2001 5.7L Mercruiser misfires around 3200 rpm when decelerating under load

[Bobp1041]

Hello everyone!!! I am new to iboats and this is my first forum post. I have a 2001 Chaperral 260 Signature with a 5.7L Mercruiser and throttle body fuel injection. At the end of last season she started misfiring at around 3200 rpm when I would slowly come off plane. This problem only occurs on deceleration. I can come up on throttle slowly, get her up on plane with no issue but when I am up on plane and try and slow down slightly and it hits about 3200 rpm she starts misfiring. If I drop her down to 2800 or lower she smooths out and I can continued to decelerate or accelerate without issue. I have already replaced fuel filter, cap, rotor, plugs, wires and sensor in the distributor. Any enlightenment into what can be causing this issue would be greatly appreciated.

 

[alldodge]

I think your running lean, suggest pulling some plugs and see what they look like.

Have you checked your timing?
Timing is set at 8 BTDC when motor is placed in base timing mode
Plugs MR43LTS

 

[boatman37]

agreed. backfire on deceleration is a sign of a lean condition. start with the timing to verify its accuracy

 

[Bobp1041]

That is what I was thinking but I am not sure how to bypass the computer to get a accurate base timing reading.

 

[alldodge]

That is what I was thinking but I am not sure how to bypass the computer to get a accurate base timing reading.

Without using a scanner you can use a paper clip and put it between A and B on the DLC connector.

On another note, if you get an LED with a built in resistor, you can find out if there are any codes but counting the flashes. If you see 14 then there are no codes and your good. 14 = flash pause, flash flash flash flash double pause

 

[Bobp1041]

Sorry for the delay in posting my results, things have been a little crazy. I checked the timing and it is spot on 8 degrees BTDC and there are no codes other than 12 which I believe means System Functioning Properly . I'm at a loss and may have to break down and call a mechanic to take a look at it. I was trying to post a video of the issue but it is too large to upload.

 

[Therapydoc]

Subscribed

 

[Bobp1041]

Ok I uploaded a video of the issue on youtube.

 

[harleyman1975]

Hmmmm...I have nothing.

 

[alldodge]

Acting lean to me, what is the engine serial number?

 

[Bobp1041]

Engine serial number 0M065221

 

[alldodge]

Your SN is for manual 24
Need to check fuel pressure, it should be 30 psi at 1800 rpm.

Going to need a high pressure gauge 0-100 recommended, and an adapter to connect gauge at throttle body by removing fuel line. Should be able to get this at most auto stores (standard GM connector). Merc part number 91-806901