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~2005 5.7L GXI-D - #2, no comp!

deezums

New member
Hello everyone!

I've been trying to help fix a friend's boat lately, and thought I would finally come here and ask for advice.

The boat is ~2005 Cobalt, with a penta 5.7 GXI-D engine and outboard. When I first saw the boat it would not start, but it only had ~25psi on the high side so I figured it was an easy fix. I replaced the pump assembly (both!) the fuel pressure regulator, cleaned the rail really well and had the injectors flow tested. I measured ~10psi/55PSI low and high side, and the boat managed to start again. The fuel injectors were tested and flowed within a few points of each other, but the shop I took them to sucked and determined this off filling the graduated cylinders to ~30mL of 200 and stopping, frustrating, I don't really trust their numbers, nor do I know how you static flow injectors off such short time period.

Anyway, the boat started and ran OK, but would miss really bad on the high end. I checked timing and found it floats around 8-12 degrees while idling and seems to lock on to 12 degrees while locked, using an advancing timing light. Does this seem right? I know I can't clock the distributor to "fix" it. Everything I read says 10 degrees, but maybe my timing light floats a bit? I figured everything was OK here, new properly gapped plugs and wires and all seem to fire well visually.

So, the boat was running but not well and I still didn't trust the numbers from the injectors, so I ordered a set of remans from the internet. I installed those, and now the boat has a dead miss at idle even. So I got the compression gauge out and all are sitting at around 155PSI, 6 cranks with the throttle wide open. Except #2, the needle doesn't even budge.

So I was getting ready to pull the head because I don't have a quality leakdown tester and I figure the head will come off sometime anyway if it's the bottom end. I am thinking I may get lucky and a valve is messed up in some way or another, probably the seat. I figure it went south when the pump went out and was ran till it wouldn't any longer, and it running lean fried the valve and it was always on borrowed time since the pump died and only just now finally gave up completely. For sanity's sake I rechecked fuel pressure and it still showing ~10/50PSI as I expect.

I am not too well versed in boats, but I know quite a bit about cars. I'm familiar with volvo's engines but never heard of a v8 5.7L, was really surprised when I first saw the boat and saw a vortec sitting in there. I've done these before, and a whole lot more of the 3/4's one, too.

If the boat is in a dry dock there should be no problem pulling one head while in the boat, right? I mean, besides my comfort :D

Thank you in advance for any and all advise!
 
It took a little longer than I would have liked, but the boat is finally all back together and healthy. It managed to split the head between valve seats so I had to get a new one. The distributor was full of crud and rust flakes stuck all over the cam sensor. Still missed, but a new distributor and 0.042 gapped plugs fixed that one. Whew!
 
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