Wanted Engine Control Module (ECU) 1991 Ranger 4.0 MT

[Maui-sprint]

I need an ECU for a 1991 RANGER 4.0 Manual Trans.

Interested in purchasing OR I have the following ECUs available for trade:
1989 2.9 MT
1991 4.0 AT
Will trade you the above TWO ECUs for your ONE.

Lemme know if interested and will provide the P/N's.

 

[gaz]

@Maui-sprint ,

You should use the 91 auto transmission ECM that you are selling in your manual, the manual will not care, neither will the 4.0l.

 

[RonD]

The CEL(check engine light) will stay on all the time with Auto Trans ECU installed

 

[Maui-sprint]

I've read here (TRS) that if I use an AT ECU with a MT application the motor will idle at a higher RPM than with the correct MT ECU? If so, how high above normal can I expect? Is there anything else I can expect beside CEL being on?

 

[RonD]

Automatics idled about 100rpm higher than manual so they didn't stall when put into R or D
So its not much
650rpm idle manual, 750rpm automatic after warm up
Either idled higher when engine is cold

Just that and the CEL

 

[Northidahotrailblazer]

I've used both 91 explorer auto ECU and manual ECU's. I had no CEL. Only thing I noticed was RPMs would do weird things at times. To be truthful I'm pretty sure I have an Auto one in it right now. That's my experience anyways.

 

[RonD]

CEL comes on because there is no 12volts on the solenoid ground wires with key on and then no feedback when solenoids are grounded
Because there are no solenoids, lol
Not really anything you can do about that except delete the solenoid software in the PCM, manual PCM doesn't have that software

Same for idle, software has "target idles" for the engine and transmission models
Just different software in manual and automatics
Like having a EGR system or no EGR system, its all software related

 

[Maui-sprint]

Based on what you guys are saying I will hold off on trying to get a MT ECU. Doesn't sound like much of a difference. Thanks for the info. Good stuff.

 

[Josh B]

My CEL stayed on so long without my ever getting it checked that after 10 years or so it just didn't come on, took me a while to even notice

 

[bergz0]

I have one from a 93 ranger 4.0 mtx if that'll work

 

[Josh B]

Probably should be 92 or before, 93 began another chapter in the generations

 

[Maui-sprint]

Update: I completed the MT conversion and truck idles between 1200-1500 rpm after warm up in neutral. Too high. Other than that motor performs perfect. Would an ECU swap help here or should I be looking elsewhere?

Unrelated to the ECU: The new MT went in smooth. Its a whole new truck. Only issue after the swap is a light "clicking" noise when I depress the clutch pedal. The noise generally occurs AFTER warm up and doesn't matter if in gear or not. I'm thinking throwout bearing maybe but I installed a new part there.

 

[RonD]

Is the idle higher when cold, if so then IAC Valve is working and yes, MT ECU might help, but it sounds higher than just an automatic ECU would do, so could be a vacuum leak

Unplug the IAC Valves 2 wire connector after engine is warmed up and idling
Idle should drop down to 600rpm barely running

 

[Maui-sprint]

Engine idles between 1200-1300 cold or warm. no difference. Disconnecting IAC when warm and no change. Will go thru and check for vacuum leaks next.

 

[RonD]

Have engine warmed up and idle with IAC Valve unplugged
Spray soapy water around the engine, engine will stumble if its sucked in, and worst case is engine is cleaner
Spraying flammable fluids around is just asking for trouble, IMO