Well I have an 89 camaro with a 305. I took out the original 305 and replaced it with an older 305 that was rebuilt. I made the switch from TBI to carb, and I got everything tuned up nice and its running good. Now I'm in the process of cleaning up the wiring harness and I got a couple of questions? I started pulling out all of the stuff that was disconnected in the engine bay and disconnected from the computer. The car did not start with the computer removed. Ive read on here that you can pull the harness out in one piece, but dont see how because there seems to be splices into the main harness, and some wires running through the firewall. Anyways, if i decide to keep the computer connected, would that save me some work as far as wiring up a new fuel pump relay, and also take care of my tcc lockup, or will that stuff have to be done either way? I just dont want to make any more work for myself than i have to.

 

My camaro doesn't have an ecu, but I went with a painless race harness and rewiredy entire car. If you plan on keeping your sensors and emission stuff, keep it. I converted mine from tbi to carb, and power everything to manual everything.

 

good question. i always thought about that myself but never researched it I am anxious to see what the answers are.

 

Check this thread out.

The wire colors will be the same and the link in this thread will give you the right schematic.

https://www.thirdgen.org/forums/carb...swap-help.html

BTW, if all the sensors are disconnected from the ECM, I doubt it is controlling the lock up converter so you will have to fix this as well.

 

Thats a good thread, but my thought is I can clean up my engine bay, and not have to mess with the fuel pump relay or tcc lockup by keeping the computer connected to control that stuff. I dont see why any of those engine sensors would effect what the tranny does in OD. I could be wrong, but just lookin for some clarification. As far as wiring the fuel pump, thats not a big deal, but I'd rather not mess with the tcc lockup.

 

Also, when it comes to wiring, I get nervous cutting stuff out. I've been fixing up my car since 2005, and finally got it running last summer and about finished, but with the mods i made, i couldnt get the tbi to run right, so i decided to switch it over to carb. I got it running good now, and thats why i'm a little nervous cutting stuff. Hope everyone understands where I'm at on this. Thanks for the responses everyone.

 

Under normal conditions on a stock system the ECM will unlock the torque converter under high demand from the engine, like going up a hill, to get the motor into a higher rpm/power range. (not talking about a down shift) In order to do this it would have to be monitoring the motor through the sensors to know when to lock or unlock the torque converter. Without sensors the ECM would not know if you were getting on the gas pedal and needing the lock-up to drop out.


After market systems use a vacuum switch hooked to the manifold and a pressure switch in the trans to know when the trans is in 4th and you are just cruising to lock up the converter.

To know for sure if you are actually getting a lock-up signal you could hook up a temporary light to the signal line with the other side grounded and see if it lights up.

 

ok, i got the ecm all disconnected and all wiring out without too many issues. I wired up the fuel pump too and that is working good with good fuel pressure. NOW ITS NOT CRANKING!?!?... any thoughts anyone? There is another connector under my dash on passenger side that goes through the passenger fenderwell and also ties into the ecm harness... can that be disconnected? I have it connected right now...

 

After doing some reading im assuming this is a vats/starter enable relay that is causing my problem. What is the best way to make this work?

 

Same problem here. I'm trying to hunt down diagrams and wire locations. I'm getting no hot to starter solenoid. I'm assuming its the VATS. When I separated the engine harness from the body harness I must have removed a needed wire or relay for the VATS. Searching now...

 

disregard this message

 

I fixed this problem, forgot to post... U just need to bypass vats

 

Thanks for posting the conclusion! It will be helpful for others. Would have been helpful for me had mine actually been the VATS. Mine was a combination of neutral safety switch and kill switch. I expected those from the start. Just had them in the wrong position. It's always something simple over looked.

 

I missed that first post or I would have responded. Glad to see you figured it out though.

Right now I'm helping a friend swap out a CFI system and going with a TPI system on an 84 Corvette and using a computer from an 89 f-body. Since 84 didn't have VATS I have to figure out what to do with the theft deterrent signal to the ECM. I know one option is to program it out and I think that is what we are going to do. This will be my first FI system swap that involves some rewiring and changing ECM sockets.

 

Ur gonna have to do some research on that, but i dont think u are gonna have to worry about the vats at all since it wasnt originally equipped with it. I would hook everything up and see if it starts before worrying about any tuning or rewiring.

 

I know the starter will turn the motor but the 89 ECM has an input from the VATS and I think it has to due with enabling the fuel injectors but I'm not 100% sure.

I have to re-wire some of the 84 harness to adapt it for the 89 TPI system. The 84 has different ECM connectors than the 89. The 89 ECM Pin outs are different than the 84 ECM. The 84 CFI was MAP and the 89 TPI is MAF. I need to add the two relays for the MAF.

Fortunately the new motor is sitting on an engine stand and I can do most of the harness outside of the car and get rid of stuff that will no longer be used as well.

 

U should just have to run a "hot in run" wire to ur fuel pump relay... Can anyone else confirm this?

 

Going by this diagram all I need to do is tie that lead to ground to enable the fuel system so I don't need to modify anything to the fuel pump relay.
http://www.austinthirdgen.org/mkport...m_pass-key.jpg

 

sorry I do not know how to start a new thread on here. I have a very simple question. If i convert to carburetor, swap in a mechanical fuel pump, and an hei vacuum advance distributor, will the car run as long as I have 12 volts to the coil?

 

Yes. However, if your car came with EFI (TBI or TPI) you have an in-tank electrical fuel pump. If you deactivate it, your mechanical pump doesn't have a prayer of drawing enough fuel through the dead electrical pump under high-demand conditions (WOT, high RPMs).

Instead of dropping the tank to take it out, a more common option is to leave it active and use a Mallory 4309 bypass-style regulator to bring the in-tank pump's pressure down to a more carb-friendly 5-6 PSI, patching into the stock feed and return lines up under the hood to hook up to the regulator and feed the carb. No mechanical fuel pump required at all.

The factory in-tank fuel pump should run, even if you take off all the EFI stuff. There is a secondary power feed to it that runs through the Oil Pressure Sensing Unit (3-wire jobbie above the oil filter, screwed into the block) that supplies power to the fuel pump any time there is oil pressure present (i.e. engine is runing) and it does NOT have anything to do with the ECM. It's battery voltage straight to the fuel pump with the OPSU triggering the connection- no relay, no nothing.

You will likely still want to keep the ECM in the car and active, however, for only one reason. It triggers the ECM-controlled fuel pump relay for 2 seconds at key-on to prime the fuel system, before any oil pressure existst to trigger the OPSU circuit. This is VERY handy for filling the fuel bowls on a carb before you try to crank it over (and is a feature of keeping the ECM not mentioned at all in this thread, so far).

I have done this on more than half a dozen EFI -> carb conversions so far. It seems to be about the easiest way to do it, if your car was originally EFI and used and in-tank fuel pump. Fuel line routing is a simple patch-in operation, ECM stays right where it is, and everything works just like stock afterwards.