2005 Mercruiser 496 problem

[Jas0n]

Hi all any thoughts are appreciated. I have a 2005 496 with a Bravo (serial unknown) that I am trying to diagnose for the local marina (just a lowly GM tech). When it is cold it will only run for a few seconds and die. If and when you manage to get it warmed up it will idle rough and stumble on acceleration. Before I became involved 2 brand new merc cool fuel 3 units had been thrown at it in the hopes one would stick. There are no codes at all minus the ghost sensors that the outdrive doesn't have. The first night I went out I checked fuel pressure and had 38 psi key on. Started engine and by the time it died pressure had dropped to 35 lbs. Unhooked rail feed line from the properly running port engine, routed it over to the starboard engine (the problem child) hooked it into the rail, jumped the fuel pump relay and she fired right up and ran like a champ.

Went out tonight to finish diagnosis because by now I KNOW the problem is between the fuel tank and the fuel rail. Started by swapping the pump feed hoses between the port and starboard tanks. That wasn't it and the port engine still purrs like a kitten off of the starboard tank and the starboard engine runs like crap / hard start off the port tank. Figured the only thing that wasn't swapped was the high pressure hose itself (That's GOT to be it, figured it was delamed like a caliper hose) swapped hoses between the motors and once again the port runs great and the starboard well ... not so much.

Removed the brand new cool fuel assembly from the starboard engine set it on the bilge step and hooked the hoses to the port engine. Once again it runs like a champ while the starboard doesn't. So I figured when it ran good off the port pump it must have been a fluke. So I had the "tech" from the marina go back to the shop and get their Diacom. When I was able to get the starboard engine to idle the iac command was at 98% and the advance was all over the place anywhere from -2 to 25 ! So with the lack of relevant data form the pcm (knock counts, cmp etc) I started swapping parts between the motors. Swapped iac,tps,ecm,cmp,iat,map to no avail.

Finally I wanted to see if the starboard motor would run off the port pump still. swapped the hose over and sure enough it ran great. So the port engine will run off of either fuel pump perfectly but the starboard will only run of the pump that's mounted to the port engine. I don't want to put the port pump on the starboard engine because I really don't think that is the root cause of the issue even thou it will run off of it (not to mention my names on it now). I haven't swapped ckp sensors yet but will try that tomorrow.

If someone comes up with a solution or Idea I haven't thought of Id love to hear it. Thanks in advance.

I have checked voltage drop across the pump circuit as well and have gone as far as powering the pump directly off of the battery.

 

[Fun Times]

What is the fuel pressure reading on the good port engine? With the vacuum hose removed from the regulator, the fuel pressure should be at 43 psi, so 38 to 35 is to low as you know.

jumped the fuel pump relay and she fired right up and ran like a champ.

What engine relay did you jump? Good or bad engine? If bad, maybe your weak on 12v power or ground.

If you have access to the original cool fuel module, open it up and inspect for peeling paint including the top cover area under the regulator. You may have a clogged fuel system between the old Gen 3 fuel module all the way to the tip of the injector due to small paint particles. If so, a general fuel system cleaning might get it. If not, some have had to remove the injector to either clean using ultrasonic or replace them along with a line/rail flush while their removed.



Just ah FYI for you is all, on the marine engines, the fuel regulator on the "fuel rail" is used only as a fuel damper. Has no affect on fuel pressure.

http://www.google.com/url?sa=t&rct=...lmfE0c2ejC7uF2LQHx37BNw&bvm=bv.71198958,d.cGU


http://www.google.com/url?sa=t&rct=...4ICoDw&usg=AFQjCNFb-K9qNJO0mmKCPpo-ItIoRdNazA

You may find this thread a little interesting/helpful. For the crank sensor, be sure to get to post #27. Keep in mind your fuel system is a newer design then his.
http://www.offshoreonly.com/forums/...gging-intermittently-lagging-100-400-rpm.html

Keep us updated with your findings.

 

[Jas0n]

The relay I jumped was on the port (good) engine to power up the fuel pump on it after I ran the feed hose to the starboard fuel rail.

The original cool fuel module has some paint delamination on it at the top but isn't horrible.

From what I understand after talking to the shop owner and his parts hanger the problem is getting worse even after throwing the two modules at it.
I am under the impression it started as a loss of power and rough idle. What I have seen is a start stall cold, once you get it warmed up enough to idle it idles rough and will not take any throttle. As soon as you start to bring the throttle back down, it will attempt to "catch up" to the throttle position.

I'm starting to wonder if it doesn't have a strange ground issue even thou it cranks fine. Possibly its getting enough of a ground from the fuel line from the other engine to run decent ? I will admit I have seen way stranger things in my 15 years at a GM dealer. I once had a no start on a full size van after changing out a leaking power steering hose. Turns out it was in a body shop and they neglected to hook up one of the body grounds and somehow the hose I replaced was providing enough of a ground for the modules to function. Still don't know how but I saw it with my own eyes.

I will admit I haven't checked fuel pressure on the port engine. I'm more curious as to what the fuel pressure difference is at the starboard engine when I have the port fuel pump on it verses when I have its own module connected to it.

I did run down to Napa yesterday and pick up a delco crank sensor to swap out, since I have never had much luck with removing these 6" long monstrosities in one piece.

Will update tomorrow evening after I get back down to the marina.


P.S. both engines were removed at the end of last season so new transom plates and steering assemblies could be installed for the Bravo's.

 

[Fun Times]

From what I understand after talking to the shop owner and his parts hanger the problem is getting worse even after throwing the two modules at it.
I am under the impression it started as a loss of power and rough idle. What I have seen is a start stall cold, once you get it warmed up enough to idle it idles rough and will not take any throttle. As soon as you start to bring the throttle back down, it will attempt to "catch up" to the throttle position.

Have you checked your spark plugs? They may be fouled due to past high fuel pressure. When you have lots of extra time to read, search online "Mercruiser gen 3 cool fuel paint problems". It don't take much to create a problem.

I'm starting to wonder if it doesn't have a strange ground issue even thou it cranks fine.

The marine environment gets it share of very strange issues too and bad grounding would be one of them. Knowing the engines have been recently removed, there's a good chance someone missed a wire someplace whether it's loose or unhooked.

Also if the transom assembly is using a transom wiring harness that plugs into the MPI engine wiring harness and there are sensors being used for things like speedometer, steering angle, digital trim readout, etc. etc. then as silly as it sounds, anything wrong will make the engine run rough or stall it. But you should/would have seen that when hooked up to the Diacom. The 5 volt system of the PCM would/should have been out of range.

I will admit I haven't checked fuel pressure on the port engine. I'm more curious as to what the fuel pressure difference is at the starboard engine when I have the port fuel pump on it verses when I have its own module connected to it.

Since you have the luxury of two engines to help with this, you've got to know what both are doing. On the 8.1's you've got to be careful if your chasing an IAC failure as a bad/stuck IAC will burn out the IAC driver internally of the PCM and if you swap PCM's first, you now have two bad PCM's in short order. Also it's been known to melt the IAC wire harness/connector.

I did run down to Napa yesterday and pick up a delco crank sensor to swap out, since I have never had much luck with removing these 6" long monstrosities in one piece.

Hopefully the one link will help you with this some. Good luck.

 

[Jas0n]

Made it down to the dock after work today for round 3. Started by hooking the port fuel pump up to the starboard engine to see how it acted cold. Started it up and it ran great with only a slight hesitation. Pulled out my fuel pressure gauge because I had not checked the pressure from the port engine myself (I know better out and had taken his word that the pressure was 43 lbs. Low and behold the pressure was 78 psi :frusty:. Hooked the new pump up and had 42 lbs on the money and a start stall with the starboard engine. So basically what I have is a partially plugged pump on the port engine that is making enough pressure to push thru the plugged injectors on the starboard that has already had the failed cool fuel III module replaced.

Tomorrow I am going to run down and swap fuel rails to make sure I am correct and the take the rail back to my shop where I have the equipment to try to flush the injectors out and flow test them.

I also pulled a plug out of the port engine and the tip was blacker than the phantom black paint on the engine. Hopefully they replace the port cool fuel III module before it screws up the rail on the port engine. After I make sure the issue is in the injectors I am going to recommend they replace the plugs and fuel module on the port engine.

Also does anyone happen to know the thread pitch for the bolts that hold the module to the bracket ? The guy who changed it couldn't get one started so he threw it in the drink. I would like to assemble it correctly because I am going to be the last one on there.

 

[Fun Times]

Sounds like you're heading in the right direction now.

If you'd like the proper parts catalog for these engines, try to find and post the engine serial numbers. There should be a metal tag on the block just above the engine starter.

Good thing you checked both fuel pressures.:greedy_dollars:

Be sure to use your GM discount when you go to buy all 16 AC 41-983 spark plugs for these engines.From Merc they'd cost you $16.92 ea.

This may help with what size bolts you need, http://www.mercruiserparts.com/Show...png&inbr=11746&bnbr=50&bdesc=Cool+Fuel+System

 

[Jas0n]

Got down to the boat this evening, after conning one of my co-workers form the Chevy garage to come with me, Figured it would be quicker with a guy on each fuel rail . Got the rail swapped from the port to starboard engine. It idles great but still has a slight hesitation going to WOT. Swapping the injector rails made a huge difference but it's still not perfect. I am also suspect of the rail from the other engine seeing as how the pump is pushing 80psi, I'm sure some of that phantom black has made it into the rail on that engine as well.

After about 5 minutes of run time got the steady "oh ****" tone from the dash. Gauges looked good as far as oil pressure and temp, but didn't have the scan tool with me. There is also a noticeable squeak/chirp sound (very slight) while the engine was running today. I didn't sound like any internal engine noise I had ever heard before and I think it might be in the coupler area.

So I called it a day until I could get ahold of the marina owner who I'm helping out (for money of course :tongue told him the same thing I've posted here and he wants to throw all 16 injectors at it, replace the port pump and go from there. He didn't seem alarmed at all about the steady tone, from which I understand is either oil psi, manifold temp, drive oil, coolant temp or water psi. Also told him about the noise and he only wanted to know if his guy had heard it (have to be accompanied because its a private club).

I also get to replace the port side intake gaskets thanks to #3 injector cap falling off in the intake :frusty:. At least its a dry intake manifold.

The funniest answer I heard today was when I asked the tech from the marina what the oil looked like. "we changed it last fall" So now I know the first thing on tomorrows agenda ... Pull the dipstick. If the oil is milky I'm going to lmmfao.

 

[Jas0n]

16 injectors, one set of intake gaskets, 2 cool fuel modules and a pair of seawater impellers and both motors are running great. The steady tone ended up being the starboard engine port manifold temp due to poor water circulation. I would hate to see the customers bill on the repair. I made out with a 350 mag takeout with milky oil that I am going to use the fuel injection system off of for the 383 I am building for my Rinker 236 sport.

 

[Fun Times]

You didn't happen to look at the oil hoes routing did you? http://forums.iboats.com/forum/engi...259965-mercruiser-8-1-oil-line-routing-issues

Awesome news! Sounds like we were able to help walk you through some of this till the end. Nice job on your part at working it to a conclusion.

Good luck with getting your Rinker going and don't be a stranger.

What year is the 350 Mag? Post the serial number if you'd like some parts info off of it for a reference point.