M127 "pinging" 220SE

[kdlemon]

hi guys, i have just joined the forum in a desperate effort to fix my 220SE! i bought the car recently with a freshly rebuilt head and a terrible pinging problem. it is very bad when cold, but most of it goes away when hot.

it sounds like pinging but i don't think it really is. when i crank the engine over by hand when cold, as the number 1 and 6 exhaust valves open, the injectors seem to make a metallic noise which sounds much like the noise i hear. when the engine is turned over by hand at operating temperature, the noise is isn't there.

is it possible for injectors to make a noise of this kind?

also, the cold start valve does not work automatically, but the car starts instantly when the solenoid is energized manually. i have been told that there is a way to simplify the overly complex cold start system on these cars without resorting to a manual switch. any ideas?

cheers!
kaydee

[glennard]

Hi, Is this a 111 coupe with a two plunger injector pump?

[kdlemon]

hi, yes it is. i know it isn't strictly the topic of discussion here, but thought there might be enough in common to be permissible.

[psmith]

Maybe Wagas will chime in as a fellow coupe owner, but I'm sure your injectors are the same as ours in that they are held closed by a spring until fuel pressure forces them open at the correct time.  I can't imagine hearing any noise from the injectors.  Since the head was rebuilt recently I would suspect that.  Take it back to whoever rebuilt it (if possible) and have them look at it.

[waqas]

Unfortunately, I know nothing about the 2-plunger setup on the 220SE's. My 250SE/c engine and injection pump are identical to those in a 250SL.

Some semi-random questions:
Have you checked your distributor for correct timing and vacuum advance/retard?
How about if you swap out your spark-plugs, does the pinging remain the same?

Probably the best person to ask here is Joe Alexander. He's drawn up charts for the various injection setups, and can likely provide some real help.

[kdlemon]

hi guys,

thanks for the help. i really don't think it is pinging. pinging is usually a problem when hot rather than cold, and as noted, the injectors do make a strange metallic noise when the engine is cold and turned over by hand. if i undo the lines at the IP and turn it over, the noise goes away.

with a stethoscope, the engine is quite quiet, but the entire injection system seems very clattery and noisy. the 220SE seems to have bakelite mounting blocks for the injectors. a stethoscope on the manifold at the base of the blocks produces the usual mechanical hum, but on the injector, the noise is quite loud and metallic.

it sounds just like pinging, but if the timing is retarded to the point the car falters under acceleration, it still pings. valve timing is correct.

i can't see how injectors can rattle either, but apparently its not that uncommon. i'm stuck!

[waqas]

ok, some more random questions:
Have you measured compression across all cylinders?
Any significant differences between hot and cold measurements?

[Ulfi]

I had/have a similar problem and I've been told that skimming the head during rebuild can cause this as the entire engine becomes a little lower which can cause slack in the timing chain. I'm having mine adjusted when I find the time for it. See my question "Pinging from cylinder #5"" elsewhere, I believe its on page 7 or 8 in this forum.

[ja17]

Hello kaydee,

Welcome to this group. These guys are really great at helping those in need even if it is not exactly a W113. The knowledge base here is much greater for these mechanically injected engines than any other MB site.

Your engine is actually a very close relative to the W113 230SL. The two piston injection pump squirts three cylinders at a time and fuel hangs around in the intake until the valves open. Amazingly it works quite well.  The fuel after leaving the two pistons of the injection pump goes to a fuel distributor block where  it splits into three lines going to three cylinders each. The injectors enter the intake manifold instead of the cylinder head on these engines. The injectors work the same but are long and curved so that they curve into the  cylinder head just above the intake valve.

There is a fine fuel screen in the fuel distributor blocks as I recall. These can become plugged.

I am familiar with your delimma from the other forum as you know. I am a bit suspicious that your pinging may be a different noise.

Typically it is not unusual to hear the injectors "chirp" as they squirt. If you are finding a suspicious noise from one injector , try moving it to another cylinder and see if the noise moves also.

If the noise is coming from one cylinder try removing the valve cover to see if you have any mechanical issues. Also if you remove the spark plug you may be able to turn the engine and actually view part of the top of the piston to see if you nave any obvious damage.

Aside from these differences the engine is basically a very close 230SL engine relative.

As mentioned, pinging usually becomes more pronounced as the engine becomes hotter.

Maybe there are also some other fresh ideas from this group. We have another member Matt Merill who has also been plagued by a pinging type of problem with his 230SL.

The starting aid systems are quite complex and vary widely on these cars. We have three or four versions on the W113 engines. You can read the starting aid tour on this site for knowledge on the systems. Your engine may have the Version II as the 230SL, or you may have an earlier Version I system. I have researched these earlier non-W113 systems also if you need additional information.

 One good temporary fix is to locate the thermo time switch and hook a jumper wire from ground to the "W" terminal on the thermo time switch (located on the pod near #4 spark plug on your W111 engine. If this does not help then it's relay is faulty.

[Benz Dr.]

The 220SEb system is far more difficult to tune than any other injection system. I cut my teeth on this type of fuel injection over 25 years ago so by the time I got to 6 plunger pumps it looked simple.

The discriptions of how the system works is correct but it's far more tricky than it looks. Every injector HAS to break at the same pressure. You are allowed 7 PSI difference between injectors. I test them all and hope they all work. If you have 3 that are 210 PSI and three that are a bit higher or lower try and keep them together as sets of three so that they all open close to the same pressure. The biggest problems with running will be at idle when a very small amount of fuel comes out.
Once you have the injectors pressure tested and matched as sets pull all the distributor blocks and have them cleaned as well. Hook everything up and pressure test the complete system as you would find it on the engine. If the distributor blocks are clean and flowing properly the same amount of fuel will be injected by all three injectors. If one is less or nothing comes out all the fuel will go out the other two injectors. You do this on a test bench with a stop watch and three vials to hold the test oil. Any reduction at this point will be a plugged distributor block. Good injectors are very hard to find and new ones can't be had as far as Iknow.

This system works on pressure in the system of pipes, blocks and injectors. If one part is plugged or weak it won't run. I finally got one good injector I needed for a 220SE cab I'm working on and it was like a completly different car. It went from rough running and missing to a smooth runner.

I doubt very much that you or anyone can actually hear a prefectly working fuel injector while the engine is running. In this particular car a blocked line or broken injector might be making some strange noise but you can't hear a working injector. They make noise when you test them but they really don't inject that much fuel during running conditions. The amount you see during testing is far more than you would see during running.
The pump timming on these engines is TDC on either stroke.

[glennard]

Hi, It is an interesting transition from the two plunger/two x three injectors to the six plunger pump with associated injector.  The two plunger pump setup didn't really synchronize the fuel charge with the piston position-two could be.  The six plunger synced the injection to intake- kinda like the diesel. The later Bosch CIS(continuous injection) went back to 'fill the intake passage'.  (sic)Transit time at high rpms!!  Direct injection coming soon to an internal in your neighborhood??

[ja17]

Hello Glennard,

Yes an interesting observation. One varialble spray all at once does all cylinders on the CIS injected cars.  This is why a very precise setting for the fuel delivery is not that critical even on the six plunger pumps of our W113 cars. I guess you could deduce that the intake valve itself is the precise valving mechanism for fuel delivery after the injector atomizes the fuel!
Now a diesel with direct injection is another story. fuel delivery must be precisely  within a degree or two.

[glennard]

Joe, The fluid mechanics(what is that?) of moving a fuel charge from dead stop to motion when the injector opens into an open intake valve at 7000 rpm is - wow!  From the tip of the injector to the far reach of the cylinder is 3-4 inches.  The intake valve is only open for a fraction of a millisecond and the injector is open for -how long?  Seems the velocity of the fuel charge has to be pretty high.  That's why MB just went to CIS?  CIS has a misty charge continuously above the intake valve ready for it to open.  Effectively the same as plungers at high rpm.  That's my story and I'm sticking to it.--------  Direct injection is coming???  Hope and Change we can believe in??

Also, What is the overhead cost of a mechanical pump and the hp to drive it vs. a single electric fuel pump atomizing the fuel thru the fuel distributor in the CIS?

[kdlemon]

hi guys

thanks for the comments, i am taking it all in!

basically i have been chasing a "pinging" problem, which largely goes away when hot. i can retard the timing to the point the car backfires/falters and it'll still make the noise. when cold, and the system is pressurized, i can hear a noise like running a fingernail (3 or 4 pulses) over a radiator core (but louder and hollower)when number one or six exhaust valve opens. if i undo the lines at the pump, the noise goes away. similarly, if i turn it over when hot, the noise is only very occasionally there, at worst one pulse for ever second crank rotation. its not hard to imagine this is the noise i'm hearing.

when the car is running, if i use a stethoscope on any part of the injection system, it is very loud and clacky. the rest of the engine has a smooth hum through the stethoscope.

the noise seemed to increase when i corrected the pump oil level. it was previously filled almost to the top.

but i just don't see how injectors can make this sort of noise! when cold the car is really undriveable because of the noise, but it almost goes away when hot.

where might i find the cold start guide?

thanks!

[ja17]

Hello kdlemon,

Try using your stethescope on the injection pump. Possibly the centrifical flyweights in the back of the pump are rubbing on something internal.

[kdlemon]

Joe.

i have used a stethoscope on the pump, and it does sound quite clattery, though i have not tried to see if it is any different hot or cold.

i found the starting aid tour on the right, but it says it is restricted, and won't let me log in, though i am a member of the forum. is there a trick to it?

kaydee

[ja17]

Hello kaydee,

Try this link for the starting aid tour

http://sl113.org/forums/index.php?topic=5486

[Peter van Es]

quote:Originally posted by kdlemon


i found the starting aid tour on the right, but it says it is restricted, and won't let me log in, though i am a member of the forum. is there a trick to it?

Yes there is. It's called a Full Membership.

Peter

[glennard]

Valve cover stands rubbing on cam shaft?