5m-ge missing badly + auto issues

**Sammich** · 21-07-2010, 03:01 PM

1985 MX-73 + 5M-GE + auto (A34D I think?)

need help with a missing issue.

Slotted it into first gear this arvo and drove it up the street to see what it would do. It goes fine up to around 2.5k and starts to miss. Its noticible around 3k and gets REALLY bad at around 4k when I backed off, it was basically bunny hopping up the road the power was cutting out that often.

Stopped a little later, put the hand brake on and put it in neutral and free-revved it. Was perfectly fine all the way up to 5k and beyond, so its only under load that this is happening.

This was done with the engine warmed up btw. It does miss a bit when its cold but seems to be fine in the 1->2.5k range after its warmed up.

Where should I be looking first to try and sort this out? I was thinking spark plugs, or should I be checking the dizzy?

also, the auto doesn't seem to drop down gears at all when in the D position. Foot flat to the floor, it just stays in the current gear. It shifts up @ 2.5k and shifts back down when you come to a stop no worries.

cheers in advance guys <3

**woggin** · 22-07-2010, 01:32 AM

the gz20 dad now drives did this once, dunno why, dunno wat caused it but its hella weird problem, we reset the ecu, hasnt happened ever since.

check over your intake, just in case its sucking in post-afm (which it isnt supposed to)

**Sammich** · 22-07-2010, 12:53 PM

righto, how do I reset the ECU? Need to get some sort of service manual for this car...

hmm good point...didnt think about the intake. Might even be the air filter covered in gunk, that loosens up once its warm.

**thechuckster** · 22-07-2010, 01:59 PM

- check for vacuum/intake leaks
- check cabling around Throttle (incl. kickdown cable going to auto)

put timing light on #1 plug lead and see if it advances as you rev motor

nothing on the ECU to reset - it's not that clever.

Trouble shooting guide:
http://www.cygnusx1.net/Supra/Librar...2/default.aspx
(is for same motor)
Check the EFI System and Ignition System sections - both have troubleshooting guides.

edit: you and M-series motor don't work well together - strongly urge you to go 1JZ

**Sammich** · 22-07-2010, 04:15 PM

awesome thanks for that chuckster

I've got a new cam cover gasket waiting for me at a mates place to go on as well as a new set of spark plugs and he's got a timing light and all the necessary tools so i'll head over to his place this week and take a proper look. Needs a service now anyway so will hopefully have enough cash on pay day to sort out new oil + filter.

re: vacuum/intake leaks, would they not also manifest themselves as high/rough idle? It seems to idle fine at this stage.

also what would usually explain the difference between load vs free revving. Thats whats been stumping me most.

ps yes I know i've not got a great track record with ye olde 5m's so far lol. Im hoping this is a fairly easy fix as its perfectly fine as long as i drive it like a nanna

and dont say its all M series! was hoping to swap in a 7m-gte in about 6 months or so for a relatively easy "bolt-in" upgrade

**thechuckster** · 22-07-2010, 04:24 PM

is not getting it's load-fueling/timing right - under lower vacuum, something could be opening up. I'd first go for the obvious stuff by checking that all fluid, air and electrical connections are actually connected.

what kind of ignition is it (e.g. ECU controlled or vacuum/mechanical advance on dizzi) - will be obvious when looking at dizzi (e.g. vacuum advance pot present or not).

**Sammich** · 23-07-2010, 08:53 AM

ah righto that makes sense. Had a quick look across the bay yesterday arvo after I checked the oil (which was worryingly low) and it seems there may actually be a hose missing? /edit its one of the vac lines off the TB
will take a photo this arvo.

re: dizzi, copied form wiki
http://en.wikipedia.org/wiki/Toyota_M_engine#5M

The 1982 version had a vacuum-advance distributor, whereas the 1983-1988 versions found in the Celica Supra and Cressida had full electronic control of the ignition system and distributor.

i'll double check tonight.

**CrUZida** · 23-07-2010, 01:10 PM

My money is on rooted plugs, most likely caused by leaking oil from the cam covers into the valley.

New plugs, new leads, clean it all up, good as gold.

**Sammich** · 23-07-2010, 01:50 PM

yer im thinking the same. Didnt think of oil in the plug valley...its leaking on the outside of the head (directly above the zorts mani...lovely smell -_-) but i guess it'd make sense that its leaking from both sides.