496 Mag hesitation issues...
 

Hi all. I'm brand new to this site and hoping to get some help with a frustrating issue. I bought a Crownline 260LS with the Mercruiser 496 Mag over the winter(157 hours on the meter). Ever since we put it in the water in early June, we've been chasing a few issues with no luck in resolving.

Issues:
1 - Motor stumbles/hesitates when I go from neutral and give it more than 25% throttle. Pulling skiiers and tubes, I have to roll into the throttle and it does fine. Basically, it falls on its face for a second or two and then builds power.
2 - Temperature gauge never gets over 145 degrees. I can let it idle for 15 minutes in Texas 100 degree heat and it gets to 140 and holds.
3 - When running at the lake trying to diagnose the stumble, I could hit the gas in neutral and hear a single beep/alarm. No idea what this beep is supposed to indicate

I reluctantly took the boat to a local shop. It was an awful experience full of delays, escuses, and odd conversations leading me to believe they were not competent. Being out of the country, the boat was with them for 3 weeks. Upon my return I told them I was picking it up regardless of what they had or had not done. Suddenly, they told me they had fixed the issues. Upon putting the boat in the water, it runs almost the exact same as it did before they worked on it. Here is what they did:

Raylar wires - I provided in advance
AC Delco plugs - I provided in advance
Cleaned/adjusted the IAC
Scanned engine and only got old codes. There were no misfire codes.
Checked the fuel pressure and said it was within spec
Scanned the engine for temperature and said it was cycling at 158-161 degrees

Based on my experience with the shop, I have no idea if they ever scanned the PCM or checked the fuel pressure. I have confirmed they swapped the plugs and wires. I'm wondering if all my issues are based around the motor never getting up to operating temperature? This assumes the gauge is correct and the shop didn't scan the PCM and I likely have a thermostat stuck open. I'm guessing if the motor is always cold then it is in a closed loop PCM program and it is running pig rich for protection. Does that seem logical? It might also explain the stumble/hesitation. One other issue might be the fuel/water seperator. It was changed in February by the previous owner but, the boat sat from February to June with 0 gas in the tank. I'm wondering if it might have accumulated some moisture and that led to the filter getting instantly clogged or some way not letting fuel to flow properly?

This week, I crawled all over the motor looking for any sensors not connected or any leaks. I found none. I did pull the IAC and make sure it was clean and installed properly. In addition, I cheaned the spark arrestor and checked all the wires to ensure they were tight on the coils and plugs. We're putting it in the water tomorrow and hoping for better results but, think I'm grasping at straws with these small changes. I'd just like to rule out any of the simple fixes before I ultimately get another shop to scan the engine for the issue.

I'm planning to drop the boat off in Fort Worth with a large, reputable Mercruiser shop in 2 weeks but, hoping you folks can lend some advice for anything I haven't checked yet.

Thanks,
Todd

BUP to the courtesy phone.......

Unless it's "his" shop that your planning on dropping it off at and he may just wait to get your money.(sarcasm)

I did notice a lot of very knowledgeable and detailed responses from "BUP" when I did some wildcard searches on this site earlier. I also saw he is in Fort Worth. Hopefully he'll chime in and I might just drop the boat off with him if he has a shop, which it sounds like he might.

Thanks - Todd

^^^ that's funny. Vindictor 101 thanks for the heads for both of us here.

I am NOT the large shop he is talking about. I never was the biggest in the DFW area nor the smallest either.

Anyways I know my way around the 496's whether its Mercruiser , Volvo, PCM, Crusader or Indmar but my experiences do not stop there either. I am still currently trained from the OEM's.

Here is the deal this boat owner (OP) is not far from me at all. With that said, I am willing to help but on a business level only sorry about that, yes as a paid for a job hopefully well completed on my part. My reasons for not posting the help is one its not fair for my local paying customers to fix other boaters over the net for free that are very close to me. This is the only way I make a living - working on boats. Number 2 the OP is willing to pay another shop in which will be a commission shop to fix and or try to fix his app anyways, so who better than possible me to at least look at it in the area. .

The choice is up to the boat owner in this case the OP.

If you want to scroll threw threads all about the 496 to see if anything stands out to help and especially anything that I posted that would be a good start as well but maybe a lot of time doing so on your part.

Do not forget I have NLA CAM sensors if needed to test with if in fact this is an older 496.

Anyways I am sure others might give me a plug or 2 for the possible person to bring in their boat app to fix especially being very close in the area.

I will ask this info beforehand - what year and what is the engine serial number ?

If you need my info I would be willing to see you this Monday or the next couple of days after that

the choice is yours or whomever and I am not going to toot my our horn about working on boats but if anyone else wants to recommend my services that's fine by me. Thanks and I can pass on my contact info if needed for the help..

You go right from neutral to more than 25% throttle ? Instead of engaging into gear first and then applying your desired throttle % ?

I am here

Thanks for the warning. :p

BUP - I'll send you a PM.

Thanks - Todd

I just type faster than I think...

I meant that I put it in forward gear and then quickly give it gas to pull kids on the tubes, etc.

Thanks - Todd

You can even call me tomorrow

I am caught up finally Just have one more to get out yeah was 6 weeks behind finally.

John

got your PM your serial number tells a lot - one you have the cam sensor that is available not the NLA you have the better crank sensor installed already and I know what fuel system you have along with which ignition coils you have. You have the Gen II coils in which are better. I know YOU DO NOT HAVE A DTS 496 because you have a IAC. With that said do you have smartcraft gauges and do you have a Bravo I or a bravo III being a Crownline as Crownline used a lot of the bravo III apps. thanks

My email is [email protected] best to email me there - thanks

put a title on the email also so I know who its from to open it.

I've seen many issues such as you describe with the 496's. The first thing you need to do is get it to a good mechanic that understands high performance and tuning on the 496's. Most shops don't have a clue. If it doesn't throw a code they are left with throwing parts at it. I'm retired now so I can't help you with the repair. "BUP" is a great resource on these forums and would be my first choice to recommend to look at your issues. I've had several customers that just were not happy with the crappy throttle response and hesitations on the 496- (mags) in particular. We resolved it by getting the PCM retuned by Whipple.

Bob Lloyd
ex-owner
Full Throttle Marine

Bob thank you for chiming in and the plug. I have the boat in my hands. Worked on it yesterday and finally got around today to scan the engine. I really have not had a day off in 2 months straight. The heat is killing me so today kind of did the complete scanning and freeze frame looks.

the boat is pristine condition and is a very nice boat but has many issues and some lack maintenance. Gen III cool fuel and the bottom 10 micron filter was very bad with even gasket material in it and large chunks of it. Very contaminated but was NOT internal paint that many see peeling from the GEN III cool fuel cell..

I feel bad for the new owner because the boat had these issues before he bought it and he was trying to learn all of this to fix it..

The biggest thing is all 3 batteries located on the starboard engine side is one of the worst cob job wiring and battery cables installed I have every seen coming from 85 K boat especially how pristine 99 % the condition is. At the starter the positive battery cables and leads were just about to fall off as the nut was not even close being tight.

12 volt battery cables and wiring were tied wrap to all the fuel lines with very sharp tie wrap cuts to bundle all that together. Huge dangerous situations could have happen from this install. Also can pull some of the battery and grounds cables straight out their connections by hand plus exposed wiring past the crimps. Very bad and poor crimps. Very poor install of the batteries, cables and wiring set up but the boat has the over powering stereo and amp set up for the listening pleasure installed. A couple of the ground cables are way too small diameter plus very cheap in quality.

History faults from the scan

Low voltage ( not hard to guess that one) but hopefully did not hurt the PCM over the long term of this.
Crank sensor - not worried about that one and same with cam fault
Shift in gear switch - will have to check on that one at the lake as well running to make sure it shows in GWR while running down the lake
Many Overspeed faults N

next the scanning parameters that stood out

IAC 64 % PWM at 2100 rpms that stands out 4 sure
MAP key on 10.54
BARO key on 14. 26 that stand out for the MAP
MAT key on cold engine 42 well hell no way on that one.

Anyways will be back on it tomorrow along with fuel pressure readings.

Lower unit severly impacted but was resanded and repainted with phantom black make over. Props have been damage at least twice rebuilt and still not right plus have many small dings and chips on them. Skeg length has at least 3/4 to one inch shorten to get rid of the damage that has taken place over time

Boat has 161 hours and had 78 hours of that 161 is idle speeds. I am sure this app was not broken in properly when brand new. Half its engine life was idle speed running around.

next again its a HO MAG and has never hit 4500 rpms - 4999 rpms in run history. never - either prop set up from day one was off or the owner was afraid of running WOT or a problem from day one not to be able to reach WOT.

Posting this as a word of warning because not the new owners fault but people who install stereo equipment or their own should learn on how to do it properly and not cause fire and or explosion problems with the install. This app could have been a bomb. The owner is extremely lucky that he still has a boat in one piece and I am not BS ing about that one. Who in the world tie wrap bundles 12 v battery and wiring cables to fuel lines. .

I hear you on the heat! That's one of the main reasons I'm out of the business. It's really hard work. Sounds like you've got a handle on his problems.

Bob

Any more updates on this?

As was mentioned earlier in this thread, I took BUP(John) up on his offer to take an extensive look at the boat. I made the mistake of buying the boat over the winter without having it water tested or inspected. It was purchased from a guy on the Crownline forums that had a very good reputation. I can't say enough good things about John. I hauled the boat to him last Monday(Labor Day none the less) and he immediately began looking over the boat. What was great about John is that he wanted me to stay so that he could show me everything. We went over the boat for nearly 7 hours. John is meticulous and was very mythodical about evaluating the boat. He found a variety of issues. The boat is in wonderful shape but, the previous owner did neglect quite a bit of maintenance. John ended up keeping the boat another 5 days, including 2 water tests with me. In the end, there were quite a few issues found and here are what was done to remediate:
Bad IAC
IAC muffler pinched
Cool Fuel filters(upper & lower) replaced. **The lower was extremely dirty**
MAP sensor was misaligned
Water pressure sensor replaced
Numerous grounds were lose causing inconsistent voltage to sensors and PCM - All tightened now

I took the boat out today and it is night and day. When I took the boat to John, it had a horrible hesitation/stumble and the top speed was 45mph at 4050rpm. Clearly the boat had issues. As of this afternoon, the boat ran 54mph at 4800rpm. The hesitation is gone and it comes out of the hole much quicker and picked up 9mph and 750 rpm.

John is the only person that will touch my boat moving forward. Again, I can't say enough good things about John and would recommend him to anyone.

Todd

As was mentioned earlier in this thread, I took BUP(John) up on his offer to take an extensive look at the boat. I made the mistake of buying the boat over the winter without having it water tested or inspected. It was purchased from a guy on the Crownline forums that had a very good reputation. I can't say enough good things about John. I hauled the boat to him last Monday(Labor Day none the less) and he immediately began looking over the boat. What was great about John is that he wanted me to stay so that he could show me everything. We went over the boat for nearly 7 hours. John is meticulous and was very mythodical about evaluating the boat. He found a variety of issues. The boat is in wonderful shape but, the previous owner did neglect quite a bit of maintenance. John ended up keeping the boat another 5 days, including 2 water tests with me. In the end, there were quite a few issues found and here are what was done to remediate:
Bad IAC
IAC muffler pinched
Cool Fuel filters(upper & lower) replaced. **The lower was extremely dirty**
MAP sensor was misaligned
Water pressure sensor replaced
Numerous grounds were lose causing inconsistent voltage to sensors and PCM - All tightened now

I took the boat out today and it is night and day. When I took the boat to John, it had a horrible hesitation/stumble and the top speed was 45mph at 4050rpm. Clearly the boat had issues. As of this afternoon, the boat ran 54mph at 4800rpm on bad props. The hesitation is gone and it comes out of the hole much quicker and picked up 9mph and 750 rpm.

John is the only person that will touch my boat moving forward. Again, I can't say enough good things about John and would recommend him to anyone. His attention to detail is second to none.

I'm working to get on John's schedule this winter to remove the (3) battery setup and awful cables in lieu of a dual battery setup(1 per side) with all HD marine cables.

Todd

Sounds like you had a lot going on. Glad it all got fixed up. I'm always interested in any problems and fixes for the 496's.
I have never met BUP but have read most if not every post he makes on the 496 and have no doubt he took care of you. After reading post #4 from him explaining why he didn't initially respond to this thread as to not step on any fellow local business toes really struck me. Talk about integrity!
Thanks for the update.