74 CIS low pressure

[gwmac]

74 CIS, system pressure is 50lbs.
Fuel pump substituted. no change
Fuel filter replaced. maybe up a pound or two
fuel distributer substituted. no change
injectors replaced. no change

Any ideas?

[ossiblue]

How is your pressure gauge hooked up? On the 74, you have a throttle positioner fuel circuit that T's off from the line to the wur. You need to hook up the gauge set so it is between the T and the fuel distributor port, not between the T and the wur.

[70SC]

Check the in tank filter

[gwmac]

Thanks for the quick respose, I will go check the tank right now.
Gage is connected to the center port of the FD just after the banjo that goes to the cold start injector.
I replaced the FD about four years ago, had about 68lbs with the gage hooked the same way.
thanks for the help.
g

[gwmac]

Update
50 oz of fuel delivery in 30 second test.

[ossiblue]

Originally Posted by gwmac

Thanks for the quick respose, I will go check the tank right now.
Gage is connected to the center port of the FD just after the banjo that goes to the cold start injector.
I replaced the FD about four years ago, had about 68lbs with the gage hooked the same way.
thanks for the help.
g

Just so we're clear, we're not talking about the cold start valve but rather the throttle valve found on 73/74 CIS. According to the Bosch manual, both the wur and throttle valve need to be connected to the shut-off side of the gauge set. If you have the gauge inlet connected after the banjo bolt to the throttle valve, it sounds as if the throttle valve in still on the inlet side of the gauge. If the throttle valve leaks, you will get a low pressure reading.

[gwmac]

I stand corrected, pulled the tank filter,cleaned and reinstalled. I have reconnected the gage before the banjo fitting for the throttle valve so the throttle valve and the WUR are on the shutoff. Pressure is 60lbs system 46 with the shut off open.

[ossiblue]

Great news! It's always nice to find out that the problem you had really wasn't a problem after all. Now, it's time to drive and enjoy.

[gwmac]

Well not exactly,system pressure is still 10lbs low, car does not run right, poor rough idle etc.

[db_cooper]

The spec..as I recall..is a minimum system pressure of 4.5 bar or 65psi. The system pressure was adjustable at the fuel distributor with some shims behind the cap and spring on the pressure regulating piston. Sorry, i don't recall if your FD has the same set up, I'm sure it is adjustable.

Could be a leaky cold start valve too or a bad "O" ring on the pressure control piston.

Will the system pressure hold with the fuel pump off? It should hold for 30 minutes or more.

[gwmac]

Pressure holds well, fuel distributer was substituted which make me think its not that. My book does not even list the throttle valve, Can anyone tell me where to find 74 specific CIS information?

[Targalid]

I don't suppose you have adjusted your fuel mixture? You can get a pretty good idea just by twisting the 3mm Allen wrench from lean to rich to see if your idle smoothes. You would need to do this after fiddling with any of your fuel system components. Since you are in NM, do you have to worry about the state inspection system? If so, fiddle with the mixture first then have it checked with a CO tester. Whenever I change a CIS component I have to readjust the mixture. Since I have an older CIS, I have to stop by the roadside and adjust for changes in altitude as well. I can have a 5000 foot elevation change in a few miles which plays hell with the mixture. As I recall NM has similar elevation changes.

[ossiblue]

Just so we're all on the same page, could you recap what trouble you are having and what you've done so far? Your thread began with a mention of low system pressure but it's never been clear why you were checking the pressure, what symptoms your car had, or what testing you had done up to this point. You gave a hint in post #9 but it's not clear that is what you originally were trying to solve.

If your problem is as you described in post #9, it could be ignition, valve clearances, fuel delivery, or vacuum leaks but we don't know what you've tested at this point.

BTW, here are some specs for the throttle valve cars (73/74):

Warm control pressure with throttle valve...
at idle=2.9-3.1 bar

partial load=3.5-3.9 bar

full load=2.7-3.1 bar

System pressure: 4.5-5.2 bar

CO content (using gas analyzer and if you fiddle with the mixture screw): 1.5-2.5%

Fuel flow: 750 cc in 30 sec. minimum (~25 oz.)

[db_cooper]

This is the piston out of the fuel distributor on a 74 CIS 911. The shim can be one of several under the spring that is behind the piston. Increase the system pressure by adding shims under the spring. The "o" ring will go bad from time to time too.

I've pirated shims from fuel distributors being returned for core. If there is a shop near by which works on older 911s..they should have some too.

Be sure and replace the "o" ring..always..if you go in there. Cheap insurance.

[gwmac]

Started down this path because the car began to stumble, hesitate and miss, first just at idle then got progressivly worse fairly rapidly. I have shimmed the system regulator and now have system pressure in spec. Will use the specs listed above and see where we are now.

gary

[T77911S]

did you ever check control pressures?

what FP did you order, there are 4bar FP's out there. what is your spec?

fuel line problem?

[70SC]

Gary , I had a similar problem . Turned out to be water residual in the tank . (Bad gas / Methanol) Mine was pretty bad . Flushed Tank, lines,WUR, new filter , injectors , & had fuel distributer rebuilt . Now my 40year old car runs like a new beast CIS HATES water & debris Ethanol absorbs moisture Clean it & Keep it clean !!!

[gwmac]

UPdate,Pumped the tank dry, checked the screen in the tank, all was good. fuel delivery is in spec. Pressures are within a pound or two of Ossiblues post. I have adjusted the mixture for a AFR of 13.
car runs but has no power, starts poorly when cold. I just rechecked cold pressures without the car running although ambient temp is 90F. System pressure 69, control is 41 at idle throttle position,51 at mid throttle and 41 at full throttle. If I plug the WUR return the control pressure is 49 at idle throttle position, 59 at mid and 49 at full throttle.
Wur resistance is 24 ohms, voltage to WUR is 11.50vdc. I do not see the pressure drop as the WUR heats but that is probably because its 90degrees already.
I have done a vacuum leak test by using propane around suspect areas like the intake sleeves, injector bungs, back side of throttle body, no change in engine speed. What am I missing?

[ossiblue]

It might be a good time to do a thorough check of your ignition/distributor advance as fuel delivery appears to be good.

[T77911S]

not to get you off track and nothing to do with your problem, but 11.5v (engine running?), you might want to put the meter on your battery with the engine running and do a quick test.

lack of power, ignition advance as ossi has said.
check air leaks