I've been tracking a weird "pop" noise coming from my motor. It appeared a couple of weeks ago, but given the limited use the car gets, I was slow to trace it to the source. I was giving the car a compression test today when I realized that the popping noise was coming from Cylinder #4. With the car idling, I pulled the #4 wire and the popping noise stopped and the idle sounded smooth again.

I'm wonder what the probably causes for this problem are?

I'd suspect a bad wire, cap, or points. However, the car has a nice set of Magnecore Wires, Crane Electronic Ignition, and Bosch Plugs. There are no points, no vacuum advance or anything like that in the system and the problem appeared suddenly, not gradually.

So any ideas? I'm planning on getting some new NGK plugs, but what else ought I consider?


--
1967 P220 Amazon, 1972 145S, 1976 245 DL, 1983 245 DL, 1986 745 GLE, 1990 745 GL, 1995 945....
You mean to tell me that Volvo makes cars that are *NOT* Wagons?!?

Change wire on cyl#4 and test. Probably cracked wire.
--
Joaquin / Rojo 121 / Lima, Peru

Well, even this test is flawed but it's a little more reliable.

I went out to find some sparks, and nobody stocks them locally. Fortuantely, "Carquest" can order them and have them tomorrow - a nice new set of NGKs.

Anyway, I also picked up a spark tester at Carquest. This is essentially a ground wire and clip and lighted tester that you hold to the wire. I started the car and was able to confirm that the pulse going to each wire was strong and regular. But as I said, this test is also flawed, since at the time I did the test, the car was fully warm and idling smoothly.

Which is kinda weird sinc it was running like like crap when I went out to get the sparks... It almost stalled a couple times. Anyway, I'll test it again when it's running like snot.

Humm... if it is an intermittent wire problem, I wonder if I can buy a single Mangacore wire...?

Thanks for the info Yogui!
--
1967 P220 Amazon, 1972 145S, 1976 245 DL, 1983 245 DL, 1986 745 GLE, 1990 745 GL, 1995 945....
You mean to tell me that Volvo makes cars that are *NOT* Wagons?!?

The "flex" test for wires:

"This should be done when the engine is cold. The colder the wire the better.
Remove the wire. Connect it to an ohmmeter (all multitester has it) on both extremes (sparplug side and distributor cap side). Flex the wire back and forth, pulling on it over its entire length. If you feel any brittleness or if the ohmmeter needle moves as you flex the wire, it means the conductor inside is ready to broke." (source: Chris Jacobs, the guy of the Jacobs ignitions).

Wires usually has a usefull (power, performance, economy) life of 2-3 years or 30,000-40,000 milles.
--
Joaquin / Rojo 121 / Lima, Peru

Magnacor wires should be pretty bullet proof... how are the distributor cap and rotor?

Well, the cap looks fairly old... Honestly I didn't pop it off yet.
But it will be checked...

Out of curiosity, is there anything "special" about the cap? Is it the same cap found on the side-distributed volvo engines (eg B20, B21, certain B230s) (vs. cam/rear cap)
--
1967 P220 Amazon, 1972 145S, 1976 245 DL, 1983 245 DL, 1986 745 GLE, 1990 745 GL, 1995 945....
You mean to tell me that Volvo makes cars that are *NOT* Wagons?!?