997 GT3 Engine Problems

I had this 997 GT3 come through the shop a few weeks ago during a cross country adventure for the customer and his wife.  They had driven out from the east coast, stopped to fill with gas in Kansas City, and starting having misfire and running issues immediately after.  I have to say, this was an absolute brain scratcher of a problem.  The customer had just had his spark plugs and coils changed out east, motor removed for coolant pipe welding, oil changed, etc. He had just filled the car with gas minutes before the misfire started.  Car came in with multiple cylinder misfires on all cylinders.

Customer stated that when he left the gas station, he got on the interstate, full throttle to about 90 and the car cut out. First time he had gotten on the car hard since leaving the east coast. Common sense told us he had bad gas, water in the gas, etc from his fill up. We pumped all the gas out of the tank, refilled with fresh gas, and cleared the codes. All codes cleared except cylinder 3 which kept coming back as a misfire. So we pulled the plugs and coils out and found a destroyed electrode on #3. Was it a bad plug, bad installation (dropped), bad fuel causing a lean issue?

We replaced the plugs and coils, borescoped the cylinders and could not find any of the missing electrode. Assuming it blew out his open exhaust, we ran the car and all seemed fine until another full throttle high speed run to 90mph where it cut out again. At that point we decided the engine had to come out, assuming a possible bent valve from the broken spark plug.

Tearing down bank 1

Once we pulled the head, I found the missing spark plug electrode had smashed itself into the cylinder head and the bottom. Due to laying flat, being beneath the valve seat, etc we couldn’t see it with the borescope.

Here you can see what it had done to the piston.

We replaced the piston and cylinder sleeve, had the head gone through and put it back together. To break the rings in, I typically drive the cars for a few days at very light throttle with a lot of deceleration. On the day I was going to start pushing the car, I was cruising down the interstate to the shop at 70mph, and felt the car cut for a second, typical fuel cut. That was odd I thought. A few seconds later it did it again. Then was fine. Got back to the shop and pulled the fuse panel apart. The GT3 and Turbos use a dual stage pump with 2 fuses, where as the non turbos only use one fuse. This is what I found.

In Row D, starting from the left, should be fuel pump 1, then fuel pump 2, then a DME (7.5amp) fuse, then a blank spot. Someone at some point had pulled the fuel pump fuses (and the DME fuse), and reinstalled them incorrectly. This allowed the car to get 1 stage of the fuel pump, but not both which it needs for higher throttle applications.

This is how it should look. So, a spark plug blew apart and major engine work required, because someone in the past had pulled the fuses for some odd reason and didn’t get them back in correctly. These kind of projects are always stressful when the diagnostics just don’t add up, but glad we finally figured it out. Customer drove her back to the east coast and has been having a blast with the car again.

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2 Comments

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Jpflip

October 22, 2015 at 3:01 PM

OMG!!! I’m impress! Very good job Doc!!! The fuses problem was not obvious! Good find!!! What is your conclusion for the broken electrode? Defect or mishandle? Also what are you using to time the camshaft on a 997 GT3? Similar to Porsche special tool 9661 or may be a Stromski kit?

    porschedoc

    October 22, 2015 at 3:59 PM

    No doubt at high load situations the engine went lean due to the fuel pump and blew the spark plug apart on that cylinder. Could there also have been an underlying weakness in that plug, possible. We use the factory timing blocks, though I have seen the Stomski kit and that looks like a nice setup as well. Steve’s stuff is good quality.

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