idles great when i put new plugs in, but......

[fishez4aliving]

I changed the plugs on my 1989 175 after i noticed the gph had gone way up on my fuel flow guage. I noticed one of the plugs was clean, as if i had just changed it. I checked the plug for spark and it was fine. I replaced all the plugs, fired it up, and it idled great, however as soon as I put a load on it, the engine would sound like it ran rough, drop to idle and the thing would idle rough, then die, unless i gave it throttle. Anyway, i started wondering about ignition coils, and it checked and i didnt get spark in the 2nd cylinder. So I replaced the coil, and it still didnt get spark, so I swaped the coil with another, and sure enough i found that it wasnt the coil it was something else. The last time i had a idle problem i ended up getting a trigger coil replaced. Is this my problem again? I didnt think i would need to replace it every few years, thought that was a fairly bullet proof part. Thanks for any replies

 

[mellowyellow]

Re: idles great when i put new plugs in, but......

water intrusion will "steam clean" a plug and<br />keep it looking brand new.<br />what is compression?<br />have you tested switch box?<br />good luck,<br />M.Y.

 

[fishez4aliving]

Re: idles great when i put new plugs in, but......

thanks for the reply. Compression is 118 on all 6 cylinders +/- a pound or two. When i said the coil was fine, i meant that it was fine if it wasnt hooked up to the leads for the #2 cylinder. i took every coil and rotated it to that position, #2 cylinder and all the same, no spark.

 

[gss036]

Re: idles great when i put new plugs in, but......

When was the last time you changed your head gaskets. If you run saltwater, I would advise you to change them if it has been 3 years or more. I agree with the water intrusion suggestion above.<br />Not a mechanic myself, just my 2 cents.

 

[mellowyellow]

Re: idles great when i put new plugs in, but......

get your manual out and follow test proceedure<br />for switchbox.<br />good luck,<br />M.Y.

 

[rodbolt]

Re: idles great when i put new plugs in, but......

hello<br /> fuel wash will keep it clean as well. test all the ignition components as well as look for a possible flooding. rebuild the fuel pump periodically as well.<br />saltwater will leave tiny geen spots on the electrode when it burns. if careful inspection does not show any small spots then I would look for possible causes of fuel washed plugs

 

[Gold Bear]

Re: idles great when i put new plugs in, but......

fishez4aliving <br /><br />Check to see if the new #2 plug is bad.<br /><br />Gold Bear

 

[fishez4aliving]

Re: idles great when i put new plugs in, but......

thanks for all the feedback, as soon as i get a chance to test the theories, ill report back, thanks again

 

[WillyBWright]

Re: idles great when i put new plugs in, but......

Your trigger is fine. There are three triggers in the housing. Each fires a pair of cylinders. If it failed, two cylinders wouldn't have spark.<br /><br />You could have a bad stator. There are high speed and low speed windings in it. It could idle fine, but lose voltage when the RPMs go up if the high speed windings are bad.<br /><br />My feeling is that you have a bad switchbox. Follow the lead from the coil on the cylinder that has the clean sparkplug to the switchbox. That'd be the most likely to be bad, but it could be the other (voltage passes thru both switchboxes and fires depending on the polarity of the trigger magnets as they pass the trigger).<br /><br />The only way to test a switchbox is with a DVA multimeter. You won't find one of those at Radio Shack. But you can test the stator and trigger with a regular multimeter. The specs will be listed in most any appropriate service manual which are frequently available at public libraries.<br /><br />One thing you might also try is to move the coil from #2 to another cylinder that you know is working and see if it sparks. That'd indicate if the coil is bad or good.<br /><br />If you have an inductive pickup timing light, hook it up to #2. If the light flashes, you have spark. Try it at low and high RPMs.

 

[mellowyellow]

Re: idles great when i put new plugs in, but......

excellent advice...you could also swap the 2<br />switchboxes and see if problem follows.<br />good luck,<br />M.Y.

 

[BillP]

Re: idles great when i put new plugs in, but......

Mercs somewhere around that vintage had major issues with stators. Two of my fishing friends had to replace them right after the warranties expired. There was no recall but Merc sent (after lots of hassle and phone calls) free stators to both after the warranties expired anyway. The replacement went bad on one of those motors a year later too. <br /><br />A merc dealer can nail the years on stator problems and the fix. Merc changed colors on the stator and I believe the latest and best is red and the old defective type black. Beware of this if buying nos parts.

 

[fishez4aliving]

Re: idles great when i put new plugs in, but......

Wow, this site is awesome, i really appreciate the feedback. I already took the coil from #2 and swaped it with another cylinder, i had no spark, so i knew it wasnt the coil. So I should look at the switch box, I'll do that tonight. Thanks again fellas, all the feedback is greatly appreciated.

 

[fishez4aliving]

Re: idles great when i put new plugs in, but......

Sorry for not posting sooner....it was a switchbox issue, I replaced it and the engine runs smoothly. I was wondering if anyone could give me advice about replacing this 175 carbed with a 150 efi. I have the opportunity to buy a rebuilt 1999 150 EFI Merc. I would like to know a couple of things. This engine is on a 20 ft. Sea Craft and currently at WOT i can run it about 41 MPH according to my GPS. Although Im giving up 25 HP, will fuel economy benefits and reliability outweigh the loss of speed. And how much fuel savings do I get? Also, i had a lot of faith in that old 175, i ran it all the time (about 1200 hrs per year, and unbelieveably for the last 3 years i got 3876 hours without a powerhead rebuild, just trim tilt solenoids have been replaced, and the lower unit was rebuilt. I run my boat offshore and need something i can trust, will the 150 EFI be worth replacing my smokey, fuel guzzling 175 with?

 

[Clams Canino]

Re: idles great when i put new plugs in, but......

Hard call.<br /><br />Usually, trying to get the same performance out of a lower HP outboard results in higher throttle settings and more fuel burned.<br /><br />Best thing to do (for economy) is run your outboard at "cruise". This is the spot where the ignition is at max-advance but the throttle bodies havn't opened up much.<br /><br />-W

 

[Elmer Fudge]

Re: idles great when i put new plugs in, but......

sorry! my error.

 

[fishez4aliving]

Re: idles great when i put new plugs in, but......

Thanks for the info. I have a floscan gauge on the boat, i know that at 3500 i can cruise at about 30 MPH and where i go, thats fast enough, unless i want to get my knees replaced when i get older. I think I'm going to keep that old Merc, and wait for An Optimax> As soon as i put that new switchbox on, i run smooth and burn a lot less fuel