M103 spark trouble

[alastair98]

Hello hello. AGAIN lol.

Just want to say thanks to everyone who has helped this far on my w124 journey.

So since taking ownership of my m103. I was aware of a slight miss on one of the cylinders. Most of the car looked untouched and factory so I’ve swapped out a load of parts that were clean and OEM from a running donor car.

HT leads, dizzy cap. Rotar arm. Coil and some fresh non resister spark plugs. But now I’m missing completely on 2 cylinders. And they happen to be opposite sides of the cap. Like 9 and 3 on a clock so to speak. These lead to cylinders 2 and 5 (front to back)

There’s no play in the shaft holding the rotar arm. The depth and gaps look good too. There is no corrosion in the leads or connections and the EZL looks good. Nothing standing out to me. The engine timing is on S, I haven’t touched that.

I’m a very new hobby mechanic and this is my first car so I’m still learning here. I’m taking my car to my mechanic at the end of the week but I would like to know if there’s anything that I could have missed and maybe try before they take a look.

For those who might have seen my previous posts. I managed to drop the gearbox and replace the flex plate successfully. I enjoy learning about the car but I hope I’ve not opened a can of worms.

Cheers
A

 

[carat 3.6]

Are you saying these two cylinders have started missing since you fitted the flexplate, or the distributor cap?

A quick test would be to refit the old cap. The m103 is very hard on HT components, what brand of parts did you use?

 

[alastair98]

Are you saying these two cylinders have started missing since you fitted the flexplate, or the distributor cap?

A quick test would be to refit the old cap. The m103 is very hard on HT components, what brand of parts did you use?

One was missing before the flex plate and then 2 after the job. I can try the old cap. The ignition parts were from an SL donor car

 

[Bellow]

For those who might have seen my previous posts. I managed to drop the gearbox and replace the flex plate successfully.

Good to hear you got that done.
To your misfires. In addition to carat 3.6's suggestion, check the leads to cyls 2 and 5 for any possibility of shorting - either to earth or each other - and generally the HT leads' routing (consider 'cross-firing'). Also - if lengths permit - try swapping leads around and see if the misfires move to different cylinders.
It will be something simple causing this.

 

[alastair98]

Good to hear you got that done.
To your misfires. In addition to carat 3.6's suggestion, check the leads to cyls 2 and 5 for any possibility of shorting - either to earth or each other - and generally the HT leads' routing (consider 'cross-firing'). Also - if lengths permit - try swapping leads around and see if the misfires move to different cylinders.
It will be something simple causing this.

Swapping leads was one of the first things I tried and the problem was consistent with the 2 cylinders so I know the leads are fine.

 

[carat 3.6]

In that case refit the old cap and see if that makes a difference. If it is the cap the only ones I can recommend are Bosch or Beru, all the others won't last more than a month.

 

[alabbasi]

Firing order would be the first thing i'd check. It should be stamped on the cam cover,

 

[alastair98]

In that case refit the old cap and see if that makes a difference. If it is the cap the only ones I can recommend are Bosch or Beru, all the others won't last more than a month.

Just fitted the old cap but no change sadly.

Firing order would be the first thing i'd check. It should be stamped on the cam cover,

I’ve triple Checked the firing order and it is correct

 

[carat 3.6]

Just fitted the old cap but no change sadly.

I’ve triple Checked the firing order and it is correct

Where did the flexplate come from? 100% from an m103?

 

[alastair98]

Where did the flexplate come from? 100% from an m103?

EBay with matching part number stamped. Like for like and same weight

 

[carat 3.6]

EBay with matching part number stamped. Like for like and same weight

Ok, I ask because the firing of the coil is controlled by the segments on the flexplate. If you fit the flexplate from an m102 to an m103 it will only run on 4cyls, cyl 2 and 5 are the pair that will drop out as they are opposite each other on the cap.

If you've ruled out the HT leads and the cap, the EZL unit is a possibility although I've never seen one fail on a m103. I think I would double check the condition of those segments on the flexplate, you can see them through the bottom of the bellhousing. Mark one of them with a black marker and rotate the engine via the crank pulley so you can check all 3 are not bent.

Edit: Just wanted to check if you have confirmed there is actually no spark at the two dead cylinders, as it might not be a ignition problem?

 

[alastair98]

Ok, I ask because the firing of the coil is controlled by the segments on the flexplate. If you fit the flexplate from an m102 to an m103 it will only run on 4cyls, cyl 2 and 5 are the pair that will drop out as they are opposite each other on the cap.

If you've ruled out the HT leads and the cap, the EZL unit is a possibility although I've never seen one fail on a m103. I think I would double check the condition of those segments on the flexplate, you can see them through the bottom of the bellhousing. Mark one of them with a black marker and rotate the engine via the crank pulley so you can check all 3 are not bent.

Edit: Just wanted to check if you have confirmed there is actually no spark at the two dead cylinders, as it might not be an ignition problem?

Thank you for your input. I don’t have my old flex plate at hand anymore. But it was identical in most if not all manners and the sale page said it was from an M103

I don’t have the tools to conduct any tests on the EZL and as much as the Internet is a great resource. I don’t have the wits to start further investigations. I’m going to leave it to the mechanics. I tried my best as a first timer. Glad I tried though and managed to rule out a number of possibilities.

Thank you to the other contributors of this thread so far!

I’ll try to remember to update you all on the outcome.

Peace

 

[alabbasi]

Just fitted the old cap but no change sadly.

I’ve triple Checked the firing order and it is correct

Try checking it at night to see if you can see spark jumping. The leads may have been damaged. Did you gap the plugs?

 

[optimusprime]

My check tells me unless both flex plates are identical in every way not to use them ..
They both have different part numbers - = 103 = 260E = 1030300012
= 103 = 3L= 0020320606
Can someone else check this and give a thumbs up ?