AX993

I have done a brief search, but must have missed the thread, so please forgive me but I have some questions about my 1996 993 C2 with about 64K miles.
This weekend I changed out both resistors for the A/C and Oil Cooler fans (both were bad) and took the car out for a long drive with the A/C finally working good. Keep in mind that I live in north Ala where the temps have been well over 100 F, but the temp gauge never got much over the 9 O'Clock position. After the drive, I shut the car off and went inside to open the garage door, then tried to start the car to move it inside, and the engine kinda turned over but stumbled and didn't start. After a couple more tries, sometimes ending with a "clunk" noise, I then tried to start the engine while giving some gas (kinda feathering the gas pedal), and it started .
The next day I go for another drive and it started normally, but when I got back it did the same stumble-with-no-start thing. So basically it starts fine when cold and not when it gets hot unless I give it some gas. This never happened before changing out the resistors.

Questions: Did replacing the resistors/ballasts for the fans somehow cause this problem, does the ecu have to relearn that the slow fan speeds now work, is some sensor relating to ignition/fuel causing a hot start problem, or is a new starter in my future ????

TIA
Glenn

Terry Adams

Fuel pump or vapor lock due to hot weather, though I thought vapor lock was no longer an issue in modern engines.

AX993

Terry Adams said: "Fuel pump or vapor lock due to hot weather, though I thought vapor lock was no longer an issue in modern engines."

I'm open to any & all suggestions. If it was the fuel pump or vapor lock would the engine run ok once the engine was started ? It seems to run ok if I rev it once or twice once I get it restarted.

Glenn

BS911

During my car's starter failure period, I would have a real hard time starting when hot that sounded sort of like yours. Run for a couple hours and shut off.... a few minutes later it would crank slow and then sort of kick out wheezing. Try a few more times and it would stumble alive... slowly. Hot starting is hard on a car, batterym and starter anyway, but for me, the weak link was the starter. With a new starter and battery - nothing else changed - my car cranks hard and fires up hard when just as hot. You could have issues with a sub-par battery that just can't crank enough current. I don't see how the replaced resistors would have anything to do with it. Unless now that they are functional are just one more current draw on the battery. Anyway, I'm not a mechanic, I'm not a scientist, I'm not an electrician. But just wanted to throw out a couple suggestions. Hope it helps.

JasonAndreas

no

no

With hot start problems the first thing to check is the age of the DME relay. Failed solder joints (from vibration, etc.) inside it are responsible for most startup failures. If the warm start problem is happening ALL the time then you can test it with a jumper in its place. Most people carry a backup relay in the glove box just in case.

AX993

Thanks for the info Brian and Jason !!
Battery is only about 15 months old but I'll check it, and I believe I replaced the DME relay soon after getting the car (around the same time frame as putting the new battery in it). I do carry a spare DME relay in the glove-box (learned that with my 944S, but when it failed on the 944S it would crank forever but not fire/start at all) so I'll try that next time, check the battery, and report back.
THANKS,
Glenn

JasonAndreas

When the DME relay begins to fail it usually takes a few separate cranks to start the engine and then eventually it won't start at all. If you are pushing the gas pedal down what you're actually doing is opening the throttle to bypass the ISV. A dirty/gummy ISV will usually give you cold start problems but its worth a look, possibly clean it out if it has never been done? What exactly did you disconnect when you replaced the resistors?

TomF

+1 Always test this first...

AX993

Jason,
I haven't done the ISV and don't know if the PO had it done or not. Its on my (long) list of things to do. The only thing I disconnected on the A/C resistor was the resistor itself, and on the oil cooler, I dropped the oil cooler down to remove the upper baffle plate to be able to replace that one, but I think just the resistor connection on that one as well. Haven't driven it again yet to try the DME relay, maybe tonight or this weekend.
Thanks for all the responses guys!
Glenn

AX993

OK,

Went for a drive tonight. Temps in low 80s, humidity around 65%. Very mild compaired to daytime temps over 100F. Engine temp gauge never went over 8 O'Clock mark. Also didn't use A/C for what thats worth. Spare DME relay close at hand.

Monitored battery voltage on newly installed ScanGaugeII: 12.6 volts before turning key, 12 volts with key at position just before starter turns motor over, jumps to 14 volts as soon as engine starts, then settles to 13.5 or 13.6 volts. I need to put a regular volt meter on battery as my wife starts engine to better see what the battery pulls down to as the starter engages . Seems the response time of the ScanGaugeII is not fast enough to display this info.

Went for spirited drive.

Pulled up to garage, shut engine down, opened garage door, went to start up the car to move into garage.....drum roll.... started right up, no problems, no stumble, no clunk.
Guess I'll try again during hotter time of day so the temp gauge gets closer to the 9 O'Clock position.

Jason, I forgot that I also disconnected the passenger side headlight (aftermarket HID) to get to the upper oil cooler bolt. But I wouldn't think that would be anything that could cause my hot start problem.

Later,
Glenn

Edit: some new info: Got better half to start car as I read the voltage on a digital volt meter. Results are 12.6 before start, 12.2 with key just before starter engages, momentary drop to 10.6 as starter engages, then up to 14 volts when engine is running. I'm guessing that the battery is OK.
Glenn

AX993

Update :

Posted this in edit form on 8/30; some new info: Got better half to start car as I read the voltage on a digital volt meter. Results are 12.6 before start, 12.2 with key just before starter engages, momentary drop to 10.6 as starter engages, then up to 14 volts when engine is running. I'm guessing that the battery is OK.

Yesterday (Sat) I cleaned the Idle Stabilzation Valve using p-car.com DIY. Didn't seem that dirty but sloshed brake parts cleaner around in it several times and blew it out with compressed air to dry it out.
Kinda thinking someone has cleaned it before because the gromet that holds the valve to the intake manifold had the wire holder on the wrong side I think.

Afterwards went for a drive and all seemed normal. Even let the engine idle in the drive (and with the A/C on) afterwards to warm engine up enough to start the oil cooler fan running. Then I turned it off & let it sit for a few minuets before starting it up with no problems.

SO I'm leaning towards the DME relay MAYBE being suspect. The daily temps haven't been nearly as hot for the last week or so, high 80's to mid 90's, so maybe back when the temps were in the 100's, the fusebox area got somewhat hotter and effected the DME relay some way (opened up a solder joint crack ??). Guess I'm going to put my spare new DME relay in, and buy another one for a glovebox spare.

Thanks to all who offered ideas!
Glenn

Marlon

My 95' w/106K miles did that last month when it was about 100 deg outside. I stopped the car at a military base to get my new car pass and when I came back outside to start the car it did that stummble-bumble thing. I had to crank it again and it started ok. I was new to the car though and I'm guessing that I did not push the clutch pedal all the way in and it was turning against the friction plate a little. Has not done it since. I also had the A/c 'on' fwiw.

AX993

Marlon,
I try to never push in the clutch when I'm starting the engine, at the recomendation of Steve at Rennsport Systems . I don't know if my car has been modified to bypass a clutch switch or not. It was that way when I bought it. I just make sure its out of gear and my foot firmly on the brake !
Glenn