6.9 cold start issue

[QLD6point9]

Hey there guys and girls,

Just hoping for perhaps an easy answer here as opposed to diving back into the Bosch Kjet diagnosis manual (having been through the process before).

Story is, 6.9 that I own has all of a sudden (after previously working perfectly) presented with an issue whereby cold starts are not possible (cranks but doesn't start) unless you disconnect the fuel pump safety switch (blue plug on the fuel distributor housing) - see photo attached. (note: as described, if I do disconnect the blue fuel pump safety plug, the vehicles fuel pump will audibly be heard pumping fuel and the vehicle will start normally).

Recently, all k jet components had been refurbished by a Kjet specialist (auxiliary air valve, fuel distributor and Warm up regulator). New injectors have been installed, new fuel pump and new filter in the tank and also new inline filter.

I've got an exhaust probe that measures AFR (air fuel ratio) and I had previously tuned the fuel system to achieve almost perfect AFR results and had no issues with the vehicle for quite a good while (started first time every time).

The only items that haven't been replaced are the cold start injector and the accumulator.

I am wondering if this sounds like accumulator type troubles. Either way, it sounds like I am going to have to hookup the pressure test gauge and do some tests from the Bosch diagnosis manual.

I did however want to check firstly if anyone else has experienced this cold start issue, and whether it was for instance an accumulator issue.

It seems almost like a tired accumulator has decided to give up the game after perhaps 45+ years.... And or, I may have more debris blocking optimal fuel pressure delivery which I may need to also tend to (despite having previously replaced and cleaned all filters and gauze filters - including in tank filter).

Any and all suggestions welcome

Cheers James

 

[c107]

I would test the fuel pressures. a gauge set is not all that expensive off ebay (at least it wasn't a few years ago) and the various fuel pressure readings normally quickly point to issues. It will show you if the accumulator is functioning properly.

 

[QLD6point9]

I would test the fuel pressures. a gauge set is not all that expensive off ebay (at least it wasn't a few years ago) and the various fuel pressure readings normally quickly point to issues. It will show you if the accumulator is functioning properly.

Hey there c107,

The problem appears to be solved!. I do actually have a gauge set (I used it alongside the Bosch diagnosis manual to identify I had a blockage in the return line when I purchased the car). After that scenario was resolved by the gauge tests, I now swear by my gauge and trusting the values meet with the specified values in the manual. Definitely invaluable !!

In this scenario today, it would appear as though I had set my vehicle to run too lean when I was using my exhaust probe analyzer to tune the system. 1/4 of a turn (of one revolution) of the 3mm Allen screw in the fuel distributor and I have now resolved the matter of cold starts. Beforehand the air flow flap on the FD housing wasn’t fluttering down far enough during cranking to activate the fuel pump safety switch and therefore I was cranking the vehicle to no avail when it came to fuel supply. The 1/4 turn of the Allen screw appears to still achieve a range (when running) within 1 - 2.5% CO value. Instant startups are now back.

I figured while I was back mucking around with the fuel system once more, I treated it to a new inline filter. I also cleaned the various gauze filters, one on the WUR and the other on the fuel line leading into the fuel distributor. When the tank is next low I will drop the sock filter inside the tank and clean it (replaced it about a year ago with a new one).

thank you again c107 for your response and happy motoring !!

 

[c107]

Yeah i think these K-jet cars are happier running slightly richer than a modern car would.
Nice result.