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2006 Mercruiser 496 HO Engine starts, rough idle, stalls Help!!!!

17K views 7 replies 5 participants last post by  BDMarine 
#1 · (Edited)
Hello,
My apology if this questions has been asked many times. I did a search but could not locate an answer.
As the title indicates, my 2006 496 HO starts then stalls. I called for service. I was told they had to replace both fuel pumps (Low & high pressure). They contacted me said the boat is running. I went to start the engine -- same problem. The engine cranks then stalls within 5 seconds. The engine never runs normal then stalls, more link a rough idle. I replaced the IAC, no change. I try to advance the throttle while I'm trying to get the engine to run. It dies.
I called the tech to come back to the boat. He connected his computer for diagnoses. It indicated both cam and crank sensors were bad. He replaced them. Now the boat will not start -- almost like its not getting a spark (where is that old distributor cap. I will see if its providing a spark!) I asked him if either one of the sensors he replaced could be causing the engine not to start? He said NO. He came back the next day. Spent 8 hours trying to figure out the problem. He disconnected all the electrical connections from the boat network to try to isolate the engine. He connected a start button to crank the engine. The engine would crank but never started.
He said the boat needs to come out of the water (Formula 370 Super Sport). The engine needs a new wiring assembly. You have got to be kidding! The engine started before you messed with it. Now it will not crank over. So he said, I have no other option.
Today, I decided to reconnect everything he disconnected. I removed the cam & crank sensors he installed. I looked at all the connections looking for any wires that might have been frayed/damaged/etc... I checked all the fuses, the lanyards, anything I found on the internet that provided some clues.
The engine now starts (again) but stalls. I am back to where I started after spending $1300 for travel, labor, and parts to put me back at square 1 again. I am not a mechanic but I can read and follow directions. Can someone help me figure out what is wrong with my engine? Initially, everyone I spoke to said it was -- 100% the IAC. Now that I replaced it and the IAC did not solve the problem, what other options do I have? Here is a recap: both fuel pumps were replaced. Technician said the boat was running -- I doubt it!!. Replaced the IAC. NO change. Engine starts then stalls. Technician comes back. Replaces CAM and Crank sensor. Now the engines cranks but does not start. I removed the sensors he replaced and put back the old ones. The engine starts, rough idle, stalls. Where do I go from here?
Thank you in advance for your recommendations.
Jeff
 
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#2 ·
Where do I go from here?
Thank you in advance for your recommendations.
Jeff
To another mechanic.

I would check fuel pressure, KOEO. Should be 43psi or +/- 1 to 2.

IF FUEL PRESSURE is good: See if it will start with throttle forward from idle about an inch or so. IF it does run, check the IAC WIRES. They have been known to fry, become brittle, and break.

Have a certified mechanic with the Rinda software (on a laptop) hook up to the motor and see what codes have been set. There should be one or two. Write them down, clear them, and try to run again. See if any codes re-set.

Check the TPS. My throttle position sensor went and caused kinda the opposite of yours. It would idle high and surge-idle. Made it hard to shift and dock. Replaced IAC, no change. Put in Irridium plugs, the surging got SMOOTHER, but still surged. Found TPS had stuck at 3/4 throttle position and was telling the motor to fuel and time accordingly. New $80 TPS sensor and all was fixed. Code said "TPS OUT OF IDLE SPEC". Told me right where to look!
 
#3 ·
I will try advancing the throttle an 1" to see if it will start. I will check the IAC again. I looked at the wires yesterday. They were in great shape. Looked new. I will check the TPS. If I remove the IAC from the other engine, do I have to replaced it with a new gasket? I have no way of checking the oil pressure guage. My Formula 370 SuperSport does not have an oil pressure gauge. I will try to get the tech to come back out.
 
#4 ·
I agree with looking into the TPS. However find a certified mechanic with the Merc CDS. It will give way more information than the Rinda. We have both and when it is a 496 the CDS is the only choice.
Your previous mechanic is just throwing parts at it hoping it will fix the problem. Find someone that can actually diagnose what the problem is.
 
#7 ·
I am glad you got it running again! One thing I would check is the Dielectric grease on ALL connections. It is amazing how that electric lube will effect the function of the electronics. By changing out parts that are prelubed or old parts that still have the dielectric grease may fix a simple problem. Just a thought and good luck!! M
 
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