norton

Frustration leads me to ask for your guys help! 1999 502 Mag efi (gen VI) with 250 hours on it. Had to be totally rebuilt last year at 150 hours (heads redone two new pistons, etc) due to an overheating and detonation scenario. It's in a 30 foot Mariah that normally does 57 mph on GPS-- but over the last month or two will now only do 35 MPH at 4000 rpm and no more! Boat is slipped in a lake and has a dirty bottom, so I can see losing 5 or even 10 mph, but something's definetely wrong. Spark plugs look good, checked the Corsa switchable exhaust-- seems like the flaps are opening, checked throttle-- butterflies opening fully, etc. Was going to check the ignition timing and any error codes as per the procedure outlined here elsewhere, but my diagnostic connector is a bit different than the one pictured and didn't want to risk hosing an ECM. Distributor seems tight, but could my timing have slipped? What does an engine that goes into 'protect' mode act like? The engine starts and idles fine, acts perfect-- just doesn't seem to make the power. I do have a pronounced 'ticking' when it idles, but I think it has always been there. Have I got a hosed cam? Spent $8k for a rebuild last year and now this!!!! ARRRGGGG!!!!! Any help would be appreciated-- thanks!

LS1 MOLESTER

At WOT RPM's won't climb above 4K and 35MPH?

SB

iTrader: (1)

GEN VI has a roller cam, so that shouldn't be it.

I've seen this scenario many times on OSO and other sites right after engine work. Probably the biggest % of what was wrong was 1st ) Knock sensor unplugged , 2nd) Incorrect base timing, 3) Improper voltage to ignition / computer from loose cables, connectors, harness plugs, etc

Sorry - can only give you guesses without more diagnostic info given to us.

Dave_N

I'll bet thats your problem. Don't do anything until you clean the bottom and retest.

Dave

norton

The engine ran fine after the rebuild-- good power and that's when I recorded the 57mph (I head to make sure that it ran ok!!), so I don't think that the knock sensor is disconnected-- although I will look for it and insure it's ok. I hate to take it out of the water to get it worked on now since in another month I'm pulling it from the slip, but I may have to to get someone to see if it's logged a code or something. I'll try to do a compression and leak-down test and see if I've blown a head gasket or something. So frustrating...

norton

And yes, MOLESTER-- at WOT 35 mph and 4,000 RPM is all she has. No engine miss, no stumbling, no over heating- nothing, just no poop.

Wobble

Pointless going much further without checking the codes. The previous overheat may have damaged/weakened one of the sensors. Might be a failed injector also.

Dave_N

Norton,
I really think your problem is just a dirty bottom, but checking for codes would not be a bad idea at all.

You mentioned a picture of a Data Link Connector, are you referring to the picture below?

Dave

norton

Yep-- I used that same pic and procedure (done very well, btw) but my connector has no electrical 'female' pin in position 'j' (like the connector pictured) and mine DOES have a pin in position 'I'-- where the picture doesn't have one. So I backed off. Would a bad injector or 2 throw a code? I though about that and even considered running some Technolene injector cleaner through my gas to see if one is sticking or something. Gas is fresh, no more than a month old. Thanks for helping me guys. Da** boats are like drugs-- too expensive, but what a high!!!!!!!!

Dave_N

The code reading procedure will still work with your engine. The one pictured is an earlier (A '96 as I recall) 8.2 inboard, but the terminals that you connect to ("A","B","E" and "F") to read the codes are the same.

A bad injector will not set any codes on a MEFI3 system.

Dave