1989 GMC Sierra ST. Aaaand now I have 3.

[Jrgunn5150]

That wire coming off the coil that is just sitting there is probably your tach wire.

Don't TBI trucks only have two wires like the older distributor's?

 

[Justin S]

i looked up the diagram, and yes, it must be for the tach signal. This cluster doesn't have a tach, so not sure where it went to. This coil has 2 plugs with 2 wires each going to it. One plug goes to the distributor.

 

[Dylan1991_1500]

Yep, you can splice an aftermarket tach right to that wire. I plan to do that with the tach that you gave me for Bob1500. MSD makes an inexpensive blaster coil for these trucks that are a direct replacement for the one on it now, uses the same brackets too. That's if yours is bad of course.

 

[Justin S]

After doing a few things this morning and taking a test drive, it seems like the ignition issue is fixed, I cleaned the cap/rotor, removed the ignition control module and cleaned the connection points, etc. It still seems to lose steam under heavy load, and if I unplug each injector one by one, one would cause it to stall, the other one wouldn't. That makes me think one is clogged, so I took apart the throttle body and cleaned everything up. One of the screens was covered in gunk, so I'm thinking that was part of the problem. Only issue now is the injector O rings are all stretched and I can't get them to sit back in place, so I think i'm going to buy the overhaul kit from advance auto and throw it all back together.

 

[Justin S]

So I took the whole throttle body off, and I found an open port on the backside between the fuel lines, not sure what it was meant for, but it was definitely not helping it run any better! Popped a vacuum cap on, and will throw everything back together tonight and see how it does. I also did some hood swapping.

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[dave_erald]

While you got it apart did you take the pressure regulator apart as well? They were bad for splitting the diaphragm and breaking the spring

 

[Justin S]

While you got it apart did you take the pressure regulator apart as well? They were bad for splitting the diaphragm and breaking the spring

Yes I did. the diaphragm and spring were fine, but the rebuild kit i'm getting comes with a new one too. I think I might also do the "quarter mod" while its all apart just for the heck of it.

 

[Dylan1991_1500]

That port is part of the PCV system.

 

[Justin S]

Ok, finished the TBI rebuild and quarter mod, and it definitely runs better, but now it's back to having the spark issue. There was a point where it went from roughly 4000rpm all the way down to what felt like it stalled, then stumbled back up and ran better, all while the gas pedal was all the way down. I might throw a coil or ICM at it to see if it changes anything.

 

[Justin S]

Ok made some big improvements to the acceleration. I got a dealer plate to take it to work in the morning, and figured i'd drive it to the local gas station a few miles away first. It would break up under load still. I put 6 gallons in the tank (I had put about 4 in before) and it IMMEDIATELY made it run way better, I wonder if it was just because the gas was sloshing around it wasn't able to hold pressure. It runs so much better, aside from a slight bog at mid range. The CEL popped on, and got a code 43 for the knock sensor, which I bet explains the bog. I'll have to go out and look, but my guess is the connection is bad/non existent judging by everything else i've found.. Still had a code 22 for the TPS, but right now i'm gonna stick with the fact that its there because I unplugged it while running to see if it changed anything.