CIS pressure test, question

[manbridge 74]

Sensor plate should be flush with base of tapered section.

The lowest portion of plate should be no more than 0.5mm below base.

You should have an adjustable screw in center of plate IIRC. Mine has a clip that has to be bent.

You might still have a fuel pressure problem but checking everything from stem to stern will eliminate variables etc.

[npresley]

please excuse my ignorance, but what is IIRC?

[boyt911sc]

Originally Posted by npresley

please excuse my ignorance, but what is IIRC?

IIRC , If I Recall Correctly......

Tony

[boyt911sc]

Originally Posted by timmy2

Hot start problem with no residual fuel pressure. Classic accumulator symptoms. Lets not send him chasing everything in the system until the main problem is fixed.

Dennis,

You are correct that a defective FA could cause low residual fuel pressure in the system. However, there are other culprits that could cause the residual pressure to drop drastically like a leaking FP check valve and FD return valve. And there's another culprit that's easy to detect (???) and the most serious of all. This could cause serious havoc and disaster when undetected. Any guess?

Tony

[manbridge 74]

Originally Posted by npresley

please excuse my ignorance, but what is IIRC?

And I didn't recall correctly. Post above should read upper portion of plate not lowest.

[npresley]

Originally Posted by boyt911sc

Dennis,

You are correct that a defective FA could cause low residual fuel pressure in the system. However, there are other culprits that could cause the residual pressure to drop drastically like a leaking FP check valve and FD return valve. And there's another culprit that's easy to detect (???) and the most serious of all. This could cause serious havoc and disaster when undetected. Any guess?

Tony

What's the other culprit? I connected the thermal valve. The car starts like crap, so I'm going to disconnect. Thanks again for everyone's input. I hope this is helpful to others and not just me. At some point, in the next week or so, I will try and check some of the other things brought in this discussion since I replaced the fuel accumulator (FA).

[npresley]

Disconnect the thermal valve, and go to start. It starts rough, takes a few turns of the key. It coughs and sputters, then revs to about 1500 rpm. Is that to be expected?

[timmy2]

Answer to Tony's quiz... A split fuel line,,, Or a failing fuel pump, or a stuck fuel distributor plunger.....Did I win a prize?

(Perhaps more to come as I muddle over the question! )

[boyt911sc]

Originally Posted by timmy2

Answer to Tony's quiz... A split fuel line,,, Or a failing fuel pump, or a stuck fuel distributor plunger.....Did I win a prize?

(Perhaps more to come as I muddle over the question! )

Dennis,

A stuck FD plunger won't cause adverse fuel residual pressure loss......
A failing FP won't cause adverse fuel residual pressure loss......
However, a split fuel line or a leaking fitting would.........

Please PM me your SSS #, address, email, and bank account so I could forward the information to the Nigerian National Bank to claim your prize!!!! And it's all tax-free. Congratulations. BTW, there is also another winner (HarryD) from Oregon State.

Tony

[timmy2]

Too late Tony, I already received the money from the same Nigerian benefactor...
Harry and I are meeting this Saturday at the Portland C&C to split the cash!....

Rats, I knew I shouldn't have added anything to my original answer about a fuel leak, I came back and edited it with the 2 additional responses....

[npresley]

Drove it to work today. Went out this afternoon to start it and go home. It is a nice muggy 91° here. Had to hard the ignition to start for almost a minute, and the engine didn't roar to life. I revved it a few times and it settled and idled at 1000 rpm. Any ideas?

[timmy2]

Maybe too rich to start.
Or plugs, wires, dizzy cap, rotor or timing may need attention.
Get a CO meter and set the car up right, you're just guessing right now. Ebay has Gunson testers. Sometimes they come up for sale on the pelican classifieds too. Easy to use and fairly accurate.
Once the mixture is set you will know for sure if you have other problems like leaking vacuum lines etc.

[E Sully]

Good thread on CIS. Just curious, do you have a pop off valve installed? I have a 73.5 cis. Since mine was early there is no cold start manifold in the air box like later ones. By opening the pop off valve I can see inside to check to see if the cold start valve is working correctly. If yours is similar I would check it. If you don't have a pop off valve, now would be a good time to install one, and also check the air box for leaks. They do have a tendency to develop very small cracks around the bottom seam.
You say you pulled the injectors and had no leaks, but have you checked them like boyt911sc did for spray pattern and volume to make sure they are equal?

Never hurts to check the ignition system. Here is a link to a thread I did on your distributor if you want to look it over.
Distributor Maintenance

[timmy2]

Much better indeed. At what ambient temp was this CCP taken?



Does it start well at that pressure and does it do its high idle routine for a minute or 2?



@Timmy 2 how much pressure is added between the WUR heated only by internal bimetal and the WUR also heated by engine heat? I assume it could be 0.1 or 0.2 bar but not 0.5 bar right?



Michel

I just checked my service information booklet from Porsche for my '78 and it is indeed a .5 bar difference spec. For plugged in and car running versus just with pump running and plugged in.

[npresley]

Update: I replaced the accumulator last fall and everything came back to working order (or as before the hard start issue). Drove a few times this winter...got a little warmer yesterday, and drove the 911, warm hard start hard start issue came back. It was about 80deg outside. Started it this morning, no problems. This afternoon I started it, let it run for about 10mins, then cool off for about the same amount of time and puller the fuel line from the bottom of the accumulator. Fuel spilled out, like the last one. So, what causes an accumulator failure? Would you expect one to last more than 6 months and about 1000 miles? I have the internal check valve fuel pump; is there a way to add another check valve without replacing the FP, say on the inlet side of the fuel filter? I haven't checked my pressure readings, but I am assuming they haven't changed since this past fall. Comments?

[ossiblue]

Before you blame the new accumulator, you might want to try a little test. (Practice fire safety!)

Disconnect the return line from the bottom of the accumulator and plug it. Connect a short bit of hose to the bottom of the accumulator and put into a fuel safe container. Now, have someone start the car and watch to see if any fuel is coming from the line into the container. If so, your accumulator is, indeed, bad.

The reason for this check is because the return line that is connected to the bottom of the accumulator fills with returning fuel and some is forced into the return line from the accumulator and into the bottom of the accumulator--I believe Tony has confirmed this in another thread. So it is normal to have some fuel spill from the accumulator when the bottom line is removed. It is not normal for the fuel to be in the bottom of the accumulator if it is entering from above the internal diaphragm. That's what the brief test with the return line disconnected would determine.

[range83]

Hello,

A small question, when you tested the pressure, turn on the fuel pump or do you start the engine? The pressure is not the same in both cases.

Thank you in advance and excuse me for my english ....

Thierry.

[boyt911sc]

Originally Posted by range83

Hello,

A small question, when you tested the pressure, turn on the fuel pump or do you start the engine? The pressure is not the same in both cases.

Thank you in advance and excuse me for my english ....

Thierry.

Thierry,

No need to run the engine just the FP. What made you think the fuel pressures in the system is different in both cases? Have you measured them? The fuel pressure is delivered by the FP and the engine running or not would not affect your fuel pressure readings. Go ahead and try to get a different reading.

Tony

[npresley]

What size plug fits the return line that connects to the bottom of the accumulator? I'd rather put a plug in it, as opposed to using vise grips to crimp the hose.

[npresley]

Got a chance to do some checks, about 60deg ambient. Unhooked the return line from the bottom of the accumulator, let car run for a few minutes, no fuel ran or dripped out from the bottom of the accumulator. Did some pressure checks:

Valve closed pump running pressure is what? (system pressure) 4.5 bar

Valve open pump running pressure, wur unplugged pressure is?(cold control pressure) 1.3 bar

Valve open pump running wur plugged in pressure?(warm control pressure) went from 1.3 bar to 2.4 bar (as engine warmed)

Valve open after warm pressure check, turn off car and residual pressure reading immediately and after 30, 60, 120 seconds and then 15 and 30 minutes? 1.5 bar immediately, 1.3 bar @ 30 secs, 1.2 bar @ 60 secs, 1 bar 120 secs, 0 bar @ 15 min, & 0 bar @ 30 min