Misfire

[Volvoluke]

So after my lengthy head gasket replacement on my project car I have finally got it on the road. It did have a slight misfire after approximately 30seconds of running for a minute or two but then ran beautifully for 40 miles. However after parking up for an hour on return the misfire was back with vengeance. It was present the entire drive home! I can confirm the misfire is on cylinder 2 (second from front), there is a spark on the lead... I dont believe it appears week. Could this be a timing problem? But I dont understand why it would run well initially. Hopefully it isn't all my hard work wasted and the cylinder head hasn't sealed. Any ideas very welcomed as always👍 I'm planning to swap over my distributor plus leads and plugs from my other car to see if that makes any difference

[volvo always]

I guess you have looked to see if the plug lead is firmly clipped on and the little ferrule is screwed on tightly on the plug, that the HT lead clips onto?

If not I would fit new leads and new spark plugs.

James.

[Laird Scooby]

I'd do exactly as James suggests, don't touch the dizzy, at the most give it a new rotor and cap but leave the dizzy alone as you have narrowed down the misfire to one cylinder (#2) so you know it's not global and random.

Have you checked the injector plug si securely fitted to injector #2? Could be another cause of the misfire!

[Volvoluke]

Thanks for the replies. Feel like a plum now... it was just the spark plug😅 i always seem to expect the worse. Anyway new plug and she was happy again! The car itself drives lovely far better than my existing one. Going to order a full new set of plugs now. Thanks guys

[volvo always]

Originally Posted by Volvoluke

Thanks for the replies. Feel like a plum now... it was just the spark plug😅 i always seem to expect the worse. Anyway new plug and she was happy again! The car itself drives lovely far better than my existing one. Going to order a full new set of plugs now. Thanks guys

We always think the worst. Glad it was an easy fix.

James

[arctan]

Hello again Luke.
I had a misfire going on. So I asked a garage (the same one that changed my plugs in March) to fit a spare set of leads and rotor and cap that I had. (used).
I also wanted to see was there any oil in the dizzy cap, which there wasn't. ( In earlier times there was a bit).
No joy and no ideas from them.
Misfire continued.
I sought advice from a couple of other mechanics, and a Volvo independent who said ignition amplifier, vacuum test, compression test.
I went off down the avenue...
Swapped the ignition amp for a used spare- I needed to do the heatsink paste anyway.
Smoke tested the intake and found a leak at the T junction just after the MAF plus smoke from the dipstick which has an oil seal. Sorted the first with sealant and a recheck. I should get the dipstick O ring soon.
Cleaned the MAF with the right stuff.
I then allowed a garage to fit a new O2 sensor based on Lambda readings.
I had been thinking about changing it as preventative maintenance but off put it because of cost. (I've had one go in earlier times, different car. Some sites say do it every 100k, which is the mileage I've just done since car purchase) .
Can't remember the Lambda figures, possibly 1.24. So a £50 new old stock NTK. Marginally better readings. Whilst doing that they found a hole in the downpipe, 4 inches ahead of the CAT junction. About 5mm diameter.
Welded that. I borrowed compression tester off them, and did some readings.
Range 162 to 170 which may be around 7 percent variation, so not a worry?
And I had a spare set of new plugs lying around, so I fitted them.
Colours on old plugs seemed OK, all the same shade.
One plug, cylinder four, had a loose nipple. Not very loose. The other three were beyond finger tight.
And the misfire then disappeared.
I had a stare at the old plugs again, and found that number four plug was also bent, where the nipple meets the insulator.
Now I've just sailed through MOT.
And I now have an Oscilloscope, and the leads for HT. Partly for automotive fun, partly because I have a pro audio background, and the scope has a versatile signal generator, and DMM built in. (Hantek 2D82, £128 with loads of leads and two clamp meter add ons, originally circa £350 the lot)
So much for allowing other people to fix my car. And me overthinking it.
The car is now flying around. I'd better be (more) careful...

[Laird Scooby]

I did type out a long and (i think) useful reply John, for some reason the forum won't let me post it, usual forum thing "you don't have permission to reply".

Anyway, the funny thing about fault finding is the evidence is always there when you find the fault so the simpler you keep things while doing that, the quicker and easier you get there usually.

[TonyS9]

Check the compression before going any further.

I just found that I had damaged my gasket when I put the head on 3 yrs ago. Think I must have dropped the edge of the head in the middle of the gasket, it had a dent on the metal ring and a line on the gasket.

It ran badly for 30s then ok, but always not quite right. This was used as a track car. Only now checking the compression I found it was low on 1 cylinder.

If you have a smilar problem then its just a lsight leak, then when you get some heat into it, it seals better but probably not perfectly.

[arctan]

Originally Posted by Laird Scooby

I did type out a long and (i think) useful reply John, for some reason the forum won't let me post it, usual forum thing "you don't have permission to reply".

Anyway, the funny thing about fault finding is the evidence is always there when you find the fault so the simpler you keep things while doing that, the quicker and easier you get there usually.

Hello again Dave. It would have, as always, been good to hear your valuable input! But, I know what you mean about doing a load of typing and it disappearing when hitting 'post'. I think some sites may log people out after a period of time, then back in when a new page is requested? One possible workaround might be to open a new tab on the site, just before posting. Nowadays, on long posts, I copy and paste my efforts in to notepad, before posting, just in case!
Just to say that I also did Cataclean, throttle body cleaning, and the PCV was cleaned recently. So my efforts to find the fault where a mixture of
Parts swapping.
PM that should have already happened.
Luck.
Sometimes I need just standing back, have a break, rather than zooming in too far.
And not move on until happy with the current step etc.
I want to add a little Carlube ATF to the petrol tank, as a kindness to the fuel pump, and anything else that might benefit. I'm running mainly a full tank of petrol, as I haven't sorted the gauge yet. As it's mainly on LPG, I do £20 or so petrol top up per month to get a full tank. Can you suggest an amount please?
I've just been to Bournemouth and back. At 70 mph the car just seems to want to keep accelerating up to higher speeds. Needless to say, I try and stop this from happening...

[Laird Scooby]

Originally Posted by arctan

I want to add a little Carlube ATF to the petrol tank, as a kindness to the fuel pump, and anything else that might benefit. I'm running mainly a full tank of petrol, as I haven't sorted the gauge yet. As it's mainly on LPG, I do £20 or so petrol top up per month to get a full tank. Can you suggest an amount please?
I've just been to Bournemouth and back. At 70 mph the car just seems to want to keep accelerating up to higher speeds. Needless to say, I try and stop this from happening...

With that amount of fuel in the tank (i'm guessing 1/4-1/2 a tank) i'd suggest about 50ml ATF-U at the most, it will certainly quieten the pumps and clean the injectors too. Just re-read what you put about keeping the tank near full so more like 100ml but as you mainly run on LPG anything that helps the petrol pumps is a good idea in my book.

As for that post, i do similar to you and copy the post if i think it's going to have problems and i can normally find it again using the Back button if i get caught out. On that day though, no matter what i did it wouldn't let me post that reply. I posted a longer reply to another thread just before and just after so it seemed there was a glitch with this thread.

Not to worry, you've solved the problem which was the main thing!