2000 Tige 20i - Heavy carbon on spark plugs, hesitation

[jgdethloff]

I recently purchased a 2000 Tige 20i. It ran great on the sea-trial but since then I have had some issues and would like some help diagnosing.

The first weekend out, vapor lock. No fuel coming out of schrader valve, just air. Added check valve and low pressure fuel pump/filter kit. Changed fuel/water filter.

Did general tune up stuff: New rotor/dist cap/spark plugs/spark plug wires. Also installed new coil, old one wasn't bad, just 15 years old.

Boat isn't as responsive when accelerating. When at 2500 rpm and give throttle, there is a lag before it picks up. Pulled new plugs to inspect. They are heavy carbon, except one. Broken electrical connection on injector. Two other injectors have loose connection on the injector. I bought and installed 3 new injectors, replaced o-rings and cleaned the other 5 injectors, putting power to the injector to check that it opens properly.

Boat still isn't responsive when accelerating. Idled through no-wake zone after running for an hour or so, when leaving no wake zone, boat almost stalls when I try to accelerate. Slow throttle application gets me up and going and boat seems to perform fine at speed. Pulled plugs, heavy carbon on the 4 that I pulled (Pulled 2 from old injectors and 2 from new injectors, all look the same). Some puffs of dark smoke when accelerating and when putting boat on trailer. Checked pressure at fuel rail, 26 psi. Disengaged trans and throttled up to 3,000 rpm, fuel pressure drops to 22psi. Is this a problem? I could not check fuel pressure while under load on this trip out. (BTW: I replaced the fuel pressure regulator when I installed the vapor lock kit, just because I had everything apart).

I tested the throttle position sensor, have 5 volts, monitored voltage as throttle lever moved back and forth, no spikes in voltage, very smooth.

Checked MAP Sensor, have 5 volts, voltage changes when vacuum applied

Check coolant temp sensor, OHMS at about 2,200.

The boat motor is a 350 MAG MPI. Serial number 0L393831.

Can someone help me with what I should check on next? Just no idea why the hesitation, rich smell, dark smoke, and carboned up plugs. Thanks so much!

[boatwakes]

Replace the ignition control module in the distributor 87-892150Q02 and your fuel pressure should be 32psi +- 2 psi. Even though the fuel pressure drops to 22psi it's not the cause of your problem. Verify the vacuum hose from the base of the throttle body is still connected to the fuel pump and in one piece.

[boatwakes]

AND this happened to my boat which presented with the same issues but the manifold air temp sensor may be toast. I've seen it happen with too much oil in the crankcase which then ended up covering the mat sensor from the pcv vapor. The mat sensor is in the intake manifold engine aft just behind the throttle body and if you use a 7/8" deep socket you can pull it and clean it with brake cleaner and then retest.

[jgdethloff]

Thanks Boatwakes! I have the boat level and the engine is cold and see that whoever changed the oils before I purchased the boat has overfilled it. I am in the process of draining some out as we speak. Hoping that is the cause. I tested the Manifold temp sensor and the resistance is corresponding to current temps, and it fluctuates as I heat it with my breath by blowing on it. I took it out and cleaned it with brake fluid too just to be sure.

I have not looked it up, but is there a test for the ignition control module that I can do to make sure it is faulty? How do I know the ignition control is the cause of the low fuel pressure rather than a failing high pressure fuel pump?

Should I pull all my plugs and clean them before my trial run or will they clean themselves once the oil is at the proper level?
Thanks again for your expertise!

[boatwakes]

The ignition sensor is a separate issue that MUST be upgraded if you only have the two wire unit installed now. The new units are completely potted and have an external black ground wire that must be attached to a bolt to provide a good ground. The old unit does not have a potted surface and the contacts fry out or crack and cause the timing advance to go all over the place which would really only show up under acceleration with engine load, as you are experiencing. The ignition module is usually responsible for fouled plugs and rough running etc.. and once it's changed out you can test it right away. I would recommend changing the plugs out at the same time and DO NOT USE ANY CHAMPION SPARK PLUGS!!! EVER!!! NGK BPR6EFS or AC Delco MR43LTS ONLY!!! (those numbers are for the efi engines and BR6FS and AC Delco MR43T for carbed units for all of you reading this).
The fuel pump issue is lack of pressure and those units unregulated can produce in excess of 80psi but even at 22psi in the rail the injectors can atomize perfectly fine. Did you install the boost pump with a Hobbs oil pressure switch too or just run it on the key? If it's on the key I would highly recommend installing an oil pressure safety switch to eliminate the explosion factor and using a marine boost pump too.

[jgdethloff]

My current ignition sensor is a three wire system. It is pretty grimey/greasy - I'm not sure if that makes any difference in performance of the part. Being that it is a three wire ignition sensor, do you still recommend replacement? I am thinking most of my issue with hesitation was due to the oil vaporization due to overfilling. (But that is just a guess until I can get the boat out and check for sure).

Why do you think there is a lack of fuel pressure? Is the low pressure an indication that the fuel pump on it's way out? I thought I read somewhere that you had to replace the entire fuel cooler/fuel pump assembly, that you couldn't buy just the new pump. Is that true, or is there a source for the pump only, if I need to replace it?

The low pressure pump I installed is the Quicksilver/Mercruisuser kit that piggybacks on the electrical wiring for the existing high pressure fuel pump circuitry, so no need for a second oil pressure safety switch since it is protected with all the same protections/safety features as the high pressure pump.

Thanks again for your help!

[boatwakes]

Had no idea quicksilver had a pump set up, could you throw the part number up for everyone so people stop installing dangerous set ups?!!! As for the fuel pressure, it should remain steady at all rpm regardless of load or rpm.
For clarification when exactly did the symptoms present, before tune up, after?

[jgdethloff]

The kit is: "Mercury Mercruiser Quicksilver OEM Part # 862264A 7 PUMP KT-NO CKVALV" It is the kit that is recommended in their vapor lock service bulletin (I have attached the bulletin for anyone who needs it). I also installed the check valve that is listed in the bulliten.

The hesitation issue with my boat started prior to the tuneup.

Based on your expertise and the varying, lower than recommended fuel pressure, would you say that my high pressure fuel pump needs to be replaced?

Based on the fact that I have the three wire ignition control module, do you still think it should be replaced?

[boatwakes]

No to the ignition module and no to the pump, for now. Are you positive the symptoms did not present at all during initial sea trial and when precisely did the symptoms begin? After you filled the boat with gas, drove home on a dirt road, saw a chicken cross ththe road, etc. I'm going to hafta start with the simple and work from there.

[boatwakes]

I ask because vapor lock denotes fuel that has vaporized and cannot pressurize within the pump. If you were only getting air and it was under pressure then there was/still is a suction side problem either in the pickup or the fuel line between the tank and the new low pressure pump. The Mpi system on that engine returns to the filter and not the tank so we need to determine where the air came from which could also be a contributing factor to the low fuel pressure.

[jgdethloff]

The sea trial was short, maybe twenty minutes. So the vapor lock did not present itself, but it might have if the motor had a chance to heat soak. It FIRST presented itself after an hour run around the lake. We parked the boat at our dock and went inside for lunch. A couple hours later, I came out and the boat started, idled, but when we gave it gas, it died. It started a couple times and quit. After that, the motor just turned over and over.

The next morning I replaced the fuel/water separator. Everything in it looked fine and didn't smell funny. I went for a ride, everything seemed fine. Let the boat sit and heat soak - then vapor lock. When we cycled the key a few times, the schraeder valve on the fuel rail would spit SOME air and a LITTLE fuel- other times after the problem it would spit no fuel and a LITTLE or NO air. Once the engine cooled WAY down, you could cycle the key and after a little air bleed, the schraeder would push fuel.

I cut the ends of the fuel line off at the fuel/water separator and the fuel tank and then re-connected. I just wanted to eliminate any possibilities of air sneaking in around the old ends of the fuel line. At this point I did all the tune up items I listed. I also added the check valve between the thermostat housing and the fuel cooler to try and prevent hot water from boiling fuel in the fuel cooler. Same vapor lock problem happened.

I added the low pressure fuel pump and filter, I also added a new fuel pressure regulator (I don't think the old one was bad - just did it because I had everything apart). The boat has not vapor locked since!!

What would you like me to check regarding the low fuel pressure? Just FYI - I have put about 17 hours on the boat and have only used non-ethanol fuel.

[boatwakes]

When you put the fuel pressure gauge on the rail, cold engine, and cycle the key to get pressure, does it hold after the pump stops or drop to zero in less than 5 seconds? If it stays, the injectors are good. If it drops you've got either a stuck open injector or faulty pressure regulator allowing fuel to return to the suction side of the system. A stuck injector would also present the same way. If the oil level is high and smells like gas and the pressure drops immediately an injector or two is stuck open.
If that's the case, the only way to find it is to remove the entire bank of injectors still keeping them connected to the rail and then cycle the key to find the leaker.

[jgdethloff]

Fuel pressure gauge hooked up. Cold engine. Cycled key several times. Pressure gets to 32 psi but immediately drops to 27 psi. After 3 minutes on the stop watch it reads 25 psi. Another 2 minutes and it reads 24 psi.

[jgdethloff]

After an hour it reads 22psi

[boatwakes]

Perfect injectors. Next most likely culprit is the coolant temp sensor or ect. Even though the ect may show resistance changes as the temp changes, those resistance readings need to be precise and give the ECM correct engine temp readings in order to supply the injector driver with correct pulse width. For example, the ect can send a false reading of 10 degrees when it's actually 80* to the ECM which then tells the driver to keep a longer pulse width in order to help warm the engine. Once the engine reaches 140* the pulse width is decreased for optimum performance and fuel economy. The only way to check the sensor correctly involves using the diagnostic computer and reading directly what the sensor output is in degrees. If the sensor never reaches operating temp, the system is constantly over fueling to try and compensate for engine temps. The ect works in conjunction with the mat on those engines. Later models dropped the mat and just used an ect to do the job.