I've been busy after buying my '93 Mk2f 1.3 (SPI) polo giving it a full service and replacing any old or duff parts. The thing was running like hot garbage when I bought it but now is running great and doing just shy of 50mpg on a proper run.

 

However...

 

When starting cold it misfires on one cylinder, clearing up and idling properly when it warms up a bit (i.e. not ~90 degrees, just when its a bit warmer so still in the temperature-controlled fuelling schedule). This problem went away totally when the plugs and leads were changed a few hundred miles ago - it started on a dime and idled correctly from cold. However slowly but surely the misfire has crept back - its not a dealbreaker as it runs perfectly within a few minutes but all that chug-chug-chugging in the morning is quite frustrating!

 

Things I've tried:

* Cleaned the throttle body - no change to the misfire but picks up better once its warm

* Plugs and leads are new, as is the distributor cap and rotor

* Ignition timing 5 degrees before TDC, checked with a timing light - again a positive change here

* Fuel filter new just before i bought it in November

* New blue temp sensor - not OEM (Hella) but made no difference.

* Checked for air leaks around the inlet manifold - none found and unlikely the cause because it runs great once warmed up? Also checked vaccum leaks and everything is airtight.

 

Has anyone had this kind of cold misfire and found a solution outside of anything major? I know its Cylinder 1 from pulling leads when its misbehaving. Why should brand new plugs cure it temporarily? Could it be a dodgy tappet for cylinder 1? There's no excessively bad tappet noise but if one is taking extra long to puff up with oil could it be messing up the firing until it does?

 

 

 

 

is that plug worse looking than others ? oily /black or wet?

 

my thoughts would be possible head gasket leaking a little coolant into that clyinder and it burns off after starting , had it on one of my golfs and you could see the piston was wet after standing overnight

 

or an issue making that plug oil up ...should be obvious if you look at it , new plug was clean and ran great until it fowled up ? 

Just now, steveo3002 said:

is that plug worse looking than others ? oily /black or wet?

 

my thoughts would be possible head gasket leaking a little coolant into that clyinder and it burns off after starting , had it on one of my golfs and you could see the piston was wet after standing overnight

 

or an issue making that plug oil up ...should be obvious if you look at it , new plug was clean and ran great until it fowled up ? 

 

Thanks for that - I'll have a look at the plugs after its stood for a while. From memory there wasn't any oil on the old plugs when they were changed (just a lot of carbon - but that was from rich running from years of never getting to temperature I think).

 

Incidentally the head gasket is slightly leaky in the usual area (towards the timing belt end of the block, front corner) - I wouldn't be surprised if its leaking into cylinder 1 as well.

 

How much of a faff is head gasket replacement? Its not something I've done before and I don't have a garage to do things in (just the street unfortunately!). Would it be the kind of job thats actually worth paying for?

 

Thanks for the help!

 

yeh see how you get on ...the fact youve pin pointed which clyinder is a great help

 

inlet gasket leak would /could improve once warm ..but isnt explained away by the new plugs

 

id say replacing the gasket is pretty easy , way easier than alot of moderns , ive done mine in the street, if you have a decent tool kit and some common sense you will be okay , always happy to help just ask , a garage would prob charge more than the car is worth

There is a hg change thread around with some decent tips in it 

3 minutes ago, kiran_182 said:

There is a hg change thread around with some decent tips in it 

 

not the one that makes his own timing marks and reccomends cuting the covers off ? 

No, those are not good tips, things like wd40 exhaust nuts a few days before, razor head and block, clean headbolt recess with cotton buds

 

Stuff like that

 

If you want bad advice ask.about fitting 8.5j ona  breadvan

only needs a few camber washers 

 

seriously ask first ...doesnt need a stupid amount of tools or know how , but theres right and wrong ways to go about stuff 

Very true, plan ahead, work in order. Have some thick card to put the head on when off the car

 

When you put it together check the timeing marks 3 times and turn the engine by hand to make sure you have clearance

All brilliant stuff - thanks everyone!

 

Not sure when I'll be able to get round to it, might have to wait until there's more light in the day and I can spend some annual leave on the problem!

Started it up again this evening and it was awful - If its not a wet cylinder I don't know what it is. Worth doing the head gasket to try and stop that oil leak anyway so I'm going to have a crack on Friday.

 

Ordered an elring head gasket set and some 96mm Febi cylinder head bolts. Got another pair of hands as well hopefully as I'm guessing lifting the thing out carefully is easier with two?

 

I'll follow Haynes but got all of the tips from various threads so think I've got it. Is it worth doing anything else while I've got the head off? Thorough clean of the intake manifold? I've incidentally got a pot of valve grinding paste that I've never actually used for valves (good for back-lapping lawnmower blades!) and have a valve spring compressor lying around - is it worth grinding the valves in? Thinking effort/benefit analysis here... Could conceivably replace the tappets while I'm at it but one doesn't need to remove the camshaft for a head gasket change necessarily? Could also do this when it actually needs to be done...

 

Thanks for the help!

 

 

 

your more than half way to changing the cambelt and water pump if its never had one 

 

id suggest you undo the mani- downpipe bolts and lift the head off with bolt manifolds, tb etc still on 

 

devise a method to hold the camshaft pully while undoing the bolt, you can make up a Y shape peiece of wood with 2 bolts in it to replicate this https://www.ebay.co.uk/itm/Camshaft-Injection-Pump-Sprocket-Pulley-Cam-Holder-Holding-Counterpart-Tool/332465940546?hash=item4d6883a842:g:7tUAAOSwC85cG35G:rk:19:pf:0

 

have you got the spline tool and a trusty torque wrench?   remember to oil the bolt heads /washers when fitting

oh and cut down 2 old head bolts and make a slot in the top....that way it holds the gasket in place and guides the head on (yours might have dowels /mine doesnt) 

12 minutes ago, steveo3002 said:

your more than half way to changing the cambelt and water pump if its never had one  

 

Way ahead of you! Did those a few hundred miles ago so thankfully can just slacken the belt and move it out the way.

 

13 minutes ago, steveo3002 said:

your more than half way to changing the cambelt and water pump if its never had one  

 

id suggest you undo the mani- downpipe bolts and lift the head off with bolt manifolds, tb etc still on 

 

devise a method to hold the camshaft pully while undoing the bolt, you can make up a Y shape peiece of wood with 2 bolts in it to replicate this https://www.ebay.co.uk/itm/Camshaft-Injection-Pump-Sprocket-Pulley-Cam-Holder-Holding-Counterpart-Tool/332465940546?hash=item4d6883a842:g:7tUAAOSwC85cG35G:rk:19:pf:0

 

Interesting - I'm guessing thats because they're easier to get to and less likely to be siezed? Or just fewer bolts? Reckon we should take the bonnet off to lift all that lot out at once?

 

15 minutes ago, steveo3002 said:

have you got the spline tool and a trusty torque wrench?   remember to oil the bolt heads /washers when fitting

 

Indeed - got a torx/spline/socket-head set when I had to smash those old aux pulley bolts out when I did the cambelt change. Never go anywhere without a torque wrench!

So just the bolt heads? The threads and the bolt recesses should be clean and bone dry to set the torque correctly and prevent any hydraulic nonsense right?

 

15 minutes ago, steveo3002 said:

oh and cut down 2 old head bolts and make a slot in the top....that way it holds the gasket in place and guides the head on (yours might have dowels /mine doesnt) 

 

Yeah i'm pretty sure mine doesn't have dowels. Trying to visualise this - so they'll have to be threaded in slightly into the block, head goes on and then they're backed out through the head using the slot cut into the top and a screwdriver? Kind of like a long grub screw?

yes thread the 2 cut down bolts into the block so theyre sticking up , stops the gasket falling off , then guide the head on and fit a couple of new bolts finger tight and remove the cut down ones

 

bonnet off...ive never bothered , the manifolds stay on as theyre much easier to work on once off ...and probbaly dont need touching anyway , saves time and fiddling around with hard to reach bolts , expect some exhaust ones to snap if you decide to unbolt the manifold ...id purchase some new brass nuts for the downpipe and soak the studs in penetrant now

 

bolt holes . yes clean and dry....if possible blow them out incase some antifreeze spilled in there , bolt packet may indicate to oil the heads/washers , mine did

 

yeah just pull the cam belt away ....time the engine to TDC then back 1/4 turn like it says in haynes , so the valves are out of the way

 

as for grinding the valves...not a bad idea if youre confident to get it right , can check before /after by tipping some solvent in the ports and see if it leaks out the valve face     

Edited 16 January, 20197 yr by steveo3002

is it a car you need for work monday morning?

 

not a bad idea to decoke the valves , ive always span them in a drill and used some emery paper to smooth it off , be carefull to not touch the sealing surface with sandpaper

 

if you have the valves out fit new guide seals

 

if its not silly milage /smokey id be inclined to say just do the gasket ...depends on time etc

Its a 145k head, very much doubt anything has ever been done to it. Doesn't burn oil or have any immediately obvious sealing problems around the valves (or rather no problems manifest through the temperature range etc - just this cold start misfire). I'll probably leave them well alone - never cleaned up or lapped valves in before so if there's no real reason to then probs best to leave alone! Plus its running efficiently on long runs so I doubt I can improve it much - much more likely to muck up the valve seal!

 

4 hours ago, steveo3002 said:

 ...id purchase some new brass nuts for the downpipe and soak the studs in penetrant now

 

Good idea! Any old brass nuts that fit will do?

 

Its not needed on Monday morning but I'm keen to not have it sitting around without a head for too long. Main thing is getting it running reliably again.

 

Thanks for all the help!

i like these deeper nuts...less chance of rounding them off

 

https://www.ebay.co.uk/itm/M8-Brass-Exhaust-Manifold-Nuts-8mm-x-1-25-Pitch-High-Temperature/252951666724?hash=item3ae5182024:m:mZ04WJb8pNKQMEhVvBaC_4g:rk:2:pf:0&var=551977228438

Nice, thanks!

Quick update:

 

Got the head off which is currently sitting on a table in my living room, cleaned up the mating surfaces with 240 grit emery cloth and thoroughly wiped with clean rags and brake cleaner. The gasket was a mess and came off real easy (too easy?) - it has the blue lines of an elring gasket so I think its been changed relatively recently but was otherwise dead gungy (and in places that don't account for the mess you make taking the head off). Is this 'normal'? for an old gasket?

 

Bolt recesses are cleaned out and dry. However even with cloth stuffed in the bores there's a lot of crap (carbon flakes mostly) in the crowns and plenty stuck around the edge of them. How diligent should I need to be getting all of that out of the crown edges before the crank is turned over again? I havent de-coked the crowns yet because I don't really want to make more crap if its going to be a pain getting it out...

 

Not going to touch the valve seats - if it aint broke and all that. Also the camshaft seal hasn't been leaking so is it worth replacing (the elring kit contains a new one)? I'm obviously committed to making a mess already but I don't particularly enjoy the sound of the haynes removal method...

 

I've also got some elring gasket compound to potentially put a smear around the leakiest end (where the high-pressure oil channel sits just above the oil pump). Should I bother? Belt and braces?

 

 

 

Some pics:

 

(apologies for links - didn't tell my phone to save them small enough for the forum!)

Before:

https://drive.google.com/file/d/1NdvZTCOxZ9XNqYZDFMHVeKTfRaQGyQK1/view?usp=sharing

After:

https://drive.google.com/file/d/1oCXwjjM8QBQBHtxdHf_v076OvEV_TWoJ/view?usp=sharing

 

Block after cleaning:

https://drive.google.com/file/d/1sF1mpBB6XRWWf0UsYxT-0UVG8Q7F5CYv/view?usp=sharing

 

 

 

 

 

ive sometimes used the smallest of smears only around the corner oil hole...hasnt caused any problems , never use it near the pistons

 

dont have to clean the pistons at all if you dont want to , when i have done ive cleaned up with rags then moved the engine a little and rewipe etc 

 

do all the pistons /valves look the same? ...if it was leaking then id expect one or two to have a differant appearance  

21 minutes ago, steveo3002 said:

ive sometimes used the smallest of smears only around the corner oil hole...hasnt caused any problems , never use it near the pistons

 

dont have to clean the pistons at all if you dont want to , when i have done ive cleaned up with rags then moved the engine a little and rewipe etc 

 

do all the pistons /valves look the same? ...if it was leaking then id expect one or two to have a differant appearance  

 

 

Thanks - I'll leave the then.

 

There wasn't any major difference to be honest - at least not an obvious steam-cleaned / oilier appearance.

right..

 

might be worth doing an inlet gasket then for belts n braces ...they often leak worse when cold then seal up as it gets hot , but doesnt explain why the plugs fixed it

 

if its still there after the work , then swap the plug and lead to another cly see if the fault moves

Cool - I'll have a go at that then, thanks!