George993

All, as I posted last year, my 2007, S600, 100k miles had cylinder #1 misfire error, later multiple misfires on the same bank. I changed the spark plugs on that side and the ignition cassette. No improvement. So I changed the center ignition module/voltage regulator. Problem fixed. Several weeks later cylinder 1 misfire was back. (Only #1). Any ideas? I put a bit of dielectric grease on the plugs so the cassette slides easier next time and someone told me this could be a problem and I should remove/clean the grease. But I don't really feel like taking the ignition cassette out again, plus I had identical symptoms before I started doing anything to the car. So I don't want to be replacing the same parts again. No other error except #1 misfire and the usual low engine power.

So what are the recommendations for a next step? Could the problem be related to a poor fuel mixture/injector, and say swapping injectors 1 and 2 plus new injector seals/checking the fuel pressure would be the next step? Is there anything else that could be going wrong? I don't suspect low compression as the car was running well many times after resetting the error.

What is so special about the cylinder 1 that the problems always seems to start there?

thanks for your help

alexanderfoti

Yes, Suspect fuel side now. Swap injectors as you say and see what happens.

George993

Hi the fuel pressure is 55-60 psi at idle and 50 under throttle which is good. I replaced the injector with a brand new Mercedes part - major pain with so many parts including throttle and wiring harness needing to come out. Still same error. Btw there is so much work with the injectors that I think buying a new makes more sense than swapping. Btw there are no rebuilt available- a few companies sell such incorrectly but they don't fit - ask me how I know.

So I took the plugs out and checked compression- luckily good!

Any thoughts on how to check electric signal going to injector? Has anyone tried looking at a spark using removed cassette with a plug inserted and touching engine block- just like it's done with old cars using ignition cables? Or will it damage the cassette? Thanks!

George993

Minor correction there are both new and rebuilt injectors available directly from China for $30 including shipping but I've passed

alexanderfoti

That is odd.

It will damage the coil pack doing that, it has very sensitive electronics.

What part number is your coil pack?

UNderdog

When replacing the coilpack I assume it was new and came with new red insulators? That would rule out a bad insulator.

George993

Coilpack was sent for a full rebuild including new transistors and coils and testing (to a reputable person who rebuilds many), so "should" be like new, and yes the red insulators were new as well. I attach the coil pack numbers. Another data point is that one of the cylinder 1 spark plugs (rightmost in the picture) is slightly cleaner than the 2nd and remaining plugs of the bank. Is the difference significant enough to indicate a different spark?

George993

Also I'm planning to look at the injector triggers with an oscilloscope and compare the signals between the cylinders, to eliminate the fuel side possible problems...

g60wall

How is she coming along?

George993

Actually some good progress, I will post details and summay tomorrow, thanks for asking!

George993

In summary the problem was the Voltage Transformer for the second time (VT - the box in the middle on top of the engine). The long story from the beginning (each step no impact unless noted):
- cylinder #1 ignition failure started showing up
- replaced the ignition cassette, spark plugs and red insulators, worked briefly but multiple different cylinders started failing
- replaced the VT: the car worked briefly but the ignition failure came back only on cylinder #1
- of course each failure was being cleared many times and it kept coming back
- checked fuel pressure, good
- replaced the fuel injector with brand new MB part
- checked compression - good/same as other cylinders
- swapped spark plugs on cylinder 1 and 2
- looked inside the cylinders with that camera on a wire gadget, same carbon buildup on cylinder 1 and 2 (if anything, there is more carbon on 2)
- listen with a stethoscope to the valve noises - same on all cylinders
- so decided to start from the beginning, borrowed the cassette and VT from Clark at V12icpack
- swapped ignition cassette, no change
- swapped VT, problem solved. So my VT went bad again first time shortly after installation.

In summary if anyone gets that problem I would recommend starting with swapping the VT with a known good one, as it only takes about 5 minutes and (unlikely the fuel injector for example) is probably the easiest job on this car.

One thing which I still don't have the answer for is: why was the bad VT only affecting cylinder #1? (VT has 2 halves each serving one bank). I can understand that if voltage of VT goes below a certain level, an imperfect cylinder (e.g. inferior spark plug coil or transistor etc) could, combined with that lower voltage, cause misfire.

But why was only cylinder #1 misfiring with all the other parts good/the same as on the other cylinders?

Thanks

Clark Rupp

OK George, Looked into your VT and here's what happened..... There's a 200v 3w zener diode on the 180v output rail that shorted to the engine ground. When that happened the switching transistors (more FET's - but different than the ones on the coil pack) got so hot they literally lifted off the heat sink pads on the printed circuit board. In that heating process they too shorted out but allowed shorted current at the zener to increase and it literally burned the trace open between the zener and the 180v output. Because we're dealing with burned traces and fried components it remains somewhat of a mystery why #1 crapped out and not the whole bank - but that's what happened. Thanks for mentioning V12icpack.com ! There is a protection circuit built into the VT's so they don't self destruct but it doesn't work. I'm close to having a new design and a replacement part for these VT's. In its final form it will be fuse protected and run much cooler than the original part. In other words, it will be the last VT your V12 will ever need.

LGAFF

Two thumbs up for Clark...he stands behind his work and is there to support even when its not always his problem.

George993

Thanks Clark for the explanation! (and for loaning the parts to test). Clearly either the other company which originally rebuilt the VT made some mistakes or an inherent VT design problem popped up. Looking forward to your design! (Hopefully I will not need it, but if I do I will have more confidence with it :-). Thanks

alexanderfoti

Good info on this thread.

So in the event of a vehicle that has multiple cylinder misfires, this would be the diag step:

Spark plugs + boots
If still misfiring
VT
If still misfiring
Coil packs.

Mine only misfires at very high loads so hoping its worn plugs.

Clark Rupp

There are always qualifiers...... George's VT is the only one I have ever seen that only killed off 1 cylinder - an electronic fluke. The voltage transformer or ignition control unit is literally built in two identical halves. Each half controls one bank or one set of coil packs. If you're having misfires on cylinders 1,3 and 5 that's not going to be a VT issue. If you've changed your plugs in the last 40,000 miles I wouldn't expect changing the plugs to make any difference. I would say go ahead and change them for the sake of process of elimination, but my expectations would be very low for a cure. It's more than likely going to be the pack. The exact scenario would be true for misfires on 1, 3,5,8,9 and 11. Except both packs are now shot. If those plugs were 100K miles old you might eliminate a good percentage of those misfires but it would be unlikely to get them all.... coil packs again. The roll of the dice is when you have a total bank failure 1-6 or 7-12. From everything I've done, its probably close to a statistical dead heat of coil pack vs. VT. You want to get your troubleshooting right at this point as random component replacement can get pricey. For members that bump into this thread, you can go to V12icpack.com and rent to own these components to be sure you're applying the correct fix. More information and options on the website as well.

alexanderfoti

The last misfire event logged misfires on 1, 2, 5, 6, 11, 12.

I have no record of plug change on the car, so suspect they have done at least 60k.

Is it likely that I have 2 duff packs then?

Its a shame you are in the US, being in the UK, trialling the packs gets very expensive with shipping. With a VT for example, its more than halfway towards the cost of of a new VT in the UK.

Clark Rupp

Well........... for the record. I have more coil packs in the city of London than in any other city on the planet. It costs about $125 to ship 2 packs there. With just a high speed misfire it is likely to be the plugs. However, here's the ugly part. When you change the plugs they're going to flow more current for each firing due to the fact they'll have less resistance than the old plugs that are in there. In many cases, that extra current going through the spark can be enough to take out the packs. The coil packs were never meant to last forever ! Talked with a guy in London that bought a 2006 S600 from the Saudi embassy. They used the car to go from the embassy to Heathrow. The car has 12K miles on it and he's looking at both packs. Here's why. There is another common denominator that is showing up and that is age. My theory is the polymers in the plastic that makes up the insulation in the ignition coils seems to dry out in the 10-12 year mark. As the plastic dries out, micro voids are created and the electrical current is able to create a path through the plastic and short out. This is the scenario when people accelerate and get a CEL but are able to reset the "limp mode" by turning the car off and restarting - the electrical current has to recreate or create a new path to ground. Do it long enough and get a "good" short and components within the pack start to go. Anyway, you're approaching that 10 year mark so don't be surprised if a plug change fixes you and shortly thereafter you loose the entire pack. Sorry.

alexanderfoti

So packs here are around £1000 each.

Assuming shipping is $125 there and back, how much is the repair cost roughly? I was not able to find the info on the website (sorry).

Clark Rupp

Only $699 US$ to rebuild plus $300 core charge if rebuilt ones go your way first. When I get your old ones I refund the core charge. Add $90 each for the rental option and I'll waive that fee if you purchase.

alexanderfoti

Ah I See, so $699 per coil pack plus shipping essentially (if I ship mine to you in advance, for example).

Clark Rupp

Yes, my email is clarkruppjr@gmail.com if you want more info - that way we don't clog up this post. Thanks !

alexanderfoti

Of course! Thanks for your help.

alexanderfoti

Just for completeness on my thread hijack ,

New plugs/boots today.

Misfire on 5/6 and occasionally 2/3/1/4 but only once.

Always on one bank

Only under hard load

George993

So most likely the coil pack. But if you can borrow from someone locally the voltage regulator and try it out (which only takes a few minutes to swap) you can get a 100% confirmation which of the two (coils or VR) is bad.