Completely stumped with TBI prob

[Madbomber88]

Ok, just finished installing a TBI conversion on my 72 K20 using a new painless harness and donor everything else.



Here's the problem...

It will start and run fine, but will not turn off. Everything else turns off (radio, heater, etc...) when I turn the ignition on, but the truck keeps on running. THe pink/black wire from the computer that is labeled "connect to ignition" is what powers the computer in the harness. I have connected that to a million different feeds that are only hot on start and run. But when you connect it to the pink wire, it fires up and runs, but stays hot when you shut it off. What does this mean?

[Deuce]

For trouble shooting sake try a wire from the battery with a toggle switch for any power wires to see if it still does the same thing.

[rage'nrat638]

I HAD A SIMILAR PROBLEM AFTER I INSTALLED MY MSD IGNITION..
i had to install the supplyed resistor after the alternator seemed just the littlest power from the alt spinning was enough to keep the truck running.

you might have a similar problem with the new wiring try pulling the wire on the alt after the keys turned off and see it the engine quits

just a thought

[Madbomber88]

Well I've tried all of that and still no luck. no matter what wire I hook that pink wire to, it makes it hot after running and turning the key off, but not off when it isn't running.

I have no clue but have temporarily gotten past it by installing a simple switch to kill it. So now I have to turn the key off and then flip the switch to turn the truck off...

[tallhoedude]

Any More Pics Or Infor On The Tbi Swap?im Getting Ready To Do This,just Not Sure Of Using Factory Harness Or Painless Kit.you Said You Used Both?mind Telling/showing What You Did?thanks

[Myself]

I've experienced this run-on before in older vehicles. It's generally caused by a small amount of power backfeeding through the instrument cluster. A one-way diode attached in-line will cure the problem.

[Madbomber88]

Hmmm...that might work, I'll give that a shot, thanks!

tallhodude, no pics yet but I will try to get some up tomorrow. I used a new harness from Painless and definitely recommend it, it is really easy to use. I also used a new painless harness for the truck wiring since I didn't want to hook up a nice new efi harness to the 34 year old wiring in the truck.
Talk about a spaghetti mess of wires...
other than that I used all donor parts from a 91 K5. Good thing too because I had to take the fuel pump relay off the used harness. I hooked everything up but bypassed the neutral safety switch, and knock sensor.
If you have any specific questions, let me know and I'd be happy to answer.
-Tim

[Madbomber88]

What size diode do I need?

[stsalvage]

what a about a voltage drop that the old trucks us to us but i hate computer crap

[High Speed low Drag]

I'm kind of slow abd maybe you already tried this but.....

Hook it to a circuit that is ONLY hot on the START position. Either that or you'll have to get a diode for the alternator and power it off of that.

[Greubin]

Originally Posted by Madbomber88

Hmmm...that might work, I'll give that a shot, thanks!

tallhodude, no pics yet but I will try to get some up tomorrow. I used a new harness from Painless and definitely recommend it, it is really easy to use. I also used a new painless harness for the truck wiring since I didn't want to hook up a nice new efi harness to the 34 year old wiring in the truck.
Talk about a spaghetti mess of wires...
other than that I used all donor parts from a 91 K5. Good thing too because I had to take the fuel pump relay off the used harness. I hooked everything up but bypassed the neutral safety switch, and knock sensor.
If you have any specific questions, let me know and I'd be happy to answer.
-Tim

Hi Tim,

Just curious what the parts ran you for the TBI? I'm contemplating this upgrade

[Madbomber88]

I got everything from a donor truck for $100 (this included intake, complete harness, computer, all sensors, TBI, distributor, all necessary brackets, and air cleaner assembly. The painless harness was the most expensive aroun $300. I had to modify the intake to match my heads, and that was no fun.
Other than that, the fuel pump from arizonatpi.com was about $175 or so but is a quality Walbro and came with both inlet and outlet filters. Lastly I bought some good aeroquip socketless fuel tubing that was simply awesome.

[Greubin]

Originally Posted by Madbomber88

I got everything from a donor truck for $100 (this included intake, complete harness, computer, all sensors, TBI, distributor, all necessary brackets, and air cleaner assembly. The painless harness was the most expensive aroun $300. I had to modify the intake to match my heads, and that was no fun.
Other than that, the fuel pump from arizonatpi.com was about $175 or so but is a quality Walbro and came with both inlet and outlet filters. Lastly I bought some good aeroquip socketless fuel tubing that was simply awesome.

Thanks for the info. What was the reason behind modifying the manifold? What engine are you running?

Thanks again

[red71cheyenne]

Newer heads have different angled bolts. Have to either shim the bolts or modify the manifold to match.

[Greubin]

Ah ok that makes sense. I was surfing the trans-dapt website. Looks like they offer a carburetor-TBI manifold adapter plate..I wonder if that would work with an Eddy Performer manifold and TBI ?