Misfiring when warm & under load. Coolant in spark plug wells?

[Mike2JZ]

Hi all,

 

Couple of weeks ago I did a full fluid service + oil filter on my n/a supra as I was preparing to go on a long journey into Europe.

 

The drive over took around 10 hours in very warm temperatures (35c). Car felt a bit sluggish compared to normal due to the temperature but it ran absolutely fine.

 

Had a day off soon after so I decided to give the engine bay a bit of a clean. Whilst removing the spark plug leads I noticed they were all covered in coolant. So I cleaned them off and dried up the spark plug wells again.

 

The following day after driving somewhere and parking in the sun, I went to go start the car and it sounded like a tractor. Misfiring very badly and just about got her home again.

 

Didn't touch the car for a little bit after that but tonight I started her up again to see if the problems persisted.

 

Whilst the engine was cold it fired up and idled nicely at 1'000, no misfire to be seen or any smoke etc.

Took her quickly up the road and was starting to get misfire after 4'000 rpm under load so brought her back home again.

 

I've taken the cam covers off and checked the spark plug wells again and was greeted with the following again:

 

 

So here's what I've checked tonight:

 

- Start up both cold & warm, no smoke of any sort. Smells a bit rich when it's warm and misfiring but thats to be expected I guess

- Coolant was topped up before going for test drive, though the expansion bottle and radiator had lost some by the time I came back.

- Radiator cap has no signs of milky liquid, or anything that would indicate a blown headgasket.

- Coolant in the wells have no signs of oil.

- Both coolant hoses leading in/out of the intake manifold have no cracks or leaks

- Rear coolant return hose sitting behind cam covers is not split or leaking

- Car temperature remains dead in the center of the gauge when throughout all testing

- Cam covers were removed to check the cams, and there was no sign of water in either of them, just engine oil.

- No visible coolant leaks around head gasket area, or anywhere else on the exterior of the engine.

- No cracks visible anywhere on the head.

- Spark plugs firing ends are brown, so no reason to believe that they have come into contact with anything abnormal.

- No coolant or puddles under the car or on the engine tray

- No engine warning light, or master warning light or any error code saved.

 

Theory time:

 

1) The coolant hoses on the intake manifold have never had any jubilee clips on them and in english weather has never been a problem. Suddenly with really warm temperatures, during operation the rubber expands with the heat and some coolant escapes, dropping straight on top of the spark plug wells. This coolant then interferes with the HT leads & spark plugs causing a misfire.

 

2) Head gasket is gone, and somehow warped/cracked the head so water is being projected up through the spark plugs where it gathers in the wells?

 

 

When I get some time soon I will be ruling out #1 above by securing everything as best I can and seeing if coolant still appears.

 

Can anyone else think of anything I might of missed or can steer me in the right direction. Also please note im stuck in a foreign country with a small toolbox of essential tools so won't have anything too fancy to do extensive testing.

 

 

thanks!

[Swampy442]

Theory 3, the hose at the back of the head that leads to the heater control valve is split. Very common on various JZ engines.

[Mike2JZ]

Theory 3, the hose at the back of the head that leads to the heater control valve is split. Very common on various JZ engines.

 

As in the hose that fits onto this?

 

[Mike2JZ]

Any ideas anyone?

[T2 MSW]

Yes it's got to be coolant link to the heater matrix that has a split in it. If you clean it all up and the run the car up to temp with the heater on full whilst examining the coolant pipe at the back of the engine you should see where the leak is.

[Mike2JZ]

Worked a few hours on it tonight and it's back up and running again.

 

I'm quite sure that the coolant in the plug wells were leaking from a loose hose on the intake manifold that leaked under hot conditions, as I couldn't see any splits or cracks in any of the heater pipes at the rear of the engine

.

Now that the wells have been cleaned and the hoses have new clamps, the coolant hasn't returned even after a 100 mile journey and water temp on the dash is stable even after a prolonged period. So good news there.

 

I'm still getting an occasional misfire when idle'd, again only happens when hot and to be safe I've ordered a new set of plugs, rotor/dissy cap & ht leads. Not sure if my current leads are still the same ones from factory, but I've noticed that they have some cracks which no doubt expand with 30c+ weather at the moment which I don't think is helping the misfire situation

 

Either way at least the car is mobile again now and feels like 95% of the car it was before, will update later in the week when I've got the new bits installed to confirm if they helped or not.

[Scooter]

Was it the coolant hose you have to pop off to get the y branched intake manifold off, sort of low and front right over the plugs and fairly thin in diameter?

 

If so and just in case it helps in the future these could be sealed off as I think they are just to warm the intake in winter.

[Mike2JZ]

Was it the coolant hose you have to pop off to get the y branched intake manifold off, sort of low and front right over the plugs and fairly thin in diameter?

 

If so and just in case it helps in the future these could be sealed off as I think they are just to warm the intake in winter.

 

Yeah thats the one, I did wonder why water was needed going to the throttle body/y piece, I would of thought the engine heat would of been enough but good to know in case.

[Mike2JZ]

Solved: New sparks & ht leads sorted the issue. I should of spent some time testing to see if it was the sparks, or the leads that fixed the issue, but I put them both in and no more misfire.