Hi....

1990 stock Miata...lots of mile.....was running fine....stopped running...pulled over.....a few almost starts then nothing......towed it home....removed plugs which were blackish and soaked with gas.

Cleaned plugs......cranked engine over and got good sparks at all
four plugs.

******WITH PLUGS REMOVED, CRANKING ENGINE OVER CAUSES
WHAT I THINK TO BE AS WAAAAAY TOO MUSH FUEL SPRAY COMING
OUT OF THE SPARK PLUG HOLES...ALL FOUR OF THEM.

So....I think I have a problem wherein my air to fuel ratio is WAAY
to rich.....and it happened suddenly.

Any suggestions as to the cause are appreciated!!!

Thanks...

Dave

 

All of them?

Try having someone hold the throttle on the floor while you crank it over with the plugs out. That should trigger the ECU to not add any more fuel (flood clear). IF it is still dumping fuel into the cylinders with the throttle all the way open, something else is going on. I'll have to think about this one.

 

I've been mulling over this as well.

First thought was that since the AFM in a '90 outputs a signal inverse to airflow, that a false-low (either because of a stuck flapper or an electrical fault) would drive the ECU to full load. This would definitely kill the engine once it's started and trying to idle, or at damn near any other load condition for that matter.

It merits looking at. Use a voltmeter to measure the signal at pin 2M of the ECU (red / black wire) relative to ground, with the key on, engine off. Should be somewhere between 4-5 volts. If it's significantly lower, that's a problem. (Sadly, there's no easier place to measure the voltage- you'll have to stick a needle or similar into the backside of the ECU connector to hit the pin.)