B230E K-jet hassles

Spac

It seems that my 30 year run of knowing only the bare minimum about K-jetronic is about to come to an end…

1985 240GL with a B230E. Clean fuel tank, good pump, new fuel filter (along with a bunch of other stuff like timing belt and spark plugs etc etc).

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Symptoms are:
Car will fire and run for a couple of seconds on cold start, but then stumbles and stalls.
Will not run again in the next hour or two.

Unplugging the main fuel pump will have it run for a bit longer, before it runs out of fuel pressure.
This all suggests that the engine is getting too much fuel and is flooding.

With the fuel pump plugged back in, the injectors
have a good spray pattern, and similar flow rates.
When you stop cranking the engine, they all keep spraying until the fuel pump turns off.

So… where do I start looking/what do I start blindly replacing? 😆

ramrod

What’s the fuel pressure?

That’s the end all and be all of kjet diagnosis

Major Ledfoot

According to the fault finding guide on page 7 in TP 11121/3 (in the tech archive), the probable causes for no start / hard start when cold are:

weak battery
ignition issues
air intake system issue
fuel pump issue
air induction system problem
main relay problem
cold start injector / thermal time switch / injector problems
air flow sensor problem
fuel line pressure and rest problems

Eliminating 1, 2, 4, and 6 has already been done.

If the thermal time switch is okay, I'd be looking seriously at the air flow sensor, then checking the line and rest pressures.

Rory

Major Ledfoot still learning about the k-jet system, this is more of a personal question.

Possibly the plunger in the fuel distributor is stuck open causing the engine to run rich?

The cold start valve and thermal time switch only recieve power whilst the starter motor circuit is powered? I.e. they only recieve power and let fuel in whilst the starter motor is turning? Or do the cold start valves continue to recieve power from the starter circuit even once the starter motor is off and the engine is turning?

If its running too lean on start up, it could be the warm up valve no? If that is clogged it would result in excess pressure, posisbly close to the 'control pressure' causing the car to run too lean on start up? When fuel pump is disconnected it would result in this blocked pressure being reduced, meaning even though the fuel pressure is lower, its resulting in the engine running more lean, because there is less pressure from the warm up valve and thus more fuel is allowed through? This could possibly explain why it wont start on second attempt, since the intial start was thanks to the cold start valve spraying fuel into the engine, but on the second attempt the thermal time switch is hot and open, meaning the cold start valve doesnt ground, and doesnt spray additional fuel into the engine.

Also do the k-jet systems have a airflow sensor? Its just a mechanical airflow meter on the k-jet isnt it?

Major Ledfoot

Rory Also do the k-jet systems have a airflow sensor? Its just a mechanical airflow meter on the k-jet isnt it?

Yeah, it's the flap thing.

Ayup; it's mechanical.

Anyway, here's a screenshot of part of the troubleshooting guide from one Green Book.
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Rory

Id be interested to see what happens if you try and manually ground the cold start valve whilst cranking the engine.

dmc

check the pressures, anything else is just a guess.

a couple of 'agriculrural grade' gauges can be made by little dash fuel pressure gauges and some old injector lines cut up with flex hose joining it all together. rough, though they worked for me.

jamesinc

If it's bogging down rich and you're happy with the main injectors remove the cold start injector and see if it's leaking. Also worth checking the aux valve and cold start injector valve plugs are not swapped, if you put noid lights on everything the aux valve should have power constantly when motor is on and cold start injector only for a couple seconds.

I'd start here bc it takes like 2 minutes to rule it all out, after that look at pressures and/or clean the fuel distributor/check free movement of metering pin.

With the fuel pumps running, checking the metering pin function isn't hard at all, take the intake hose off and reach in and push the flap up with your hand. The fuel pressure pushes the pin which pushes the flap back down with some authority. If unsure just compare how it feels with pumps running v pumps off.

Spac

jamesinc

Cold start injector does what it should - sprays when connected, doesn't spray when it isn't.

Jaz

This sounds exactly like whats happening in my 85 b230e, ive got an old bloke who worked on these when they were brand new coming around in a couple of days and he thinks he knows exactly what the problem is, but who knows. Ive pretty much done everything bar check fuel pressure at this stage

Major Ledfoot

Hey @Spac - have you had a chance to deal with the K-Jet problem? Very curious to see how you fixed it.

Spac

Major Ledfoot
Not yet!

I bought an ebay fuel pressure tester which helpfully says that it’s not for CIS systems, but doesn’t explain why…
It’s rated to 140psi which is a start.

I also grabbed the fuel distributor from a mate’s wreck. It has been sitting out in the weather for a couple of years now, but at least is a source of parts and something I can pull apart without fear of causing a catastrophe.

Matt1275s

K-jet specialists will discount an additional $50 for every fuel distributor you send in if you get it rebuilt with them.

I had a go rebuilding one myself but could not get it to seal again so sent mine in to them for exchange. They were good to deal with and helpful on the phone if you have any questions around the whole k-jet operation.

I also bought one of those ebay test kits (comes in a red box?) it did the job once they resent the correct adaptor for the warm up reg. It had the same thread pressed on each side of the adaptor hose and it took a bit of swearing before I realised what was going on, something to keep in mind.

Spac

Some tinkering today…

The tester says that the pressure out of the filter is at least 150psi… this seems quite a lot.

Pressure at the injectors is about 50psi while cranking, but then jumps to 70psi when you stop cranking.

I also confirmed for myself that the injectors flow about right while cranking, but then “turn on” hard for the few seconds after you stop cranking but before the fuel pump turns off - this fits with the pressure readings.

Spent ages pulling the spare fuel distributor apart, trying to properly understand it.
Interestingly, the steel gasket between the two halves was fatigued and cracked under one of the feed ports. Image description
This is the SPARE one, so is not related to the problem in the car but I found it interesting nonetheless.