[FredWinNH]

Hey folks,I'm new to this board. I just found it yesterday and it seems like a great place to exchange info.What I have is an '89 Mercury V6 150 (non EFI) that is having some problems with a rough idle and misfiring. At higher RPM you can feel a sudden change as the missing cylinders begin to fire and the engine runs well. Once the engine gets warmed up it runs smoother and idles somewhat better but it still seems to be missing on at least one cylinder.My question is; What's the best way to troubleshoot a low voltage spark condition like this on a CDI system?I get a spark at each plug, but some are stronger than others. Not knowing how the "black box" switches actually work, is it most likely just a couple of weak coils? I have done resistance checks on the coils and stator and trigger coils and they all check out OK.

[mbb]

You need a peak reading volt meter (called a DVA, stands for direct voltage adapter) to measure the fluctuating voltage signals of an ignition system. With it you can check your stator output, switchbox output, and coil voltages. the merc one runs about $70.There is a spark gap checker device that measures the strength of a spark by the distance of the gap it will jump, but Ive never actually used one.

[hondon]

take about ten minutes and look at the recirc lines that run behind the switchboxes on the right side of this engine.They are in tight quarters and often get cracked leading to your symptoms.Also timing AND sync should be checked.This will include idle mixture settings.Oil warning module works off of level sensors in your engine oil tank and a motion sensor on your oil pump.Warning module sends failure signal to switchbox that disables two cyls.One cyl failure at idle on these V6's is hardly noticable.

[FredWinNH]

Thanks for the replies.mbb - Can I use a Fluke multimeter that has peak hold capability or is the Mercury adaptor something different?hondon - Interesting that the alarm disables 2 cylinders. How does it do that? It only has one wire running to the #4 coil switchbox terminal. All the other wires are the sensors (oil level, pump rotate and overtemp), +12v and ground. How does it disable more than one cylinder?Also, is all of this stuff covered in the factory repair manual? I'm going to order one ASAP but I'm curious how much more complete the factory manual is than the aftermarket ones.Thanks again!

[clanton]

Yoy can get the adapter from www.esitest,com. I use Fluke 88 with the adapter.

[FredWinNH]

That link didn't work. Is it correct?

[FredWinNH]

bump - clanton?

[Backlash]

Hey Fred, Try www.esitest.com (I think Hondon used a comma after the esitest).

[Backlash]

Hey Fred,I think Clanton used a comma by mistake instead of a period..........it should be www.esitest.com.

[FredWinNH]

yep that comma was the problem. I didn't even notice it...Thanks!

[ODDD1]

Fred, the alarm system disables absolutely NOTHING on these engines...it just turns the horn on.... You need 3 things to do this trouble shooting..... 1...a spark tester that you can hook all 6 plug wires to an once...with plugs out a merc should fire across a 7/16" gap at cranking speed.....this is VERY important to verify what actually dont work..... 2...a peak reading voltmeter....to verify stator output and switchbox output....the ohms test on the trigger can be done on any meter...mercs analog meters arent that expensive...call your dealer.... 3....the FACTORY service manual [an the brain power to follow a step by step procedure]

[hondon]

I owe you a big apology. After checking manuals this afternoon on lunch ,I found that as ODD said this engines warning module sounds only the warning horn .Makes me curious why the green wire to #2cylinder.If you decide to buy a factory manual,which I think you should,make sure you provide the serial # for your engine.Around this vintage, i.e.OCWHATEVER,there were enough changes tp warrant new manuals being printed.I also think that you may find some frustration in even the factory manual.

[ODDD1]

Hey, Hondon...I got an answer for you....the way the alarm system works..a motion sensor on the oil pump driveshaft gives the oil control box [little black box] asignal every time it rotates..now the box has to compare this signal to someting, so a signal from one coil output on a switchbox is hooked to the oil control box too...so if the oil gear fails, the signals dont match an alarm goes off...or if that coil output fails the alarm goes off too! signal usually comes from #4 cyl...

[FredWinNH]

ODDD1,Thanks, yes that is how I had it figured in my mind that it works. Also, thanks for the suggestions for what tools I will need. I actually already ordered the factory manuals from MasterTech web site. I haven't received any confirmation back from them. Anyone know if they are still alive? Anyway, I think I will build a spark tester box and a peak reading adaptor for my fluke voltmeter. I actually also have a handheld o'scope I could use to see the waveforms and compare between cylinders.-FredPS - my serial no is 0B374582. That is an '88 right?

[Nago Marine Service]

I realize this is kind of late but I just stumbled on to this thread now. The Mercury Service Manual for 135 ~ 225 (P/N 90-824052R1 July 1996) that I have, shows the green wire from Oil Warning Module (Lubalert) on the GRN terminal of the outer switch box which is connected to cylinder #2.