Sputter...sputter...phut - UPDATE!

[n/a]

Hi,

As mentioned in a previous post, my recently acquired '71 280SL came with a Crane XR3000 ignition kit, but the wrong coil. I upgraded it to the silver, high-energy Bosch and it runs much smoother. However, depending on its' mood, I have problems on take-off.

If I accelerate from a dead stop, GRADUALLY, it is smooth. But if I give it moderate to heavy gas it misses until rpms pick up- then she smooths out fine. Also noticed that she starts fine cold, but when warm she sometimes makes me crank with pedal to the floor.

I thought the timing was off, and maybe the mixture needed adjusting as she stinks of gas as I slowly tool through the neighborhood coming home. As I used to adjust timing as a teenager on my beaters, I attempted to do this here. No go. Darn hood gets in the way- then concerned about if possible with Crane system.
I finally gave in and made an appointment with Import Autohaus, here in Richmond. The other MB mechs suggested them because they have a CO2 meter to set mixture.

I left it last Friday, and finally got a call yesterday. They say that they've been unable to get her to run correctly. That they reset rods, linkage, etc. to factory specs and now it runs much worse than when it came in. Great! He suggested that someone had made adjustments for something previously and now they have to "trace the whole system" to figure out what it could be. They suspect the fuel system.

Any suggestions? I hate the think what "exploratory surgery" is going to run into hour-wise.

Thanks everyone,

David

[Jonny B]

I purchased a 250SL this spring, and it really did not run very well. I took it to my mechanic and can let you know about some of the things he found/did. The gas tank was in need of relining as there was a lot of junk plugging up the filters, that was completed. There was not enough fuel flow/pressure, so he replaced the fuel pump (ouch this was an expensive piece), new plugs, and he installed a breakerless ingnition. As per other posts on the site, he adjusted the linkages to the correct tolerances, and reset the timing. I also found the vent tubes (that lead to the funny little funnel at the back of the car - to vent the gas tank) were plugged up. I only had to rod those out with a thin wire. Even with all that, the car still idled iffy. I took it back, and he did a few more adjustments of the idle air flow (screw at the front of the intake runner), and some further tweaks of the adjustment screw on the back of the injenction pump. This was the majic set up, the car runs great.

His contention, and proven out on my car, is that it takes some patience and fine tuning to get all the various combination of things correct.

I don't know all the specifics of the adjustments and timing etc, but these should be in the Haynes manual or the BBB. I wanted to let youj know what we found.

Jonny B.
1967 250SL

[Naj ✝︎]

David,
Have you got the correct distributor for the car? My 280 came with an '048' vacuum advance type distributor and caused similar running problems. Fitting the correct '051' changed it hugely. Further tinkering was required with idle fuel/air adjustments and it runs much better now. Not yet perfect though!!
naj

naj
'Kloines Scheisserle'
65 230SL
68 280SL

[n/a]

Hi Naj,

Thanks for the reply.  Is there a way to easily tell which I have?  I'll tell the shop to check.  Were ALL 71's outfitted witht the 48?

One other question:  The other day I was fiddling with the car and noticed a screw/shaft/adjusting something coming out of the right side of the injection pump.  (on drivers side of engine with 6 fuel lines coming upward, correct?)  It looks like a skinny 1 inch long screw that apparently is spring loaded.  As I tried to "screw" it back into the pump body, I noticed that even though I could easily turn it, it does not screw any more into or out of the body.  I can push it a little, but it is very springy.  What is this?

Thanks, Naj!

David

[n/a]

David,
The correct distributor for a 1971(and 1970), US emission spec engine ends in 062, according to the BBB.
The screw that you mention is for adjusting the idle fuel mixture. You push in on the knob and turn it until it engages. Then, turning this knob while it is engaged, you will feel it "click" as the adjustment is being made.
I have been told by my mechanic not to play with this adjustment.

Regards,
Stan

[Cees Klumper]

David - do NOT attempt to turn the spring-loaded idle mixture adjustment screw at the rear of the injection pump with the engine running. The engine needs to be off for this adjustment to be made, or you'll break something in the FI pump. This screw is vital for the correct idle mixture setting, in conjunction with the large (also spring-loaded) screw on the intake manifold. Then you have your cold start thermostat on top of the FI pump that can be adjusted (by adding or removing shims inside) and you have te make sure that the cold start injector valve (activated for a few seconds when cold starting) is in good shape (i.e. functioning when supposed to, and not leaking when it is supposed to be closed).

On the side of the distributor body, there should be a small, oval metal "Bosch"plate with the serial number. You may have to clean it off a bit to see the number.

It's time we got around to rounding up all of the old posts on these (ignition and FI pump, mixture settings and cold start devices) subjects and make a comprehensive "how-to" and "troubleshooting" document out of it, because the same questions and answers start to come up time after time ... we're working on it!

[n/a]

Thanks for the feedback, guys.  When I sent the car in to the shop I asked for a. check & set the timing b. adjust the mixture since they have a CO2 meter.

Well, as previously related, they "reset all the linkage and rods to factory specs" and it ran worse than before.  They assumed that some sort of adjustment for something had been made before.  And without knowing what it was they would have to trace the fuel system first and try to deduce the problem.  

They called me a few minutes ago and stated that plugs I had just put in were too cold (9's, I believe) and he replaced them with 7's.  Next said that the engine was burning very lean.  Also, that the dwell, while running, was 17 degrees and should be 36 degrees.  If you remember, the car came with a Crane XR3000 electronic ignition.  I called their tech support line and asked the difference between the more common XR700 and the 3000.  The tech sounded very surprised there was a XR3000 in the car.  He said that this was a VERY high energy system used for race cars, turbo and supercharged vehicles.  He laughed and said that he was not surprised that the car was burning lean as the spark on this unit was very hot and very efficient.

Ok, back to the shop...The mechanic is also the owner and his shop has a good rep.  Apparently he is the resident expert on these older classics.  Seems knowledgable enough, and a friendly person.  He said that it appears as though this has a new injection pump and that he is unable to enrich the mixture any more than it is.  Could this be a fuel delivery problem?  ie. filter, obstruction?  After a test drive he noted that if you punched the gas off the line it did well.   But hesitated if given a moderate pedal of the line.  Higher rpm's and it smoothed out.

After all this, I get another call telling me that the timing is way off.  It is 15 BTDC and this is a swing of over 20 degrees.  When he tried to adjust the timing at the distributor the nut was rounded off.  He is working on that now.  I am somewhat concerned because this is what I asked to be checked out first.  Am half hoping this is the big problem, but am worried that there will be a large diagnostic time charge since they've had it since Friday.

Ideas?

Thanks again,

David

[Cees Klumper]

There are several adjustments possible to the mixture, and it's hard to believe that, in conjunction, these adjustments would not yield a sufficiently rich mixture. Unless the FI pump is not operating properly of course. It is concerning that only now the shop comes with reports of incorrect dwell and timing when, as you indicate, this is one of the first things they should have checked. I am afraid they are not quite the experts that you should ideally have. So you pay for thier learning time. You may want to ask the group for some references for other mechanics in your area, for 'next time'.

I had similar experiences with my various mechanics. Finally, I decided to just try and do everything myself with the help of this group and the various manuals. I can now do most everything, and did find a reliable and knowledgeable 'back-up' mechanic for the really tough calls.

It will be of great help when we have the comprehensive ownership, maintenance and repairs manual finished that will incorporate all of this tribal knowledge that has been accumulating on Yahoo! and here. We are working on that now, and expect the first chapters to be ready sometime late this year/early 2004.

[n/a]

Well, I was pretty psyched going to pick up my 280 this afternoon. It had been in the shop since last Friday to set timing and adjust mixture. To recap: The mech./owner said that it looked as though the injection pump was new/rebuilt, but he was unable to enrichen the mixture. This was puzzling because I brought it in because it was eye-burning rich. First thing they did was "reset everything to factory specs including linkage and rods." After that was done they said it ran very poorly- and it ran very lean. The last thing he did was finally set the timing- which was way off at 15 degrees BTDC. This whole deal was pretty uncomfortable, as it was running very well when I brought it in except for a slight hesitation on medium-brisk take off from stoplight, and a slightly uneven idle.

When they called to tell me it was ready, the mech. stated that it was still very lean and that he thought I'd need a new injection pump within a year! When I went to pick it up I took it for a test ride prior to settling up and it ran terribly. The idle speed was now correct, but was trembling and rougher than I remember. When I left the lot it accelerated slowly and would not shift into 3rd gear unless the rpms were much higher and I let off the gas. NO mid-range power now and, at highway speed the exhaust has a gasping rough sound. Not the sweet, mellifluous tone from before. Shifting is practically non-existent.

In summary: smooth low speed take-off
very anemic take-off under power
And oddly: Good full throttle take-off but stays in one gear mostly - and now slightly backfires. never did before

Am pretty bummed as I'd been recommended to this shop by several mechanics who knew they had a CO meter to set mixture. Now with Labor Day Weekend here I'm doubtful of a solution when they work on it again tomorrow.

Cees, am axiously awaiting that knowledge-base you spoke of.  Any suggestions I might offer to the mech. tomorrow?  As I mentioned, he is the owner and is the one who works on the older classic cars.  Or do you think it might not be kosher to make any suggestions?
Am really disappointed that she's now exhibiting problems that I'd never had before.

Thanks again!

David

[rwmastel]

David,
It does not surprise me that if they started from scratch by correcting the linkage that other poor adjustments would expose themselves.  That is, if the linkage was wrong, then adjustments of other components had to be made to compensate and are now making things difficult.  As Cees said, there are many adjustments that need to work together and these topics of adjustments are common.  Now, throw into the mix an uncommon XR3000 ignition and you get an extra variable in the problem.  Does anyone have experience using this model ignition?  You might want to document and share with us what specific componenets your whole ingition system consists of: coil, distributor, ballast resistors, spark plug wire resistance, spark plug resistance, etc.  You say that the F.I. Pump is new?  Does that mean a new model, or a correct old model that's been rebuilt?  This should have a Bosch identification plate on it, like the distributor, so that info would help us help you.

I'm not going to recommend that you not take the car there, but I do recommend educating yourself as much as possible so you can understand what they are doing with your car.  Its for your own protection.  Several people have actually helped their mechanic after researching problems in the on-line Pagoda community (here, Yahoo!, and Pagdoa113).

Let us know what you do and how it comes out.  We'll try to answer any of your questions.

Rodd
1966 230SL Euro
1994 E420

[ja17]

Hello David,
It sounds like they may need some help. What is their background on these cars? The shift problems are probably due to the linkage not being sychronized to the "three position solenoid switch" on the venturi. In addition if they are not familiar with the backwards working vacuum ignition retard on the distributor, they may be setting the timing incorrectly. These running complications or mis-adjustments will cause the spark plugs to become fouled complicating tuning even more and aggrivating the shifting problem. I would check the linkage settings (especially at the venturi linkage screw and three position solenoid switch) static set the timing at TDC (for now) install the new plugs after doing a resistance check on the plug wires, and start it up.
If it seems better re-set the timing to specs and adjust injection mixture if needed.
Of coarse all of this is in vane if you have problems with fuel delivery or basic ignition. If they are having difficulties in any specific area let us know and we can walk them through the process if needed. There is a lot of information to digest on this site. We need to pinpoint the problem area without resorting to needless replacement expensive major parts as a diagmnostic tool!



Joe Alexander
Blacklick, Ohio

[Tom]

David,

I just sent you a private email offering some help if you are not successful with your local mechanic.  It could be alot of things as Joe and Rodd mentioned.  The optical trigger of the Crane ignition may be off if they have been into the distributor.  Could  be linkage, fuel delivery, bad wires, bad plugs (for sure by now).  Poorly adjusted idle throttle switch can cause performance and transmission issues at the same time.  Poor performance impacts levels of vacuum which is essential to proper shifting.  Etc, etc. The last place to look, however, is to replace the FI pump.  There are so many likely places for the poor performance to be corrected before looking into the FI pump.

Best,

Tom