Misfire

[Davidbolam]

Is anyone an expert with mx5 engine.

My car idles fine but as soon as I touch the throttle the engine revs drop. This is the point where the throttle position sensor switches in. (I got my multimeter out to check). The engine misfires throughout the rev range and seems to be getting worse.

I have changed the coil and the ht leads.

The engine seems to be running rich as my plugs have black deposits on them and I've got the same in the exhaust. (Powdery deposits so not oil)

Has anyone got any ideas. I have checked everything I can think of apart from the temp sensor for the ecu which I will do next. I have also tried unplugging the lambda sensor but this didn't make any difference.

David

[flyerncle]

Temp switch and front O2 sensor all control mixture,crank and cam sensors will also give problems,have you got OBD socket ?

[alga]

Clean/check/replace the MAF sensor maybe? I suspect what happens is when you touch the throttle acceleration enrichment kicks in and that's when the mixture becomes too rich to burn.

[flyerncle]

Mixture is controlled by the length of time the injector is open,also known as duty cycle,fuel pressure is also critical.


Have scanner if you need it .

If I remember correctly there is a fuel micro switch in the tps to cut the pump off on overun to stop excess fuelling.

[Davidbolam]

I should have an LED turn up in the post tomorrow so I can interogate the ecu to see is there are any (or more likely how many)error codes. I am going to replace the temperature sender that goes to the ecu. I will check the MAF next as well.

Do you fancy having a look at it? I can supply you with unlimited cups of tea lol

[flyerncle]

Sure, you only have to ask.

When ?

[Davidbolam]

Thanks . I will run the diagnostic test first then drop you a message

David

[flyerncle]

OK let me know.

[vmax1974]

My old mx5 had similar problem was using a tank of fuel to do 10 miles and overheating cause I had to keep the rev's on to make it move

Turned out it was plug leads changed plugs and put a decent set of leads on and it was cured

[Davidbolam]

Originally Posted by vmax1974

My old mx5 had similar problem was using a tank of fuel to do 10 miles and overheating cause I had to keep the rev's on to make it move

Turned out it was plug leads changed plugs and put a decent set of leads on and it was cured

I'm on my 3rd set of leads. I'm going to see what the diagnostic light says tomorrow. The plugs are black so they may need changing but they have only turned black. I did replace the plugs when I put the ending in.

I've just tried to reset the base idle.

David