Running issues on 1976 W114 280 Sedan M110 engine - PeachParts Mercedes-Benz Forum

Bad Benzo · #1 04-15-2018, 10:53 AM

Preface: My previous build thread on "Bad Benzo" can be found here.

Current:

I've done about 10k miles on this thing since I last updated my build thread. The car was running well, maybe a little sluggish at times, so I figured it would be time to tackle some maintenance items that I hadn't done before. My first order of business was to change the plugs. I had a set of new Bosch spark plugs that I purchased several months ago. Part number: W0133-1803344, they were supposed to be OEM for this model according to the vendor. I pulled out the old, mismatched plugs (I don't think anyone ever replaced the one on cylinder 6) and installed the new ones. The old ones were really worn, maybe 30 or 40k miles past when I would have wanted to replace them. My immediate thought was "oh yeah, I need to do this, changing these out will make a big difference!"

New plugs looked good, I gapped them all to .8mm, then vacuumed out the holes where the plugs go in before installation. A routine procedure, I've done the same for many other cars before.

Once I was done, I fired the car up, car sounded normal, then I shut it down. Later that day, I went to move the car and it died in drive. I thought that was weird, went back, checked all my connections, checked the timing, cap, rotor, points, condenser, etc, all good. I started looking for vacuum issues, none that I could find. My only thought was that I should adjust the timing, so I advanced the timing a little bit. The car seemed happier at idle when in gear and not die in L, S, or D.

Once I could keep it in gear, I took the car for a test drive. Before the spark plug change, I could cruise happily at 85mph, however now I struggled to get up to 55mph on the flats. Hills are now near impossible, I quickly slow down to 20mph at WOT, and fall down to 5 by the time I hit the top. We have an ice storm right now, so I won't have an opportunity to try the old plugs today, but my plan is to try the old plugs and see if the situation improves.

Do you kind folks have any other ideas as to what I should be looking for? Thanks in advance!

Diseasel300 · #2 04-15-2018, 11:42 AM

Were the old plugs resistor or non-resistor? What are your new ones? If you mix resistor plugs with resistor wires, you're in for some really "fun" running issues.

Bad Benzo · #3 04-15-2018, 12:36 PM

Quote:

Originally Posted by Diseasel300

Were the old plugs resistor or non-resistor? What are your new ones? If you mix resistor plugs with resistor wires, you're in for some really "fun" running issues.

I believe the old plugs were non-resistor. To be honest, I don't know how to identify whether or not the new plugs are resistor or not, they were packed in generic packaging. IIRC, the cross-reference guide for them said they were pretty much intended for many MB models 1984 and earlier, as well as many VW models.

Diseasel300 · #4 04-15-2018, 01:03 PM

Which ignition system do you have? Points and condenser, or transistorized? If you're running points/condenser, you may need a slightly narrower gap.

Bad Benzo · #5 04-15-2018, 02:45 PM

Quote:

Originally Posted by Diseasel300

Which ignition system do you have? Points and condenser, or transistorized? If you're running points/condenser, you may need a slightly narrower gap.

Stock setup with points and condenser. My car uses an ignition control unit that was an item equipped at the factory. I don't know much about it, but I did replace the leads to it when I bought the car in 2015.

Frank Reiner · #6 04-15-2018, 03:18 PM

BB:

The aftermarket plug part # given above cross references to a Bosch WR8DC. It is a resistor type ("R"), and is incorrect for the rest of the ignition system. A non-resistor plug is required, such as NGK BP5ES.

Benz Dr. · #7 04-15-2018, 04:27 PM

Generally speaking, if you can hold your throttle at WOT and it won't throttle up or your car slows down, it's probably ignition related. Always go back to what you changed and only make one change at a time.

Bad Benzo · #8 04-15-2018, 09:19 PM

Update, I changed the Bosch plugs out, put in new non-resistor plugs from NGK, and the car runs beautifully once more. Huge difference, thanks for the help everyone!

Tomas7 · #9 04-16-2018, 03:37 PM

Quote:

Originally Posted by Bad Benzo

Update, I changed the Bosch plugs out, put in new non-resistor plugs from NGK, and the car runs beautifully once more. Huge difference, thanks for the help everyone!

Awesome when things come together!