Starboard engine not keeping pace

[src]

I'm on my first real cruise, and I've noticed that my starboard engine sometimes doesn't seem to have a lot of "grunt". I'm in a 2000 310 with twin 7.4's.

After about an hour of cruising at around 3200 RPM, I noticed that my speed was falling off. Revs were down a bit, so I gave it a little more throttle. The port engine responded as expected, but starboard didn't change right away. It seems as if once the port engine gets up to speed, the starboard starts creeping up, never quite matching the rev's. Even giving the starboard more throttle doesn't help. Once it gets to around 3K, it poops out unless I goose the port engine.

Other times, it seems to work fine, with both engines keeping pace and responding to the throttle smoothly.

Oil pressure and engine temps are fine during all this, and I did check the temps with an IR thermometer just in case, and nothing seemed out of line. One thing I noticed is that the starboard intake makes much more of a "scream" than the port when I'm running with the hatch open. It is a VERY noticeable difference. Could it be as simple as a semi-clogged flame arrestor?

One other item - getting on plane seems to be more of an effort than I expected. I really can't get it there until I pass 3K RPM, and it really feels as if the boat is "dragging", but I don't have enough experience with this size boat to know if this is normal or not.

 

[testlab]

The additional noise is the wider open throttle. Sounds like your Stbd engine is well down on power. When you throttle up the port the boat does increase speed and allows the Stbd engine to also increase its rpm due to prop gaining some freewheeling assistance, but it may not be pulling its weight, so to speak.

Can it achieve the rated wide open throttle (WOT) rpm? This should be printed on the engine rating plate.

 

[jason78]

When is the last time you did a tune up? I have seen changing plugs/wires/cap/rotor help resolve similiar problems if it is due.

 

[src]

I just bought the boat 2 months ago, and during the sea trial it reached WOT. I haven't run it up since then. The surveyor also did an independent WOT test (port engine neutral, stbd WOT to record RPM, reverse the procedure port/stb, compare RPM reached on each side), and everything seemed good.

I guess a tune-up is in order when I get back from this trip. On the first leg this morning, it was behaving as noted previously, but after a fuel stop it was closer to normal. Stbd was still lagging a bit, but not nearly as much. However, fuel consumption is higher than expected (which could be just about anything).

Yesterday and on the first leg this morning, I was seeing about 25 knots at 3300 RPM, second leg today I was seeing 26 at 3000. Something is up, but so far it seems to be a mild issue. Both engines are running on spec for temp and oil pressure, so no "Oh god!" problems yet. I'm just hoping I don't have low compression on the stbd.

 

[highball]

had a similar problem. i changed the fuel seperator, distibutor cap and rotor but same results. then I changed the plugs and all was good. i'd change the plugs first and try it before changing all

 

[Air O'Nautical]

+1 on the plugs.
But, might be just a wire not making a good solid contact with the spark plug terminal..
Try to tell if the wire boot is snapping on.
Might have to give the boot a little squeeze with pliers before installing.

Most of the time it's just easier to replace everything with new so, you can start to narrow the search for the real problem.


Another thought, check to see the props aren't wrapped up with some line.
Tilt drives up and spin by hand.....don't fall in!


Good luck,
Mark.

 

[src]

Thanks for the advice. I'll try to check the plug boots today before I start up. It would be fantastic if it were that simple. I'll also try to find a spot where I can get in the water away from the nettles and check for fouling of the props. Either way, I guess I'll be putting a full tune-up on the schedule when I get home.

 

[src]

Just looked at the plug wires on the stbd engine. I can only really see the inboard side, and it looks like #8 was SERIOUSLY pinched during the exhaust manifold installation. It is wedged in between so hard that I'm going to have to cut it to get it out. So that'll be replaced when I get back home.

On the outboard side, I can't even see the wires (I can see #7 and 5 kinda-sorta using a mirror on a stick). The manifold runs up within an inch of structure, and I do believe it will have to be removed in order to access the plugs/wires. That's going to be a whole other thread.

So, do you think being down 1 cylinder (#8) would be enough for what I'm seeing, or would it take more than that? That's assuming, of course, that the pinched wire is killing the spark on that plug, which could be a faulty assumption on my part.

 

[testlab]

The standard tune up procedure for these 7.4s is to replace the dizzy cap, plug leads and plugs. It's not expensive but, yes, the access can be difficult (it's bad enough on my 330DA). I think the loss of one cylinder would have quite an impact. I would replace the above.

On TB5 ignitions the knock sensor module can also give trouble, but leave that until getting the basics sorted out first.

 

[src]

I was able to get to a parts store and pick up a new set of wires, but they were (a) automotive and (b) had the wrong connector at the distributor end. I was able to get a new wire on, but the distributor end wasn't tight and the engine was running rough and missing on that cylinder. So right now I think I can say that the pinched wire is NOT the core problem. The engine runs smoothly with the pinched wire, and rough with the new wire (i.e. new wire isn't working right).

Looks like I will have to continue troubleshooting this one, but I am going to order a new set of the correct wires and plugs for it and plan for a full tune-up.

 

[src]

Just to update, I was able to change the plugs and wires on the inboard side of the starboard engine (cylinders 2, 4, 6 & 8). The plug for 8 was completely fouled, 6 didn't look great, but 2 & 4 looked reasonable. When I had it out this weekend, it did MUCH better. The stbd engine kept up into the low 3K range, and only stopped keeping pace around 3400 or so. I was able to get both up to around 4K, and hit about 36 MPH GPS, but again the stbd was lagging behind a bit.

I think I'm definitely on the right track here, and just need to find a way to access the plugs and wires on the outboard side. The alternator is sitting high enough that it is out of the way, but the power steering pump/bracket/hoses and fuel filter are squarely blocking access from the front, and there is no access at all from the side or top unless I remove the manifold & riser.

But I'll be happy with the progress so far. I plan to pull the inboard plugs again this week to see how they look now that I have a few miles on them. I also plan to replace the cap/rotor just to round out the job.

Edit: Here's what the plugs looked like (in order, 8 on the left, 2 on the right).

 

[cjcray]

I'm on my first real cruise, and I've noticed that my starboard engine sometimes doesn't seem to have a lot of "grunt". I'm in a 2000 310 with twin 7.4's.

After about an hour of cruising at around 3200 RPM, I noticed that my speed was falling off. Revs were down a bit, so I gave it a little more throttle. The port engine responded as expected, but starboard didn't change right away. It seems as if once the port engine gets up to speed, the starboard starts creeping up, never quite matching the rev's. Even giving the starboard more throttle doesn't help. Once it gets to around 3K, it poops out unless I goose the port engine.

Other times, it seems to work fine, with both engines keeping pace and responding to the throttle smoothly.

Oil pressure and engine temps are fine during all this, and I did check the temps with an IR thermometer just in case, and nothing seemed out of line. One thing I noticed is that the starboard intake makes much more of a "scream" than the port when I'm running with the hatch open. It is a VERY noticeable difference. Could it be as simple as a semi-clogged flame arrestor?

One other item - getting on plane seems to be more of an effort than I expected. I really can't get it there until I pass 3K RPM, and it really feels as if the boat is "dragging", but I don't have enough experience with this size boat to know if this is normal or not.

I am having the same issue with my Starboard engine on my 370 sundancer with 7.4 MPI.
i put new plugs in last year. They have about 75 hrs on new plugs.
they ran flawlessly until about a week ago. I noticed the Starboard side was down on power.
i have changed the fuel filter/separator, but that did not help. I am going to change plugs and wires on the Starboard engine this weekend to see if that fixes it. From all of the info. That I am getting from Club Searay, Plugs and Wires should fix it.
I will keep you posted.

 

[cjcray]

Sorry about the late reply back.
i had family issues that kept me from the boat until this weekend.
here is the update.
i changed the plugs and wires on the Starboard engine as suggested.
Boat runs like new now. Problem solved.
ordered another set of plugs and wires for the port engine so I have them both on the same maintenance schedule.
Thank You Club Searay!

Chuck