'79 California Bus Ignition Miss

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hansh
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Location: Bend, OR
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'79 California Bus Ignition Miss

Post by hansh » Thu Dec 11, 2008 7:02 pm

I've nearly worked all of the gremlins out of my new van. It's feeling pretty good. Since I got it, and through all of the repairs I've made, there has been a miss. It is not very consistent (i.e. not rhythmical) but, it is persistent. I believe that it may be related to the problem below.

I have a new cap, rotor, and wires. The issue I'll describe has happened through several new caps though. All of the ignition parts are definitely the correct numbers for my month/year van. Here are the details:

The plugs on the right side have a lot of soot on them while the left side plugs are clean or a nice brown depending on how long they've been in. This is the condition after driving and/or idling. The injectors are all brand new, I've watched each of them spray, and they look good. The fuel lines on each side have been drained a couple of times recently also. It's odd that it is a right/left situation because of the symptoms described below.

The wires are all getting spark. Looking at the posts in the cap, 2 and 4 have a solid black line across them, but 1 and 3 do not. #1 has a track that begins light and then darkens toward the end (in CW motion). #3 only has a thin little track. There are carbon deposits on the new cap just after posts 1 and 3 (again, always talking CW) so, the deposits are between 1 and 4, and also between 3 and 2. The carbon deposits are not track-like, they are powdery, circle-like deposits that can easily be wiped out. The timing is set correctly using both full advance of 40* at 3800 rpm (everything connected) and also verifying 5* ATDC at idle with the DIS connected to itself (Cali model with DVDA).

I borrowed a coil and an Ignition Control Unit from my neighbor and neither made a difference (exact match parts). As far as I can tell, the only thing left to blame is the distributor. Is this something that the distributor can cause?

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vwlover77
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Post by vwlover77 » Thu Dec 11, 2008 7:20 pm

Colin pointed out to me that the amount of soot on the base of plugs can be dependent on how much oil slips past the rings. It may not be an indication of any real problem, just variation between cylinders. You may just coincidentally have two with a little more on one side of the engine. Can you post some photos of the plugs?

As far as your distributor cap, it sounds like the cap is not seating squarely on the distributor causing the rotor to contact the posts unevenly. I'm not exactly sure how that can happen, but I would take a careful look. Also, be sure that the rotor is fully pressed down onto the distributor shaft. A lot of carbon on the cap may be due to the rotor pressing too hard against the carbon button in the center of the cap. Now that I think about it, the rotor could be preventing the cap from seating properly if it's not fully pressed on. I like to put the rotor on so I know it's not positioned right and then rotate the rotor while pressing down on it until it "falls down" into the slot on the distributor shaft.
Don

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78 Westy
71 Super Beetle Convertible Autostick

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hansh
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Location: Bend, OR
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Post by hansh » Thu Dec 11, 2008 7:33 pm

Thanks vwlover. I can post a pic of the plugs tomorrow. The soot on them seems...sooty. It doesn't seem like burned oil but, I'm not an expert and could easily be wrong.

The cap and rotor are seated correctly. I've checked over and over trying to get to the bottom of this miss. The miss may or may not be related to the distributor, but it seems likely given the indications in the cap. This is the 3rd set I've had on it. I accidentally smashed one and the other I switched out to see if it was causing the miss. It is possible that there is something wrong with the distributor, but there is nothing obvious. I've taken a few apart for cleaning before and understand what they should look like. With this one, I just pulled it and cleaned the magnet and sensor, checked the wires, and put a couple drops of oil in the center.

From the marks, it looks like it is firing after #1 and #3 since their tracks are very faint with the carbon behind them. While #2 and #4 have normal carbon tracks.

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Amskeptic
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Post by Amskeptic » Thu Dec 11, 2008 9:58 pm

hansh wrote: From the marks, it looks like it is firing after #1 and #3 since their tracks are very faint with the carbon behind them. While #2 and #4 have normal carbon tracks.
If it were carbon misfire, you would be symptom free after the easy wipe-off you mentioned. The only thing that would intrinsically affect two cylinders ACROSS from each other is camshaft wear or two paired plug connector resistances being wrong for your engine (2 & 4 have those long reach and 1 and 3 have the short 1k ohm resistors inside of the connectors. Incorrect flycut or deck height or an intake /exhaust leak or other intrinsic assembly anomaly could cause two cylinders on one side or the other to both misbehave simultaneously, as could a stuck cooling flap or anything your mind can come up with that relates two cylinders to each other. Swap plugs from left to right after you address your suppositions. I have seen the soot follow plugs across the engine because people did not note that they had different heat values than the other two!
Colin

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