Cold Start Misfire A4 B5 AVV engine code

[JhAudi]

Hi to everyone, I am pretty new to the forum I have a 2000 X Regd 1.8SE which I intend to use for the forseeable as my daily driver. I have a 54 Modeo TDCI Zetec which I am going to sell in favour of the Audi but I have some mechanical issues pls see below.
I also have and am rebuilding a Mk1 Golf GTi 1982 this is a rolling resoration and is going quite well. Any way on to the problem

Apologies if it is a bit of a missive.

AudiA4Misfire
In May 2010 I bought a 2000 X Regd Audi A4 (B5) 1.8se off a friend the engine code is AVV
The car had snapped a cambelt 2 years prior but the cylinder head had been rebuilt/reconditioned. I don’t know exactly what was done but it cost him c£700. He later spent a similar amount on the bottom end.
I drove the car over 3 or 4 days (150 miles) it drove fine there was a bit of a rattle from the cam chain and when I checked the oil it was a bit low. I topped it up with about 1 litre of oil
I then booked it on for an oil and filter change with the local garage that I have been using for 15 years
I picked the car up it drove fine on the day but when I started it next morning it drove fine for the first 100 metres and then started misfiring badly as if it was missing on 1 or 2 cylinders.
I called the garage they said bring it round straight away which I did but on the way to the garage after 1.5 to 2 miles the problem cleared and the car drove perfectly.
I took the car home it drove fine for the rest of the day but when I started it the next day I had the same misfire after 100 metres I called and booked it into the garage and once again the problem cleared by the time I got there
I left the car overnight and the garage had the same issues when they started it in the morning. It appears that misfire or maybe I should call it a backfire is gas being sent back down the inlet manifold I think due to the inlet valves not closing/sealing
We had noticed earlier the cam chain was catching the rocker cover and they had ordered a cam chain which they fitted but the symptoms still persisted
As the car has done 120k miles and I had only paid £1000 for it I had budgeted for some mechanical repair work and my thoughts were that it may need a top end rebuild
Having discussed the issues with the garage owner (a personal friend) we thought it may be damaged valves so they removed the cylinder head sent it to the engineering workshop they normally use
The cylinder head was returned some of the valves had been replaced as they were sticking and then all the valves were lapped in etc
The head was refitted and the misfire is still there from cold start and once again disappears when it is warm
Also the misfire seems to have moved from cylinder one to cylinder two
Some people I have discussed the matter seem to think it is a slightly warped valve but other say if a valve is bent it will stick whether the engine is cold or hot
Any help advice or views would be very welcome
This has all happened over the last 5 months or so I may have omitted some info by error
The garage I use is run by someone I know and trust and in the past fifteen years they have resolved problems for me at very low cost they are therefore very trustworthy

[burkey1]

Have you good fuel pressure, cylinder pressure. were these tests done?

Run a diagnostic test to pinpoint cylinder(s) you suspect are misfiring.

[iwaters]

Has a fault code scan been done? Has it shown anything, other than the missfires?

Also when the chain was replaced was it installed correctly? There should be 16 rollers on the chain between the markings on the head. Was the tensioner checked/replaced at the same time?

The only other suggestion I have is a compression test. I wonder if something is not sealing correctly when cold but once the metal warms and expands it does seal. Although the head has recenbtly been inspected they may have missed something. Or it could be a problem with the piston rings.

The thing that I find odd is the previous owner had the head re-built, then later on had to have to bottom end done? Was there damage not discovered at the time the belt snapped?

Edit: Also the head has been off at least twice, has it been checked that it isn't warped?

[JhAudi]

The mechanic at the garage has done a compression test and that was ok

I will ask him re the fuel pressure

He has run a diagostic check I cant remeber the results I will ask him

The misfire is coming from the exhaust gas being blown back down the inlet manifold

you can feel the manifold for cylinder 2 getting warm when it is misfiring

Thanks for your help it is much appreciated

JH

[JhAudi]

The mechanic has run a fault code scan no faults were shown

He is certain the chain was fitted correctly I asked him and he double checked

Compression check came up ok

I took suspected it may be someting sealing post warm up

The previous owner is not very knowledgeable re mechanics I thinkthe bottom end work he had done was the sump removed sludge cleared etc and new oil pump fitted

We have had the sump off checked for sludge and fitted yet another new oil pump

I did ask if the head was warped the mechanic said he had checked with the machine shop who said it was all ok

Many thanks for your help this has got me stumped and my mechanic friend is very frustrated at not being able to repair fault he has 30 years experience and owns a Golf mk 1 and a mk2

Once again thanks for your help

[burkey1]

Its strange you say the compression test was ok yet you say exhaust gasses are getting back down the inlet.

Was there any difference between cylinders, did you reference it against this engine code spec?

[JhAudi]

Hi Burkey,

I will check info with mechanic as he undertook compression test

I believe he also did cylinder leakeage test, not sure if that is the same thing

[iwaters]

Hmm something doesn't quite make sense with all that but I am not sure what.

I am not sure if this is against the forums rules (advertising another forum) but the only thing I can suggest is posting in the Engines & Drivetrain section on Pistonheads. There are a couple of guys on there who build engines, one used ot build race engines they may have a better idea. Be warned though one can be a bit crabby, but he is ok.

[JhAudi]

Apologies if I am a bit sketchy with some of my replies. All of the work done to date has been performed by another person so I am having to rely on my memory relating to events that have occurred over the last 3 to 4 months.

he has certainly scanned for faults and undertaken a compression test

I will note down the questions I have been asked and ask him

In essence when the car is first started from cold exhaust gasses are retrurning back down the inlet manifold.

When the car warms up within 1-2 miles the problem goes away

Thanks for your help. I will go and have a look at the forums on PistonHeads

[burkey1]

In essence when the car is first started from cold exhaust gasses are retrurning back down the inlet manifold.

When the car warms up within 1-2 miles the problem goes away


Sorry, but i can't see further then the inlet valves not seating right when cold then, or a crack..

[JhAudi]

Thanks for info

The search goes on....

[iwaters]

Sorry, but i can't see further then the inlet valves not seating right when cold then, or a crack..

I agree, I would have expected this to show on a compression test though. Same with a crack. I think you need to check that the mechanic did the compression test when the engine was cold.

When the belt snapped orignally, did the previous owner replace the head or was the damage repaired? I suspect the head has not been properly checked and repaired. I know it was looked at again recently but I can't think of anything else.

[JhAudi]

I will check with mechanic exactly when compression check was done

When the belt snapped originally the cylinder head was repaired not replaced

The cylinder head work was done by a third party engineering workshop.

I will ask the questions relating to whether it was done correctly

Thanks for help once again

JH

[JhAudi]

Update
Cylinder leakage test was done again this time we had 30% reduction on number 3, we then checked cylinder 2 that was ok, we then checked number 3 again and there was no leakage at all (strange).
We started the car it ran ok but when we revved it slightly the misfire came back
The head was removed and taken back to the machine shop that had undertaken the head work previously , my mechanic was present for the strip down
Number 3 had a broken inlet valve spring, this was replaced along with all inlet valve springs. Head was refitted started ok and I have driven the car for 350 miles. It runs like a dream
Thanks for everyone’s help