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mk1Miata 03-13-2003 06:27 PM

1991 300 2.6
I've been getting no help through local shops with this problem:
1991 300 2.6 Canadian model. Poor starting, stalls occaisonally, and check engine light comes and goes, but usually off at highway speeds.
Nobody seems willing or able to pull ECU codes. What exactly is involved for this car? Does it really take an hour to set up the equipment like the dealer claims, or is as simple as my Miata (2 minutes max)

chicago124 03-13-2003 06:44 PM


I think you'll find that searching the archives will point towards your OVP relay.

A good Craftsman or other multimeter with Duty Cycle can read the codes. Again, the info you need is a search a way. Try searching on 300E and OVP. More threads than you can imagine since it's a common ailment.

Good luck,

mk1Miata 03-13-2003 06:46 PM

I've done some search before asking my question, but have not had appropriate results. Since this is not my car, I'm not even sure exactly what the specs are (OBD, OBDII ect). Thanks for pointing me in the right direction.

chicago124 03-13-2003 06:58 PM


So a search for Fault Codes and Duty Cycle will bring more help.

The OVP is the usually the first suspect. About $50 to $60.

Regulator brushes might be another. About $25 to replace.

Post the fault codes and I can tell you what the readout is telling you.


mk1Miata 03-13-2003 07:07 PM

Although I doubt he's being taken for a ride, my Grandfather has been told that getting the fault codes is a waste of time. You would expect more from a shop that you have been taking your car to since 1957! It's his first gas model and is losing confidence. I'll keep you posted.

maheath 03-14-2003 02:30 AM

When you say poor starting, is that always? or only when the engine is cold? or only when the engine is hot?

When you say stalls occasionally, is that at idle? or when coming to a stop? Is the engine cold or hot or both?

The diagnostic connector is not OBD or OBDII. Look at this page to read the engine codes with a multimeter that has duty cycle:
Evaluating Electronic Engine Controls or you can navigate to it yourself by selecting the D.I.Y. tab at the top of this page. If you don't have a multimeter that has duty cycle, Sears sells one for about $30. A search should come up with a model number.

When searching this forum, keep in mind that you have essentially the same engine as the 300E, 300CE, 300SE, and 300SEL from the mid '80s to the early '90s. Of those, the 300E is by far the most common. It's the M103 engine.

mk1Miata 03-14-2003 10:37 AM

Thanks for all the help.
Poor starting and stalling from cold, engine sometimes cycles when started hot (RPM from under 1000 to about 2000) and will stall coming to a stop occaisionally.

sbourg 03-14-2003 11:18 AM

Do a search for OVP to locate it for this car (check through the 'FastLane' catalog for a picture of it), then pull it out and check driveability. This car uses Bosch KE engine management, which has electronic fine-tuning of a basically mechanical system. The OVP is a relay which provides power to the ECU, so pulling the relay disables any electronic control - reverting to mechanical injection.

Now, if the engine continues to have poor driveability with the OVP removed, then ignition or mechanical injection components are suspect and need replacing. This would include vacuum connections and air supply hoses in the idle system, coil, plugs, wires, etc. If it runs pretty well - and much better than before, then the ECU is screwing up operation, probably due to a failed input sensor or bad contacts in the OVP you removed.

Note with the OVP removed, emissions will be out-of-whack and ABS disabled, so consider this as a diagnostic, not a solution.


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