95 E300D: Poor fuel economy, wvo related?
 

*Skip to post #10 for a more up to date description and additional symptoms*

Over my last two tanks of gas, I've noticed that my tachometer has been reading a little high. During this time, my fuel economy has also dropped from the usual 26-28mpg, to around 22. Acceleration, coasting and general power all feel the same, so I doubt the breaks are sticking. I don't think a fuel leak would explain the above normal rpms. In a previous thread I had idling problems that were mostly solved when I removed some plastic garbage from the throttle linkage. My idling is much better but still a bit high (700-750). I have a bad feeling that it's a vacuum leak. There is a small (immeasurable width) crack running between the outer edge and a bolt hole in the intake manifold. It doesn't reach any air passage though. Yesterday, I replaced my crumbling intake gasket with a new metal one to no avail. The mechanics there told me I didn't need to apply gasket sealant so I didn't. The seal rings on my crossover pipe are still flexible and seem to be in good condition but I wonder if I could tell were they not. It seems that most of you replace them anyway. I've read that in order to find a leak you just spray carb cleaner in the suspected area and check for a jump in rpms. Does that work on the intake manifold, and would WD-40 work as well? I should also mention that there is a sheered thread in the third intake manifold bolt hole from the back if you're facing the engine compartment. I know it seems obvious, but I just want to make sure I've eliminated everything else before I end up possibly buying an expensive manifold. Something else I've noticed (may be unimportant) is that after a drive, the crossover pipe doesn't heat up. The manifold may be burning hot, but the crossover pipe remains at or near air temperature.

Something else perhaps worth mentioning
 

Could a bad/seized ac compressor have anything to do with this? The reason I ask is that since February, my ac has been killing the engine as soon as the compressor engages. Since then I have left the ac off or in economy mode, leaving the compressor wheel to spin freely. I guess the only possibility here would be that the wheel itself is seizing or something, causing the engine to work harder. Sounds unlikely now, but I just thought I'd throw it out there.

Bump
 

Anyone?

I think you think too much in terms of gasoline engine behavior. To my knowledge vacuum leaks on a diesel have nothing to do with mileage. I'm also assuming that when you say "last two tanks of gas" you don't mean it literally. ;)

I would free-spin all wheels to check for brakes sticking. I would also check all over the engine for fuel leaks. This includes under the black plastic cover where the injectors are. It is not uncommon to see diesel fuel pooling up in the injector wells if you have leaks. Is the air filter still in good shape? Another possibility is injectors, but if the engine sounds good at all RPM's, this is unlikely. Oh, and don't forget about tire pressure. Badly under-inflated tires can kill your mileage pretty quick.

As far as the AC compressor goes, if you're concerned that it's dragging even if it's off you could spin the engine by hand (using the crank bolt) or take off the belt and spin just the compressor. You just have to eliminate all these variables one at a time.

On a naturally aspirated diesel, the manifold runs at (virtually) atmospheric pressure - there's no vacuum to speak of. The engine will run OK with the intake manifold removed!

As already stated, check the obvious first; tyre pressures, brakes sticking, and fuel leaks! There are lots of places on OM606 engines where fuel can [and does!] leak out, including;

- the many low pressure connections, where the O ring seals fail
- the fuel heater
- the injector leak off pipes
- the fuel lift pump

As usual, I suspect if you keep running gas in that car, you are going to break it. Then it won't matter if the brakes are sticking or not.

What they said. Your original mileage of 26-28 is low to begin with and 22 is WAY low. My '95 with 263K gets 33 +/- and I track every single tank. There has to be something substantially wrong to get such low mileage. The crossover pipe stays cool because it is the path from which your engine sucks ambient air. If you check it immediately after driving it will be cool, if you let it sit and heat soak for a while it will be as hot as everything else.

I doubt you have vacuum issues. Don't bother buying a manifold. If you have a fuel leak, it would have to be massive to kill your mileage like that. It would be dripping like crazy somewhere. Keep looking... and let us know.

Rgds,
Chris W.
'95 E300D

You may check the wheel bearings to see that he wheels rotate freely when not braking. These can sometimes mimic a sticking brake but can cause much more severe issues than poor fuel economy.

Just jack the car up chocking the wheels and give each wheel a good spin. For rear wheels put it in neutral but be certain that the front wheels are chocked for safety. Good luck

If your tachometer is reading a little high, it is possible that the real problem is that the speedometer is reading a little low, which can easily lead to low apparent fuel mileage.

I would verify the speedometer and odometer accuracy first, then compare the tachometer to speedometer correlation with others driving '95 E300Ds.

If the engine is truly spinning faster than normal, it would indicate transmission slippage or a torque-converter failure. How's the fluid?

Yes, well, maybe if the price of diesel continues to rise higher than that of gas, it might eventually be cheaper to run on gas and have the engine replaced every couple of tanks. Anyway, I inflated my tires to spec about three weeks ago. Pressure hasn't changed much, if at all since then. When I jacked up my car to spin the wheels (spun pretty freely) I decided to change the parking brakes, one of which was down to the metal. I kind of doubt it's a fuel leak because I haven't seen so much as a drop of fuel come out of my car. Plus, as Chris says, it would have to be massive. There's nothing in the injector wells either.
Something did, however, come to my attention as I was driving on the freeway yesterday that might help explain some of this. I don't remember my exact speed (60 maybe), but as I stepped on the gas (not very hard) to speed up a little, the transmission down shifted for maybe a second then went back to 4th. This seemed very unnecessary as I could have easily sped up in 4th and I wasn't driving on an incline. Then, as I got off the freeway, the engine didn't really want to go back down to idle speed until I had almost completely stopped. It would hover at around 900-1000 rpms as if it had a very delayed reaction. I know this isn't just a bad tachometer because I could hear the engine running faster than it should have been.
This has actually been happening for a while. I guess the reason I hadn't noticed it sooner is that I have been running my car on diesel the past couple of months. I had a frybrid vegetable oil kit professionally installed around February. Perhaps I should have mentioned that but it didn't seem relevant until now. Why? Because I had my wvo tank filled up for the first time in a while on Friday for a trip to Santa Cruz. I haven't tested the down shifting yet, although, the rpms drop to idle speed much more smoothly on wvo than when running diesel. High tachometer reading remains at freeway speed.
If it's the fuel that is causing me problems then I'm kind of stumped. I couldn't really find anything relating to my issue on the Frybrid forum. Could it be that durring the conversion they adjusted the bowden cable or something to shift better on oil? I know they had to take off the intake manifold which required them to partially disassemble the throttle linkage. Anyway, I wouldn't be surprised if my problem has multiple sources. I will be replying more often now that I'm back as well.

b u m p

:confused: Not so easy I guess.

This has actually been happening for a while. I guess the reason I hadn't noticed it sooner is that I have been running my car on diesel the past couple of months. I had a frybrid vegetable oil kit professionally installed around February. Perhaps I should have mentioned that but it didn't seem relevant until now. Why? Because I had my wvo tank filled up for the first time in a while on Friday for a trip to Santa Cruz. I haven't tested the down shifting yet, although, the rpms drop to idle speed much more smoothly on wvo than when running diesel. High tachometer reading remains at freeway speed.
If it's the fuel that is causing me problems then I'm kind of stumped. I couldn't really find anything relating to my issue on the Frybrid forum. Could it be that durring the conversion they adjusted the bowden cable or something to shift better on oil? I know they had to take off the intake manifold which required them to partially disassemble the throttle linkage. Anyway, I wouldn't be surprised if my problem has multiple sources. I will be replying more often now that I'm back as well.[/quote]

from my standpoint, I think that the conversion should have been mentioned from the gitgo. The individuals that answered your posts, did so on the assumption that you were running standard diesel fuel that was called for in the owners manual, and were basing their suggestions on that assumption. Now, the conversion is mentioned, and anyone running a standard system is in the dark as to what was done, who did it, and what effect the conversion would have on your mileage. I don't mean to sound harsh, but when modifications are made to a car, those modifications sometimes cause issues that are detrimental to the car in question. When I see a post concerning WVO, I pass it right by because I have no idea what the effect of running that fuel would have on a car, and can be of no help regarding suggestions. Good luck with finding an answer to you problem.

X2.

Is it possible the fuel return lines were botched up? Maybe the return fuel circut when you are running on Diesel is being routed to the tanks used for WVO? Maybe the switchover valve for the return line is stuck?

I know. Those were exactly the answers I wanted at the time. My problems were occurring while running on diesel, not wvo. Because much more is known of running these cars on diesel, I thought (correctly as it turns out) that I would get more answers this way. If I was lucky, maybe I would have found that one of the above suggestions were true and I wouldn't have to worry about my conversion. I haven't mentioned it in any of my other threads and you guys have helped me solve problems that could have been complicated by something that turned out to be unrelated. If I thought my conversion was involved from the beginning I would have mentioned it in the beginning. However, at the time, I hadn't ran wvo for months. Based on what I've said previously, it is looking like my conversion has something to do with it, but I still think it's entirely possible that my cars symptoms have multiple sources. If your expertise is in diesel, I am still open to your suggestions.
I honestly don't know whether those possibilities could cause the problems I am having. My wvo tank has been empty since March, so I don't think it's trying to drive on cold oil. In a little while, I'm going to the mechanic who installed my kit, and I will run all that by him.