troubleshooting injection system

[Ziggy]

Hi all, actually I don't have a 113 :oops:  but a German W108 280SE which has the same injection system and this seems the place on the net with the best knowledge about that    

The problem is cold and 'half warm' starts are poor, it takes about 5 seconds of cranking, and then idling speed keeps going up and down in a more or less steady rhythm. At the lowest point the engine almost stalls. Interestingly enough, the engine idles stable for like the first 20 seconds on a real cold start, though at very low speed, and then it goes in the 'up and down' mode. The engine runs very poorly cold especially with speeds between 40-80 km p/h. Once the engine is warm it idles ok most of the times, and runs much better although still not as smoothly as it should be. Also at high speeds like above 170 km p/h it lacks the power that it used to have...
Thanks for any suggestions !  

[George Davis]

Ziggy,

I suspect your up and down idling and poor running when cold is due to a stuck Warm Running Device (WRD).  This is the part on the injection pump that has two small coolant hoses running to it.  There is a piston inside that may be in the stuck in the warmed-up position.

The WRD is easy to remove.  You'll only lose a little bit of coolant when the hoses are disconnected, it's no big deal.  There is another hose connected on the other side, disconnect it, too (it's for air, not coolant).  There should be 4 screws, two at the base where it attaches to the body of the injection pump, and two screws halfway up that hold the two sections of the WRD together.  Take the WRD off the pump, keeping careful watch for shims underneath it.  Then disassemble and clean it all up.  Watch for more shims on the top of the piston.  Lightly lube the piston when you reassemble, and a small amount of sealant is useful to prevent coolant leaks when you put the top section back together.  Put all of the shims back where they were.  Figure about an hour's time.

For tons of info on this beast, do a search on Warm Running Device.  Good luck!

George Davis
'69 280 SL Euro manual

[jeffc280sl]

Ziggy,

I would also look at the cold start valve and relay.  Do a search under CSV.

Jeff C.
1970 280SL 4-speed

[rwmastel]

Isn't the first step in setting everything right to establish correct length of all the fuel linkage rods?  Since there is only one factory setting for this, I think you should start there and see how that effects your problem.

Do you have proper maintenance & repair manuals from MB, Haynes, or other reputable publishers?  They should have these measurmenets.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Ziggy]

Thanks for the replies, this is a great forum !

After reading through the forum I think there are probably more problems. It does seem that the CSV at the intake would be leaking, do I get this right that you remove the screw on the CSV when the engine is warm, and if there is gas coming through, the CSV must be replaced?

I also need to change the oil in the injection pump, I can imagine that with old, thick oil it will not work as smoothly cold as with new, or is the effect of an oil change generally unnoticable ?

Oh and it is a '72 280SE, one of the very last...

[jeffc280sl]

Ziggy,

The CSV is a very simple device.  My experience is that it can be easily repaired as the cost of replacement is prohibitive.  The CSV consists of a solenoid and a ball/spring valve. When triggered by the cold start valve relay the solenoid pin extends which opens the ball/spring valve to blow in a mist of gas through a spray nozzle to aid in a cold start.  Sort of like a choke system in a carb. The solenoid could be bad, the spray nozzle clogged or the ball/spring valve is dirty.  I can't think of another failure mode.  The CSV is controlled by a relay which in the case of my car was fouling.  I simply removed the relay cover and cleaned the contact points and the problem was fixed.  Using a volt meter see if you gat 12V at the CSV when cranking a cold engine.  There are some other inputs to the cold start relay that may need to be considered.  I recommend starting with the CSV and relay first.

Jeff C.
1970 280SL 4-speed

[ja17]

Hello ziggy,
The injection pump oil on the (M130) 280-SL engines circulates with the engine oil so it does not need changed as in the ear4lier w113 cars.

The "warm up device" on the injection pump can be checked by removing the small metal air filter canister on the back of it, and seeing if the passage closes as the engine warms up. Check this air filter to make sure it is clear also before re-installing.


Download Attachment: 20046281523_InjPumpWarmUpDeviceParts_1.jpg
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The "cold start solenoid" on the intake manifold should also be checked to make sure it is not leaking fuel into the engine.


Download Attachment: intake starting solenoid.JPG
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All ignition, linkage adjustments and the fuel delivery system should be thouroughly checked before making any injection adjustments.



Joe Alexander
Blacklick, Ohio

[A Dalton]

The CVS is suspect for leak by and there is a simple test

 Remove small hex plug from side of  valve... turn key ON..[ energizing electric fuel pump].. NO fuel should come from plug port.
 The port is after the valve seat, so it sould only see fuel when cranking engine.
 Place towl near port..[ to catch fuel].. remove distributor wire, crank engine .. you will see fuel squirt, verifying CSV normal operation..
 Up/down rpms at idle are common complaint on leaking CSV as there is no control on fuel mixture.. not as noticeable at higher rpms.....

[Ziggy]

No need to check/change/fill the oil on the injection pomp of a M130? So that's why I couldn't find a dipstick. I do have a an article about that, it must be for the 250SE 108 then.
Thanks all, I will check these things out and keep you posted.

[ted280sl]

Ziggy,
  An easy upgrade to improve starting on earlier 113's is to upgrade the coil. I am not sure of the ignition system in the 108's but, I would take a look at the ignition coil. If you have an electronic ignition or the "red" coil you can ignore this.
Ted 1969 280SL w/ upgraded "Red" coil

[Ziggy]

Ok, so far I've

-removed airhose from air filter on IP to intake manifold one mechanic once put in [:0]
-took out the injectors tested and cleaned them with diesel
-cleaned contacts on the cold start solenoid
-checked the warm running device, seems to be ok high vacuum when cold and none when warm
-checked the pressure of the fuel pump, above the fuel filter when cold it's stable at 18 PSI

Putting the original airfilter on the IP made the biggest difference. The engine starts better and idles fine now cold.
On higher rpm's cold however (like 50-80 km) it still runs very poorly. It misfires and backfires,  stutters, has poor power and the transmission won't even shift unless you get your foot off the accelerator. Once the engine is warm it runs fine.

What should I do next, any suggestions? It's not the ignition or timing, those symptoms lead me to think the mixture is too poor but if that was the case wouldn't it also run too poor warm? :?:

[Ziggy]

I've tested the CSV now and it seems to work ok. I turned the idle screw 3 clicks richer and  that was a bit of an improvement when driving cold, no more misfires although it certainly wasn't running smoothly. When I started it again half warm when it fully warmed up it began misfiring and stumbling again however.

I do have the Haynes manual but I find it a bit unclear. It doesn't describe the problem I am experiencing. One thing that applies is the 'poor pickup', also warm it doesn't take off as it should when I floor the accelerator. The first seconds it goes slowly... until 20 km's or something and then it really takes off. I am thinking maybe it is the lower range partial load which needs to be adjusted....

Any suggestions ?

[ja17]

Hello Ziggy,
Make sure you have gone through the linkage set-up before adjustments are made on the injection. In particular check to make sure the intake venturi flap and linkage are adjusted fully closed first (check the posts). If not clear about this let us know. Your fuel filter should be checked or replaced. It is important since this can restrict volume and is independant of pressure. When your car is cold it requires a higher volume of fuel to run correctly until warm.
Other checks will follow to pinpoint your problem if the linkage and filter is ok.

Carry on!



Joe Alexander
Blacklick, Ohio

[glennard]

quote:Originally posted by ted280sl

Ziggy,
  An easy upgrade to improve starting on earlier 113's is to upgrade the coil. I am not sure of the ignition system in the 108's but, I would take a look at the ignition coil. If you have an electronic ignition or the "red" coil you can ignore this.
Ted 1969 280SL w/ upgraded "Red" coil

Zigy et al, Could injection nozzle drip be some of the problem?  Atomization is critical on MBs, etc.  Other MB owners and myself have perceived improved performance with a bottle of injector cleaner every couple thousand miles. A return to a conical spray pattern and total atomization?

[jlennon3]

Ziggy - I'd advise not not to fiddle with the internal adjustments on your FI pump unless you are certain that's where the problem lies. Even then you might want to take car to a good MB mechanic thats familiar with the older FI systems. I think you need to start a process of elimination to narrow down where your problem (or problems) is. Let me make a few suggestions.

I'd start with the ignition system. Check that timing is correct (both at idle & higher rpm), check dwell angle, check spark plug gap. When car is running pull one of the HT leads off a plug (careful not to get shocked!) and make sure you have a strong spark jumping across the gap at least a few mm distance. Finally (my favorite) go out at night when its dark and start your car. Look under the hood around the disributor, coil, HT leads, etc. You shouldn't see any sparks or blue "corona".

Next move to some basic checks on the fuel system. First make sure the linkage between the FI pump and air intake is set up properly (see your shop manual). In particular make sure that in idle position the lever on FI pump come to full rest against the idle stop and also the butterfly valve in the air intake is fully closed. Also check that you don't have air leaking through the little air filter on FI pump when the car is fully warmed up (you have to screw off the littel filter to check). Assuming linkage is OK, check idle mixture when car is fully warmed. I assume you don't have a CO meter, so here is the "shade tree mechanic" method to check mixture. With car idling (and fully warmed up) disconnect one of the linkage ball joints at a convient spot so that you can move the intake air butterfly valve independently of the lever on FI pump. Very slowly start to open the butterfly valve. If idle mixture is correct, the engine speed should increase slightly (say a couple hundred rpms?) as you open the butterfly valve and then will suddenly drop off as you continue opening the valve. If the rpm continues to increase a lot as you open the valve, your idle mixture is too rich. On other hand if idle speed doesn't increase at all, but instead starts to stall, your mixture is too lean.

Next check your "running mixture", once agin using shade tree mechanic method. Take the car our for a nice long drive at freeway speed (say 40 - 50 km or so). Once you're back at home and cooled down a bit, remove a couple of your spark plugs. The plug tip and electrodes should have a nice "tan" appearance if your running mixture is right. If black and sooty appearance, your mixture is too rich. On other hand if appears very light off white, your mixtureis too lean.

Why don't you do these checks and let us know what you find. Then hopefully the forum members will be able to help you pin down your problem

Good luck!
John
280SL (Euro)
280SE (US)

[Ziggy]

Thanks for all your suggestions.

I will check the fuel linkage rods before making any adjustments on the IP.

Last month I replaced the fuel filter. It didn't make any significant difference. Incidentally, the filter I was given was a Mann P707 and I pulled out a Mann BF700. I am wondering now which is the right one?

I used an injector cleaner once and there was no noticeable effect. The injectors are average at best, I did notice everytime I test them on a diesel pump the engine is running somewhat smoother (warmed up) for a couple of 100 km's. I've been hearing about people getting good results with adding 250ml of ATF on a full tank, did anyone here get good results with that?

The ignition (electronic) is fine. I will recheck the timing soon though, last time I set it was something like 600 km's ago.

I did read about the 'shade tree mechanic method to check mixture', but can this also be done on a cold engine? Cold it runs at it's worst.

So to sum it up;
- idling cold = fine
- idling warm = fine
- running warm = acceptable, but should be able to run smoother
- running cold = poor

[ja17]

Hellow Ziggy,
The BF700 mann fuel filter is for a diesel Mercedes engine. The P707 Mann is correct. You can also use a Hengst E5 KP or a Knect EK 402.

Yes you can use the linkage method to check injection mixture on a cold engine also.


Joe Alexander
Blacklick, Ohio