Wot RPMs only get to 4000 to 4100 on 2007 5.0 gxi

[hansenfarms]

I have a 2007 5.0 gxi with an sx drive. I put a new 19p 4 blade stainless prop on yesterday and ran it and wot was 4100 rpm at 44 mph. Just wondering if anyone else has had this problem? I was told by one guy to check the timing at wot because possibly the timing is not advancing for the RPMs to go up. Which he said could be caused by the knock sensor he said from past experience. I am OK with the way it runs but would like to see it be able to run up to the 4600 to 5000 rpm at wot like it says it should. I am open to any advice and will be back in the boat Sunday to check the timing and try anything else.

 

[dypcdiver]

I had a similar problem on my 5.0 Gi last season, turned out to be the ignition pickup coil that was breaking down, eventually went open circuit and wouldn't start. With a new coil I now get 5000 RPM.

 

[hansenfarms]

Was there any way to test the ignition coil before it goes out to see if that is the problem?

 

[mklearl]

Did you have the issue before you changed the prop?
Put the old prop back on if you can. I have read about people having the same issue going from 3 to 4 blade props and also upgrading to stainless. I would rule that out first.

 

[hansenfarms]

Before when I had the stock 21p 3 blade aluminum on I could barely get to plane without putting everyone in the front of the boat. It would sputter and hesitate until on plane but once on plane it would run a little better. It also was sucking down fuel like crazy so I put a fuel pressure gauge on it and checked that. It read 60 psi when I turned to key on, when I started it it went to 10 psi and not back to 10 all the way past 100 to 10. So i pulled it off and cleaned the screen and there was some gunk in the vac side of it, I put it back on and it ran 55 to 60 psi consistently then. The most rpms i got out of it with the old prop was 4400 @ wot. It ran really good with a great hole-shot and quick to plane after the regulator cleaning and new prop but I have a buddy with the exact same boat other than a mercruiser instead of a volvo-penta and he runs 4800 rpm @ wot with a 21p 3 blade. I'm heading to the boat today with the timing light to check the timing @ wot.

 

[mklearl]

Sounds like the original problem was the fuel pressure regulator and not the prop. Curious to see how this all works out. Good luck!

 

[hansenfarms]

I checked the timing @ wot yesterday going down the river and @ 4050 rpm on the timing light the timing was 25* advanced. I am not 100% sure what it needs to be but from what I read it seems to be a little low.

 

[rs1lollie]

give it a tune up, (plugs, cap, rotor, and wires) then check timing, i dont know if you need the timing shunt to check timing on a fuel injection

 

[Senior B]

total timing needs to be closer to 28 30 degrees.