Hi Folks,

I've been lurking at OSO for a long time. I've never owned a true 'performance' boat but I'm working out a problem right now on a rebuilt Volvo Penta 8.1 Gxi and I was hoping that the the more technical folks at OSO might be able to help. The base engines between the 8.1Gxi and 496MagHO are the same, and I know a lot of you have your own scan tools and have probably datalogged your engines, so I was hoping that I might be able to get some useful comparative information as it's not so common to find that with Volvo Penta folks.

I have a 2004 Cobalt 250 with the 8.1. It was a Gi last year and over the winter I pulled it and rebuilt it. It started as a simple exhaust replacement, but the PO didn'tdo such a great job keeping up with the maintenance and the exhaust replacement escalated to a full engine build. It's now +.030, with the HP2 cam and a ported out intake manifold. Other than the pistons/rings, all of the parts are stock GM parts and I believe that I followed the engine assembly process to the 't' (based on the Volvo Penta engine service manual).
It's back in the boat and running, but I have low idle vacuum - approx 9inHg - pretty steady (fluctuates only about 0.5 total). This corresponds to the MAP sensor which is reading around 62kPa.

Vacuum diagnostic guides suggest the likely reason for this would be incorrect valve timing, but I was pretty diligent about the cam and timing chain installation. Unfortunately, I did not degree the cam (I assumed it was pointless, since nothing was adjustable, but now I am regretting that decision).

Because of the cam change and intake porting, I purchased MEFIburn to allow me to reprogram the MEFI-4b that the volvo uses. Bob at OBD Diagnostics gave me a "gxi" tune, but it's not clear if it's actually the factory tune or just a starter tune to get me close enough to work with. One reason I'm curious is because in the spark tables, at idle it's basically programmed for 0 advance, and this seems odd to me. Full disclosure - while I have a very solid understanding of the mechanics and electronics of engines, I've done little so far with tuning them, so there may be some basic things that I'm missing. I wondered, for example, if there was a 'base advance' setting in the tune somewhere and the tables are just on top of that... but I didn't notice anything.

So - my question. Does anybody with a 496 Mag HO have datalog info that they could share? I'd love to see what a stock 496 with the HP2 cam is getting for manifold pressure and ignition advance at idle.

Thanks!!!!

Is this boat in Dallas Texas ?

No, Central Massachusetts.. Why?

Here's a short video of the engine idling with the vacuum gauge attached:
[link deleted until I have 10 posts]

Here's a Scannerpro datalog of the engine idling:
[link deleted until I have 10 posts]

One note - the GM manual states that the assembly process for the rocker arm nuts is to "Tighten to 18ft-lbs". There is no process described for going through and setting valve lash in the 'old fashioned' way that I'm used to. As I said, I followed the manual to the letter, but now one of my concerns is that the valves are all overlashed and maybe hanging open. My other concern is that perhaps the guy who ported the intake manifold managed to create a leak between the intake and the lifter valley... I've got a smoke machine on order to try to help me check that...

Same ordeal in Dallas and same boat Cobalt - Volvo 496. They would call me alot looking for free help. Finally told them to bring in and I will fix all their Rookie poor mistakes and they bought the boat to use not be wasting years of money and time with a dead boat..

Never seen or heard from them again 8 months ago.. this went on for 2 years. Thank the lord so glad for the stopped 3 phone calls per day with every question under the sun taking up alot of my time. This is my means for a living Professionally working boats.

No offense telling it like it is - this site is really not much in the way Volvo specific nor I doubt not many even scanned a volvo penta engine up here. Again no offense to anyone -- it is what it is. . Volvo did things differently than Merc. -- Their tune was not the same. just one small example -- They even safe guarded the engine at running temps 140 and below for operation about 3 K or 3.5 K rpms. The Volvo 2004 is a MEFI 4 ecm --- Mid 2005 went to E controls for Volvo.

Stock OEM marine apps what data logging with the marine specific scan tools ? They monitor parameters and log hours and fault codes-- there is no ARF s or any vast data logging with marine specific scan tools. MEFI burn as you mentioned is the only source for MEFI 1 thru 6 only.

I'm sorry you had a bad experience in the past. I can assure you that wasn't me and I'm not looking to put anybody out. But an HO and a Gxi in stock tunes should be pretty close to each other in terms of idle MAP values and ignition advance regardless of the fact that they're on different ECU platforms, so I was just wondering if anybody at OSO had a log of those values for their HO motor. Fixing this issue is totally on me and I'm working to solve it.

Thanks again in advance for any information anybody has to share.

The Merc 496HO tune at idle will constantly go from a few degrees positive advance to up to -12* advance to keep a smooth idle. I've also noticed alot of negative advance when coming off plane down to idle from 1500rpm to idle. I do not remember MAP values.

The 18'lbs is correct per my Merc FSM on the rockers. Was the cam on the base circle when rockers were torqued? IMO I would rather torque to spec with cam on base circle/valves closed.

Thank you Ryan! That helps.

I thought I torqued each valve when it was on the base circle, but when I went back to my manual to double check the procedure, it doesn't even say to do that, so I'm not sure. It sounds like I ought to pull the valve covers and go through them to make sure...if it was, it would be better than discovering that the cam was out of spec.

Merc FSM wants piston @ TDC and valves closed. Torque each respective rocker nut to 18 ft lbs when above is correct.

Easiest way to accomplish this with an engine like the 8.1 with an unmarked balancer is going thru the firing order following the EOIC method. 8.1 firing order is 18726543.

This vid explains it pretty well.

https://youtu.be/89o5rLpbCgI

IAC totally different and Volvo do not use a IAC muffler - a mechanical throttle & shift might not be what you have as well depending on your volvo app. So with that said you might not even have an IAC. The throttle body set up is different than Merc. Neither are the same DTS or Mechanical inwhich is different between the 2.

Alot of Volvo 496 were NOT closed cooled --- most inland volvo 496's sold were not closed cooled. All Merc 496 are closed cooled. The tunes are not the same regardless I am telling you first hand. . Volvo do not use a shift in gear switch -- Volvo do not use a water pressure monitor set up either.

Volvo cam position sensor install is different as well. -- I understand the basics and MAP / speed density system all going to be the same -- but for a scanned engine the Merc 496 and Volvo have alot differences as far as some of the things monitoring. Volvo use different Knock sensors as well compared to Merc.

If I recall corectly the timing tables being different as well compared to Merc. . Also around 2005 Volvo went to returnless fuel system. I might have to check on that one to be sure of the year. It might have been when the got away from MEFI 4 possible 2006.

Mercruiser stock 496 exhaust is also better flowing than the stock Volvo 496 exhaust. But Volvo thru the prop exhaust is better flowing than Merc thru the prop exhaust. I am talking about the Y pipe and down. I am putting this all out cause the tune will not be the exact same as Merc. I am making aware the changes between the 2 as it might be hard to find that info out cause most are going to talk about the Merc set up / tune / and so on inwhich is not apples to apples.

Also do you have Volvo DP outdrive ? Volvo only offered a DP out drive for the HO 496 / GXI model. No single prop was not used for the gxi model. Volvo

To be clear I understand that was not you as per calling me for the help in the past -- hence from your first post I had to ask not knowing the location either. Same boat and a same Volvo engine. Just saying