misfiring Supra

Was looking for a bit of advice with my friends Supra. Basically it has just started misfiring. I have gone over the plugs, leads and ignitor and all of these seem fine. The plugs, leads and dizzy cap were all new about 12months ago and all look in good nic still. The car isn't pulling up any error codes nor is it loosing oil or water.

Today i took the plugs out, unpluged all of the leads and put it all back together again and the misfire has gone almost gone away, i think there is a slight one still although its hard to tell with the loud exhaust. The plugs were a little wet, but im asuming this is the misfire that is responsible? Or could the car be over fueling and this be the cause?!

Just looking for some advice please

The ignition system on an NA is very simple. Have you taken a look to see if there is any water in the plug wells? A cracked spark plug? Poor lead? Try the drop test to establish which cylinder is misfiring:)

The ignition system on an NA is very simple. Have you taken a look to see if there is any water in the plug wells? A cracked spark plug? Poor lead? Try the drop test to establish which cylinder is misfiring:)

No water, they were a tad damp around the outside of the plug on a couple but nothing major. Dried them off to be sure anyway. It was the 6th ad first cylinder that were a tad damp.

The leads are only 12months old but i assume the age doesnt matter if one of them has failed. There is a smell of fuel from the car, even with it running ok now, but i can't see a leak at all from anywhere.

No water, they were a tad damp around the outside of the plug on a couple but nothing major. Dried them off to be sure anyway. It was the 6th ad first cylinder that were a tad damp.

The leads are only 12months old but i assume the age doesnt matter if one of them has failed. There is a smell of fuel from the car, even with it running ok now, but i can't see a leak at all from anywhere.

I'm not sure how it would cause a misfire, but when where the 02 sensors last changed?

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No water, they were a tad damp around the outside of the plug on a couple but nothing major. Dried them off to be sure anyway. It was the 6th ad first cylinder that were a tad damp.

The leads are only 12months old but i assume the age doesnt matter if one of them has failed. There is a smell of fuel from the car, even with it running ok now, but i can't see a leak at all from anywhere.

I'm not sure how it would cause a misfire, but when where the 02 sensors last changed?

I'm not sure how it would cause a misfire, but when where the 02 sensors last changed?

 

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I'm not sure how it would cause a misfire, but when where the 02 sensors last changed?

Lambda sensors are brand new.

Sticky injector?

You did check the dizzy cap ?

You did check the dizzy cap ?

Yer, There was a small build up on the contacts which i cleaned off. There was no moisture in there at all.

Did the car just suddenly start misfiring? was it washed or was any work done to it before the misfire started?

Were the new plug leads, distributor cap and rotor arm that were fitted all genuine Toyota parts? If they were genuine OEM parts then they will be fine after 12 months use, if they weren't genuine parts then even if they look okay any one of them could be the cause of the misfire.

Depending on how good a friend he is (and assuming your car is running fine) you could try swapping over one part at a time, this will at least rule in or out each of the ignition parts.

Did the car just suddenly start misfiring? was it washed or was any work done to it before the misfire started?

 

Were the new plug leads, distributor cap and rotor arm that were fitted all genuine Toyota parts? If they were genuine OEM parts then they will be fine after 12 months use, if they weren't genuine parts then even if they look okay any one of them could be the cause of the misfire.

 

Depending on how good a friend he is (and assuming your car is running fine) you could try swapping over one part at a time, this will at least rule in or out each of the ignition parts.

They are just Denso parts from a motorfactors as far as i could tell, they wont be from toyota though.

The car was washed the day before the misfiring started, but i haven't been able to find excess moisture.

Watch the distributor cap at tick-over in a dark place and look for any tracking, there could be a fine crack in the cap that's become conductive after it's contact with water.

They are just Denso parts from a motorfactors as far as i could tell, they wont be from toyota though.

 

The car was washed the day before the misfiring started, but i haven't been able to find excess moisture.

Misfires after washing is very common on the NA, use a pressurised airline to blow out all the spark plug wells, inside the distributor, lead connectors and any other wiring. After that leave the car idling so it gets up to temperature and evaporates off any moisture that may be left.

Misfires after washing is very common on the NA, use a pressurised airline to blow out all the spark plug wells, inside the distributor, lead connectors and any other wiring. After that leave the car idling so it gets up to temperature and evaporates off any moisture that may be left.

Cheers, i will give this a go today then. So far the car has still been running ok, so perhaps it was just the small amount of moisture that was the culprit.

Ok the car is still misfiring. It seems to be ok once you get going, but is lumpy on idle or when you initially pull away. It will misfire once or twice when moving but is mainly when starting or first pulling off.

I genuinely cant see anything wrong with the dizzy or rotor and apart from getting an electric shock from one of the ht leads, they all look in good condition too. Is there anything else i should be looking at?

Ok the car is still misfiring. It seems to be ok once you get going, but is lumpy on idle or when you initially pull away. It will misfire once or twice when moving but is mainly when starting or first pulling off.

 

I genuinely cant see anything wrong with the dizzy or rotor and apart from getting an electric shock from one of the ht leads, they all look in good condition too. Is there anything else i should be looking at?

Has the battery been disconnected? If the ECU has been reset it can run a bit lumpy and not idle properly, it'll take a couple of miles for the ECU to relearn the parameters.

Has the battery been disconnected? If the ECU has been reset it can run a bit lumpy and not idle properly, it'll take a couple of miles for the ECU to relearn the parameters.

Nope battery has been connected the whole time. And the car has done a few miles today and hasn't seem to have cleared it up at all. The engine is still a bit fumey smelling but i assume this is from the extra fuel it is dumping when misfiring?

Have you checked for any stored error codes? http://www.mkivsupra.net/vbb/showthread.php?35920-How-To-Check-the-diagnostics-codes&highlight=diagnostic

Have you checked for any stored error codes? http://www.mkivsupra.net/vbb/showthread.php?35920-How-To-Check-the-diagnostics-codes&highlight=diagnostic

Yer its not pulling up any codes at all.

It may be worth resetting the ECU (disconnect battery for a few mins) to see if that makes any difference.

It may be worth resetting the ECU (disconnect battery for a few mins) to see if that makes any difference.

As in to fix the problem or to get the car to register an error code, or both?

As in to fix the problem or to get the car to register an error code, or both?

Just to see if it makes any difference, it probably won't but worth a try.

Plugs have all been checked and gapped? You could try reducing the gap of the plugs slightly to see if that makes a difference or better still try a new set of plugs. http://www.mkivsupra.net/vbb/showthread.php?41927-FAQ-Spark-plugs&highlight=spark

The only other thing I can suggest is what I mentioned early, try swapping over the leads, distributor cap and rotor arm one by one (ie. test the car after each part is swapped) and see if that makes a difference. At the very least, it'll eliminate these parts as the cause of the misfire, at best you'll find the culprit.

Also thoroughly check all hoses, sensors and wiring in the engine bay to make sure nothing has 'popped off', split of is loose.

Just to see if it makes any difference, it probably won't but worth a try.

 

Plugs have all been checked and gapped? You could try reducing the gap of the plugs slightly to see if that makes a difference or better still try a new set of plugs. http://www.mkivsupra.net/vbb/showthread.php?41927-FAQ-Spark-plugs&highlight=spark

 

The only other thing I can suggest is what I mentioned early, try swapping over the leads, distributor cap and rotor arm one by one (ie. test the car after each part is swapped) and see if that makes a difference. At the very least, it'll eliminate these parts as the cause of the misfire, at best you'll find the culprit.

 

Also thoroughly check all hoses, sensors and wiring in the engine bay to make sure nothing has 'popped off', split of is loose.

Ok cheers. I dont have my car at the moment so will have to wait until i get that back. All parts on the car are oem ones just not direct from toyota except for the leads so im guessing that this is probably the cause. Bit of a pain of a job having to remove 2 sets of intake and throttle bodies but will have to go that route....

Cheers again