1999 Mercruiser 350MAG Issues

HighFlight2k2

HighFlight2k2

New Member
Mar 11, 2007
105
Bear, DE
Boat Info
1999 310 DA
Engines
T/350 Mag
Hello all. Any help would be greatly appreciated.

1999 310 Sundancer, T-350Mags, Inboard

Items replaced to date by dealer:
- Exhaust manifolds
- 3 of the injectors (they broke them)
- fuel pressure regulator
- MAP sensor
- cap, rotor, wires, plugs
- computer (swapped with both the port engine and a "known good")
- fuel filter many times

Also the fuel tank was checked for water (baffle containing fuel level sending unit). Water treatments were added as well as 70+ gallons of fresh fuel to ~20 gallons of existing fuel.

So...to the issues/questions.

The engine runs fine at low to medium RPMs. Anything above ~2800 RPMs it has the following symptoms:
- Oscillating RPMs (~200RPMs)
- Inability to maintain high RPMs many times limited to 3200 RPMs regardless of throttle possition.
- When RPMs drop down, they will surge back up without throttle position change by over 500 RPMs.
- When RPMs won't spin up and throttles are mashed, it sounds like it's laboring and trying to spin up but just won't. At times, it almost seems like its starving for fuel.
- A couple of times, at cruise RPM, the oil pressure dropped by half. Oil is clean and at the correct level.

My plan for next weekend is to run the engine from a portable tank. That will at least rule out the fuel tank and fuel as a problem...even though I am pretty sure they are not a problem.

Any suggestions?

- Could timing cause this?
- Could them setting the timing without putting it in "Base Timing Mode" cause it?
- Could it be the fuel pump...even though their handhead computer didn't show a pressure drop?
- Can oil pressure sending units be intermittant? If so, can this be misinterpreted by the computer?
- One person suggested the knock control system. Their handheld computer didn't show any knock issues. Can this be missed by the computer interface?

Sorry for the book, but as you can see, it's been an ordeal. We bought the boat last spring and had problems all summer without any resolution. I am about to start it back up again with them but they have lost all credibility and I am telling them what to do this time around.

Thanks very very much for any assistance.
 
Sorry to hear about your troubles - Do Both engines do the same thing at the same time ie: the surges, oil pressure drop, RPM variations etc.? How many hours? Raw water cooled? Why were the manifolds replaced? intrusion? I know you mention the ignition parts were replaced but were the distributors checked - I've had similar symptoms with automotive applications and traced the problem back to worn distributor shaft bushings/shaft and or stuck mechanical advance system even though the initial timing was properly set. Although a long shot another possibility is that the valvetrain (springs) may be weak - this would most likely be caused by over-revving (Boat knocked out of gear under cruise and allowed to rev free) - I'm sure someone here may be able to shed some light on your problems or has seen them before - try not to get even more discouraged - you'll find the problem
 
Nope. The Port engine runs like a top. They have a bit over 100 hours and are freshwater cooled. The manifolds were changed because of a crack that was letting in coolant. Honestly, I doubt they did much more than replace the cap, rotor, and wires. But I can tell you that the engine didn't have this problem before they started working on it and they wouldn't have removed the distributor.

I should also mention that the injectors were replaced because they broke them when they took the top end off while diagnosing the coolant ingestion problem (the origional problem).

Thanks.
 
YES, setting the timing without first setting the ignition to "base timing mode" could cause this. If your engine manual says that the timing for your model year engine needs to be set in this mode and they didn't, then they need to start all over by setting the timing properly before troubleshooting any further. Who knows what ignition advance you end up with at running RPMs. When the ignition is NOT in base timing mode, it constantly changes the ignition timing to adjust for temperature, mixture, speed, etc.. There simply is no way to set the proper timing if it is changing all the time while you are adjusting it. Make sure it is required for your year engine.

The distributor shaft drives the oil pump. If the distributor is loose, the rotation of the camshaft gears meshing with the distributor shaft gear will put upward pressure on the distributor. It may lift up enough to disengage the bottom of the distributor shaft from the oil pump. I have never seen an engine run past 1500 or so RPMs for very long with this condition. The distributor needs to be VERY loose for this to happen. Check to see if they installed the little "fork" that holds the distributor in properly, and have tightened it down all the way. You should not be able to turn the distributor without a little "oomph" if it is tightened down properly.

After having them reset the timing propery, I would have them do the following if it still doesn't run correctly:

1) Run a compression check on all cylinders (since it sounds like they removed / reinstalled the heads and intake manifold).

2) Swap the entire distributor with a "known good" one.

3.) Try a new coil - they can sometimes work fine under lower RPMs and "break down" at higher RPMs.

4.) Try a new ignition module (not the "computer" the IM is the little module under the cap that reads the pulses from the little magnetic wheel with fins on the dist. shaft and triggers a spark each time a "fin" passes by it)

5.) Have them check for vacuum leaks - everywhere. Sounds like they took her pretty far apart. It might be something really silly like a missing vacuum line.

6.) Verify that they have properly grounded the engine to the same place as the other engine. A missing, damaged, or improperly installed ground strap can cause all kinds of strange problems. If you don't see a ground strap, check the negative battery cable connection to make sure it is OK - it may be the only "ground" for the engine.

Good luck,
Michael
 
Something silly as Michael said. Check the Air/Vacuum hose going in to your carburetor.
Maybe loose or full of dirt. If the carbs cant get air,they will run like s**t
Just a thought
 
Not that it is related to your issues, but has the exhaust system on the boat been retrofitted to the water lift muffler design? 99 310's with the original log style exhaust collector systems are well known to have suffered from water ingestion problems and most of them were updgraded by either Sea Ray and/or Mercrusier when they were relatively new. If you dont know about this topic it is pretty well docummented on this site and others, search on water ingestion.
 
Also check the chock in the carb, might not be staying open.

sticking, out of adjustment, or vacuum line off

good luck let us know
 
Thanks all for the replies. All is appreciated and is very helpful. I do know a couple answers:

They did a compression check after the headwork was done. So I don't think that is a problem.

I also found out, after I started having all these problems, that the engines were replaced (many years back) under warranty after having the water ingestion problem due to the riser issue that J Levine mentioned above.

Sounds like the first step regardless is to ensure the timing is set properly. Maybe I'll get lucky. :) It's been so very very frustrating.

Thanks again.
 
Base timing and timing at engine start is controlled by the TFI module mounted to the distributor. Once RPM exceeds something like 300 RPM, timing is set by the MEFI module. Therefore
  1. Set base timing
  2. Put a direct reading gauge on the fuel rail and watch the pressure during these oscillations.
  3. Check the wiring. They might have damaged the wiring harness during other repairs.
  4. Swap distributors port and starboard

It's probably the wiring harness or fuel pressure on the rail. If it is not fuel pressure and the problem doesn't follow the distributor, it's probably wiring. Odds are, they twisted the wiring harness around to get it out of the way while the monkeys worked on the other problems.

I've seen this type of stuff before, most recently with a Porsche doing nearly the same thing. I bet on an intermittent in the wiring harness. Porsche had the dealer do everything, including pulling the heads and swapping the flywheel. It was the wiring harness.

Best regards,
Frank C.
 
Is there an inexpensive solution for me to attach a pressure gauge to the fuel rail? Would I have to put it on both rails?

How involved is swapping the distributors? Is it as easy as removing the retaining bracket and pulling it out? Is it more likely to be the ignition module or the distributor itself?

Thanks for the help.
 
Fuel pressure gauges aren't expensive. The one I have was about $50. Here's a decent one from Amazon. A distributor swap is easy. Pop the cap and see which way the rotor is pointing. Disconnect the wiring harness. Leave the cap and plug wires in place. Remove the hold down bolt. Pull the distributor and carry it to the other engine. Point the rotor in the same direction as it when you removed it from the engine you're installing the distributor. Install hold down. Install wiring and cap. Set base timing. Test.

The TFI modules are pretty robust. Can't think of a time I saw one fail. I don't remember the details about it and my Merc factory service manuals don't appear to be here, so they're probably on the boat.

If I remember, the easiest way to set base timing is with the Rinda EFI tester. You connect the tester, set the unit to "set timing" mode and go at it. You might be able to borrow a tester. I have one, but it's on the boat, I think.

Best regards,
Frank C.
 
It's only been a short time that I've been dealing with marine engines, but you'd think a portable engine analyzer would be able to figure this problem out in about 5 minutes. In real time you can monitor timing, spark duration, injector pulse width, etc. I'm frequently amazed at how many shops that don't have the proper equipment to do what they're getting paid to do.

I'm assuming the engine is multiport injection, three of the eight injectors were replaced, is it possible that they used the wrong injector? Engines really like all of their injectors to have the exact same spray pattern, flow rate, droplet size...
 
I'm challenged in that I don't have the tool to set the base timing. Armed with a little bit more knowledge, I'm hoping my engine is the simpler of the MPI engines that has the single wire next to, but not attached to, the distributor that you just need to run a ground to. I'm sure, however, that my luck will not be so good. So I'm probably going to have to find someone with a computer.

What do you think about this: http://www.knizefamily.net/minimopar/quickfpg.html

The location of the rotor makes sense to me and I've helped change one in a car before. So it doesn't sound like an difficult job to swap the distributors. My challenge is going to be setting the timing.

I'm going to start with what I can test, and that is the TPS. Maybe I'll get lucky. Maybe my marina will happen to have a computer and I can also reset the timing.

Is there an easy way to determine which version of MEFI it uses?

Jim...I'll be honest...I never even considered that. But I will have to leave that up to the dealer to verify because that's entering the relm of much more cost on my part if I screw something up. I'm ok with basic tests, but they still own the problem as of right now. But after the past FULL SEASON of them trying to fix it, I'm stepping in with a much more active role this time around.

Thanks again all for the help. Man I hope this ordeal comes to an end soon.

And just for the record, if anyone is considering buying a boat from the MarineMax in Bear, DE...you might want to reconsider. My problems are far from the only ones after talking with several former customers of theirs. I'll will, however, tip my hat to the new management that is trying to turn the place around because they have shown me they are trying. But they have a long road ahead of them unless they can do something about their current support staff.
 
Typically in a car, if I have a bad injector, I replace all of them. The computer thinks they all perform the same. If there are three of the eight dumping a lot more (or less) fuel with the same pulse from the computer, it's not going to be pretty. Even if they replaced with the exact same part number, depending on wear or state of gumming up, they're still going to perform differently. I'd expect there to be issues at low power too, but maybe the low demand masks it. Since you've been running the engine a bit, you might be able to inspect the plugs. There's also the possibility that when they had the injectors out they got something into fuel rail?

I've seen messed up timing and bad advance systems in auto engines and typically it's been stumbling during acceleration or loss of peak power. But you seem to have surging at power. It just seems to me, like you pointed out earlier, it seems like a fuel issue.

Good luck! I hope to hear how it turns out!!!
 
Probably you have MEFI-3. MEFI-1 and MEFI-2 are long rectangular boxes on top of the manifold. MEFI-3 is a small, square control box. There are pictures in the FSM that I don't have right now. If you want to do some driving, and don't mind waiting a bit, you can borrow my Rinda EFI tester, which is on the boat, but the boat is still shrink wrapped.

I don't remember ever seeing the shorting plug on either of my MEFI-3 7.4s.

Injector balance is also easy to check if you have the tester and a fuel pressure gauge. That home made one looks OK, but there is no place on the fuel rail where you can splice it into the system. Dad always said "The right tool for the job." It makes doing the job much easier. As usual, he was right.

Best regards,
Frank C.
 
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I appreciate the info. I'll have to check the fuel rail when I go down this weekend to see if I can hook into it. I did find http://www.crowleymarine.com/mercury_parts/2716/120.cfm. If you look at item #6, I assume this is what you would attach the guage to. Seems to be the same type of Scharder fitting that is on a car. I might be able to find someone who has a guage that I can borrow. I hear ya about having the right tool.

Someone mentioned in another forum about interfearance from the plub wires to the knock sensor wire too. He thought it could be making the computer think it needs to modify the timing.

So this weekend my goal is to:
#1: Run from the portable tank to rule out fuel and/or fuel delivery from the tank.
#2: Test the TPS
#3: Hopefully fit a fuel pressure guage to it.
#4: Hopefully find a tester and set the timing.
#5: Examine in detail all the wiring for any possible damage.
#6: Since the plug wires were replaced early on, I may do a swap to validate them.
#7: If I have the gumption, and have access to the tester, swap ignitions.

Just for my edification, how exactly does the computer modify the timing on an MPI engine without electronic ignition. The rotor has no mechanical advance/retard does it? Is it just modifying the timing of the coil?

Thanks again for all the help. Thanks for the offer of borrowing the tester too Frank. I appreciate it. It's probably too far of a drive unfortuntely from Delaware. :)

Jon
 
I have recently replaced my starboard engine (350 MPI) on a 2000 310 and seem to have exactly the same problem. Are you able to get full revs out of the engine when its not under load ie. not in gear? Please let me know. I have had the mechanics run their computer on the computer while the boat is in the pen and everything runs without a problem. Take it out and open it up and I have exactly the same problem as you. I have even had prop balanced and pitched so it matches the port prop identically and still no remedy. I watch this thread with keen interest as I'm going beyond being frustrated. I live in Australia and trust me get way less support than what you are getting.

Regards

Wayne
 
You have had a couple of strings of good advice here.
I have one other suggestion for you that noboday has mentioned yet.

We have run into lots of problems with the IAC (Idle Air Control). This often gets missed because you would assume that is would affect the engine at idle and not on the top end.
I can tell you it will affect the top end with symptoms similar to what you describe. (usually accompanied by the alarm sounding) The scan tool should tell you what the IAC position is (or should be) but if you don't hear a change in the whistling sound, it is not working. I'll bet we replace one or two a month.

The first one took us forever to diagnose.

I would to the remote tank test before doing anything else. Then as long as you are swapping parts from engine to engines, consider the IAC.
 
2 other things to consider.
1) The TPI, trottle position indicator.
2) Possibly the transmission hydraulic pump slipping.
 
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I like keeping things really simple before you start swapping parts back and forth. You mentioned that you got fuel pressure readings. What were they? Use the other engine as the baseline and check the pressure on both rails at idle and 3000 rpm. What you are looking for is any fluctuation on the reading.

If there are no fluctuations then, we have eliminated fuel delivery to the injectors. (I'm a little mystified how you break injectors doing other work....back to that in a minute.) The issue of fuel quality can be eliminated by running the other engine off the suspect tank. That leaves us with the injectors as the final component before we move on to the electrical system and computer components.

I'm curious about the injector repair. Things worked before and then had issues after the repair ..... the engine doesn't spin up. What exactly went on and did they connect things properly?

I like geriksen's suggestion...... problems with that valve look like fuel delivery and electrical problems.

-John
 
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