CIS Lessons learned. Topic: Hot Start
 

Some learn the hard way. The hard way may hit you hard in the wallet when it comes to diagnosing CIS problems. Instead of swapping out every possible component I decided to follow the logical procedure of testing pressures, just like all the people that really know these cars preach. Are you reading this Ed Sully?

The $100 I paid for the CIS pressure gauge was just a little more than a fuel pump check valve (albeit by $15), less than an accumulator, MUCH less in stress and uncertainty in rebuilding or buying a rebuilt fuel distributor, etc,etc.

The classic hot start issue turned out to be caused by a fuel pump check valve. The WUR's numbers were within spec - both cold and warm, the throttle pressure valve was functioning correctly, and the system pressure was also within spec. The residual system pressure was horrible. I had a quick bleed off to .5 bar for 30 seconds and then none.

I replaced the check valve, high pressure hose that runs from the fuel pump to accumulator line. (On a 74 it is a two piece line which meets at the sheet metal). I purchased a "real" Porsche fuel line. I was very happy that my residual pressure numbers went up, not so happy my dealer supplied fuel line seeps at the crimped tube to rubber junction. ARGH. Oh, it's just seeping a little. The dealer supplied line is a Cohline. A replacement is on the way. It is always easier the second time around. I used dish soap as a lubricant to get the line through the new grommets.

I can't tell you how many times I read on this forum "did you test the pressures?"

If you have a CIS car and work on it yourself, buy a CIS fuel pressure gauge. CIS is not a very complicated system, especially the early. With CIS it is ALL about the pressures.

Scott S.
73.5 911t

+++1 and an amen to that. Add "use the search tool" to educate yourself and you got a DIY wrencher on your hands!!!!

Great post.. could you share a link to the pressure gauge you bought?

Just started a thread about high idle on my SC..sounds like I will be purchasing a pressure gauge. Second to mike, which gauge did you buy?

Mike and jpgroth I sent you a pm.

I wasn't going to post the source of the CIS fuel pressure gauge due to selling away or advertising for a competitor of our host, but after reading several other posts I don't think this is a wrong thing to do after all. Delorean Auto Parts specializes in FDs and WURs, rebuilding FDs, copper washers, etc. They don't directly compete with our host, more like compliment. The guy I spoke with was kind of a tool but the gauge works and it arrived quickly.

That's fine, but our host is no longer Wayne, it's now a big corporation that sends most of there parts from down south and other places now...just saying.

Heard this a while back. Is this confirmed? Anyone seen Wayne? Is he on an island somewhere?

Let me tell you from recent ordering experiences that a lot has gone out the window.

Wayne I am sure has a very sweet home in SoCal so that's as good as an island. Last thing I read on here is that he was writing a new book on body work.

Things are Not quite the same around here. :confused: :rolleyes: To be polite .

yeah some guy came on Rennlist looking for sources as he refused to order from Pelican , I was quite shocked to hear things have gone downhill.

Yeah, that 73.5T is a bear in the heat when it comes to hot start. I replaced my pump with a Pierberg, which I believe does NOT come with a built in check valve. It never fails that after a run, when I stop the engine, the fuel flows back to the tank up front and I have to leave the key on to energize the injectors so that the "sputtering" of the start up is not that bad. The question then , is where to install the inline fuel check valve? Just behind the tank or at the pump? Consider though that you have to PULL the fuel rather then PUSH the fuel as with the 1974 CIS models onward, since the pumps are installed behind the tank not in the rear wheel well! Their are days I curse the CIS systems and would happily settle on the DME (1984 on).

Bob
1973.5T

The fuel pump check valve on a 7.5 is mounted on the fuel pump itself. It is inline between accumulator. I tried 2 accumulators btw. Still don't understand why the accumulator needed pressure maintained by the pump check valve. Apparently, at least based on my situation, the check valve and the accumulator must both be working to help avoid hot-start issues associated with vapor lock fuel starvation issues.

Nope.......
 

SS,

No amount of vapor pressure (vapor lock) could withstand against the system fuel pressure in CIS. A typical CIS has 65~75 psi. system pressure, a turbo CIS has 90~105 psi. SP. A carb system has 5 psi. this is where vapor lock occurs not in a fuel injection system. Gasoline is an incompressible fluid and will readily displace any vapor or gas present in the fuel system. Do a test if you could produce a vapor lock condition in a CIS. This is a myth (vapor lock in CIS) specially for early CIS models because the FP starts to run once you turn the ignition switch to ON position to pressurize the fuel system.

Have you actually seen or experience a vapor lock in a CIS? Keep us posted.

Tony

ECS Tuning in Wadsworth Ohio.

http://forums.pelicanparts.com/porsche-911-technical-forum/1001212-pelican-parts-ecs-tuning-heres-what-you-should-know.html

Regardless of who owns the enterprise, we are all guests. I greatly value the the experience and I will continue to plan my purchases accordingly.
Rob

Tony,

Isn't it true that the WUR, sensing the heat of the motor ( the ambient temperature) will adjust the control pressure to produce less fuel due to a warm state? And isn't it true that this may result in an overly lean pressure?

Also, as I understand it, Porsche realized this issue and moved the injectors away from the head and into the intake runners.

The factory manual addresses the hot start issues by running tests on fuel volume, the accumulator, fuel pump check valve, fuel distributor as the primary causes.

When I changed the fuel pump check valve my issues were over. Originally, I had no residual pressure after shutoff. My question was about the accumulator holding pressure, and the need for pressure being held between the pump and and accumulator. Isn't a functioning accumulator holding pressure at the outlet side between it and the FD? The fuel pump check valve seems redundant.

I have read and appreciated your posts Tony.

Scott S

Residual fuel pressure........
 

Scott,

If you think the FP check valve is redundant or not necessary, remove it and see what happens to your residual fuel pressure. Like you said, the installation of a new FP check valve solved your fuel pressure loss problem. The fuel accumulator will not work without a FP check valve because the FA will NOT be able to hold the residual pressure. You need a FP CV and FA in ‘76~’83 CIS. Otherwise you will encounter hot start problem. You can get away with the FP CV in earlier CIS because the FP runs as soon as you put the ignition switch to ON.

Tony

Is this a big corporation? I say small to medium at best. A big corp would be Summit Racing.

http://forums.pelicanparts.com/uploa...1532572621.jpg