Carrera - wouldn't start, cutting out

[rbertels]

Yesterday at 5:30 in the morning on my way to an Auto X, my car wouldn't start the first 3 or 4 times I tried. The battery was strong and cranked the engine without hesitation. The car simply showed no signs of life. This had never happened before.

I spent a few minutes checking fuses and making sure that all of the relays seemed connected. The next time I tried the car started right up. I drove to the Auto X and at the event with no problem. On the way home the car briefly cut out for second and then continued. This happened twice within about five miles of the parking lot. I safely made it home which was about 75 miles.

I'm thinking along the lines of the DME relay. Although I don't know if this would show up as an intermittent problem, before finally quitting.
I'll order the relay from our host today (as I should have a spare anyway).

By the way does the driver's seat have to be removed to replace the relay?
The car has only 26,000+ miles on it.

Am I going in the wrong direction or does anyone have any other ideas?

Thanks
rbertels
87 Coupe

[Joeaksa]

Check to see if you have the updated cylinder head temp sensor on your motor.

Look on the left side of the motor and you will find a piece of metal holding three wiring connectors right under the blower motor. Usually the top one is the cyl head temp sensor. Look on the right side of the connector (the wire going to the back of the motor and not to the wiring harness of the car) and if you find only one wire going out then you have the old style unit. The new sensor has both the sense wire and its own ground, thus two wires.

Mine was doing exactly the same thing, and would work fine one time and not start or cut out the next. Replaced the temp sensor and it works fine now.

Could also be the DME relay and I would try switching it out before doing the cyl head temp sensor only because the relay is easy to get to and you should have a spare anyway. Slide the seat full back and you can get to the relay with no problem. A 10mm socket wrench is all you need and its in and out in 10 minutes.

BTW, this is a Bit*h to replace and if you are not good with working on cars, leave it to a mechanic. The sensor is hidden in the back of the motor on the drivers side and a real bear to get to.

Joe

[JDaniel]

Joeaksa,
Not to start debate about what is a PITA and what's easy, but I found the head temp sensor to be a relatively easy swap. I do have a cat bypass pipe so perhaps it was easier for me. The only trouble I had was pushing the ruber grommet back into place.
I'd recomend that anyone with the original DME and HTS on their Carrera replace them as soon as they can scrounge together the $100. It's an easy update to make sure the car is running as it should.

[Fun911]

rbertels,
What your describing is identical to a problem I had with my Carrera. I finally had it fix when my wife took the car with her best friend to go shopping. Well, it came no surprise to me when they called up and said the car was dead. My wife's friend got out and pushed the car off the road. When they left, she was wearing some pretty tight fitting jeans. I would have paid money to see her pushing from behind. Well, an unknown person in a 930 pulled to the side and helped them with getting the car into a parking lot. The guy mentioned to my wife, you sometimes got to push these things..My wife said no one would stop to help them. Figures a brother in another Porsche would be a hero..Thanks to whoever that was !!!

I updated the head temp sensor and DME and have not had a problem since. I also notice since doing that the druck pressure gauge seems to be working better too..

Good luck !!

Pat

[Joeaksa]

Dan,

Yours may be easier than mine. I have SSI headers on the car and it was a real PITA to get to with the headers and shock in the way.

I was a aircraft mechanic for many years and am used to working in tight spaces, and this one was as bad as any airplane! I have seen posts of "just tighten it with a needle nose pliers" and such and on my car there is no way to get a normal tool in this area.

I have medical hemostats that are longer and smaller than the pliers and still had a difficult time getting in to work on the sensor.

I ended up borrowing a socket that had been modified with a slit in the side with a grinder that I borrowed from Tom Owen to tighten mine. You are correct that working on a 911 makes you very adaptable!


Agree with you that anyone with a sensor or relay that is 15 years old needs to switch them out.



Joe

[JDaniel]

I tried needle nose pliers (didn't fit), a regular box wrench (didn't fit). socket (ha), and then decided to try one of my craftsman flare end wrenches... it fit like a glove.
There is a special socket for this replacement. I've also seen some "normal" sockets with a groove cut down the center. Not much torque is required... hand tighten and then another 1/4 twist.
Since I began working on my 911 I've become very crafty in my approaches to reaching things.

[schulr]

Add me to the list, was returning home from dropping my daughter off at college and motor cut off about 6 different times but always came on. Seems that if I slowed down to 70, it ran fine. Had my mechanic pull the sensor ($300) and have had not further problems.

[logician]

Hi,

Regarding engine not starting and intermittent engine cutout: I had exactly the same problem in my '85 Carrera, and it turned out to be the DME relay.

First time it happened was while I was on course at an Autocross. The engine just cut out for a second, and then kept going. On the way home, it did the same thing on the freeway. It kept cutting out intermittently for the next few weeks. In the next few weeks, it would sometimes die completely while driving around the block. I would crank the engine to try to restart it, but nothing would happen. However, I would always be able to get it to start within a few minutes. My recollection is that hitting the relay with a screw driver when it was broken seemed to help bring it to life.

I did not have to remove the driver's seat to replace the relay.

-Juan

[rbertels]

Thanks for your recommendations and for sharing your experiences. I have ordered the DME relay and will now add a cylinder head temp. sensor to the order.

I can't wait (?) to try and see what tool I'll end up using to replace the CHT sensor.

rbertels
87 Coupe

[JDaniel]

To remove the sensor just cut the wire and use a socket. It'll come out easy once you manage to get into position. Spray a little silicone on the grommet to slip it into place (keep away from O2 sensor). The sensor does not have to be tighted too much. There are no "forces" trying to pop it out. If you put too much torque on it the end might snap off... and THAT IS a real PITA.
Good luck ,and yes, it would be a lot easier if the damn shock wasn't in the way

[Joeaksa]

Dan,

Also, the sensor that replaced the old one in my car was a different size from the one that was in my car from the factory. Threads were the same that went into the cylinder head but the bolt size that you tighten it up with was different.

One was a (I believe) 14 mm and the replacement was a 13mm so pls get the new sensor in hand before you start grinding on a socket.

Taking the shock off would be a big help and might be the way to go... did not have that option when I did it as was working out in the open with minimal tools.

Joe

[rbertels]

I Just wanted to post a quick update on my replacement of the DME relay and the CHT sensor this weekend.

The replacement of the relay takes about 5 minutes. As everyone told me, the real issue was replacing the CHT sensor.

JDaniel - your suggestion re. the flare wrench was the ticket for me. The pliers solution wouldn't work and I left the idea of cutting a slit in my 14mm socket as a last resort. In the middle of the job I ran out to Sears and picked up a flare wrench.


Joeaksa - You were right as this was an incredibly tight space to work in. I started to get used to laying under the car with my head in the wheel well.

I'm glad it's done and I don't expect any future problems in this area.

Thanks.
rbertels
87 Coupe

[Joeaksa]

Do not just leave us hanging! Did it cure the problem and does the car run any better?

Sure made a difference in my car but you will want to keep the old DME relay as a spare in the trunk. If its there, you will not need it, and so on!

Glad to hear that its done and hope that it cured your problem. After switching them out on my car I have not had one problem again with starting/cutting out.

Joe

[rbertels]

I only had a chance to start up the car. Everything seemed fine.

This weekend will be the big test as I'm going to Pocono on Friday for a DE with the Metro NY Region.

rbertels
87 Coupe

[jabb]

Can someone define what they mean by engine cutting out is it just a brief hsitation or is it no power like the tach drops to '0'

I changed plugs wires cap and roto the problem I was having has gotten much better but I get an intermittent hesitation at about 2500 to 2800 rpm's BTW 84 Carrera

[Joeaksa]

Joe,

I was having a momentary hesitation on my 85 car and could not find it for anything. It would drive fine, but would hesitate at times and was not pulling strong like normal. Finally gave up and took it to a shop and paid the bux to have it scoped.

They found what I had not, a cracked dist cap (on the back side where you do not look!) that was causing the problems on my car. You have already changed yours but you might look again to make sure that your new cap is not cracked. Did not take much on my car and after looking closely I could see the carbon tracking easily...


JoeA

[scottb]

I'm relatively new to P-cars. How can you tell if the DME and CHT sensor are original and have not been upgraded? (Where are these parts located?)

Thanks.

[jabb]

Hi Joe

I will check the cap make sure its good.....

Top end or when I push the car it pulls stong no lack of power just this annoying hesitation that happens ocassionally seems like 2500 - 3000 rpm