olddirtbiker

Hello,

I'd like to ask the group for some advice regarding my 996 turbo. This car was recently bought by myself after hankering after one of these for years. The 996 turbo was chosen for the specific reasons of power, handling and reliability.

My car is a 2001 tiptronic model that I purchased in Abu Dhabi which is close to where I currently live in Oman. I brought the car over the border and got it registered here.

I was delighted with my car. Tons of power, great on the back roads we have here and real smooth for taking to work down the highway.

Anyway, I pull away from the lights and the car suddenly develops a misfire. Really bad from zero upwards. Once the revs build it is still down on power but the misfire seems to smooth itself out.

I did a quick look around the net and found out about the issue with the plugs and coil packs. The car was getting due a service anyway so prior to leaving on holiday I left the car with the local dealer here asking for a full service with new coil packs to be fitted.

On my return I find that the fault still exists despite the plugs and coil packs having been changed. (Old coil packs had numerous cracks in them).

In order to eliminate possibility of mechanical damage causing the issue a compression test was done with the result that there is zero compression on No 4 cylinder.

I am now being faced with a possible 900 gbp bill to pull the engine and strip to investigate.

There is another part to this story that might have relevance. After I have had the car about a month I get hit from behind by a truck that knocks the car in to the middle of a roundabout. I am talking a real hard thump that really shocked the car. Expecting total carnage at the back I get out the car to find really minimal damage. A split to the little rubber extrusion and very light creasing of the paint on the bumper. A check underneath revealed no visible damage. From the time of the collision to the start of the misfire is less than 1000 kms. Immediately after the accident there was something different about the way the car drove that i find difficult to pinpoint and describe. Still plenty powerful but slightly less so on acceleration. Not something that you would say was areal problem. I felt that the engine may have moved about a bit more as well.

So my questions are:-
1.) Do you think it is possible to get the compression test on no 4 cylinder wrong due to access issues. The tool used was a press in rubber cone type. Not a scew in type. The zero reading is ringing alarm bells for me. All other cylinders were acceptable.
2.) Only one cylinder has zero compression. How likely is this. I am tending to point to a valve problem.
3.) Can you think of any scenario that could cause zero compression on one cylinder as a result of the collision. The location of the collision rear right hand corner coincides with location of no 4 cylinder.
4.) If the zero test is a red herring is there anything that should be checked prior to pulling the engine (thinking fuel injector connectors that might have been displaced etc)

Thanks in advance for any advice received. I've spent all my money buying this car and need to keep costs down in trying to repair it.

neanicu

Ask the technician to do a leak down test on that particular cylinder in addition to the compression test. The leak down is more accurate and can show you the percentage of leakage you have on the cylinder. It can also pinpoint in which part of the engine the leakage is occurring,whether it's an intake or exhaust valve,piston rings or even a failed head gasket.

Macster

That rear end collision I suspect did more damage than has been reported. The car should be torn down -- the rear bumper cover and some other hardware removed along with the wheels/tires -- and placed on a Celette Bench and various hard point locations checked.

An experienced tech very very knowledgeable with Turbos needs to check the exhaust system, the intake system, the intercoolers, to name a few things, to be sure there is no "hidden" damage from the imho moderately severe impact.

My first guess is I do not think the collision had anything to do with the engine problem based on 1000kms is a "long" distance to drive for something arising from the collision to make itself known. It is not exactly the kind of symptom or behavior I would expect to arise. Or maybe it is... More on this below.

Assuming the lack of compression in the #4 cylinder is real the problem it is likely a burned exhaust valve. Were there anything wrong with the piston/cylinder, wrong enough to produce no compression, I think you'd know about it from other behavior. The same goes for the block or the head or head gasket. You'd know about it, that is have other things going on with the engine.

But you have to be sure the compression test results are valid. If you are using a shop that doesn't use a screw in adapter to do a compression test I would pick another shop. I would certainly not rely on this shop to do any Turbo engine work.

If the compression test results are invalid then there are various possible explanations for the problem with the #4 cylinder -- besides the coil or plug -- that could be explained by the after effects of the collision. One is some body or other part is in contact with the wiring harness and has caused an electrical problem with either the coil or the fuel injector. An impact hard enough to push the car like it did is a substantial hit. I can't believe that just cosmetic/superficial damage is all that resulted.

'course the problem could be just a bad injector or the coil is not plugged into the wiring harness connector properly.

But where you go from here depends upon accurate and reliable compression test results. There can be no question of the results.

So you have to get the compression test done again and this time at a place you can trust to deliver to results you can then act upon, move forward with.

If the compression test finds the #4 cylinder low then a leak down test is called for. This will help the tech determine if the leak is due to a block or head or cylinder/piston/ring problem or an intake valve or exhaust valve problem.

Regardless then the engine will have to come out of the car and at least be partially torn down to deal with the root cause of the problem.

rmc1148

I do not believe the car has zero compression on one of the cylinders as it would run very rough. You need a leak down test as noted.

Kevinmacd

Is your check engine light flashing as you drive and experience the misfire?

olddirtbiker

Gents,

Thanks for the responses I have received

I am in the middle of something just now so there will be a short delay in getting back to you with more detailed information. However very quickly:

Neanicu: I will be asking for the leak down test. Will provide details once I get them.
Macster: thanks for your comprehensive analysis on the information I have provided. The description of the method of doing the test was provided by the service desk rep. I am going to try to talk to the technician personally to get confirmation of how the test was done. I have access to only one garage the works with Porsches. I believe they can do a good job for me.

olddirtbiker

Rmc1148: the car is running really rough. As mentioned I will be requesting the leak down test.
Kevinmacd: the check engine light is on once the car is started up. Will check to see if it is flashing. Does the flashing have significance.

nigelhenry

Hi dirt biker,

I live in Dubai, also own a Turbo.

I had a power issue and it turned out to be a fuel pump hose leak.

In any case, Alex Renner motors here in Dubai are excellent and could be a good source of a counter point for solutions to this.

Also if you need to spend big to fix this, it could be worth trucking the car here rather than letting the dealer spend your money....

olddirtbiker

Thanks Nigel, and everyone else. I am in the middle of negotiations with the insurance company right now so no immediate progress. Will keep you informed once things start moving on this.

Cheers

olddirtbiker

Just wanted to confirm, the compression test was done using a screw in adapter. Engine is coming out round about now.

Viperbob1

Before going into it they should have done a leakdown as suggested. This would have told you WHERE the compression was going. Also, a boroscope is great and very detailed these days for seeing inside the cylinders.

olddirtbiker

Dear all,

The engine is out and the heads are off. Valve seat in no 4 cylinder just about to fall out. Feel really lucky considering I actually drove it to the garage.

Macster

Wow. That was a close one.

rmc1148

Happy you made it to shop without real problems=hopefully you'll be back on the road soon.

olddirtbiker

So it looks like a new head will be fitted. I will be asking for the valves in the other head to be removed and all valve seats to be checked and valves lapped in.

Is there any other jobs that would be wise to get done while the engine is out?