Misfire
 

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

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

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.

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.

aghhhhh
 

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

Sure, you only have to ask.

When ?

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

David

OK let me know.

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

The last leads I sent you have exactly 2 miles on them and I didnt have a misfire using that coil and lead combo so I think you can rule that out.

I had this problem and sorted it and I am trying to figure out if it was just resetting the base idle that fixed it or If I did something else. Might have been that I had 2 of the loom plugs in the wrong way and it was giving me a solenoid error on the diag LED. The vacuum solenoid has the same plug as something else in that general area and i got them the wrong way round.

Cheers
Stot

Cheers
Stot

I think my problem may be fixed. I have replaced the plugs, the ecu temperature sensor and also the lambda sensor. Total cost 15 quid. The engine now revs nice and smoothly. I still need to check the ecu for faults as the light didn't turn up in the post. I know there will be one fault on the for the purge valve leading to the carbon canister as this was removed.

Thanks for the help and advice . Fingers crossed it keeps working....
David

Not sure with jap ecu's but vag ones can be reset by taking both batt leads off and clip them together for ten minutes or so.

Will be in the circuit at 17:30 if you are interested.

I will keep an eye out for you . Are you in a warrior or a trauma hawk? I am presently in Kenton school so probably at the top of your down wind leg if your doing a left hand circuit

Warrior David,not keen on t hawk or cesspit but will fly them if forced too:D
After 6 when I took off and one circuit rht hand 25 took 25 mins,ready to turn base and got sent 2 miles north to avoid inbound traffic and three others in the circuit due to crosswind.

Its back aghhh
 

Looks like I still have a missfire......

I have used the diagnostic "Tool", well an LED and I am getting error codes 8 and also 23(i think from memory its 23 - this is the carbon canister which I was expecting as I had removed it.)

Error code 8 means there is a problem with the air flow meter.

I have ordered a replacement from ebay £16 delivered so hopefully this will cure it.

If it doesn't I will have run out of ideas......

David

Could it be a bad earth or a wiring issue to the MAF (airflow meter)?

I don't think so as there is no error code for the air flow thermistor

David

Found this on my travels if the new part doesn't solve the issue then maybe this will give you some more ideas. Got my fingers crossed for you.

http://www.aa1car.com/library/misfire.htm

I'm still waiting for the new afm to arrive. In the meantime I decided to get my haynes manual out! Totally forgot to look in there...

I have tested the resistance of the potentiometer in the afm and it's bust. There is no movement on the multimeter until it is fully open. The fuel pump switch operates as soon as it is opened.

The thermistor also seems to be not giving a reading.

I have had a good "dismantling session" in the kitchen tonight and think this must be the cause of the problems.

Ie when the throttle is opened there is no change in the fuel supply causing it to miss and the thermistor is most likely confusing the situation as well (without the ecu knowing as there was no error code showing for this)

Let's hope Hermes turn up tomorrow with my parcel!

David

Is there a fuel pump cut off on the TPS .

Have u changed the belt recently? Was it ok one day then not the next? Is it more noticeable when the engine is hot? It sounds like a maf sensor but it may be worth checking things like fuel filter fuel pump delivery if the new maf doesn't fix it also if it does it when it is hot what plugs u running? They could break down when hot. Just chucking out some more ideas and hope u get it fixed soon which I'm sure u will it is starring u in the face laughing at you like these faults generally do!

Very good. Well done. Fingers crossed. Have you applied for your IVA yet?

The fuel pump cut off is a micro switch in the afm. As soon as the vane moves a tiny bit the fuel pump works.

Still not applied for my iva yet. I want to sort out all these niggles first.

In the diagnostics port you can override the fuel pump to test it's operation and that side is all working fine.

Thanks for the ideas

David

We'll.....

I have changed the air flow meter and the misfire is still there!

I'm now stuck for ideas.

I'm thinking there may be a link to my base idle. Since I adjusted this as per the manual the problem seems to have for worse

David

My guess, and it is a guess, is a blocked or faulty injector. Is it one particular cylinder or random?

I think all of them

Daft question but you don't have your HT leads mixed up do you? Does it idle ok but when the throttle opens is stutters?

Can you film it?

Are you still getting an AFM error code? Have you cleared the codes? Have you checked the wiring to the AFM?

I'm just thinking out loud in the hope it might help you to find the issue.

Have you pulled individual HT leads to see if it gets worse or stays the same?

have you checked inside the afm connector for corrosion and or sprayed some WD40 in there?

Thanks for the other ideas I will check them out.

David

Fixed!
 

Took my car apart again last night. Turn out the problem was a looks wire going from the air flow meter to the ecu. It now revs really smoothly and also smells a lot better!

The wire that had a bad connection was linked to the potentiometer so the engine had no way of telling how much fuel to inject.

Fingers crossed it works when it's back in one piece! It's certainly in a few bits at the moment scuttle off an wires everywhere!

I can also give my steering lock catch a grease at it was sticking a bit!

Thanks for all the help. The donor parts and various pictures they have emailed me. Without these I would still be in the garage swearing and throwing spanners at my cat!

Nice one David, glad you got it sorted!

Good! Now apply for the IVA. :)