Hello

I have had previous posts about recently failing the california emissions / smog check.

I just recalled when I last changed the spark plugs I believe I put Bosch Platinum plugs in. I recall these vehicles not liking platinum plugs.

Could this be part of my HC issue?

I am thinking it might be best to switch back to copper plugs. I think Bosch stopped making the copper plug for this vehicle but perhaps I could use the Denso T16EPRU 5022 or the NGK TR5???

Hydrocarbons are unburned fuel coming from the tail pipe. Your spark plugs may be the issue. Did you car pass the emissions test previously with copper plugs ? Also, make sure you drive your car for at least 10 miles before the emissions test. An engine which is up to operating temperature has a better chance of passing the test.

I always take my cars for a 45 minute high spirited/rev drive, preferable on a FW with an incline, before I smog it. Both my 1990 300SE and 1988 300CE, both M103, were in pretty deplorable state when I had to smog them, they both passed.

I have Bosch H9DCO plugs (hard to find as they are discontinued) in my 300SE and Bosch HR9DC in my '88 300CE, the H9DCO are the correct ones, but my 300CE with the HR9DC runs smoother and is more responsive.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

You could try Beru Z7 working fine for my engine - M103

In my experience RESISTOR type plugs cause idle roughness (misfires) and increase HC. All the plugs so far mentioned are resistor types (an R in the designation), and so are Bosch Platinums.

I believe NGK makes a non-resistor plug equivalent to the H9DC, but don't remember the number. The NGK Web site should have a cross reference chart.

The OE H9DCO has a "heavy duty" (larger) electrodes, but that's no big deal. The H9DC does the job.

I recall there was a recent thread on this issue and some found the H9DC on ebay or somewhere else on the Web.

Duke

Hi,

I use in my R107 300 SL Year 1986
NGK BP 6EFS No.3812

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R107, 300 SL Year 1986
C124, 300 CE-24 Year 1990

I just called and talked to someone at NGK, they do not make a "non resistor plug for my vehicle.

The recommended the TR5 2238, he said the resistor value was 5k ohms.

If this is the case should I just order the Bosch 7978 HR9DC?

Lastly should I gap them .030 or .032 or other?

Thanks!!

Correct non-resistor plugs are available at the dealer.

part no. 003 159 0403

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Watch him go!!! link

#dontdealwithkahlil

.032/35

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

thanks what does the 35 mean?

Between 0.032 and 0.035.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Took the plugs out from the 300SE and changed the gap from .034 to .038, much more responsive now and smoother at idle. At one point I even "panicked" because I thought for a split second the engine stalled when I came to a full stop.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

I ordered new plugs BOSCH HR9DC, I know they are not non-resistor but at least they are copper and not platinum like the ones in the vehicle now.

They should arrive in the next day or two. I will gap them on the wider side around .034.

Curious to see how it will run.

Your car is NOT set up for resistor plugs. Benz built in the resistance in the plug wiring. Did you look in your manual to see what Benz recommends? No manual, call the local Benz dealer and ask the parts department or the service department. I've owned a '97 300E, a '92 300CE and a '95 E420 and have never had a problem finding the CORRECT plug. Get the CORRECT plug number and put in into your browser. You should get sources all over the World! Amazon.com probably has access to them!
Anziani
'97 CL600 69K

Does anyone know of non resistor plugs for my vehicle that I can get from Rock Auto, ******** Arizona or O'Reilly.

I do not want to go to the dealer and pay steep prices.

Thanks