79 SC Warm Start

Kurt Anderson · Kurt Anderson's Garage

My 79 SC has started and run great for the two years I have owned it.
But now if I drive for about 30 minutes and then stop somewhere for 10
or 15 minutes, when I go to start it, it sounds like it has started on
only four cylinders. About 10 seconds later it sounds like another
cylinder kicks in, and then about 5 seconds after that it sounds like
the 6th kicks in. Then it runs just fine with good smooth
accceleration and very smooth constant idle. Always starts well when
cold.

Any thoughts here?

Kurt (A 30 year 356 and 912 guy, but new to this "black box" stuff).

yelcab1 · 06-24-2004, 06:41 AM

A bunch of possible culprits, some are expensive and some are not. You probably need to start from scratch by checking the cold, warm, and hot fuel control pressure. Then, report and we'll go from there.

hkspwrsche · 06-24-2004, 06:50 AM

If the fuel pressure is low then it would need to build before the dead cylinders fire... but if they are leaky( sticking open).... it could wash the cylinders with gas and the rings would need to reseat.. how many miles on those rings? Leak down and compression might be handy info too. definitely need to check fuel pressure.. even the individual injectors possibly... buy new seals if you pull those.. The higher idle when the engine is stone cold could hide the slow progression to all the cylinders firing...

Harold

Kurt Anderson · Kurt Anderson's Garage

I will have to check my SC service manual on how to check fuel pressure. I looked very briefly at that section the other night. The engine has 102,000 miles with no rebuilds or significant maintenance. Good even compression. This will be a learning curve for me. I've spent 30 years doing a twice yearly 90-minute points, plugs, valves, and timing routine on totally non-electronic 356/912 systems. This will be new stuff.

Kurt

hkspwrsche · 06-24-2004, 07:04 AM

Let us know.. I'm curious..
Harold

yelcab1 · 06-24-2004, 07:08 AM

You will need to have/buy/borrow a CIS fuel pressure test guage. There is a fuel line between the WUR and the Fuel Distributor, that needs to come off, and the fuel gauge connects in between there. Check it while it's cold, warming up, and fully hot.

Kurt Anderson · Kurt Anderson's Garage

Harold,

Will do. MIght be next week though. Tonight and tomorrow I'm pulling the engine from our 356C for a big-bore rebuild (it came apart last weekend after 104,000 miles).

On the SC, I'm also going to try turing the key to the on position, and then letting it sit there for about ten seconds before I turn it to start. Don't know if this would allow fuel pressure to build, but might be useful information if it then starts up smooth.

Kurt

s_wilwerding · s_wilwerding's Garage

I bet it's the fuel accumulator. I had roughly the same problem on my SC - bad hot starts, wouldn't fire right for a few seconds. The next time it won't start, turn the key on, pull off the air filter boot, and push the sensor plate up with your hand. You should hear the fuel pump run. If the car starts after that, you've got a fuel pressure problem, and usually that means a bad accumulator.

Kurt Anderson · Kurt Anderson's Garage

What is the cost of a CIS fuel pressure guage? Where can I get this? Can something else be made up to work?

Kurt

yelcab1 · 06-24-2004, 08:42 AM

Whitney CIS tester, $50-$60.

sammyg2 · 06-24-2004, 09:18 AM

My bet is either fuel pump check valve or fuel pressure accumulator.
Sounds like a classic case of vapor lock due to loss of adequate fuel pressure in the fuel lines to the injectors.

It could be other things but this is where I would look.
My car did the same thing but to a larger extent when I bought it.