350 TBI Swap Hiccup :/
 

What up boys?

I hope y'all doing great. I am just about to finish up my 2 years build, finally! :metal:

In this final stage of swapping the motor, I ran into a wiring problem(s). I got everything of a '90 Silverado 2WD (motor/trans/harness). I did an inline fuel tank set up, instead of the gas tank from the donor truck.

That being said, my problem is the injectors are not getting power. Motor will crank and run if I pour gas into it, but that's about it. I tried tracing the issue. But then figured out that half of the fuse box is not getting power.

Here's a video to show the fuse box issue:

I have also checked the ECM, power is coming in, but no power is going out to the injectors. I have tested everything using a test light. Check this video as well:

I have tested pins [B1,C16] for 12v from battery, and it is indeed coming to the ECM. But when I checked the injectors [pink/black] wire. There was no power. Even though there's power in the fuse box to "INJ A+B"..

Please if you have an idea how to deal with this issue let me know!

Thank you!

Re: 350 TBI Swap Hiccup :/
 

Try reading some of these to solve your problem.

https://www.google.com/search?domain...D%3A1%3B&hl=en

Re: 350 TBI Swap Hiccup :/
 

Thanks. I did search everywhere. Looked at all the diagrams I got, but no luck so far.

Re: 350 TBI Swap Hiccup :/
 

In the first thread I linked you to, there is a post by ChevyTech where he states that he knows this system backwards and forwards. I would advise you to PM him and ask for his opinion.
You might also get more help in the 88 to 98 boards if you start a thread there.
I wish I could be of more help.

Re: 350 TBI Swap Hiccup :/
 

Thank you! PM sent!! :banghead:

Re: 350 TBI Swap Hiccup :/
 

You're welcome, and I would be curious to know the outcome as I always like to learn.

Re: 350 TBI Swap Hiccup :/
 

Hi NF6,
I got you PM.

The injectors should have power to them when ever the key is on. There is a fuse in the fuse box for the injectors.

The ECM grounds the other side of the injectors to make them spray fuel.

Half the fuse box not getting power can be from a burnt fusible link out under the hood on the passenger side of the firewall. Lose nuts at the junction box can also cause this problem. Another thing that can cause that on these trucks is a bad ignition switch which is at the lower end of the steering column. A rod comes down from the top end. Don't tare into the upper end of the column to fix it.

The scotch locks under the hood are a No No in my book. I won't probe wire insulation because it can lead to corrosion problems making opens in the wire in the future.

I am crazy busy, and have not been making it to the boards lately, but if I can find some time over the next days I will look at a schematic for your truck and get back to this thread.

CT

Re: 350 TBI Swap Hiccup :/
 

Hi CT,

I will be checking the fusible links today to see if one of them is burnt. The injectors do get power at the fuse box, I have tested their fuse using a test light and I showed that in the first video I posted. But when I check them at the injectors end point there's no power at all.

I checked couple of diagrams, and they show that there are fuses that should be "hot at all times", but those aren't hot, but maybe as you said, it might be one bad fusible link.

For the ignition switch, I am using the original 70 switch, I rewired it and it seems to be working. Because when I crank it, it does work and if I pour some gas in the TBI, the truck runs then dies of lack of fuel.

I did use scotch locks to ground two things temporarily where it connects to the ECM. I thought ground was the issue at first, that's why I went with them scotch locks. But the issue seems that it isn't a ground.

It is confusing. I understand how busy you're and I appreciate you getting back to me. Please get back to me when you get a chance!

-Naz

Re: 350 TBI Swap Hiccup :/
 

Anyone knows where this purple wire go? It is located near the intake, on the driver side.

Please check the attached picture.

Thanks.
-Naz

Re: 350 TBI Swap Hiccup :/
 

Scotch locks, Poking of wires, the use of the cheap test light........I just cringed watching your videos.

As ChevyTech said, the injectors are powered in ignition/run/crank. If there is not power on the injector leads the circuit is open.

O2 sensor? Won't keep it from running.

Re: 350 TBI Swap Hiccup :/
 

Hi Bigdav160,

Thank you for your reply.

Haha, I am using my buddy's garage as I don't have one at the moment. I just used whatever could identify the issue. Of course, all them scotch locks are temporary until I find a solution.

I am positive it is an open circuit, because it ran and it was running before I pulled everything out. No luck so far finding the reason.

The O2 sensor, is plugged already, unless it the other end of it. Hmm.. :barf:

-Naz

Re: 350 TBI Swap Hiccup :/
 

You are going to have to trace the power wires for the injectors from the fuse box out to the TBI unit. I would be looking at the connector that was on the passenger side in the donor truck just before the big harness goes out through the wire wall to the engine compartment.

The TBI trucks had multiple power supply circuits through the ignition switch.

The purple wire in the photo is an oxygen senor wire. Earlier TBI trucks had the O2 sensor on the passenger side and later it was move to the drivers side.

For the lack of power in part of the fuse box the first place I would look is the first two fusible links on the left end of the junction block.

Re: 350 TBI Swap Hiccup :/
 

I hooked up the 90 switch back and that helped the A/C fuse get power, other than that, still got the no power to the rest.

I checked all the fusible links. None was bad. Power runs through them.

--

I figured if I jumped the injectors, they would work. So, I hooked up a 12v to them and that gave them power, but then the ECM isn't grounding them for some reason. Even though power is getting to the ECM. Does that mean I got a bad ECM?

Thank you,
Naz

Re: 350 TBI Swap Hiccup :/
 

I doubt the ECM is bad. They don't fail very often.

If power is not getting to the injectors, then power may not be getting to all the power circuits to the ECM. There are multiple power circuits that supply the ECM.

Here is a link to a ECM connector pin out chart that should be correct for the 1990 system you have.

http://www.wedgeparts.com/images/747ecm1.jpg

Re: 350 TBI Swap Hiccup :/
 

Make sure you have ref from the distributor. The injectors won't fire without rpm signal.

Re: 350 TBI Swap Hiccup :/
 

Thank you guys for your replies. I apologize about not getting back to y'all.

I tried messing with it for few weeks, even with the help of couple of buddies. No luck at all. I found a used stand alone harness for a hundred on Ebay, it was cheaper than taking it to a shop. Boy, she fired right up.

Again, thanks for the responses and help!
Naz