QuestionQUESTION: Hey Ron! I am having another problem with the good ol' Mercedes. I recently threw a rod in the engine and had it replaced with an engine from another car with significantly less miles. After the mechanics had everything supposedly done, I picked up the car and things seemed fine. However, I noticed that start-up was much more rough and difficult, until one day it wouldn't start at all. I towed it back, and the mechanics are now saying there is a subtle difference between the glow plug modulator (or something along those lines)that was in my original engine and this new engine. However, the mechanic is becoming increasingly difficult to work with, and is now depending on me to find this part. I would take it somewhere else, but they are offering to do the labor needed for free as a result of their failed first attempt. The mechanic told me that he is trying to figure out if there are two different glow plug modulators for this car, that might be similair enough to work somewhat, but different enough to not work properly. He tells me to ask if one would run parallel and the other would run in a series. I have no clue what this means, but I am hoping you might. Thanks Ron.
ANSWER: Well Cody , free labor is hard to beat, a key you left out is what year engine did they put in? Are the glow plugs cycling, is the dashlight coming on? can you hear the timer kick off?
He may be reffering to a fast glow tip 12mm tip glow plug, these are known as series glow plugs and are un upgrade. older models used an 18mm tip, so yes there is a difference. I thought the 81 used the 12 mm but I may be wrong. Each set must have a modulator to time them on /off for specific time. I am not sure when the change was made, but there is a difference depending on age of engine. Tell me the year of the engine that was put in and I will tell you if the glow plugs set up is the same. There are lots of reasons associated with the GP that can make a no start situation. Valve lash, fuel delivery, Is the strip fuse still in the controller? Another thing to try is to take off all the wires between the glow plugs and at each end (even the end that grounds to the engine itself) and give them a good cleaning with a wire brush until they are nice and shiney. Do the same with the glow plugs themselves. Clean any metal connection that makes electrical contact. Then reattach everything and give it a try.
Slow starters or weak battery can also be sign of a no start. If its really cold , wait 10 seconds after glow plug light goes off , or cycle 2 x's
Sorry I cannot be more specific ,but need a little more information
Ron
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QUESTION: Ok. I talked to another mechanic at the shop and I think we are getting somewhere. The engine that is now in my car is a 1980 model as opposed to the 1981 that was in there before. Another difference I forgot to mention was that this engine came with a block heater, whereas my 81' engine did not. The mechanic says the glow plugs are cycling. If you are reffering to the dashlight that relates to the glow plugs "heating up", that light was not coming on. He says you can hear the timer kick off as well. This guy was much more helpful and he wants to ask if the 1980 glow plugs are in series or parallel and if the 1981 glow plugs are in series or parallel. I again want to thank you for all the information Ron. I think we're getting somewhere!
AnswerSorry I am late , I have been calledd out of town. My thinking is that is the early series style but I am away from my service manuals .If you call 1-800-741-5252 and ask for rusty he will help you out. He is a big and very reasonable parts supplier out of Atlanta. He also knows his MB's I am sur ehe can help you out.
I also think there is an upgrade for that year that supposedly is a better glow plug system. Good Luck and let me know what you find out
Ron
