I just got a 1228079 ECM from a 1987 Monte Carlo SS. I know those had an L69 just like my car, but were there any small differences (sensors, etc) that I might have to deal with? I just found out that the Monte Carlo SS had the TH200-R4 transmission but my car has the TH700-R4. Will that be a problem with TCC lockup or anything else?

The text on the PROM chip is:
AHWL
DELCO
7318

There was some other text on the other side of the chip but could not read it all since it is covered by the chip carrier plastic.

 

Great, just great. I plugged in the new ECM and as soon as I turned on the ingintion, I was greeted by the "Check Engine" light. Error code 32 (Barometric Pressure Sensor voltage too low).

I take a look under the hood and I cant seem to find the darn baro pressure sensor anywhere. I finally find a green 3-pin connector cable-tied to the wire harness behind the engine. I look at the wire and it is gray with a red stripe, the same as the cable going to the ECM terminal 1.

WTF!?!? Did someone yank out the baro sensor at some point or did some cars come from the factory without one? My previous ECM did not give me the error code 32 so I never knew until now.
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Can someone provide me with a closeup picture of how the Barometric pressure sensor is mounted on the car? Thanks.

 

It depends on the engine type, which sensor setup was used.
I found an AHWJ chip in a '88 Caprice Classic Brougham LS (B-carline) with an LG4 (H-engine).
Take a look at this thread and see if there's anything you can use.:
https://www.thirdgen.org/forums/diy-...-diagrams.html
Here's also a sensor wiring diagram for an '84 T/A.

 

Since the darn Baro. sensor is like $40 bucks, can I just temporarily make a voltage divider with a 470 ohm and 4.7k ohm resistors to provide the ECM around 4.5V at pin 1? That voltage would be in the range (3.8-5.5V) stated by the manual for elevations under 1000ft. I would only use this until I go to a junk yard and get a sensor for cheap.

Also, does not having the Baro sensor affect the operation of the motor significantly? It seems to be running fine, although I noticed yesterday that when I turn on the ignition, I hear the MCS clicking for a fraction of a second until the Check Engine light comes on and then I dont hear it anymore. Could this mean the MCS is not pulsing at all?

 

Yes, you can make temporary use of a voltage divider (or simply a potentiometer) to simulate your altitude.
Note that the Baro sensors and the MAP sensors are identical exept for the Baro sensors being fitted with a small piece of foam over the port.
If you have a MAP and need a Vac and a Baro, you can use the MAP as a Baro, and only need to get a Vac sensor.
The Vac measures the manifold vacuum relative to atmospheric pressure and so needs the Barometric pressure to know what's going on, whereas the MAP measures the Absolute Manifold Pressure and so knows it all at once.
Some cars runs the MCS longer than others but it's normal that it quits after a while when not starting. Having the CEL light on might affect the ECM's operation and so make the mileage suffer. Try to listen for the MCS clicking when the engine runs. If it clicks then it's working but you'll need a dwell meter to know exactly what it's doing.

 

I put the voltage divider on the baro sensor connector and the ECM is getting 4.2V now so the Check Engine light turned off. The MCS also clicks for a while when I turn on the ignition, so that is working correctly now. It used to only click for a fraction of a second before when the Check Engine light turned on.

I got this '8079 ECM to replace the '2455 that came with my car originally hoping it would be a faulty ECM that was causing the TCC to not engage, but I dont think the new ECM fixed that problem. I already tested the TCC circuit and I can lock it manually at the ALDL port, but it seems like the ECM never grounds the line to lock the TCC.

Would there be a difference of when the TCC is locked considering this new ECM was from a monte carlo ss that had the 200R4 transmission instead of the 700R4?

Also, ever since I bought the car, I have only been getting 14mpg. I even had the carb rebuilt more than a year ago but it didnt change the gas mileage. My car has a small vacuum leak that I can hear hissing while inside the car with windows rolled up. Could this vacuum leak be causing the bad mileage? I thought the L69 could get at least 20mpg highway, so my combined mileage should be higher (maybe around 18mpg).

Thanks for your help so far.

By the way, I plugged in a dwell meter and it stays around 30 degrees. When I increase the throttle a bit the dwell goes into the 20's. When I release it, it goes back to around 30 deg. Is this normal?

 

In general the ECM uses the 4th gear switch, the VSS, & the TPS to decide when to disengage the TCC. I have seen that there are different layouts of the 4th gear switch between cars. You'll have to check if that is so in your case. The VSS are also made with different # of pulses per mile. Check if they match. If the TPS is in too far it won't lock, thinking it's near WOT. The rear gears are the same in the SS and your car. Double check if the ECM really came out of an original & untampered SS.
The mileage really should be better (my wagon gets 18-22). I'd doubt if the vacuum leak would cause that, but an exhaust leak could make the ECM think it's running lean.
The dwell numbers sounds normal to me but I don't have any experience in how it behaves off-idle as my own car has problems.
Sorry I can't be more specific, but my best bet is differing 4th gear switching between the tranny models.

 

barosensor uses the same mount as a map sensor on a 89-92 LO-3 it mounts to the lip of the firewall by the reciever dryer

 

I got the ECM on ebay and I asked the seller if the Monte Carlo SS also had the L69 and he said yes. The ECM is remanufactured and a white sticker says "Remanufactured by General Motors Corp. Service Number 1228079".
The circuit board inside is different from the one on the thread you linked me to. The PROM is rotated 180 degree, but is in the same general location.