496 mag throttle hesitation
07-07-2015, 09:56 AM
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496 mag throttle hesitation
2003 SeaRay 340 DA with 496 Mags/Bravo 3 drives (245 hours). When its cold, they will start, but will hesitate or die when I try to ramp up in neutral. When it warms up a little, 110 degrees, throttle response is right and I can put it in gear and go. I replaced plugs with AC 41-983, but made no improvement. Both engines run flawlessly when above 110 degrees and both have the "hesitation" when cold start up. Any ideas ? Please help.
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07-08-2015, 02:47 AM
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I am not 100 % convinced that you even have a problem. I think some routine maintenance might help here, but with that said you can never rule out an IAC especially in a Mercruiser 496.
The first QUESTION is Sea Ray 340 DA do you have DTS = Digital throttle & shift I would think that you would for this app so if you do have DTS - YOU DO NOT have an IAC or an IAC MUFFLER nor a cavity in the throttle body for any of it. If you DO NOT have DTS then here my story book. Sea RAY 340 DA and not having DTS might be rare. But I will still write.
You report no rough idle no matter what the engine temps are, also says engines runs great after warm up. Bad or problem IAC's will still cause running / idling / stalling problems even when engines are fully warmed up or at 110 degrees. Also reports no hard starting / nor extra extra cranking times to even start the engines, if these problems were taking place usually signs of a problem IAC or a bad one. This leads me to believe possible IAC's are fine unless you report these problems as well.
When was the last time you cleaned your flame arrestors ? Have you ever changed the IAC muffler and clean the cavity it sits in ? have you ever changed the T stats, they are 12 - 13 years old now If never changed - they maybe stuck open some ? Have you ever change the coolant ? its rated for 5 years max even with no time on it.
I would scan the engines and check the coolant temp sensor and MAP sensor and MAT sensor.
Both motors doing the exact same thing at the exact same time and at the exact throttling and temps ? Maintenance or lack of it kind of stands out for me on this one. Just saying
Next info you know these engines have to warm up a bit and 109 degrees and below temps is still a very cold engine here for ramping the throttles up. The MAP sensor and the coolant sensor are reading and throwing a rich mixture for the PCM output to dump extra fuel for cold start up and then if you throw in the maintenance items that I listed possible needed to be done will make the fuel mixture even richer until the coolant temp sensor reports some heat to the ECM then it will start to lean the fuel mixture out making the engines run better.
Anyways maybe something to look at beforehand plus a couple questions how long does it take your engines to get up to full operating temps to a bare min of 160 degrees ? And how much throttle are you throwing at your engines at start up / cold ? Again 109 degrees is basically a real cold engine and the t stat has not even started to open.
Next question how long have you owned this Sea Ray ? if a long time, I take it then this is a new problem you are experiencing and did not do this before.
Lets take a carb engine with a choke for an example - at 109 degrees temp showing on the water temp gauge, the choke is still closed shut and the engine needs to warm up. Heck it will stumble to trying to ramp up throttles at that temp. just saying
Also if your IAC's have never been changed - it is wise to change them and keep the old ones as spares. A dirty flame arrestor and a dirty IAC muffler really hurt the IAC over time. You will need a new gasket with each IAC to and buy new IAC mufflers as well. And I will repeat you can never rule out the old Ford IAC on these marine GM engines.
The first QUESTION is Sea Ray 340 DA do you have DTS = Digital throttle & shift I would think that you would for this app so if you do have DTS - YOU DO NOT have an IAC or an IAC MUFFLER nor a cavity in the throttle body for any of it. If you DO NOT have DTS then here my story book. Sea RAY 340 DA and not having DTS might be rare. But I will still write.
You report no rough idle no matter what the engine temps are, also says engines runs great after warm up. Bad or problem IAC's will still cause running / idling / stalling problems even when engines are fully warmed up or at 110 degrees. Also reports no hard starting / nor extra extra cranking times to even start the engines, if these problems were taking place usually signs of a problem IAC or a bad one. This leads me to believe possible IAC's are fine unless you report these problems as well.
When was the last time you cleaned your flame arrestors ? Have you ever changed the IAC muffler and clean the cavity it sits in ? have you ever changed the T stats, they are 12 - 13 years old now If never changed - they maybe stuck open some ? Have you ever change the coolant ? its rated for 5 years max even with no time on it.
I would scan the engines and check the coolant temp sensor and MAP sensor and MAT sensor.
Both motors doing the exact same thing at the exact same time and at the exact throttling and temps ? Maintenance or lack of it kind of stands out for me on this one. Just saying
Next info you know these engines have to warm up a bit and 109 degrees and below temps is still a very cold engine here for ramping the throttles up. The MAP sensor and the coolant sensor are reading and throwing a rich mixture for the PCM output to dump extra fuel for cold start up and then if you throw in the maintenance items that I listed possible needed to be done will make the fuel mixture even richer until the coolant temp sensor reports some heat to the ECM then it will start to lean the fuel mixture out making the engines run better.
Anyways maybe something to look at beforehand plus a couple questions how long does it take your engines to get up to full operating temps to a bare min of 160 degrees ? And how much throttle are you throwing at your engines at start up / cold ? Again 109 degrees is basically a real cold engine and the t stat has not even started to open.
Next question how long have you owned this Sea Ray ? if a long time, I take it then this is a new problem you are experiencing and did not do this before.
Lets take a carb engine with a choke for an example - at 109 degrees temp showing on the water temp gauge, the choke is still closed shut and the engine needs to warm up. Heck it will stumble to trying to ramp up throttles at that temp. just saying
Also if your IAC's have never been changed - it is wise to change them and keep the old ones as spares. A dirty flame arrestor and a dirty IAC muffler really hurt the IAC over time. You will need a new gasket with each IAC to and buy new IAC mufflers as well. And I will repeat you can never rule out the old Ford IAC on these marine GM engines.
Last edited by BUP; 07-08-2015 at 03:32 AM.
07-08-2015, 09:42 PM
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A new IAC did not help. I'm beginning to believe the hesitation is designed ? Isn't it odd the problem goes away when the engine reaches 110 degrees ? Both engines, same "dead spot" on ramp up. Then at 110 degrees, they both run flawlessly. Thanks for imput from all. I regret I don't own a scanner, any ideas on what I can change next. LOL.
07-08-2015, 11:27 PM
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In my post above - paragraph 3 was I believe why an IAC was not a problem.
So no DTS since you do have an IAC but you only change the IAC and nothing else ?
I post a story book and maintenance most likely needed but I have no idea as you did not answer any of the questions nor about if any of that maintenance was done or not.
Paragraph 4 thru 8 says it all, I would read it very closely
Good luck with it
So no DTS since you do have an IAC but you only change the IAC and nothing else ?
I post a story book and maintenance most likely needed but I have no idea as you did not answer any of the questions nor about if any of that maintenance was done or not.
Paragraph 4 thru 8 says it all, I would read it very closely
Good luck with it
