Hot start K Jetronic

[sean sherry]

Maybe I have found the root cause of my hot start issues after trying everything else.
The feed hose to the fuel distributer, down the back of the inlet manifold , has a large kink ......severely restricting the fuel flow.
I want to have one made up using the original fittings.... But where ???
I need someone with the correct equipment to crimp the new hose.

Thanks Sean

 

[Styria]

Hi Sean, could you be a bit more specific ? What is the hose made of ? On Gleaming Beauty there are two fuel lines (as in hoses) made of hard, black plastic (?), and I don't believe that they would kink. The set-up should be the same as on your car. Maybe Helmet can shed some light on this issue for you. Regards. Styria

 

[Helmet]

Maybe I have found the root cause of my hot start issues after trying everything else.
The feed hose to the fuel distributer, down the back of the inlet manifold , has a large kink ......severely restricting the fuel flow.
I want to have one made up using the original fittings.... But where ???
I need someone with the correct equipment to crimp the new hose.

Thanks Sean

Not sure that would cause a hot start issue if the engine is performing OK. If the fuel flow was restricted it would affect on road performance more that hot start.
Two common causes of hot start issues are a leaking fuel accumulator and leaking injectors.

 

[sean sherry]

Thanks .... the hoses are made from tough rubber and reinforced with (linen ) ? thread. The hose was jammed up against a bracket and badly kinked where it joins to the steel pipe .. I guess from the petrol tank. Hard to see where everything is coming from and going to on these 6 cyl engines. everything is buried under, or behind the Manifold.
I have replaced the injectors and the Accumulator, also the O rings on the regulator Valve. The problem is still intermittent.
My understanding of this purely mechanical K Jetronic , is that , ( as with an Automatic Transmission), it is dependant on Flow as well as Pressure. And add vacuum to modify the Pressure dependant on load , either low or high.
On the road I cannot fault the Car. Runs like a little Turbine. Though after straightening out the Kink it seems to have better acceleration through the gears.

........ Might be my imagination

 

[sean sherry]

Fuel hoses no longer available from Mercedes. Pirtex came to the rescue making up two new ones for $49 for both while I waited. They used the original fittings.
There was a slight difference in the mixture and Air adjustments .
Not much, and I'm thinking that with the Flow partially blocked the pressure from the pump delivery would increase. Now the balance has been restored everything can function as was intended. Well my theory anyway !
And the Hot Starting ? No different 0r 4 seconds before the engines fires.

If at first you don't succeed ......To hell with it !!!

 

[RANDYS]

HI SEAN

I DON'T OFTEN POST THIS SITE HOWEVER YOUR DILEMMA WITH THE CIS CAUGHT MY EYE.. WHILST THERE ARE FOLK OUT THERE DOUBTLESS MORE FAMILIAR WITH THIS MONGREL SYSTEM THAN MYSELF, ALLOW ME TO OFFER A COUPLE OF SUGGESTIONS.

I'M GUESSING YOU HAVE A 6 CYL 280SL r107? DOES YOUR BOSCH CIS HAVE THE HOT START MAGNET FEATURE? IF SO, ALL BETS ARE OFF.

ANYWAY BEFORE WE GO ANY FURTHER DO YOU HAVE A CIS TEST GAUGE AND ARE U FAMILIAR WITH ITS OPERATIONS ETC.? IF SO ,WE CAN DO BUSINESS. IF NOT WE CAN GO NO FURTHER AS IT'S A SHOW STOPPER.

 

[sean sherry]

Yes , I do understand how the System operates. I have bought a Pressure Test Kit and am currently sourcing some connectors so that I can check the Pressures, particularly the At Rest pressure, which I feel is at the root of the problem. I want to do this myself ,as at times there is no hot start problem. I want to check it over a number of days.

On the other hand maybe I'm expecting too much with this issue. In all other respects everything is 100%.

If the At Rest Pressure is too Low I'm at a loss as what else I can do. I do not intend just to throw Parts at it and hope for the best. If I can't come up with a diagnosis I will learn to live with it.

Maybe I could turn the ignition on and off a couple of time to prime the system when it is hot as I'm 100% sure that it is weakness issue and not over fuelling.

Good thing I'm retired with time to splurge !

 

[Helmet]

HI SEAN

I DON'T OFTEN POST THIS SITE HOWEVER YOUR DILEMMA WITH THE CIS CAUGHT MY EYE.. WHILST THERE ARE FOLK OUT THERE DOUBTLESS MORE FAMILIAR WITH THIS MONGREL SYSTEM THAN MYSELF, ALLOW ME TO OFFER A COUPLE OF SUGGESTIONS.

I'M GUESSING YOU HAVE A 6 CYL 280SL r107? DOES YOUR BOSCH CIS HAVE THE HOT START MAGNET FEATURE? IF SO, ALL BETS ARE OFF.

ANYWAY BEFORE WE GO ANY FURTHER DO YOU HAVE A CIS TEST GAUGE AND ARE U FAMILIAR WITH ITS OPERATIONS ETC.? IF SO ,WE CAN DO BUSINESS. IF NOT WE CAN GO NO FURTHER AS IT'S A SHOW STOPPER.

Hi Randy, why are you shouting?

 

[RANDYS]

Sorry about the Upper case folks.! My key board needs upgrading.

In the meantime, Sean, you will be cooking with gas once you get that test kit.
I agree that the at rest or static pressure is ebbing away. Until you measure it ,we are all guessing but I wouldn't have thought 4 seconds for a hot start to be unreasonable.
I see u have replaced the accumulator.

Just carefully double check the O ring on the press reg valve in the fuel distrib.

I just bought a so called "remanufactured" unit and this O ring was damaged and caused me all sorts of grief until I found it. One of the symptoms was rapid drop in static pressure.
As matter of interest what model Merc are we dealing with?

 

[sean sherry]

It is a 280 Sl 107 1981 Model ....... A Euro Spec. 110 engine.

I replaced the regulator O Ring with a Viton one ,obtained from Peter Bowers who specialises in K Jetronic bench repairs. The O ring had plenty of "rubber volume " sitting proud of the valve. The old one was flat at the top.
The new pump I had fitted is supposed to have a check valve, are these valves internal ? I see them advertised on the net as a separate external item.
Crawling under cars is now getting beyond me. Getting down is ok ... it's getting back up again .........

Thanks Sean

 

[sean sherry]

Fingers crossed .... my Hot Start issue seems to be solved.
.
Blowing out the "as new" one way valve at the Fuel Pump , I think I saw a small piece of something fly out ?????
Pressure tests are normal , and after 3 or 4 , cold to hot starts, and also hot to cooling down.... starts were 100 %.
Though I still feel that the sharp kink in the hose to the Fuel Distributer restricting Flow didn't help.
Some one said that the K Jetronic System is simple .... but very complicated to diagnose. So many things are inter dependant. There is no magic bullet

Still ........All is well that ends well !

 

[CraigS]

As an aside to your story, I found this company in Queensland that is rebuilding WUR's and fuel distributors.

http://www.k-jet.biz/

I am going to give them a try with the Porsche ones.

 

[Helmet]

As an aside to your story, I found this company in Queensland that is rebuilding WUR's and fuel distributors.

http://www.k-jet.biz/

I am going to give them a try with the Porsche ones.

Have you tried Bower Power in Frenchs Forrest ?

 

[CraigS]

Have you tried Bower Power in Frenchs Forrest ?

Yes, Peter rebuilt the WUR and fuel divider on my 6.9.