Tuning 280SL in storage for 15 years

[wayneesch]

After sitting for 15 years, getting it back on the road. Engine was running smooth when parked. Now engine needed rebuild which was done by Metric Motor,  Injection pump reworked by Fairchild, fuel pump functioning after a little work, new water pump, radiator rebuilt, many new gaskets and seals. All linkages refastened with no adjustments. Engine started right away but running rough. Adjusted dwell angle to 32, still rough. Adjusted timing with strobe, could not get smooth run. Tried dwell angles at 36 and 40, no success eliminating all rough running. Can adjust for smooth idle at 850 RPM - but misses with acceleration.  I have a good very experience mechanic who has never worked on this engine (could not find 280SL experienced mechanic locally). Mechanic thinks the fuel/air mixture may not be correct and wants to start adjusting the linkage or fuel injection. I am hesitant to make these changes since it was running fine with current adjustments when parked.  Recommendations?

[Jonny B]

One item you did not mention is the gas tank. Has it been checked? Also the three fuel filters (at the tank, at the fuel pump and at the engine) - are they clean and clear.

You also don't mention if you checked the linkage - split test (use the search function) and the linkage tour to be sure all the angles are where they should be. Lots of things could have affected it after that long of an idle period.

Also be sure to take a look at the search function (the one in the line of items at the top (sort of) left of the home screen, not the one at the top right.

Try "rough running" with the quote marks as that will limit the search to that phrase. I tried that and got three pages of results, but you should be able to read through a few of those to see if the information appears to be helpful. You might be able to narrow the search further. Don't be afraid to poke around a little.

This is not a terribly rare issue (unfortunately) so there has been a lot written/discussed about it.

[wayneesch]

I forgot to mention the gas tank was empty. It was flushed and all three gas filters were replaced. I will read about the split test - I had already read many of the forums posts and printed the linkage tour. I will search for "rough running", I was using the top right search function, thanks for pointing out the other search function.

[Garry]

For all,


The top right search function will only search the particular area you are in. To search the whole forum you need to use the search button in the highlighted Home line.

[wayneesch]

Thanks Jonny B for guiding me to the right method to search the forum and the linkage- split test!

Checked many possibilities today and did the linkage - split test. This test clearly demonstrated that it is running lean. Tomorrow I plan to test the fuel pressure to make sure that is not a problem. If not a problem, then adjust the linkage. This is a rebuilt engine and the linkage was reinstalled as removed.

The intake venturi stop screw did not need adjustment. However, I noticed that the linkage to the intake venturi ball connector stop nut had a large gap about 1/2" from ball (clearly has been this way for many years while it ran very well). See attachment.

Also, the Linkage Tour states to adjust the other end of this linkage by placing a rod thru the bracket hole so that the end of the linkage ball rests against the rod. To do this the linkage needs to be adjusted about 1/2" shorter which matches with the stop nut gap at the other end. See attachment.

I am reluctant to change this linkage length that has worked well in the past because this will cascade to other linkage adjustments;  instead only lengthen the linkage that comes up from the injection pump (supposed to be 233mm - I need to measure the current length).

Any thoughts on this?

[wayneesch]

Another question, what does the adjustment in the photo do (the hose connects intake manifold to air between air filter and intake venturi).

[roymil]

That screw on the intake is only for idle air adjustments to effect idle mixture.   On a warm engine this screw adjusts idle air volume and it works hand-in-hand with the idle fuel control adjustment screw on the injection pump.   During idle adjustments the assumption is that the intake manifold's butterfly valve is completely closed on its stop and that the injection pump linkage is also at it's stop.  That way the idle can be precisely adjusted with fewer variables.   If you think idle is too lean then you can just try turning this screw clockwise a 1/4 turn at a time to reduce idle air and see how that effects idle speed.   Keep track of your adjustments in case you need to go back.   There are detailed instructions on the iterative idle adjustment process in the tuning guide but just remember the injection pump is never touched while running.  You must shut off the engine to make fuel adjustments on the injection pump.   My experience is that it should only take about 1/2 turn max to notice a distinct difference in RPM and smoothness.  If you have to go further than that then something else may be malfunctioning and dominating the idle air volume, possibly because the WRD isn't completely warm or there is some other air leak.  Good luck, this is the fun part!

[wayneesch]

Thank you Mark, I understand your detailed explanation.

Does anyone have recommendation regarding my previous question about changing linkage?

[Pawel66]

You mean the linkage length? Just apply the Linkage Tour recommendations. The length of the linkage is necessary to be correct so that the FIP shaft and throttle shafts are turning with certain proportion.

It is not really the rod to put through the orifice in the cross-rod bracket. It is. Best to have ca 10mm pipe put through it to grab the ball of the ball joint steady to determine the length.

[ja17]

The set screw with 10mm lock nut on the intake must be set correctly. disconnect the linkage rod going to the lever on the intake. Next loosen the 10mm lock nut and turn the slotted screw in just enough to keep the intake flap in the intake venture, from binding when closed all the way. The venture setting is correct at this point and the lever must rest on the slotted screw stop at idle with flap closed all the way and without binding. Follow up by adjusting the rest of the linkages. Follow the tour.

[wayneesch]

After following the linkage tour instructions and verified the linkage was correct, I contacted a 90 year old retired Mercedes mechanic who agreed to look at the rough running. Since Hubert has not worked for over 20 years, it took him a little time to recall (no manuals). Within a few hours, he had it running very well. I had sent the injector pump to Robert Fairchild Industries for complete service. Hubert determined the injection pump was too lean and he went home to get his specialized tools to adjust the full load adjusting screw (spring loaded) thru the guide tube on the rear of the injection pump. I kept quiet and held my breath as I thought the injection pump should not be adjusted after servicing. Six turns counterclockwise, a few tweaks to the idle adjustments and it purrs smoothly. Experience counts! Note a bolt on the side of the injection pump needed to be loose for the adjustment. Hubert also did the split throttle test, examined the exhaust and the spark plugs to determine that it was running lean. Hubert also checked the vacuum, dwell, timing, warm running device and cold start valve which were all operating correctly. Perhaps this post will help someone.  Now on to figuring out the transmission problem which is why the car was parked.

[Pawel66]

I wish I had someone like Hubert here...

Important: what screw on the side of the injection pump had to be lose for adjustment???

And for which adjustment???

Please kindly specify.

[bracurrie]

Have you considered giving Fairchild some feedback on their work.  I know from discussing my pump with him that he tweaks the mixture to compensate for gasoline with ethanol, but I don't remember whether that was to the rich or to the lean. He does a lot of custom work for Porche racing guys so he might be interested in just how you had to change the settings to get the car running right.

[wayneesch]

Here are photos showing the guide tube for the full range fuel mixture adjustment screw and the 14mm bolt that needs to be loose to turn this screw. You need a long very, very thin screwdriver. Gently feel for the spring loaded screw head notch. Counterclockwise to make richer, clockwise to make leaner. Tighten the 14mm bolt before starting the engine. To adjust the idle, there is an air adjustment large screw on the intake manifold near the front of the engine; and for fuel adjustment look on the firewall side of the injection pump near the bottom that you push in and turn.
NEVER ADJUST THE FUEL WHILE THE ENGINE IS RUNNING. Count your adjustment turns so you can go back if needed.

I did call Robert Fairchild before Hubert came to my rescue. Robert had a number of suggestions to correct rough running without adjusting the injection pump. If the adjustments did not work, he offered for me to send the injection pump to him to check the calibration - no charge.  Note Robert Fairchild serviced this same injection pump 35 years ago and it installed perfectly then. I plan to call Robert and let him know the resolution. I have always found Robert to be knowledgeable and helpful.

[Pawel66]

Thank you for sharing this.

Loosening the 14mm bolt down below to adjust full range is new to me... did I miss it??

[wayneesch]

The full range fuel mixture adjustment screw did not turn counterclockwise until Hubert remembered to loosen the 14mm bolt. I do not know if it would turn clockwise.