Question about ecu/memcals

[gtmattz]

I have taken the 2.8 mpfi from a 89 celebrity with auto trans and am going to put a 5 speed manual transmission on the engine. Am I going to have to get the memcal/ecu from an auto trans car to get the engine to run correctly, or will it matter for this application?

[Fierobsessed]

It will run with the Auto ECM, but it will have a bunch of problems, mostly stalling and Idle problems, and a code 24 Vehicle speed sensor. The reasons for this: the engine is expecting a Park/neutral signal from the transmission switch that you have to eliminate. If you leave the wiring so it thinks its in park/neutral, it expects the car not to have over a certain amount of manifold pressure for extended periods of time (indicating the car must be accelerating or going uphill) in other words it MUST be in gear, so it throws a VSS code which is misleading. If you wire it so it thinks it is in drive all the time, when you free rev it, it will think that it should be accelerating, and its not seeing a VSS signal, it will also throw a VSS code again. So expect that.

The Idle trouble, Sometimes can be related to the fact that there is no automatic transmission load, like where you are in gear and stopped.

Stalling will be caused by some tables in the ECM's code that control throttle follower. Once a car with an automatic transmission is moving, the engine needs little or no help to keep it from stalling since the transmission is controling engine speed. Since there is a switch telling the ECM that the transmission is in gear, it knows it doesn't have to worry about the idle too much till the car slows down to nearly a stop, this isn't true at all with a manual transmission. When you let off the throttle with an automatic transmission, the computer will dial back the idle, and the fuel (sometimes completly) to slow you down, now lets say you have a manual, and you push the clutch in while this condition is present, the fuel and idle are both down or even off completly, and you just disconnected the engine from the wheels without telling the computer you did so. Instant stall. Think about how this situation applies everytime you shift, You let off, and pushed the clutch, engine goes right into a stall because the ecm doesn't know the engine is not being kept alive by an automatic transmission.

A manual transmission code only has a few goals, Decrease idle slowly when the throttle is let off so the engine doesn't go straight into a stall (this is called throttle follower). And kick up the idle a little once the car is rolling, and decrease it to an idle when the car has nearly stopped or crusing to keep the car from stalling while driving slowly.

Long story short, you must have a manual Memcal/Prom if you plan on using a manual transmission, or else the drivability will be destroyed, and you will get a code 24. Luckily, that manual code is widly available.

[ryan.hess]

If you are having trouble finding a manual memcal, buy one of these:

http://60degreev6.com/showthread.php?t=34182

and I will burn whatever manual binary you need on a chip. Free of charge.

So that would be just $23 to convert your auto memcal into a manual memcal. Otherwise I know you can always get new memcals (even the rare ones) from the dealer for about $50-60(?)

[SappySE107]

Is this going in the MG? What trans is that? You should just use a manual trans chip (the ECU itself doesn't care, its all in the chip), but if its a swap, you will need some custom tuning most likely.

[Scott_68B]

I'm using a manual chip in my MG (GEN II 3.1, T5 5 speed) and it works pretty well. I thought I could get away without one but I found that I had to add a VSS sensor because of a stalling issue when coming to a stop. Adding a VSS signal solved the problem. FWIW.

-- Scott

[gtmattz]

I'm using a manual chip in my MG (GEN II 3.1, T5 5 speed) and it works pretty well. I thought I could get away without one but I found that I had to add a VSS sensor because of a stalling issue when coming to a stop. Adding a VSS signal solved the problem. FWIW.

-- Scott

Yes this is going in the MG. The transmission is a T5 from a S-10 pickup (I have been told that 1st gear will be a little low, but the transmission is in great shape and best of all FREE). I am not sure of the year of the S-10, some time in the mid 80's. As for the VSS sensor, is this something that will already be in the transmission?

[Scott_68B]

Not sure if your transmission will have a VSS in it. I got mine off of an 86 F-body and it did have a VSS but I'm not using it...I'm using one mounted between the driveshaft and rear end. I'm driving my stock speedometer with a cable mounted where the VSS would live. I had to modify the Road Speed Sensor Constant and burn it into the chip to get the ECU to read it and you may run into the same issue if the VSS you choose doesn't generate close to the same signal the unit original to the ECU you are using generated.

You may have an issue with the S-10 transmission because of the location of the shifter. It is located much farther forward on S-10 T5's when compared to F-body T5's. The F-body T5 shifter pretty much lines up with the stock shifter hole on an MGB. The S-10 shifter ends up close to or under your radio so you'll have to chop up your transmission tunnel to get it to fit and there still might not be enough room to actually shift the thing. You may find it easier to get a rear housing assembly from an F-body tranny or another transmission altogether.

Kind of getting off subject. Hope this helps.

-- Scott

[sharkey]

i actualy have been running an auto chip in my ecm for 3 years now with a standard. no stalling problems, the idle doesnt just drop, it slowly comes down. i also have no vss codes, ever. the vss code will only set if you are over 10% throttle with a certain map/maf value for 3 seconds with no vss signal. the early gm vehicles dont send a signal for line pressure to the computer, only newer electronicaly controlled transmissions do that. and as for the idle, when its warmed right up, if it idles to low, just tweak the throttle blade, it will bring the rpm up a bit. the older computers, even 89 still isnt that smart to detect every little difference and correct it.

[gtmattz]

You may have an issue with the S-10 transmission because of the location of the shifter. It is located much farther forward on S-10 T5's when compared to F-body T5's. The F-body T5 shifter pretty much lines up with the stock shifter hole on an MGB. The S-10 shifter ends up close to or under your radio so you'll have to chop up your transmission tunnel to get it to fit and there still might not be enough room to actually shift the thing.

-- Scott

Thanks for the heads up about the transmissions. I am sure I can find one from an F-body and will use that. As for the memcal, I guess I will see how it runs with the auto mem and if its too bad see about going with the setup mentioned above.