uh...a bit of a bump....

pressures are correct, mix seems ok...any other suggestions?

Ron, when the problem happens, have you tried lifting up on the sensor plate as John suggested?

Doug
75 911S

yes, and that is how I've been starting it when warm so as not to have excessive cranking

so...yes...pressure issue...but - check valves have been replaced, residual pressure is ok according to 2 pressure testers...in all modes, ie cold, warm, hot. Accumulator replaced, and reswapped. Do I start in on the fuel distributor which seems to be a thorny and costly device?

Ron, it sounds like a residual pressure issue, so it's hard to reconcile this with the fact that your pressures all seem to check out.

Seems to me there are five possibilities:
1) You have a slight fuel leak somewhere.
2) One or more injectors is not closing all the way and seeping.
3) Fuel seeping back through the pump. (System pressure supply line)
4) Fuel is seeping past the system pressure regulator on the fuel dist. (System pressure return line)
5) Fuel is seeping past the WUR. (Control pressure return line)

Doug
75 911S

Thanks. I will check the control pressure return line and the injectors; fuel pump is new (I know, no guarantee of it's precision). Thanks for the additional pointed guidance, and I will let you know what the research turns up.

I took it to my mechanic, who after testing it, suggested that the first step should be to replace the injectors, and that would most likely cure things (this is a noted independent Pcar shop that supports PCA racing / SC cars in particular). 775, 1/2 for parts, 1/2 for labor - is this reasonable, both as a solution and a cost?

IMO reasonable only if the injectors have been tested and shown to be leaking; not a hard test to do. What does "after testing it mean"? Replacing parts without troubleshooting and pinpointing the problem is wasteful of time and money.

clarification - they did all the pressure tests that I did, and did not find anything out of spec with the residual pressures. Injectors seem(ed) to be the weakest link. But it is a chunk of $$, I don't have the experience to check whether or not they are faulty. I did clean them last summer at which time I also checked the spray pattern. To my uneducated eye, they seemed ok, not too ragged. However there's about 9k of mileage since then.

Six new injectors with new o-rings are $187.70 total plus shipping at Pelican. Jim

Ron,
I went to the dealer here(sorry Wayne, needed it then) and asked for a fuel pump check valve for a 79 SC. They gave me the part on the left. That night, I took the old one out and found the part on the right. The new valve wouldn't fit. Went back to the dealer and talked to a mechanic who told me my car's check valve was actually built in to the pump and the part I pulled out was just a transition fitting to connect the pump to the banjo fitting on the fuel line. I ended up getting a new banjo fitting that had a check valve built in to it. Had to cut the old one off the fuel line and install the new part. Worked like a charm. I know you said you replaced the check valve, but is it possible you just replaced the transition fitting and still don't have a working check valve?
Mark

http://forums.pelicanparts.com/uploads/2ggf.jpg

Mark thanks for the reply. I did replace the check valve. Essentially, I'm an automotive empiricist...I've never seen any of this before...so I compare all pieces to a manual all the time (and so consequently have found that there are a few things on my sc that rather vary from stock, eg a carrera exhaust instead of the sc exhaust). On the fuel pump check valve...did replace it. I'm a bit stymied - which is why I posted, did all the tests a few times, and then went to the mechanic. While I do have a lot of regard for the mechanic, to not have a more definitive cause, even though CIS is notorious etc etc, does give me some concern. Although if it comes back and is running fine...that would be it I imagine. Although - also - they are going to keep it to see if in fact the new injectors do make the difference (quote - we're 90% sure this is it).

Ron,

I have the same problem with my 78 SC Targa which I still have but I havn't been annoyed with it enough to fix it yet. I did all the preliminary checks which included the following:

Checked the system pressure - 78 psi with the engine running warmed up.

With the pressure gauge installed between the fuel distributor and the warm up regulator, turned the engine off and watched the pressure - it gradually dropped to about 20 psi and stabilized for about a few minutes and dropped to zero.

To check and see if the problem was related to the area of the fuel distributor, cranked it up again to build up pressure - shut the engine off and closed the valve to shut off the fuel between the fuel distributor and the warm up regulator. Pressure still dropped.

I then installed the pressure gauge between the leaving side of the fuel filter and connected the other end to the line which goes from the fuel filter to the fuel distributor. Cranked the engine to run and build up pressure. Shut the engine down and closed the valve to stop fuel from going back towards the fuel filter/fuel pump. This test was to see if I had a bad check valve at the fuel pump. The pressure still dropped.

Next removed the injectors - still connected to the fuel line placed them into a container and had someone turn the engine over while I watched to make sure they all were spraying. You have to be careful when you do this so I would recommend doing it outside of the garage. Turned the engine off and watched for any leaking injectors - none leaking.

Next, I removed the pressure relief from the back of the fuel distribu to to check for trash which might keep it in the partial open position which could also cause the pressure to drop. None found.

My next check which I havn't done yet is going to be to remove the return line from the fuel tank, plug it and the line on the tank. With the pressure gauge installed again between the fuel filter and the fuel filter line to the fuel distributor, turn the engine over to build up pressure. If the pressure still drops then the problem will most likely be in the fuel distributor.

I have taken my fuel distributor apart a few years ago and found two of the "O" rings which seal off the slits to the injector which keeps them from leaking cracked and broken. I replaced all of them with new "O" rings which were a challange to install. This is the only other area on the fuel distributor which could potentially creat a leaking problem. The rest of the fuel distributor is all mechanical.

So, as you can see by the above information, a lot of investigative work has been done to determine the problem. If I do decide to conitnue on with the rest of the tests, I will keep you posted.

Steve

"A Porsche does more then just go fast in a straight line"

Ron
How did you come out m with your car ? I'm fighting the same problem with my 77s . Any info would be greatly appreciated. Thanks
Jim

Just got done today (at the mechanic's). In fact the first fuel accumulator I put in was defective; it leaked slightly. I had ruled out the accumulator because it was new, and that's why the board (and mechanic) tried other options. They decided to try a different accumulator; it worked; and then they figured out that the one that was there was leaking. Argh. However, the injectors were leaking and not reallly spraying well either...so an expensive way to find out that the accumulator was no good.

Ron
Thanks for the reply. I ( my wrench ) found the problem today. I've never heard of this in all my years but the points were closing up as they got hot , hince no hot start. I drove my car in to the shop heavy on the throtle to keep it running and shut it down , after a few checks my wrench goes for the dwell meter and informs me the points aren't opening. I watched him adjust the points and the car fired right up and he also found the timing off, just two weeks ago the car ran just fine. What changed I don't know but I'm sure it will show it's ugly head some day. Oh, by the way I did put new points in and so far everything is fine. You can teach an old dogs new tricks.
Jim

If your mechanic didn't do it, you need to put a little dizzy grease on the part of the point that is in contact with the lobes of the dizzy. If you don't have grease on the lobes, the rub block on the point will wear quicker and the gap will decrease to the point that the point is no longer opening.

Alternate is to replace the point with another mean of triggering the CDI such as pertronix, or crane optical trigger.

Yes , there was grease on the points and thats why even more this makes no sense. Had I not seen this for myself , I would have a hard time believing this. Just a note , these were Bosch points .
Jim