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  #1  
Old 02-26-2005, 09:01 PM
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Cylinder Compression????

Does anyone know what an acceptable range is on an 85 380se. I've searched but can't find any hard numbers. I'm trying to find why It's fouling plug #2. That cylinder shows 145 psi cold. The others are above 150. The car has 205k miles. Acceptable?? Car starts easily hot or cold and runs good anywhere above idle. It has new plugs, wires, cap, rotor, injector seals and fuel filter. But still has rough idle. I've tried swapping an injector from another cylinder but the problem remains. Any ideas appreciated.

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Old 02-26-2005, 09:15 PM
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Sounds like you're OK but you need to be more specific - how much above 150? I think the general rule is that they should be within 15 percent of each other. And they should be checked at operating temperature.
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Old 02-26-2005, 10:21 PM
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Quote:
Originally Posted by lilblkbnz
Does anyone know what an acceptable range is on an 85 380se. I've searched but can't find any hard numbers. I'm trying to find why It's fouling plug #2. That cylinder shows 145 psi cold. The others are above 150. The car has 205k miles. Acceptable?? Car starts easily hot or cold and runs good anywhere above idle. It has new plugs, wires, cap, rotor, injector seals and fuel filter. But still has rough idle. I've tried swapping an injector from another cylinder but the problem remains. Any ideas appreciated.
Compression pressure is a quick way to check.
It tells you nothing about how the compression is achieved.

You need a leak down tester to quantify the pressure or lack there of.
A L/D will tell you if piston rings or valves or gaskets are leaking and how much.

The motors I test need to have below15 % leakage.
More than this means unless you repair the 'leak',
your wasting time patching or hoping it will get better.

My rebuilt blocks are often1% or less ....I test without the head installed.
Then after the head is on, I test again to see if the whole motor is okay.
Total leakage I'm looking for is 2 to 5 % maximum.

Used motors shipped here to install are checked and the owner told about the results..
I will not install a used motor with more than 20% leak down after I have seated the valves and wet tested.
This removes my time from hunting a misfire when it's running due to poor compression or wondering if the 'nailing' is due to wear.

Most 350 and 450's I have tested for compressions have been around 160 to 170 psi.
Full charged battery and throttle propped open, and usually allow 8 cycles to get a reading.
this is at 1100 feet above sea level...Your location may be different.

On diesels like the 240 and 300d's they will be 360 to 430 psi.
Anything below 350 psi is cause for concern.
That is, after cam timing and valve adjustments have been set.

The US cammed gasoline models usually show a little less, about a 30 psi reduction in compressions
although this is not always.
So....your pressures are about right as long as the conditions where the same as I use..
Your plug fouling is most likely a displaced or bad intake valve stem seal.

PS... You know Ironzy ? ATC Guy ?

.
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Old 02-26-2005, 10:52 PM
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Thanks for the quick responses. I have not done a leak down test yet. I'm trying to eliminate all possibilities that I can do myself in my garage. Keep in mind this was a cheap project so I don't expect perfection. If this is as good as it's going to get I'll just have to live with the miss. It's not that bad but noticeable. I haven't put much money into this thing and probably won't. I just want it to be a decent daily driver. So far (1500 miles) I havent seen any oil loss and power seems ok. Just that annoying miss at idle.

And dkveuro, I do know Ironzy, we work in the same control tower. Tell him you ran across "GN" on the board. He'll know who you're talking about. As a matter of fact I helped him find his car, 300E. Small world!!

For now I'll keep trying to find the culprit. Thanks for the help.
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Old 02-26-2005, 11:36 PM
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Quote:
Originally Posted by lilblkbnz
Thanks for the quick responses. I have not done a leak down test yet. I'm trying to eliminate all possibilities that I can do myself in my garage.

And dkveuro, I do know Ironzy, we work in the same control tower. Tell him you ran across "GN" on the board. He'll know who you're talking about. As a matter of fact I helped him find his car, 300E. Small world!!

For now I'll keep trying to find the culprit. Thanks for the help.
Tell Ironzy to get on the forum. I have not seen him for some time...think he lurks about on the Wetdub or Votex sites.
He was putting together a turbo in his GTi last I heard.

Is his 300 running okay...he had a head gasket problem I understand ?

Bye....
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Old 02-27-2005, 04:18 AM
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Are you getting oil or fuel fouling? If you have swapped injectors, I can't see a problem with the fuel dist. I suspect a valve seal.

Peter
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Old 02-27-2005, 09:00 AM
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My problem is fuel fouling, not oil. #2 is covered in black powdery soot after only a few miles of driving. When I first start the car from cold, after running about two minutes, I hear a "click" and the idle slows down. Then it starts to run rough and emit black soot from the exhaust. It sounds like the a/c compressor kicking on, but the compressor is not plugged in and has no belt on it yet. There's a nice black patch on the ground under the exhaust and smells like raw gas. Once it warms up the black stuff goes away but still misses. Even with a fresh plug in it. Really strange. She still seems to run fine anywhere above idle, with a slight stumble initially. This car did sit for almost two years before I got it, only started occassionally. Any idea what the "clicking" could be? Are valve stem seals a difficult diy job? Special tools required? I've done complete rebuilds before but not on Mercedes. I guess I'm a little intimidated by the prospect of digging too deep into thing. But hey, it is a project car!!

P.S. dkveuro,
I'll probably see Ironzy on Monday. I'll pass your message to him. He's still working bugs out of his GTI. He's got it running but having issues with plumbing for the turbo. His 300 seems to be running pretty good although he's been complaining of a slight miss at idle. He had valve seals replaced last year due to smoke on startup.
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Old 03-01-2005, 12:24 AM
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Originally Posted by lilblkbnz
My problem is fuel fouling......................
If that is so, pull the fouling cylinder injector and swap it with another , easy to reach......
See if your 'fouling' follows the change...CIS injectors are prone to hang open after shut down...do it soon, as a hydro' lock could bend a rod !
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Old 03-07-2005, 02:02 AM
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I swapped injectors and the problem is still there, same cylinder! Could it be something in the fuel distributor?? Also is it possible to adjust valves on this motor??
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Old 03-10-2005, 12:13 AM
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Just a little experiance I would like to share about compression test and why I take them with a grain of salt. When I repaired lawn mowers we used to check the compression of evry engine we repaired. Typically you wanted to see 60 PSI for your typical 3.5 HP Briggs and Stratton engine. 50 PSI or less or 70 PSI or more would typically result in noticable problems with the way the engine ran. I found high compression to be just as bad as low compression in fact it was worse because this was always cased by rings. The high compression would result from the rings leaking allowing the oil to saturate the cylinder and essentially case a wet compression test to occure. So therefore leaking rings caused high compression. You should be scratching your head now.

The Briggs and Stratton recomended method for checking compression was to remove the cover and spin the engine by hand backwards. The technichian was to observe the bounce back of the engine. It should bounce back at least 1/2 turn (180). Engines that had 80 PSI compression would not bounce back more than 10. Some times you would have an engine with 60 PSI that would have a lazy bounce of only 1/4 turn (90). Any engine that bounced back less than 1/2 turn ran poorly despite its compression. This bounce back method never failed but it did required some disassembly of the engine to get at the fly wheel and therfore was not used as much as the compression check.

It's too bad this method cannot be used on autos. The problem with leakdown is it only checks the rings at TDC and its a real pian in the but to do.

John Roncallo
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  #11  
Old 03-10-2005, 08:48 AM
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This is sounding more and more like a fuel distributor problem. Can you bend up a couple of long injector lines, swap positions on the FD and see if the problem moves to the other cylinder?
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Old 03-10-2005, 10:37 AM
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Roncallo,
You're saying what I've said for years. High compression does not mean a healthy engine. As far as gas engines are concerned I have never seen much value in a compression check inless the car had running problems, and I'm looking for dead cyls. If you have a car that starts well, idles smoothly, and performs ok, but has higher or lower than specs compression, what are you going to do about it? Are you going to spend a fortune to rebuild the engine so you have normal compression redings?

Llblkbnz,
It does sound like FD problems, but the problem may be from under fueling rather than over fueling. There is a little screen in each hole the injector line connects to. Perhaps that one is restricted. I would try hooking up to one of those machines at a repair facility that runs your car on a recycled solution of one gallon of fuel with a cleaner added. Your engine is disconnected from the fuel tank. These cleaners work well.

Peter
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Old 03-13-2005, 01:36 AM
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Thanks for all the inputs. I found the best fix for the problem at least in my opinion. I traded the car for another one!! I've been wanting to try a diesel model and I found one, an 84 300SD. Traded even up for it. I've only had it for a few days but so far I'm really liking it. Hope you guys don't think I'm a traitor. I just happened to find this one and couldn't resist. Much better condition and didn't cost me anything! I'll still be lurking around here and the diesel forums cause I don't know much about diesel power. I guess it's time to learn! Thanks again everybody.

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