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1978 280ce euro found dead on Ebay
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1,805 Posts
Discussion Starter #1 (Edited)
K-Jetronic Gurus Needed, :bowdown:

I have verified my problem with Cheapo is in the K-Jetronic system.
My car now runs on ether and/or gasoline down intake.
Ignition timing has been set with timing light. Car fires right over revs good with spray of ether and then dies. :thumbsup:

Here are my readings.
K-Jetronic Pressures:

System pressure 3.4 Bar
Control Pressure 3.4 Bar (WUR unplugged 12.5 volts at plug) 40 degrees F
Rest pressure 0.0 Bar

Changed back to my old Fuel distributor and got same readings.

Removed fuel regulator added shims from second Fuel distributor and no change in System Pressure or Control Pressure or Rest Pressure.

Swaped O rings on system pressure regulator and same readings.

Removed O ring (green one in picture) system pressure regulator and got following readings.

System pressure 3.4 Bar
Control Pressure 1.0 Bar (WUR unplugged 12.5 volts at plug) 40 degrees F engine cold
Rest pressure 0.0 Bar

Fuel Pump is New
Fuel filter is new
Injectors and Injector seals NEW
Return Line has been cleared



1) I am thinking both O rings are bad, since both come from used fuel distributors.
I am thinking this because system pressure should have risen with added shims (right). :confused:
Anything other than O ring can result in this? :surrender:

Anyone know where to get O rings or what size it is hate to buy the shim kit just for O rings.

I see in picture there are two smaller o rings where do they go? could those be bad ? Anyone ever replae the fuel regulator?


2) May have leaking cold start valve but would think car start if this was leaking.
 

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1978 280ce euro found dead on Ebay
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1,805 Posts
Discussion Starter #2
O.K. guys what you you think

fuel accumulator? zero rest pressure and low system pressure

system regulator? low system pressure and when I removed the green O ring it changed the control pressure to correct control pressure.

fuel pump check valve? no rest pressure.


Do above look reasonable? any favorites?
 

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1979 280CE
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6,118 Posts
Sorry dude, I can't help you now.
 

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1979 300TD naturally aspirated
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66 Posts
Well cheap ol, I recently purchased a book called "Bosch fuel injection & engine management" By Charles O. Probst and published by Robert Bentley(ISBN 0-8376-0300-5). Its a pretty thick book thats currently next on my reading list. I would be happy to look up anything on your K-Jetronic that might help you. Drop me a line.

I just took a quick look at the book and it stated in a table:

K-basic-first use 1974 porsche 911 T Fuel preassure 4.8-5.2 bar no computers or pins and no lambda control (I assume this is where your car fits)
K-lambda first use 1980- almost all mfrs fuel preassure 4.8 bar analog computer 25 pins utilizes lambda control

It would appear to me that you dont have enough preassure! You also provide evidence that the car responds to added fuel confirming this!
My verdict based on what youve mentioned and replaced: faulty preassure regulator. Should it have not responded to the added shims????
 

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Registered
1978 280ce euro found dead on Ebay
Joined
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1,805 Posts
Discussion Starter #6
Well cheap ol, I recently purchased a book called "Bosch fuel injection & engine management" By Charles O. Probst and published by Robert Bentley(ISBN 0-8376-0300-5). Its a pretty thick book thats currently next on my reading list. I would be happy to look up anything on your K-Jetronic that might help you. Drop me a line.

I just took a quick look at the book and it stated in a table:

K-basic-first use 1974 porsche 911 T Fuel preassure 4.8-5.2 bar no computers or pins and no lambda control (I assume this is where your car fits)
K-lambda first use 1980- almost all mfrs fuel preassure 4.8 bar analog computer 25 pins utilizes lambda control

It would appear to me that you dont have enough preassure! You also provide evidence that the car responds to added fuel confirming this!
My verdict based on what youve mentioned and replaced: faulty preassure regulator. Should it have not responded to the added shims????
I have to agree with you

The are three possible reasons for total system pressure loss and they overlap the problems with low system pressure.

1. The check valve on the fuel pump is faulty. (not likely becasue it's a check valve a spring and a ball bearing what can go wrong) but I have a new on on way cheap item $14.

2. The 'O' ring on the system pressure relief valve is leaking. As shown in picture there are three I only replaced one and it was not the front one which controls system pressure. If the front seal is leaking adding shims would do nothing becasue the fuel is just going around the piston and not moving it. The piston needs to seal against the fuel and then the shims and spring pressure will make a difference. This is where I believe my problem low system pressure problem is. I am ordering shim kit which contains seals that should correct any problems with system pressure.

3. The fuel accumulator diaphragm may have a hole and is leaking from rear discharge pipe back to the fuel damper before pump. I will need to pull of the connecting hose and see if there is any fuel and replace accumulator if leaking.
 
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