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Really regretting TBI swap.

79rustyk10

79rustyk10

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Cant get this POS to run right, has had a terrible off idle stumble since the swap 5 years ago, I can floor it, and it will pop and run on a cylinder or two for a while and it might eventually take off. runs OK at WOT if it can it there. Its borderline immobile.

Didnt have vss hooked up at first, but got that taken care of with no change

Replaced TPS, no change.

Overhauled the throttle body, newer injectors since the ones in it had large amounts of rust and scale in the little screens. added the CFM tech adapter and pressure gauge. has 12 PSI at idle, good spray pattern from the injectors. It starts right up better than before, but if I snap the throttle open it stumbles like normal.

Theres also no CE light for any of this. All I can think now is that its an ignition issue.

I havent had a scanner on it yet. Thats the next step.

Any ideas?
 
What injectors are in it? There is a part number on the tops of the injectors (sometimes hard to see with a magnifying glass) and "supposed" to be a color code to the injectors but the part number is what you really need.
 
You need an old school scanner. I had replaced everything due to a crapy idle and occasional backfire. No CE light or codes. When I was at jason4x4's house in Pheonix, he scanned it. No TPS output.????

Wires were bad at the broken plug. Put a new plug end on and it has been great since.
 
off idle stumbling, I always check the EGR...
 
4X4HIGH said:
What injectors are in it? There is a part number on the tops of the injectors (sometimes hard to see with a magnifying glass) and "supposed" to be a color code to the injectors but the part number is what you really need.
Click to expand...

I dont remember a color code, and the truck is 2.5 hours away at my parents place for the time being. Injectors came from a 95 1/2 ton though.

ktmoutfront said:
You need an old school scanner. I had replaced everything due to a crapy idle and occasional backfire. No CE light or codes. When I was at jason4x4's house in Pheonix, he scanned it. No TPS output.????

Wires were bad at the broken plug. Put a new plug end on and it has been great since.
Click to expand...

I'll have to check into that.

ryoken said:
off idle stumbling, I always check the EGR...
Click to expand...

Its not so much an off idle stumble, as off idle dying for the most part. Its very hard to keep it running. Could the EGR cause that?

When I have some more time, I will get a scanner and some coolant, go out and try to diagnose more. Its been almost a year since the thing has ran. Just sucks being so far away from the truck and trying to do this.

We will be hauling it to a friends place in the next month or so, I will have alot more time to mess with it there also. Gonna try to get it setup to have something to beat on at the farm this summer.
 
If I were to convert back to a carb, what would be the best fuel pressure regulator to be able to keep the return line functioning? If I were to do this, I would like something mounted probably on the firewall, to keep things cleaner on the engine.
 
95 TBI systems use a different pressure and flow vs the older style. That could be your problem right there. Unless you used a 95 donor truck with that 95 computer.
 
454Sub said:
95 TBI systems use a different pressure and flow vs the older style. That could be your problem right there. Unless you used a 95 donor truck with that 95 computer.
Click to expand...

This is why I asked about what injectors he installed.
 
The donor was an 88 K5 blazer.

interesting that the 95 injectors are different. Looks like i'll have to track down a pair of earlier ones. Its too bad too, that day I was at the yard, that was the ONLY TBI vehicle there that had the injector pod and injectors still.
 
how have the plugs looked/run? a plug reading would show that...
 
I havent pulled the plugs. They are the ones that were in the K5 when I pulled the engine I believe.
 
yeah, invaluable oldschool diagnostics, usually overfueling will soot em up, even leave em wet if bad enough...
 
I would also be quite suspect of the distributor if it is the original. They get sloppy with time and don't work properly anymore. I'd also check the throttle shaft bushings for vaccum leaks. I've seen that a lot on TBI rigs up here lately... As mentioned above, make sure that you have the right injectors in your truck to match your ECM and fuel pressure!
 
Second the distributor. My buddy has an 89, idle was low, occasional stalling, falling on it's face etc etc. We went through everything before finding the dist pretty much ground itself to rusty colored dust under the cap. The rotor itself looked fine, as did the cap...but everything under that was junk. We swapped out dist's with a good one I had lying around and it runs like a dream again.
 
Was looking at Rock auto, and it looks like the injectors interchange according to them, Ill have to do some more digging on that topic.

They also have a reman distributor for $67. Made by world power systems, never heard of that brand before... Might give it a shot.
 
post this in the injection section also...great bunch of folks in their with lots of knowledge :waytogo:

don't give up on this...there's been hundreds of swaps done successfully. When you find the problem I'm sure it will be something "small".

I would start by checking my grounds and power feeds, then all my connectors.
 
Don't give up for sure. TBI is the good stuff. Probably something simple. Like Ryoken said though. Go back to old school diagnostics.
 
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