Excessive fuel consumption

[Jagsare1]

Twin inboard setup. 5.7 liter carbed small blocks.<br />They are 2000 models installed in 2001 with approx 550 hrs on them. Religious maintneance. The boat runs perfect and sounds perfect. I have a floscan that shows the stbd burns significantly more than the port engine(but only at 3000rpm cruise). Port burns 9gph and the stbd burns 12gph at the same rpm. Had the props redone to make sure and the problem continues. The stbd is losing a little oil after a long run but don't know exactly where it is going. The engines do not smoke and the oil is not in the bilge. I have replaced the plugs, wires, distributor, rotor but I am still burning too much fuel in the stbd side. Any suggestion where to look?

 

[Boatist]

Re: Excessive fuel consumption

First question I have is are you sure it is burning more fuel or could the flow scan just be reporting it burns more. Second are you sure both engines are running same rpms. If you do not have a syncroniser then I would take both engines to 3000 rpm shut one down and messure speed the back to 3000 rpm on both and shut other down and messure speed. If you find both engines are indeed runing same rpm and one actually uses more fuel then I would Timing first, carb adjustment second and Valves adjustments 3rd. Also check thermostat as if it running cold will use more fuel. Good luck.

 

[Trent]

Re: Excessive fuel consumption

Try swapping the flow scan transducers. And gages and see if the problem swaps sides.

 

[mabbott]

Re: Excessive fuel consumption

As already mentioned, check the accruacy of the flowscan by swapping.<br /><br />Then I would check the following:<br />- Timing<br />- vacuum at base of carb. are they the same?<br />- compression test....bad valve rings etc.<br />- swap the carbs from side to side and see if the problem follows.

 

[Trevor]

Re: Excessive fuel consumption

Is this a Racore floscan?<br />I have had problems with mine removed installed one that just told me total fuel instead of individual readings.

 

[Jagsare1]

Re: Excessive fuel consumption

Try to answer all. <br />Floscan readings were verified by the amount of fuel needed. Each engine runs on a dedicated fuel tank so it was easy to confirm Floscan readings. <br /><br />Timing has been checked and re-checked. <br /><br />By vacuum adjustment, do you mean fuel/air mixture? If not, I am not sure what that means. <br /><br />I do not have a synchronizer but when on the tower, I can clearly hear "sync" and the tachs are reading the same at that point. <br /><br />What carb adjustments are you recommending? <br /><br />The valves are non-adjustable. <br /><br />More info: A slight amount of water and I mean a drop or two of water got into a cylinder. I only noticed water had gotten in there because there was a salty tasting scale on the spark plug tip(plug had 19 hrs on it). We removed the valve cover and noticed the rocker arm and push rod in that cylinder looked different than the rest. Looked like heat got to them. We went ahead and replaced them. Before we replaced them, all cylinders had a compression of 170psi except that cylinder and it was at 160psi. Here is the strange thing, after replacing the rocker arm and push rod, the compression rose from 160 to factory spec 170psi? Makes no sense. The rocker arm and push rod seemed to be functioning normally, they just looked different. With that info, could there be some valve damage caused by the water that is causing higher fuel consumption? There is a slight "tick", like a valve tick, in or near that cylinder. Seems I am the only one that hears it but it is there without a doubt. <br /><br />2 mechanics have checked it out(without breaking down the engine) and have said it runs perfect! One suggested I not mess with a good thing. I know my engine and something isn't right. I want to fix it before I cause more damage.<br /><br />More suggestions?

 

[Boatist]

Re: Excessive fuel consumption

Jagsare<br />Ok time to tell us what you have.<br />5.7 L what? Chev, Ford or what?<br />What type lifters Hydrolic or solid, how do you adjust Valves, rocker arms or grind valve tops.<br />Carbarator or EFI?<br />Inboard or I/O, or What type drive system.<br />Motor turn same way or counter rotating, Right or left props.<br />Gas or Deisel<br /><br />Ok your compression sounds fine at 170. To get good fuel mileage you have to get lots of air into the cylinders. That means the backflame arrestor needs to be clean the choke system has to be opened all the way up, the intake valves have to open wide.<br /><br />Your fuel system has to mix fuel air to proper ratio. Carbrator adjustment set right. Power valve or metering jets working correctly. No vaccum leaks, vaccum at base of carbs the same.<br /><br />Valve close and compress fuel air, 170 is good. Next must get GOOD SPARK on all Cylinders at right time at all rpms. So check Timing at adel speed and also at 3000 RPMS. Check proper plug Gap.<br /><br />After burn fuel must open exhaust valve wide and get exhaust out. No restrictions in exhaust flow.<br /><br />Engine has to turn you drive system. Drive system must have oil, no bent shaft or bad bearings, Props must be clean Straight and right pitch and right angle to the water.<br /><br />Good Luck and tell us what you have if you really want help. Someone will know your system.

 

[Jagsare1]

Re: Excessive fuel consumption

Boatist, some of the info you requested has already been mentioned but I want to put it here so no one has to go to the top to see it all. To the point with no fluff. <br /><br />5.7 GM block. Marine Power brand. Gas.<br />Lifters? Don't know type. This is a Vortec engine. Roller? I was told valves are not adjustable. Has rocker arms. <br />Carbed engines.(Edelbrock carbs)<br />Straight inboard. Counter rotating.<br /><br />Flame arrestor is always clean. I am fanatical about maintenance. <br /><br />Haven't checked timing at 3000 rpm's.<br /><br />Drive system: No vibrations, props just re-conditioned to eliminate that from the problem list. <br /><br />You touched on something that a retired mechanic friend mentioned. Possible problem with the exhaust valve. When the drops of water got into the cylinder, the theory is that during compression, the water turned to super heated steam and that is what discolored the push rod and rocker arm. There is a "ticking" in that valve. <br /><br />Do you agree that my next action is to remove exhaust manifold and riser, remove valve cover, remove head and possibly remove intake manifold. This way I should be able to eyeball suspect internal components. What do you think? Thanks for the help.

 

[Jagsare1]

Re: Excessive fuel consumption

^^ to the top

 

[DJ]

Re: Excessive fuel consumption

Jags,<br /><br />A vacuum guage is a very powerful diagnostic tool on a four cycle engine. They're relatively cheap too.<br /><br />I would put a vacuum guage on each engine and compare readings.<br /><br />You are looking for a constant-non varying-vacuum reading at a constant speed. A varying vacuum reading usually indicates, timing issues, valve timing issues or valve leakage. Also compare the inches of vac. for each engine, they should be very close.<br /><br /> You should hook the vac. guage to a "ported" vacuum port on the carb base plates. You may have to "t" it in.<br /><br />Any v

 

[Jagsare1]

Re: Excessive fuel consumption

Thanks DJohns, That sounds very simple and I do 99% of all my own work but have never done that. I will look for a vacuum port and see what I find. Thanks again.<br /><br />I have an exploded view of my carbs and found what is called a " full-time vacuum port" and another called a "PCV valve port". Does this sound correct? Which should I use? What, specifically, should I ask for when I go to get a vacuum gauge?

 

[Boatist]

Re: Excessive fuel consumption

Jags<br />I have not worked on a GM 5.7L Vortec engine. Too me the fact that the compression is ok says Intake and Exhaust valves ok. Also Rings and head gasket. Since I do not know engine I am not sure how to adjust valves but GM trucks do have roller lifters. If valves were too tight you would have low compression so if any thing with the valevs it would have to be not opening enough. I might check exhaust manifold but see no reason to pull head. I do not know the valve adjustment for that engine but must be many truck owners that can help. All the GM truck engines have electronic fuel injection instead of carbs. I agree with Djohns to check the vaccum is a good idea. Vaccum in many carbs is what regulates the power valve or metering rods and controles fuel flow. Timing in most engines is very inportant in the GM 5.7L truck Vortec engine it is controlled electronicly. The static or idel timing should be the same and the advance curve also. most engines I have worked by 2000 rpms you have full mechinical advance. If engines are counter rotating advance will be in reverse directions. I think I would swapp carb first. You could just have a bad or stuck power valve in carb. I wish I knew more about the vortec engines as my next engine will either be a 4.6L or 5.7L Vortec EFI engine. Good Luck and please let us know what you do to fix it.

 

[Jagsare1]

Re: Excessive fuel consumption

Boatist, I will swap carbs to see what happens. This has been a frustrating problem because the engines run so good. If I didn't have a floscan, I would not have noticed the problem. Will definitely keep you updated on the problem.

 

[DJ]

Re: Excessive fuel consumption

Jags,<br /><br />You DO NOT want the PCV port, use the other.<br /><br />Most auto parts stores have a variety of guages. You may want to get the type that you can pump to induce vacuum or pressure. These are quite useful for other purposes too.

 

[desertmariner]

Re: Excessive fuel consumption

What was the final outcome of this discusion? was it the carb? or the distributer?<br />Rich

 

[boater4life]

Re: Excessive fuel consumption

You don't mention what drives you have but you have to remember that one engine will burn more becuse it is running your hydraulic steering pump, alternater, and seawater pump which require more power.. Usually these items are on the stbd side. I have twin big blocks with a Floscan and mine burns 2 gph more because of this. Being you have smaller blocks it is using more power. As mentioned in earlier post: switch your Floscan instrument wire connections for each engine. Try the easy things first, it's better than rebuilding. Good Luck!

 

[vinney]

Re: Excessive fuel consumption

Has this boat been repowered? If this boat has been repowered with the new style engines. You need to check the static line first. What year are the take out engines? Vinney

 

[vinney]

Re: Excessive fuel consumption

Water should not be in the cylinders. This is the number one issue you have. You need to solve this first. If you dont get a hold on this you will have premature engine failure or the cylinder heads will be off this engine many times. When you have had enough and sell the boat the next guy will go thru the same problem. I see this every day. You find these boats that have had many engines and the cylinder heads have been removed many times. No one ever fixes the problem. Low hour boats that have had many engines till the engine manufacture says no more.

 

[geriksen]

Re: Excessive fuel consumption

I have one for you that nobody has mentioned yet. You say that this boat has inboards and you have already done the props. Have you checked the cutlass bearings? A swollen, or worn out cutlass bearing will cost you rpm/economy. If you can't haul the boat to check them, grab the shaft couplings and try to turn them by hand. If the side that is using more fuel is harder to turn. Haul the boat and check out the cutlass bearing. The alignment should be checked as well. You have probably already done that. If the cutlass bearing is worn out, you won't feel it when you turn it by hand but it will chatter at speed. The only way to find that one is to haul the boat. If you decide that you are chasing a ghost in that engine it would be worth a look. We had a 340 Sea Ray that acted like yours and we tuned that engine until we were blue in the face. Then we turned the shaft and we found our problem. Replacing the cutlass bearing fixed it right up.