ldrhawke

The topic of injector problems has been bantered around over the last week on the board and a lot of good information has been disseminated. It is amazing how many 928 owners that have allowed their cars to sit up for long periods of time have come out of the woodwork. Myself being one of them.

Simply cleaning old or installing new electric injectors isn't always the total solution. As I have found out and a guarantee others with the same problem will also find out. The problem can very well continue to reoccur even with new injectors installed. WHY?

It occurred to me on the way to work today that a major problem is the injector layout as designed by Porsche. Porsche didn't design these cars to sit not being used.

Allowing the car to set up for long periods of time allows the fuel impurities start to coat the inside of the fuel tank, lines, and injector rails. All you need to do take off the injector fuel rail and look inside to see the orange rust like coating that covers it and the inside of the total fuel system. This goop at some point in the life of the car will start to flake off.

Putting the car back into service allows the fuel flow to start breaking this coating up. A good quality gasoline with cleaning additives or the addition of stronger separate cleaning additive accelerates this action. Keep in mine we are talking about micron size particles that clog micron size injector nozzles.

My car with brand new injector still has good and bad days. It isn't hard for me to tell a good day from a bad. If the car starts hard and a little black smoke kicks out of the exhaust when I start it, I know a micron size particle has been setting on an injector seat and keeping it from closing all the way. By the time I get to work it may have worked itself out of the injector.

This morning was good day...the car kicked right over. The Borla exhaust pulse sounded sweet running down the back roads to my office in third gear. It was running on all eight and the injectors clear. I pulled up and it idle smoothly. Based on past experience over the last few months , it may be different when I start the car to go home. It may crank hard because an injector has partially hung up again from a micron size particle that is setting inside the injector. <img src="graemlins/c.gif" border="0" alt="[ouch]" />

Thankfully these good bad days are starting to get a little longer in between as the system slowly clears itself out from my continuing effort to chemically clean the system up.

Why does this problem continue ? As I said earlier Porsche didn't design these cars to set up and not be run. As I expressed in earlier posts to the list.......the fuel system has no down stream filter or strainer just before the injectors. Any junk that has coated out in the lines and fuel rail can get into the injector nozzle, before it is recirculated an finally removed by the main fuel filter. <img src="graemlins/a_smil17.gif" border="0" alt="[blabla]" />

And the additional realization this morning as I rolled over the actual flow path of fuel and particles in the system through my mind driving to work. The particles that break off sit at the bottom of a loop in the fuel feed line under the car. They have a slightly heavier specific gravity than fuel; collecting at the bottom of this loop. Priodically the fuel flow does finally move them up to the injector rail, which probably happens directly you've run the car hard , they then find another perfect place to resettle out.

All the injectors come off the bottom of the rails, forming a dead space between the electric injector and the fuel rail. A perfect space for crap rolling along the bottom of the fuel line to drop into and build up. As the fuel flows through system it has a built in collection point in the absolute worst place. Just above the injector.

My point....don't believe simply installing new or cleaned electric injectors puts you home free. Porsche didn't design this fuel system to sit unused....

hawke <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

Ern

Hi Hawke,

I have had my 928 for over twenty years and it has been idle months at a time, over it's life with me. I have the mechanical CIS system and just replaced all the injectors myself as it was not ideling and starting quite the way I wanted it to. It now runs perfectly for which I am very happy after spending a week leaning over the engine cleaning and fixing. I took the injectors to an independent Porsche mechanic and he tested them and said I need new ones. I was too busy to witness his spray tester but wish I had for education. That is the first work on the system since the car was new. The CIS system must pass larger particles than 928s with electronic injection, as I have never had the problems that you describe. I do throw in a can of injector cleaner every once and a while, but have never used gasoline stabilizer when putting the car into storage. I have used the stabilizer a few times on some old MGs that I store for long times before driving them (SUs are a bugger to work on). Just wondering why I have had such good luck with so little care. What do you thnk of regular use of addatives for cars with limited driving?
Ern

P.S. I enjoyed the discussion with you and John, it got me to thinking again about my system.

LDRHawke

Ern,

My experience with my 1980 is the same as yours.....no similar problem as I have had with the1988. I still have original injectors in it.

I think a lot has to do with the older mechanical injection system develops higher pressure, has a perfect circle as an orifice (electric injectors have a pin in the center...making the opening more a donut shape), and each injector in the old system gets a distinct pulse (not simply pressure of the fuel rail). I think these differences have a lot to do with the difference in problems cause by foreign particles in the fuel.

I got you one better...owned the 1980 for 22 years...Purchased both 928's new. The 1980 also has 100k plus miles.

hawke <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />