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Old 23rd March 2017, 10:26   #11
bluemalbert
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Quote:
Originally Posted by Ravinder View Post
Hi guys

I've got a slight misfire or hesitation under load, around 3k refs on the 1.8 turbo 75. I will be getting the car on the T4 very soon hoping it will tell me the issue. Any ideas here what to look for? Many thanks.
I have just had exactly the same problem with my 2.5 ZT. A diagnostic plug in (not as good as a T4) showed which pot the misfire was on and so I replaced that plug and coil pack as a starter. Cured immediately So then went on to replace the rest of the plugs as a matter of keeping a matched set. You can measure the gaps with a feeler gauge set bought at any half decent auto shop. (I dont know if the 1.8 has individual coil packs like my KV6 engine!) When you have the T4 plug in, it will tell all.
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Old 23rd March 2017, 21:15   #12
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Took my car up today to a good friend of mine who had a look at the car on the machine. No obvious signs of misfire showing on any cylinders. He checked the plugs and the plugs were well over 1mm. These were adjusted to 0.6mm.

Result - misfire/hesitation gone.

I no longer have a misfire, but can't help the car could be smoother. It feels through the rev range that it's not as smooth as it could be. This was present before. Any thoughts?
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Old 24th March 2017, 05:30   #13
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I would simply replace the plugs, the 1.8 is very sensitive to plugs it seems to me.
I would also make sure the air and petrol filters are clean, and lastly that there is no leak from the inlet manifold.

If all this is done, there is not much else there can be done, provided your leads are good and no water is entering from the cooling system.

But then it should also be smooth!
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Old 24th March 2017, 06:36   #14
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We did check the plugs and agreed the plugs looked in very good condition. I'll have a look at the other things too. The car seems to drive fine. Maybe I'm just being picky but I just notice these things.....
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Old 24th March 2017, 07:17   #15
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You cannot judge a spark plug by its cover!
If you want, see how it fires under pressure.
You could be surprised.

What does 4 plugs cost?

Change them and eliminate them as a source of problems.
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Old 26th March 2017, 18:33   #16
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Read your recommendation about plug gaps on 1.8 turbo, took mine out yesterday, cleaned them, and set the gap down to 0.7mm. Went for a run today around Kent to see my son, opened it up a couple of times and all the "flutter" on acceleration has gone! Approx 60 miles and the trip computer reads 37.8mpg, all on mixed "A" roads and country lanes so I'm well happy with that, thanks!
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Old 27th March 2017, 15:30   #17
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My 1.8T is currently running beautifully on new spark plugs straight out of the box (i.e. 1mm gaps) plus new coils.
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Old 27th March 2017, 21:42   #18
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The resistance of plugs increase with age. It also increases with pressure!!

Many years ago, Champion (I think) made a small tester. It only needs compressed air and a power supply, and some sand. (My dear friend Hamish Morrison has one, he fixes RR and Bentley and Jaguars!! and has done for many years)

You can sandblast the plug on the one setting, and then fire the plug behind a glass. At the same time you can pressurise the chamber and watch the spark.

Often, on an older plug, it will fire happily at normal pressure, but fail, as the pressure is piled on.

So, my advice is to replace the plugs, it might just work!!
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