Hi guys,

First, I will excuse my bad English. I’m from Denmark (Scandinavia).

I am the happy owner of a 993 (C2) 3,6 tiptronic from 1994.

Normaly I use my car every day, but it until a couple of days ago, it had been standing for two weeks, because my wife gave birth to my son
When I started it, it made a huge backfire, and seperated the intake… And wouldn’t start afterwards.

To be sure every thing was okay, I bought all new clamps for the whole intake, and the car started, and the car and I had a perfect drive for half an hour. I parked the car and I was convinced that I had solved the problem.

Today i would go for a ride, and it did the same again… BOOM! And the intake was seperated again.

I searched all the forum threads I could find, and most of the threads says ”timing belt on the distributors”… But that’s not the problem in my car. Both of the distributor caps looks good – no tearing or black spots, the rotors looks good, and the timing belt is not broken.

Any ideas what could be the problem?

I believe it’s some kind of sensor maybe?

Could it be the fuel pressure regulator? I ask because I know, that the guy I bought the car from, (two years ago) told me that he changed the fuel pressure regulator to a used one, because it made a backfire once.

 

Are you sure the distributer belt is good?

Something is wrong with your timing and that belt is known problem.

1) pull both distributer caps and confirm the secondary is locked in time with the primary.

2)use a timing light to confirm it has not slipped... if the belt is "good" i'm wondering if it may have missing teeth and allowing the timing to fluctuate.

 

Check the Disti for a breather tube. The 94, and maybe 95, did not have this tube. If you don't have it, then the belt is most likely bad. I believe they started to use the breather in 96 (I have it).

I had just dropped the motor and was considering rebuilding the disti, but my Indi(Bill Pfister @ Eurotech, best in Metro-West Boston!), educated me. My 96 is fine and we did not rebuild it.

Its actually easy to check the belt. Just remove the secondary cap, the one that is offset, and then have some one turn the car over... If the secondary rotor does not turn, then its the belt.

Good luck!

 

I would check the head temp sensor as well as the fuel pressure to make sure they are both working properly since lean fuel mixtures can create backfires.

Naturally, the distributor rotor phasing must be perfect so make sure the rotors are both pointing to the little indicators (points) on the distributor bodies.

 

Check your vacuum lines

 

You blew the welds on your intake? Now, me and the mad scientist got to rip apart the block and replace the piston rings you fried.

If you don't get the reference

 

It is unclear to me how such a serious symptom can happen. I would not run the engine again until the problem is resolved.

 

Your English is fine.

I had this problem a few years ago and in my case it was a bad reference sensor. These sensors can and do go bad, usually from heat soak. It is located at the flywheel. Part no. 996-606-105-00. This sensor is critical to timing. Also this sensor needs to be a certain distance from the flywheel or it will not work correctly. If memory serves me it should be 1mm +/- .2mm. Have you had any clutch work lately?

Another way this can happen is leaky fuel injectors. The car sits for a while and gas drips into the chamber. When you start the car, K-boom! Get in there and see if you can smell any gas.

One more culprit could be the MAF sensor. When this starts to go the car usually runs rough and has poor acceleration.

 

94 has plastic intake, no welds

 

Hey guys,

Thanks for your replies. Keep 'em coming!

jscott82:
I didn't have a timing light available today, but both of the rotors is moving, and I got them to stop at the marks on the distributor "casing", so I'm sure that's not the problem.

levtron:
It has a breather tube, and it is attached and not blocked in any way. The belt is good, and the timing is good.

Steve Weiner-Rennsport Systems:
Can you tell me where this temperature sensor is placed?

Juha G:
I didnt pull it apart and vacuum tested the vacuum lines, but I checked them all, and there is no visible damage on any of the lines.

Andy Hodapp:
I got the reference ;-)
Fortunately it's not a japanese car with NOS and welded intake (and over dimensioned fiberglass body kit :-))

pp000830:
I wont start it before I find the problem :-)

Vorsicht:
I actually thought about a sensor like that, but I wasn't sure where to look for it on the car. But are you sure about the part number? on a 94 porsche, it should be at 964 or a 993 part number?!
Didnt fix a clutch - it's a tiptronic.

The leaky fuel injector was also in my thoughts, because the problem comes when the car has been standing for some days/weeks.

I dont think it's the MAF, because the car has been running great until I parked it, and again after i changed the clamps and put the intake together again. A lot of power, and a very smooth idle.

All:
How about this bastard? The guy I bought the car from, sent me this picture he took, when he put a used one in the car (because he had to take it from another 993 he had). I never gave it a thought, if a bad fuel pressure regulator (993 110 199 00) could make a backfire in some way... What do you think?
Would it be able to do something like that?

 

Yes, I am sure. I am assuming you have a model year 1994 build 993. I have the same! Porsche decided not to make the original sensor and uses this as the replacement. Also take note, if you replace the sensor you will need to order some add'l parts:

(Qty.) (1) 999 652 916 40 oval plug housing (3) 999 652 871 22 connectors (3) 999 704 161 40 grommets.

These parts allow you to change the receptacle that this sensor plugs into. If you don't use these parts the connector will not fit!

 

Yes, if the chamber is getting too much/too little fuel it will mess up the lean/rich mixture. Given your story you probably should check the fuel pressure/ fuel pressure regulator first. Most auto parts stores (at least here in the US) will let you borrow a fuel pressure guage.

 

EDIT: See post no. 2 here: https://rennlist.com/forums/993-foru...re-sensor.html

Steve is a very busy guy so here you go:

You can access the CHT sensor from underneath the car. It is located right next to the reference mark sensor (next to flywheel). Number 18 below. Simply remove the rubber grommet and you'll see it.

 

BTW, are you able to check your car's fault codes? That could help.

 

Hi Vorsicht,

Thanks for your great posts! I've been a little quiet until now, because I was waiting for my new Durametric tester. I had a small hope, that it could find some faulty codes. It did, but nothing usable (see picture.. sorry about the size). The "23", I believe is there because of the backfire, that separated the intake.

I've ordered the 996-606-105-00 and the add'l parts... and then I've ordered the fuel pressure regulator. I hope one of those things will solve it.

I get the parts next week, and I will post the result asap.