89/90 240 with B230E rough idle after cold start
 

Hi, as a newbie on here I can see a lot of threads on similar situations on here, but non for the K-Jetronic. It's a B230E with K-Jetronic starts well but after a minute or so starts to rough idle, and I was wondering if its eithewr the warm up valve or the thermal timer, once the engine has got warm and run for at least 15 mins it runs great. After stopping engine and left for 2 to 3 hrs it strats and runs ok, which is leading me to the warm up valve? Any thoughts.

The thermo time switch opens the cold start injector and provides additional fuel when needed during starting. The control pressure regulator is the "automatic choke" allowing more fuel to be injected for a given amount of air when cold and as the engine warms up. It works by lowering the "control pressure" - that's the pressure going to the center of the top of the fuel distributor holding the plate down, resisting air flow. Less pressure=higher plate for given volume of air = more fuel sprayed.

I would connect your fuel pressure gauge and measure your line, control and rest pressures, starting from cold to verify those values are correct (or not).

I don't believe you have a O2 sensor and a catalytic converter in your market - but If you have an o2 sensor - I would suggest that part might be bad. The o2 signal is ignored for the first minute or so, then when switched to closed loop, a lazy sensor can cause mixture/idle problems until it heats up and starts working properly. Those old sensors are very easy to test with a voltmeter - or by simply leaving it disconnected and try to duplicate your problem.

240 B230e K-jetronic rough idle after start up
 

hoonk;504201 thanks for your reply, and I hope I'm replying correctly? Your correct in your assumption regarding O² sensor. My thinking was the CPV because of the the way it starts after a couple of hours run and standing for 2 to3 hours, residual heat in the block keeping the valve warm.
I made a pressure gauge system so I'll have a look at it later and post a further update and see what we get. Thanks again.

240 B230e K-jetronic rough idle after start up
 

Hi, I have checked the pressures and it starts at 20 psi, and it steadily rises to a max of 56 psi within 15/20 seconds. When the pressure reached 35 psi it starts to idle roughly, engine temperature had hardly moved. And looking at the graph I have found max pressure is not reached till 68⁰C approx. So am I looking at a thermal timer sensor issue?

I always thought the thermal time switch only opened the cold start injector when starting, as in when the starter was engaged. But I could easily be wrong. What's the line pressure?

Have you checked the spray pattern from the injectors?

You can pry the injectors out of the black plastic holders, lay them on the valve cover, use a jumper wire to activate the the fuel pumps, then using a suitable tool push the metering plate up make the injectors fire. Many times there would be terrible spray patterns, dribbling, squirting to one side - and pushing the plate all the way up for maximum fuel flow for a few seconds cleared / improved the spray patterns.

Hi Hoonk, I've already been there, found the cold start injector was dribbling and didn't always work.
It's I feel that it's time scale that it takes to reach full pressure, is far too quick, I would have thought 10/15 mins at least, the only thing that controls it is the thermal timer. I've 20ohms on it I'm wondering if it's possible the bimetallic strip that's failing (I mean it's 31 year old and 144,000 miles).

Control pressure is changed by the control pressure regulator. Rectangular box with 2 hoses and an electrical connector behind the distributor - disconnect it electrically and watch the control pressure stay at 20 psi longer. Or see if it runs better, or changes the way it runs rough after a few minutes with the CPR disconnected.

The thermo time switch's only function is to control the cold start injector.

Thanks Hoonk, this is all I wanted to know, what controlled the excess fuel/choke, so what you say is that I will have battery voltage @ the plug on the CPR during cranking, and controls its self similar to the thermal timer, with its own bimetallic strip? Obviously if the bimetallic is faulty I'm going to give the wallet hinge a test 😅🤑.

The CPR has 12v all the time with the engine on - not just during cranking. This picture - and with perhaps a bi-metallic strip (a very reliable technology) opens the passage for fuel to flow and increases the pressure on the top of the piston in the fuel distributor. More pressure = less fuel for a given volume of air. That's what's needed once an engine warms up. The "choke" turns off.

https://parts.darcarsvolvocars.com/i...R-69664_45.png