New to the forum and posting for the first time. I have a 1996 Cobalt 253 with a 2004 VP Gxi and SX Duo Outdrive. This is my second season as owner, but owned countless others and I'm an above average driveway mechanic and am a mechanical engineer by degree and profession. I was referred over from iboats and told to title this post exactly like this. This person did not specify which issue I'm having is the known issue but heres what I'm dealing with....

Per my diagnostic and my shop manual its MEFI-4

I was in a long no wake a few weekends ago and the fuel pump just started screaming. A few moments later with the hatch popped the engine started surging and then stalled... I flagged my buddy down and he threw me a line to get back to the dock. Wife tied and bad knot and it came undone and before I had him circle back around I decided to start and start it again. Started up, and ran all the way back to the dock. Was a little sluggish but still could plane the 2 or so miles back to the ramp.

Started reading up and saw that the pumps (fuel cell) is problematic so I pulled the pump removed the paint inside, cleared the screens, replaced the filter and reassembled. It was scaley but all the screens were clear. Reinstalled it and took it out from the ramp and it was worse than before, no get up at all. I can still plane but 3K is about all I can do without forcing it (and dont want to). I had a group with me and a place to be so I limped it around for the day. Figured in my disassembly process (which involved a hammer) I ruined the fuel cell so I ordered a new one. Installed it and headed to my parents with the family on the 4th. Issue was unchanged. No ass, and wont comfortably go over 32mph or 3K rpms

My dad has a Techmate Pro and while I was there I ran the codes and three popped up. MAT sensor, Crankshaft Position, and Cam Shaft Position. I cleared the codes (and borrowed the scanner) and went home which was 25 miles or so and ran the codes again and the only one that reappeared was Cam Shaft Position sensor. Thinking i was a fool for spending 695 bucks on a fuel cell I bought the $30 sensor and replaced it and thought I was in the clear.

Went out the following weekend, and the problem is unchanged AGAIN. Same symptoms... Same exact. Ran the codes after a few mins of cruising and none reoccurred. Ran it a few more miles and tested again, no codes. Ran it back to the dock (8-10miles), no codes.

So I decided to start chasing fuel issue again. So I started the troubleshooting the fuel system section of my shop manual. I got to the point that I need an injector tester which I don't have so I went a little rouge and ran the engine at 2000rpms with the gauge on the fuel rail and holds at 40psi. Removed the regulator and it looks clean. Pumped up the system and did a bleed down test and it drops from 40psi to about 37-38 and holds for 10 mins (maybe more but I didn't want to wait). But everything seems to check out up to this point.

My Techmate Pro that has the ability to do a power balance test that, if I understand it correctly, would point me towards a faulty injector or coil pack and i'd just replace both and still be ahead of paying a mechanical to trouble shoot and labor.

My problem is when I select the test, rev the motor between 1000-2000rpm it only allows me to select A or H. It says that it's disabling for 5 seconds. I notice no change and the screen doesn't stay on testing screen but for a second and goes back to the screen to select A or H. I really need some suplimental literature for this because the book is vague. I would think I'd be able to select A,B,C... One letter per cylinder, not A or H only. And it still doesn't seems to do anything.

I'm at the brink of blowing my savings account up and paying someone to fix it because I'm at my limit of ambition, tools and knowledge. Hopefully I have found my new home for boating information and thank everyone in advance for their help.

Before we even get going here post your model # of the engine and engine serial #. Thanks. year model does not mean nothing as to when and what actual parts are on the engine OEM stock. It all goes by engine model # for Volvo and engine Serial # for Mercruiser. Just saying.

Also is your engine completely Volvo Penta OEM stock ?

The Carter made for Volvo cool fuel cells are a big problem. Just upfront info first of all.

The plaque is really hard to get to and its partially rusted but I was able to make out GXi-D and the line above is 3869264. God I hope that's right, I have to be a contourionist to get to it. From what I can tell it's bone stock. If they replaced anything they painted it red to match haha. The pump I replaced the old one with is the same Carter pump SN 21608511.

I know the pump is problematic from my research, that's why it was the first thing I replaced. Thanks for the quick response.

There google that part number 3588865

I googled that and it appears to be the same pump I put in, I just simply replaced the entire fuel cell (LP pump, HP pump, Filter and housing) not just the high pressure pump. The S/N I provided is for the entire fuel cell and is located on the housing. The new part I purchased matched the exact part I took off that ran fine for 100+ hours. Please elaborate if I'm misunderstanding you.

Start simple, how old is the fuel and have you done a fuel quality test? I had a Volvo 350 a couple years back that you would have sworn was running lean even though fuel pressure was spot on. Took a fuel sample, did not like what I saw.Pumped the tank, changed the filter, and the boat is still running like a top.

the issue happened all at once is why I'm leaning away from it being fuel. It ran well for 2 months this season and then one day the problem I described above happened. I've burned 40-50 out of an 80 gallon tank this season too. So is not old. Actually it ran better this year on season old gas. Fuel quality test is not something I've done though, nor can I say I'm really aware existed. Ive never gassed up at a marina either (not that I know for a fact it much matters).

I pump fuel into a clean snapple bottle (I prefer the lemonade flavor), let it sit for a while and look for signs of separation. If I see anything suspect I pump it out and start fresh.

good call, and best of all its free

Put the fuel pressure gauge back on and monitor pressure when the fault happens . Think it was 3500rpm?
if that one has voltage fed to operate the cam sensor, make sure its not dropping off , that one will make grown men cry..