Cylinder not firing

Did you check the spark plug extender?

 

If you confirm that it isn't a wire, extender, spark plug problem (and the other three plugs in that bank are firing), another possibility is that the spark for that cylinder is wrongly jumping from the contact where the carbon button rides, thru the rotor plastic, and to the end of the distributor shaft. I think there was an FSB to address this. You can always just try swapping the dist rotors to see if there's any change (and give them a visual inspection while doing that).

Post #1 in this thread has some good photos showing how a rotor was arcing from the metal contact on the top (where the carbon button rides) thru the plastic and onto the metal spring clip that contacts the flat on the distributor shaft:

https://www.ferrarichat.com/forum/threads/have-you-lost-power-in-one-bank-of-cylinders.525461/#post-144754234

And this thread:

https://www.ferrarichat.com/forum/threads/ignition-problem-on-308-qv.642903/#post-147929536

has additional photos and information.

 

Vacuum leak will actually raise the idle, have you tried switching the dist. cap and see if the problem switch over to the other bank?

 

I think that would just be the result of the loss of spark on the #4 cylinder. You know it could be the spark plug, have you tried swapping it out?

 

Yes. A buddy had the same issue and his regulator was weak. After chasing a whole lot of parts on his QV, he replaced the regulator and all was fine.

 

With your symptoms and the fact that you checked the plug and the plug wire/extender, a carbon-tracked distributer cap is where I'd be looking first. If there is good spark on other cylinders in the same bank, it is not likely to be a coil or engine ground issue. Also, if there is good spark on other cylinders it is not likely to be a low voltage or alternator/regulator issue. It is most likely a secondary ignition issue affecting the particular cylinder.

Check the resistance of the faulty cylinder's plug wire + extender with a multimeter. There can be dramatic differences in resistance depending on the type of cable but standard ignition cables - NOT solid copper wires - will show considerable resistance. Around 5000 Ohms per foot of cable is quite common though it may be much lower, again, depending on the type of cable. Check several cables to see if any are dramatically different, again, remembering that unless they are solid copper, the resistance will change based on cable length.

Do the old shade tree ignition test... After dark, open the hood, start the engine and observe for any visible sparking. If none, using a spray bottle with some tap water in it, spritz some water on the secondary ignition components - coils, dist caps, wires and again look for sparks. Sometimes it is quite a light show! With these engines you can't get a "complete" spark test because you can't see the portion of wire/extender/spark plug. But this test is surprisingly effective at finding secondary sparks "leaking" from the system.

 

Good suggestions overall. I would agree that a single bad cylinder would not be indicative of an alternator issue but under 14v output is. It is very easy to confuse a dead cylinder with a poor overall spark that is bad at this cylinder and then bad at another next time you try to diagnose. This feature comes with Dinoplex at no additional charge.

 

No (not on a euro QV), but one easy thing to do is swap the connectors on the two Digiplex ignition ECUs to see if the "problem" stays on the same bank, or not. Same idea with swapping the coils. Have you had a look inside the distributor cap of the bank with the trouble to see if there is something obviously wacky inside?

 

Change your voltage regulator.

 

I understood initially that there was poor spark at ONE cylinder at idle. If there is poor spark on ALL cylinders at idle then I agree that it could be a low voltage issue as opposed to a secondary ignition issue. Low voltage at the coils could be a result of some poor/corroded connections as opposed to faulty components.

If you have sufficient power to spin the starter, there is plenty of power to run the engine. Once started, most cars can run for quite a long time on battery power only (no charging output from alternator) as long as other electrical items - lights, etc are off/not drawing power. In any case, check the voltage at the battery with a multimeter with the engine running and the RPM around 1000 (normal idle speed at operating temp). I would expect to see at least 13 VDC.

REMEMBER that these cars may not engage the charging system on startup until the RPM has hit around 1800-2000RPM. So it may be necessary to blip the throttle after startup to "activate" the charging system.

 

"The battery voltage is 12.5-12.7. I don’t think I have ever seen over 13."

Is that with the engine running or engine off? If running, and after the throttle is blipped to activate the charging circuit/turn off the red battery light on the dash, you should see more than 13V at normal idle and up to 15 volts as the RPM rises. If you don't, there is a charging problem either a regulator, alternator, or connection issue. With ignition off, a fully charged battery will stabilize at around 12.6V so 12.5-12.7 is fine.

 

If it's happening around 20-30 seconds, my guess would be the warm-up enrichment is deactivating. There is also cold-start enrichment but that typically lasts less than 5-10 seconds. Idle stabilization (through the aux-air valve) typically lasts 30-60 seconds. Both warm-up enrichment and idle stabilization times depend on ambient temperature so these numbers are general. What was the ambient temp when you noticed this? Cold engine I assume?

 

According to the Bosch CIS guide, the warmup-enrichment cycle would run about 90 seconds at that ambient temp based on electric heating of the WUR, or cut off sooner if the engine heating was greater. I don't have a feel for the actual timing or whether the idle speed / aux-air would kick off sooner, but maybe @Steve Magnusson would know. Either way, the mixture will be rich during that warmup period and then lean out to a "normal" level, so it cold be indicative of a problem with the default mixture level if the engine dies after warmup-enrichment ends.
Image Unavailable, Please Login