Advancing injection timing? - PeachParts Mercedes-Benz Forum

gsxr · #1 05-30-2002, 07:20 PM

Car: 1987 300D, 124.133
Engine: OM603.960, 3.0L, 6-cylinder with aluminum head

I just advanced the injection timing from the factory spec of 15 degrees ATDC to about 13 ATDC. Perhaps it's the placebo effect, but it *seems* to be a hair more responsive off idle and at lower RPM. The top end seems just as good if not a hair better (hard to tell). However, I'm getting a decent amount of smoke at full throttle runs to redline above about 3500-4000rpm. Not a huge cloud but enough to easily see in daylight. The smoke does not appear at lower RPM's. Has anyone else experimented with this? Should I expect a drop in fuel economy? Or am I the guinea pig?

Note: The head was recently replaced and I used a dial gauge to set the TDC indicator, so yes it is accurate. And I have the static RIV timing tool to set the pump exactly at 13 ATDC, it's not a guesstimate setting.

Best regards,

gsxr · #2 06-02-2002, 11:47 PM

Well, this thread sure got a lot of response (not!). What, no enterprising folks out there willing to fiddle? Anyway, I just returned from a 1300 mile round trip. Maybe it was a fluke but I got better mileage than ever before on the freeway, two tanks at ~32.5mpg and one at 31.x. This was mostly at 70-85mph, flat road, with some mountain climbing between CA and ID. I have done this trip the last two weekends and got consistently 28.x MPG each time.

I was a little softer footed this trip... but 32mpg? With 17x8.0 wheels? The best I ever got in the past was 30-31mpg under similar driving conditions, but that was on the skinny stock wheels & tires. The big wheels cut a good 10% off my mileage and I almost never got more than 27-28mpg after mounting them 18 months ago. Now, I advance the injection timing and get noticeably better mileage... hmmm. I wonder what it would do with the stock wheels on there, maybe 33-35mpg!

Or it all could just be a fluke, like I said. I'll be watching my MPG numbers carefully over the next few tanks...

Regards,

#3 06-03-2002, 12:07 AM

32.5mpg? At 70 to 85?? That is amazing. My routinely do a 240 mile round trip at 75 to 85 and I am still returning a very consistent 23.5mpg.

gsxr · #4 06-03-2002, 01:03 AM

Yep, the OM603 engines are remarkably efficient at higher speeds, plus the W124 chassis has a lower cd as well. From my experience, the MPG doesn't change drastically up to at least 90mph, perhaps 100mph. I don't know of anywhere in the USA that I can do extended periods of 90-100mph to find out. Oddly, the MPG doesn't improve much at lower speeds, it seems pretty constant between about 60-85mph.

BTW, the W124 is geared lower, at 75mph it's 3000rpm, at 100mph it's 4000rpm. I did a top speed run last weekend and saw 120mph and it was still pulling, I backed off due to a car coming - didn't want to chance it being the fuzz.

The best I've ever heard of from a W123 turbo is 30-32 but that was RARE and I have no idea at what speeds those numbers were attained.

#5 06-03-2002, 01:07 AM

120 and pulling? That is excellent also. My SDL took forever with my foot thru the floorboard to get to 110, and was really loosing steam. I'm guessing 115 max.

gsxr · #6 06-03-2002, 01:22 AM

I shouldn't say "pulling". The speedo needle was still sloooooowly creeping up and I don't think it was done yet, plus I wasn't at redline. It slows down over 100, and even more over 110. I think the top speed spec for the 124.133 is something like 122 or 125mph.

One of these days I'll get a GPS that will read over 100mph and try to find out exactly. According to the mile markers and my stopwatch, my speedometer is a few percent slow (larger wheels/tires) but the odometer is almost dead accurate, less than 1% slow. That's bad because I just got a ticket (in Nevada, on 95, in the middle of nowhere) when the cop tagged me at 90mph when my cruise was set at what I thought was 85. Oooops.

Luckily he lowered the speed on the ticket so my fine was less. My insurance agent's pupils just changed to little dollar signs, I bet.

#7 06-03-2002, 01:40 AM

Did the smoke appear after the timing tweak? If so, smoke can be indicative of less-than-optimal timing advance. Since the injection timing advance increases with RPM, advancing the idle timing may push the high RPM advance too high and result in some mildly incomplete combustion (from early injection).

If I ever set the ignition timing on gasoline or diesel engines, I always set it to the maximum factory tolerance. For example, the timing advance spec on my Peugeot TD is 7.0 deg BTDC +/- 0.75 deg. I set it to 7.75 degrees BTDC. This gives a little sharper throttle response (as you noted), but keeps the engine's smoke output pretty consistent.

The same thing has been done to the 190D when I replaced the seals on the injection pump. Now it feels a little closer to its 93bhp spec.

-Joe

#8 06-03-2002, 01:44 AM

I was reading where the 300D Turbo 3.0 liter was the fastest diesel powered passenger car when it was introduced. Of course, Mercedes-Benz has topped that with the intro of the E300 Turbodiesel a few years back.

According to this source, it claimed a top speed of 129 MPH for the '87 300D Turbo. Considering horsepower, torque, and aerodynamic drag, this figure sounds just about right.

-Joe

Dana B. · #9 06-03-2002, 02:04 AM

I have a '91 300D 2.5T (w124.128, 602.962). I get the same mileage, about 32.5 mpg, on the highway at around 80 mph.

Congratulations. Don't know about the timing/smoking issue, but sounds like you have a winner.

psfred · #10 06-03-2002, 07:41 PM

Advanced timing will give you more smoke, more power, and at lower speed, better milage. When the smoke appears, you will be getting less power for the fuel burned.

Sounds as if you are right on target for milage, though -- I get 31-32 consistantly with light AC usage, less in town and with heavy AC -- it is in the 90's here with high humidity, so the AC compressor never shuts off in traffic. Milage only varies a little -- lots of heavy accleration and/or grade climing will reduce it some, but in general diesels don't show the same decrease in milage in slow traffic that gas engines do. I get about 29 in the Volvo in town, but never more than 33 on the highway. Disappointing, as it has a 2.4L motor (105 horsepower, 145 ft/lbs torque).

I've gotten the injection timing screwed up on the Volvo -- lots of smoke and no power at less than 2000 rpm. The timing is a huge pain to set on this engine (belt driven pump, off the back of the camshaft with a friction driving gear ------!) and I think maybe the valve timing is off, too -- this weekend's project.

A young friend of mine asked me how much power my 87 had yesterday -- told him I thought it could out-do his roommates "new" '79 Ford pickup. I didn't realize I could outrun him, too!

If it were me, I'd set the timing back to 15 ATDC to eliminate the smoke -- diesel particulates are nasty.

gsxr · #11 06-03-2002, 07:50 PM

The 90-93 W124 diesels have a 2.5L 5-cylinder and get better MPG, they just have less power. 32mpg for one of those is normal on the freeway. The 1987's with the 6-cylinder don't often break 30mpg. On both of mine I usually get 22-25 in town (lead foot) and 26-30 on the freeway.

I might back it off to 13.5 or 14.0 ATDC to reduce the high-RPM smoke. However, since I don't often rev it up that high anyway, I wouldn't bother going back to 15. It doesn't smoke any more than before at ligher load and/or under 3000-3500rpm. XN6guy's idea was right on, 14 could almost be considered factory spec... :p

Jim Anderson · #12 06-03-2002, 08:13 PM

I used to play with the timing on my diesels and knew a guy who knew tons about diesels and their pumps. He mentioned too far advanced and you would put holes in the top of the pistons.

I also found a relationship between best timing and altitude, the higher the more advanced. But perfect up high might put holes in the pistons at the beach

Brian Carlton · #13 06-04-2002, 07:43 PM

Since you guys were discussing injection timing for the 300D, I have a couple of questions since I need to perform this task for the first time.

1) The Haynes manual refers to a timing of 24 degrees Before TDC for the turbocharged 300D. However, I see several posts of timing AFTER top dead center. Is the Haynes manual wrong?

2) Is is accurate enough to time the engine using the drip tube and the "1 drop per second" calibration spec? Or is this task better left to a shop with higher precision equipment?

Thanks for your help.

engatwork · #14 06-04-2002, 08:11 PM

There is a "mark" on the splined part of the injection pump that has to be lined up with the mark on the bearing cap when the injection pump is installed into the block. The engine has to be at 24 before TDC. The engine book goes onto say that if it is a Bosch injection pump code number "251" (November 1982) the mark for begin of delivery may be applied to the wrong spot on the bearing cap. It goes onto provide details of how to set it up if it has this code number if anyone needs it let me know. I have tried to get a photo showing the marks lined up on the IP.
The drip tube method works fine for me.

lrg · #15 06-04-2002, 11:14 PM

Do the mechanics at the dealer use a drip tube method or do they have a fancier method? I know the manual suggests the injection be retimed periodically but I've never done it. If the car runs OK I'm guessing no harm done. Or is there?