The 242 is finally running and rolling after a complete rebuild of all major systems. I'm now beginning to sift through the list of secondary issues.

First on the list is K-Jet, which seems to have a rough and lumpy idle when cold or when warm. At higher RPM's, it runs perfectly. I can adjust the idle with the screw, but anything below 1000 RPM and the engine practically dies. It just gets very rough and lumpy, barely hanging on. At higher speeds, there is no detectable miss or roughness, and it pulls hard during the rest of the power band.

Some facts:
1. Engine is newly rebuilt.
2. Has a new and tested engine wiring harness.
3. Has gas in the tank that is about 9 months old.
4. Has confirmed spark to all 4 cylinders.
5. Has timing set to 15 deg at 1000 RPM.
6. Has a new fuel filter. Has previously replaced main and in tank fuel pumps.

K-Jet components examined so far:
1. Tested the motion and centering of the airflow sensor. Appears good.
2. Tested resistance of control pressure regulator as per K-jet.org instructions. Tested good at 23 Ohms.
3. Checked function of aux air valve. Motion is smooth and easy and it is not stuck open.
4. Removed the AC solenoid from the intake circuit to eliminate that as a possibility.
5. Frequency valve appears to be working, I can hear it while running.
6. Systematically removed other vacuum circuits while running. No changes.
7. Unplugged cold start injector while running and warm. No changes.
8. Checked connections at CIS computer in cabin. Everything was clean and in good order.

Things I still need to test:
1. Measure fuel pressure (a pain to build the rig, but I know it needs to be done).
2. Adjust fuel pressure regulator?
3. Adjust mixture?

I'm currently looking for other things I can test to better understand and fix this problem.

Cheers,
Jason

I have to resurrect this thread to post the solution to the original problem. Its a little embarrassing, and very strange.

It turns out that the car didn't really have a lumpy/poor idle, it's just that I was trying to get the darn thing to idle at 300-400 RPM! I was using the dash tach to measure engine speed, which turns out was reading over 100% higher than reality. As soon as I used another engine speed meter, my issue became painfully clear.

Now that I understand the true engine speed, it idles smoothly at 500 RPM and above. Simple but strange fix!

That is a bummer! At least you solved the problem. Did you figure out why your tach was so off? I just picked a tach up on eBay and before I install it I'd love to know if I should doubt its accuracy all of the time, or just some of the time.

Sorry if I'm being simple, but have you replaced the injector seals and plastic holders, cleaned the throttle body, and changed the intake manifold/throttle body gaskets? Also, do you know for sure that the in-tank pump is running?

the first and easiet thing to do is to check/adjust the mixture.

even if you don't use any instruments...a Dwell Meter or a Digital Volt meter,
Just turning the adjustment screw to see if there is any change in the idle will tell you if that's the problem.

And since you've done a complete rebuild...odds are it's running too rich

You need a long 3mm Allen Wrench. Clockwise is richer/CounterClock is leaner.



ps there is a complete section in the Volvo Prb Solver on troubleshooting the K-Jet.

some people have had problems getting it to download....I have not...downloaded a second copy last evening with no problem

Adjusting the mixture is on my list, but I've been told on this board it should be the last thing I touch, and that 9 times out of 10 it can be left alone.

Can I adjust by feel like changing mixture on carbs?

Also, where is the problem solving section you talk about? I've looked through the links on this site's FAQ, but nothing specific to K-Jet comes up. Most of my information thus far has come from K-Jet.org.

the reason I suggest the CO///mixture adjustment is because that screw physically changes the fuel input at base idle...just like a carb.

If your only problem is at idle then I'd go there first.

The reason I say go here now is that you've check off all these other things on your list, is as I said you just did a complete rebuild and the setting here the CO was for the engine as is ran before and who knows who adjusted it when.

If it has an effect then you can proceed to set it with either a Dwell Meter....Test Point is on the Drivers side just in front of the shock tower...Black cnnector single wire. Set Dwell to 4 cyl....45Degrees is the where you want to get it with the screw. Lift the Allen wrench off the screw to confirm...the weight of the wrench will effect the reading.





Volvo_Problem_Solver_--_Advanced_Edition(1).pdf

cut an paste this link into your browser...you should get a pop up dialoge OPEN or DOWNLOAD

https://files.me.com/dustinl.c/le9rdc

So I got a 3mm allen that is long enough, along with a dwell meter. I set up to adjust the mixture according to that guide, but I could not for the life of me find the allen screw head with my allen key.

My allen key drops down inside the hole about an inch before encountering an object. I fished around with the key for near 20 minutes looking for engagement to a screw head, but to no avail. When doing this while the engine was running, I was able to simply press down on the object my allen key was touching and was able to get the engine to stumble. I take that to mean that I was successfully pressing down on the arm itself.

That said, I can't find that darn screw to turn. Any advice?

Finding the 3mm socket head screw can be tough, and over time it fills with gunk. Try coating a 2.5mm allen wrench with WD40 and inserting it into the socket to help clean it out. Then see if the 3 will fit. Do all that with the engine off. In fact you can make adjustments with the engine off, and then fire it back up again.
However you mention that the engine is rough when cold and warm, and that means it probably isn't the sensor height. When warm yes, but cold the mixture goes very rich, outside the adjusters range.
If it were me, I'd pull the injectors and get the pump turning, and lift the sensor plate and check the injector spray patterns - just fire them over the cam cover. They should all produce a nice even cone of fuel, and make a whistling sound. When the plate drops back, they should shut off cleanly, no drips. All should begin flowing fuel at the same instant as well.
If that check is passed, you're on to something else.
Rhys

Thanks Rhys, I was doing just as you suggested when you were most likely typing that post. I used a remote camera probe to discover gunk, and used a pick to clean out the head enough to make adjustments.

On to the interesting stuff:

Before any adjustments, the dwell was about 55 deg. I managed to get it down to around 45 deg after adjustment, although it jumps around between 40-48 deg.

Just as a test, I turned it to both extremes to see what would happen. Going higher to 60+ deg produced more of the same symptoms, chugging and rough running, but steady RPM. Going lower got it smoother to a point, but then around 30 deg, it began surging until it died. However, it was clear to me that at lower degrees, it was much smoother running, it just won't remain steady.

The problem I have is that it is still equally rough at 45 deg, and won't really idle below 1000 RPM. Going lower than 45 helps, but it begins surging uncontrollably.

I also note now that I can screw the idle screw all the way in and lower the idle to around 800 RPM, but can't completely kill it. Is my idle control valve making up the difference?

"5. Has timing set to 15 deg at 1000 RPM."
++++++++++++++++++++++++++++++++
I went out a looked at the tune-up specs on the label pasted on my 1980 240DL ---drivers side shock tower. normal B21F

Timing with vacumm hoses off : 750 +/50 RPM 8 deg BTDC +/- 2 deg.

CO adjustment: 900+/- RPM

Idle (Normal): 950 +/- 50

============================================================================

"
I also note now that I can screw the idle screw all the way in and lower the idle to around 800 RPM, but can't completely kill it."
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
I have removed that Plastic idle screw and found its end to be pretty dirty. Just keep unscrewing. It's just a large needle valve. And I remember an O-ring too.


At least you've eliminated the CO adjustment from you list.

"5. Has timing set to 15 deg at 1000 RPM."
++++++++++++++++++++++++++++++++

I noted the spec timing as well. My experience with the pushrod engines gave me the impression that they'll run fine from 8-20 deg at idle, with more advanced timing promoting smoother running. My plan was to run this engine advanced because of the higher CR I built it with, thus why I started at 15 deg. I will back that off to spec and see what difference it makes.

"I also note now that I can screw the idle screw all the way in and lower the idle to around 800 RPM, but can't completely kill it."
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

I will unscrew that idle screw and clean accordingly.

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Another interesting note, the trouble shooting guide in the Greenbooks indicates the first 4 things that should be checked in case of rough idle are:

1. Ignition timing
2. Engine compression
3. Ignition spark at each cylinder
4. Injection at each cylinder

In that order of likelihood. I will go down that list next.

OK, a bit of follow up on the troubleshooting I did tonight.

1. Ignition timing: I moved the timing around from 20 deg down to 6 deg, eventually settling on the stock setting at 8 deg for now. While advancing the timing did slightly increase the idle, no setting seemed to affect the underlying rough idle.

2. Engine compression: Checked compression warm, 170 psi across all cylinders.

3. Ignition spark at each cylinder: Strong spark at each cylinder.

4. Injection at each cylinder: Pulled each injector and tested for spray pattern per green book instructions. All four had an absolutely perfect 35 degree spray cone. It actually surprised me they all looked so good.

In addition to those tests, I also used propane to test for vacuum leaks at the manifold, all five injectors, and vacuum connections. No leaks found.

I also confirmed that the in-tank pump is working.

I test drove the car to confirm the engine performance above idle. It did indeed perform flawlessly. Plenty of power at all speeds, no indications of stumbling or any other problems.

Some other observations:

1. When starting cold, the dwell sits firm at 54 deg. During that time, the engine runs much smoother. After a minute or two, there is a sudden change and the dwell starts to fluctuate between 40-48 deg. I take this mean the mixture control has been handed over to Lamda at this time. When that change takes place, the engine starts running much rougher. Funny thing is, if I manually adjust the mixture to 54 deg later, after it is warm, it doesn't run as smoothly as it does when cold at 54 deg.

2. I think the aux air valve is stuck closed. That is to say, when totally cold, the passage looks totally closed. When totally warmed up, it looks the same way. I can manually slide it open easily. It seems to spring closed. Sometimes the car wants to die when starting, which I take to mean the air valve is not properly supplying extra air when cold. I don't think this matters at all when warm.

3. Idle remains high at 1200 RPM. Even when the idle screw (now cleaned) is all the way in the idle won't get lower that 1000 RPM. Even if the engine was running smoothly, I'm not sure how I would get the idle low enough.

I'm wondering if this all could be bad gas. The fuel I'm running on is about 9 months old. Any opinions? Could it cause rough idle, but run OK otherwise?

I'm running out of green book inspired troubleshooting ideas. Any thoughts?

I keep thinking that the high idle has something to do with it. And that air continues to cause a lean condition - perhaps explaining why the idle mixture adjustment has little effect.
Good to hear the injectors are working properly - that eliminates them as a cause too.
The other thing that can cause a rough idle ( but not the fast idle ) is valve clearances that are too tight. Anything less than .012 will make the idle lumpy, but affect nothing else.

My problem is I've worked on only one K-jet B21 with a frequency valve - only the V-6's had FV's in Canada. On those I always set the mixture with the O2 sensor disconnected for smoothest idle and then just reconnected the sensor - normally the engines ran fine and little different.
If the idle screw is the plastic bypass one, then the fact you can't stall it is the air flowing around the throttle plate. The stop screw on the throttle plate is really just to prevent the plate from jamming in the tight closed position. You could reset it - unless it has a throttle switch, in which case it has to be set as the factory dictates - and I don't know what that is. In Canada I set the standard ones to tight closed plus 1/2 turn.
The other reason it may run with the idle closed is a vacuum leak. And surging with the sensor hooked up means lean, which is what a leak would do.
I imagine you've got a good intake gasket, so it's somewhere else - brake booster, etc. You don't have one of those goofy vacuum pumps on the cam cover do you? I pulled a lot of those things off in my time....
And as you mention "equally rough" it still could be a bum injector pattern which would confuse the O2 sensor.