ECM Question / swapping engine.

[KevinB]

I am swapping the Olds 307 for a sbc in my '86 Cutlass. I plan on keeping the a/c, lock up trans and cruise. I know those items are all controlled by the ecm. I do not plan on using the egr, electric q-jet, etc. Do I just use the wires for the cruise, a/c and trans and cut the rest? I guess the engine light will always be on, but I can disable that. Anyone ever do something similiar?

TIA

 

[jerrycad472]

I am not sure that the cruise, lock-up and air are controlled by the ECM. I am not sure that the ECMs were that complex back then, They mostly controlled the carb and emissions. But I am not qualifed to give this advice so consider it my opinion. There are a few places out there that specialize in swaps of Overdrive transmissions (look in the back of Hot Rod or Car Craft) give them a call and see if they offer some sort of stand alone harness. Could try Painless Performance also.

I swapped a 231 for a SBC, but never connect Air or cruise and I used a TH350. I disconnected the ECM. My check engine light never came on , that I can remember, but its been a long time.

 

[ryanwitski]

the ECM does control the lock up. found out the hard way. As for the cruise i'm 80% certian it does not.

 

[KevinB]

I'm not too concerned about the lock up b/c I think the only thing that affects that is the VSS and brake switch, whitch are all signaled to the ECM. I am more worried about the A/C. What locks up the compressor?

 

[joe_padavano]

The computer does not control the A/C compressor. The compressor clutch is controlled by the switch on the dash and the associated freon pressure switches. There IS a connection between the A/C and the computer, but it goes the other way. The computer monitors A/C clutch engagement so it can bump up the idle speed when the A/C clutch is engaged. On the 307 this is done with the vac diaphragm idle control on the left front of the carb.

 

[KevinB]

The computer does not control the A/C compressor. The compressor clutch is controlled by the switch on the dash and the associated freon pressure switches. There IS a connection between the A/C and the computer, but it goes the other way. The computer monitors A/C clutch engagement so it can bump up the idle speed when the A/C clutch is engaged. On the 307 this is done with the vac diaphragm idle control on the left front of the carb.

Thanks a bunch for the info!!

 

[joe_padavano]

Corrected info

The computer does not control the A/C compressor. The compressor clutch is controlled by the switch on the dash and the associated freon pressure switches. There IS a connection between the A/C and the computer, but it goes the other way. The computer monitors A/C clutch engagement so it can bump up the idle speed when the A/C clutch is engaged. On the 307 this is done with the vac diaphragm idle control on the left front of the carb.

Thanks a bunch for the info!!

Don't thank me too soon - I gave you some bad info.

It turns out that the V6 configuration does not use the computer to control the A/C compressor, but the 307 does. Most cars disconnect the A/C clutch at wide open throttle to provide a little more performance. On the V6, this is done with a simple switch. Unfortunately on the 307 the computer uses the throttle postion sensor on the carb to identify WOT, then opens the ground in the A/C clutch relay to disconnect the compressor. This relay ground is provided by the computer, so if you don't use the computer, your A/C will never engage.

The easy solution is to simply run the brown wire on the A/C relay to a chassis ground. This bypasses the computer control of the compressor and allows the clutch to engage. Unfortunately, this also bypasses the ability to disconnect the compressor at WOT. To regain the WOT cutout function, get the switch from a V6 G-body and wire this into the green wire that feeds the compressor clutch. Now you should have complete A/C function.

 

[KevinB]

Thanks again. Is the V6 basically a switch on the carb linkage?

 

[joe_padavano]

Thanks again. Is the V6 basically a switch on the carb linkage?

Actually, the switch is mounted on the accelerator pedal. It looks like the same switch used for the kickdown on the TH400 cars in the 60s and 70s. Should be pretty easy to find one.