911 sc starting issue

[scott.k]

As of right now, whenever I start the car up it drops to a very low idle and then dies out, except for 1 or 2 lucky times a week, when i start it and it runs normal/well as a running engine should. Im not sure what the cause is for it running occasionally. When I run the engine, (when it actually starts and runs), I do hear an air sucking noise, and I think it might be something other than the air intake for the engine, but I cant figure out what it is. Any suggestions would be appreciated,
Thanks
Scott

[ossiblue]

Scott,

I have stayed away from this thread for a while because you were in good hands with Tony and Paul. However, I just reread the posts and thought I would offer up an observation. You likely have more than one issue so eliminate the possible suspects by dealing with the easy ones first. Your problem appears to be an overly lean, cold start condition which could be from too low fuel pressures, a vacuum leak, an overly lean fuel mixture setting, or a combination of all three.

I have not read where you have checked the fuel pressure settings yet. This, IMO, would be the first step in diagnosing cold start/lean conditions. It's easy to do and will quickly point you toward or away from one particular cause, depending on your results. I would hope you do the fuel pressure tests, then report the results. If they're in spec, vacuum leaks would likely be next on your list.

[scott.k]

Originally Posted by ossiblue

Scott,

I have stayed away from this thread for a while because you were in good hands with Tony and Paul. However, I just reread the posts and thought I would offer up an observation. You likely have more than one issue so eliminate the possible suspects by dealing with the easy ones first. Your problem appears to be an overly lean, cold start condition which could be from too low fuel pressures, a vacuum leak, an overly lean fuel mixture setting, or a combination of all three.

I have not read where you have checked the fuel pressure settings yet. This, IMO, would be the first step in diagnosing cold start/lean conditions. It's easy to do and will quickly point you toward or away from one particular cause, depending on your results. I would hope you do the fuel pressure tests, then report the results. If they're in spec, vacuum leaks would likely be next on your list.

thanks a lot for the help. I will try to get the necessary tools to check the fuel pressure. Not sure if this means anything, but if i have the ignition on in the car and i give the lever in the air box a quick tap to prime the fuel system, a seemingly sufficient amount of fuel sprays out of the injector. I know I probably cannot judge well by sight of it but it doesnt seem like a problem. I think my problem is most likely in the vacuum system (probably a leak somewhere). But I will check the fuel pressure first just to be sure.
Thanks
Scott

[ossiblue]

Your quick test confirms the fuel is getting to the injectors, but it really can tell you very little about pressures. The CIS is a bit counter-intuitive with regard to fuel pressure--lower pressure makes the fuel/air mix richer, high pressure makes it leaner.

You are probably correct that your problem is due to a vacuum leak which also leans out fuel/air mixtures but you'll never be certain about the fuel pressure until you check and it's much easier to test than trying to find vacuum leaks--and that will come soon enough!

[scott.k]

Originally Posted by ossiblue

Your quick test confirms the fuel is getting to the injectors, but it really can tell you very little about pressures. The CIS is a bit counter-intuitive with regard to fuel pressure--lower pressure makes the fuel/air mix richer, high pressure makes it leaner.

You are probably correct that your problem is due to a vacuum leak which also leans out fuel/air mixtures but you'll never be certain about the fuel pressure until you check and it's much easier to test than trying to find vacuum leaks--and that will come soon enough!

Yeah, I agree. What type of tool is needed to check the pressure? Is there any specific fuel testing pressure gauge that I need for my car?

Thanks
Scott

[ossiblue]

Originally Posted by scott.k

Yeah, I agree. What type of tool is needed to check the pressure? Is there any specific fuel testing pressure gauge that I need for my car?

Thanks
Scott

You need a pressure gauge with a shut-off valve and adapters on the ends to fit your fittings. Pelican has a couple of examples in the catalog. I have the Tool Aide model 33865 and am very pleased with it.

[scott.k]

Ok, thanks a lot for the help. Is there an order of checking to take both with testing the fuel system pressure and checking the vacuum system for leaks?
Thanks
Scott

[ossiblue]

Originally Posted by scott.k

Ok, thanks a lot for the help. Is there an order of checking to take both with testing the fuel system pressure and checking the vacuum system for leaks?
Thanks
Scott

Typically, fuel pressures are checked in the following order due to the need to have a "cold" engine for some of the tests: (gauge set hooked up between the fuel distributor and the wur, with the shut off valve on the wur side of the T)

1) System pressure check

2) *Cold control pressure You will need to identify the number on your wur and know the ambient temperature to perform this test. Someone will link you to the charts needed to check the cold control pressure, I'm sure.

Given your problem, this is the most critical pressure for you to check as too high a pressure will cause an overly lean cold start condition which may be part of your problem--this is the factor you want to eliminate before hunting down vacuum leaks.

3) **Warm control pressure

4) Residual pressure

*During the test for cold control pressure, be sure the wur is not energized. I am not familiar with your year system so I don't know if the wur is energized when the fuel pump is running (it is on an 82 but someone, please reply.) To be safe, you can simply unplug the electrical connector on the top of the wur.

**For the warm control pressure, you must have the wur energized and observe the increase in pressure until it stabilizes. Again, my lack of knowledge will require someone else to help here. You can simply plug the connector back into the wur or, if the wur doesn't get current while the fuel pump is running, you can simply use a jumper wire from a know voltage source to the terminal on the wur.

As for order of vacuum leaks, all areas are equally suspect. I would follow the order of checking the most easily accessible hoses and components first and move on from there.

[scott.k]

i am finally going to go through with the fuel pressure tests, and i was wondering how to depressurize the fuel system (it seems to be an important step in the fuel pressure test kit i have.

thanks
scott

[j911brick]

Originally Posted by scott.k

i am finally going to go through with the fuel pressure tests, and i was wondering how to depressurize the fuel system (it seems to be an important step in the fuel pressure test kit i have.

thanks
scott

Lift up on the air flow sensor a till it stops humming.

[scott.k]

Originally Posted by ossiblue

Typically, fuel pressures are checked in the following order due to the need to have a "cold" engine for some of the tests: (gauge set hooked up between the fuel distributor and the wur, with the shut off valve on the wur side of the T)

1) System pressure check

2) *Cold control pressure You will need to identify the number on your wur and know the ambient temperature to perform this test. Someone will link you to the charts needed to check the cold control pressure, I'm sure.

Given your problem, this is the most critical pressure for you to check as too high a pressure will cause an overly lean cold start condition which may be part of your problem--this is the factor you want to eliminate before hunting down vacuum leaks.

3) **Warm control pressure

4) Residual pressure

*During the test for cold control pressure, be sure the wur is not energized. I am not familiar with your year system so I don't know if the wur is energized when the fuel pump is running (it is on an 82 but someone, please reply.) To be safe, you can simply unplug the electrical connector on the top of the wur.

**For the warm control pressure, you must have the wur energized and observe the increase in pressure until it stabilizes. Again, my lack of knowledge will require someone else to help here. You can simply plug the connector back into the wur or, if the wur doesn't get current while the fuel pump is running, you can simply use a jumper wire from a know voltage source to the terminal on the wur.

As for order of vacuum leaks, all areas are equally suspect. I would follow the order of checking the most easily accessible hoses and components first and move on from there.

does anyone have the chart of the pressures that the fuel system is supposed to read?

thanks
scott

[scott.k]

also, when i test this with the engine off, how do i get the fuel pump running? will this flood the cylinders with gas?

thanks
scott

-just thought about it for a moment, and it should only flood the cylinders if the flapper valve is lifted, so if there is a way to run the pump without the flapper valve lifted, that would be great, just let me know

thanks
scott

[scott.k]

i just set up the fuel pressure gauge/tester in line from the wur to the fuel distributor, so i will carry out the uncharged wur pressure, and the charged wur pressure. so, the way i understand it, if everything was working right, i will turn on the fuel pump, get a reading, then plug the plug into the wur, and the fuel pressure should increase.






and yes, in case your wondering, that "screen", is temporary, i will get a real air filter soon

[scott.k]

Porsche 911 CIS Cold and Warm Control Pressure Test - YouTube

in this video, what im about to do, he made a little switch for the fuel pump. should i have the key in the on position in the ignition so that the wur will run when i plug it in?


thanks
scott

thanks
scott

[scott.k]

anyone know how to wire a temporary switch to run the fuel pump?, im eager to get this thing running

thanks
scott

[Bob Kontak]

The guy in the video hooked up the wires to the female ports in the fuel pump relay socket between terminal 87a and 30. FP relay is closest to the driver. I think key had to be in the on position.

Terminal 87 feeds 30 when you crank the starter. Terminal 87a feeds 30 when the air sensor is lifted.

See diagram in the tech info section.

http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_82SC_Part1-2.jpg

[scott.k]

Originally Posted by Bob Kontak

The guy in the video hooked up the wires to the female ports in the fuel pump relay socket between terminal 87a and 30. FP relay is closest to the driver. I think key had to be in the on position.

Terminal 87 feeds 30 when you crank the starter. Terminal 87a feeds 30 when the air sensor is lifted.

See diagram in the tech info section.

http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_82SC_Part1-2.jpg

Bob, thanks a ton for the help. Now its my turn to research a little to learn about the fuse and relay wiring.

Thanks
Scott

[Bob Kontak]

I like the later SC diagrams. They are better set up for the "electrically challenged" like me vs the older ones. Bummer is to make it more pictorial it takes many pages.

[scott.k]

Originally Posted by Bob Kontak

I like the later SC diagrams. They are better set up for the "electrically challenged" like me vs the older ones. Bummer is to make it more pictorial it takes many pages.

Thanks for the suggestion
I am definitely in that "electrically challenged" category with you. Do you know where one could find the later diagrams?

thanks
scott

[scott.k]

i am clearly a beginner, but where is the gray box labeled fuel pump relay? Is it one of those circle relays above the fuses in the fuse box?

Thanks
Scott