Hard Hot Start

79-911SC · 08-11-2002, 02:42 PM

I have a 79 911 and it takes a lot cranking to get it started when the engine has been running for a while and the temp is up. I have replaced the fuel accumulater hoping that was the problem ,but its not any advice on what to replace next? thank you.

MTH · 08-12-2002, 08:25 AM

After the accumulator, try the check valve on the fuel pump. I believe the '79's have the external check valve so you don't have to replace the entire pump.
Mike

Jamie79SC · 08-12-2002, 09:41 AM

This story is out of left field but might be enlightening.

This summer, in the middle of a very long, VERY hot cross country trip I too had this symptom. The car behaved as if it had a vapor lock problem and it got progressively worse throughout hot weather part the trip. When cool, it started fine, when hot it would either fire once and die, or would not fire at all. After a number of tries, it would finally start.

At 5:30 on Saturday evening in Ealey Nevada (105 degrees in the shade and approximately 250 miles from nowhere and 1,000 miles from home) the problem went from bad to stranded. The car wouldn’t start at all, even after sitting for two and a half hours in the shade with the lid open. After fooling around with a number of things in the back of the car, in desperation I thought I'd change out the fuel pump relay. Guess what, the old one was hanging half out of the socket. I pushed it back in and all was well.

Apparently, when it was cool, that connection was enough to get the pump motor turning. Once the fuel pump was going, that poor connection was sufficient to keep it turning, even when hot. When starting hot however, there was just too much resistance across that connection to reliably get the fuel pump going.

Anyway, check the simple stuff before you get into the complicated stuff. I keep re-learning this one

targa80 · targa80's Garage

My 80SC had the hot start problem and I went through the troubleshooting process with pressure guages and jumpering out the relay so the fuel pump would run without the engine running. I finally narrowed it down to the check valve in the fuel pump. Since the fuel pump had the internal check valve all I did was add an external valve to the output of the pump. Problem was solved and has ran great ever since. Plus it was a cheap fix. Many different things can cause the hot start problem, and if that check valve doesn't work properly all the pressure drains back into the tank. You might want to just order the external valve and install it to see if it makes the difference. If that doesn't fix it, then your looking at an investment in a pressure test kit to locate the real culprit.

Andrew9146 · 08-27-2002, 04:43 AM

What is a check valve?

I have a 914 with a 2.0 six and suffer hot start problems. Do I therefore already have one of these in my fuel pump. If I purchased an external one, what do I ask for e.g. pressure etc?

jwetering · jwetering's Garage

The CIS (Bosch K-Jetronic) fuel injection system run very high system pressures (> 60 psi). The check valve's job is to keep the fuel system pressurized when the car (and fuel pump) are not running.

The fuel pump on a 911 lives right next to the steering rack, just under the fuel tank. The check valve is mounted to the discharge (high pressure) end of the fuel pump. In "newer" cars (1979 to 1983) the check valve was a separate piece of hardware that could be replaced. On older cars (before 1979) the check valve was actually inside the fuel pump.

The old pumps can be retrofitted with the external check valve, but you need a couple of fittings which may not be listed in the normal parts lists. Best plan is to take the pump out and bring it to a shop so various fittings can be tried.

Joe Bob · Joe Bob's Garage

To answer the 914/6 question....find you fuel pump. I had mine under the battery behind the passenger....

The banjo fitting, the 90 degree one....it is screwed into the head of the fule pump under the banjo fitting. 12 dollar part.