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Can"t Get My 454 Mercruiser over 3000 RPM

If you have a knock sensor then there has to be two modules, One is timing the other is knock..........

If your pics wont load maybe too big. go into Paint and shrink!! then save and try again......
 
Not sure if it is the same with the marine knock senser but on a car, tap quickly on the block next to the senser with a wrench while watching the timing marks. The timing should retard with the tapping. Do not tap on the senser they are brittle.
 
Yes it works the same...........it will retard the timing when a knock is sensed.



I am not 100% sure what happens if the wire is disconnected............Not sure if the timing module will still advance timing.

Also if it is sensing a knock then it could contribute to lack of full advance......???

Not sure as I have never come across any issues with any of these.......
 
Will try to shrink and post after. I ran the boat today and tested the advance. It runs at 9 at idle but does not advance uniformally. At one point I was running 1500 RPM at just under 30 degrees, later I ran up to 2500 then 3000 but it did not advance over 30, then back down to 1500 and up again to 2500 but not change in timing as I did this . I suspect the timing module is bad. Is that a separate part or built into the distributor??
 
I don't think the knock sensor is the problem as the engine runs pretty smooth. I looked up what I THINK is the ignition module for Mercruiser engine serial # OF 305171 and the parts list shows an "Ignition Sensor" located inside the distributor .. Sierra part number 18-5116 -1 . Is this the right part I should be looking for?? Thanks
 
OPPS ..or after further digging ..Quicksilver Ignition module OEM part number 806745A01 ................ or at least where to look next .. ;-)
 
If the timing is advancing then the timing module is working.

If you look at the graph that was posted earlier you will see about when full advance cones in...

So if by 2500 rpms you see ~30* total you are good.

Dont start swapping parts until you are sure about its fialure.....it will get very expensive and you cannot return electrical parts once used....
 
Can you get your hands on a good prop with less pitch. 2 inches less should bring the rpm up around 350-400 rpm. It should give you a better hole shot as well.
 
Is the outdrive the original?
I was helping a friend last summer and it turned out his O/D was not original and was not a 1.50 : 1 it turned out to be 2 : 1. He had a 350 motor....had to make a large prop pitch change.
 
I've been running a 21 Inch stainless prop for several years. By less pitch I assume your talking going to 19? I have a 23 I ran on the old engine. The outdrive has not been changed. Its supposedly 1.5 . I usually cruise around 3000 rpm but I'm showing the boat should be pitched for a max rpm of 4600-5000 RPM in the Mercruiser specs.
 
What was the original motor?

I am not 100% sure but most 454 with bravo 1 typically have a 1.32:1 ratio....not 1.50:1...

More specifics on past set up...
 
I am not the first owner of the boat and we did not get exact specs from the previous owner The original engine was a 1994 454 Magnum carbed engine also. This is the original out drive and I have a serial number for the Bravo 1 of OF 387387 and 1.5 gear ration written down but that was a long while ago and no idea where I got that from. ( tried to track the serial number down further but no luck yet). The out drive has both side and front bottom water intakes on it which I thought indicated it was not the basic casting which only has side intakes if that means anything. I see that they actually made the bravos that year with 1.36, 1.50 and 1.65 gears. Not thinking they would pair a 1.36 with a Mar engine in a Baja but how knows. For reference with this prop the boat used to max out just under 60 MPH at full throttle and a clean hull , now at 3000 RPM 1/2 throttle is maxing out at 30 MPH .. . it did about the same or just a bit slower on the original motor but wth a 23 prop.
 
ehlien said:
The original engine was a 1994 454 Magnum carbed engine also.
Click to expand...
Your engine serial number 0F305171 is coming up as an 1995 MERCRUISER 454 model number 4454110HS TB5, W/PS, TWO PC EX System, WORO, GEN V 454 BRAVO.... Here's your parts guide for the engine, http://www.marineengine.com/parts/mercury_marine_parts/sn/0F305171

This is the original out drive and I have a serial number for the Bravo 1 of 0F387387 and 1.5 gear ration written down but that was a long while ago and no idea where I got that from. (Tried to track the serial number down further but no luck yet).
Click to expand...
Your serial number is coming up as an 1995 BI-ROTATION BRAVO 1 1.50:1 Model number 5120150HS.... Here's your drive parts guide, http://www.marineengine.com/parts/mercury_marine_parts/sn/0F387387

The out drive has both side and front bottom water intakes on it which I thought indicated it was not the basic casting which only has side intakes if that means anything.
Click to expand...
Being that you drive serial number is a 1995 model year, it sounds like the lower gear case housing may have been changed to a newer year model somewhere along the line as I believe Merc didn't start using dual water pick-up till somewhere around 1997ish.
Be careful when running the engine at home on the garden hose (muffs) because since you have 2 water pick-up holes, you'll be sucking air through one of the holes if they are not covered in turn shortening the life of the sea water pump rubber impeller dramatically...if you don't have the orange lower water pick-up flusher, It's best to cover the lower holes with duct tape. http://www.bing.com/images/search?q=mercruiser+lower+water+flush+kit&FORM=HDRSC2

I see that they actually made the bravos that year with 1.36, 1.50 and 1.65 gears. Not thinking they would pair a 1.36 with a Mar engine in a Baja.
Click to expand...
Most standard bravos with 454, 502's came with 1.50:1 while 1.36's where more on the special fit side of things for/from some boat manufacturers or Merc service dealers changing gear sets for certain high performance boats.

Bear in mind that since you are seeing/hearing some sort of miss/backfire while trying to go above 3000, chances are you're going to have either a fuel, ignition timing, not enough spark from coil or to spark plugs related issue or as the testing you've tried thus far, it's looking to be more of an internal engine problem vs a prop or gear size problem per se.

Knowing what the fuel pressure is at the carburetor would help a lot.
Could still be an internal carb problem too but adding fuel without change almost seems to alleviate that in theory.

Cap/Rotor and spark plugs are good/new I'd assume. Check to see if there's a ground wire running to or near the distributor assembly, if so be sure it's connected.

May want to perform an engine cylinder compression test and a leak down test too if possible. Possibly you have a valve issue such as tuliped valves for example.

Hope you find the problem soon, good luck.
 
The dealer i worked at in the early 90's, most of the 454 bravo 1 boats we dealt with had the 1.3(?) 6 i guess gear ratio... did not see many with the 1.5....
Been a while..... and these days its 99% alpha 1's.....
 
For the service only Merc dealer I worked at, it was for the most part just the opposite as most of the boats started off with the "standard" (1.50:1) drive and as they added HP (or went boat racing) and didn't have big enough props available at the time, they'd switch to 1.36:1 to help spin a smaller prop plus hoping to alleviate some of the stress in hopes to make the drive live longer as the 1.36's are a bit stronger with less material.
We serviced many of the local SoCal custom boats, such as Eliminator, Warlock, Shockwave, Advantage, just to name a few....Come to think of it, The boats started off small and light weight but slowly got bigger and heavier with more power over the years so more started to use the 1.36's. Boats back in your area where already bigger and heavier first so I could see where you were use to seeing the 1.36:1 more than us on the west coast.:):cool:

One issue to be careful of knowing that the possibility of this stern drive in question seems to have a different lower gear case housing is to ensure a XR lower gear housing wasn't added mistakenly because of the differences of how the gear ratio is changed. With the older Bravos the gear change is done in the upper driveshaft housing but in the newer designed XR drive, the gear ratio is done/changed inside the lower gear case housing....Not in the upper like the old days. The Upper XR only has one set of cut gears... GEAR SET, (16/19) see item number 20, http://www.mercruiserparts.com/bam/subassembly/30991/11406/130
Item numbers 21 here, http://www.mercruiserparts.com/bam/subassembly/30991/11406/150
Here's the Sport Master lower gear housing design if interested, http://www.mercruiserparts.com/bam/subassembly/30991/11406/160

The driveshaft between the lower and upper housing is the same size/part number between standard bravos and XR bravos. 45-858517A3

Here's three informative topics covering most of the changes,
http://www.offshoreonly.com/forums/drives-lower-units/338136-bravo-xr-gear-change-1-5-1-36-a.html
http://www.offshoreonly.com/forums/general-boating-discussion/313000-gear-ratio-1-5-1-vs-1-36-a.html
http://www.offshoreonly.com/forums/drives-lower-units/157533-bravo-xr-upper-standard-lower.html

Just to reiterate for ehlien, since the engine is exhibiting mis/backfire symptoms, the engine should be suspected as to the hold of 3000 RPM....Unless the tachometer is way off and you happen to be hitting the built-in rev limiter of the TB5 ignition system due to wrong gearing/prop too.:eek:
 
Good stuff ... backing up remember the boat was running fine when it was put up. It still has all the same mechanicals and electrics it had for years its just now for the first time not able to get over 3000. Since nothing has changed with the prop or bottom end I think problems in that area are unlikely. Also after a lot of engine diagnosis including a leak down test its also unlikely there are problems with the short block or probably the heads. That leaves Ignition timing or fuel delivery as the probably causes. So far I have learned a lot about the ignition system but have not been able to confirm it is malfunctioning. That is bringing me down to possible problems with the carb. At this point its starting to get a little over my backyard mechanics head and maybe time to bring in the big guns..
 
Plugs look ok ,,its not running lean but the carb has never been rebuilt and sat idle for 3 years. The boat runs like it a 2 barrel maxing out at 1/2 throttle and almost exactly 3000 RPM and I suspect the secondaries are not functioning properly ..but then again I am not a mechanic
 
So I had a mechanic check the boat today. he confirmed the ignition module is ka put. The next step is finding the right part to replace it with.
The module is mounted to the back of the distributor. The motor has the original heads which are 1994 Mag heads but the block is a 1996 up Gen iV block. The module itself was made by Nippondenso and has these numbers on it 13100-2230 and T34984.14 . Problem is I can' cross reference these numbers to any Mercury numbers. The best I have done so far is identified part number 806745T-5 as the module for 94 through 97 mag engines. Also, anybody know if 806745T-6 would just be a newer replacement for the 806745T-5?
 
What exactly did the mechanic find that made him say the timing module was bad??

You did not include his findings? That is the key!
 
Disconnected the knock sensor to take that out of the equation. Confirmed good spark to all cylinders. When he revered up to 3000 RPM initially the timing went up with the revs to 30 degrees but staying at 3000 or trying to go over, or going down and back up to 3000 the timing was falling all the way back to almost TDC and staying down there. He determined it did not need to stay up at 30 but basically no way the boat was going to run right if the timing kept falling and staying that low. ...after falling back low .it seemed like timing was not advancing at all to significant throttle and engine RPM increases.
 
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