Folks on the benzworld g forum said perhaps someone over here could help on this. I have a 1996 G-320, LWB 463 with a M 104 engine with 156,000. I have had an intermittent miss/power loss for some time now that motivated me to buy a retriever to pull fault codes. There is a fault (92 – ECR switchover valve Y27 open/short) which was not a faulty valve (replaced it, and old seem fine with one ohmmeter). This is located in the front of the engine under the plastic cover. The wire also seemed OK – good ground and other lead with high resistance. There is a second connector tie wrapped to one of the vacuum hoses which apparently goes to an air pump not fitted to this engine. This unused connector has a straight connector and longer wire then the right angle and shorter cable connected to Y27. If I connect the unused straight connector to the valve, the fault goes away. It seems rather obvious that at some point in the past this was connected wrong, but the shorter cable with the right angle connector is a much better fit. Can someone verify this on a similar engine? It seems that if it was switched, it would have happened about 60,000 miles and 3 years ago when the head was pulled. It does not seem to me this would be causing my current miss. The miss I have started about 7,000 miles ago as a significant loss of power – probable more then 1 cylinder – for about 10 seconds every 300 miles or so. It seemed that perhaps a coil was at fault and I replaced all three of them – no change. It has gradually gotten much worse, in that when it happens it lasts for minutes. It seems to never occur until after the engine has run 75-150 miles but does not seem to be related to temperature, and I recently discovered that it will go away as soon as the ignition is turned off and engine restarted. The fault it brings up is 55 – Ignition out stage or coil T1 misfiring and shuts down 2 cylinders associated with that coil. Any help on this problem would be greatly appreciated.

I would replace the part between the coils and the plug beneath.

I doubt the EGR would be your miss unless it is applied at idle. The switchover valve is usually next to the switchover valve for secondary air. The secondary air switchover is powered only when cold and the EGR is powered always after warm-up.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

On the stacked SOVs , the top one uses the right angle connector and the vac line out goes to the egr...
the engine vac feed line is common to both sovs...[single , common hose]

If I understand you correctly, that is part of the spark plug wires. I will look at them again, but they were replaced about 1 year ago. Also would that give this fault and repliably go away when the engine is switched off for just a second??

The plug ends under the coils (three on HFM motors) will NOT set a code on a non OBDII car.

Any detected misfire will trigger fuel shut off on the offending cylinder. Restarting will reset the fuel untill another misfire is recognised. So a recognised misfire will perpetuiate itself. Not all misefires will be recognised so some can be felt and go away. Once they are recognized they stay until the key is cycled.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Late OBD1 HFM-SFI have individual ignition misfire code storage.
These are 16 pin diagnostic connector pin 8 access and are both HHT readout and flash code.
Flash will retrieve each coil secondary output/misfire only,
[ codes 21,22,23 for T-1,2 and 3] ,
However, same access pin with HHT will specify each plug firing and secondary coil out ..codes 055 thru 063.
This is only on pre OBD2 HFM only ..and this module does not trip the CE .
[ although, if the skip/coils output persist long enough, the info does get back to the DM and fault a CE as a non-specific Ignition detected fault....

This problem has come back. I replaced both the wires and plug ends and even replaced the O2 sensor and fuel pump -- with 160,000 miles it seems time anyway. The coils have also been replaced, and 1 and 2 swapped again without changing anything.

The problem usually only occurs after driving a coupel hundred miles, but now is happening on shorter trips.

It seems to always happen after letting off the gas for a hill or cornor, then applying gas. There will be a miss and if one backs off the gas and then accelerate slowly -- no problem. If one continues to push the pedal, then it will miss until the ignition is shut off, then all is well. The codes show it shuts down the 2 cyclinders associated with T1 due to misfire. No other codes are set.

There do not seem to be any other problems with the truck.

It has been suggested to change the computer. Since this is a G-wagen, that is a very expensive part, but if that is the problem I will do it. I guess the worst is I will have a good expensive spare.