Logo
FULL SITE MENU

Need some help

P

paul_rodgers

Regular Contributor
I have a 454 7.4 litre L29 BBC, When under way I have no power, It will only get to 3000 Rpm's. But when it is in the slip it gets full trottle 42-4600 Rpm's without problems. The engine is a MPI, Timing is set right on at 8 Degrees BTDC. When accelerating in slip the timing advance works fine at 3000 RPm's the advance is about 24 Degrees when running the boat in water it appeared to have only about 10 degrees advance, The book says that at 3000 RPM,s the advance should be 24 degrees and then add the 8 degrees and it should be around 32 degrees total advance. In slip fine under load no where close, What can cause this as I am now very preplexed I don't know where to go. Thanks in advance Paul
 
paul got compression ?

useless running rpm in the slip that high says nothing tells you nothing.

You could also do a vacuum test.

The motor ruuning hot ?
 
Yes, I have good compression 137-143 on all cyl, I havn't done a vacuum test yet..
Motor temp is right on at 160, This engine went through a complete rebuild. All is new on the inside and. As I stated earlier I checked fuel rail at 3000RPM's 36 Psi so I feel it is not fuel related, Timing is set at 8 degrees BTDC and is right on. As I was underway I looked at the timing advance and it seemed to only advance 12 degrees or so, it should have been 24 degrees plus the 8 degrees for around 32 total. The ign module controls the timing advance, I will try to check that next but do you guys have any other ideals, thanks pAUL
 
who set up the valves, they too tight. Had that with a rebuilt drove us nuts cause we just assumed they would be right coming from michichan motors.
 
I would have thought that 137 to 143 Cranking Compression wasn't all that good.

But, then it also depends on your Compression Ratio, and Camshaft overlap as well.

Will it rev correctly when out in the bay in Neutral, as in the dock?

Bruce.
 
Bruce if it were me, i would reset the lash on the valves they have to be reset anyway.

Run it still having the problem i would check the psi the fuel pump is giving. Still doing it after running it ?

Check the timing chain.

Paul me before anything else run a vcuuum test heres the links :
How to Use and Interpret a Vacuum Gauge
On Fire vacuum gage

Both links are good.

Keep us posted i have confidence in you to finding the solution.
 
Paul

One thing to consider is that with newer igintions and I am sure it also true with efi or tbi systems you have a knock sensor that detects preignition noises from the block.

This sensor is typically installed at the starter side block drain hole.

If this sensor is detecting knock type noise it will retad your timing and cause a situation similar to no full advance.

Just my first thought, I do not have any real experience with EFI so that is about is from me......

Double check your spark plug wiring as this could cause a knocking sound and not a rpm issue as the right wires croosed may not show up under 300 rpms.

just another thought.
 
I will try to answer all questions, the Boat is 29' maxum about 6000lbs, It does rev fine out in bay up to 4500 RPM's. Prop is double 22 pitch same as was on it before rebuild, nohing done to drive except I replaced all anodes. Ghost I checked the knock sensor and it appeared to be working. Thats if I did the test correct.. Wires are not crossed and are new as the plugs are also. I did have the heads reworked and new seals installed, How would one check to see if a Valve was too tight? Chiefalen I will do the vacuum test next and post results and I value your opinion as some of you guys are really sharp on the trouble shooting aspect of this forum, I will keep trying one thing after another until I get it right. My weak point is trouble shooting slow but usually get the job done..Thanks to all for your help...Paul
 
Paul

My question was not just if it works.

What if it is causing the problem???

I do not know how it actually works, IE: what signal it produces and what is does with that signal BUT if you could bypass it so the ecm see NO KNOCKING signal when trying to rev up under load.


I guess what I am suggesting is what if the sensor is seeing a knock and doing what it is suspose to do????
Next time out, by pass it ( not sure how) and see if you are able to reach max timing advance........
 
Ghost, I had not thought of that, I am sure I can figure out how to jump them out as I have two, one on each side of engine.. I will bypass them and see if it will ramp up as it should,, Thanks will update when I get that done..
 
Back
Top