9 replies to this topic

[Svenska]

I offered to help my friend out with his 1992 240 (B230F) by doing his plugs and cap & rotor. Prior to doing this, his engine ran/idled without any problem. While replacing plug #1/cylinder #1, I somehow crossthreaded the very beginning of the plug (I don't know how the hell that happens, it always seems to happen to me on the 240s though). I ended up having to insert a Heli-Coil in that cylinder. I am using only Volvo-brand plugs from the dealer and a Volvo-brand cap & rotor. I installed the other three plugs, the existing plugs were platinum tipped and didn't have a brand-name on them... I used di-electric grease on the inside of the plug boots too. I replaced the cap and rotor which were all scorched and worn out. After replacing everything, I started the engine up and it shakes at idle like nothing you've ever seen. It shakes like there's a misfire or the timing is way off. There is no check engine light on either. Yes the check engine bulb does in fact work too. I immediately thought I somehow messed up the plug wires on the distributor cap. I put the engine at TDC, the rotor is positioned to fire at cylinder 1, then 3, then 4, and then 2. The plug wires are in that same order. I have no idea what is going on here.

The car drives beautifully at speeds over 35 mph, on the highway, it still cruises without incident at 75 mph. It's only at idle or at very low speeds like cruising up to a stoplight that it shudders. I'm guessing a misfire more than timing? Is it true you can't adjust the timing on these engines? You can only verify the timing? The only thing I neglected to do was check each plug wire for continuity from end-to-end (I will do that when I see his car again), I'm thinking maybe with removing the boots from the plugs, the wire broke internally on one of the wires, thereby killing power to one of the cylinders.

[Three Fat Tigers]

Firing order is 1-3-4-2 (clockwise) with the #1 distributor position pointing toward the front of the car. No way to adjust the timing. Sounds like a defective spark plug or wire. With the engine running, unplug each fuel injector, one at a time and try to isolate which cylinder is at fault. Then measure the plug wires (ohm meter) and see if the suspect one shows a significant difference from the others; and or try swapping the spark plugs around and see if the fault follows the plug. Maybe there is too much non-conductive grease? I've never used it myself.

I always screw in spark plugs with my fingers only, until I am very certain it's threaded properly.

Also I have run into more than one defective cap and or rotor, might try putting the old ones back in.

[Svenska]

Wow, I thought for sure it was the Heli-Coil. I suppose if it were, I would have a problem with the engine starting/compression. I'm always paranoid when using those thread inserts. The plug is in as deeply as the other ones though (as far as I can see). Maybe it's because the older Volvos use a M14 diameter plug as opposed to other European cars which use an M12 plug. I just can't seem to thread those in correctly.

I did have the rotor facing forward in the distributor, toward the front of the car. Why is there a small bolt at the 1:00 position on the distributor? It looks like it allows the distributor to rotate slightly left/right. Swapping plugs from one cylinder to another wouldn't help since I have no idea which one is at fault. The whole engine shakes. The CEL is not illuminated either, so there is no code to tell me which it is.

Unfortunately, I tossed the old cap & rotor. I've never had this happen to me before...

[Three Fat Tigers]

Why is there a small bolt at the 1:00 position on the distributor? It looks like it allows the distributor to rotate slightly left/right.

Yes that is a leftover from '88 and earlier 240s where the timing was set by the position of the distributor. You can put a timing light on it, rotate the distributor, and you will not see the slightest change in the ignition timing.

Timing in '89+ 240s is handled by the ignition computer (ICU), which has an crank position sensor located above the flywheel/drive plate (aka speed sensor), load signal from the fuel computer (ECU), and also input from the throttle position switch (TPS) and temp sensor (ECT).

Swapping plugs from one cylinder to another wouldn't help since I have no idea which one is at fault. The whole engine shakes. The CEL is not illuminated either, so there is no code to tell me which it is.

As I mentioned before, you may be able to determine which one is at fault by unplugging the injectors one at a time at idle, where if you find that one injector/cylinder dropping out has less of an effect than the others, that would indicate the fault is with that cylinder. You should check to see if there are any stored codes even if the CEL stays off, for reference: http://www.brickboar...ineOBDCodes.htm

[phunktified]

I had a similar issue on a 90 240 , the fourth and last plug (near firewall) didnt want to thread right, and the gap ended up closing on the plug somehow when I first got it in and started it up hoping for the best.. it was running similar to yours (not firing on all cylinders) but I was luckily able to correct the gap and finally get it to thread correctly after much frustration .. and then it ran fine ... good luck

[Svenska]

Phunktified-I noticed that right out of the box, these plugs weren't gapped properly. They were gapped at 1.0mm, I corrected it to .8mm. I'm wondering if I made them too tight, like maybe .7mm...

[James A Sousa]

To check for a bad plug or wire, you could disconnect one at a time - the bad one will not make any difference, BE CAREFUL and use a really thick wad of rags to grip the plug - you do not want to see how muck a shock will hurt!

I always keep a set of used tune up parts in my trunk. whenever I change something, I throw the worse used one away.

[Three Fat Tigers]

To check for a bad plug or wire, you could disconnect one at a time - the bad one will not make any difference, BE CAREFUL and use a really thick wad of rags to grip the plug - you do not want to see how muck a shock will hurt!

Note a much easier way to do that: unplug the injectors one at a time, same effect as pulling the wire off, without the risk of serious shock.

[Svenska]

Problem solved, it was a dead spark plug. Weird. I've changed a LOT of plugs and have never encountered a dead plug. These were brand new Volvo-brand plugs from the dealer too. Unplugging the fuel injector electrically is a great tool to use, but when the engine is shaking/rocking so violently at idle, it's really hard to discern which injector/cylinder is suspect. I tried a new cap & rotor with no luck, then I did the plugs and the problem is solved. Thanks to everyone here.

[Three Fat Tigers]

Yeah I should have mentioned that you might have to hold it above idle while going through the injectors.