Mercury Mystery.......

[DavidWebb]

I have a 1998 Mercury 225 3.0L Carbed. I took it to a mechanic to have the carbs cleaned. He calls me 3 days later and tells me its ready. I go pick it up, take it straight to the lake to do a little fishing, it won't get above 2500rpm and the alarm is sounding. I take it back to him, he keeps it for six weeks, hooks a DDT scanner to it and finds two codes. One for the throttle position sensor and one for the crank/timing sensor. He says the throttle position just needs to be reset/repositioned and the crank sensor needs replaced. He resets the the TPS and replaces the crank sensor. I go pick the boat up, take it to the lake the next night and same thing, the alarm is still going off and it won't get above 2500rpm. So, instead of taking it back to him and waiting another six weeks for him to throw some more parts at it, I downloaded the Mercury 3.0L service manual and start dignosing it myself. Here's what I found; all the sensors are operating within specified voltage. The TPS, however, is showing 0.00 at idle and 4.92 at WOT. Well outside the recommended operating voltage. So, I order a new TPS. I installed it, hooked my multimeter to it to set it. Here's where the mystery starts. According to the service manual, the voltage should go up from idle to WOT. The new TPS goes down in voltage (the outbound voltage) as the carb opens up. So, I pull the TPS back off, hook the meter to it and discover that the TPS needs to turn counter-clockwise to go up in voltage and the carb turns clockwise. I hooked the old TPS switch back up and tested it and found it to be the same way.


I have been able to set the TPS at the maximum voltage (3.8 volts) at idle and it drops to minimum voltage (0.90 volts) at WOT. The alarm has shut off, the engine will rev (on dry ground with water hooked up) to 6000rpm. I am afraid to take it to the lake and run it, because it might be advancing the timing in the wrong direction and may hurt my engine.

Is the service manual wrong??? Should the voltage be high at idle and lower at WOT??? I know on a diesel engine, the TPS voltage goes from high (at idle) to low (at WOT). But, this is not a diesel engine.

Any help would be greatly appreciated. And if you have any questions about the way I have tried to describe my problem, feel free to call me at 706-264-4304 before 10pm EST

[lpugh]

I suspect you are testing it incorrectly, Mercs TPS are not tested the same as Autos.
one wire is the ground 0 volts
one wire is the reference 5 volts
the last wire is the signal return, varies 0 to 5 volts
connect one test lead to the signal return
connect the other one to the 5 volt reference.
DO NOT CONNECT THE NEGATIVE TEST LEAD TO GROUND.

916 333 4105

[EuropeanAM]

I would strongly suggest (as Mr. Pugh suggested) that you look carefully at "how" you're taking your TPS readings.

I think you've made a "connection error".

As for the "Trigger Signal" fault (crank position sensor).... you'll get that fault any time the key is on, and the engine is NOT RUNNING.

[DavidWebb]

KUDOS to Mr. Pugh!!!!!!!!!!!!!! I took the readings between the feed wire and the feedback wire, found my low voltage and was able to set the TPS.

By taking the reading between the feedback wire and the ground, I was picking up the residual voltage from the feed wire. Thats why I was getting a high reading at idle and it seemed that the TPS was reading backwards. Sometimes it just takes a second pair of eyes to say hey stupid, turn it around and look again. Thanks again to Leon. And to the European Boat guy.


Modified by DavidWebb at 7:31 PM 6/28/2010

[DavidWebb]

Ok folks.... I was able to set my TPS, thanks to Mr. Pugh. But the mystery continues!!!!!!! To date, the engine still hasn't planed out. There is sufficient fuel coming from the tank, the carbs are clean and all jets are correct size and in correct placement, the floats have been checked and rechecked and are correct to Mercury specs. As for the electrical, the crank sensor has been replaced, the TPS has been replaced and set via multimeter and timing light, base timing is at 4 degrees ATDC. New plugs installed (Mercury recommends Champion QL77CC, in which Champion doesn't make anymore), it took some calling around but I found 6 new plugs, gapped at 35. I do not have a DVA, so I cannot check the stator, nor do I have the 4-pin hookup to check the coil packs. I do plan on purchasing a spark gap tester. I figure, if the coil packs can push enough voltage to jump the 3/16" minimum gap, the they should be good. If that doesn't tell me the problem, then a couple of M-80's in each cylinder should either fix it or totally f--k it up!!!!!!

[dhagemei]

how did the motor run before the shop cleaned the carbs?
2500 rpm is the transition between intermediate jets and main nozzle on each venturi where fuel starts to deliver for higher speed. so, a simple shot of wd-40, carb cleaner in the bores at this rpm will tell if the problem is still with the carbs. How to this with safety in mind. call me 703-517-2626. Thanks, David.

[kllr bee]

If the alarm you are getting at 2500 is a constant buzzer I would be checking the temp sensor in the head. If it is bad computer may be holding back thinking the motor is running hot. Service manual should show you how to test it. You can test the stator with a ohm meter. Unplug harness and set meter at 2000 ohms.Put positive to pins from stator and neg to block. They should read close to each other around 1150 I think, it's been awhile since I did this. Champion still makes QL77CC someone just wanted to sell you NGK's
Richard

[JAZII]

Champion QL77CC are now 941M.
JAZII

[EuropeanAM]

<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by kllr bee &raquo;</td></tr><tr><td class="quote">If the alarm you are getting at 2500 is a constant buzzer I would be checking the temp sensor in the head. If it is bad computer may be holding back thinking the motor is running hot. Service manual should show you how to test it. You can test the stator with a ohm meter. Unplug harness and set meter at 2000 ohms.Put positive to pins from stator and neg to block. They should read close to each other around 1150 I think, it's been awhile since I did this. Champion still makes QL77CC someone just wanted to sell you NGK's
Richard</td></tr></table>

+1

[DavidWebb]

Sorry guys, I guess I should have said the TPS fixed the warning alarm. The alarm that was going off was intermittent. I have not ohmed out the temp sensor yet because there wasn't a solid alarm for it. No alarm, no reason for computer to hold the engine back, right???

[DavidWebb]

the boat ran fine, well, it was a little slow out of the hole and the carbs would load up if you idled for a considerable distance and you would have to put it in neutral and rev it up to clear out the carbs before it would take off. I bought the boat in January and when it started getting sluggish and loading up, I decided to have the carbs cleaned hoping that would solve the sluggishness. Since then the boat hasn't planed. I pulled the carbs yesterday, made sure the jets were correct and in the right carb. I also pulled the bowls and checked the floats to make sure there were set correctly, and they were. Now, thinking on that line, he did tell me that when he cleaned the carbs, the floats were set a little high and he set them to Merc spec which is were they are now, even with the edge of the bowl. But it's not running out of fuel, or losing power on top end, like a float set to low would cause. Monday, my girlfriend and I were on the lake. When we finished fishing, I took the cowl off, and pulled the air box off the carbs, told her to drive the boat while I sprayed carb cleaner in the carbs. All the carbs reacted the same way, about a 200rpm momentary drop for a quick mist over each barrell. If my hair were long enough, I would be pulling it out about now. Looking for the tweezers!!!!!

[DavidWebb]

Just went out and ohmed out the temp sensor. Figured the engine was at least 98-100F, and it ohmed out at 615ohms, which is about right acoording to the manual.

[krich77]

Sounds like you need to haul it to Greenville SC and throw the service man. and the ohm meter in the trash.

[Props4u2]

Dumb question. Did anyone change the prop or plug the relief holes if your prop has them?

[DavidWebb]

same prop and vent holes. At this point, I would almost pay him to come up here. I would at least throw some ribs on the smoker and give him a room for the night. Plus BEER!!!!!!

[EuropeanAM]

Interesting question:

Your carbs have been off several times now.

Was a complete Sync-n-Link proceedure performed EACH time they were removed (most specifically, the last time)?

This is covered in the Synchronization and Linkage Adjustment section of the Repair Manual (and is MANDATORY any time a carb is removed from the engine).

Failure to perform this proceedure PROPERLY can result in VERY poor performance.

[dhagemei]

You brought boat to have carbs cleaned on first post. What were the running symptons that required that? Lots of good intentions and thoughts up to this post. as I and others have recommended, isolate your boat fuel system with a portable one to see if your problem goes away. Simple but effective test. Thanks, David.

[DavidWebb]

The symptoms causing me to take to the mechanic in the first place were; it was sluggish out of the hole, and carbs were loading up to the point were I had to put it back in neutral and rev it up to clear out the carbs so it would take off. I didn't know when the last time the carbs had been gone through/rebuilt. So, I decided to have some preventive maintenance done, and it bit me in the keester. I will, from now on, attempt to fix my own boat if I can and with yall's help. One, it's cheaper than paying someone to throw parts at it, two, I love tinkering and working on motors both marine and auto.

Now, here's what I did today. I pulled the carbs back off and cleaned them. When I took the bowl off of the #1 carb and started taking it apart, a connector wire (the little wire that connects the float to the needle) came tumbling out. Upon further inspection, I found there was a connector wire already in place. Only thing I can figure is whoever rebuilt the carbs before, lost it and left it in there. Must have gotten stuck in the bottom of the bowl. May have something to do with the way it has been running. Don't know yet. I also bought a spark gap tester, all cylinders are jumping up to 1/2". So the CDM's should be good, I also ohmed out the stator, between 1160 and 1172ohms. I know the manual calls for 1100ohms +/- 10%, so that's within specs. When I put everything back together, I hooked it up to the hose, and it idled beautifully. No heavy smoke or gas smell. No neighbors slowing down as they went by to see if the house was on fire.

So, I guess I'll find out tomorrow night. I will be taking a spare tank with me.

AND, when I put the carbs back on, I used the manual, step by step, to sync the carbs.&lt;br /&gt;&lt;br /&gt;
Modified by DavidWebb at 9:44 PM 7/8/2010&lt;br /&gt;&lt;br /&gt;
Modified by DavidWebb at 9:48 PM 7/8/2010


Modified by DavidWebb at 10:17 PM 7/8/2010

[dhagemei]

We are anxiously awaiting results.

[kllr bee]

One thing you need to remember when idling a 3 litre. You have to keep the port on the rear of the motor( by the tell-tell or pee hole to some) above the waterline so the motor can breathe. This is the main cause of a 3 litre loading up when idling. Just keep the motor trimmed out enough to keep it above water til just before you punch it to get on plane. Good luck
Richard