K Jetronic info.

Luddite · 3 Jan 2020

Currently helping a pal bring a Ford Capri back to life after body shell restoration, and having issues relative to getting the engine to run. Remembering that my 77 and 82 911 SC used a very similar K Jetronic system, I thought to post this link in the off chance that someone might be in search of a breakdown of the basic operation of the system...?

https://www.zeepoort.nl/jetronic/K-Jetronic-troubleshooting.html

deMort · 3 Jan 2020

I've recently been getting acquainted with this system .. it's a far cry from the modern systems i'm used to that's for sure ..

Fuel pressure gauges to check unlike multimeters on the new cars lol .

Pressure above and below a control plunger at different temps .. a very interesting way to control fuel injected.

I have to admit the plunger and the tiny holes .. how well its machined and how accurate it is .. very impressive ... tiny seals as well !

Also .. warm up reg .. mate that's one of the main problems or if its been stood for a while the the plunger itself in the metering head .

The actual warm up reg and its adjusted in the micron range .. i found the entire system very clever but from an engineering point of view .. modern electrics make it almost simple compared to this system for fault finding .. although i must admit .. checking the different pressure does lead you to the fault .. its just weird working that way ..

I don't think you actually need info on this but if so then let me know .

Over all i prefer modern cars .. but as an electrician then i would

Luddite · 3 Jan 2020

Ian, thanks for showing interest. In truth I was only posting the link for anyone to add to their library of K Jetronic info, was not looking for info, though more happy to share my fumblings if there is interest. I have no access to the kit required for fault finding so I am indeed fumbling... The Capri system is very similar to the 911, given it is of course Bosch system and used by a multitude of car manufacturers from the seventies through to the early 80`s and not designed Specifically for 911s.

The similarity between the 2.8i Capri system and that of the SC is considerable given they use so many of the same components and both are six cylinder.

The 911 fuel injection systems have varied considerably over the years, I guess the K Jetronic was perhaps the last of the mechanical systems though it did use some electrical control, though nothing too sophisticated a few heating elements operating on bi-metal strips in some devices, and one electrically operated injector used for cold start.

I think that EFI in 911s arrived with the 3.2 Carrera and the Bosch Motronic system, and things went all electronic from there on, then with the 964 came the ability to interrogate the system using the "hammer." I baled out of Porsche with the last of the SCs... But have been contemplating a come back.. :?:

Luddite · 4 Jan 2020

In the off chance someone somewhere beams this thread up looking for further info... The Capri was a 1981 vintage and brought back from the dead having lain for a couple of years... Very similar K Jetronic system to the 911 of 70s to 82 vintage.

It would randomly fire occasionally, run while misfiring and only once ran smoothly for a few seconds..

Always look for the simple stuff first.... found the fuel accumulator dripping from the vent to air (on the opposite end from the fuel connections)

This unit contains a heavy duty spring and a diaphragm. There are warnings not to cut it open.... I cut it open CAREFULLY... the diaphragm was crumbling. New accumulator fitted.

Given the disintegrating diaphragm, a new fuel filter was also fitted.

Problem still persisted, cracked fuel supply connection at the fuel distributor, pressure available...Same intermittent firing and spitting.

Removed the return to tank pipe and put it into a can in order to measure if after 30 seconds 750cc of fuel was returned.... hardly any fuel returned..!!!

Disconnected the pump output and ran it into a tube and can.... spluttered with no great pressure... 4 gallons of fresh fuel in the tank.

Removed pump... fuel dribbling from tank output.. Put more fuel in the tank, flow at output increased.

Refitted pump, put more fuel in the tank..refitted the pump and connected up the fuel line. then ran the pump to check the return to tank was 750cc after 30 seconds... Looking GOOD.

Fired up the engine with the return line still in the gallon can, engine fired up and ran well but was filling the can FAST..

Refitted return line to the tank... fired up the engine and it died after initial fire up.

Return to tank fuel line was leaking at it`s joint to tank.

Fitted a tube to the tank return connection and tried to blow through it... BLOCKED.... put an air line on it and could hear the fuel bubbling in the tank though on removing the air line there were traces of back pressure from the tank..... YEAH, the fuel cap was off all during tests... (-:

The cause of the problem.... sure the fuel accumulator, though I suspect it may still have initially run with its leaking diaphragm.

Seems to me that given the age of the vehicle the tank pick up and return pipes are rotten inside the tank.... Seems the pick up pipe may be perforated and thus requires to have over four gallons in the tank to have fuel level above the height of the perforations of the pump just sucks mostly air.

With the return pipe blocked the fuel supply pressure would be too high upsetting the calibration of the system... which would have perhaps shown up in other ways if it had ran long enough initially...

New tank ordered..

deMort · 4 Jan 2020

The mechanical system was replaced with electric components but i think you would easily understand how each one works .. injector for instance is no longer pressure opened but an electric trigger .. it works the same way though .. the trigger is different is all .

Far quicker to read fault codes and actual values to have an idea as opposed to fitting a fuel pressure rig and basically testing each part of the system to find the .. or the several faults which seems to be the case in my experience .

Each component went the same way though ... anyways ... ive PMed you

Luddite · 5 Jan 2020

Thanks for the heads up Ian, I have some knowledge of the Bosch KE system that followed on from the K-Jetronic.. Not sure if it was used in 911`s.

Replied to your PM..

Marky911 · 5 Jan 2020

Some interesting info from this guy bringing a TVR back to life.

https://www.pistonheads.com/gassing/topic.asp?h=0&f=47&t=1825244&i=40

Luddite · 5 Jan 2020

Thanks for posting the link Marky, great that it has loads of pics too... Very informative.

Logically enough it is the same system as the Capri..(-: Hope he checked out the simple stuff before tearing it all apart.. :?:

K Jetronic info.

Luddite

Indianapolis

deMort

Monaco

Luddite

Indianapolis

Luddite

Indianapolis

deMort

Monaco

Luddite

Indianapolis

Marky911

Portimao

Luddite

Indianapolis

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