Hello,

I have a 2005 E320 CDI, runs and drives beautifully however I have been experiencing a hard start for the past 12-months or so. The car basically backfires once or twice when starting cold, then sputters and has inconsistient rpm for the first 10-20 seconds of running and often some light smoke. After about 20 seconds it generally idles out smooth and if I drive it until warm, it starts perfectly the next time and the rest of the day. It does not seem to make a difference if you leave the key to the pre-glow for a long time or cycle it multiple times to pre-glow up before starting. The pre-glow indicator also does not stay on partictularly long. It seems to be slightly worse when colder, but it will still start even when very cold, which leads me to believe if it was a glow plug issue, it may only be a single cylinder.

First diagnosis: I changed all 6 plugs to brand new correct BERU 5V ones. Old plug #6 was an incorrect 12V plug, so I was happily thinking I found the issue and swapped in the new ones. In fact it made zero difference on the hard start condition. Strange. Next I got the glow plug module down to verify it was the right one (previous owner had mentioned changing it), and indeed it was the correct module OEM part number A648 153 02 79 / 002. I thought to myself perhaps the single 12V plug mixed in with the 5V plug had created issues for the module, but I checked the output of the module with a multimeter and it reads ~7V in the pre-glow cycle, both on cylinder #6 and the others. I also checked resistance of all plugs which is 0.6ohms (makes sense as they are brand new). Again I have never had a single code for any glow plug or module.

So I'm seeking thoughts / feedback on:

1. Did I test the glow system thoroughly enough? Does the ~7V output of the glow plug module, tested at the lead for the top of the glow plug during pre-glow phase, proove that it is working correctly?
2. Could this be related to parasitic battery drain somewhere else in my system? I'm probably going to check this next, but I'm wondering if for my 12-months of ownership the battery was draining ever so slightly and causing a rough start because it's turning over too slowly or not having the power to run all the systems correct. Sometimes for the more extreme hard starts (rougher for longer, more black smoke), the battery protection mode would come on on the dash. Perhaps it could be an alternator?
3. Could the swirl flap valves being broken and stuck in the wrong position do anything to cause this type of symptom. The lever arm is definitely broken off and flap valves stuck in place. It's on my list but I'm not ready to tackle it yet unless it could be related.
4. Anything else to check next?

Thanks in advance!

 

Have you asked the car what's wrong with a good scan?

 

Yes I have no codes at all.