car wont start when hot!!!!!

I finally got my 1972 911 on the highway. After a 30 minute highway drive and 210F I turned the car off when I went back to turn it on again all it would do is crank over. I am running webers and the fuel pressure was good so I believe its not vapor lock. Once the car cooled (20min). it started right up. I am suspecting the CDS box but thats my question. Also, is 210F a bit high for a freshly rebuilt 2.0 911s engine with 11:1 comp? Since I just got it out there are little bugs I have to take out but in time I guess. I do have the overall timing set about 2 degrees before I think is the 35 degree mark making it about 37 degrees. I also have a bypass hose that I will soon replace with an auxilary oil cooler. I live in San Antonio and it was 100F when I was driving. Woulkd all these little things effect that 210F temp?
Thanks louis

If it fails to turn over, or turns over with less gusto, check the tranny ground strap. About 8 years ago, I had a similar problem that I fixed by putting new battery wires and grounds in the car.

I now know that more resistance exists in hot wires so that at some point, you don't get enough juice to fire it up. When it cooled (usually 20 minutes or so), the juice would flow and vrooom. Just something to check.

I have Webers in my 70 911E and have the same problem but not as bad. Don't count out vapor lock. In 90 degree weather in Florida my engine will run up toward 210 degrees depending on the driving conditions. If I stop for 20 - 30 minutes it will not start immediately. In this case I turn off the ignition, pump the accelerator to the floor three times then start the car with the throttle wide open - it always starts but after a few turns.

Good luck.

Can someone tell me the normal operating temperature range for my car. At what temperature should you start getting really concerned.

In the most recent issue of Excellence, Bruce Anderson said the 'normal operating range' to be 180-220 F, and I agree with that range, anything above 230 F being of concern to me!

I don't know for sure about the vapor lock problem with Weber's, but it may be a factor, though allowing the fuel pump to run for a couple of minutes should be time enough to refill the float chambers.

My belief is that it is an electrical problem, as previously suggested ... be sure to clean the cables at the battery terminals, and at the chassis grounds for both battery cables, and clean the ground strap at the transaxle (both ends) and clean the battery cable at the starter main connection. If the Voltage was being reduced at the starter, it was also diminished at the CDI-unit, and may have been below minimums for acceptable output. If you can take an assistant along for a test drive, and also can take along a battery-powered digital multimeter, have your assistant crank the engine while you check the supply Voltage at the fuse panel in the engine compartment ... anything less than 11.5 Volts during cranking indicates insufficient Voltage and that cleaning of all of the above mentioned connections is definitely called for!

------------------
Warren Hall
1973 911S Targa

Warren, Thanks for the operating temperature information. In my case I'm pretty sure the problem is vapor lock. When the engine is cold and I turn on the ignition the fuel pump makes a ticking sound for a few seconds. When the engine is hot the ticking sound goes on for a long time. In these circumstances I wait about 30 seconds, pump it, hold the pedal down and it starts every time.

People say the 2.7 motor has a short life regarding the working temperatures.
Assuming one´s motor works always at that normal temperature range - 180° and 220° -, will the 2.7 motor still have a short life?

11:1 is a fairly high compression ratio and requires a "hot" spark. This means that your electrical system needs to be just about perfect. Batteries, electrical devices and electronics do not fair well in the high ambient temperatures you have down south. Added to that, you have a hot engine radiating heat when you shut down. Finally, batteries age rapidly in high temperatures. You said your fuel pressure is good, so it does not sound like vapor lock in the fuel pump or fuel lines.

I would start by checking battery voltage during cranking as suggested by others. If the voltage is good, and your battery cables and ground straps are good, then pull one of the plug wires, connect it to a spare spark plug, ground the threaded part of the plug, and watch the spark while someone cranks the engine for you. If you do not see a strong spark, the coil could be breaking down, or the capacitive ignition system could be breaking down. I have heard that after market ignition coils are generally not compatible with the Porsche CD units, so if your coil has been replaced, that could also be a source of problems. Until you find the problem, open your engine lid to help cool things down faster and get you on the road sooner.

Good luck!

------------------
Bob Thayer
1971 911T
rthayer@hdrinc.com

I was wondering if that stated 11:1 compression ratio was a typo or not?

If that is the correct ratio, or even if it is 'only' 10:1, then the starter performance is quite CRITICAL, and, as such, if the Voltage is found to be 'normal,' or 11.5 Volts or higher during cranking at the fuse block, then I suspect a dragging starter ... one that needs to be removed, disassembled, cleaned, and lubricated with a good quality moly-grease such as SWEPCO 101. Corrosion, and depletion of lubricant in the area of the starter 'bendix' assembly ... can cause significant drag during starter operation, and is, of course, exacerbated by high temperatures and low Voltage!!!

Marcello, I think the '74 2.7 is a special case, and may very well be not much worse than the 2.4's in terms of valve guide wear. The head stud pulling problem may still be an issue requiring Time-Serts, due to the aluminum cylinders (Nikasil or Alusil) ... even though you don't have the extra heat from thermal reactors or smog pump. It seems to me that a top-end rebuild on a '74 2.7 that includes Time-Serts, silicone-bronze valve guides, and 24 new plain steel ('65 originals) head studs would be as reliable as a 2.4 rebuilt with the same care and materials. Time-Serts are recommended for ALL magnesium-cased engines!!!

------------------
Warren Hall
1973 911S Targa

thanks for the replys. The engine does crank over easily and I do have pressure in the fuel line (3.5lbs). I can also hear the cd box ring. The compression is high only due to the fact that first of all the comp. was 9.8:1 but someone else milled a head fairly bad. Due to this I had to mill all others to match. Machinist said it was around a point so I am estimating 11:1 for simplicity. I didnt check the spark when it wouldn't start so I will be getting it hot again and checking this. thanks for the advice.

I read an interesting article about gasoline which I found on the net. I think it was titled Gasoline FAQ's and it mentioned that modern gasoline formulations will tend to cause carburated vehicles to suffer from vapor lock more often due to higher Reid Vapor Pressures and higher volatility in order to meet tighter emission standards for todays fuel injected engines.

By design, modern pressurized fuel systems are immune to vapor lock and is not a major concern for refineries since the majority of cars today are injected.

Joe Garcia
86 Carrera

Just a suggestion,

You might try keeping an inductive timing light in the car. When the problem shows up, hook up the light and turn over the engine to see if your ignition is at least attempting to give a spark to the plugs. Of course sometimes even if the plug is fouled (or the gap is bridged) you can get the light to fire because it's current (not spark) triggered. I once had a problem with an ignition coil where, when shutting off the car, and the under hood temp went up, the coil outut was almost non existant. The timing light showed this.

Good luck,
Leon

Where does your ignition coil sit? If it's up by the fan shroud you might try moving it away from the engine to cut down on the heat getting to it.

The Performance rags always suggest to test the check valve for the fuel pump. There is also an article on this in one of the older UpFixin's that I will pass along if I can ever find the darn thing...

Lee

My 1983 SC has the same problem after being driven for a few hours in warm weather. I'd read about the check valve thing after checking my starter and plugs (both ok), but I've heard it's easier to replace the fuel pump than fix the check valve. Anyone performed this fix?

Btw, I hadn't heard of that battery-ground thing. I'll check that in the morning. It would be great if it were that simple!

------------------
Emanuel Brown
1983 911 SC Targa
http://home.att.net/~epbrown01/91183.jpg

Does not PMO make a drill fixture to fix Weber boil over. As the carbs sit on top of a hot motor they get hotter cause the fans not running and the fuel boils over into the carbs and down into the cylinders gets the plugs wet and that's all she wrote.

well guys, I di alot of messing around this weekend and I think the problem has been corrected. I brought down the timing to 35 overall and I installed the 28-row factory cooler in the front pass. side fender. The thermostat opened fine. I played with several things so I dont know what was the root cause. I did wait a while and hold the gas pedal in during cranking and that seemed to work. Right now I am now dealing with changing the rear wheel bearings. It feels and sounds like you are driving a 4wd toyota with 40 mickie thompsons. Got to get the old slid hammer out baby!!!!

thanks again louis