K-Jetronic vs. D-Jetronic - Page 2 - PeachParts Mercedes-Benz Forum

psfred · #16 08-16-2003, 11:16 AM

Tomguy:

Resistances are correct. Only the "sensor" with the rectangular plug on the manifold is connected to the ECU, the other two are a temp switch for the aux fan at 212F and the thermo-time switch for the cold start valve.

Black at the base and white on the tip means rich running, especially at idle.

The best way to adjust the mixture is to use a CO meter for both open throttle at high load (a dyno is best, just stand on the brakes with the engine in gear otherwise, set parking brake and make sure no one can get crushed if the brakes slip) and with throttle closed.

There is an enrichment at full throttle feature on the D-jet on this car, so that's where the black smoke comes from.

If the wires are OK on the connector for the air temp sensor, turn the allen on the MAP a quarter turn clockwise and set the mixture "wheel" on the ECU (up front, by the rad, under a rubber cover, peel the rad side end up) two or three click counterclockwise.

This should get rid of the puff of smoke, but remember, there is also an "accelerator pump" feature, and a puff of black smoke visible from behind the car isn't unusuall on these things. Setting them for milage rather than power should get rid of ti -- certainly you should not see smoke in the rear view mirror.

There is a big difference in power between the richest and leanest settings for the 4.5, though -- if you don't care how much fuel you burn and how stinky the air is, there is probably a 20-30 hp difference! I set mine to get at least 15 mpg, I'm trying for 17 in town!

Peter

Tomguy · #17 08-17-2003, 06:03 PM

Well, anything is better than the 10-13 it gets now

I'll have to wait till Monday or Tuesday - just moved back into school today and waiting for header pipes still

Tomguy · #18 08-20-2003, 11:41 PM

Ok to update:
Yes, the idle speed DOES change when the plug on the intake is removed/replaced.
Turned my idle speed screw CCW a bit and it did indeed raise my idle.
I turned my MAP screw 1/4 turn and the ECU screw 2 clicks and took it out up the road quick... seemed to be low on power, so I reset them. No change. Right now I turned the MAP towards lean again but left the ECU alone... still seems rich.

A couple things:
1) I didn't have a 100% working exhaust system before, but do now... so now I can tell how the engine sounds. Almost like it's struggling and pinging and/or misfiring... but not a miss, it's just... well, I can hear every fire of the engine. I checked the timing, 5 ATDC on the dot. I disconnected the vacuum, 7 BTDC on the dot. Neither change how it seems to run.
2) Seems to have low power... some struggling (it won't peel out at all! Seems sluggish in the lower RPM range especially in 2nd gear)
3) Still the puff of black smoke

Any ideas?

psfred · #19 08-21-2003, 12:28 AM

Does it pop off throttle decelerating? If so, way rich.

Turn the MAP a half turn clockwise and see if the idle smooths out -- sounds like it is "slobbering" -- my brother's term for over rich running. Sounds strained, has poor power, and is loggy.

If that doesn't improve things, try the other way -- go a full turn (the half you just put in plus another half) CCW on the MAP. If the idle speed doesn't change, and the engine note doesn't change, you have either a large vac leak (unlikely as the idle speed screw won't work if you do) or the MAP is questionable.

I'd also pull a plug -- if they are black, you probably need new ones. Bosch plugs are particularly bad about never cleaning off from rich running. The carbon fouling will cause bad enough missfire that you cannot set the misture "by ear".

Check the mechanical advance, too -- turn the rotor clockwise and let go -- it should turn against a spring and snap back to initila position without help. If it is stuck or won't snap back, the mechanical advance needs work (I'm going mine this weekend).

Tomguy · #20 08-21-2003, 07:23 AM

I'm 99% sure I have no vac leak(s)! I went over every line and hose.

When it needed the exhaust pipe, there was DEFINITE popping when I let off the throttle. Now I can hear it but not very loud at all (it's subtle but still there).

It's got Champion plugs. What are the best plugs for it, the NGK ones? I might get a set of those...

Tomguy · #21 08-21-2003, 05:09 PM

Ok, another update:
While it was idling, I fiddled around with the ECU and the MAP. The ECU seemed not to change anything, but I didnt turn it much. When I turned the MAP CW the engine slowed, and when I turned it CCW it went up. I turned it to the point where the engine stopped idling faster, and turned it a bit after that. This was going CCW.

psfred · #22 08-22-2003, 07:24 PM

Tom:

Put it back where it was, you were probably just about right. You are WAY rich now -- it will go like a stripped a.. ape, but it will eat fuel terribly!

I suspect you problem is the low temp -- it runs rich until you get to 175 or so -- I can feel mine lean out when the engine temp gets to normal. If you have a weak thermostat that isn't closing and it's not as hot as blazes outside, you can be running too cool for short distance operation. This will result in rich running.

A puff of black smoke when you suddenly open the throttle is normal on these cars -- there is a ten step "accelerator pump" feature on the throttle switch to momentarily enrich the fuel mixture on sudden throttle opening. Gives you that sudden leap of power, which is nice, but it burns lots of gas. I've learned to go easy on the pedal, and amy currently getting 15.5 mpg mixed city/country/highway.

You will have to turn the ECU wheel considerably if it is way off, and if the throttle switch isn't working properly, it will have no effect at all. Only does anything when the switch is closed.

Peter

Tomguy · #23 08-23-2003, 09:44 AM

Well, when on the highway, it didn't come CLOSE to 175! Probably 10-20 below the mark! So I guess I should get a thermo.
Also been thinking of pulling the plugs and manually cleaning them... some crap might be keeping them stuck open. It sat for ~5 yrs and I just put fresh gas in the tank and drained the lines, but didnt drain injectors or any lines under the hood, plus I had to replace 2 sections of busted line and I think crap (rust, dirt, whatnot) may have gotten in there.

tosbt · #24 08-23-2003, 08:34 PM

The orginall question on this particular tread has led to such woulderful information. I must congraulate myself for getting it started. well done lad! My car is still in the shop, trying to find replacement mufflers.

psfred · #25 08-24-2003, 12:30 PM

Tobst:

Have you tried the original header pipes (with crossover) in combination with the TimeValve mufflers?

Peter

tosbt · #26 08-24-2003, 01:34 PM

No, we took the rear off and then the front, the rear off was of little help, and to be candid when we took the front it was hard to tell because of both noise. Removing rear muffler did reduce some overheating but perfomrance was not there. The OEM front muffler was 16", the replacement was 13", I just cant get past that the front should have the same displacement ability as the original. We put the old system back on and ran like is was supposed to. My deal was why fight it. My old headers are fine all I really need it the proper mufflers plus connection pipes in the rear. What I did notice was on TIMEVALVE web page there appeared to be a crossover or a joined pipe in their picture, not so on the one they dilivered me. Thanks for your valued information I'm not much of a mechanic and you and others have really helped me with this car.

Darrell Woods · #27 08-24-2003, 02:52 PM

I've seen several references to the air temp sensor located on the air intake housing. I know my wires are bad, because the plastic connector broke and I currently just have the spades pushed on the connectors. I don't even know if they're on the correct side. As suggested, I pulled the wires with the engine running and there was no change in idle speed. As a result, I guess the sensor itself may be bad as well as the wires. Any suggestions from anyone who has purchased these regarding a good place to purchase. I did a short search for temp sensor, and all I got was "contact us for $$ and availability". My car is a '75 450SL, but the engine is a '71/'72 or '72/'73 4.5L from a 300SEL (117.981). Thanks.

psfred · #28 08-24-2003, 05:52 PM

Darrell:

Get an ohmmeter and check the resistance of the temp sensor at about 70F -- should be around 300 ohms. If shorted or open, replace.

Check the wires to make sure there are enough strands actually connected to the spades -- if there are only one or two, it will read high on resistance and make you run rich. I replaced mine, just find some spade lugs that will fit (we had them lying about) and crip onto the wires after cleaning them up on the end.

Tobst:

The physical size of the muffler isn't nearly as important as the back pressure it creates. It consists of the case and two sets of perforated pipes, or two short sections of perforated pipes, so that the exhaust goes out into the case (which is probably lined with fiberglass) and back into the other set of pipes. Some designs simply run the pipe straight through with slots in it. The only thing that really matters is flow resistance, and if the gasses won't go through, it won't run right. Note that is can ONLY be the case if there is something wrong inside, like a pipe not perfed. External size and internal size aren't necessarily related -- if the TimeValve is a single wall design (due to the supperior corrosion resistance of stainless steel) it may in fact have identical interior size.

If you originally had a crossover pipe, it WON'T run properly without one in place, you have a resonance of some sort in the exhaust that causes flow problems conpletely unrelated to mufflers, pipes, etc. All V8 SL 4.5's have a crossover pipe.

This is why I suggest trying the new muffler on the old headers. If they are in good shape, it should work just fine.

Peter

tosbt · #29 08-24-2003, 09:55 PM

Well the original equiptment has a crossover pipe, that is being joined above the upper muffler and has some cross flow before reaching the upper muffler. Timevalve did not send me the same with their system. I just no longer trust the timevalve system for my car, I think they know for most but for mine there is a slip up somehere. I do not know the interior configuration of the upper muffler but I know it is smaller that the original which makes me beleive their could be an internal difference. I have confidence in your advice, but just am not confortable with a shorter muffler.

psfred · #30 08-24-2003, 09:59 PM

Tobst:

My 280 SE 4.5 does NOT have a crossover pipe, and none is listed in the factory manual. This leads me to believe you don't a a typical installation, and you may need the crossover to cure a resonance problem peculiar to you particular car.

Worth a try anyway, as the new system didn't work and the old was is probably like mine -- rather "holey".

Peter