misfiring

[capehorner]

i'm firing on eveery other piston, have electronic ignition on my 2800cs, distributor cap and rotor appear good,,,HELP

 

[dang]

Do have a set of points you can put back in to check with? I've had problems with the inductive pickups in the past.

Dan

 

[capehorner]

engine has just been rebuilt. ran great to the upholstery shop and went to hell after that, the back 3 cylinders are not firing. i put the timing light on each plug wire and there is nothing there. plugs are new. wire is 1.4 ohms which i believe is correct.

mb

 

[steve in reno]

Capehorner
I would guess it to be related to the distributor cap and rotor. Cap not properly secured?
Rotor on crooked? Cracked cap?
They are cheap, or use an old one, change to another set. With a new engine, it can get worse from here.
My $.02
hth
reno

 

[MMercury]

engine has just been rebuilt. ran great to the upholstery shop and went to hell after that, the back 3 cylinders are not firing. i put the timing light on each plug wire and there is nothing there. plugs are new. wire is 1.4 ohms which i believe is correct.

mb

Unusual upholstery allergy?

Even if your distributor cap is not correctly seated or the rotor is slowly disintegrating, I would not expect the misfiring order you described. Conversely, if the distributor shaft or distributor body was worn permitting the shaft to move laterally, I still would not expect only every other cylinder to be dead. I wouldn't rule either part out as a cause though since they are so easy to check. Also, is it possible that your distributor is loosely mounted, or unseated in the housing on the cylinder head, so that the whole assembly is vibrating or subject to position changes with engine operation? As anyone who has left a distributor hold down assembly loose, it is possible to get an engine running with the distributor only partially seated in the head and not completely meshing with the drive gear.

Temporarily swapping the position of the leads to see what happens should eliminate the cap or rotor being the issue. Taking a spare lead, known to be good, and connecting that to one of the dead distributor cap terminals is just as easy to watch for an arc against a good ground.

Are you using OEM plug leads? The plug wires typically used are solid-core non-resistor wires. While the wire is non-resistor, there usually is resistance in the spark plug connectors (1K ohm) and on some wires this may be found on both ends including the bakelite attached to the plug (no. 13) and the screw-on 90 degree connectors that can fit on the cap (No. 1) (1K). The number you stated sounds about right with the inclusion of a "k", but is that for each wire? I would be more concerned that all the wires give similar readings.

Copper alloy cap terminals should not have noticeable resistance. Even after-market aluminum terminals should be shiny. Rotors are typically 5000 ohm too, although I have a few non-resistor variety.

Plug leads can look great but looks can be deceiving. You rarely see the working ends where there can easily be corrosion or a wire that is pulled. But what you describe suggests voltage is not delivered to or carried by the wires. Using a timing light to test for voltage at a given plug or plug wire may be a simple method, but it is not infallible. Is this an inductive light? I have/had a very expensive light that I gave away because of an issue with the inductive pickup - the light fired - intermittently. If wires, cap, rotor test good I would likewise swap out the points-replacement device- if that is what you are using.

Good luck.

 

[bert35csi]

I'm with MMercury's suspicion about the ignition wires. While a wire set may seem like an unsophisticated device, the resistance of the wires and plugs need to matched up correctly. If not, it can play havoc with the ignition system, such as erratic misfires or no spark at all.

Stay with oem BMW wires or from long time ignition wire manufactures such as karyln. Kind of leery of the newer Bosch wires and stay away from the Bavarian Autosport ignition wires.

Bought a set of the Bavauto 'high performance' 8mm wires a few years back. Upon installation, it caused all kind of erratic misfires and wildly fluctuating tachometer readings. Put old wires back on and all the problems went away. There was probably no engineering that went into the manufacturing of the wires. The thinking was probably the bigger the wire, the better and no attention was pay to the wire and plug resistance

 

[BarryG]

Fuel injector Ground...

 

[nashvillecat]

Fuel injector Ground...

Poster's inquiry concerns a 2800cs. There may be exceptions, but I believe there is no injection system to ground.

Grounds are always important but even if this were a Djet, how would the failure of the injection system relate to spark plugs not firing? (You may have more info, but at least that's what I interpreted as happening here.) I could understand if the injectors were dry or not firing, but those at least give an audible click.

I have found that the plug wires are critical in the newer injected vehicles as the resistance provides feedback to the computer. Solid core wires are generally more forgiving. They generally last a long time yet not forever. I have a number of examples that look good but are rock hard and would probably leak voltage if they needed to be conformed to a different shape.

 

[capehorner]

still no luck

i now have new cap, rotor, and bmw wire harness. engine starts but only front 3 cyclinders which is eevery other plug. i am confused beyond my imigination

Unusual upholstery allergy?

Even if your distributor cap is not correctly seated or the rotor is slowly disintegrating, I would not expect the misfiring order you described. Conversely, if the distributor shaft or distributor body was worn permitting the shaft to move laterally, I still would not expect only every other cylinder to be dead. I wouldn't rule either part out as a cause though since they are so easy to check. Also, is it possible that your distributor is loosely mounted, or unseated in the housing on the cylinder head, so that the whole assembly is vibrating or subject to position changes with engine operation? As anyone who has left a distributor hold down assembly loose, it is possible to get an engine running with the distributor only partially seated in the head and not completely meshing with the drive gear.

Temporarily swapping the position of the leads to see what happens should eliminate the cap or rotor being the issue. Taking a spare lead, known to be good, and connecting that to one of the dead distributor cap terminals is just as easy to watch for an arc against a good ground.

Are you using OEM plug leads? The plug wires typically used are solid-core non-resistor wires. While the wire is non-resistor, there usually is resistance in the spark plug connectors (1K ohm) and on some wires this may be found on both ends including the bakelite attached to the plug (no. 13) and the screw-on 90 degree connectors that can fit on the cap (No. 1) (1K). The number you stated sounds about right with the inclusion of a "k", but is that for each wire? I would be more concerned that all the wires give similar readings.

Copper alloy cap terminals should not have noticeable resistance. Even after-market aluminum terminals should be shiny. Rotors are typically 5000 ohm too, although I have a few non-resistor variety.

Plug leads can look great but looks can be deceiving. You rarely see the working ends where there can easily be corrosion or a wire that is pulled. But what you describe suggests voltage is not delivered to or carried by the wires. Using a timing light to test for voltage at a given plug or plug wire may be a simple method, but it is not infallible. Is this an inductive light? I have/had a very expensive light that I gave away because of an issue with the inductive pickup - the light fired - intermittently. If wires, cap, rotor test good I would likewise swap out the points-replacement device- if that is what you are using.

Good luck.

 

[MMercury]

i now have new cap, rotor, and bmw wire harness. engine starts but only front 3 cyclinders which is eevery other plug. i am confused beyond my imigination

I am reluctant to offer any additional thoughts given your continued problems. Still, I also know what it is like to be stuck, only to discover something obvious was overlooked.

Since you quoted my post, I reread it and stand by it. I did not tell you to go out and immediately purchase new parts without making sure that it was those parts that were causing the problem. I posted a picture of the parts so that it might have provoked more possible solutions. What did you do with the old plug leads that worked for the forward three cylinders? Did you try any (that fit) on the rear cylinders?

Going back to basics - are you certain your problem is ignition-related? You stated having three dead cylinders and that you determined there was no voltage to those three cylinders because - your timing light "did not fire." Again, this may be one way to test for spark, it is not the best method, nor is it definitive. I do not think you will find this testing method recommended by any authoritative diagnostic texts. Depending upon the type of light and its condition, the spark may be too weak to trigger the light.

Have you pulled the spark plugs and examined them? If you don't have any spark delivered to three of them, I would expect they are wet with fuel. Have you pulled a plug from at least one dead cylinder, and then watched for a spark by leaving the wire attached to the plug and grounding it against the block or head? I am saying this because you claim you are getting a spark to every other terminal on the distributor cap. It makes little sense to have some cylinders getting a spark - but not every other one. If that is really the case, you possibly have something patently wrong with your distributor, or you are using a hand-carved distributor cap missing one half of its terminals or they are poorly installed, or you possibly have a loose primary coil wire (or two) that is/are barely making contact as the engine rhythmically misfires. The only other thing even remotely related to the problem (as you have described it) might be the wrong sized rotor.

In an earlier post you mentioned that you have a transistorized points replacement unit or an electronic ignition of some sort. Dang suggested going back to the old tried and true points, have you tried that? Any noticeable changes?

The fact that you have cylinders 4, 5, and 6, and one carburetor coincidentally fuels those cylinders - makes me wonder if your problems are fuel related - rather than ignition caused. Again, there is no point in condemning the gas if you have no spark. Likewise, even if you have marginal compression, without a spark, the rest is unimportant. You need to definitively test for a spark reaching those cylinders. If it is just a "weak" spark, I might redirect the attention to the rear carburetor and a vacuum leak or (bad or a leaky one way check valve to brake booster?) or a carb that is seemingly dry due to a stuck needle valve etc.

Sorry I cannot be any more definitive. You need three things: Spark, fuel/air and compression. Please make sure you have sparks. The fact that your car sat at an upholstery shop for 3 weeks made me wonder if someone hadn't listened to the radio with the ignition on and that might have cooked something in your so-called electronic ignition. Yet that would not account for a non firing on the rear three cylinders. If all else fails, re-read the Autobooks chapter on ignition, the pertinent pages are attached.

GLuck