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Old 11-18-2000, 09:08 PM
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My 1979 240D with aprox. 300K has run OK with a slight miss at idle when warm. The first time the temperature fell below freezing the car would not start and now at 50 deg outside with a heat lamp on the block and starting fluid I canít even get it to pop!
I had thought about doing a valve job in the future in hopes it would solve the miss but have been afraid of what might happen to the bottom end, you know, blue smoke out the tail pipe and who knows what else.
When I crank the engine I get a puff of smoke out of the intake manifold with every revolution. The starter also seams to surge in tune with the puff of smoke. If I hold my hand over the intake manifold I can feel pressure along with the puff of smoke.
I would like to get the thing running again before I pull the head off in case something else is making it not start.
Talk about frustration, any help would appreciated.
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Old 11-18-2000, 11:13 PM
Dale W
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Having just gone through a similar experience with my '82 300TDT, I might be able to shed a bit of light on your problems even though I'm the first to admit I'm not diesel expert yet.The valves tend to tighten up over time so if you haven't done a valve adjustment for a while, this could explain the miss at idle. A valve is being held open. I had the same problem. I am told that properly adjusted valves are the most critical component of cold starts. Obviously faulty glow plugs will give you no end of cold start problems. As for the "backfire", if it were a gas engine I would say your timing is way out. Being a diesel, I would imagine the puff of smoke you get is unburned fuel being forced up through an unseated intake valve. The reason the starter seems to surge would be lack of compression on that cylinder. A valve adjustment might cure your problem but if the offending valve has been held open for too long, you may have built up residue on it and it won't seat properly even when it's adjusted. If that happens, don't know if there's much to do but pull the head and regrind the valve. If you pull the head you might as well do the rest of the valves while you're at it. Could also be a case of a timing chain that has finally stretched too much and has thrown the timing out too far. I'd say get the valves adjusted first. While the valve cover is off have the tech check timing chain stretch. If it's out of spec, you won't solve too much until it's replaced. Whatever else you do, never use starting fluid on these engines, if it does fire, you could end up with a hole in your garage roof in the shape of a 4 cyl head. Way too much help for these engines. Maybe others can shed light on something I have missed but hope this helps you out.

'82 300 TDT 330,000 km
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Old 11-19-2000, 07:27 AM
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Gib, Dale's advise is pretty accurate! A few comments and clarifications. If the valve has been out of adjustment for extended periods, it may not be build up that prevents an adjustment from fixing it, but rather erosion from the combustion gases passing through the "gap". Either way, a valve job should be able to fix this.

My only other recommendation is to have a qualified mechanic check out the motor. You do not want to throw money away doing a head job only to find out you have bad rings as well. There is a considerable difference in the cost of these two repairs. The "smoke" coming out the intake certainly indicates that there is a valve problem, but you may have a piston ring problem as well. With only one bad cylinder, the engine should still start. Bad compression from worn rings could be the reason, as well as pump timing, glow plugs, etc. A compression test will do you wonders. Also, if you can tell the mechanic about oil consumption, this will be another useful clue, as worn rings usually results in increased oil consumption as well.

87 300TD, 160,000 miles
72 280SEL 4.5, 250,000 miles
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Old 11-19-2000, 10:10 AM
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You need to first ensure that the glow plug system is working properly. Use a voltmeter to check voltage at every plug. The 12 volts or so will be divided at each plug since this is a series system.

Then, check the compression, you should have about 300PSI at all cylinders.

I am going through all this right now with my daughters car and it points toward a bad tank of fuel. Ensure that your fuel filters are clear.

Good luck,

Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles
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