2000 mercury 200 efi loses power gradually as day progresses

[Luis D.]

I have a 2000 mercury 200 efi on a nitro 901 CDX. I am having problems with motor. In a regular outing motor fires right up in the morning then gradually loses power throughout the day. As the day progresses it is harder to get out the hole and loses a little topend power. It gets to where I can not get out of the hole at all. I notice that the finder will turn off when I crank it. My finder shows voltage but will show couple volts under what it really is so don't know if voltage is dropping. Compression is good between 105 and 110 on all 6 cylinders. Alternator is charging fine checked at home. Have not checked it on the water. Could this be a voltage regulator or stator problem?

Any help is greatly appreciated! Thx in advance!

 

[jimmbo]

You are saying the engines starts fine in the morning, progressively loses Hp throughout the Day, but is fine again the next morning?

 

[Texasmark]

Ambient temperature and humidity do have an effect on "naturally aspired" engines in that the more dense the air being mixed with a given quantity of fuel, the bigger the bang in the cylinder....theory behind turbo chargers. So, boating in the winter vs summer and dawn vs hot summer afternoon can cost you some MPH....but I really doubt as much as you are indicating.

You could have a thermally sensitive CDI and with a 6 cyl engine, would be hard to catch without instrumenting HV pulses to the plugs. I had one that worked the other way. Wouldn't generate HV pulses at the plugs in the early morning on a cold day, but later on in the day, or on hot days it worked just fine. Was lucky one day and caught it doing it's thing.

You could test your rectifier/regulator at your battery when having the problem, and any voltage above 12v would surely be ample to power your CDIs.....and up around 14.5V says your battery is getting charged properly so power to the CDIs is surely adequate.

On compression, I have mid range engines of 3 and 4 cylinder 2 strokers and the Sev. Man. states that any compression below 120 PSIG could be cause for concern. Given your compression being what it is, you could be vulnerable to minor causes that may not be an issue if the compression was higher.

 

[Faztbullet]

Recheck charging system...sounds like you lost one of the two rectifiers. As voltage drops fuel pressure drops resulting loss of power Engine and acc's are demanding more power than engine can produce ...

You could test your rectifier/regulator at your battery when having the problem, and any voltage above 12v would surely be ample to power your CDIs.....and up around 14.5V says your battery is getting charged properly so power to the CDIs is surely adequate.​

The CDi's or CDM do not get power from VR or 12V system...power comes off stator.

 

[Luis D.]

You are saying the engines starts fine in the morning, progressively loses Hp throughout the Day, but is fine again the next morning?

Yes, it's starts fine everytime. It does not matter what time it is. Let's say I start it when I put it in the water. I let it get to operating temp and head to a spot. The motor runs good and gets out of the hole easily. Then when I go to move to next spot it takes a bit longer to get out of the hole. After x amount of times it gradually loses so much power that eventually won't get out of the hole.

 

[Luis D.]

Ambient temperature and humidity do have an effect on "naturally aspired" engines in that the more dense the air being mixed with a given quantity of fuel, the bigger the bang in the cylinder....theory behind turbo chargers. So, boating in the winter vs summer and dawn vs hot summer afternoon can cost you some MPH....but I really doubt as much as you are indicating.

You could have a thermally sensitive CDI and with a 6 cyl engine, would be hard to catch without instrumenting HV pulses to the plugs. I had one that worked the other way. Wouldn't generate HV pulses at the plugs in the early morning on a cold day, but later on in the day, or on hot days it worked just fine. Was lucky one day and caught it doing it's thing.

You could test your rectifier/regulator at your battery when having the problem, and any voltage above 12v would surely be ample to power your CDIs.....and up around 14.5V says your battery is getting charged properly so power to the CDIs is surely adequate.

On compression, I have mid range engines of 3 and 4 cylinder 2 strokers and the Sev. Man. states that any compression below 120 PSIG could be cause for concern. Given your compression being what it is, you could be vulnerable to minor causes that may not be an issue if the compression was higher.

It does the same thing when I go try it out afternoon or later in the day. Ambient temp is not an issue, I don't think. I checked battery and it will charge at idle normal to about 14.6

 

[Luis D.]

Also the manual states 105-110 compression is perfectly fine for my motor.

 

[Texasmark]

Also the manual states 105-110 compression is perfectly fine for my motor.

Interesting.

 

[Texasmark]

Recheck charging system...sounds like you lost one of the two rectifiers. As voltage drops fuel pressure drops resulting loss of power Engine and acc's are demanding more power than engine can produce ...


The CDi's or CDM do not get power from VR or 12V system...power comes off stator.

Oops, senior moment..... sorry about that. Didn't have my manual handy and just now recollecting the need for a DVA to measure the high voltage pulses that charge the storage capacitors in the CDI surely isn't needed for a 12v power source.

 

[jimmbo]

Have you ever tried taking the Cowl off once you get to a spot, leaving it off the whole time, till you're about to start it to move to the next spot? It sounds a bit like a Heat Soak issue. Have you checked all the wiring for good Connections?

Does the worsening of the Symptom vary by the length between each run?

 

[Luis D.]

Have you ever tried taking the Cowl off once you get to a spot, leaving it off the whole time, till you're about to start it to move to the next spot? It sounds a bit like a Heat Soak issue. Have you checked all the wiring for good Connections?

Does the worsening of the Symptom vary by the Number of times the engine is called to duty, or by the length between each run?

No I have not done that. I just bought the boat so I am barely messing with it. I checked all the wiring physically and it seems fine. I will take it off next time and check for voltage and heat with my laser thermometer right there when the problem starts.

I think it is a combination of both. Let me explain. I fish two different lakes. Casa Blanca lake is a very small lake that I fish so I move a lot of times and the distances between spots are very short. Falcon lake on the other hand is huge and I have to go long distances between spots but fewer.

 

[jimmbo]

Sounds like we have the reason it was for sale

 

[Luis D.]

Sounds like we have the reason it was for sale

Yup. I drove 400 miles to get it. I put it on the water to make sure it worked fine. Test drove it and worked fine. Got out of the hole quick, accelerated good throughout rpms, overall was good. Now I'm stuck with a problem that I have to fix.

 

[jimmbo]

When it is acting up, have you tried verifying that all cylinders still have spark?

 

[QBhoy]

If your compression gauge is correct, you are very close to the lower acceptable figures for a worn engine.
Other than that, it sounds like your rectifier or coil packs are breaking down. Have a test at these. And the coils

 

[Dukedog]

Also the manual states 105-110 compression is perfectly fine for my motor.

what manual, oem or aftermarket?.. any V6 with those numbers are a tad low.... and may get worse as it builds heat under a load.

 

[Texasmark]

Moving on to possible vapor lock???? Know nothing about EFI systems but on a carb system, I had a problem with a clogged fuel filter. I had installed an after market fuel filter preceding the fuel pump on my car. The pump suction against the resistance created a partial vacuum and on a how day, with hard running and AC heat load, towing a trailer and kids and camping gear and all that, that partial vacuum was enough to gasify the fuel delivery into partial vapor and the engine had a hard time running till you stopped and let it cool off.

You could have a dirty fuel filter caused by fuel line degradation particles clogging it. I have had it on a 3 and 4 cyl carb 2 stroke, 10+ year old engines...fuel systems. Cutting the filter open revealed the smoking gun. Anything down wind of it, with a black cowl and closed (pretty much) engine compartment could/might vapor lock.

 

[Faztbullet]

Maybe he will reply to your post Duke..totally ignored mine.

 

[Chuck4741444]

It does the same thing when I go try it out afternoon or later in the day. Ambient temp is not an issue, I don't think. I checked battery and it will charge at idle normal to about 14.6

Sounds like the fuel pump is shorted when it's hot, this would also cause the scanner to lose power for sec