K-Jet Idling troubles on initial startup
 

Hi All, I have a 1988 240GL with a B200E K-Jet engine

The engine runs sweet as a nut once it's up to temp but there's a couple of problems when first starting it up/running cold.

First one is tricky: The engine fires up instantly in all conditions which is great. However the engine is really lumpy as soon as it fires up and can last anywhere from 3-15 seconds. Feels like the engine is firing on 3 and sometimes 2 cylinders only. I usually rev it up to 1500RPM for a few seconds, still feeling lumpy and suddenly the engine will go smooth and give flawless performance until next startup. Sometimes if you don't catch it with the throttle in time, the engine will stall itself and takes a while to start back up because the initial pressure from the accumulator is gone. What could the cause of this be? Injectors, fuel pump, fuel distributor?

Second problem is simpler: The engine idles at around 1000RPM on cold startup due to the aux air valve but after about a minute the idle speed drops to around 5-600RPM making the engine very lumpy, equivalent to pushing the choke in too soon on a carburated engine. To counter this I have to manually bring the revs up to around 1000 with the throttle while at a standstill. The idle speed will slowly improve as the car warms up to the ideal 900RPM when it's fully up to temp. I've read somewhere that the aux air valve takes around 8 minutes to fully close. Is mine closing too fast and needs replacement?

Cheers
Peter

You need to get the control pressure checked , that is what richens the mixture for the first 2 minutes or so . it may be stuck on the warm pressure all the time . It starts off low from cold and should slowly rise for the first 2 or 3 minutes .....

Peter:~ I’ve had similar problems with the same car- problem one could be a rotor arm beginning to falter ( I purchased a new one that failed within a few months- replaced with Beru & fine since)

Problem two as you already mention is worth checking out- i.e. the auxiliary air valve should be open when cold and gradually close as the engine warms up, you can flick the fibre valve open with a thin tool and it should spring back to close (may be stuck- so lubricate)
These can be repaired if necessary? But review the manual for associated temperature fitting.
Good luck
Bob.

I'll see if I can buy a pressure testing kit and have a look but in the meantime I'll look into getting a new rotor arm, distributor cap and HT leads. The rotor arm is the governor type which I'm told is less reliable so I'll replace it with the standard type. Both the rotor arm and distributor contacts seem quite worn.

its never a bad idea to replace old ignition parts of course but IME if the sparks are weak this is most likely to manifest itself when the engine is warmer and the plugs are trying to fire a leaner mixture at part throttle, i.e. at higher cylinder pressures, not when trying to fire a richer mixture at low engine speeds. The spark jumps the gap with more difficulty whenever the mixture is leaner and the cylinder pressure is high.

This makes me think that the fuelling is more likely to be the problem. Firing promptly every time from cold signifies that you have a functioning cold start valve, but bad running immediately afterwards signifies that there is something wrong with the fuelling thereafter, probably the control pressure but it could be other things such as a slight leak in the flexible fuel pipes from the fuel pump near the engine.

If there is a tiny leak then not only does fuel bleed out (which can make a strong petrol smell on a warm engine, NB you will only see wet petrol on a cold one) but air bleeds into the fuel line when the engine is stopped; this means that there is a mixture of air and fuel in the fuel line when the engine is started from cold. This is rarely so bad that the engine won't fire when the cold start valve opens, but (with most fuel injection systems of this vintage) it can interfere with the fuelling from the main injectors until the air is cleared from the fuel system.

cheers

I had a similar problem about two years ago, changing HT leads fixed it completely.

Seems like you have a few different issues here...
I have the same engine. What ignition do you have ?

The misfire could be due to worn out ignition parts. I have the same problem, im doing a complete ignition overall, I'll tell ya if it did anything.

As for the pressure thing, you absolutely need a K Jet pressure test kit. Its around a 100 bucks but can be made for cheaper.

K Jet heavily rely on fuel pressure to work well.

You should also check the injector seals. If they have never been replaced/you don't know, its a good idea to change them. They are quite cheap, just be careful with the injector holders.

I have the same issues as you do with my car but I can't help much for now as I need to finish my 123Ignition conversion.

After that I'll dig deeper down into my K Jet. Im also adding a pump switch to prime the system *before* putting the key in the ignition position, switch I'll run for a few sec before startup to pressurize the thing and flush away deposit. Its an easy addon so might be worth it as well. I'll update on that too.

edit (cuz I forgot) : I have the same misfire issue but no leak at all. I do have a strong gas smell up to the metering plate with heavy deposit, which shouldnt happen really. I suspect my injectors are leaky... I will be able to test that with my pump switch + gently pulling up the metering plate. These mechanical injectors can get clogged, they have a small filter screen built in, it can be back flushed tho (Mercedes guys do it on their K Jets)

Hope this can help somehow

the fuel pump relay is designed to do that for you , doesn't it prime for 2 or 3 seconds when you turn the ignition on?

Nah, the pumps don't prime up before cranking. It has a fuel accumulator that will holds pressure for a few hours tho. The pumps keep running for a sec or two after shutting off, to build up that pressure

the pumps should prime for a couple of seconds when you put the ignition on with K jetronic , do you have the genuine volvo electronic green fuel pump relay ( with VOLVO embossed on it? a lot of weird things can happen in 30 years ...