502 mpi problems...alot of them!

[hammer250v8]

i have a 1999 mariah z302 with a 502mpi and bravo3.

my motor surges when i come off crusing and drop into idle. somtimes staying at about 1200rpm. if i rap the throttle in netural a few times it will settle down to about 900-1000rpm.

i also have alot of trouble docking this boat. i think this problem is related to problem number 1. the boat will move forward or reverse at about 6mph at idle. you could see where this would pose a problem while trying to dock. backing it in a slip......forget it!

i also stall the boat alot while goining from forward to reverse, or netural to forward or reverse. this problem also probally stems from problem number 1.


i've had all these problems since the day i bought the boat. i've always been an outboard guy so this is all new to me(4 seasons now)

any insight on these problems would be great. thanks!

 

[Bondo]

Re: 502 mpi problems...alot of them!

i've had all these problems since the day i bought the boat.(4 seasons now)

Ayuh,... Has it been Tuned-up in these 4 Years,..??..??

Fuel Filters changed,..??

Any diagnostics,..??

 

[havasuboatman]

Re: 502 mpi problems...alot of them!

The shift problem is at the remote shift assy on the engine. It's out of adjustment. If you don't have the tool, you will have to have it done by a shop.
The surge and high Idle you describe is usually caused by the throttle cable being adjusted just a little to tight.
At the engine end of the throttle cable, remove the cotter pin and washer from the anchor. slide the cable off of the anchor and rotate the adjuster ccw (unscrew) you may have to back off a little locknut.
You want the eye to be putting slight pressure on the anchor pin towards the closed side with the throttle in the full slow position.

 

[hammer250v8]

Re: 502 mpi problems...alot of them!

i think i changed the plugs the first season i had the boat, but not sure. did oil and filter(royal purple) and fuel last season then only used boat once.

i'm 1500 miles away from home in the florida keys now. there are tons of boat mechanics down here. i'm going to see if i can have somone come take a look at it. i have a great mechanic up north but the boat has to be in the water to diagnose these problems.

i'm going to attempt to adjust the throttle cable today, Havasuboatman. what is my target netural idle rpm supposed to be?(warm of course) also, what should my rpm be at idle while in gear?

 

[Don S]

Re: 502 mpi problems...alot of them!

The idle speed should be 600rpm in gear in the water.However, it is non adjustable and is controlled by the ECM. You might try disconnecting the throttle cable to confirm the that cable adjustment is or isn't the problem.
I doubt the shift adjustment has anything to do with the engine stalling while shifting. There is no shift interrupt system on the Bravo drives to interrupt the ignition.
I would indeed replace the fuel filter. And empty the contents into a clear container and check for water in it. DO NOT reuse the old filter.

Other than the above, you will need DDT of some sort, OEM service manual, fuel pressure gauges, vacuum gauge, DVM and some troubleshooting tools to isolate and repair the problem.

 

[hammer250v8]

Re: 502 mpi problems...alot of them!

the boat is idleing at 1000 in netural. i'm going to disconnect the cable and see what happens. i'll also put it in reverse hooked to the slip and report back the rpm in gear.

 

[QC]

Re: 502 mpi problems...alot of them!

I'm thinking 1000 RPM, Bravo 3, in gear, tied up, uhhhhhh . . . I'm also thinkng the same thing for four years, every reverse and every forward, bang.

I couldn't imagine handling that boat around a dock. If the tach is right (indicated by 6 MPH) that thing is unsafe dude.

 

[hammer250v8]

Re: 502 mpi problems...alot of them!

yea, it's been way too long. i've come to live with it. i always dock nose in. while docking i'm constantly in and out of netural. always have somone up front and in the back so we dont bump anything. i always dock way away from any boats!

i did the gear test yesterday. IF the tack is righ it's about 8-900 in gear. speed in gear is by gps. could never get the speedo to work.

i disconnected the throttle cable. same thing. 1000rpm in netural warm. i'm gonna try to get a mechanic to look at the boat while i'm down here. i'm leaving a week from today. although the engine will lope on the hose i think it's easier for a tech to diagnose problems with it in the water!

 

[hammer250v8]

Re: 502 mpi problems...alot of them!

just down messing around with the 502. staryed it up and tried blocking the intake screen on the mpi. i thought it would stall the motor but it didnt even drag it down. is this normal?

 

[Don S]

Re: 502 mpi problems...alot of them!

At idle the throttle plate in the throttle body is all the way closed and air get to the engine through the IAC valve. So yes, you could close of the flame arrestor and it won't change the engine, AT IDLE. As soon as you try to give more throttle and the throttle plate opens, then you would notice it.

Head up to the adults only sticky at the top of this forum and download the manual for your engine. Should be manual #23