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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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Old 03-09-2010
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Question Rebuild Injectors - Fuel Consumption?

I dropped my injectors off today to have them rebuilt. I'm hoping it improves cold starts and lowers my fuel consumption considerably?

Currently the engine averages about 1.5 gallons/hr Most other T37C owners say they average about .75 gallons/hr so I know something is out of wack. (I have a Westerbeke 50 41hp 1980's era with about 3500 hrs)

I also had the injector pump rebuilt by the same guys last fall and saw noticeable improvements in the smoothness of the engine, and less vibration it seems. I didn't see any noticeable improvement in fuel consumption however...

Any other ideas whats going on pertaining to the unusually high fuel consumption?

BTW: A plug for Arundel Injectors, near BWI Airport. Excellent service, reasonable costs, and in my experience they have completed the work BEFORE their said completion date and at or under the estimate. My Injector Pump looks and runs like a brand new one. I highly recommend them if your in the Baltimore/Annapolis area.
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Old 03-09-2010
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What kind of RPMs are you getting at what speeds....if your prop is wrong, you'll use a lot more fuel to go the same speed as other boats. What prop diameter/pitch are you using compared to what other T37C owners have.
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Something definitely sounds out of wack if your fuel consumption is that high. The natural tendency is to immediately blame the engine although there is often a different culprit. The energy has to go somewhere so you are either not burning the fuel, it is being lost as heat, or it is being lost to doing useless work in the water.

The first thing to look at is the person operating the throttle. Do you like to motor around at hull speed and 3000rpm? The fastest way to increase fuel consumption is to throttle up. If you motor around at 2/3 of hull speed, then this isn't the issue.

What are you running for a prop? Is it a very inefficient blade design? Is it damaged or fouled with sea life? Is it properly pitched? You can tell that this is in the ballpark by making sure that you can reach both hull speed and redline rpm.

It is unlikely that the problem is in your shaft since there would be another problem to dissipate that much energy. It is possible that you have a transmission problem. Does the transmission operate normally? Is it scalding hot to the touch?

Then you get to the engine itself. The first thing to do is check all your filters to make sure that they are clean so that the engine is getting good fuel and air. Then take a look at your exhaust, is there a lot of black smoke under load or unburned fuel coming out? If something is coming out, you have a problem which needs to be diagnosed. A poorly tuned engine will get worse fuel economy but it is hard for one thing to make the engine burn double the fuel. Valves that are out of adjustment will decrease fuel economy but by something like 10% max. If the engine's timing has slipped, that can have a very large effect.

To answer your original question, I doubt that you will see large improvements from getting your injectors rebuilt unless there was a major problem beforehand. Your injector tips can get carbon buildup on them which causes the fuel not to atomize as well but this usually does not have a large effect. In addition, over time the holes in the injectors will get larger flowing more fuel less efficiently but this doesn't have a huge effect. If one injector was hanging open, you could see this drop in fuel economy but you should have noticed other problems as well such as black smoke, unburned fuel in the exhaust, the engine not sounding right.

Unfortunately, there are a lot of factors at play. If the problem is in your engine, a good ear should be able to hear the problem the vast majority of the time. Don't rule out all of the other factors too soon.

Good luck.
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Old 03-09-2010
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Hey you guys were supposed to answer my questions, not ask a bunch others!!! LOL

If memory serves me right, at 2200 rpm results in about 6-6.5-7 knots SOG, at 2600 I get about 7 -7.25 SOG, at or close to hull speed, 1500 will give about 5 SOG.

Prop is a 3 blade Autostream, I cannot remember what the pitch is set and what the diameter is at the moment, info is on boat...but i have spoken to Norm at West by North about it when I removed it to replace my cutlass bearing, all seemed right then. There is no fouling on the prop, always clean of barnacles and slim. Maybe I need to chat with Norm again


I have seen fuel exiting into the water from the exhaust, not allot, but enough to notice a slick on still water, one of the main reasons for wanting the injectors rebuilt.

The fuel filters are changed at least once a year, if not twice.

The injector pump was "tuned" or timed when reinstalled? However, nothing else was.

Thanks for the responses so far...

Last edited by T37Chef; 03-09-2010 at 10:41 PM.
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Old 03-09-2010
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Quote:
Originally Posted by T37Chef View Post
Hey you guys were supposed to answer my questions, not ask a bunch others!!! LOL
Nah, asking more questions is more fun...
Quote:
If memory serves me right, at 2200 rpm results in about 6-6.5-7 knots SOG, at 2600 I get about 7 -7.25 SOG, at or close to hull speed, 1500 will give about 5 SOG.

Prop is a 3 blade Autostream, I cannot remember what the pitch is set and what the diameter is at the moment, info is on boat...but i have spoken to Norm at West by North about it when I removed it to replace my cutlass bearing, all seemed right then. There is no fouling on the prop, always clean of barnacles and slim. Maybe I need to chat with Norm again
This doesn't answer whether the prop is pitched or sized properly...

Quote:
I have seen fuel exiting into the water from the exhaust, not allot, but enough to notice a slick on still water, one of the main reasons for wanting the injectors rebuilt.

The fuel filters are changed at least once a year, if not twice.

The injector pump was "tuned" or timed when reinstalled? However, nothing else was.

Thanks for the responses so far...
Be interested to hear about what other T37C owners have for prop pitch/diameter.
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Old 03-10-2010
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I think you will see an improvement in gph. Over time the injector nozzles can get worn and the result is the fuel is squirted into the cylinders instead of being atomized. If you are seeing a bit of a slick from the exhaust it's a good indication that you've got injector problems.
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I would agree with jrd22 that if you see fuel coming out the exhaust, chances are you have an injector problem that is hurting your fuel economy. Either you are not atomizing fuel or an injector is staying open to get raw fuel out the exhaust.

They would have to be pretty bad to be loosing that much fuel so there still is a chance that something else is up. You should know once you get your rebuilt injectors in and run it some.
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Injectors alone won't account for a 100% increase in fuel consumption. The prop is the logical place to look.
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I don't think the prop would increase fuel consumption if it's pitched properly. The prop could cause you to have to run the engine at a higher throttle setting to achieve the same boat speed if it was fouled or under pitched, or in the case of over pitching it could cause lugging and black smoke which would cause increased fuel consumption, but the OP said rpm's were normal IIRC. As long as the engine is able to turn the recommended WOT underway (not over pitched) fuel use should be normal IMHO. 1.5gph is way over what a 50 hp engine should be burning at recommended cruise rpm (our 62hp averages 1.0gph). If the prop were improperly pitched, or fouled, resulting in double the gph rate I think there would be a lot of black smoke in the exhaust. I would guess you could burn 3-4gph at WOT with 50hp.
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Old 03-10-2010
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Quote:
Originally Posted by jrd22 View Post
I think you will see an improvement in gph. Over time the injector nozzles can get worn and the result is the fuel is squirted into the cylinders instead of being atomized. If you are seeing a bit of a slick from the exhaust it's a good indication that you've got injector problems.
Ditto that:

The issue could still be partly in the pump as well.
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