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Engine miss problem that I can't track down...

1110 Views 6 Replies 6 Participants Last post by  ninog
A friend of mine has a '94 MX6 with a 2.5 MTX. The engine misses at almost any driving speed.(under load) The other strange thing is that it doesn't do it all the time, just does it randomly. Feels like half the cylinders just go dead.

We have changed out a bunch of parts to track down the problem, and still nothing.

There are no codes.

Anyone have any thoughts.

Parts changed:

Disty (new one from mazda in there now)
EGR (Cleaned)
Crank senser
fuel filter
spark plugs

Anything you kids can think of?


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You have already done all the obvious things. Two guesses:
1. A bottle of fuel injector cleaner in the gas tank is cheap and easy (though usually dirty injectors don't cause an intermittent problem).

2. Engine coolant temperature sensor. Sometimes they go bad, and don't always throw a code. You could check the resistance specs: 1993-1995 Engine Controller Malfunction Codes , or try disconnecting it and seeing how it drives. (It's the 2-wire sensor by the timing belt cover at the end of the fuel injector rails).
check the o2 sensor that can cause that feeling in the car
i'd check the timing. new disty could be 180 out. A compression test won't hurt either
Get a compression test, i had an engine die on me that way, it was doing exactly what you describe.
Thanx for all the input

Let you know what we find


I had a very similar problem. Whenever my engine got too hot from gunning it down the highway all of a sudden one of my cylinders would stop firing which you can tell by the shaking of the engine and the noticeable loss in power. Then when the car cooled down overnight it would be fine in the morning. So it was an intermittent problem for me too. What I found out was that 2 of my injectors were going bad. I first diagnosed the problem by pulling out the spark plugs one by one when the engine was misfiring to see which cylinder was misfiring. When i pulled out the spark plug and nothing changed in the dynamic of the engine running, then I new that particular cylinder was not working. Then I took a digital multimeter and checked the resistances of each fuel injector. You can do this by unplugging the connectors at the ends of the fuel rails and testing the one of the pins against the other three. (If you need me to find a diagram let me know) The Ohm resistances should be between 12 and 16 ohms. My faulty ones were at 27 and 140 while the other ones were at around 13.8 ohms. I'm about the replace them as soon as I find a reputable place to buy them from.
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