Bruenein 911sc

[enjefriy]

Hi all.
New to post but not with 911sc & our host.
I now have perplexing problem with starting my 1982Sc.
Starts & run perfect, but a restart may not be achieved immediately upon shut down.
A 10minute wait consistently before a successful restart may be obtained.
Persistence will only mean cranking away, or on rare occasions smoke exiting from the air filter, post some popping burbling noises of some effort by the engine to start up.
Otherwise simply waiting 10 minutes will always give a successful restart.
Followed the Hard warm start up forums, but no joy.
Most recent replacement was of the accumulator.
Only parts not replaced yet it the Metering Valve, Fuel distributor, & WUR.
WUR mod carried out to make it adjustable. Fuel Pressure gauge fitted permanent.
Parameters checks out as per bentley.
I am going crazy trying to figure this out.

[Flat6pac]

How about if you want to restart, remove the aircleaner, with the key on raise the airflow sensor and charge the system for a couple seconds. Try to start it
Now what happens?
If you have installed a defective accumulator, the pressure goes back into the return line. Just an after thought
Bruce

[easelboy1]

+1 on Bruce's Comment - he knows his engines.

[Gunter]

On a warm-start problem, I'd suspect the check valve for the fuel pump first and then the accumulator. Post a picture of your pump.
Some pumps have an internal check valve and some have an external one.

If your pump is really old, consider a new one. I prefer a pump with an internal check valve like a Bosch 0580254984 or Pierburg 7.21659.70.0

Important is the outlet nipple to match the banjo fitting, usually M12x1.5mm and the inlet should be 12mm.
When replacing the pump, the short hose from tank to pump is also replaced; 1/2" fuel hose will work.

Your pump should look like this:



Post a picture.

[enjefriy]

replaced with new accumulator from pelican. Non return valve is the external type also replaced.
Carried out the pressure checks as per bentley, and parameters checks out.
Pressure retained by the line. Pressure retention test carried out with the Shut off valve open and closed, as per bentley manual.
The things is, the cars starts great each time. Only restarts is the issue. Even without allowing engine to warm up, a restart attempt without waiting for 10minutes will not be successful.
once the car is started, no other symptoms. Only when i need to restart the car under 10minutes from the time it was shutdown, will you then notice the problem of restarting.

[enjefriy]

BTW, pump is a bosch unit. Same removed with replacement.
As for raising the airflow sensor, no joy either.
But out of curiousity, if it did work with the raised airflow sensor, what would this indicate then.
Carried out the cold pressure tests and warm. All down to the bentley instructions.
Pressure retention not a problem, as well within specs after 30minutes even.

[enjefriy]

BTW, pump is a bosch unit. Same removed with replacement.
As for raising the airflow sensor, no joy either.
But out of curiousity, if it did work with the raised airflow sensor, what would this indicate then.
Carried out the cold pressure tests and warm. All down to the bentley instructions.
Pressure retention not a problem, as well within specs after 30minutes even.

[Gunter]

Originally Posted by enjefriy

BTW, pump is a bosch unit. Same removed with replacement.
As for raising the airflow sensor, no joy either. ??? With ignition ON, you cannot hear the injectors squeal when raising the airflow plate?
But out of curiousity, if it did work with the raised airflow sensor, what would this indicate then. It indicates that the pump is running and providing enough pressure to open the injectors
Carried out the cold pressure tests and warm. All down to the bentley instructions.
Pressure retention not a problem, as well within specs after 30minutes even.

It's a tough one with everything sounding normal.

[enjefriy]

I know. Runs great too. When it starts, it does so in one kick. Unless it's an initial start from no use of about couple of days, it would b so easy to start. This problem only appears when trying to restart after the car was shutdown. New finding now. If I kill the fuel by closing off the fuel from the WUR to the fuel distributed, I was able to restart. Must be an issue with my WUR then right?

[enjefriy]

Wit ignition on, raisin d plate will run the pump. Did that til I flooded the engine even. Would have chucked the cis system if carbs wasn't so expensive. Anyone know of companies doing turn key engines wit carbs, that would ship to Brunei. Carbs looks much easier to work wit & u don't see them wit this sort of problems

[enjefriy]

Also any idea wat pressure I should see during warm starting. I see about 30+psi out from the WUR. Warm running pressure now at about 44+psi. Bentley states 50-55psi. Donno if relevant

[Gunter]

Sounds like a wrong mixture scenario during hot-start immediately after shut-down.
You mentioned that you made the WUR adjustable?
Did you try adjusting it for higher PSI for warm-running?
Is the small screen in the line on top of the WUR clean?
Is the AAR working properly? Closed completely when hot?
When trying to restart hot, do you press the gas pedal down completely to open the butterfly?
Or do you leave the gas alone?
How do the plugs look right when the hot-start fails? Are they wet?

[enjefriy]

Hi Gunter,
I use an oxy sensor to tune the mix and timing checks out good too.
I would like to try setting a higher pressure as you mention it now. I was doubtful what this might do to the other parameters however.

The cold test, leak down test are all smack down as per the manual. The warm running test however is almost 10psi under the specified, so You may have something here Gunter. (mine was at 40++psi, Bentley states 50-55psi)

Anyway, WUR filter was mucked up. Clean it already.
The AAR is something i haven't checked.
When restarting, i've tried both ways. I typically start without needing any pedal footing, so i tried with full depress, no difference.

Plugs are sooty when i pulled them out. But i guessed this was from all the idle runs i been doing to sort this prob. I just changed all the spark plugs yesterday. Same prob.

So next up, i'll checked the AAR operation, then see if i can bring the Warm running pressure up to 50-55psi. Wish me luck.

[enjefriy]

Just has a thought about my WUR warm running pressures. If i increased the control pressure, would this make it more resistive for the sensor plate to lift upon start-up. Viceversa with a lower control pressure.

i.e. a higher control pressure is set by the WUR for a warmed engine in order to set a leaner mix. Hence on a cold engine, a lower control pressure is used to give a richer mix.

Am only checking this for my understanding of the system, as the warm control pressure is found to be 44psi whilst the engine is running.

My question is, In order to set my Warm control pressure, do i do this with the engine running.
I tried increasing the WUR control pressure by raising the Bimetallic Strip more, and instead i couldn't even start the engine. I did eventually after some severe re-adjustments of the 3mm idle mix and idle screw.

Worst even was that with the engine running now in this set up, the Warm running control pressures fell even lower to 25psi.

Should i have instead nock it down to increase the control pressure?

[enjefriy]

Remove AAR. tested good. Was closed when removed from a ran engine, which then reopened when cooled. 12vdc fed to check it's closure.
Had a play with the WUR again. Tried to manipulate the pressures whilst the engine was running.

Hence I realized that I didn't know what I was doin. When Do I make adjustment?

Cold pressure looks good, so in order to check warm control pressure, do I make my adjustments with a running engine? Or just on a warmed up engine?

[boyt911sc]

enjefriy,

I re-read your posts several times and find it hard to make any suggestions to your current problem because you keep giving us in formation like 'everything normal per Bentley'. And many times guys come to this forum seeking help and there are plenty available here.

If you provide us with data like residual, control, and system fuel pressures you have obtained in your investigation would give us a more clear picture for your non-starting problem. This problem of yours is a typical CIS problem that has been discussed so many times in this forum and sounded like a broken record.

Another problem that contributes to other problems is tinkering the mixture screw during non-starting issue. This will compound your problem more than help you. The air to fuel mixture should be adjusted when the engine is fully warmed up with a gas analyzer after it has been vacuum tested for air leak/s.

Lastly, you could test your WUR without running the engine. The test itself will tell you if your WUR is the culprit or not. So getting the information like fuel pressures (bar or psig) is critical for FI troubleshooting. I would look into the control and residual pressures for this kind of problem/s.

Tony

[Joe Bob]

Hot start on an SC, try the check valve in the neck of the fuel pump. Used to be an 18 dollar part.....

[boyt911sc]

Originally Posted by enjefriy

Remove AAR. tested good. Was closed when removed from a ran engine, which then reopened when cooled. 12vdc fed to check it's closure.
Had a play with the WUR again. Tried to manipulate the pressures whilst the engine was running.

Hence I realized that I didn't know what I was doin. When Do I make adjustment?

Cold pressure looks good, so in order to check warm control pressure, do I make my adjustments with a running engine? Or just on a warmed up engine?

enjefriy,

You could check the cold and warm control pressures of the WUR without even running the engine. With the ignition switch @ ON or RUN position, connect terminal #87a & #30 (FP relay socket) using a suitable jumper wire with in-line fuse. Record the control fuel pressures versus time.

For example:
start........
after 30 sec.
after 1 min.
and so on until you get the control fuel pressure to stay steady. Within 5 to 7 mins. you should be able to get the max. control pressure if the heater is working right.

If you could re-set the mixture screw where it was before would be great. Otherwise, you have to deal with it later. Altering the mixture has added another variable in your problem solving. Keep us posted.

Tony

[Gunter]

Originally Posted by enjefriy

Just has a thought about my WUR warm running pressures. If i increased the control pressure, would this make it more resistive for the sensor plate to lift upon start-up. Viceversa with a lower control pressure.

i.e. a higher control pressure is set by the WUR for a warmed engine in order to set a leaner mix. Hence on a cold engine, a lower control pressure is used to give a richer mix.

Am only checking this for my understanding of the system, as the warm control pressure is found to be 44psi whilst the engine is running.

My question is, In order to set my Warm control pressure, do i do this with the engine running.
Bentley 240-15 states: Control Pressure check for cold and warm is done with engine running.

I tried increasing the WUR control pressure by raising the Bimetallic Strip more, and instead i couldn't even start the engine. You mentioned earlier that the WUR was made adjustable. How?? Like the scetch below??I did eventually after some severe re-adjustments of the 3mm idle mix and idle screw.
Not good, I'd concentrate on the WUR. What is the Bosch number on the WUR?

Worst even was that with the engine running now in this set up, the Warm running control pressures fell even lower to 25psi.

Should i have instead nock it down to increase the control pressure?

Is the WUR adjustable like this:?? What is the number on it??

[jmohn]

If you've got fuel (and it appears you have, from the testing you've done) the next thing to check is spark. Have you tested the coil, cold and hot?

Jerry M
'78 SC