496HO issue - won't rev past 3,400 rpms
07-10-2012, 06:26 PM
#21
Gold Member
Gold Member
Its not the NSS
You have an obstruction at the inlet side of the raw water supply. The system will knock you back down @ 3500 everytime. You have a low water pressure issue, the 555 will post a low water pressure fault and a host of other related faults that are trying to tell you in a round about fashion that you have no pressure. Ignore your gauge you have no water pressure, or at least inadequate.
Post backflushing the oil cooler on top of the rear most part of the engine, remove the raw water hose and water neck at the inner transom assembly first and formost. More than likely that inlet port behind the water neck is constricted as Dynojet & Sydwayz touched on earlier. This is especially the case if the boat has seen salt.
Another option but unlikely given the age of the boat, is if it has a LWP then the side pickups could be aerating the incoming water from the LWP if you are at full plane at 3500, which I would hope you would be.
Post backflushing the oil cooler on top of the rear most part of the engine, remove the raw water hose and water neck at the inner transom assembly first and formost. More than likely that inlet port behind the water neck is constricted as Dynojet & Sydwayz touched on earlier. This is especially the case if the boat has seen salt.
Another option but unlikely given the age of the boat, is if it has a LWP then the side pickups could be aerating the incoming water from the LWP if you are at full plane at 3500, which I would hope you would be.
Last edited by Trippin; 07-10-2012 at 10:54 PM.
07-10-2012, 07:38 PM
#24
Registered
Expensive Date,
I am going to order the Neutral Safety Switch, just in case that's the problem. I've heard conflicting things on this. Some say when it goes bad, you can't start the boat, others say it can be bad and put into guardian at rpm. I will go with your thoughts and at least have it on hand in case that's the issue. It's a cheap part. Not sure how your's broke. My switch is on the controls (Livorsi Standard Mechanical controls). Is your's in the engine bay?
I am going to order the Neutral Safety Switch, just in case that's the problem. I've heard conflicting things on this. Some say when it goes bad, you can't start the boat, others say it can be bad and put into guardian at rpm. I will go with your thoughts and at least have it on hand in case that's the issue. It's a cheap part. Not sure how your's broke. My switch is on the controls (Livorsi Standard Mechanical controls). Is your's in the engine bay?
http://www.mercruiserparts.com/Show_...ket%28Bravo%29
Part number 18 is what was causing my problem, yours might be a little different. But as Trippen said check the water inlet very common is easy to check 11 mm bolt on top of the transom assembly, just follow the inlet hose. Pull it off, after taking bolt out you will know if thats your problem as soon as its off.
Last edited by Expensive Date; 07-10-2012 at 07:57 PM.
07-10-2012, 11:01 PM
#25
Gold Member
Gold Member
Number 18
Number 18 is a shift indicator/position switch it only tells the ECM that the engine is in or out of gear, true it will not allow the engine to start if it is indicating an in gear position, then again it might, i've never deliberatley tried. But when all is said and done it theoretically is not a NSS. That switch would in fact be integrated into the actual shift lever at the helm.
Last edited by Trippin; 07-10-2012 at 11:04 PM.
07-12-2012, 10:18 AM
#26
Registered User
Thread Starter
Join Date: Jul 2010
Posts: 26
Likes: 0
Received 0 Likes
on
0 Posts
Problem fixed
Well, yesterday was a good day. I finally resolved the issue.
I visited the dealer, and was going to have them look at all the water lines to find any blockage. I was also going to have them replace the Water PSI sensor, per Ray's (Raylar) suggestion. As I was there, I decided to peak in the engine bay again just to see if I could see anything.
Came to the conclusion that it wasn't related to the fresh water flush. I don't have any of those ball valves, and the cap was on tight.
Looked at the bilge again, and didn't see much water, so I figured I didn't have any serious leak, hopefully meaning the air actuators were fine.
Then I noticed something. The T-Valves at the bottom of both Dana Marine Headers were OPEN! I did not do this, and the dealer who changed the water pump says they did not touch those either. The only thing I can think of is the other dealer who winterized it and then commissioned it in the spring open them to drain the liquid out of the manifold and forgot to close them. Hard to believe, but I must have been running with them open all year so far (although I have not had the boat out much this year).
So I closed them and took it out on the water. Thought I had it licked, but guardian again, this time at about 2,200 rpms. I was bummed.
So went back to dealer, and we replaced the Water PSI sensor. Went back on the water, and problem fixed! Boat ran great.
What a relief. Thank you all for your input. It really helped.
I visited the dealer, and was going to have them look at all the water lines to find any blockage. I was also going to have them replace the Water PSI sensor, per Ray's (Raylar) suggestion. As I was there, I decided to peak in the engine bay again just to see if I could see anything.
Came to the conclusion that it wasn't related to the fresh water flush. I don't have any of those ball valves, and the cap was on tight.
Looked at the bilge again, and didn't see much water, so I figured I didn't have any serious leak, hopefully meaning the air actuators were fine.
Then I noticed something. The T-Valves at the bottom of both Dana Marine Headers were OPEN! I did not do this, and the dealer who changed the water pump says they did not touch those either. The only thing I can think of is the other dealer who winterized it and then commissioned it in the spring open them to drain the liquid out of the manifold and forgot to close them. Hard to believe, but I must have been running with them open all year so far (although I have not had the boat out much this year).
So I closed them and took it out on the water. Thought I had it licked, but guardian again, this time at about 2,200 rpms. I was bummed.
So went back to dealer, and we replaced the Water PSI sensor. Went back on the water, and problem fixed! Boat ran great.
What a relief. Thank you all for your input. It really helped.
