Hi all,
 
A few months ago I pulled the engine from my MR2 and a did a bunch of maintenance (timing belt, clutch and all that fun), and now after putting everything back together it won't run properly! My mechanic has been tracing the fault around and believes that it's the ECU, but he hasn't been able to find a known-good one to test the theory.
 
Does anyone in Brisbane (preferably north side) have a spare ECU to suit a 3SGE in a 1991 SW20 that I could borrow to confirm the diagnosis? If it does prove to be the problem, I definitely wouldn't mind buying off you either :P
 
Thanks!

hi kain, the forum is a good place to start. contact me if your still stuck.

Thanks Ben, I've made progress but I'm still stuck! I'd posted up a bunch of details on the Brisbane MR2 facebook page, but only got fairly general advice so far. I'll copy-paste it here soon.

Okay, I managed to borrow an ECU off Monty, but it wasn't compatible with my car (the engine wouldn't even try to start). However, many of the strange symptoms that pointed in that direction originally have been sorted after finding the alternator not properly connected in the fuse box.
 
I've still got a confusing set of symptoms:

• The car will sometimes start okay and idle, particularly when it's been off for >1min
• Otherwise, the car will start poorly, idle for a few seconds while stumbling & missing then stall, most often if it's started right after it was shut down
• If it does manage to idle, giving it part throttle makes it stumble & miss, and the tacho bounces around randomly
• Giving full throttle brings the revs up okay with just the odd miss, but the missing and tacho bouncing comes back as the revs return to idle
• While idling, there is a CEL. The CEL goes away at >3000 rpm, but comes back <2000 rpm
• The ECU will occasionally store a 31 code - open or short circuit on MAP sensor input

At the moment I suspect either the MAP sensor or coil/ignitor. I can't see how the MAP sensor would cause bouncing tacho, as the tacho is driven directly from the ignitor, but the ignitor wouldn't be causing MAP sensor codes :(

I've done as many BGB tests as I could:

• ECU provides power & ground to the MAP sensor. I have no vacuum pump to do the signal tests, however.
• BGB says resistance of primary coil should be 0.4-0.5 Ω. Mine measures at 1.5 Ω.
• BGB says resistance of secondary coil should be 10-14 kΩ. Mine measures at 13 kΩ.
• BGB has no tests for ignitor, so nothing done there.

Anyone have any ideas, or has a known-good MAP sensor and/or ignitor & coils package they'd be willing to lend me? Thanks for any help you can give!

My suggestion is to try a different ecu with the correct part number in your car to see if there is any change. You could also take the cover off your ecu and check for blown capacitors.

Kain
 
Anyone have any ideas, or has a known-good MAP sensor and/or ignitor & coils package they'd be willing to lend me? Thanks for any help you can give!

Hi Kain,

I believe that I have a map sensor, ignitor etc at home. I'll have a look for you tonight. 

You're welcome to borrow them and if they work you can swing me some cash for them, say $50? they are no use to me. 
 
I'm located on the south side

Thanks Eric, swing me a PM when you've had a chance to take a look!

Had a similar issue with idle, fixed by removing the sensors from the coolant neck in the engine bay, wiped the end with smooth sandpaper to refresh the surface and reinstalled.
I also cleaned the throttle body (spray cleaner), as well as dialled up the air screw in the throttle body so when warmed it would sit on about 950rpm.
I think your issues are more involved.... possibly refreshing rotar and distro, sorting out your fault code, general service items (spark plugs, check timing / timing belt (that timing belt is firm and has not stretched or the pin not pushing to create correct tension)....
Good luck,

Pop the cover off your ecu n check the caps are good. Easy to do before replacing a heap of potentially unneeded parts.

Thanks Tony, all good ideas! Most of that I've checked - it's got a new dizzy (I rebuilt mine and the NE coil lost a connection somewhere ), plugs have been checked, timing belt tension is good (was an issue before, brand new tensioner was DOA), cam timing has been checked. Just got to sort the fault code, all indications are that the sensor is faulty.
 
5SGTE, great idea, I never thought to actually look for a failure mode in the ECU. I've just pulled it out and checked it - I've never seen a 26yr old PCB so spotless! All components look perfect, and no flaws in the board or coating.
 
Thanks for the ideas guys, keep them coming!