4B150 Cummins in boat

[SnoKing]

I have two 4B150's in my boat. They are rotory pump injection. They are rated at 2800 RPM Max. I do not run them very hard most of the time. 1500-1600 RPM. I was changing oil (Get rid of CJ-4 Delo) and I decided to run them up to make sure that they are still running to spec. Well the port one peters out just over 2600 RPM and the starboard one continues to gain RPM's past 2700, but is being held back by the weak one.



The engines have 1700 hours on them and have only had routine service, and the valves adjusted at 200 hours. I changed fuel filter primary and secoundary and have the same results.



I was thinking about getting someone to drive while I use the infrared heat gun on the exhaust ports to see if one cylinder is weak or all.



They have the small mechanical lift pumps like my 93 Dodge/Cummins had. I have spares for those.



I was thinking about trying to connect my 24V service fuel pressure gauge to verify the fuel pressure.



Any thoughts? Other than this condition, they both seem to run fine, and use the same amount of fuel running at 1600 RPM's, based on 80-90 gal fuel ups.



SNOKING

 

[dpuckett]

That's just the nature of the beasts. Are the "twin" engines the same CPL? If not, that could be the cause, as different CPLs will have different injectors, fuel rates, springs, etc, etc. Some pickups will turn 3000rpm all day long with stock internals; others take a 366 governor spring to get to 3000.



Daniel

 

[SnoKing]

The are the same engine, at in the past have turned the same RPM at WOT. I rigged up my test gauge and it has only 7 lbs of fuel pressure at idle and 2500 in neutral. I will have to take it out of a test with the gauge install to see if under load the fuel pressure pulls down to zero. Anyone know what first gens have for fuel pressure idling? It is the same or similar lift pump. SNOKING

 

[PToombs]

5-7 idleing. Shouldn't drop below 3 or so at WOT, under load.

 

[KOG]

It would be worthwhile to examine the props VERY carefully. Even better would be swapping them to confirm that it's an engine problem and not some subtle prop damage that's almost undetectable.

 

[SnoKing]

Well here is deal, at around 2600 RPMs it does not continue to increase as that throttle continues to move forward. The props are one left and one right hand so they can not be reversed. I will do a test run tomorrow and if fuel pressure stays up, I will put the infrared heat gun to work on the exhaust ports. I also have fuel manifolds and can switch the engines for run on the opposite tanks. SNOKING

 

[KOG]

Is one of these a reverse rotation engine or do they have different gearboxes? In either case they must have reverse available so you could switch them if necessary. It does sound like an engine/governor problem, but I've seen some weird stuff with props before.

 

[InfernoB]

Check throttle lever travel at the pump, check fuel restriction, make sure your tachs are right. What is WOT no load RPM? As it stands now you are not making rated RPM.

Rated RPM is 2800, so you should be around 2968 to 3080 no load per spec.

Any smoke?

How's the bottom, and your shaft bearings? Props been changed/tuned lately?

 

[SnoKing]

Is one of these a reverse rotation engine or do they have different gearboxes? In either case they must have reverse available so you could switch them if necessary. It does sound like an engine/governor problem, but I've seen some weird stuff with props before.

Reverse rotation is handled in the gearbox. SNOKING

 

[SnoKing]

Check throttle lever travel at the pump, check fuel restriction, make sure your tachs are right. What is WOT no load RPM? As it stands now you are not making rated RPM.

Rated RPM is 2800, so you should be around 2968 to 3080 no load per spec.

Any smoke?

How's the bottom, and your shaft bearings? Props been changed/tuned lately?

*Check throttle - Did that.

*Check fuel restriction - changed filters and will run today with fuel pressure gauge.

*Any smoke? - no

*How's the bottom, and your shaft bearings? - Fair, I used a 3M scratchy pad on it swimming a month ago. Cleaned the barnicles off the props and rudders.



This appears to be fuel related somehow. If it was air related, I think that it would smoke badly. With the fuel pressure gauge and infrared heat gun, I should be able to figure out more today.



SNOKING

 

[InfernoB]

Put a vacuum gauge between the primary filter and the engine. If there is more than 4 inHg restriction, than you have a problem with the fuel intake.

Lift pump pressure is . 5 to 10 psi.

When they warm up, check the no load, and confirm you get the WOT RPM of around 3080. Could be a pump getting tired, but hard to say in internet land.

 

[Don Tanklage]

how could his pump be getting tired?



i thought @ 1700 hrs the thing was not even broke in yet?



don



ps - and how do you check for vacuum between the filter and the engine?



shouldnt that be under pressure, not vacuum?

 

[SnoKing]

Primary filters on boats are ahead of the lift pump. I vacuum gauge installed between the lift pump and the filters/tank will show a vacuum reading if the pump is having trouble pulling fuel thru a dirty filter. Very common to see these install in boats.



SNOKING

 

[Don Tanklage]

oh, i see what he is talking bout... but you did just change the filter, right?



how many hours are these motors good for before rebuild?



don

 

[SnoKing]

OK, fuel pressure is fine. NO load RPM's heading pass 3K. Got some more RPMs out of it today. Speed is cleaning bottom or engine is clearing it throat with some higher speed usage.



Also the throttle level on top of the injection pump is two arms, one the throttle cable moves that the other on the injection pump is moved via a spring setup to the other lever. Seems a little bindy, but engine was hot and hard to work across, so I will take it apart and lube as necessary when the engine is cool. I will do this test again in the spring after the bottom is clean and freshly painted.



Thanks to everyone.

Endless Summer - Bayliner 3388 Motoryacht

SNOKING

 

[JLEONARD]

One thing to check that is very common is to make sure the throttle linkage can move the pump lever completely to the stop. I just went thru this two weekends ago on a friend's boat with a 6BTA 315. I was able to get the last 150 rpm by manually moving the lever while he was running the boat.

Also you MUST make sure your tachs are accurate and calibrated via a handheld optical tachometer. I also verified his helm tach at 200 rpm increments.

As you already realized bottom condition is critcal in obtaining WOT rpm in a boat.

Another point to consider is that although your props may LOOK ok they do wear and straighten out over time... it may be time to get them at least inspected via prop scan or the Hale system. Any decent prop shop today has one of these inspection tools and they will all inspect and give you a report for free. It only takes them a minute or so to do the inspection... . I recommend you do this before spring launch.

Have you checked out SERVER BUSY ? You should. they have some good Cummins discussions there.

Happy cruising.

Jay



edit... I don't know why the admin doesn't let the web address post correctly??

 

[SnoKing]

When I bought the boat new the tach's where way off. I had the dealer try to calibrate them. I then had a small guy that builds tach's for RC airplanes build a custom optical tach, it works with 1 or 4 makings on the crank. So I calibrate the tach's at 2500 RPM (with four reflective marks on the front pully) which is my normal fast cruise speed. Works great. Have check the linkage etc, and have to check on a bind on between the two arms on that engine. SNOKING

 

[dpuckett]

how could his pump be getting tired?



i thought @ 1700 hrs the thing was not even broke in yet?

Don, 1700hrs is nothing for the engine. Fuel system is a different story. DIesel fuel wuality varies so much, it is hard to know what you are acutally putting in your tank, and how fast it will wreck stuff. I know a guy whose pickup died within a 1/4 mi of a station after fillling up. Got fuel to 3 injectors, but not enough to pop them open and fire. He had to rebuild his injector pump and injectors. Fuel tank was half water, and the station refused to reimburse him for it, saying the water was from condensation on the inside of his plastic tank. Att'y General's office didnt do anything about it, either. My (now ex-) finacee managed the only restaurant in town and told EVERYONE who drove a diesel (2/3 of the customers) about the guy's experience with the wet diesel.



Though with that horror story out of the way, I have noticed that engines that run hard do seem to last longer.



DP

 

[Don Tanklage]

Don, 1700hrs is nothing for the engine.



I have noticed that engines that run hard do seem to last longer.



DP

that is what i was thinkin, they are not even broke in yet, are they?



i have a friend that drills holes for a living. most of his rigs are cummins powered. he says he gets the most hours out of them if he runs them between 1600 and 2100 rpm. i dont really know what you mean by "run hard". i am sure you dont mean 50 psi and 1600+ egts, right? lol

 

[JLEONARD]

Granted 1700 SHOULD be nothing, but in boating it depends on lots of things.

If the engines have been overloaded, as i if the boat is over propped it is easy to score cylinder walls.

Some "looking" at the engine will reveal lots of history... ie is the compressed air plumbing discolored? That would be one indication overloading. Is the turbo paint discolored? That's another.

Cruise rpm on a B should give you about 10-14 psi of boost or less. That will yield a very long life.

For example I used to run my 6bta 270 at 14 psi. That was approx 2000 rpm on an engine rated at 2600.

You should also be monitoring EGT, which is done post turbo on a marine engine because of the wet exhaust manifoild. Not sure what the specs are for a 4B, but the spec for the 6bta I had was 805 F.

Jay