh*t

These readings look good? After rebuilding the throttle body it will idle but with any throttle at all it will stumble. Has code 33 stored.
 

ck80

Comic Book Super Hero
Feb 18, 2014
4,637
113
Code 33 is your MAP sensor.

At idle should be right around 1 volt which your scanner showed. Key on engine off should be around 4 1/4, 4 1/2, varies with altitude.

Could have a vacuum issue at the MAP as well. IIRC, around 15" is what you're expecting.
 
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Oct 14, 2008
8,323
113
Melville,Saskatchewan
As said make sure there isn't a vacuum leak. The voltage mentioned above is correct above for KOEO. Also check for ground or wiring issues at the sensor. I see it is in open loop, does it matter whether it is open or closed? Also make sure timing isn't off. Another quick check is TPS check for the voltage sweep with meter with KOEO. It should be the .6 to about 4.5 volts a full throttle with a nice clean sweep with around 5 input volts. Anytime a TBI truck came into the shop I worked at years back, the first thing we checked was the cap and rotor. Usually bad, blue corrosion and stumble/miss was fixed. We used the Blue Streak brass cap and rotor. Good luck. I miss my 94, I really need to find another to Olds power.
 
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Supercharged111

Comic Book Super Hero
Oct 25, 2019
3,969
113
Colorado Springs, CO
Check your fuel pressure too. Those are notorious for low pressure causing issues. 9-13 is spec, but anything under 11 and it'll be hot garbage. You want to be at the high end of spec for it to really run good. This means you'll have to buy a new inlet fitting. I got mine from RV Morse Marine eons ago but sadly dude kicked the bucket a few years back. One time I had a plugged fuel filter and another the spring in my regulator had broken. I think at one time I had a stock type regulator that was adjustable but it maxxed out at 11 or so psi.
 
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airboatgreg

Comic Book Super Hero
Oct 2, 2016
2,779
113
Check your fuel pressure too. Those are notorious for low pressure causing issues. 9-13 is spec, but anything under 11 and it'll be hot garbage. You want to be at the high end of spec for it to really run good. This means you'll have to buy a new inlet fitting. I got mine from RV Morse Marine eons ago but sadly dude kicked the bucket a few years back. One time I had a plugged fuel filter and another the spring in my regulator had broken. I think at one time I had a stock type regulator that was adjustable but it maxxed out at 11 or so psi.
In this case I don't think the fuel pump is an issue but could be. We found running pressure was usually not an issue BUT dead head pressure was. Causing sluggish performance on high demand and hard starting hot due to vapor lock. Connect a known accurate fuel pressure gauge at the fuel filter. Allow vehicle to reach operating temperature. While watching fuel pressure temporary clamp off return line and you should see a spike of about 18 PSI or so
 

MrSony

Geezer
Thread starter
Nov 15, 2014
6,494
113
Des Moines, Iowa
Installed a new map sensor, no change.
I noticed the distributor cap was wobbling while running and I noticed one of the mounting screws was snapped off in the distributor housing. Also the rotor wasn't on all the way and it was grinding in to the cap. The stem the rotor sits on was all crusty and pitted. Cleaned it up but had to stop working to eat dinner with the gf. Work will resume tomorrow after work.
 
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CopperNick

Royal Smart Person
Supporting Member
Feb 20, 2018
2,382
113
Canada
Might be time to revisit the throttle body and make sure all the screws and bolts are tight and no air is getting by any of the gaskets or seals. it could be a loose screw or maybe a warped or nicked gasket surface that is allowing air to get sucked in when you whack the throttle lever. Apart from the code you mentioned, has the diagnostic reader shown or thrown any others??



Nick
 

MrSony

Geezer
Thread starter
Nov 15, 2014
6,494
113
Des Moines, Iowa
Might be time to revisit the throttle body and make sure all the screws and bolts are tight and no air is getting by any of the gaskets or seals. it could be a loose screw or maybe a warped or nicked gasket surface that is allowing air to get sucked in when you whack the throttle lever. Apart from the code you mentioned, has the diagnostic reader shown or thrown any others??



Nick
No. No CEL either.
 

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