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  1. #1
    Join Date
    Oct 2006
    Location
    Oakland, NJ
    Boat
    Sea Ray
    Details
    1998 330 DA E80 GPS, Radar, & heading sensor
    Engine(s)
    7.4 Mag. Horizons 380hp
    Posts
    1,094

    7.4 Horizon (380 hp) idling rough

    Well here is the background, this started at the beginning of last season as just a nuisance that my strbt motor would sometimes stall when it was in gear at idle. I could cheat the throttle up a crack and it would be fine (after it was in gear), I spent days trying to diagnose and repair myself (changing all basic stuff cap, rotor, new platinum plugs and even the IAC). I finally gave up and had my marina do there diagnostics on it, they said it was low compression (90 psi) on the center 2 cylinders on one side due to the obvious exhaust failure. We decided to put the valve job off till the off season and just due the exhausts on this engine to prevent further damage and deal with it for the remainder of the season.

    Fast forward to this week:
    I had the marina that I had the boat at for the winter do the heads, finally got it in the water this week and they did the final adjustments and timing of the motor, and to my disappointment it runs just like it did last year... So now we eliminated the internals of the motor having any issues. It still sounds like it is "loping" at an idle and sometimes stalls at idle in gear. So that is why I am throwing this out to you guys, any ideas? I did get a code 33 on the scan tool which is MAP sensor failure, I cleared it and it came back a little while later, could this cause the symptom I have or is this an affect of the idle issue?

    Remember the IAC was replaced, I have not replaced wires yet they could be original but are the good Merc blue wires and "look" good. The only thig left that I can think of is the MAP sensor, TPS sensor, ECM, knock sensor?
    Last edited by Larry; 05-26-2010 at 04:32 PM.
    Larry

    1998 330 Sundancer "Miss Melina"
    2 X 7.4 Mag. Horizons 380hp FWC
    Ryamarine E80 GPS, Radar, & heading sensor
    Home Port: Norwalk Cove Marina, Norwalk CT

  2. #2
    Join Date
    Apr 2010
    Location
    Lake Travis
    Boat
    Sea Ray
    Details
    340 Sundancer 2000
    Engine(s)
    Twin 7.4L V-drives
    Posts
    582

    Re: 7.4 Horizon (380 hp) idling rough

    Sure it could. Easy test - swap parts between engines and see if the problem moves with it (MAS, ECM, etc.).

  3. #3
    Join Date
    Sep 2009
    Location
    Great Lakes
    Boat
    SeaRay
    Details
    88 268
    Engine(s)
    7.4L Alpha One
    Posts
    717

    Re: 7.4 Horizon (380 hp) idling rough

    Try to do a little maintenance on the throttle body:

    See if its fouled near the low idle closed position. This could block a little air flow and result in a rich low idle.

    Also see if the butterfly stop is still set correctly. Over time it can become warn/bent and need to be reset. This and a fouled butterfly area can reduce air flow and throw a false MAF code.

    I'm not saying this is your fix, just something to look at. Definatly less costly than a professional valve job.
    ...Ron
    Current Boat: 1988 268we 7.4L Alhpa1
    First Boat: . . 1989 230cc 5.7L Alpha1

  4. #4
    Join Date
    Oct 2006
    Location
    Oakland, NJ
    Boat
    Sea Ray
    Details
    1998 330 DA E80 GPS, Radar, & heading sensor
    Engine(s)
    7.4 Mag. Horizons 380hp
    Posts
    1,094

    Re: 7.4 Horizon (380 hp) idling rough

    I am going to try to swap out some parts this weekend, maybe even change the spark plug wires.

    BonBini, the throttle body was all cleaned last year when I changed the AIC, and the valve job is allready done now.
    Larry

    1998 330 Sundancer "Miss Melina"
    2 X 7.4 Mag. Horizons 380hp FWC
    Ryamarine E80 GPS, Radar, & heading sensor
    Home Port: Norwalk Cove Marina, Norwalk CT

  5. #5
    Join Date
    Aug 2007
    Location
    Marysville, WA
    Boat
    Searay
    Details
    2000 260DA w/Garmin 545s GPS with Standard Horion GX1500S DSC VHF
    Engine(s)
    5.7L EFI with New Gen Bravo III Merc
    Posts
    10,043

    Re: 7.4 Horizon (380 hp) idling rough

    I saw this on another site yesterday. This advice helped my friend get his "2000 7.4" running right.

    Quote Originally Posted by 2859er
    I had a problem with my 7.4L MPI. It wouldn’t start cold without advancing the throttle and giving it some gas. While this is common and normal for a carbed engine, not so for a fuel injected one. I was worried I would have to take it into a mechanic and pay through the nose, or buy a $400.00 electronic diagnostic tool. Neither option appealed to me in the slightest. So I brough it up here.

    This is what BrooklynJim advised:“Go to autozone/pepboys and tell them you have a 2000 GMC k3500 with a 7.4l engine, auto trans and want a TPS and an ECT sensor.. they have a money back guarantee that is second to none, swap them out one at a time and then start the engine...

    when the problem goes away.. that’s the bad sensor.. return the other one or keep it as a backup”..

    Well I didn’t go to auto zone/pepboys, I went to NAPA. But I got the TPS and the ECT. Total cost about $60.00. Now, how many times have you done some trouble shooting by swapping out parts into a boat (truck parts no less) to eliminate the variables and had the engine fixed on the very first part change? It has never happened to me before.

    Until today. I changed out the TPS or throttle position sensor, a part didn’t know existed until two days ago, turned the key, and varooooom. The engine came right to life from being stone dead cold, and held a steady idle with no throttle input whatsoever.

    Tomorrow I will return the ECT to NAPA for a refund. Total cast of the fix $46.00.

    BrooklynJim You Are The Man!!!
    Skål, Todd

    ~Nehalennia ∆~ Celtic Goddess of the Seafarers
    2000 ~ SeaRay ~ 260DA, 5.7L EFI, Bravo III

    www.vikingbay.co

  6. #6
    Join Date
    Oct 2006
    Location
    Oakland, NJ
    Boat
    Sea Ray
    Details
    1998 330 DA E80 GPS, Radar, & heading sensor
    Engine(s)
    7.4 Mag. Horizons 380hp
    Posts
    1,094

    Re: 7.4 Horizon (380 hp) idling rough

    Thanks Todd!
    Larry

    1998 330 Sundancer "Miss Melina"
    2 X 7.4 Mag. Horizons 380hp FWC
    Ryamarine E80 GPS, Radar, & heading sensor
    Home Port: Norwalk Cove Marina, Norwalk CT

  7. #7
    Join Date
    Aug 2007
    Location
    Marysville, WA
    Boat
    Searay
    Details
    2000 260DA w/Garmin 545s GPS with Standard Horion GX1500S DSC VHF
    Engine(s)
    5.7L EFI with New Gen Bravo III Merc
    Posts
    10,043

    Re: 7.4 Horizon (380 hp) idling rough

    Quote Originally Posted by Larry View Post
    Thanks Todd!
    Hopefully that works. Best of luck!
    Skål, Todd

    ~Nehalennia ∆~ Celtic Goddess of the Seafarers
    2000 ~ SeaRay ~ 260DA, 5.7L EFI, Bravo III

    www.vikingbay.co

  8. #8
    Join Date
    May 2008
    Location
    Cape Cod
    Boat
    Sea Ray
    Details
    1997 370 DA
    Engine(s)
    454 MPI's
    Posts
    60

    Re: 7.4 Horizon (380 hp) idling rough

    Larry -

    I have a '97 370DA and had the same problem with my port engine cutting out when I fist launced last Spring. Luckily I had a buddy that is a Master Electrician and is used to dealing with elecrical troubleshooting. From the DC control panel I had power to the starboard engine (and house loads) but when I pressed the momentary switch to check the voltage from the port battery bank the needle would drop from 13+ volts to zero.

    From there we went into 'troubleshoot" mode and went from the battery connections all the way through the DC Breaker Box (engine compartment with resetable trips) and from there to the wiring to the Control Panel (cabin). We found a loose wiring harness connector behind the dashboard that when we put pressure on it we got power back and when we let go we lost power on the port side.

    Unscrew the section of the dashboard with the Tach's/gauges on it and you will find a few wiring harness cables and connectors where the harness from the DC Breaker Box meets the harness to the DC Power Panel in the cabin. Wiggle the connector for the Port side and see if this works.

    After finding the problem we used small tie-wraps to hold the harness connector together as best we could. We haven't had a problem since.

    I hope this helps
    _____________________________
    1997 370DA Sundancer
    Twin 454 MPI's

  9. #9
    Join Date
    Apr 2011
    Location
    St. Thomas, USVI
    Boat
    Sea Ray
    Details
    99 Sea Ray 310 DA, '09 complete machinery, electronic, and cosmetic restoration.
    Engine(s)
    5.7 MAG Horizon MPI
    Posts
    19

    Re: 7.4 Horizon (380 hp) idling rough

    Does a 5.7 MAG Horizon have the same pair of sensors?

    My boat is in the USVI, and we don't have the option or luxury of a dealer, a technical expert, or a test computer.

    My STBD has been dead matched rpm for rpm with Port since the day they were installed. Without any degradation, it just suddenly ran very poorly at cold start. Stbd runs at 850, port runs roughly at 500. You do have to pull the throttle open to get it to run at all smoothly.

    Is there a comparable GM motor I can buy these sensors from to replace?

  10. #10
    Join Date
    May 2012
    Location
    Toms River, NJ
    Boat
    Sea Ray
    Details
    1995 280 SunRunner Raymarine C70 Chartplotter
    Engine(s)
    7.4L MPI Horizon Mercruiser Bravo III
    Posts
    13

    Re: 7.4 Horizon (380 hp) idling rough

    Quote Originally Posted by Larry View Post
    Well here is the background, this started at the beginning of last season as just a nuisance that my strbt motor would sometimes stall when it was in gear at idle. I could cheat the throttle up a crack and it would be fine (after it was in gear), I spent days trying to diagnose and repair myself (changing all basic stuff cap, rotor, new platinum plugs and even the IAC). I finally gave up and had my marina do there diagnostics on it, they said it was low compression (90 psi) on the center 2 cylinders on one side due to the obvious exhaust failure. We decided to put the valve job off till the off season and just due the exhausts on this engine to prevent further damage and deal with it for the remainder of the season.

    Fast forward to this week:
    I had the marina that I had the boat at for the winter do the heads, finally got it in the water this week and they did the final adjustments and timing of the motor, and to my disappointment it runs just like it did last year... So now we eliminated the internals of the motor having any issues. It still sounds like it is "loping" at an idle and sometimes stalls at idle in gear. So that is why I am throwing this out to you guys, any ideas? I did get a code 33 on the scan tool which is MAP sensor failure, I cleared it and it came back a little while later, could this cause the symptom I have or is this an affect of the idle issue?

    Remember the IAC was replaced, I have not replaced wires yet they could be original but are the good Merc blue wires and "look" good. The only thig left that I can think of is the MAP sensor, TPS sensor, ECM, knock sensor?
    I have the same exact issue, same exact engine.

    Valve job was done over the winter. Changed the IAC today.

    Idles fine in neutral. Idles and stalls in gear all the way back at Idle....unless I shutoff and restart the engine OR I take it out of gear and rev it up and back..... work out the rough idling......then idle returns to normal.

    Curious what was the fix?
    Last edited by ShoreFlyer; 05-23-2012 at 11:08 PM.

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