Blow by or fuel

oilcan93

oilcan93

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Ok, guys. Here is the deal. You know I just got my '73 3.0 CSI about a month ago. It has almost 52k miles on it so I decided to do a little tune up to see if it would run better. At this point, it idles smoothly, albeit around 1100-1300 rpm range rather than the 950 where it should be. But when I get past 40-50 mph it sputters and coughs. I ran a Seafoam fuel system cleaner to remove carbon. And it seemed to do a nice job....the spark plugs were really fouled after I removed them.

I bought some new NGK Iridiums and replaced all the plugs and replaced the wires with a new set of Bosch wires (still need to tuck those wires back neatly within the plastic loom). The car runs great while sitting still and giving the accelerator a good workout. If I try floor it too suddenly, it does hesitate if not outright sputter. I checked the plugs again and here's where I am wondering which way to go. They look dark. Not dry either....a little moist. I would think at < 52k miles I wouldn't need a valve job already. There's also a prominent black residue on the tree about 4 inches away from the exhaust pipe that will come off using my finger to wipe.

Is it too much too hope that this is just a case of the fuel mixture being too rich or a timing issue and not an oil blow-by problem? Your input greatly appreciated.

carl
 
Did you get all the Seafoam out? That stuff can stay in the system for some time.

Also, did you check the coil?
 
A CSi engine trends toward rich with age and almost any other nonstandard condition... you need to get a manual that discusses the D-jet system...

The D-jet system is easy to work on but you need to know what order to diagnose and adjust or you'll never get it dialed in.
 
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Speaking of blow-by, does the coupe a PCV mechanism to reduce the fuel blow by buildup on the crankcase? I did a search on PCV valve and did not find it.
 
That's good to know. I'm going to take the Green Meanie to a mechanic recommended by the local BMW club to let him dial in on things in the ignition and intake systems so it can be driven. I'll ask him about his experience with a D-Jet system. And I'll look for a manual to use in the future.
 
oilcan93 said:
[W]hen I get past 40-50 mph it sputters and coughs.

If I try floor it too suddenly, it does hesitate if not outright sputter.

I checked the plugs again and here's where I am wondering which way to go. They look dark. Not dry either....a little moist. I would think at < 52k miles I wouldn't need a valve job already. There's also a prominent black residue on the tree about 4 inches away from the exhaust pipe that will come off using my finger to wipe.
Click to expand...

I'll wager it's something obvious that you have overlooked, but knowing where to look is helpful.:wink::wink: Unfortunately, off the top of my head I can think of a fairly lengthy list.

Your flat spot / hesitation could be due to many causes, including: a maladjusted or worn throttle position sensor/switch, a weak coil, maladjusted points, defective condenser, improper plug gap, large rotor to distributor cap gap, plugged fuel filter/s and so on. The mileage is not as much of an issue as the age of a vehicle's components - especially if they spend much of their lives in a humid climate. Humidity leads to corrosion and corrosion can lead to any number of electrical issues. Parenthetically, even in a dry climate, "dry rot" can affect rubber components so that even extremely low mileage tires can crack and harden after merely sitting. The same logic might also apply to the need for a valve job, but it is doubtful that this has anything to do with your symptoms. Valves and valve train parts that are maladjusted or poorly maintained (infrequent oil changes or the wrong oil) can wear just like anything else except faster than normal.

The throttle position sensor has several mechanical fingers that wipe/ride on what might be described as a gold plated circuit board. Although it is long wearing and corrosion resistant, it may need some attention to function properly. Not saying this is your problem, only that it is something to consider. If, for example, you had a perfectly functioning TPS, by driving it with the TPS wiring plug disconnected you would experience bogging down under acceleration. It is the analog to the carburetor's accelerator pump. It is also possible but unlikely that the plug connections are corroded or loose. Same with other areas of the injection and ignition wiring harness.

Other things mentioned are part of the standard tuneup. Acceleration and higher speed operation places more stress on ignition components than at idle. If the points are worn, they will likely affect the ignition timing. Any corrosion under the cap or at the rotor might have a similar degradation of higher speed - acceleration operation. If you have a weak or failing coil, as mentioned by Steve, it will tend to be most pronounced when engine is under load. I personally have very little experience using Iridium plugs in an M30 engine. I would not expect this to be a problem even if the plugs had a preset gap that was larger than the factory recommendations. And even though the Iridiums are reputed to have greater heat range and wear resistance than the more typical copper cores, it might be possible you have plugs that are too cold for the application and that is causing them to foul. I am also somewhat reluctant to suggest this, but the fuel you have in the tank might have been sitting too long - although this is unlikely if you are able to obtain a decent idle.

Another consideration due to age alone might be vacuum leaks. This not only covers rubber vacuum hoses, but also the pressure sending unit mounted near the brake booster.

You might also have the prettiest fuel pressure regulator in its existence, but if it is out of adjustment and leaves the system with inadequate or more than adequate pressure, this can also affect engine operation.

Plenty more in the archives: e.g., http://www.e9coupe.com/forum/showthread.php?t=4781

It is doubtful that blowby is a substantial cause of your fouling and hesitation. The easiest way of testing this would be to disconnect the vent tube and rig up a downdraft tube. (On your djet you would have to plug the port to the intake.) If the engine pumps massive quantities of oil, there is an obvious issue. Alternatively, if the engine exhibits the same problems with the tube redirected away from the intake (with the intake vent port plugged) that should also yield an obvious answer.

In puttering with many M30 and M10 engines I don't believe I have ever encountered one with a Positive crankcase ventilation valve. I am sure there is a red front auto store that will try to sell them for all cars, but so far as I am aware, the engines weren't designed for this seemingly ubiquitous device. I have however seen examples of the same engines where the crankcase ventilation system was redirected to a catch can or downdraft tube - on both fuel injected and carburetor equipped engines. This is more typical on carb engines and race engines.

hth

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I have been over this before, but will reiterate. On D-jet you must first pull and check the coolant block under the right side of the intake. This where the aux air valve or "slide" is mounted. Dump the coolant. The temperature sender is screwed to this. It will plug up and no coolant will pass, the sender thinks "cold engine" to the ECU resulting in an always overrich condition. You have heard of the term "KISS" I would be willing to bet this is the problem. pvc ....vents to the throttle body and the crankcase is evacuated by vacuum. I have 20 years of D-jet, Carl N. has the same, I have a friend who has 20 + and then sfdon. We will fix your CSi do not hesitate to PM....This one is not intuitive. I check with the IR thermo gun....experience is all. Also your description indicates need to time. Do as I suggest with new plugs after.
 
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