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Starting on 3 cylinders on my turbo

H

homesea

New member
Right I have a question for you clever guys and girls. When the car is cold i.e. been sat all night and I start it up it only runs on 3 cylinders, then after a few revs it fires on all 4. It's been doing this for a while (over a year) but the time it takes to run on 4 is getting longer, about 30 seconds now!

So what do you think? Plugs about a year old, leads 6 months old and cap and arm one week old.

 
I was thinking HG. But now you have me thinking about the sticking valve!

Not sure it has been happening for a year, I had the cam tower gasket replaced a few months back. Can a mix up of tappets cause a valve to stick?

So why would it only stick when cold?
 
I would also add tappets to the list. 944s do have large tappets.

At least this was the reason for why my Passat started on 2 or 3 cylinders, but the tappets really had seen better days. Amazingly, they only became noisy on a few occasions:

AC2A5C27-A7AF-4ABC-87F3-AC8FC34CF8D8-568-0000003CAA5244A4.jpg
 
As above, this is exactly how my failed HG started showing.

A small amount of coolant was creeping into Cyl 4 when cold. On start up it would fire on 3 and a blip of trottle would sort it. After a few weeks it started taking longer, up to around a minute.

Compression test did not find the problem fyi.

EDIT

Just thought I'd add to this in case it helps anyone.

Up until I decided to rally prep my car I was using it as a daily, doing roughly 300 miles per week.

On one journey it lost the little retaining screw on the rotor arm and started backfiring like a Sherman tank.

I replaced the dizzy and rotor arm and all was well. Shortly after that it started missing on start up and I automatically assumed that it was something to do with the ignition or possibly injectors.

I ran a bottle of Wynns injector cleaner and that didn't do anything. I took off the dizzy and rotor and refitted with a dab of Loctite. That didn't work either. I checked that the timing belt hadn't slipped a tooth and it hadn't.

The misfire got steadily worse. At first it would start on 3 and literally on the first dab of throttle it would clear itself and run very cleanly on all 4. Over the course of the next 2000 miles or so it started taking longer and longer, up to around a minute of stationary idling plus blipping the throttle before it righted itself.

Then the other week it had a couple of oddities while being shunted around the work shop while it awaited work to start. It was an odd thing, happened twice to me and then twice to my mechanic - On a cold start, on the very first turn of the key it wouldn't take. The first time it happened to me I genuinely thought I may have not turned the key all the way or leg go too soon. These things happen all too quickly to take them in and on the second turn of the key it started as per normal.

It happened to the mechanic too and like me he didn't twig immediately.

Then last week we were about to start replacing the 2 sensors on the top of the block and took off the rocker cover and upper manifold.

Just by chance my mechanic looked down at the valves and saw that Cyl 4 was full of fluid. On inspection it turned out to be coolant. Oops. Within an hour the whole head was off and off for work (as detailed in my recent thread below.)

It turned out that the non-start on the key was due to Cyl 4 being partially flooded with coolant - it was ever so slightly hydrolocked and the engine didn't have the guts to turn it over while full of fluid (good!) Obviously the very slight movement in the cylinder was enough to dispel enough of the coolant to fire and the second turn of the key had it sorted.

Anyway, long story short: it was of course the HG around Cyl 4 failing very slowly. The compression test done just a week before (in the midst of the firing problems) showed 185/185/185/185 so that didn't give us any indication.

I think you're probably at the very early stages of what I had so I'd prepare for a new HG.
 
Whether it's valves or HG, the actions are the same in both cases. You'll be taking the head off, and while it's off it only makes sense to replace the gasket, decoke the head, inspect and rebuild whatever's worn. If it hasn't had a head rebuild in recent memory that will include cleaning up the valves, checking the stems carefully for wear, and almost certainly having new valve guides in any case.

The reason valves tend to stick when the engine's cold is simply that everything sticks more when an engine is cold rather than hot: they've been stationary for a while and the low temperature means tight clearances, and any unpleasant goo, crud, and carbon deposits at their stickiest.
 
Thanks for the info guys, its in being looked at so will see what they come up with.

Just started it up to take it in and it fired straight up on all 4! First time its done this for a long time, very odd.
 
Well I've just got it back and it passed all tests!

Been running fine all day. Don't know what to think now.

Might do a flush and oil change and throw some new plugs at it, not sure what else to do.

Guess it could still be first signs of HG failling but seems a bit daft to start pulling it apart yet.
 
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