OM603.960 Low power, high consumption - PeachParts Mercedes-Benz Forum

FrodeS · #1 10-30-2010, 07:53 AM

Hello, all.

I own an 1992 MB 300 TD Turbo with the OM 603.960 147 HP Turbo Diesel engine. (car is Europeean, this is basically the same engine as sold in USA as 1987 300 TD Turbo)

Current mileage is 316.000.

I've owned this car since 178.000 miles.

The problem with it is a lack of power, and increased fuel consumption. I can get 32 mpg out of it if, but usually it end up around 28. The first years I had the car, I had no problem getting 36 mpg out of it. When towing a caravan or 2 ton trailer, consumption can go up to 15 MPG. It used to manage 22 earlier.

this is done :
-Measured the boost : Correct at approx 0,85 bar (12,5 PSI), but it seems to drop when revs goes over 4000 rpm. At 4600 rpm where next gear is engaged, boost is down at 0,7 bar (10 psi). When "new", boost was steady at 0,85 up to 4500 rpms.

- Injectors overhauled : This gave some more torque in the lower revs and faster spool up, but no more at the top, and no decrease in consumption.

- Timing chain renewed and timing adjusted controlled : No effect at all.

Car have been like this for some years. It runs fine, but it would be nice to have it like it is supposed to be.

The cylinder head was renewed at 250.000 miles. The new head was from one of the earlier models (1987 / 1988) with different injectors. It had not been used for 2 years after overhaul.

Oil consumption is "normal", like it has always been, uses 1 liter each 10.000 km. (1/4 gallon each 6250 miles)

Where to go next?
All suggestions are welcome.

FrodeS · #2 10-30-2010, 08:01 AM

BTW.
No catalyc converter and no EGR on this one (original)

babymog · #3 10-30-2010, 11:32 AM

Is there any visible smoke? Normal? If no smoke, it would have to be a restriction of either air or fuel.

Fuel can be filters, including the tank strainer, air can be intake or exhaust.

The only other thing can be the governor function of your injection pump, which does decrease in RPM over time, but not nearly as likely as the others (nor as inexpensive to check).

FrodeS · #4 10-30-2010, 03:03 PM

Quote:

Originally Posted by babymog

Is there any visible smoke? Normal? If no smoke, it would have to be a restriction of either air or fuel.

Fuel can be filters, including the tank strainer, air can be intake or exhaust.

The only other thing can be the governor function of your injection pump, which does decrease in RPM over time, but not nearly as likely as the others (nor as inexpensive to check).

Hello. There is a little black smoke before the boost build up, but then nothing. I've had friends driving behind me to look for smoke.

If the governor function is malfunctioning, how will that influence on the consumption?

babymog · #5 10-30-2010, 03:18 PM

The consumption is puzzling. If there is no smoke, then it appears that the engine is burning clean. If it were consuming significantly more fuel at reduced power, it should be partially burning the excess fuel, and producing smoke.

In this diagnostic suggestion, I had eliminated one of the factors: the increased consumption as it conflicted with the other symptoms, hoping that it is either a measurement error or unrelated as a dragging brake, alignment change, etc. If it has occurred over a long period of time it might not be engine related and frankly 32mpg if you're driving 70mph-75mph seems quite good.

If I put that symptom back in, to make sense I would need to remove another symptom like the good boost at low-mid RPM to pull any other diagnostic opinion from my bag, then I'd throw in things like restricted exhaust, an exhaust leak pre-turbo, intake air leak, sticking AFM, bad turbo, bad timing, most of these needing more smoke or reduced boost.

Eliminate the things that are working properly: ALDA, turbo and wastegate, cylinders & heads, valves. Really only leaves the intake, exhaust (restrictions), IP governor, and fuel delivery IMO.

What is your max. RPM under load? Un-loaded? Does it have problems reaching the full-throttle shift points?

FrodeS · #6 10-30-2010, 03:45 PM

Hello, thanks for your thoughts. There might be a small leak before the turbo, but not a big one.

My brake discs have done 100 k miles, and the brake pads around 40. They are still good for lots more, so there is no faults in the brakes.

Power is good in the lower RPMs, but decrease in the higher. It does reach shift point at 4600 rpm pretty fast in 1. gear, takes some time in 2., and it struggles for a long time before reaching shift point in 3rd gear. I tested the car at higher speeds in Germany last summer. Top speed is supposed to be 121 mph. It pulls OK up to 80 mph, but then it starts to struggle a bit. At 95 mph it really starts slowing down, and getting it from 100 to 105 took "ages". I don't think it would go over 110. This support my feeling that there is 20-25 hp or so missing.

My measurements are right, I alway reset the counter when I fill up the tank, and I don't really need to calculate mouch. We measure volume in liters (3,8 liters = 1 gallon , 1 tank = approx 60 liters), and we measure distance in "mil" (10 km). The car normally uses 1 liter for each mil. This means I fill as many liters as I drive "mil". This is 23,52 MPG, and that is almost exactly the consumption at normal driving.

I might have miscalculated in my first post. Normal consumption is 24 mpg. The best I can do is 26. Towing the caravan, I get approx 13 mpg.

Some years ago, I would get 32-33 on normal driving.

Tecnical data say:
56 mph : 39 mpg
75 mpg : 29 mpg

babymog · #7 10-30-2010, 09:25 PM

The Technical Data mileage figures posted seem high for a sedan, unrealistic for the T-sedan. Still, if you found that you were getting this mileage at one time, seems that something must have changed. Certainly the top speed figures are weak, and I expect that 0-55 is no longr 8.5seconds.

Can you push the car fairly easily on level ground or is it difficult? Have you changed to an inexpensive tire? How does the tire wear look? If there's no smoke, fuel consumption is up, boost is good, and power is down I can only postulate that you have some increase in drag causing your issue, or that your fuel has changed significantly to a lower BTU/h and/or lower Cetane. The lack of high-end boost however indicates a restriction either in airflow (intake or exhaust) or in fuel (which can be filters). Since the shift point is only 4600, which from memory seems low, it is hard to tell if the governor / high-idle setting is low enough to be in the throttling zone where it is starting to reduce fuel flow too early.

Have you tried shifting it manually to see what max RPM it reaches and whether it is within spec?

layback40 · #8 10-30-2010, 09:39 PM

You havent mentioned if you have ever replaced the air cleaner element. Pull it out & take the car for a short drive. See if the power is any better. If you have an EGR on it, you could have a blocked up inlet manifold.
You may also have low fuel pressure because of the pressure control on the return fitting at the IP is weak.

Has the car been running progressively warmer? That extra energy from extra fuel burn must be going some place. My guess is that you wont see much smoke out the back as the cat converter takes care of that.

Good luck with your diagnostics

Bio300TDTdriver · #9 10-30-2010, 10:56 PM

Quote:

Originally Posted by babymog

The Technical Data mileage figures posted seem high for a sedan, unrealistic for the T-sedan. Still, if you found that you were getting this mileage at one time, seems that something must have changed. Certainly the top speed figures are weak, and I expect that 0-55 is no longr 8.5seconds.

Can you push the car fairly easily on level ground or is it difficult? Have you changed to an inexpensive tire? How does the tire wear look? If there's no smoke, fuel consumption is up, boost is good, and power is down I can only postulate that you have some increase in drag causing your issue, or that your fuel has changed significantly to a lower BTU/h and/or lower Cetane. The lack of high-end boost however indicates a restriction either in airflow (intake or exhaust) or in fuel (which can be filters). Since the shift point is only 4600, which from memory seems low, it is hard to tell if the governor / high-idle setting is low enough to be in the throttling zone where it is starting to reduce fuel flow too early.

Have you tried shifting it manually to see what max RPM it reaches and whether it is within spec?

Jeff,

My wagon shifts at 4600 and I think that is correct. I get 23 mpg with 95% city driving and burn B-25 to B-100. I have gotten 28 with all highway driving. You might be on to something with the governor.

FrodeS where are you from in Norway? We are currently hosting an exchange student from Tromsø. What is the service history of the transmission?

Bio300TDTdriver · #10 10-30-2010, 10:57 PM

Quote:

Originally Posted by layback40

You havent mentioned if you have ever replaced the air cleaner element. Pull it out & take the car for a short drive. See if the power is any better. If you have an EGR on it, you could have a blocked up inlet manifold.
You may also have low fuel pressure because of the pressure control on the return fitting at the IP is weak.

Has the car been running progressively warmer? That extra energy from extra fuel burn must be going some place. My guess is that you wont see much smoke out the back as the cat converter takes care of that.

Good luck with your diagnostics

Per post #2 no EGR.

babymog · #11 11-01-2010, 01:37 PM

B25-B100 is a significant range in energy content, all slightly lower than pump diesel. Are you comparing to old low-sulfur pump diesel?

Regardless, the boost drop does indicate something is not right.

FrodeS · #12 11-01-2010, 02:32 PM

Sorry I haven't had the time to comment yet.

Quote:

Originally Posted by babymog

The Technical Data mileage figures posted seem high for a sedan, unrealistic for the T-sedan. Still, if you found that you were getting this mileage at one time, seems that something must have changed. Certainly the top speed figures are weak, and I expect that 0-55 is no longr 8.5seconds.

I don't know the 0-55 mph spec, but the 0-100 km/h (0-62 mph) is 10,9 sec for both W124 (wagon) and S124 (estate). Consumption is also the same.

Quote:

Originally Posted by babymog

Can you push the car fairly easily on level ground or is it difficult?

As I said, this has been going on for quite a time, so if this was due to friction, I would have known long time ago because of something being worn out very fast. I've been thru different sets of tires, with no influence on consumption or power.

Quote:

Originally Posted by babymog

The lack of high-end boost however indicates a restriction either in airflow (intake or exhaust) or in fuel (which can be filters). Since the shift point is only 4600, which from memory seems low, it is hard to tell if the governor / high-idle setting is low enough to be in the throttling zone where it is starting to reduce fuel flow too early.

I am pretty certain the issues I am experiencing is because of the engine not being able to use the fuel as efficient as it is supposed to, therefor demanding more fuel to do the same job, and not being able to deliver enough power. As I said, I -think- this is why, but I am listening to all theories.

Quote:

Originally Posted by babymog

Have you tried shifting it manually to see what max RPM it reaches and whether it is within spec?

I have tried, but I don't like it. 4600 rpm is the correct shift point, it is where max power is, and it also shift corretly as the shift points in the taco indicate. 1-2 is at approx 60 km/h , 2-3 at 96 km/h and 3-4 at 140 km/h (divide on 1,6 to translate into mph)

babymog · #13 11-01-2010, 02:35 PM

I guess I have my wagon shifting high, seems like it's around 4900. I'll have to floor it today and see. I guess I don't drive full-throttle often enough.

FrodeS · #14 11-01-2010, 02:36 PM

Quote:

Originally Posted by layback40

You havent mentioned if you have ever replaced the air cleaner element.

Good point, but all filters (air, both diesel, hydraulic, oil, steering) and all oils (engine, gear box, hydraulic, differential, steering) are changed regularily, and always at or before the point Mercedes say.

Quote:

Originally Posted by layback40

You may also have low fuel pressure because of the pressure control on the return fitting at the IP is weak.

Can you explain this a little more?

Would that increase consumption and decrease power?

Quote:

Originally Posted by layback40

Has the car been running progressively warmer? That extra energy from extra fuel burn must be going some place. My guess is that you wont see much smoke out the back as the cat converter takes care of that.

No EGR, no Cat.
Temperature is normal.

Quote:

Originally Posted by layback40

Good luck with your diagnostics

Thanks :-)

FrodeS · #15 11-01-2010, 02:43 PM

I got a tip this weekend that might be worth digging into.

I was representing the club at the Oslo Motor Show trade faire. I found a stand with some turbo overhauling company and explained the problem to them. They knew the 300 TD Turbo very well and told me there is a common problem that soot build up in the wastegate, making it leak. This would make the turbo slow to spin up (check), increase consumption (check) and reduce boost at higher rpms (check).

I was reccomended to remove the pipe from the compressor, and apply air pressure to it from a normal power tools compressor. This would make the wastegate open and shut a lot faster than normal and with more power. If a little lucky, this would make the soot come loose, and the wastegate being able to close normally.

Does this make sense??