Mercury 150 problems

lesroc · Jul 10, 2011

I have a 150 v6 (early 80's) that will not come out of the hole when on the lake. When it is on the muffs it will open up to full throttle, but when it is on the lake you can only get about 2500 rpm's. I have replaced all fuel lines and bubble, rebuild the fuel pump and carbs, new plugs too. It has 110 psi plus one each cyl and fire to all plugs. The engine has a 21p prop and it is on a 17ft fish ski so it should pop out of the water. Anyone have any ideas?

Chris1956 · Jul 11, 2011

Re: Mercury 150 problems

The stator that powers the ign system have a low speed and a high speed winding. If the high speed winding is bad, you will have no high speed operation.

I recommend you go on the CDIElectronics.com web site and get the procedure to troubleshoot the stator windings.

j_martin · Jul 11, 2011

Re: Mercury 150 problems

It'll wind right off the top on 3 cylinders with no load on it. Under load it won't pull at all on 3. I suspect that if you rigged a timing light so you could see which plugs are firing, one bank is dropping off when you hit the wall.

Could be switchbox (low probability) and could be stator. Both are high buck items. It's worth it to do the DVA testing to isolate the problem.

lesroc · Jul 11, 2011

Re: Mercury 150 problems

If the high speed winding is bad would it still be able to reach the high rpms while on the muffs? Thanks for the experienced advice.

j_martin · Jul 11, 2011

Re: Mercury 150 problems

Read my post again. It'll wind to the moon on 3 cylinders with no load. Under load, it'll hit the wall at switchover speed when 3 drop out, about 2500 - 3000 rpm.

(edit) maybe you don't realize that water is thicker than air.

lesroc · Jul 12, 2011

Re: Mercury 150 problems

Ok, I looked up the DVA chart and am going to check it this evening, thanks again for your help. I will keep posted on what I find.

lesroc · Jul 14, 2011

Re: Mercury 150 problems

So I referenced the DVA chart and checked the stator. The low side (blue wires) had no resistance while the high side (red wires) had target ohms. So I think I am going to replace the stator and see what happens.

lesroc · Jul 30, 2011

Re: Mercury 150 problems

Sorry its been a while since I have gotten back, so I replaced the stator with a CDI replacement. Boat still will not get up on plane. To recap what I have done: new stator, rebuilt carbs, new switchboxes, rebuilt fuel pump, replaced ALL fuel line componets. I have checked the coils in accordance to to Manual and they ohm out fine. In my research I have ran across several people that say to trash the spark advance box that sits above the carbs, any advice?

j_martin · Jul 30, 2011

Re: Mercury 150 problems

You didn't do the DVA testing. You did an ohms test, apparently with a faulty meter, because if it read what you said it wouldn't fire at all.

Now, if you want to limit your losses, acquire the right test equipment and do the testing. The symptoms are high speed failure on one bank. You already replaced a perfectly good stator, so it's likely one of the switchboxes. DVA (Direct Voltage Adapter) tests will isolate the faulty part.

I'm outa here.
John

lesroc · Jul 30, 2011

Re: Mercury 150 problems

Did the DVA test on the stator. Result was BAD stator. Ohm test was on the igintion coil. First piece(s) changed on the engine was the switchboxes. Local Merc mechanic informed me that the trigger will rarley go bad? Sorry that you jumped to conclusion about the type of test I did and to tools I have.

Rocky

CharlieB · Jul 30, 2011

Re: Mercury 150 problems

Trigger WIRES can get broken where they flex, dropping a pair of cyl;s when the broken wire disconnects during movement.

Disconnect the throttle cable, DVA each trigger cranking while moving the throttle throughout its range to see if trigger voltage/current falls off.

j_martin · Jul 30, 2011

Re: Mercury 150 problems

lesroc said:
So I referenced the DVA chart and checked the stator. The low side (blue wires) had no resistance while the high side (red wires) had target ohms. So I think I am going to replace the stator and see what happens.

This isn't dva testing. DVA measures peak voltage. This is what you said you did.

lesroc · Jul 31, 2011

Re: Mercury 150 problems

Ok j_martin, I tested the stator with a DVA adapter. The voltage dropped off when i went over 2000rpm's so I replaced the stator. I was reading on the CDI site and they reference the trim switch could cause the problem?

lesroc · Aug 14, 2011

Re: Mercury 150 problems

Just wanted to put some closure on this whole ordeal, ended up being the idle stablizer. After replacing the stator (that did check out bad on the high side) I still had the same problem. So I metered all the coils with it running to see what was going on. I found that the even bank (2,4,6) cyl had a noticably lower reading and as I brought the rpm's up it dropped off where the other side was a bit higher and stayed the same or rose just a bit. So naturally I thought it was the switchbox (powerpack for some of you). So before I spent another cent on this thing I decided to switch them, glad I did, still had the same problem, low and dropping voltage on the same side (should have moved to the other bank with switching the packs. So being some what confused I looked for things that stayed the same on pack. Only thing I saw was the idle stablizer, so I removed it and now I have a very smooth running machine. Thanks to all who offered help, just a tip to those who will read this far, not everyones problem will be the same as yours even though it may seem to have the same issues. Stop and look at the whole picture!

j_martin · Aug 14, 2011

Re: Mercury 150 problems

Is there a jumper between the switchboxes where the white/black tracer wire from the idle stabilizer was connected.

If not, there should be, and that is why the idle stabilizer only messed up 3 cylinders.

Thanks for the comeback.

lesroc · Aug 15, 2011

Re: Mercury 150 problems

The jumper wire is there. Will the engine be ok without the idle stabilizer? I hear a lot of different opinions.

j_martin · Aug 15, 2011

Re: Mercury 150 problems

lesroc said:
The jumper wire is there. Will the engine be ok without the idle stabilizer? I hear a lot of different opinions.

As I think through it a bit more, the red/white connection between the stabilizer and the swtichbox is the high speed stator connection, and if that were shorted to ground, you'd get the bank it's connected to dropping at high speed. Makes sense now.

If the engine is in good tune, the idle stabilizer isn't needed. What it does is advance the timing a few degrees if idle speed drops below a set point.

Some engines had only an idle module on them. some had 2 modules on the, one idle and one advance module, and some had a combination module on them with both functions.

If the advance function is on the engine, WOT timing will be specified at 18?, and the module will move it another 6? at over 5000 rpm. If it doesn't have an advance function on the engine, WOT timing will be specified at 22? - 24?. So if you remove that function, you have to advance the WOT timing or it'll be pretty lazy at high speed.

Most of us just pitch all timing modules and set idle where it wants it, and WOT at 23?.

hope it helps
John

Faztbullet · Aug 15, 2011

Re: Mercury 150 problems

Will the engine be ok without the idle stabilizer?

It will be fine with out it.

I hear a lot of different opinions.

That because a lot of people dont know that there are 3 types of modules:
1) Idle stablizer: advances timing up to a max of 9? if rpm falls below 550rpm. Does not effect WOT timing unless it fails
2)Low/High speed box (early): Does the same as above box for idle purpose's but advances WOT timing 6? above 5600rpm and stays locked in untill rpm drops below 5400rpm then its retarded 6?.
3) Low/High speed box (late) Does the same as the idle box at low rpm. This box raises the timing 6? when rpm reaches 5000rpm and holds it till engine reaches 5700rpm then it will retard WOT timing 4? untill engine rpm drops below 5700rpm.

lesroc · Aug 15, 2011

Re: Mercury 150 problems

Thanks John and Fatzbullet, that is what I wanted to know. I was able to take my teenage son fishing today and for the first time in a while we were able to actually run the big motor!

Thanks Again
Rocky

Mercury 150 problems

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