Speedraser

Since last summer, my '95 993 occasionally refuses to restart when the engine is warm and I shut it off for a few minutes, for example, when getting gas. It cranks, but it doesn't even attempt to fire. If I then just shut off the ignition again and wait 60-90 seconds, it starts normally and runs fine. This is an intermittant thing. It used to happen only on very warm days, but it started to happen more frequently, and on cooler -- around 60 degree -- days. It hasn't happened in a while, but the road salt has kept me from using it much lately. I took it to the dealer today for tires and an alignment, and mentioned this problem to the mechanic. He hooked up the diagnostic machine, which showed one recorded fault involving the hot film mass airflow sensor. He says the sensor will slowly deteriorate, and ultimately the car won't run (when the computer no longer knows where to set the air/fuel mixture).

Has anyone had this problem? Does anyone know how rapidly it will deteriorate? Does it also impact the car's performance (when it is running, of course)?

tom_993

Since you have a ’95, I’d be very suspicious of the engine wiring harness. Look here: <a href="http://www.pcarracing.homestead.com/wiringharness3.html" target="_blank">E.J's Wiring Harness page</a>

aston

Hi Todd,
I had the same problem 6 months ago, and I went ahead and changed out the Mass air flow sensor, and $600 later, the problem was still there. I turns out it was the DME relay. A quick $40 bucks and I have not had any problems. I think you should change out the DME relay prior to changing out you Mass air flow sensor. I think it is worth a try and it is pretty cheap.

Aston.

tom_993

$40 for a DME relay? I link list is $25. I paid $15 at Suncoast.

Speedraser

Aston,
Did your car show a fault on the plug-in dealer diagnostic machine that said the problem was the mass air sensor? If it did, I'll definitely try $40 (or $25) before I spend the $340 I was quoted for the part. Does anyone know how accurate the diagnostic machine is?

Tom,
I looked at the wiring harness when I was at the dealer, with the mechanic, although we did not take anything apart. What we could see looked fine. My car is a late '95 (May '95 build), so I'm hoping and praying I'm ok (I know some say that the wiring harness issue may not be a '95 only problem). By the way, the dealer's mechanic said he has not seen any 993s with the wiring harness problem.

tom_993

[quote]Originally posted by Speedraser:
<strong>
Tom,
I looked at the wiring harness when I was at the dealer, with the mechanic, although we did not take anything apart. What we could see looked fine.</strong><hr></blockquote>

Todd,
This doesn’t surprise me. Just looking at it won’t reveal much. Take a look at this picture. This is the area right behind the alternator. To see this, you have to remove the fan and alternator, then slice open the main sheath to see the individual wires inside. Also note that this is apparently heat related. If your car has lived in a cold climate, and/or has not seen a lot of hot running at a track, you may delay or never see this problem.
None of this is to say that your harness is what’s causing your problems. It’s just that people with bad harnesses typically experience weird electrical symptoms. Good luck!

Tom

tom_993

Todd,
I saw in another thread that the dealer wants $400 to replace your MAF. This would a very simple DIY and you can save a lot of money (the $400 is parts AND labor, right?). The MAF is right on top of the engine. This easy to access location is what makes this an easy DIY. Simply remove the air box first, then the tube that contains the MAF. Get the part number right off the unit itself, then use one of the on-line vendors to get the part at approximately half off list price (Suncoast is recommended). If you need more info, let me know.

Tom

aston

Aston,
Did your car show a fault on the plug-in dealer diagnostic machine that said the problem was the mass air sensor? If it did, I'll definitely try $40 (or $25) before I spend the $340 I was quoted for the part. Does anyone know how accurate the diagnostic machine is?

Todd,
yes the diagnostic machine showed the fault as the mass air fow sensor. When it was replaced, the car ran fine for a few local drives, but the same problem arised again, which was permanently solved by the DME Relay. It is an easy unplug and plug in a new one DYI job.

Aston.

Speedraser

Aston,
Very interesting . . . Looks like I'll be trying a new $40 dollar part before I try a new $340 part. Thanks for the post.

Tom,
If the relay doesn't do it, I may well change it myself -- it didn't look like that big a deal.

BTW, I drove the car alot over the last two days -- so far, no problem.

tom_993

Sounds like a good way to go. Check the relay first, if it has the 944 part number, replace it regardless. This one is known to blow. There are several threads that relate to this:

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=3&t=002179" target="_blank">DME Thread</a>

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=3&t=000561" target="_blank">Another One</a>

There are more; I did a search on "944 relay" and got a bunch.

Tom

Speedraser

Update:
I hope I can say this without provoking Murphy's Law
I finally (I've been busy temporarily relocating for the summer) replaced the DME relay. The hot start problem seems to be cured I paid $26 for the relay from a dealer, rather than $360 (w/o labor) for the MAF.

So far, so good . . .

Aston -- thanks lots for the advice.