Author Topic: ‘69 280sl - Rough Idle/Rough Running (Read 4709 times)

cjpoulos · « **Reply #25 on:** April 15, 2025, 17:53:30 »

I think the main issue with my current plugs is that one or more of them is faulty - I may or may not have knocked two of them off the workbench late one night... They foul very quickly as well, which I'm currently going to blame on the mixture issues and whatever may be causing that. I've ordered an injector tester/cleaning kit from MercedesSource, so I'll start chasing the final fuel issues there. I think between that and the new NGK's, we will be in good shape!

sens · « **Reply #26 on:** April 15, 2025, 18:27:45 »

If you have a multi-meter you could:

1/ Test the spark plug between the thread that goes into the block and the tip coming out of the ceramic tube. Resistance should be very, very high, infinite.
2/ Test between the same tip and the point where your cap fits on the plug. Should be around 1100 Ohm
3/ Test the wires including caps. Should be around 0 Ohm.

If you clean a fouled plug and sand a little the spark points, you should have a good spark.

Now if this is OK, I would do the split linkage test to see if you are realy running so rich. (I think you do)

Good luck.

twistedtree · « **Reply #27 on:** April 16, 2025, 11:24:47 »

Another test of the CSV is to remove it from the manifold, but keep the fuel pipe connected. Then turn on the ignition and let the fuel pump run a bit. Look for any leakage of fuel from the CSV spray nozzle. If it's dry, then you know it's not continuously over fueling the engine.

sens · « **Reply #28 on:** April 16, 2025, 12:19:37 »

Spot on!!

That is a very good test to make sure the CSV is OK!!

cjpoulos · « **Reply #29 on:** April 16, 2025, 13:26:47 »

That is a great test. I did all the tests mentioned and it turns out that my CSV is working very well, no leaks and it's not stuck open or closed. I think the initial spray at start up is just adding unnecessary fuel because of how rich the mixture already is, so it runs a bit better with the CSV disconnected.

The car will start and run (a bit roughly) every time now! Dwell is set to 36 degrees, points are at .012, and I gapped the plugs down to .027 from .031, which seemed to help a lot - did not think that it would make a noticeable difference, but I'll take it.

Now I'm just going to clean the injectors and throw the new BP5ES's in - the NGK BP5ES 7832 are available on amazon now for anyone who's had trouble finding them. Make sure to buy the 7832 part number, those have the twist of caps (7732 BP5ES plugs have a fixed cap that threads into the ceramic bit).

Almost there!

sens · « **Reply #30 on:** April 16, 2025, 13:51:45 »

Well you are msking real progress!!
You can exclude your CSV.

On my 280SL I had one plug (No4) that fouled. (see post) The others were ok.

It was solved completely by setting the valve clearance correctly (was far to high) and cleaning the injector No4. It had a bad spray pattern.

So I would check the injectors as soon as you receive the kit!

Please let us know!

Good luck!

cjpoulos · « **Reply #31 on:** April 19, 2025, 21:16:06 »

Update - she’ll run now! I did not expect those spark plugs to make such a difference. Unfortunately, the BP5ES-11 plugs I received were the 7732 version that don’t have twist off terminal caps like the 7832 part number. They were mislabeled online. I was able to carefully grind down the terminals and thread them, and it worked great. A little unorthodox, but I’ll take it for now.

I haven’t received my injector testing/cleaning kit yet, but the injectors seem to be working fine after see it run like a normal Pagoda this morning.

Despite the good news, the problems persist. I now have an oil leak coming off of the crossmember just behind the oil pan. Any insights on what may be leaking? I haven’t seen this before so I’m a bit stumped. Could there be a leak from the FIP?

I’ve never seen a true “one step forward, two steps back” situation until I bought my Pagoda last year - but still, I couldn’t be happier with it.

sens · « **Reply #32 on:** April 20, 2025, 10:20:08 »

Oil leak can be a lot of things.

Is it black/braun oil? Engine.
Or red? Stearing system.

Valve cover gasket leaks sometimes a little on my engine.
But also FIP is possible.

Give your engine a good clean and look where the leak starts.

cjpoulos · « **Reply #33 on:** April 20, 2025, 19:36:06 »

It was just the oil inlet for the FIP. Must have forgotten to tighten it all the way when I installed it.

Got my first drive ever today! 1.1 miles down my road haha. All we need to is to fully sort the rich mixture and buy some new tires - mine are from ‘72. Thanks for all the help guys!

sens · « **Reply #34 on:** April 21, 2025, 06:23:02 »

Great!!
Enjoy your nice car!!!

cjpoulos · « **Reply #35 on:** April 24, 2025, 04:15:49 »

I was able to test all six injectors last night. They all seem to be releasing around 230psi, but I don’t think they’re very healthy. None of them are failing to atomize the fuel, and the spray pattern in general is very nice. However, 4 of 6 injectors are not holding pressure and they continue to release until the pressure drops to about 100psi. It’s a constant spray until they reach that low point. Does anyone have some insights on this? Does this warrant an injector replacement or do I need to do a better job of cleaning them? I’m guessing that the constant spray is not a great sign

It will start and run without trouble now, but after a split linkage test I’ve been able to verify that it runs very rich. Sometimes the car does not want to drop below 2,000rpm and it will idle there until I shut it off - I’m not very thrilled with this. Adjusting the idle air screw does nothing for the car at this point, presumably because of just how wrong the mixture is. The FIP rack moves with ease though, so I’m glad I won’t have to free that. The car also has trouble moving under load at times. I’m obviously not out cruising in it, but even pulling in and out of the garage can be a seemingly impossible task when she enters these bouts of rich-running-rage as I’m now calling it.

Thanks guys!

sens · « **Reply #36 on:** April 24, 2025, 07:41:01 »

Did you read this? Might help...

https://www.sl113.org/forums/index.php?topic=37588.msg274764#msg274764

A very simple way to lean your mixture is to remove a shim under the barometric compensator.
Keep good track of the changes you make!

https://www.sl113.org/wiki/Engine/AltitudeCompensator

cjpoulos · « **Reply #37 on:** April 25, 2025, 01:58:28 »

Very good thread. I was able to use some fine metal polish to get the injectors working well. 5 of 6 injectors chirp and hold pressure pretty nicely, the last injector is functional but doesn’t hold pressure as well as the others. That didn’t fix my issue though! Still running very rich.

I’ve taken the shims off of the WRD, and ensured that the rack is free. When the car got up to running temp, I noticed that the WRD was cold and so are the inlet and outlet lines - could this be the real issue? I do have a small coolant leak from the coolant bypass at the front of the cylinder head, so maybe the water isn’t circulating properly. Any ideas?

sens · « **Reply #38 on:** April 25, 2025, 07:17:13 »

Very good news that you saved 5 out of 6 injectors. $$$! Keep on trying for the last one! You know how to do it!

About the warm running device: that is definitely a problem causing your issue!
If the WRD is cold, it will give more fuel and more air to the engine, supposing that the engine is cold. This causes the engine to run very rich, in your case even when the engine is hot.

One remark:
I suggested to remove a shim from the Barometric Compensator, not the WRD!
Removing the oval shims from the WRD makes the mixture leaner only during warm up. So I would put them back!

I would try to find out why there is no coolant flow through the WRD. It could be an obstruction in the device itself. Try disconnecting it and look if you observe flow.

Good luck!!
I am very curious about your observations!

ja17 · « **Reply #39 on:** April 26, 2025, 05:54:48 »

If the coolant lines going to the WRD are not getting hot when the engine reaches temperature, you may have a plugged coolant line! The small diameter steel tubing can corrode and get plugged internally. Do investigate ASAP before making more modifications to the injection system.

cjpoulos · « **Reply #40 on:** April 26, 2025, 17:35:11 »

Alright, so the cooling system is my task for today. I haven’t let the car run since I noticed that the water wasn’t flowing properly. I need to replace the small brass bypass line at the front of the head because that’s leaking, and I removed my heater core bypass and put that back to normal after doing a light flush of the core itself.

I believe I have the FIP tuned properly now. I put all the shims I had removed back, bench tested the WRD thermostat, and now a split linkage test shows that adding more air or fuel when the linkages are split stalls the car out.

Based off of how the engine sounds, I’m thinking that this is now down to a good ignition tune up (maybe the distributor needs a thorough evaluation), and another going-through of the cooling system. The revs at idle still bounce from about 600 - 1000 revs with no noticeable pattern (at least to me), and it continues to stumble with higher revs. I have set the dwell to 38 degrees now. I’ll let you know what I find!

Thanks!

sens · « **Reply #41 on:** April 26, 2025, 19:17:59 »

You make good improvements!

Is your WRD getting hot now when the egine is hot? And does the air suction on the WRD stops when hot??

Cees Klumper · « **Reply #42 on:** April 27, 2025, 02:25:34 »

I recommend you install a 123 electronic distributor/ignition.

cjpoulos · « **Reply #43 on:** April 27, 2025, 07:46:22 »

It was the distributor! I’m happy with my 051 for now, and I’m planning to keep it because it’s in really great shape - the car only has 14,800 original miles and although it was sitting for over 25 years, it’s in incredible shape and almost all of the original parts have been very nicely preserved and “easily” serviceable.

Today I disassembled the entire inner workings of the distributor and found that the plates/weights inside were, simply put, sticky. I cleaned all the parts and greased what needed to be greased and that made an absolutely massive improvement. Idle will bounce from 800 to 1000 RPM, but after about 1100 RPM it’s unbelievably smooth - beautiful sound, not a single stutter, and zero vibrations!

Now I’ll chase down the idle issue, fix my water leak, and replace the tires from 1969… and then perhaps we’ll have the first real drive since the late 1990’s!

sens · « **Reply #44 on:** April 27, 2025, 09:42:03 »

Congratulations!!!
You did it!

cjpoulos · « **Reply #45 on:** **Today** at 18:45:28 »

Very happy!

We have more issues! The car refuses to climb hills, which is very unfortunate because my house is situated at the bottom of two hills... I'm guessing this is due both the mixture and ignition. A split linkage test shows that we aren't running too rich, so I'm thinking the its a simple ignition problem (yay!).

To be fully honest, I messed with the vacuum advance rod a couple of times (bad idea probably), and I'm wondering if that is where my issue is coming from. I had to turn the distributor counterclockwise all the way to get the most smooth performance from the engine, so perhaps the advance rod needs a turn or so?

Thanks for all the help guys - I think this counts as another Pagoda saved!

Cees Klumper · « **Reply #46 on:** **Today** at 20:29:02 »

It is important to set the ignition timing per specifications, just the right amount of advance will make a significant difference in the amount of power the engine makes. Similar to all the adjustments really, of fuel flow and pressure, fuel/air mixture throughout the operating range, and so forth. I know you know this already, but just responding to your comment about turning the distributor 'all the way'.

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Author Topic: ‘69 280sl - Rough Idle/Rough Running (Read 4709 times)