Talk to me about 930 fuel lines
 

Hey guys,

as per title. Now I'm quite confused, from the manual and diagrams I've seen the lines I believe are fuel tank through the system to the engine. But then I've watched videos and they're talking purely fuel head and CIS. Can anybody explain to me what's involved altogether and if possible what I need to do to remove the full setup. As my previous post, the car sat for 30 years, thought I had WUR issues, got no fuel pressure so 30 year old pipework may well be the cause. Just a little overwhelmed with the info as I'm new to old porches!

Thanks in advance for any help/advice.

Rhys

When I first purchased my car 30+ years ago, I too was a bit lost with the fuel system. I purchased the Bosch "Mechanical Gasoline Fuel-Injection System with Lambda Closed-Loop Control" "K-Jetronic" Technical Instruction manual. It breaks down how the whole system works and and includes deep dives into every component. What I learned is just how simple (and genius) this system was for its day. Its a short read, 24 pages in all with lots of diagrams.
The ISBN on mine is: 1-85-226030-0

I did a quick search on Amazon and eBay, its obviously out of print and neither had it but there were others for L & KE Jetronic. Maybe post a WTB in the classifieds.

Once you understand the system, purchase a proper gauge test kit with the necessary fittings and you can diagnose issues.

Bill

Better yet, get the book Bosch Fuel Injection and Engine Management by Charles Probst...how to understand, service, and modify. 1989 copyright by Bentley Publishers.
Indispensable.

Talk to Len, @BoxsterGT
He should be able to get you all the lines you need.

There are supply and return lines from tank to the engine including the lines through the tunnel, there’s fuel pump lines, there’s the filter, accumulator, fuel head, both fuel pumps.

Yep, and to feed the lines in/out of the tunnel with a minimum of cursing, you'll want to at least partially drop the engine...

This is what I'm struggling to understand, I've seen people discussing the lines but nothing to and from the tank, purely on the engine!

This isn't what I wanted to hear!!

Basically fuel goes from tank to engine and excess fuel goes back to tank.
So it goes:
Tank -> fuel line to pump #1 -> pump #1 to tunnel supply line -> tunnel supply line to pump #2 -> pump #2 fuel line to accumulator/filter -> filter fuel line to fuel distributor -> fuel distributor to return line and through the tunnel back to the tank.

If you have pressure issues test the pressure at different points in the system with proper gauges and make sure both pumps are running properly.

Super super helpful! exactly what I was after. I have a full testing set, so next step is to test at various points. Was getting 2.6bar system pressure at the WUR/Head so something is amiss!

30 year old fuel components. even if you do get it running correctly it will be short lived... as fuel passes through it will dissolve the crud intermittently clog stuff. fuel leaks and so on lots of frustration and confusion second-guessing everything . you will replace or clean a part eventually it will muck up again. As previously mentioned i went through the same thing. On a positive side you will learn every square inch of that car chasing each new issue . and become very very familiar with how each component effects the next.
a wide band afr gauge is a must you don't want to think its running great and have it be super lean. They run great when they are lean, Then not so good ... if you do eventually rebuild and replace everything fuel related . when you go to set it up you will be like wow it all makes sense and it works .
does your car have the three pipe fuel accumulator? if it has a small leak it will blead directly into your return, reducing fuel pressure and you wont know it. The easiest way to test it is remove and dry it out put a balloon on the bottom port and run some compressed air through the supply 100psi and use your finger to close off the outlet side the balloon should not inflate.
i saw this post yesterday and have been super busy lately and haven't driven my car in a few weeks. took the old girl to work this morning , The turbos sure like the cooler weather.
good luck keep us informed of your progress.

Thank you! I'll be replacing all of the fuel components! the only thing I know which the previous owner did was reline the fuel tank and clean it. Hoses are all OEM I'd imagine. The thing had original plugs in which were almost seized to the heads. Electrical has all been done, I almost pulled the trigger on a turbokraft IC kit as well to get rid of that ridiculous recirc system. That's next!

Yeah it's more I'm not kitted up space wise to drop/lower the engine. My garage isn't large sadly (sore subject). So I'll need to find a space/place I can do the work. I have spoken to a few friends who will most likely be able to help! I knew for the bargain price I paid for it that it would need some finessing! lucklily I've worked on many old cars/bikes for a fair amount of years so I'm not phased, more hamstrung by lack of space at the moment!

Lots of horror stories about cleaning and sealing the 911 style tanks . usually causes more problems than good, if not done correctly . There is a plastic swirl pot( keeps air bubbles out of the cis system) in the tank. caustic tank cleaners will melt and deform it . hopefully he did the job correctly and added an access cover ( like the ones they uses on marine tanks ) and cleaned the inside by hand to remove the swirl pot cover and all the sludge before sealing. if there is no access or if the tank wasn't opened. there is a really good chance your swirl pot is a big wad of sludge and sealant. easily causing enough restriction so you cant get enough fuel pressure. most people just replace the tanks with an aftermarket tank without the swirl pot. ( that's what i did ) works fine without a swirl pot just as long as you fill up just before or soon after your reserve light goes on . That sucks about the lack of garage space .

I've changed fuel lines through the tunnel without dropping the engine. A little trouble fitting around the transmission mount but not that hard.

meh, it's easy peasy. Especially just a partial drop as there isn't a lot to disconnect.

Plenty of instructions on here.

Feeling a little better now! haha. Thanks guys. I've got a few old harleys to work on first and then it's prio nr 1! also have a collapsed rear bearing which I'm very much not looking forward to!

After reading this I looked in my library and I have this one as well and agree with Mark, its another very good reference. Its been well over 25 years since I've messed with CIS but at the time I was pretty proficient with it.

for reference here is the ISBN: 0-8376-0300-5 on AMAZON

Already procured!!

Bringing one of these back from a 30 year slumber is quite a challenge to say the least. First thing is to $hit can everything fuel system related. The main components can be rebuilt but the lines must be new. If the tank isn't new it must be fully restored, inside and out.
Here is a link to our CIS Primer:

https://rarlyl8.com/

That along with the other guides available should give you the knowledge you're after to tackle this. Good luck, we're here to help!

.

I have done it with both of my cars, never dropped the engine.

Thank you! got ahead of myself as it was running okay and then ran worse to the point of almost not running.

Fuel tank luckily has been relined/cleaned but all lines are old from what I can tell. Going after the WUR was like putting a banage on a dam it seems!

All learning! appreciate the help!