83 sc backfires won't run help please

[Farrell]

I had very small backfires on my car. I can't see where my airbox is broken but that's what my shop told me is wrong. From what everyone says here it sounds like a shotgun goes off and I should here a loud pop from my airbox too I would assume. Thing is, none of that happened.

My car runs just has no power when I try and accelerate. Is it likely the same culprit?

[boyt911sc]

Originally Posted by tirwin

My understanding of the fuel accumulator is that it does two things. It acts as a sort of check valve to help maintain residual pressure after shutdown and it acts as a smoothing function for fuel delivery rate. The fuel pump has some small amount of variation in the rate of fuel delivery at a certain pressure. The FA smooths out the variation to make the fuel pressure more consistent. In a telecom network we would call this a shaper, buffer or a queue.

Tim,

First of all, I am not picking on your post but just wanted to get your attention. Since you are collecting pertinent information for your "Dummies thread......" The above post needs some further review. Not only it is misleading, you were successfully able to convince Mr. BK to agree. It did not describe what it really does.

These are my comments for the above post:
1). The fuel accumulator is not a check valve in any way or manner. Dissect an old FA and you will see what's it does.
2). It has not described what a FA does and the information is partially true and partially false. And misleading to a point that BK accepted or agreed to them as a fact.
3). Find a Bosch technical bulletin about "Mechanical Gasoline Fuel-Injection System..........K-Ketronic" (ISBN:0-8376-0468-0). Everything you need to know about CIS are well detailed, demonstrated, and explained. Highly recommended reading material.

You are doing a very good job in educating fellow CIS enthusiasts by collecting pertinent and well documented posts in your thread. We all make mistakes including myself but if we don't try to correct these mistakes, we would be contributing to the spread of misinformations. This is a technical forum and we could discuss, disagree, or contradict each other but end of the day we all are still friends.

Tony

[Bob Kontak]

Originally Posted by boyt911sc

This is a technical forum and we could discuss, disagree, or contradict each other but end of the day we all are still friends.

Hey Tim,

I am feeling a lot of friendly "team" love as a result of that ass kicking you just received from "Chuckles" Donato.

Chuckles,

If you would have asked me two days ago, before I posted and received info from Tim, I would have said it's a shock absorber and check valve.

I just was not sure it was or was not a regulator.

I does have a one-way flow function, correct?

[roadster49]

Hi Tony & Bob,
I will return to Michigan on Friday and will do the procedure recommneded. As a benefit I am getting quick at setting up the pressure testing and learning a systematic analysis.

thanks,
Michael

[boyt911sc]

Originally Posted by Bob Kontak

Hey Tim,

I am feeling a lot of friendly "team" love as a result of that ass kicking you just received from "Chuckles" Donato.

Chuckles,

If you would have asked me two days ago, before I posted and received info from Tim, I would have said it's a shock absorber and check valve.

I just was not sure it was or was not a regulator.

I does have a one-way flow function, correct?

Bob,

The technical bulletin has the literature to describe it and comes with a very understandable illustration. It is not a pressure regulator nor a check valve. Inside the FA is spring loaded diaphragm that absorbs or dampens the sudden flow of fuel from the fuel pump. In short, it has an expandable volume. A shock absorber is an acceptable description.

Imagine taking a deep long breathe and inhale some air and hold it for a few seconds. Your chest cavity expands and stomach contracts (ignore the stomach it might not be applicable to you.....just kidding). Hold your breathe as long as you could comfortably and slowly breath out. This is what the FA does with the residual fuel pressure. When you stopped the FP from delivering fuel the control pressure would register slightly higher the instant the FP stops. Why? The spring loaded diaphragm inside the FA reacts/contracts against the FP delivery pressure. Try to observe the pressure deflection next time you measure the control fuel pressures. If you do not observe this small pressure deflection, either the FA is bad or the fuel is leaking back to the tank.

Lastly, what do you mean one-way flow function? The correct installation of the FA is inlet at the side port and outlet at the center. However, if you installed it the other way around (inlet at the center) it still would work. I had inadvertently installed the FA (center port as inlet) in my CIS bench tester until I noticed it. And it was months and lots of testing done with this set-up and found no adverse effect on my data.

BTW, how's the restoration and repair of your car now? Done with the repair?

Tony

[tirwin]

Tony,

I have been traveling on business and working on my car when I haven't been at work so I didn't see your response.

I want to clarify my previous statement - perhaps I was unclear. As I understand the general function of a fuel accumulator (not necessarily specific to a Porsche) is to provide one-way delivery of fuel (i.e., keep the unused fuel in the fuel lines from returning to the tank) and maintain pressurization after shut off. A symptom of a failed FA would be rapid loss of residual pressure, no?

In some countries, they call the FA a Fuel Damper. Maybe it is a terminology difference but I think this actually might be a more descriptive term for what it does. Sometimes our choice of words get in the way of communicating the intended meaning.

If there is a difference in the way Porsche used the FA in the CIS system, then that's fine and duly noted. But I don't think my explanation is entirely wrong either. We could talk in more detail about what happens and why but I'm not sure it helps the OP.

My intention was not to create a diversion. Apologies if that was the case. Carry on...

[Bob Kontak]

Originally Posted by tirwin

I want to clarify my previous statement - perhaps I was unclear. As I understand the general function of a fuel accumulator (not necessarily specific to a Porsche) is to provide one-way delivery of fuel (i.e., keep the unused fuel in the fuel lines from returning to the tank) and maintain pressurization after shut off. A symptom of a failed FA would be rapid loss of residual pressure, no?

Tim,

Tony is correct. All these years I had the same faulty image of it's function. When descriptions say it "holds/maintains residual pressure", I think check valve.

Even if "sort of" a check valve, it should not allow fuel to flow backwards.

It's neither.

Fuel can flow through the accumulator unrestricted. It's an open tube with an in and an out on the bottom. That's it. However, there is a big spring and diaphragm that forces down upon the fuel, essentially creating residual pressure.



See pdf page 7:

http://www.usefulstuff.pwp.blueyonder.co.uk/myfiles/KJet.pdf

Cool beans. Thanks, Tony.

[roadster49]

As Tony suggested, I removed all six shims from the primary valve






With the shims out I checked pressure with the return line connected




So 5.5 bar is better but still above 5.2, and I have no shims in the FD

Retested with the return line disconnected



Recomendations please

[boyt911sc]

Michael,

The reason I requested you to remove the primary valve's shims was to see if the high system reading was caused by a flow restriction or by the primary valve itself. That's a new primary valve the previous owner installed including all the shims that came with the repair kit!!!!!! The system pressure without any shims at all is still out of spec. at 78 psi. Like to drop it 72 psi. (+/-1).

Let's do a quick test. Do you have another crush washer for the primary valve available to use for the test? If you install a second crash washer, check the resultant system pressure for me. Keep us posted.

Tony

[boyt911sc]

Michael,

Could you post a picture of the primary valve's piston/plunger? I like to see the top of the plunger. Thanks.

Tony

[roadster49]

I put an aluminum washer on the valve:



Pressure is down to 64 PSI



Next steps?

Michael

[roadster49]

Here are the requested pictures

[boyt911sc]

Michael,

Where is the primary valve's piston/plunger? Use a magnet to pull it out from the FD's cavity in case you left it inside. I like to see how it looks and I am beginning to connect the dots showing the root cause of your very high system fuel pressure.

Remember what I told you before you went to the hardware store to look for a washer? I said if the system pressure would drop to the 60's (psi.) with additional washer, the problem is not the return line by the PV's setting.

Could you check also the Fuel distributor Bosch ID number on it? Thanks.

Tony

[roadster49]

Here is FD Number ending in 077



Here are pictures of plunger




Please let me know what else to test.

Michael

[roadster49]

better picture of plunger

[boyt911sc]

Originally Posted by roadster49

better picture of plunger

Michael,

Attached below are pictures of the FD-031 and FD-077 primary valves. I've suspected something was not right with your FD-077 primary valve configuration or set-up. Take a good look at the pictures and compare. Did you see the difference?

http://forums.pelicanparts.com/uploads19/DSCN39621319150874.jpg
http://forums.pelicanparts.com/uploads19/DSCN39641319150894.jpg

I have not investigated or tested if the primary valves for FD-031 and FD-077 are interchangeable. They could well be and the springs for these are not exactly identical.

Connect all the fuel lines and calibrate the system fuel pressure using double sealing rings and the appropriate shims. Measure the different shims' thickness and install one or two shims and check until you get the desired system fuel pressure. You are doing a good job. Keep us posted.

Tony

[roadster49]

Hi Tony - mine looks like the 78???

How would the valve body machining accommodate the difference, which looks significant?

I will build it out as you say and let you know.

Tony, thanks for all your help, your training as a scientist, engineer, and forensic investigator are exemplary.

Michael

[roadster49]

I kept the two outside washers on the valve and added shims in the following sequence:
1


2


3


Looks like # 2; unless I swap out the copper washer for just the aluminum one to get to the 70 PSI range.

So do I try to start it now that the pressure is in line?
Do I need to do anything with the adjustment key on top of sensor?

I have had this jalopy since 2011 and it has never run well, so I am anxious to fire it up, but can wait until all testing is done as I want to avoid issues later

Michael

[roadster49]

tested control pressure. it is 72F or 22 C

here are test results (valve open and Wire plugged in) note I am only posting the first and last as the PSI did not change:





So not sure what happened the WUR did work before.

[roadster49]

So I tested the resistance across the WUR and it is now 9.4 ohms. Previously it was 26.6 ohms. Not sure what caused the deterioration, but thats the current value and probably why the pressure does not drop.

Suggestions?