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  #1  
Old 04-04-2004, 04:06 PM
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Engine Missing - Timing notch on dizzy

Hello,
I put new trigger points in this weekend only to find out they were not the problem causing my engine missing on 4 cylinders. I did notice something that I cannot beleive I missed before, however.

When the engine is at TDC on cylinder 1 and the rotor is pointing to the #1 plug wire on the distributor cap, the alignment notch on the distributor housing DOES NOT line up with the rotor, it's off by about 40 degrees. Please correct me if I am wrong, but the rotor should be exactly aligned with the notch, right? Before I pull out the distributor to fix this, I wanted to get confirmation so as not to cause a bigger problem.

Thanks for the help. -Mike

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  #2  
Old 04-04-2004, 04:31 PM
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What does your timing look like?

There is a condition refered to as phase shifting that can occur in distributers. To understand shifting one must understand timing.

The relationship of when the coil fires to where the rotor points is built into the distributor. So your basic problem shouldn't be any worse than just correcting the timing.

To describe an instance of phase shifting imagine the later v8 distributor that uses a four armed wheel spinning like an alternator to induce a pulse that is used to time the firing of the coil (openning the primary circuit - triggers the coil). The little wheel spins with the distributor shaft and the poles of the armature are fixed in the housing. For various reasons that wheel has been known to twist on the shaft creating spark when the lug in the dist isn't facing the rotor finger.

If you ever install one of the optical triggers (to replace your point triggered transistor unit)you will find instructions for getting the phase right. As long as you haven't changes the position of the points radially in the distributer the phasing is created with the design of the distributor (if the cap is on right).

BTW, one bit of trivia I picked up a generation ago is that the MB D-jet controllers are really modified dual VW units, with each side doing 4 cylinders. I have seen numerous 4 cyl failures of the controller for this reason. One side fails.
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  #3  
Old 04-04-2004, 04:49 PM
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I have the timing set to 5ATDC. - Mike
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  #4  
Old 04-04-2004, 09:01 PM
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If cylinder 1 fires at 5 degrees ATDC, but the rotor is approx. 40 degrees off from lining up with the alignment notch on the distributor housing, aren't the trigger points opening/closing at the wrong time? -Mike
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  #5  
Old 04-05-2004, 08:11 AM
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It really doesn't matter where the rotor is for timing. You must understand that the poles of the distributer cap are only 45 degrees apart. When the secondary voltage potential rises it takes the shortest path to ground; normally through the rotor across the gap into the plug wire and finally across the plug gap to ground.

If as you say the fire is coming to the rotor when it is 40 degrees off it will thus only be 5 degrees from the next pole. The previous firing was actually number one by that account.

I don't think that when the trigger points fire, makes much difference. The Jag V12 of the same era fired six injectors at a time; timing of injection isn't of much consequence at the mixtures those cars ran at. Besides what applies to one cylinder applies to all. The important point is that fire went through the number one plug wire at the proper time and the rest follow in proper order.

I will say that I haven't set a D-jet MB to factory timing specs in atleast 30 years. I would jump that timing atleast 5 degrees maybe ten. Another point is that many 5ATDC settings are really wrong because that factory setting was based on a good, functioning vacuum retard being hooked up and operating. I always check the timing with all the lines disconnected first and then replace the vacuum retard line and see what happens. The timing should jump 10 degrees at least when the vacuum is removed. Thus I look for 15 degrees BTDC with the vacuum line off to add 5 DEGREES to the factory setting.

That fuel system does much better with some manifold vacuum. I try and get 17in at idle through timing and mixture control.
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Old 04-05-2004, 06:38 PM
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Steve,
When you said you have seen many 4 cylinder failures because of the controller, did you mean the electronic control unit( $800)?

I am running out of ideas. The car has spark, fuel, new trigger points and correct timing, how can 4 cylinders not fire?

Is the ECU kaput? Maybe 4 or more valves are shot. I appreciate all the help I receive on this forum, but so far we have not found that gremlin. Thanks -Mike
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Old 04-05-2004, 07:13 PM
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I’m curious, how did you check the cylinder firing? My engine (another thread) is missing on one cylinder. It seems smooth then stumbles. If I were missing on 4, I don’t think mine would run.

If your only hitting 4 of 8, what 4 are missing? If your hitting 4 of 8 and the missing cylinders are getting spark, then your hitting very strong on the good ones to turn the engine enough to set timing. Have you tried moving the timing light pick-up unit to other cylinders while the engine is running? This would show spark and if cylinder one hits at 5 ATDC then all others have to hit in that same sequence. So with the pick-up at #2 cylinder and if your crank is marked it should read 270 degrees.

I was shown a trick by an Ex-Mercedes mechanic at work. The rotor should flex with tension on the shaft. Lift the rotor from the shaft. Pull the felt from the center of the shaft and oil lightly (1 drop) with machine oil while exercising it back and forth.

Good luck to you. I think mine is an exhaust valve. L
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Old 04-05-2004, 07:19 PM
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Stinger.
The car runs the same if all plug wires are attached or if I take off 2,4,7 & 8 at the distributor. Runs rough at idle. -Mike
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Old 04-05-2004, 07:33 PM
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WoW – is your firing order like mine 1-5-4-8-6-3-7-2 ? If so, that means your hitting 2 in a row then miss 2 in a row and you said the missing cylinders had spark.

I would think the rotor was flexing out of position on the missed cylinders. Double check for spark on the bad ones…
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Old 04-05-2004, 07:37 PM
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Well every time I get in this situation I plug in a good used one and verify the controller. Drop on by (bg).
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  #11  
Old 04-05-2004, 07:37 PM
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I put in new rotor, plugs, dist. cap, trigger points & wires so I can eliminate those. Timing , dwell & compression fine. -Mike
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Old 04-05-2004, 07:43 PM
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Steve,
If I don't figure this out, a 1000 mile trip to Florida isn't sounding that crazy to me anymore. -Mike
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  #13  
Old 04-05-2004, 07:46 PM
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Not on 4 cylinders.....
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  #14  
Old 04-07-2004, 01:19 AM
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Silly question....but-

The distributor cap has the cyl. #'s labelled on the plug wire terminals. Are the correct wires going to the respective terminals?

It's very easy to pull out and rotate the distributor back the 40 degrees -it should pull out when a single bolt (the one that you have to loosen to set timing) is removed. Quick and painless experiment worth trying....I think.

Does the missing improve much at higher rpm? I wonder if you have a lean miss, possibly made worse by the throttle position switch being out of adjustment so that the idle compensation at the ECU isn't working.
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  #15  
Old 04-07-2004, 05:18 PM
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I pulled the distributor and lined up the #1 wire with the alignment notch and then checked the timing. The timing is perfect at 5 degrees ATDC, but runs a little rougher. Whoever had the car before me had the timing advanced a bit to raise the RPMs to smooth out the 4 missing cylinders.

AT higher RPMs the missing smoothes out a bit, but I believe the 4 missing cylinders are still missing.

I wish I knew for certain if the ECU is working because I do not want to spend that kind of money on a guess, but if it is not the ECU I have no idea where to look from here. I believe I have eliminated all other possibilites. -Mike

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