350SL No power
This is a 1972 350SL 4.5L with about 145k miles on clock.
Car was running OK, just a small stumble once in a while and perhaps slightly less power than I recalled, so as a start, I decided to replace some of the original and older stuff. Changed spark plugs, plug wires, distributor cap, rotor. When I went to start, it started OK, but on road test had no power - would not go over about 40mph. Tried switching back to old rotor and cap and slight improvement - Still awful performance. Checked points gap and it was small, so opened it up a bit - Tried 0.35mm and 0.45mm. No improvement and now I hear slight popping or backfiring sound when driving. PLugs should be OK - they were the proper Bosch plugs and I checked gaps - all 0.032". I have checked that wires go to proper plugs. I have removed points (no pitting) and cleaned everything with contact cleaner. I don't have a dwell meter, so can't check dwell. At my wits end! Any suggestions for things to check before I take into shop? Questions: - Bosch pamphlet that came with rest of stuff said something about need to change coil when changing ignition wires because of possible damage to ecu. Not sure what they meant. - Old (original) plug wires were different - they had hard plastic inserts that seemed to have resistors in them at distr. end. New Bosch wires don't seem to have those. Graham |
Just some thoughts here
knocked out of time when you replaced rotor ? ( my bet) the rotor on in correct oriention? Points should be at .014in clean the trigger points Make sure the plug wires are secure over the ends of the plugs. On mine you have to remove the small end cap make sure your wires are going to the right plugs off the distributor (this is easy to mess up) (second bet:wacky:) I have a diagram if you need it |
Thanks very much for your comments melted panda- Seems like a good check list!
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Lets say: #1 is at N or 12 o'clock then #5 is at NE or between 1 & 2 oclock #4 is at E or 3 oclock #8 is at SE or between 4 & 5 oclock #6 is at S or 6 oclock #3 is at SW or between 7 & 8 oclock #7 is at W or 9 0clock # 2 is at NW or between 10 and 11 oclock Does this match your diagram? Regards, Graham http://www.ke4nyv.com/compass.jpg |
yes pretty close, firing order is 1-5-4-8-6-3-7-2, and looking at the engine on the left bank 1-2-3-4 ane the right 5-6-7-8 cyliders.
So if everything is going the right way and hooked up properly make sure the plug wires are not wrapped around each other. Also make sure the wires are pushed all the way home, especially in the cap and coil. Sometimes the boots hold them up in a way that they do not conduct properly There is a small hex nut to rotate entire rotor, I am just thinking if it was loose, taking cap off may have moved it , just a guess. I think it is 5MM hex, you need a long extension to reach it. Clockwise retards, CCW advances. Trigger points - you are correct Did you change out condenser with the points? Let me know what you find, we can figure this out, It has to be something to do with your service so retrace your steps? |
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BTW - Thanks a lot for your help! |
I would recheck the plug leads, I have been doing it for years and still been known to get it wrong. also you say you have your points at .035 (I think you mean your spark plugs but you said it under the points question from melted panda) that would also kill your power (if it started at all). also check you didnt break the carbon rod in the centre of the dist cap when you reinstalled it, it might then only make intermittent contact and you could run but have little power.
cheers len |
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Points were set at 0.35mm not 0.035in. ,0.35mm is about 0.014in. Plugs were set at 0.032in. Carbon rod is fine. In fact I switched caps and rotors several times to see what problem is, but now I am convinced it is left side plug leads going to 4-3-2-1 instead of 1-2-3-4! Will update later today! |
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Would be interested to know which plug is right and whether it really makes a difference or not. |
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W7DC or NGK BP6ES. No resistor plugs, the wires provide all the resistance needed.
230/8 |
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In retracing what I did, I realised that I probably messed up the wires when I put the plastic covers on to tidy them up. With new plug wires properly directed to new plugs, new points, rotor and distributor cap in place and injector trigger points cleaned, car is running MUCH better than before I started all of this! I had local mechanic who owns an SL remove distr for trigger point cleaning and then reset the timing and dwell . I am a bit concerned in that ******** sent me WR7DC+ resistor plugs while the old ones were W7DC,s. My mechanic says it should make no difference. New Bosch wires are different from old ones too: - New ones have brass connectors at each end that plug directly into the distributor cap. They are Bosch Premium Wires - Opti-Layer Mag wire. Box says Fits Mercedes 8-cyl Engine. - Original wires have a hard plastic end that plugs into the distributor. I took one of these apart. It has a small resistor inside!! It's about 5/8" long x 1/8" diam. I measured it on my old analogue meter and it reads 16 on the 100X scale, 160 on the 10X scale - 1600 Ohms? Would it then not seem that if we don't have these old plug wires, we should have resistor plugs? |
Glad to hear things are working out, I use the NGK BP6ES, and have no problems. My wires are the old style. Not sure about the resistor wire idea, but you points are logical. Did you measure the resistance of an old wire VS a new one? That may help to see if in fact there is a big difference
My original manual had Bosch W175T30 for the plug ( we have the same car) these are what it crosses with W175T30 NGKBP6ES Champion N12Y, UN12Y, |
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But, I wonder if they would recommend same plugs today given changes in fuel and condition of these aging engines! And especially if the wires have a lower resistance, as do the aftermarket Bosch wires I just bought! |
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