I've got a '76 242DL with a bit of a running problem. She idles very rough and has absolutely NO *****!
I'm nearly positive the engine is running on 3 cylinders until about 2000-2400 rpm and then sort of like a turbo lag the fourth starts to fire and the engine runs smooth and normal at raised rpms.

The car has ~157K miles, the problem started when the water pump decided to blow out and dump my precious coolant while I was driving. I religiously check my water temp and sure enough, it was on the rise. I then proceded to the safest location to stop the car and beat my head against the hood, but up until that point the engine stalled twice due to the lack of low-rev power and didn't fire on all four cylinders.

After replacing the water pump and all that fun stuff, I'm clueless on what would cause the fourth cylinder lag.
Anything I should take into consideration?

 

How about the normal tuneup parts -- ignition wires, plugs, disty cap, rotor. When's the last time they were changed?

 

I'm not exactly sure, I bought the car used but they all seem to be in decent condition at least cosmetically(they're some of the cleanest parts on the car). I haven't checked the plugs but I get spark from the wires on all four.

 

Checked all the plug wires, and sure enough one was disconnected at the boot end connector. I reconnected it and the rough idle smoothed out a little, but it still seems to only fire on 3 cylinders. When in first gear the engine sometimes pops and then gets a boost of power near 2k rpms.

 

so, make sure you also do a compression test. easy-sqeazy.

 

replaced plug wires, idle has smoothed out some and power band is leveling to where it was normally

engine still pops when stressed/uphill below ~2200rpm
would busting out the timing light help?

also, I replaced the cruddy metal one piece fan+clutch with a plastic blade with clutch of some junked volv
and when sitting in place idling the car starts to heat up in a hurry. Could the fan clutch be bad?

 

I would check the valve timing. That sounds like a timing problem. I would run a compression test too. You might have a bent valve on one of the cylinders that would be causing it not to fire correctly at low speeds.

 

set the timing to 10*
lots more power. The timing was fully retarded and now it runs smoother and more efficient however the low end chugging still remains.

 

does your car have exaust recirculation? If your EGR seizes up (which it may have cause of the excessive heat) and sticks open at low RPMs when it should be closed it'll run like garbage until high RPMs.

Also, overheating a few times causes havoc on all sensors, vaccum lines, and other nessesary stuff. The extra underhood heat can mess al kinds of things up.

 

There is no exhaust recirculation. No EGR.
I've replaced all vacuum lines and all sensors are working properly.

Low end chugging and bucking was solved by swapping the fuel injectors off a volvo with ~260K miles on engine from a junk yard. The injectors worked and there is very very slight bucking and lots more *****. The efficiency has raised too.

I replaced fuel filter, dizzy cap+rotor, belts, emissions hoses, flushed oil and replaced, lots of fun stuff.
Would brand new injectors be much of an improvement? I'm assuming the 260K engine had injectors replaced and the ones I have now have around 100K on them.

 

First thing you ALWAYS do is check ALL your fuses. Most times it is either # 7, 21 or 33. First two under hood, 33 under driver side dash, fuel pump relay. These three fuses can save you thousands of dollars at the dealerships. I just got a quote of $1,540.00 at the KC dealership and it was a 60 cent fuse. How many people have they screwed over the years with this one. Remember guys...FIRST AND ALWAYS check your fuses. Work your way up to problems rather than take a hose down from dealers.

 

you can take/send the injectors to a diesel injector service place where they will clean them and flow check them for quite a bit less than buying new. I'm assuming that car is a K-Jet aka CIS system... I've not dealt personally with a volvo k-jet, only with 1980s VW and early 90s mercedes...