The warm-start issue...

[Type17]

I have only just got a W116, and it's a good one, a 350SE with only 31,000 miles and two owners from new (Link to recent pics). I've spent some money getting the brakes done and some minor welding and a full undersealing and cavity-waxing, but one problem remains - hot/warm starting...

(also, I'm not getting great fuel consumption - only ~17mpg on a motorway run and only about 10-12 around town)

The warm-start issue - if the car is hot and it is stopped for longer than 3 minutes, but less than about 1.5 hours, it will start immediately (as if cold) but only run for about half a second or so, before cutting out. Restarting will take about 10 seconds of cranking with no catching at all, after which it will catch fairly easily, and will then run normally. Cold starting is perfect - starts within half-a-second, runs a little faster while warming up (airbypass valve open), and all warmed up within 5-10 mins.

After thorough reading of the book How to tune and modify Bosch fuel injection, I suspect that the control pressure regulator (aka warm-up regulator) is faulty, meaning the control pressure when hot is wrong (too low) which would also cause rich running (perhaps also causing the poor mpg) but, as the book says, all of the parts of the K-Jet system are interlinked, so any symptom can be due to a number of causes, so the real test is to follow the instructions in the book using a fuel pressure test kit, like this one.
However, this seems to be the only kit on the market, and all the suppliers that I've found are in the US, and none of them will ship internationally - does anyone know where I could get this kit, or one like it, where the supplier will ship to Europe? (I can pay by credit card or PayPal).

I'll update this thread as I discover more, but if anyone has any experience with these issues, please let me know (or point to other threads on here - I did a search, but may not have found everything...)

[koan]

A quick guess would say you are loosing fuel pressure or flooding due to one or more leaking injectors.

Something to try, next time you are in the situation where the car will be hard to start, slip it in to "R" and turn the key to start for 5 secs, it won't crank but you should hear the fuel pump run, now try to start the engine normally.

If it starts without the stall and runs first time it is a fuel pressure problem.

A fuel pressure tester would be useful.

Are you assuming US suppliers don't ship out of the US because they don't list post rates?

Make email contact with them, I've found it rare that a supplier won't ship to AUS.

I had a fuel pressure tester made by a local hydraulic hose repairer if that's an option for you.

koan

[Type17]

Thanks for the reply

I'm tending towards ruling out the injectors, because I previously had leaking injectors on my daily-driver '93 Audi 80 (Bosch KE-Motronic, same type of injectors as K-Jet), and the symptoms were the opposite - would start fine whilst hot, but was really hard to start when cold, due to fuel build-up in the cylinders. Of course I'm not actually going to rule anything out or in until I've tested everything.

Sorry, I forgot to mention, I've tried the 'starting in R (or D)' test, and there was no difference, so I'm fairly sure that the fuel accumulator is ok, and the fuel pump was replaced a year ago, so it should also be ok (I'll be testing it anyway).

I can try and get a pressure tester made up locally, but a purpose-made one would be easier to get and guaranteed to be the right connections, etc, so I think I'll try emailing the US suppliers.

[koan]

I'm tending towards ruling out the injectors, because I previously had leaking injectors on my daily-driver '93 Audi 80 (Bosch KE-Motronic, same type of injectors as K-Jet), and the symptoms were the opposite - would start fine whilst hot, but was really hard to start when cold, due to fuel build-up in the cylinders.

OK, what about a leak past fuel metering piston in fuel distributor.

My car has never maintained fuel pressure overnight, I've replaced check valve on fuel pump twice, primary pressure regulator twice, all injectors, fuel accumulator and cold start valve is not leaking.

Cold, the engine fires instantly if I do the "R" prime otherwise about a second of cranking while fuel pressure comes up. Hot is a different story, standing a few minutes instant start, anything over about five minutes it needs a bit of cranking to blow out the excess fuel, more that a couple of hours standing is back to the cold start condition.

Fuel pressure and fuel are going somewhere, I suspect leaking past fuel metering piston. I have a spare fuel distributor I'll fit when I get a chance.

A pressure gauge would show what fuel pressure is doing.

Pull the warm start injector to make sure it isn't dripping. Pressurising the system then disconnecting the fuel return hose and looking for drips checks the primary regulator. Closing the valve on the pressure test gauge isolates the warmup regulator to eliminate that as a leak path. If pressure still  drops it has to be injectors or fuel distributor.

Two version of the fuel pump setup, later one has a some sort of pressure compensating valve (not the check valve), don't know what the effect of it leaking would be.

koan

[Gerard]

Hi Type17

I'm in Dublin aswell.  Beautiful car by the way.

I recently bought some parts from AutohausAZ.  Ordered Monday 1stNov, despatched Monday night (Irish time) Received Friday morning 5th.  UPS expedited service.  They even forgot to attach the customs declaration so no duty.

Hope to meet you soon maybe at a run or something.
Gerard

[Type17]

OK, what about a leak past fuel metering piston in fuel distributor.

I sound like I'm withholding information(!), but I also forgot to mention that the fuel distributor is the only other part of the system that was changed, apart from the pump and filter - the first owner died in 2004 and the car sat in his garage until after his widow passed away in 2008 - the pump and distributor were gummed up with stale petrol, and were replaced by the guy who rescued the car (I bought it from him in August '10).

All of the possibilities that we've discussed could be the cause, but only a pressure test of all of the pressures (system pressure, cold control pressure, warm control pressure,rest pressure, etc) will determine the actual issue - anything before that is (educated) guessing...

I can't wait to get a suitable pressure tester, to see what the actual story is - I haven't had a good 'Sherlock Holmes' hunt with fuel injection since I had an '83 Mk1 Golf GTI in the 90's (also K-Jet).

Hi Type17

I'm in Dublin aswell.  Beautiful car by the way.

I recently bought some parts from AutohausAZ.  Ordered Monday 1stNov, despatched Monday night (Irish time) Received Friday morning 5th.  UPS expedited service.  They even forgot to attach the customs declaration so no duty.

Hope to meet you soon maybe at a run or something.
Gerard

Hi Gerard,
Excellent, nice to meet another 116 owner from Dublin. I might give AutohausAZ a call tomorrow, as they don't list a pressure tester, but they might not be listing it on the website.
Talking of runs, I usually go to Octane.ie Cars + Coffee, which was on today (first Sunday of the month) at the car park at Cherrywood, Loughlinstown. (See the photos on the last pages of this thread). I'm Type17 on there too.

[Type17]

I promised to update this thread as I got more info, and I've learned a lot about K-Jet since then so, for the record, here are some extra details:

The problem turned out to be a dead accumulator (acc) - this caused the symptom I mentioned above: "if the car is hot and it is stopped for longer than 3 minutes, but less than about 1.5 hours, it will start immediately (as if cold) but only run for about half a second or so, before cutting out. Restarting will take about 10 seconds of cranking with no catching at all, after which it will catch fairly easily, and will then run normally."

The system pressure is maintained at close to operating levels for the first few hours after engine shutdown by the acc. It needs to do this to take advantage of the scientific principle that a fluid under a higher pressure will have a higher boiling (vaporisation) point. The purpose of the acc is too keep the system pressure high enough to prevent the heat from the recently-shut down engine from causing fuel vaporisation. However, it doesn't need to maintain a high pressure indefinitely - just until the engine's heat has gone, and the risk of vaporisation has passed.

Does this mean that, a few hours after shutdown, the system pressure will be much lower than it is during running? Yes - the pressure of a system that has been at rest for more than a few hours will be at or near zero - BUT, in a healthy system, there will be actual no fuel-loss back to the tank, or air admitted to the system - the system will still be "full", but at, or near to, zero pressure. This is fine for cold starting, as the fuel already in the system is pressurised to full system pressure almost instantly by the pump.

What happens with a faulty acc:
Soon after engine shut-down with a faulty acc, the lack of pressure in the fuel in the engine bay area allows the heat from the engine to vaporise the fuel in the fuel distributor and the last bit of fuel line leading up to it. However, the fuel in the lines between the fuel distributor and the injectors remains at a higher pressure (unless the injectors are also leaking), which prevents it from vaporising, and that is why the car will start and run for about 1 second - when this liquid fuel is used up, the stuff behind it is just fumes, so the engine stalls and the driver has to crank the engine for 5-10 seconds until fresh (cool) liquid fuel reaches the fuel distributor and injectors once more.

Hope this helps...

[George]

Schweet find.

How many times did you say it has clocked over?