Problem with VP 5.0Gi upgrade to VP 5.7Gi

Fin Man

Cadet
Joined
Oct 8, 2015
Messages
7
I had a 1999 Volvo-Penta 5.0Gi vortec with TBI, not happy with the performance, decided to upgrade to a 5.7Gi. Bought a block and heads from Craiglist. Had a local machine shop rebuild c/w new pistons, camshaft etc..I put everything from the 5.0 onto the 5.7 ( ECM,TBI new ex-manifold, risers) I also put new filters,coil,dist'cap and rotor) plugs and wires were new last yr. I took it to a local marine shop to have the base timing set.The motor starts easy and idles smooth while on the driveway.
Took it out last Saturday for it's first sea trial. Idled out of harbor, throttled up to 2K and it backfired thru the carb. could'nt get past 2K without backfiring. Took a hour break and tried again. This time I accelerated very slowly and seemed OK at 2K. Slowly stepped up 200 RPM at a time.. OK to 3400 then backfired again. Seas were too rough to continue but want to try again this weekend. Any suggestions on what the backfiring problem could be? I have read numerous forums about changing the ECM. 50% say "Yes" it must be changed the other 50% say "no" its OK...confused!!!
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
Ayuh,..... Welcome Aboard,.... Hook up a can of fresh gas to the fuel pump, 'n try it,....

Check the fuel pressure, when it starts breakin' down,....
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
You are going to need to get your ECM flashed. Don't run it anymore until you do. You are running too lean.

https://www.obd2allinone.com/mefituning.asp

[FONT=verdana,helvetica,sans-serif][FONT=verdana,helvetica,sans-serif]If you have upgraded your 5.0L to a 5.7L or 6.2L on your Volvo Penta or Mercruiser engine, it will run too lean, but the calibration can easily be updated. When going from a 305 to a 350 or 377 or bigger, the engine will flow more air and the stock fuel maps will not have adequate fueling. This applies to any of the OEM manufacturers calibrations when doing engine upgrades or modifications. Whether you have a Volvo Penta, Mercruiser, Indmar, Pleasurecraft, Crusader, Marine Power, or GM Performance Ramjet setup, we can do custom MEFI ECM reprogramming for you. Our price for calibration updates is $200. [/FONT][/FONT]
 
Last edited:

Fin Man

Cadet
Joined
Oct 8, 2015
Messages
7
Hi, I finally got the boat out for another sea trial. I Jerry-rigged a can of gas to the intake of the water separator. I drained the water separator... the gas looked good. I tried getting up to speed and same thing ..backfiring. Reconnected the gas tank. I did manage to get to full throttle but my maximum RPM was 3500. RPM was not stable it oscillates a couple hundred RPM...very noticeable at lower RPM's. I did not get a fuel pressure gauge connected. That is the next step. I do plan on getting the ECM flashed but I would like to solve the current issues before I introduce new parameters. Thanks for your help, I'll check the fuel pressure next
 

Tail_Gunner

Admiral
Joined
Jan 13, 2006
Messages
6,237
As Bruce pointed out your going to need to have the ecu tuned @ OBD ...your simply beating your head against the wall. The heads flow completely different the cam profile is different even the injectors are different...I believe even timing comes into play. Your running lean now and may burn a piston if you dont retune.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
WOW! You need to stop using your boat until you get the ECU flashed. You are running super lean. Hope you haven't damaged anything already.
 

funk6294

Petty Officer 1st Class
Joined
Apr 26, 2009
Messages
294
As pointed out it sounds like you need to have the ecm recalibrated for the increased displacement. The occallation in rpm you are describing is called surging, which is a classic lean mixture sign. That coupled with the popping through the intake again points to a lean mixture. With how's it's driving, I wouldn't continue to use it unless you want to rebuild the motor again.
 

Fin Man

Cadet
Joined
Oct 8, 2015
Messages
7
Ya, I guess I'll get the ECM flashed before I do anything else. I understand the burning lean argument because of the larger displacement,but I am confused as to why 50% of the people I talk to say it will run Ok. These people are long term experienced boat mechanics that have done this 5l to 5.7l conversion before with apparently no issues!
 

Fin Man

Cadet
Joined
Oct 8, 2015
Messages
7
One more thing....why is it so hard to find someone that does the flashing. The only place I know of is OBD Diagnostics in California.
 

Tail_Gunner

Admiral
Joined
Jan 13, 2006
Messages
6,237
One more thing....why is it so hard to find someone that does the flashing. The only place I know of is OBD Diagnostics in California.


Mefi is very old stuff and was proprietary software...https://en.wikipedia.org/wiki/Proprietary_software Today's modern fuel injection software is much more robust and tinkerable. Not much can be done with mefi in terms of flexability but it is very very reliable and more than capable of running your boat...OBD is a very good source to have your tune done.
 
Last edited:

Fin Man

Cadet
Joined
Oct 8, 2015
Messages
7
The ECM is in route, I should get it back by the end of the month. Looking forward to it. I have talked the people at OBD and I think they are very knowledgeable and will do an awesome job. I was just surprised at the lack of places that do the flashing. Most people I talked to, said it couldn't be done!!!
 

Fin Man

Cadet
Joined
Oct 8, 2015
Messages
7
Well, its been a month or so since my last post. I did have the ECM flashed for a 5.7 and it did run a lot better, but I'm not out of the weeds yet. On the last sea trial, the motor started and ran well out of the harbor but on acceleration it ran great up to about 3800 rpm, after that it stumbled and backfired thru the carb. Max RPM was 3900/4000 rpm. I checked fuel pressure on the low pump it was about 8/9 PSI when idling and about the same at max rpm. The hi pressure pump was about 30 PSI. That seemed to be inline with the maintenance manual I have. The spark plugs were new last year when it was a 5L. I don't know if they are worth changing again. Any more suggestions?
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
but I'm not out of the weeds yet. On the last sea trial, the motor started and ran well out of the harbor but on acceleration it ran great up to about 3800 rpm, after that it stumbled and backfired thru the carb.

Ayuh,.... Sounds like it still runnin' lean,....
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,798
You need to check for other conditions related to running lean such as a rusty sticking anti siphon valve or partially blocked fuel pick up...
 
Top