496 MAG HO Fuel Regulator replacement


Groovitz

New member
2002 400SS 496 MAG HO. 1000 hrs. Both run strong on plane, BUT... STBD idles ruff and smokes a little at idle only. Scan tool says the IAC is NOT cycling at idle and NO alarm or codes. Running super rich is what I think. Fuel regulator or hung open fuel injector?Just replaced all plugs and they did not tell which cylinder might be the problem, that's why I'm thinking Fuel Regulator (common rail). NEXT issue: It seems there is no direct replacement only a rebuild kit?
Any ideas?
NOTE: I do not see a snap ring on the top of my Fuel Regulator.
 

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I'm pretty sure being a 2002 model you would have cool fuel Gen II with a boost pump, a serial number would help verify.

Your motor will have two regulators, one you posted and the one on the cool fuel module. In link below note item 18.
http://www.mercruiserparts.com/bam/subassembly/31823/6708/50

That said, the 496 has had issues with the IAC, and the bad thing about it starting to go, it can also take out your ECM. The typical IAC problem is it will either die or struggles when at idle. To verify it is the regulator you need to connect a fuel pressure gauge to the fuel rail. It should read close to 43 psi with the vacuum disconnected
 
Thanks AllDodge. Just picked up the fuel pressure gauge today, 43 psi is what I'm looking for. I have replaced a few IACs already, and always change out the IAC muffler/filter when it gets dirty. I'm concerned about this condition because I have a lot of "No Wake Zone"s around here and I'm afraid of fouling the plugs at idle if this is not corrected. I REALLY hope it's not in the Cool Fuel box, coz that looks like a #@$&er to get at!
 
Understand the Starboard side would be a something to get at. Being you have 43 psi then your good, the next thing I would look at was the MAP sensor. It should be a 1 Bar sensor and if defective it will cause the motor to run rich.

Remove it and check its condition
 
UPDATE: The actual fuel pressure reading on my STBD engine was 80 PSI!!!! Coincidentally, on this last oil change I sent in both samples (Port & STBD) to be analyzed. Port readings were perfect and exactly as I expected. My STBD motor oil was contaminated with gasoline and had a viscosity rating of 9...!!! From 25W-40 Quick Silver oil. OMG! Almost running WATER VISCOSITY in there!!! As we feared, the over pressurized fuel rail was pushing raw fuel past the rings and into the sump. Fresh oil & filter immediately and did not attempt to start again until the fuel pressure regulator was changed. NOW, 3 days later I still CAN NOT get the engine to start. It chuffs a few times on the initial cranks, like it WANTS to start, but then goes completely cold and just cranks with no signs of life at all. I have bled the bicycle type pressure valve on the top of the rail about 5 or 6 times already and there is plenty of pressure with no indications of air being released. I have cranked the motor with the throttle wide-open, quarter throttle, and closed.... still NOTHING. Before I completely remove, inspect, and reinstall the fuel regulator, could some one here let me know if I'm missing something before I need to also replace my starter! Thanx....
 
Sorry been out for a couple days.
Your in the area where the motor needs to be scanned for codes. As before, the early 496 have been known to take out the ECM when the IAC goes.

At 80 psi, that is high even for the standard high pressure fuel pump. The bad thing with that high a pressure it probably damaged the fuel pressure regulator. The motor needs to get a signal from the crankshaft position sensor. When your cranking you should see the tachometer move up to around 300 rpm. If it doesn't move then there is one possibility.

Another issue, is the wiring from the IAC to the ECM, need to check the wiring that it was not damaged.
 
Yes while cranking, the tach DOES move up. As a last resort, I even tried spraying starter fluid into the intake for a couple of seconds. NOTHING! Now I'm really concerned. I have a friend coming over later today with a DIACOM diagnostic tool. Hope to get this running TODAY!
 
UPDATE: The No-Start issue was that all 8 plugs were fouled! Those plugs had about 1 hour run time on them. Don't know why after the Fuel Pressure Regulator change, the plugs immediately fouled upon first attempt to start. All 8 plugs changed, started right up on very first crank. Fuel pressure still reading high (58 psi) at idle. Any other ideas???
 
With 58 psi pressure your regulator is stuck or the line going back to the fuel filter is clogged. My guess is the regulator is stuck. That high of pressure causes to much fuel to be released
 
The FINAL answer to this condition (running way too rich, smoking at idle, contaminating oil) was the fuel pressure regulator in the Gen II Cool Fuel module. Had to bite the bullet and get a whole new kit. At the same time, had the fuel rail removed, acid washed inside & out, all injectors sent out for cleaning and calibration, fuel lines, fuel filters & boost pump replaced. Runs like NEW. 915 hours on these engines and they pull like they're brand new. (Out of earshot & fingers crossed while I say that)... hahaha :cool:
 
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