IROCZ28KevinZ

iTrader: (2)

I have a 1988 GTA that has been converted to the 1992 speed density TPI setup. I am about to undergo a TPI to carb swap and it is my understanding that some of the TPI harness needs to stay to run things like the fuel pump and gauges. Car has a 5 speed so no torque convertor to deal with. I don't want to hack up my harness since it was like brand new when i got it, and my friend would like to get it.

My question here is, and this is just based on some thinking I've been doing: can I get and use a engine harness from a carb'd f body and just make small mods to the wiring for it to work right in my 88, then remove wires that aren't used since my carb I have is all mechanical, no electric choke or anything? Thanks for any help you all can give!

groundrat

iTrader: (3)

I would get a engine harness from a carb'd car. Just to make it clean and easy. However there will be a few things not used on that one as well seeing as you wont be using a computer controlled car. Do a couple searches in the Carb board and the TPI board. Are you planning on running the electric fuel pump? If so you will need a good regulator as that pump will drown your carb lol.

IROCZ28KevinZ

iTrader: (2)

Thanks for the reply. I swear I saw one of those harnesses for sale somewhere, what would be nice is if i could find one from like an 85-87 bird that had an electric speedo like my 88 does. i do plan on keeping the TPI pump in the tank and using it, I am also aware of the need for a pressure regulator that also feeds excess fuel back to the tank.

Zepher

iTrader: (1)

I personally would remove the tpi pump and slap a mechanical pump in the block, otherwise you will have to hack up the harness as the fuel pump relay is part of the engine harness.
I did the opposite 9 years ago on my 86 Trans Am, went from carb to tpi.

camaronewbie

You won't have to hack up anythinmg using the TPI pump. You just will no longer get the 2 second 'priming' function from the ECm and fuel pump relay. But that's not a problem either, since carb's hold fuel in thye bowls for starting purposes anyway, and the in-tank TPI pump will have plenty of fuel to the carb long before the carb bowls are emptied. The only time this even becomes an issue is when the car isn't started in a long time - sometimes (very rarely) the carb will use up the fuel in the bowls before the TPI pump gets more fuel to the carb - but in a few moments (after a few cranks) she'll crank right up.

This is the way my TBI in-tank pump works with my carbed 350 in my RS.

One other thing to consider. Having the stock wires in place from the TPI setup can be a blessing in disguise. I left my stock wiring in place when I went carbed, so I'd have easy access to pre-existing wiring from the interior cabin to the exterior engine bay - I've used them for all kinds of stuff from independent-controlled fan switches to fog lights to electric choke wiring to manual-on fan switches to exterior lighting. Anything that was too large a power drain for the small computer wiring I used as 12v on/off wires to power relays under the hood (ie foglights and fan switches). It's been great to have instant access to wires already running through the firewall for whatever accessories pop into mind. When I get finished (maybe never LOL) I'll take what's left out to better clean up the engine bay. But right now I just have the excess ECM wiring tucked away out of sight, but where I can still grab one if/when I need it for something.

Zepher

iTrader: (1)

TPI pump puts out 43psi and requires an expensive 3 port regulator to drop it down to 6 psi for a carb.
fuel pump relay is part of the engine harness and that harness is going to his friend so it needs to come out.

IROCZ28KevinZ

iTrader: (2)

Just thought I'd throw out an update here in case anyone else planned on ever doing this; they could find this thread with a search. I will be getting an 88 Firebird coupe parts car with a 305 TBI. I pulled out the 91 TPI harness from my car and thankfully, my friend did not modify what was in the car already; he modified the engine harness to match the car. He did modify the wiring for the buffer box for the speedo, but the original wiring is still in the car so I can fix that and bring it back to 1988 specs. The only question now is how close a 305 TBI harness is to a 305 TPI one as far as the pinouts on the driver's side firewall are concerned. I have the ones on the car side mapped out; now I need to map out the TBI harness to change anything that could be different.

On that note, anyone have the pinouts for the big firewall connector on the engine harness side for an 88 Firebird, 305 TBI, auto? I'd appreciate it!

Kevin91Z

iTrader: (1)

You have a nice '88 GTA and you want to devalue it by hacking it up for a carb conversion? Is this a race car?

If you want a carb car, just buy a car that came with a carb and save the TPI cars for those that appreciate them.

Its been my experience you cannot use wire harnesses from different years. From 82 to 87 GM had separate engine harnesses and body harnesses. In 88 they switched to one harness that controls everything and kept the same in '89. In 90 they changed again so 88-89 and 90-92 are not compatible at the firewall plug. I dont know how close an 88 TBI and 88 TPI harness are, but I would guess the firewall plugs would be identical since they're the same years... Dont take my word for it, though.

IROCZ28KevinZ

iTrader: (2)

Well tell ya what, you buy me the car since not everyone can just go out and buy one, and I'll take it. Also, last time I checked, the title has my name on it, so I can do what I want with it.

And also, this car had a 91 speed density engine harness swapped in, and everything worked as it should from the factory. I took that out and will be putting an 88 TBI harness into my 88 car so I can go carb.

John in RI

iTrader: (167)

It's been my experience that any ThirdGen Harness is a direct plug-in to the C100 fireweall connector on any other Thirdgen. I've personally converted TBI to carb, TPI to carb, MPFI to carb, and & Carb to TPI. Sometimes with complete ECM system and sometimes without.

There are differences from time to time that need to be overcome by either splicing or re-pinning, but any engine harness can be plugged in and made to work without too much effort.

From 82 to 87 GM used seperate Engine and ECM harness in the V8's. Starting In 88 the 2 harnesses were integrated into a single (HUGE) mass of spaggetti and some additional wires were added (fog light wiring for example ).

For the cleanest fit; try to find an engine harness from an 82-87 V8 car. There will be some differences from the 82-83 (wiper wiring), 84-86 (coil in cap / Electric Speedo sensor), and the 87 TPI harness (remote coil) but splicing or re-pinning a couple wires sure beats trying to hunt thru a TBI harness to find thegauge sensor & Engine wiring,....... IMO !

Kevin91Z

iTrader: (1)

Yes you can do what you want, but if its a street car, you're supposed to follow the emissions laws.

Yes the C100 connectors are the same on the outside, and will physically plug in, but the wires on the inside dont always match each other. That's what I meant. You could be plugging a ground from the engine harness into 12V power on the firewall.

John in RI

iTrader: (167)

Emssions laws are different in every state....... Mine allows for engine swaps and I'm sure otehr states do as well. We don't all live in CA. ( & I can think of several examples where CA has decided to turn it's back on the Federal Laws. ) One of my ThirdHens has NO CAT and the state just stuck a new sticker on it for me - NO problem. I'm not expecting the feds to come looking for me !

You could put oil in the gas tank too - If you were an