volvo 5.0 GL only gets 3200 rpm

[jt4237]

Hello all. I am extremely frustrated to say the least. I have a 2004 hurricane fundeck with Volvo 5.0 GL. new holley 2300 carb. a ton of engine work last October. new risers/manifolds/water pump/etc,etc. the list goes on forever. anyway, I used to get 4700rpm and about 45 mph. now I cant get the thing over 3200 rpms. compression is perfect. timing 8deg, total timing at 28@3200rpm. in neutral I can get to 4700, but not in gear. this does not have a SLOW circuit. carb is adjusted correctly. my only concern is I am only getting 14 in of vacuum at idle. does that sound low? should it be about 20? ive had a dyno engine guy look at it and he is scratching his head. new plugs / dist cap/ rotor. fuel pressure is at 8 psi which is spec. have no idea why this thing wont go. any help would be greatly appreciated.

thanks, Jim

 

[Maclin]

Valve lash too tight can cause this. What engine work was done last October? Has it acted this way since the engine work? Or was it ok for a while this season then this started? The vacuum seems low, sometimes it depends on where the gauge is hooked up.

 

[jt4237]

the engine got water in it last year that's why I needed all the work done. it had low compression on #8. attached is the work slip. they only worked on the water side and head. nothing with crank, valves, etc. my girlfriend said it didn't run right this year, but unless my memory is failing I believe it started fine this year. it always bogged down from idle to WOT. that was carburetor issues that are now fixed. I just noticed that my trim sensor wires got chopped off and are exposed in the water. could that be causing and electrical issue. I know its a long shot

 

[skydiveD30571]

Just a side idea...if it were mine I would disconnect the shift cable from the drive (under the plastic SX cover), manually shift the drive into forward, and then try again. If anything, to atleast cross out the possibility of a shift cable causing your control unit or throttle cable to not reach max travel.

 

[jt4237]

did that. sift cable opens throttle 100%. even running throttle by hand on the carb it does the same thing. every ' simple' thing has been tried. im leaning to the vacuum being an issue but the engine tech didn't think 14 was that bad but everyone is saying it should be 18 - 20. they says 14 means I have a vacuum leak

 

[jt4237]

View attachment boatwork.pdf

 

[jt4237]

not sure why motor stops increasing when given full supply of air and fuel...

 

[skydiveD30571]

I seem to remember (2 yrs ago) my 5.0GL producing about 14" vacuum at idle as well. Everything I read said that it was low but the mechanic at the time thought it was normal. I've never had power issues. Next I would take my propane torch or a bottle of soapy water and start searching for a vacuum leak.

 

[Maclin]

SkyDive, how's it goin' I had a post ready before yours then my PC died, did not want to post it again without commenting that checking for a vacuum leak around the intake and carb is a good idea.

Back to jt4237,
They had the heads off, so the valve lash would have needed to be reset.

I did not see any "RunUp" line where they started it in their tub and made sure it started and idled ok. That would not show a marginally tight lash setting though, just really loose setting. When too loose the vacuum is ok, maybe high even, but the valvetrain is noisy and power will be down at higher rpms.

Loose lash means valves close solidly but are not open for the entire duration as they are late to open and early to close.
Tight lash means the valves may not be seated/sealing all the way and this shows up almost immediately in the RPM band, as compression cannot be maintained during the compression/power stroke events.

 

[jt4237]

on another note. in neutral, the timing is 8deg. we got 28 degrees at about 3200 rpm. after that, nothing. the engine guy actually said the timing started retarding after 3200 rpm in neutral. however the boat will get to 4000+ in neutral, but not in gear. is there a difference in how the prestolite distributor advances in neutral or in gear? how can I get to 4400 rpm in neutral with the distributor not advancing, but can't get it while in gear? im hoping I just have a distributor weight issue..

 

[Maclin]

The distributor is advancing or you would not get the 28 degree reading at 3200 rpm. In neutral there is no load on the engine. You could pull 4 spark plug wires and get it to 4000rpm in neutral. Valve lash out of spec to the tight side enough to limit rpm will not show up until the engine is under a load.

The distributor advance works solely on RPM, no matter the load on the engine.

 

[bruceb58]

on another note. in neutral, the timing is 8deg. we got 28 degrees at about 3200 rpm. after that, nothing.

That's pretty typical. 3200 is usually when spark advance tends to stop.

 

[jt4237]

Maclin. going by the attached PDF from the work done, would the mechanic had to have adjusted the valve lash? they rebuilt the heads cause I had low compression on one cylinder.. what do you think about electrical? I have read that a bad tach could cause issues? I found that my trim sensor wires got busted and are hanging in the water. could that be causing bad grounding issues and causing problems?

 

[Maclin]

Any time you R&R heads part of the install procedure is setting the valve lash.

Tachometers can mess with ignition signals sent to the coil because they use the same signals to meter the rpm, easy enough to isolate by unhooking tach wire at the coil (negative terminal).

 

[Maclin]

Goes something like this... Install head, torque down head bolts. Install pushrods then topend valve train. Set lash. Install valve cover.

 

[Maclin]

By the way, the term "valve lash" refers to the play between the rocker arm and the lifter via the push rod. Cam moves the lifter, lifter moves the pushrod, pushrod moves rocker arm, rocker arm moves the valve. It is an adjustment, can't just bolt in the components and walk away.

 

[Daniel048225]

What did you end up doing? I have a very similar issue.

 

[GA_Boater]

What did you end up doing? I have a very similar issue.

Please start a thread. His last visit was 3 years ago.

Closed.