Lord Keeper

Hello and help. I just bought a 87 300E and it has emissions problems. It gives high HC , the CO is fine, and the NOx is high . I have had the O2 sensor, plugs, wires, rotor and cap on distributor, changed, and had the injectors and combustion chambers cleaned. It is a Cali emissions car with the mutli stage catalyst exhaust. I have a good temperature increase on the catalytic converters around 300 F at the front and double that on the outlets, using a raytek ir temp gun. Is there a idle regulator that adjusts mixture or timing advance at idle? Is there a temp sensor that could be sending a cold temp to ECU causing it to enrich the mixture. I am stumped here and not very familier with MB engine controls. The car did pass the test 2 months ago in IL easily, has been maintained well. It does use a little oil from the valve guides I believe, but I dont think it is enough to cause a fail. Any hints or help would be appreciated greatly.

Jer

The mixture is adjusted by a screw in the center of the air cleaner. You need a special tool (which I think is just a long hex or Torx wrench) to adjust the mixture. You also need the Bosch lambda tester, or a multimeter on the duty cycle setting, to read the on/off ratio of the lambda control so you make the proper adjustments. You must then use a special tamper-proof plug to cover the hole.

Ignition timing is automatically controlled by the EZL ignition control unit, mounted on the right-hand wheel well in the engine compartment. One of the data points it uses is the engine temp, which is acquired via a temp sensor on the right side of the cylinder head. It is the one with one wire.

Oil consumption through the valve guides and stem seals is normal. Just don't let the engine blow smoke!

If you desire more info on the engine management, I can send you pages from the shop manual.

mbtech208

If you have high HC and normal CO, and NOx is high, it's not running rich. High CO would be running rich. NOx is caused by high temperatures and lean mixtures. High HC is also caused by a misfire. I'd say you have a lean misfire condition, which is where the car can't get enough fuel, or is getting too much air. Possibly a vacuum leak, weak fuel pump, clogged fuel filter. Or the catalytic converter may be going bad, but that is the last road you should go down. Check the other things first. You should also check the ignition system. You say you replaced the cap and rotor, but what about the spark plugs and wires? Those will cause high HC. Anything that makes the engine too hot will cause NOx, so don't rule out a clogged radiator, carbon in the engine, fan clutch, etc.

Lord Keeper

Ok I went back thru the fuel/ignition system again tonight. I found no vacum leaks, I already changed a couple hoses that were leaking when I got the car. I did change the plugs but I have yet to change the ignition wires, since I was unable to find anyone locally including the dealer who had them in stock. The idle does seem to fluctuate slightly between 650 and 750rpm, not sure if that is a sign of anything wrong. I did crawl back underneath the car and checked the temp on the 3 catalysts and found nearly no differential after it had warmed up solidly. So I am going to drop the exhaust this weekend if I can find the parts. Thanks everyone for your help.

Lord Keeper

Ok I finally got new catalyst system installed and working. I tryed a emissions check again this morning and still wont pass. I have changed all the ignition parts. o2, cleaned the injectors, tested and cleaned the idle control, I cant find any vacum leaks. Anyone have anymore help. When I was going over the intake side checking for leaks I found a 500 ohm resistor wire made by someone and used on one of the temp sending units on the back left side of the head? Could one of the temp senders be sending erroneous info causing it to fail. OOps it is better now it passes everything except HC so now NOx and CO are fine but my grams of HC per mile is 2.6 and has to be down to 1 to pass and below 2 to get a waiver. Any help would be appreciated.


Thanks