1996 Mercury 175EFI OG361323 Will Not run past 3000rpm sometimes?

[Bassmar]

I just purchased a 1997 Ranger R82 sport with a 175EFI. I have ran it a few times since i got it and it runs good for awhile and then stumbles and drops down to around 3000 rpms and runs pretty well at that or lower rpms. Sometimes it will completely die and it will start right up but miss and sputter when I try and increase throttle to get on plain. I also need to say the oil injection has been removed by previous owner. I have done some trouble shooting and I will list what has been done.
I started off with checking compression. all Cyl were at 102 to 105 . I know that's kind of low but still is in specs.
I also tested spark and all looked ok. I ohmed the coils and they tested good. I did notice the wires were leaking pretty good so I have ordered a new set of plug wires. have not installed yet.
to try and eliminate the fuel sys I took a 6 gal tank of fresh gas and ran it and it acted the same way.
I checked the fuel/water sep and it didn't have much in it all. I also checked the fuel filter and it looked good. I did change it but have not ran it yet.
I pulled the VST and checked it out and the filter was clean and the screen was clean, very little trash in bottom of VST tank. Fuel pump tested and turned fine.
The stator was changed in Nov according to paperwork PO gave me and it does look new. Also temp sensor was changed at same time. I dont know when but had old Switch box in boat and looks like one of them was changed. The other looks older.

I would appreciate any help you could give me in finding what is going on! Right now we are fixing to get a hurricane run over us so it may be a couple of days before I can run it but it would be great to have a direction to go next.
I was thinking of checking the Stator and Rectifiers next when I can get the boat out of my shop and storm is over.

Thanks for any input in advance.

[EuropeanAM]

Need to replicate the problem and monitor Spark and HIGH side of stator when the problem is occurring.

Also possible that the switchboxes are failing (note the PLURAL wording). Switchboxes really should be replaced in PAIRS, as a bad switchbox will often damage it's mate.

[Bassmar]

Thanks for the reply, The only way it occurs in on the water so it will be a task to recreate the problem and monitor. I also have read what you said about switch box before so I was actually thinking of getting 2 new boxes. But I will try to test the stator first.

It just dawned on me that when I did spark test on coils the spark was reddish color not blue. Would that be a sign of weak coils or switch box problem with switchbox? I did ohm the coils and they were all over 900 something and less than 2 on other side.

Thank you again

Mark

[EuropeanAM]

Some will disagree with me on this, but I've found that trying to rely on the "color" of spark for the purposes of diagnosing problems is often misleading, unless you can duplicate very precise conditions on the secondary side of every coil (usually not realistic).

[Bassmar]

Ok I will try the other stuff that you mentioned first. Thanks

[Bassmar]

Well storm has passed and been out if elect, maybe getting it back in a couple more days.
I did take the boat out but it would not get on step again. I changed plug wires before going out. I did connect a timing light to each plug while trying to take off and all were firing ok. I could not check stator because I was by myself. I don't know if that tells you anything that might help. I will try and get someone with me next time to help out. How do I check high side of stator? And how do I know which is high side?

[EuropeanAM]

You will need a Service Manual, a DVA (Direct Voltage Adapter) and a DVOM (Digital Volts/Ohms Meter) to accurately test the stator.

[Bassmar]

I looked it up after I responded to you. I will order one. Where is the best place to get a service Manuel? I did download A CDI troubleshooting guide. I have the DVOM meter just need the adapter.

[leonreno]

Look at the post from Don, (European Marine) you can click on the link in his signature to order mercury parts, or buy it from your local mercury dealer, will need serial number to order from either.

[JOE54]

test ign system (spark) when prob occurs

[Bassmar]

Thank You

[Bassmar]

test ign system (spark) when prob occurs

I did run it and put timing light on all plug wires while running it in river and they all had spark. I took a chance and ordered 2 new switch boxes, I figure if that's not the problem at least they will be new. LOL I really need to get a fuel pressure gauge to test fuel pressure, Just running a little low on funds at the moment so I will be getting one in near future.
Thanks

[Bassmar]

Need to replicate the problem and monitor Spark and HIGH side of stator when the problem is occurring.

Also possible that the switchboxes are failing (note the PLURAL wording). Switchboxes really should be replaced in PAIRS, as a bad switchbox will often damage it's mate.

Don I have been reading and looking over my motor and my Idle stabilizer and shift module is still hooked up to my motor. as I mentioned the oil injection has been removed. Also the jumper wire is there on the switch box for the bias wire but Idol stabilizer is still hooked up to switch boxes. From what I have read on your previous post that is wrong. Should I remove idle stabilizer and nutural switch as I have read on other post?
Thanks for your help!!
Mark

[Bassmar]

Don and Joe and all of you that helped me thank you very much! I took the idle stabilizer off and also the natural switch and took it out today and it ran like a charm. I had new switch boxes but did not install because I wanted to eliminate the problem one at a time. I ran it for over an hour and probably 20+ miles and never missed a beat. However the idle was a little on low side. Idle in neutral was about 650 to 700 and in gear about550 to 600. Still think I need to have timing set for Idle and WOT. Do not really understand how to do it so i will probably have to put it in shop to get it done. Does anyone know a round a bout price for just getting them to set timing?
Again thanks to all.

[leonreno]

When you remove the idle stabalizer you must perform a link and sync to set idle and WOT timing.

[Bassmar]

Yes that is what I read on here. That's why I will put it on shop so someone that understands it can do it! Because I don't understand how to do it. LOL

[leonreno]

Not hard if you buy the Mercury OEM service manual and a few tools like a timing light.

[Bassmar]

I may give it a try. I have timing light. Just need dial indicator and figure out how to ground all plugs. I have a manual on line and it is Merc Manuel .
Thanks Again.

[leonreno]

You can ground them with alligator clips or buy a spark plug grounding block/tester.