1990 K1500 Runs... Kinda

stew86MCSS396

Apprentice
Aug 1, 2022
94
33
(808)
Couple of thoughts...did the rebuild of the throttle body include rebuilding the fuel pressure regulator? Good idea to get a read on fuel pressure and not assume it's good because you have a new fuel pump or a fresh rebuild of the FPR. Kinda pain in the arse to get fuel pressure reading as these TBI trucks, you gotta remove the fuel filter and add a "T" that the gauge attaches to.

I saw the "open" loop, too but some 1227747 tunes have open loop idle. These ECMs are incredibly slow spitting out data points once every 2 seconds. With that said, your O2 volts stayed solid @ 668 mv which tells me your a little rich on fuel. Why no cross counts...could be the open loop idle??? Maybe put your foot in it to see if it will transition to closed loop at which the O2 should start swinging.

IAC steps 39 is probably okay but I'd like to see it near 10 on a fully warmed up engine. More air through the throttle blades vs the IAC helps shear the fuel and aids in better atomization.

Are the symptoms still there after fixing the issues with the distributor cap/rotor???
Edit: Shortly after posting, I went searching for this. Basically some of the open loop idle parameters. Seems like it targets a richer than stoic afr hence the higher O2 volts. Also, it appears the vehicle needs to be moving to get it into closed loop.

1project2many;54951 said:
This may take some trial and error but you could start by comparing these values from the ASDU disassembly with your calibration:

Code:
; OPEN LOOP IDLE CALIBRATIONS
 ; L05
 ;
 ;----------------------------------------------
LD29E FCB 4 ; 4 MPH, OPN LP IDLE THRESH
LD29F FCB 5 ; 2%, OPN LP IDLE THRESH TPS
LD2A0 FCB 1 ; 25 RPM, Open loop RPM thresh IDLE OFF
LD2A1 FCB 2 ; 50 RPM, Open loop RPM thresh IDLE ON
LD2A2 FCB 160 ; 8 Sec's, Open loop IDLE AFR Ratio enable TIME DELAY
LD2A3 FCB 100 ; 5 Sec's, Open loop IDLE AFR Ratio TIME DELAY
LD2A4 FCB 137 ; 13.7 Open loop AFR MAX AT IDLE
 ;----------------------------------------------
 
Last edited:

MrSony

Geezer
Thread starter
Nov 15, 2014
6,487
113
Des Moines, Iowa
Couple of thoughts...did the rebuild of the throttle body include rebuilding the fuel pressure regulator? Good idea to get a read on fuel pressure and not assume it's good because you have a new fuel pump or a fresh rebuild of the FPR. Kinda pain in the arse to get fuel pressure reading as these TBI trucks, you gotta remove the fuel filter and add a "T" that the gauge attaches to.

I saw the "open" loop, too but some 1227747 tunes have open loop idle. These ECMs are incredibly slow spitting out data points once every 2 seconds. With that said, your O2 volts stayed solid @ 668 mv which tells me your a little rich on fuel. Why no cross counts...could be the open loop idle??? Maybe put your foot in it to see if it will transition to closed loop at which the O2 should start swinging.

IAC steps 39 is probably okay but I'd like to see it near 10 on a fully warmed up engine. More air through the throttle blades vs the IAC helps shear the fuel and aids in better atomization.

Are the symptoms still there after fixing the issues with the distributor cap/rotor???
Edit: Shortly after posting, I went searching for this. Basically some of the open loop idle parameters. Seems like it targets a richer than stoic afr hence the higher O2 volts. Also, it appears the vehicle needs to be moving to get it into closed loop.
I cleaned out the cavity for the fpr cleaned the rust off of the spring and replaced the diaphragm which was caked in varnish and rust. Truck has been stationary for most of the 14 years my grandparents have had it. It last extensively ran in 2020.
 

MrSony

Geezer
Thread starter
Nov 15, 2014
6,487
113
Des Moines, Iowa
The truck is running rich I can confirm that. The injectors seem to be dribbling moreso than spraying. The truck has sat most of its time in my grandparent's hands, but has 220,000 miles on it. I doubt they've put more than 5,000 miles on it themselves. I'm not opposed to buying new injectors but I don't think they're the issue. Engine idles fairly well but just will not rev at all. Tries to stall and will cough but come back to idle if I let off. If I hold the throttle open at all it will eventually act like it runs out of fuel when it's visibly still dribbling. I can slowwwwly get it to about 1800rpm before it wants to stall.
I will report back once the distributor situation is fixed. Cap wasn't affixed properly due to a broken screw, and the rotor wasn't installed all the way down so it was physically touching the cap.
 

Supercharged111

Comic Book Super Hero
Oct 25, 2019
3,940
113
Colorado Springs, CO
The truck is running rich I can confirm that. The injectors seem to be dribbling moreso than spraying. The truck has sat most of its time in my grandparent's hands, but has 220,000 miles on it. I doubt they've put more than 5,000 miles on it themselves. I'm not opposed to buying new injectors but I don't think they're the issue. Engine idles fairly well but just will not rev at all. Tries to stall and will cough but come back to idle if I let off. If I hold the throttle open at all it will eventually act like it runs out of fuel when it's visibly still dribbling. I can slowwwwly get it to about 1800rpm before it wants to stall.
I will report back once the distributor situation is fixed. Cap wasn't affixed properly due to a broken screw, and the rotor wasn't installed all the way down so it was physically touching the cap.

Thinking back, my friend had issues with his after sitting for a while. We rebuilt the TBI and it was still a turd. New injectors were the fix. Truck just wouldn't stay running.
 

stew86MCSS396

Apprentice
Aug 1, 2022
94
33
(808)
Supposedly you can use a timing light pointed at the injector to see the spray pattern as it's pulsed at the same time. Fuel shouldn't be dribbling out instead it should look like the picture in this thread...
 
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Supercharged111

Comic Book Super Hero
Oct 25, 2019
3,940
113
Colorado Springs, CO
Supposedly you can use a timing light pointed at the injector to see the spray pattern as it's pulsed at the same time. Fuel shouldn't be dribbling out instead it should look like the picture in this thread...

Not supposedly, it definitely works.
 

ck80

Comic Book Super Hero
Feb 18, 2014
4,602
113
TBIs aren't like normal fuel injection either, running wise. It's so simple and dumb, you can have a weak fuel pump that pushes enough at idle but not keep up with throttle.

With the truck sitting THAT long, have you dropped the tank yet, made sure there's no rust scale, co tamination on the sock, etc?

Fuel pump is cheap on those. Drop the tank, clean it up, new sock, new pump, then new soft rubber brake hoses all around. Upgrade the rear cylinders to the oversize ones.

You've had bad luck with vehicles through the years. Go system by system and drop $200 on rockauto close out parts on it.

Youre already doing cap/rotor/coil/plugs/wires. Whatever you havent of new fuel pump/sock, new brake hoses/pads/shoes/cylinders, new radiator hoses/thermostat, new setp belt. New antifreeze, trans fluid and filters. Probably one solid balls-out weekend of work. Then tires. It'll be ugly at that point, but pretty reliable which is what you need in your life.
 
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MrSony

Geezer
Thread starter
Nov 15, 2014
6,487
113
Des Moines, Iowa
TBIs aren't like normal fuel injection either, running wise. It's so simple and dumb, you can have a weak fuel pump that pushes enough at idle but not keep up with throttle.

With the truck sitting THAT long, have you dropped the tank yet, made sure there's no rust scale, co tamination on the sock, etc?

Fuel pump is cheap on those. Drop the tank, clean it up, new sock, new pump, then new soft rubber brake hoses all around. Upgrade the rear cylinders to the oversize ones.

You've had bad luck with vehicles through the years. Go system by system and drop $200 on rockauto close out parts on it.

Youre already doing cap/rotor/coil/plugs/wires. Whatever you havent of new fuel pump/sock, new brake hoses/pads/shoes/cylinders, new radiator hoses/thermostat, new setp belt. New antifreeze, trans fluid and filters. Probably one solid balls-out weekend of work. Then tires. It'll be ugly at that point, but pretty reliable which is what you need in your life.
I already dropped the tank and put in a new pump and sending unit. Has new plugs wires cap rotor already. Brakes were already redone. New lines and rubbers.
 
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MrSony

Geezer
Thread starter
Nov 15, 2014
6,487
113
Des Moines, Iowa
The rotor contacting the terminals and grinding into the top of the cap certainly I think would make it run funky.
 
Oct 14, 2008
8,310
113
Melville,Saskatchewan
Yeah, try a new cap and rotor again, if that is the case. I had that happen on my 5.9 Magnum, ran shitty. Then a new Accel cap and rotor over the cheap local part store one that replaced the eaten up one and it ran even better. Don't cheap out on the cap and rotor. Get an Accel, Blue Streak or another brass high quality one. For whatever reason, those small cap HEI are hard on caps and rotors. Yeah, those TBI are basic and simple EFI. I even got an Olds 350 to run real good in closed loop with an extra 20 degrees of timing. Cold loop wasn't as nice, that is where it needed a custom tune. That is why the circulating block heater was used that burned the truck to the ground. Nice truck by the way, keep at it.
 
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