PCM for 4ALD to mazda trans swap

piotrsko · Jul 31, 2009

apparently being POLISH has it's benefits:

I forgot to change the computer/PCM from the 87 donor 5 spd car to the 88 auto truck. Drove around for a while, didn't set any CEL lights, truck acted like normal, although the idle was a might bit high. Nothing a screwdriver won't fix.

So now I'm wondering why EVERYBODY says PCM's have to be swapped in order to work properly.

AllanD · Jul 31, 2009

Basically you are pissing away fuel economy and driveability.

The auto trans computer KNOWs it must maintain idle to keep the front pump in the trans turning.

However running an auto trans computer with a manual and not changing the wiring to reflect the change means you are less able to regulate your speed with the gas pedal
(because the computer is maintaining a higher idle at all times

You are also losing the primary benefit of a manual trans REAL engine braking.

Ont he manual trans computer if the TPS signals the computer that the throttle
is closed the computer will turn off ALL the injector pulses until the rpm falls to 1800rpm or so and will only fire half of them until rpm falls further to 1300-ish

this greatly increases engine braking , decreases fuel consumption and emissions

this may not sound like much but in my experience running an auto trans on a manual trans 2.9 will work and you'll barely noice the difference... but it'll be costing yo 1.0-1.5mpg.

AD

piotrsko · Aug 1, 2009

thanks for the GOOD answer.

Now I'm gonna have to swap the PCM and see if the idle falls. can't see any wiring differences for the 5 speed other than the trans converter and reverse lights.

PCM for 4ALD to mazda trans swap

piotrsko

15+ Year Member

AllanD

TRS Technical Staff

piotrsko

15+ Year Member

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