Twin merc 454 Mag MPI- What am I missing?

[waterone1@aol.com]

This is going to be a long one, please bear with me, any help would be appreciated. Ok, first, this boat is new to me, so I do not have any history to compare to. The symptom, or problem is that the port engine will not produce the same power or top rpm's at WOT. The starboard is hitting 4800 the port 4000-4200. The engines are 1999 Merc 454 magnum horizon mpi's, serial numbers 0L086966(port), 0L086965 (starboard) both have about 260 hours on them. The engines are coupled to V-drive down angle transmissions and are turning 4 blade broze props. Both props were sent off to be checked and matched prior to me launching boat. Also prior to launching boat, new spark plugs, caps and rotors were installed in both engines, compression was checked on all cylinders, all were between 130- 150. I have run two tank fulls of fresh gas and the fuel/water seperators have been changed twice. I have pulled each plug and tested it on it's wire to insure that each plug is firing. I have run the boat under load with a fuel pressure gauge hooked up to the injector rail, it is maintaining 40 pounds of pressure. Base timing was checked on both engines (with ecm set to base timing mode)both are at 8deg. I have run the boat(with someone else driving) through the rpm range with a scan tool and timing light hooked up and verified it is advancing up to 32 deg. There are no trouble codes in the ecm. While running under load both engines appear to be matched untill 2500 rpms, from there up the port throttle must be pushed further to maintain same rpms. I recorded all of the ecm data while running, and all I can tell is that the port engine is working much harder to produce the same rpm as the starboard, for example at 3500 rpm's the port is at 64% throttle with a tps voltage of 2.99, while the starboard is at 47% throttle with a tps voltage of 2.37. The Map is showing likewise. Prior to launching the boat, I did a power balance test on the injectors and replaced two, low flowing injectors ( on this engine), retested and all was fine. There are no leaks around the injectors. I have looked through and followed the troubleshooting in service manual # 23 and cannot find anything. Just for the heck of it I swapped ignition coils between engines....no change.The only test I have not done yet is to put a vacume meter on the intake. Does anyone have any other suggestions or ideas ??

 

[newport dave]

Re: Twin merc 454 Mag MPI- What am I missing?

Vacuum gauge may help diagnose a weak valve spring or other mechanical causes.<br /><br />How old are the plug wires? If they are the original Mercruiser wires they will have the date of manufacture on them (like 2Q99 for 2nd quarter 1999). I would replace them just to eliminate that as a possible cause. <br /><br />Have you checked the throttle linkage? I think that engine has the two stage linkage where the secondary throttle plate begins to open at about 50% throttle position. Check and verify that both the primary and secondary are opening fully at WOT. Hope this isn't one of those setups that you have to pull the riser to get the flame arrestor off.<br /><br />When you say you recorded the ECM data, is that in a Diacom software file?<br /><br />Dave

 

[Don S]

Re: Twin merc 454 Mag MPI- What am I missing?

I'd do another injector balance test. Had one that I replaced 3 injectors on, and it ran good for 2 days before going bad again. Found 2 more the next time. <br />Also checked the injector rack and found very small rust spots inside the tubes where the injectors attached.<br />Used some Muratic acid in the tube. Then cleaned and blew out the tube with compressed air a hundred times to make sure they were clean. (New manifold was not available for 2 months and costs $800) Customer never had any water problems in his filter or anything like that, so the rust was a shock to say the least. Plus the engine was several years old.<br />That was a year ago, and no problems after that.<br /><br />Uhhh Dave ...... It's MPI, no secondary throttle plates ya know....

 

[newport dave]

Re: Twin merc 454 Mag MPI- What am I missing?

Originally posted by Don S:<br />Uhhh Dave ...... It's MPI, no secondary throttle plates ya know....

 

[newport dave]

Re: Twin merc 454 Mag MPI- What am I missing?

Primary open at 50%, secondary ready to open at a ratio of 2:1 over the primary (the secondary will open 100% as the primary opens the remaining 50%)<br /><br />

<br /><br />Dave

 

[Don S]

Re: Twin merc 454 Mag MPI- What am I missing?

I was thinking about the single inlet. Hadn't even looked at the manual.

 

[waterone1@aol.com]

Re: Twin merc 454 Mag MPI- What am I missing?

Dave and Don, both throttle plates are opening all the way (yes,this is the setup that the flame arrestor is one inch away from the riser). I didn't replace the plug wires, but did pull them one at a time and put a test plug on them and was getting fire. I have also run the engine in the dark and do not see any signs of arcing. I am glad that you pointed out the injector problem, I will re-test them to see if any others have failed. Let me know if you have any other suggestions, and thanks very much.

 

[Mechlawrence]

Re: Twin merc 454 Mag MPI- What am I missing?

I'm a auto tech not a marine tech but it doesn't sound like the TPS sensors are reading right. If you push your throttles open to say half throttle then both tps sensors should be reading the same voltage and the same percentage. if they don't then either one is lying or one of your engines throttles isn't opening up as much as the other. If the PCM can only "see" so much throttle (TPS voltage) then it will only supply an appropriate amount of fuel. I would verify that both engines throttle plates are opening equally at the same throttle position at the helm. You say the MAP snsrs read likewise, does that mean they read different like the TPS does? If so then it sounds alot like one of the engines throttle plates aren't opening up correctly. MAP snsrs just read Manifold Prsr and if one engine throttle isn't opening up as much as it should then that would explain all your snsr readings.<br />Lawrence

 

[waterone1@aol.com]

Re: Twin merc 454 Mag MPI- What am I missing?

Lawrence, I think you are miss-reading my post. To get the same RPM's I am having to push the throttle on the port engine higher (thus the higher tps voltage). In your example, the tps voltage and throttle percentage would be the same, but the port engine would be several hundred rpm's slower than the stbd. engine.

 

[waterone1@aol.com]

Re: Twin merc 454 Mag MPI- What am I missing?

UPDATE. Did power balance test on injectors again. All injectors tested within 1 pound of average....no problem there. Still stumped!!

 

[Reel Poor]

Re: Twin merc 454 Mag MPI- What am I missing?

Im with Don on this

Also checked the injector rack and found very small rust spots inside the tubes where the injectors attached.

The injectors have a small screen on the inlet side that can stop up with rust deposits from the fuel rail. Partially cloged injectors may not fail a balance test but may starve the engine of fuel under a heavy load.<br /><br />The best indicator of this problem is, <br />1. There are no codes present. Sensors are working properly.<br />2. Fuel pressure is at specs and steady.<br />3. Injector problems already stated.<br /><br />I would suggest switching ecm between engines just to be certain its not an ecm problem.<br /><br />And if the problem does not move.<br /><br />Then I would recommend removing the fuel rail and injectors and physically looking for rust deposits in the top of the injectors and in fuel rail right where the injectors connect.<br /><br />Wouldnt some O2 sensor data be helpfull here.

 

[Boatin Bob]

Re: Twin merc 454 Mag MPI- What am I missing?

Could you have 2 plug wires crossed? I know you tested them all to be firing but if crossed they would be firing at the wrong time.

 

[waterone1@aol.com]

Re: Twin merc 454 Mag MPI- What am I missing?

Reel Poor, I hear what you are saying, hopefully Don can clarify this, but it would seam to me that if the injectors had rust or some blockage they would fail the balance test. When I did the test again today I was sending a 500 millisecond pulse to each injector, it was dropping the fuel pressure from 40 pounds to 20 pounds....that is a ton of fuel to flow from each injector....much more than the engine could call on durring full throttle. By the way, I would kill for an O2 sensor on each cylinder, or at least one on each side. Bob and Dave, while I have checked the plug wires, I am going to replace them......just in-case, I will tripple check the firing order again while installing the new wires....I'lll keep you posted. Again, thank you all for your help!!

 

[QC]

Re: Twin merc 454 Mag MPI- What am I missing?

Originally posted by Reel Poor:<br /><br />Then I would recommend removing the fuel rail and injectors and physically looking for rust deposits in the top of the injectors and in fuel rail right where the injectors connect.<br />

Can't you swap all of that between engines too?<br /><br />With that said, this sounds to me more like the engine is actually right and that something else is causing the additonal load on the port side . . . If this were two different trucks with the same exact specs we would send the trucks back to the customer and claim that the problem was in the drive-line. Could that be the case here? The v-drive? Looking through all of the posts and your original one, that appears to be the only link in the chain that has not been checked.<br /><br />Propeller load curves are pretty close to linear so the even performance up to 2500 doesn't bother me much as there is not really a whole lot of load up to that point anyway.<br /><br />Something to mull over. I have no experience with v-drives, but I am having trouble dismissing the logic . . .

 

[waterone1@aol.com]

Re: Twin merc 454 Mag MPI- What am I missing?

Latest update: Replaced spark plug wires.....no change. This is getting old !!

 

[Reel Poor]

Re: Twin merc 454 Mag MPI- What am I missing?

Heres a couple more ideas.<br />Restricted exhaust, ie colapsed exhaust hose, damaged muffler.<br />Check all your belt driven accessories, alt, p/s, circulating pump, raw water pump for binding, hard to turn.<br />And as Quietcat mentioned, driveline binding or trying to freeze up.<br />You could try to enrich the fuel mixture with a secondary source, ie can of carb cleaner, propane bottle with rubber hose, a small amount of either through the throttle body, to much and it may try to load up, to little and may have no effect. You may have to try different flow rates to find the sweet spot.<br /><br />Disclaimer<br />For professional service personal only. DO NOT attempt this at home.<br />This could be a fire hazard and should not be attempted. But if you must, it should only be done with great caution under controlled conditions.<br /><br />Does the engine run properly under these floundering conditions or is there any other symptoms that occur, ie missing, popping, overheating, ect.<br /><br />Does the scanner give a fuel injector pulse width reading. If so, what is it, and is it the same as starboard readings.<br /><br />Have you switched the ECMs?

 

[waterone1@aol.com]

Re: Twin merc 454 Mag MPI- What am I missing?

Latest update: Swapped ECM's between engines. Problem stayed with port engine. By the way I had all of the manifolds and risers off prior to launching boat to inspect them. There are no restrictions in the exhaust and no colapsed hoses. None of the accessory items (alternator,idler pulley, circulating water pump) are difficult to turn or making any noise. The raw water pump has a new impeller and is difficult to turn by hand, but that is normal. I'm stumped and out of idea's. I have a friend who works on V-drives, I'm thinking it's time to give him a call to look at the drive line.

 

[Reel Poor]

Re: Twin merc 454 Mag MPI- What am I missing?

Another thought.......<br /><br />Pull the plugs and see what they have to say about fuel mixture.<br /><br />

Does the engine run properly under these floundering conditions or is there any other symptoms that occur, ie missing, popping, overheating, ect.

While running under load pull the plug wires {one at a time } or the injector term connectors and make SURE ALL cylinders ARE hitting like they should, 3500rpms or higher.

 

[waterone1@aol.com]

Re: Twin merc 454 Mag MPI- What am I missing?

I pulled the spark plugs last week when re-doing the compression check. All looked good. The engine does not miss, pop, sputter or overheat. I can only get to two or three of the injector wires with the plenum on (due to deck structure of boat...thank you Cruiser's inc.). Latest development, today I found a telltale #2 code.....drive over-temp. My buddy is supposed to take a look at the drivelive on Monday. I'll keep you posted on what we find.

 

[Reel Poor]

Re: Twin merc 454 Mag MPI- What am I missing?

At least its something worth considering.