93 300TE failed emissions - PeachParts Mercedes-Benz Forum

ptempel · #1 01-15-2007, 02:13 PM

Went to the New Jersey DMV testing center and failed for the second time. Here's the test results:

Test|Standard|Reading|Result
HC|100|199|FAIL
CO%|0.50|1.40|FAIL
CO2%|--|13.6|--

and the test was only a 2500 RPM test (2362 RPM actual). I had the car in the indy shop around the corner from me. The guy claimed that the engine is "tired". He mentioned that two of six cylinders had low compression. I'm a little surprised at that since there's only 128k miles on the odometer. The mechanic also mentioned that he could get the emissions to be within spec at idle but not at 2500 RPM. Judging from some other emissions posts here it seems that the catalytic may need to be replaced. What do you think? For starters, I'm going to replace the sparc plugs with new copper champion ones (NAPA didn't have the Bosch ones) and run through a tank of gas with Techron fuel injector cleaner. Replacing the catalytic may be a little over my head (I'm a newbie DIYer) but could attempt it with two more jackstands perhaps. Am also on the lookout for a good MB mecanic in the northern NJ area.

ptempel · #2 01-15-2007, 04:39 PM

Just changed the spark plugs. Here's a nice web page I used to get acquainted with the removal proceedure:

http://mbca.org/northtexas/spark_plugs_on_m104.htm

One thing I noticed is that the plug closest to the firewall (cyl #1?) had a fair amount of oil on it. The other five were prety clean. The area under the cover was oily in general. I cleaned it up a bit but wonder where the oil is coming from. For the plugs, I used the Champion copper plus ones with a 0.035 gap and 20 ft-lb torque. Ran the motor briefly and it sounds ok. Will take it for a test drive later.

deanyel · #3 01-15-2007, 05:31 PM

You may need a new valve cover gasket including the six donuts that go around the spark plug holes. It's unlikely that you have compression problems at that mileage on that engine. I'd get a second opinion on that.

david s poole · #4 01-15-2007, 05:41 PM

the short plug connectors that join the coils to 3 of the plugs are infamous for going bad you should replace them.the other probabilities are the mass air flow sensor and the fuel pressure regulator in the front end of the fuel rail.

ptempel · #5 01-15-2007, 09:27 PM

Quote:

Originally Posted by david s poole

the short plug connectors that join the coils to 3 of the plugs are infamous for going bad you should replace them.the other probabilities are the mass air flow sensor and the fuel pressure regulator in the front end of the fuel rail.

Thanks for the tips. How do you test the air flow sensor and the fuel pressure regulator? I've read in some VW forums that some folks try disconnecting the MAF to see if there's any difference in proformance. If not, then it was usually time to replace it.

ptempel · #6 01-29-2007, 03:15 PM

I replaced the camshaft valve cover gaskets and the O2 sensor last weekend. One benefit of the new O2 sensor in that the rough idle appears to be gone.

Let's hope the the new valve cover gaskets fix the oil leak problems. Would be curious to get it tested but I think I have more work to do. How difficult would it be for a relative newbie DIYer to replace the catalytic? The O2 sensor primed me a bit for the exaust since it was a PITA to remove. Needed to get a propane torch and heated it up so it would break free. I assume the catalytic R&R would be more of the same...

ptempel · #7 01-15-2007, 09:23 PM

Quote:

Originally Posted by deanyel

You may need a new valve cover gasket including the six donuts that go around the spark plug holes. It's unlikely that you have compression problems at that mileage on that engine. I'd get a second opinion on that.

How difficult do you think it wold be to replace these gaskets? I see them in section 01-0500 of the M104 engine manual. Only have a 20-120 ft-lb torque wrench so would need to get something smaller for the cover bolts. If you or anyone else knows a decent indy in NJ, then let me know.