Hard starting after engine been running for a while
 

I have a 1980 911sc that is sometimes hard to start after running it for a while. The engine turns over strong but will not start. Eventually it will fire up, however it feels like it is flooded and is sluggish in idle. If I touch the throttle is dies out, if I let it go eventually the RPM will go up to where they should be. Any suggestion on what is the cause? I have good gas, new fuel filter, plugs & air filter...

Thanks...

You need a fuel pressure gauge to measure hot control pressure. It may be off. Let's start with that first.

Thanks Yelcab1, I hate to sound naive, is this something that I need to take to my local Porsche mechanic?

Sounds like a typical hot-start problem, which are caused by a faulty fuel pump check valve or a failed fuel pressure accumulator. The check valve and the accumulator conspire to trap CIS fuel pressure after engine shutdown. This residual pressure is necessary for a hot-start. Since the pressure bleeds down slowly anyway, eventually there is zero residual, but the engine is cold -- and starts nicely without residual pressure.

Shortly after engine shutdown (5-10 minutes), loosen the connection at the bottom of the accumulator. If it leaks, the accumulator has failed and you should replace it. (There is a current thread about repairing this accumulator, but it does not look promising.) If you get the connection all the way off and it is still dry, replace the fuel pump check valve.

More info thru SEARCH on "hot start", "accumulator", or "check valve."

Thank you very much for the detail break down Brian...I will give it a go and let you know what happens.

Best regards,

I loosened the bottom connection to the accumulator and fuel just spilled out! Found the part for $239.00 and replaced it. Car fires right up now after driving it for a while...problem fixed. After installing it and purging the air out of the line, the car blew white smoke for a while and then quit. I wonder if this is common?

Hard to tell what your question is here. Did it "blow white smoke for a while and then quit" on your first start up after replacing the accumulator? How long was a "while?" Not "normal," but is depends on what happened next. Did it then "fire right up and now after driving it for a while ... problem fixed?" If so, I don't have an answer except to say it sounds like an anomaly to not worry about.

That said, if, while your accumulator was leaking fuel, you set your CIS control pressures and mixture, you may have to redo those adjustments again. With the accumulator leaking, it may have reduced the control pressure somewhat which would have richened the mixture. "Plugging the leak" will restore the control pressure to its higher value and you will have to reset the mixture. All this, of course, depends on the rate of leak and the amount of control pressure reduction -- which may have been negligible.

accumulator

Yes, it was the accumulator that caused the problem. Once replaced, the problem of not starting when hot has stopped. As I mentioned before, the car did smoke (white) for a few minutes when I started it after replacing the accumulator. That only lasted a short while and has not done so since.

Any time you break the fuel system open; do you always have to bleed the air out?

I've never had to bleed the air out of my system. In addition to replacing fuel filter and accumulator, I also ran out of gas once.

Well, my saga continues. Just today the car would not start after running it for a while…same thing as before it would just turn over. I did replace the accumulator which fixed the problem at first. Since I did not change the fuel check valve, is it possible that it could have failed due to the higher pressure from the “new accumulator”? Or could this have been a dual issue at hand?

replace the oxygen sensor relay under the passenger seat... enjoy.

Willf, all i have under the passenger seat are crumbs...no oxygen sensor at all. Would it be somewhere else?

the oxygen sensor itself would be connected to the exhaust. 80sc with stock CIS, I would expect there to be 2 items under passenger seat. the lambda ecu (spelling) and a small relay that is refered to as a oxygen sensor relay. did you look under the carpet? it should be clipped to the floor board. i will look for a pic and reply back to the thread. take a look again and let us know.

Ok, sounds like you're on the same path I'm on. Next time it doesn't start after you drive it try short cranking it about 20 times. Short cranking is where you crank it for about 1-2 seconds. Do that about 20 times and see if it starts. I replaced my accumulator and that fixed my hot start problem that ALWAYS occured. However, when the engine was hot, like after 2 hours of driving on a 90 degree day it wouldn't restart. I happened to be at the Porsche dealership when this happened and they worked with me, for free, on it and they tried the short cranking method and it worked. The problem is the intake valves are coked with carbon deposits and when the engine is hot enough the coke acts as a sponge for the fuel spraying in. I ran 2 cans of BG-40 and the problem is gone. Hopefully this isn't your problem but it's worth a shot to see.

When I purchased the car I tore out the whole interior, carpet and all and never found any hardware under the seat…just loose change. I believe the Oxy sensor hooks up to the catalytic converter? Nothing is plugged into it though.

Mark, I will give it a go and see what happens with the short cranking. The car has 93K on it so could imagine the valves could have major deposits on it. Did you replace your fuel check valve also?

the oxygen sensor does connect before the converter; if its's not there, that woudl explain the missing items under the seat...

If your 80' was still original you would be having some serious issues with the Lambda control brain being missing. For one you have a frequency valve in the 80' that's driven by that unit. When that stops working you have major drive ability issues.

Now to get rid of these components takes backdating certain pieces of the CIS system. Mainly the fuel distributor and most of the associated plumbing. There is another 80' owner on this board that found the same thing, turns out he had a 78-79 CIS bolted into his 80' at some point.

Ok, I wonder what impact on the performace of the care this would have?

Thought it would be nice to visualize what we are talking about:
http://forums.pelicanparts.com/uploa...1183504578.jpg

Scott, how do I determine if I have a different CIS on my 80?

There are a few ways, number on the WUR, numbers on the fuel distributor. However by far the easiest check is for the frequency valve. This guy looks exactly like a modern day fuel injector in-line with a rubber hose. In fact the Lambda brain switches the ground on and off to pulse the valve.

it's part #77 in the diagram. You will also have 15 and 49 on the right side of the system, these are the aav and decel valve, 80-83 had two. 80' also had plastic fuel lines, but these are often changed out.

http://www.pelicanparts.com/911/911_...8-83/1-7-3.JPG

One of the things I noticed right off is that my distributor only has one vacuum hose port which is connected. Two vacuum hoses go to it however one is plugged with a screw. The fuel distributor has the number 158313 042 on it and I can not see #77 and #15 looks totaly different from the pic you sent.http://forums.pelicanparts.com/uploa...1183506814.jpg http://forums.pelicanparts.com/uploa...1183506862.jpg http://forums.pelicanparts.com/uploa...1183506903.jpg

You sure this is an 80? I ask because 80 didn't have air pumps, and that's clearly and older CIS setup, like a 78'. But the fact that you have a smog pump leads me to believe that the entire motor is a transplant from another year. Do you have air injection rails as well?

Better post the engine number up so one of the experts here can tell you what it's from.

The engine number is 6304271. The VIN is 91AO134541 which I looked up on the web shows to be 1980.

I am not seeing air injection rails...

thanks,

Richard

I would post a pic of my 80' engine but it's so heavily modified at this point that I doubt it would matter.

The 1980 911SC Euros had a smog pump, for sure. Didn't the US version have an oxygen sensor and NO smog pump? And with the oxygen sensor came an electrical connection to the fuel distributor to run the frequency valve? Looks like a Euro SC.

Look for an ID plate in front of the driver's seat at the base of the windshield that you could see from outside the car. Methinks the US version has that plate -- my Euro 80 SC did NOT have that plate.

Now that would be cool, and yes the US version had no smog pump in 80'

on the window frame, drivers side has the vin plate riveted to it. I wonder if this is a US body with a Euro motor put in it?

http://forums.pelicanparts.com/uploa...1183509607.jpg http://forums.pelicanparts.com/uploa...1183509663.jpg

That riveted plate on the A pillar is part of the federalization of a Euro car. That is exactly what my 1980 Euro SC has, showing the VIN.

It looks like you have a matched set of Euro body and Euro engine.

I do not mean to sound ignorant, however what does that mean in the functionality of the car?

Also, how would this apply to my poor starting when its hot? I did replace the accumulator...

I appreciate everyones input on this very much!

Congratulations! Now replace that oil feed line to the oil restrictor, don't want hose clamps on those. Little oil starvation to my cam spay bars was all it took to ruin my engine.

EDIT: Oh still having the hot start issues? You need a set of CIS test gauges to solve that. The JC Whitney set is like $60 and well worth it. You need to measure the amount of pressure drop over time on a warm engine.

You could have a few things going on here, since you already replaced the accumulator you could be in it for a simple check valve. On the other hand I had bad fuel distributor that would stay cracked open and flood the cylinders after startup. Both conditions can be checked with the tester.

Ok, I will pick up a set of CIS test gauges and go from there. I do have a new check valve and will install it this weekend.

I checked the vin out on the web and it does show this is a Euro car, however how do I determine what the motor #6304271 means?

911mnypt,

What is the engine type number near the engine number.
930/07--USA
930/08--JAPAN
930/09--ROW

These numbers will help determine what engine you have.

It has 930/09....so its "ROW" which means?

Rest of World. It means it's a grey market import. I have one as well. Good, no emission controls and more horsepower. Bad, others say the value is lessened but I don't listen to that because I have no plans to sell. Some federalized RoW cars were poorly done meaning you have to correct the problems. Also, no way to know for sure what the mileage is since the speedometer has been swapped from kph mph.

Interesting...Would you advise on taking of the catalytic converter and smog pump? What can I anticipate when I have to smog it in wonderful California?

You can anticipate a real pain in the rear most likely. These cars were federalized when brought into the states. You will still be requires to pass emission standards. A lot of people remove theses parts but I can't comment on smogging afterwards. I don't have to smog my car so I don't know how bad it makes it by not having emission controls.

Hi, I don,t know if this helps ,but i had a hot start problem with my 2.7, that sounds just like yours ,i had problems adjusting the mixture because screw was stuck, i got the mixture screw turning and adjusted mixture on machine, now car runs and starts the best it ever has and didn,t cost any thing to do.

Malpaslane,

Did you richen or lean your mixture?

Hi, i made it more lean. co was up on 8 and i brought it down to 1.5-2.0.