2003 1.8T - intermittent misfire on starting
 

It doesn't do it every time I start it, but when it does it can go on for anything from 15 seconds to a minute before it clears and then runs fine for any amount of time until I switch off.

Sounds and feels like one cylinder in particular is missing as it has a regular 'beat'. I put new plugs in, but that made no difference. I'm guessing it must be either a dodgy plug lead or one of the coil packs, but I don't want to just randomly change things out in the hope of curing it.

Any ideas people? Thanks.

PS - when I changed the plugs the plastic tops of the plug lead covers just cracked and fell apart when I pulled on them - had to pull the remaining rubber part out with a pair of pliers! Other than that an easy job.

Symptoms of a failing inlet manifold gasket:cool:

Check your coolant level in the header tank. 1.8 and 1.8T are prone to a weeping inlet manifold gasket, when the engine is cooling down/cold it allows a dribble of coolant into the inlet manifold which manifests itself with a rough idle on starting. Idle settles down once the coolant has burnt off.

I did get asked to look at a car with a similar symptom, and after checking through all the obvious things, I ended up finding that the valve timing was 1 tooth out on the inlet cam. Not entirely sure how the rough running ever cleared itself.


But, check for leaking gaskets first.

Thanks guys. But surely that would cause general rough running, and not one particular cylinder to misfire, as I'm sure is the case in this instance as I can hear and feel that only one plug is misfiring?

Coolant weeping into the inlet manifold primarily affects cylinder number 4 more than any other. Had it myself, most 1.8 and 1.8T owners will get it at some point if they haven't already.

When it's misfiring switch off and pull the spark plugs. Check for which plug isn't firing and see what is on the plug. As said, often a sign of a failing inlet manifold gasket, easy to change and not that expensive. ;)

Thanks guys. I had a mechanic friend look it over and he said he could smell petrol in the coolant and concluded that it was a head gasket failure. However that would cost me more to get done than the car is worth, so I'll take your advice and replace the inlet manifold gasket. Fingers crossed! Anything special involved, or is it just a case of disconnecting everything attached to manifold, clean up any residue once it's off, and put it all back again?

Replacing the manifold gasket won't help if the head gasket has indeed failed. That diagnosis should be verified or you could end up somewhere far away with no engine at all.


TC

True that, but if it is just the manifold one then it'll cost me a tenner rather than £600. How can it be diagnosed, as presumably the symptoms of each can be the same? Cheers.

Just undo the inlet manifold nuts, ease it back and fit the new gasket, less than an hour to do the job.

At least you can rule that out!

Perhaps putting a "skim" coat of RTV on the side of the gasket that fits into the groove on the intake manifold and another "skim" coat of RTV on the surface around the #1 & #4 ports? I think that would help prevent the gasket getting displaced when maneuvering it over the studs and also seal around #1 & #4 if there was any warping of the manifold.

Any recommendation for a brand for the gasket? Thanks.

Does anyone happen to know the torque settings for the manifold nuts?

Agree with the TLC. Mine's done 125k, so I check the basic stuff under the bonnet every couple of days, with a more thorough check if I'm driving any distance.

Get yourself a nice alloy inlet manifold, no more worries:cool:
https://i.imgur.com/b5tMBYcl.jpg

The torque and sequence re the plastic inlet manifold is shown here. Click

Interestingly it looks like the gasket is supplied in 4 pieces for at least some of the Chinese derivatives. The MG6 and Roewe 550 are both mentioned in the Aliexpress listing for the item shown below so I wonder if the 4-piece version is supplied/used at UK dealer networks:

https://ae01.alicdn.com/kf/HTB1KCg_j..._220x220xz.jpg

Great! Cheers - just what I needed. The one I ordered from Rimmers is a one piece, so it's interesting to see the separate ones on the Ali site.

Does the black uprated Viton gasket fail in time,or is it seen as a permanent fix?

The black Rimmer's ones will fail in time, but last longer imo. They're noticeably fatter than the green ones, so give me more confidence. See below:

https://i.imgur.com/y6LzYLg.jpg

Well I changed the IMG, but it's only resulted in a slight improvement. I've noticed that the cooling system seems to be getting very over-pressurised, so it must be the head gasket that's gone, and that caused the IMG to fail. Getting the HG done would cost more than the car is worth, so it looks like it's the end of the road. Shame, as I really like the car, old as it is.

Thanks John, but it must be the HG because I put new plugs in last week which I checked today. The ones in 1-3 looked almost like new, but no. 4 was black. I also shone a torch onto the top of no. 4 piston and it was slightly damp, whereas the other 3 were dry. So unless I'm missing something (and I hope I am!), then that seems pretty conclusive to me. I'd be very happy to be proved wrong though : )

PS, I can't find any roving engineers near me (Reading).

Wouldn't a black spark plug be an over rich mixture ? overfuelling ?
Surely if it was water getting into the cylinder, it would be nice and clean.
And we all know that too rich a fuel mixture would cause missfiring.

http://www.mg-rovermobilemechanics.com/ cover the whole of the UK, cost of work plus fuel cost to get to you but I'd try to get the car looked at by someone with MGR knowledge before calling them. There's a garage in High Wycombe was highlighted to me when I was compiling the T4 map, ex MGR mechanics. https://www.mgrs.co.uk/.

Thanks for all the input guys.

One thing I forgot to mention was that the inlets in the head were all clean as a whistle except for no. 4, which had black gunk accumulated at the bottom. Not sure whether that clue is any help? I have some pics but I don't know how to upload them.

One last symptom it's been getting. After 3 or 4 miles the fan kicks in, big time. When I've stopped to check under the bonnet it carries on running for a bit then stops. There are no obvious signs of coolant loss, but the hoses are bulging. After switching off, gently releasing the coolant filler cap unleashes a lot of pressure and hissing, followed by a torrent of COLD coolant when I loosen it a bit more. When at last I can release the cap fully the coolant settles down to around about the bottom of the tank.

I've bled it, refilled with about around 1/2 to 1 litre, then tried driving again and it did the same thing. Note that at no time during any of my issues has the temp gauge been anywhere but at the halfway point. Any further thoughts? Thanks.

The mid point on the gauge covers too great a temp range (75°C to 115°C) to be of any real use. The onboard diagnostic is more reliable.

Start the engine, press and hold the trip reset button until the display shows "test 1". Release the button then immediately press again and keep pressing repeatedly until it shows "test 19", release the button. The display will alternate between "Log 1 -on" & "Log 1 -off". While it is showing "Log 1 -off" press the button and press repeatedly until it shows "7" then release the button. This will give a live and accurate reading of the coolant temperature.

Cold coolant could mean a dodgy thermostat (not opening to allow circulation) or a dodgy waterpump (not circulating).

Is there a way to test if it is one of these?

Thanks yet again John.

So, if it is the thermostat, then it's locking the coolant inside the jacket thus causing an overheat which the temp gauge isn't picking up for some reason?

If it is the water pump then obviously the effect would be the same... but can they fail (i.e. stop pumping) without leaking? As they are toothed then that seems unlikely. As far as I know there is no sign of leakage anywhere, however I will check again tomorrow.

Sorry if I sound a bit lost. The last car I worked on regularly was my old '67 Minx, and I really understood how that car worked and could do just about anything to it (I still have it, by the way, though it's not run since '92.) I do miss a nice simple RWD engine layout, with everything mounted on the outside and easy to get at!

Cheers John.

"Norwegian Blue", ha ha! "Joined the choir invisibule." Blimey, that takes me back!

No idea on the stat. Take it out to find out? Where is it? I guess I should buy a Haines manual before I give up. Got quite a collection of these now. The Hillman, of course, and Renault 5, Toyota Starlet, Metro, Montego, Peugeot 309, Cavalier, etc.

Happier days when it didn't hurt so much to get out from under the car to find my 10mm socket!

OK – I’ve been mulling this over today, and thinking about all the excellent help and advice I’ve been given here. This is my conclusion thus far (sorry if it’s a bit long, but I wanted to be clear so that the wise souls out there can correct my logic if it is flawed)…

The gas that escapes from the expansion chamber does not seem to smell of exhaust, although it does have a faint smell of petrol to it. So, if we assume, for the moment, that it isn’t the HG then it seems to follow that it may be the thermostat. If it was the water pump then presumably I’d see evidence of water seepage, which I can’t, though I’ll double check that tomorrow, but either way the pump would still be working. Also, the amount of coolant I lose seems consistent with the amount that comes out when I loosen the filler cap, which seems to imply that I’m not losing significant amounts from anywhere else.

If it is a failed thermostat then the coolant locked in the jacket would presumably boil, creating over-pressure. This would account for the water bursting from the expansion tank, and the also fact that it is cold because it is not circulating.

With regard to the blackened new plug in no. 4 then perhaps this is just because the extreme over-pressure has caused the new IMG to fail again at its weakest point, so letting coolant into the cylinder once more. This also kind of makes sense as the vacuum in the inlet manifold would draw coolant in (in a way that a HGF might not) and could also leave the top of the piston damp (which it is).

So, stat is my next target.

Well, that’s my thinking at the moment!

That's a good idea. Usually when I open a cap slowly when hot, it does exactly as you say. It releases the pressure gently and you can open it a little more over time until you can take it off with no overspill or drama. When it's cold, nothng happens. I'll try what you've suggested.

Pressure in a cold system points to exhaust gases in the coolant system - i would as suggested above leave over night after giving your car a decent thrash at motorway speed for 10 miles or so - but in addition to listening for a clearly audible hiss of escaping gas when you open the cap - stick your nose near the coolant tank to see if you can smell exhaust gas as well.

Don't let too much coolant get into the cylinder. I have a friend who bent a conrod because of water in the cylinder.

1.6 k series in a 2002 TF. Plastic inlet manifold. Leak into number 1 cylinder.

OK, even more confused now. Ran the engine (stationary) up to about 80 degrees, then took it for a run. The temp then fluctuated between 97 and 104 degrees, averaging around 99.

Switched off and checked the top hose and it was rock hard. Left it for 6 hours then opened expansion tank. Slight hiss then nothing. No coolant left in tank though. Sniffed expansion tank and could smell petrol but not exhaust.

Like I said, I'm perplexed.