Need help: power loss

[MH911]

Hi all. I hope someone can help me with this problem. I did do a search and found a few threads where people had offered suggestions. The OP would give a "Thanks, I'll try that" and was never heard from again. Lot of help that was.

Car was running great yesterday on a 200 mile round trip to Big Sur ( great day ). Today, while driving on the freeway, the engine suddenly started to lose power. I couldn't go any faster then about 45 MPH. The engine would sound like it was dropping RPM's and then suddenly sound fine for a second, then drop down again. It would give off some small backfires while losing power. It seemed like it was missing.

The engine never stalled. In fact, while stopped at a red light, it idled just fine. It would even rev fine. But when I would start moving, it struggled to gain any sort of speed.

I am no expert mechanic here. I can do a basic tune-up. Hope someone can point me in the right direction here. Thanks for any help.

[Oh Haha]

I'll try.

While it could be several things, let's start with the basics.

How old is the fuel filter? How old/dirty is the air filter?

What was the engine/oil temp when it lost power?

Do you have a spare DME you could swap out with the current one?

Others will chime in but these are things we will need to know to help.

[Mark McClure]

Distributor cap cracked...? just a guess butat least a place to start.

Symptons are similar: idles fine but when load is placed on the engine the distributor can not transfer the spark effectively. Usually keeps doing it rather then coming and going though.

Mark......

[Oh Haha]

Nice call on the dizzy cap, Mark!! Easy to check out as well.

[MH911]

Thanks Wayne.

Looking at the paperwork I received from the PO, major service was done back in 2006 at 78,500 miles. I have almost 88,000 miles on her now. The fuel filter and the DME ( no spare )were both replaced at that time. I had looked at the air filter just a few weeks back and it looked in good shape. All the gauges looked fine at the time the problems started.

I have replaced the spark plugs and the O2 sensor my self in the past 2 months. Including oil and transmission fluid changes.

[MH911]

Mark,

Just popped off the Distributor cap. No sign of cracks on the inside or out. Looks like it is getting close to be needing to be replacement though.

[Mark McClure]

It just takes a hairline crack to cause issues usualy start at high revs and get lower in the rev range as the crack expands, if it needs replacing anyway!........on the other hand it may be something else. Lets see who else chimes in on the thread.

Mark........

[MH911]

FYI. The Distributor cap and rotor were both replaced during the same major service back in 2006. I look as close as I could with my old eyes. There might have been something, but I couldn't see it.

[MH911]

Local Porsche mechanic ( Tom Amon ) came out today to take a look at the problem. He really wasn't able to determine what the problem is, but it is much improved ( drivable ). Still sputters and misfires at high RPM. Here is a list of things he checked.

Check operation of air flow meter, head sensor, speed reference sensor dist advanced, fuel pressure. All was good.
Replaced DME relay. Replaced spark plugs. Checked plug wires.

The one thing that he did that improved the running of the engine was unplugged the computer and cleaned it's pins. With this action, I was able to take it out on a test drive and everything looked pretty good until I started pushing the RPM's higher. Before cleaning the pins, it was not drivable and was sputtering and misfiring pretty much all the time.

So, improved, but don't feel comfortable driving too far from home. Hopefully someone has some idea with the information I added here.

[MH911]

I thought she was drivable.

I just got back from a test drive. I was out about 6 miles away from home, going about 70. Everything before was running fine. I wasn't pushing it. Then suddenly the engine started to sputter and backfire again and the tack was bouncing around. Then the tack went down to around a 1000 and would just sputter if I tried to bring the RPM's up. I pulled over to the side of the road and turned the engine off. Sat there for a few minutes, then started it up. Seemed OK again. revving was OK. So I started again, but turned around to head home. I kept the speed and RPM's down. Then the problem came back again. Again, I stopped, shut the motor off and sat there a few. Started it up and drive a short distance before it all happened a third time. I'm thinking tow truck at this point. I was still about 5-6 miles away from home. After a short time, I started it again and continued on home. Kept the RPM's and speed down and I was able to make it home with no other problems.

Once in the garage, I noticed that when I rev it and let it go back to idle, it seems to have a little twitch around 1000. I don't remember it doing this before.

I sure hope someone out there has some idea of what my pcar is going through

[T77911S]

vacuum leak? look for cracked hoses.

fuel problem.
bad gas, clogged screen in tank, fuel going bad. does your car have a pressure regulator?

[MH911]

Thanks all for your input. I have had a Porsche mechanic looking at my car for the past day and a half with no results. Very frustrating.

[Oh Haha]

If Tom can't find it, I'm not sure what to suggest. Sorry.

[MH911]

Tom suggested I take it to a shop with more test equipment and that's where it's sitting now.

[MH911]

Well. I finally got my car back yesterday and after two months of not being able to drive it, it's fixed and back on the road. It feels great to be able to take her out again.

Problem ended up being a combination of the spark plug resisters ( minor ) and the two Reference and Speed Sensors ( major ). The mechanic said that someone at some point replace one of the cables and did not place the wiring into the grommet properly and the insulation on the wire was rubbed through. Plus at the age they are, the insulation was crumbling off. The sensors and resistors were replace and it's running great once again.

The weather has been perfect and the road calls me. Anybody doing any drives in the South Bay?

[MH911]

And here are some photo's just to give this thread some color.

[ossiblue]

Kipp,

Congratulations on getting your car back on the road, and thanks for the beautiful pictures, but I really want to thank you for posting the cause of your problem! As you stated in your opening post, you found many threads where there was no information given if a problem was solved, and that helps no one. You have done us all a great service by closing out your original post.

Happy driving!

[MH911]

Thanks LJ. Hopefully I can make someone else's life just a little bit easier.

[Oh Haha]

+1 on posted the results for the next guy.

Great looking 911. Now, get out and drive it!!!