TBI coil and other questions

[kevinr1970]

Appearently we unplugged the harness that goes from the distributor to the "coil" on my engine when we swapped them. The coil takes one plug from the distributor and one from the main harness and the plugs (and recepticles) look identical. How do I tell which side of the coil to plug which harness into?

The previous engine had a smog pump and the new engine doesn't. There is a plug on the harness for the pump. What should I do with this plug? Is it going to affect the brain not getting a reading from this? If so, what can I do to deal with this; if not should I just leave it hanging there or is there a (easy) way to remove it?

More questions to come I'm sure...

[piecesparts]

Are you absolutley sure the coil plugs are identical? Look to see if there is a slot or tab on on plug that the other doesn't have, and then check the coil to see if there are related spots on them that will take those tabs/slots.

I am not sure about the smog pump, but there is a great possibility that the pump being gone is not an issue. If so, then, I would follow the wire back into the harness and clip it and close of the end with a solder joint and heat shrink.

[kevinr1970]

I am going to look real closely when I get off work to be sure, maybe I was tired last night when I was looking at it, but they looked the same.

My other problem at the moment is the plug wire for the coil is too short. The coil was on the passenger side on the 4.3 and on the driver for the 5.0. I think on the V8 the EGR(?) is where the coil is on the V6.
There was a similar problem with the wire/plug for what I think is a temp sender. The V6 was located on the driver side and the wire ran through the sheathing in that direction. The V8 sender is located on the passenger side in front of the starter. I noticed this before we put the engine in so I was able to cut the wire, pull it through all the clamps and sheathing and splice it back in where it is now needed.
Unfortuneatly I didn't see this for the coil plug. The wire for the coil plug is a real heavy gauge wire so I am not so comfortable cutting and splicing that one? I guess I'll just have to open the sheathing and see if I can't get some slack for it; it is only about 3" too short.

[Russell]

You will need to have the smog pump disabled in the prom, or you'll have dangerously lean mixture issue. The ECM looks for a leaner 02 sensor reading when the AIR system is enabled, but if it doesn't see it, it will lean your mixture out until it gets it.

As far as the coil goes, the connectors do look the same, and they are, but they are a mirror image of eachother. They should only go on one way

[kevinr1970]

Then that should make its self obvious when I try to plug them in.

For the prom, how do I disable it?

Originally Posted by Russell

You will need to have the smog pump disabled in the prom, or you'll have dangerously lean mixture issue. The ECM looks for a leaner 02 sensor reading when the AIR system is enabled, but if it doesn't see it, it will lean your mixture out until it gets it.

As far as the coil goes, the connectors do look the same, and they are, but they are a mirror image of eachother. They should only go on one way

[Russell]

When you load the prom, look for the minimum coolant temp to enable the AIR system. Set that value to hex value FE (254 in decimal) or, some rediculously high temperature that you'll never reach without blowing the engine up. It will simply not even try to activate the AIR system, effectively disabling it

[kevinr1970]

Since that made absolutely no sense to me, I will assume you think I have some way of altering the code or program or something????
Sorry, I am just some back yard, weekend mechanic trying to do an engine swap !
Is this something someone local can do or will I need to send it to one of these TBI experts?
BTW, thanks for the input!!!

Originally Posted by Russell

When you load the prom, look for the minimum coolant temp to enable the AIR system. Set that value to hex value FE (254 in decimal) or, some rediculously high temperature that you'll never reach without blowing the engine up. It will simply not even try to activate the AIR system, effectively disabling it

[Russell]

Sorry, the way you worded it you seemed to know what was going on with prom burning, lol

If you can find someone local with a UV eraser and a burner, then yeah, someone local can do it, and would probally do it free if you were only disabling AIR. I personally would avoid sending it to some big time online chip company, they'll want at least 50 bucks to change it out. Maybe check out the local dyno equipped shops that do EFI tuning. They'll likely be able to help you out

I'd do it for you, but I dont have UV eraser to erase the TBI style chips. All of my chips are Flash EPROMS which can be erased electronically in my programmer.

[piecesparts]

I would contact somone like Street and Performance, TPIS, or Howell Engineering and find out what data they would need to burn a new prom. Then I would get ahold of someone that has a Snap-on data scanner (or equivalent) and take the vehicle for a drive. Write the data down and have it sent to whomever you contacted. They will burn your new chip.

[kevinr1970]

Originally Posted by Russell

Sorry, the way you worded it you seemed to know what was going on with prom burning, lol

I like to sound smart!

I guess I'll just try to get it to a point where it fires up this weekend, then I'll deal with that.

!!!EDIT!!!
OK, so maybe I am stoopid sometimes?!? Did I mention previously that I pulled the computer/box/brain out of the donor truck and was planning on installing it in the recipient truck???
Will this help the situation? Or is this even a good idea?
The only difference I see besides the location of two parts is the smog pump lead. The donor truck never had a smog pump. At least it doesn't now nor does it have bungs on the exhaust manifolds?

[Russell]

If the donor truck didn't have a smog pump, had the same displacement and the same service number on the ECM, then just use the donor truck's ECM, and you'll have no worries!

ECM = Computer BTW

[kevinr1970]

Originally Posted by Russell

If the donor truck didn't have a smog pump, had the same displacement and the same service number on the ECM, then just use the donor truck's ECM, and you'll have no worries!

ECM = Computer BTW

Yes!
I drove the donor truck home so it is the same ECM that was running the engine before. It did not have a smog pump and if I read the decal on the core support correctly it never did?
Thanks again for the input!

[Russell]

If the service number is the same on the ECM, you'll be good to go

[kevinr1970]

Originally Posted by Russell

If the service number is the same on the ECM, you'll be good to go

I am confused?
When we pulled the engine from the donor truck, we took the complete harness all the way back to the ECM (the box under the dash, behind the golve box).
I was going to put this box in to the new (well, not really new...) truck in place of the one that is there now.
If the service number is the same as what??

[Russell]

Ah, in that case, no worries, you're already good to go, and don't need to worry about the AIR stuff at all

For some reason I assumed that the truck already had EFI

[kevinr1970]

Maybe I am confusing you with what I am telling you???
The donor and the new truck are both 1987 1/2 ton 2 wheel drive.
They are both TBI, although the donor truck was a well optioned Silverado with 305 (no AIR) and the new truck is a spartan Custom Deluxe (I think?) with a 4.3 (v6 w/AIR).
The donor was an automatic and the new truck is a 3 speed manul (granny/compound low).
I was going to swap the complete harness and box (ECM?) from the donor but at the time that looked like more trouble than it was worth so we hooked the harness that was in the 4.3 truck to the 305 engine. I am hoping that all I have to do is swap the box (ECM?) behind the glovebox and I will be done?
I am sure I say something that makes it seem like I might know what I am talking about, but I usually know just about enough to be dangerous!
So I guess what I am saying is that the truck DID already have EFI???
Am I confusing it even more now?

Originally Posted by Russell

Ah, in that case, no worries, you're already good to go, and don't need to worry about the AIR stuff at all

For some reason I assumed that the truck already had EFI

[Russell]

Ahhh, it all makes sense now!

As I mentioned earlier, you will need to be checking that the computers from each truck are the same service number (the 305 will be 1227747, make sure that the 4.3 ECM is the same) and also compare the ECM connectors from each truck to make sure that they are pinned the same. I have a hunch that they will be, but I am not 100% sure on that point.

4.3 and 5.0 TBI are very similar systems, with many components interchanging, so I'd say you thought well to use the 4.3 harness on the 5.0, just need to make sure that they are both wired the same way, and you should be good to go after that point

Switching from an auto to a standard shouldn't cause much greif. Technically you should be changing the prom (which is the chip) out for one with a manual, but I don't think it will cause any noticeable driveability issues. You will just need to make sure that the ECM thinks that it is in drive all the time, not in park by hooking the orange / black wire that runs from the park neutral switch to the ECM straight to ground.