85 Mercruiser 170 runs bad when warm

[cgreen5760]

When the motor warms up about half way aroud my lake the engine starts to run bad and I have to back the throttle off. The volt meter is at 16 and the engine is runnig cool. The points, distributor cap, rotor, and wires are new. When anything electrical is used the motor runs worse. I have checked every wire connection and switch for a short and could not locate one.Could this be the voltage regulator? any suggestions

 

[webnetxpress]

Re: 85 Mercruiser 170 runs bad when warm

well i'm not a mechanic, but i have never heard of a car engine running at 16v. Have you double checked that with a digital meter? if so, i would think you are overcharging something somewhere. I believe (I'm sure other's more knowledgable will correct me) it should be around 14v with the engine running, not much more than that.

 

[fireship1]

Re: 85 Mercruiser 170 runs bad when warm

Hello, Sounds like you may be overheating your ignition coil. I would check a few things to narrow it down. Check the battery voltage at idle like Webnetxpress suggests 16 VDC at the battery is too much voltage and will boil your battery's electrolyte as well as shorten the life of all your bulbs onboard. Check the voltage at the coil when cold and see what you get. Extend the leads on your meter, keep it wired in place and position it on the dash where you can see it while you run on the water. I suspect that the voltage will climb as you run and warm up. Volts at the coil should be 6-9 VDC. If you are getting 10-12 VDC you are getting too much. The coil will overheat and the motor will run like it hasn't been tuned up in 10 years! The external resistance wire that is used on these models is to blame. I would replace the wire as well as the coil with new parts. That will more than likely solve your problem. Or get a Pertronix ignition upgrade and a universal 12 volt coil and be done with points, resistance wires and stock coils forever! Either way should solve your problem.

 

[cgreen5760]

Re: 85 Mercruiser 170 runs bad when warm

Thanks I will try replacing the coil and resistance wire and try it on the lake later today. I am very greatful for the help.

 

[cgreen5760]

Re: 85 Mercruiser 170 runs bad when warm

Took the boat out on the lake today and same problem after replacing the wire, coil,and points, Seems that when I use anything electric the motor runs bad if I turn the blower on the engine misses or I trim the boat the engine misses. any other suggestions.

 

[fireship1]

Re: 85 Mercruiser 170 runs bad when warm

Hello, Sorry to hear that it did not work out for you. You need to put a meter on your battery and see what kind of voltages you get at idle and at upper rpm's. You never said if you checked this out. I don't want to tell you to change anything else without some more testing. Could be alt or voltage regulator, but you need to be sure. Marine parts sure get expensive in a hurry! Let us know, We'll try our best to help out!

 

[fireship1]

Re: 85 Mercruiser 170 runs bad when warm

One more thing, When you installed the points did you set the dwell and then set the timing? Just trying to help you narrow it down.

 

[cgreen5760]

Re: 85 Mercruiser 170 runs bad when warm

timing and Dwell were checked and set. Every thing works good when its cold. I will check the voltage this week and let you know thanks for the suggestions.

 

[Northern Eclipse]

Re: 85 Mercruiser 170 runs bad when warm

Chris Is your motor the 3.7l I4 also known as a 470....if so you need to check the voltage reg. with voltmeter., your gauge may be not be true 16 volts is to much, the V.R on these motors are water cooled and can cost big bucks, so a heat issue could be at play here.

 

[kcole683]

Re: 85 Mercruiser 170 runs bad when warm

16 volts is pretty normal on a 3.7 liter with original equip charging system.<br />The turn on range on the regulator is between 16 and 18 volts. That is how high they get before the regulator kicks in.<br />The turn off range is from 13.5 to 15 volts. This is where the regulator shuts off and allows charging.<br /><br />My 3.7 liter regularly sees 16 to 17 volts before the regulator reduces it.<br /><br />I haven't had any problems with the engine running.<br /><br />Make sure the resistor wire circuit is reducing voltage to the coil.

 

[DJ]

Re: 85 Mercruiser 170 runs bad when warm

16 volts will heat up a coil in a big hurry.<br /><br />How many volts do you have at the coil?

 

[cgreen5760]

Re: 85 Mercruiser 170 runs bad when warm

Ok I checked the voltage in the driveway with muffs on (don't have time to take it out on the lake today) the voltage at the battery was over 16 volts and the voltage at the coil was 5 volts. When I turned on the blower and the bilge pump the voltage at the coil went down to about 3.5. If this information helps let me know but I will try and test it on the lake this weekend. Thank all for any help.

 

[DHPMARINE]

Re: 85 Mercruiser 170 runs bad when warm

Chris G.<br />You have (I think) a bad connection on one of your battery cables.This is making the big demand on your charging system.<br /> 3.5 volts at the coil is not enough for the motor to run,or run well.<br /> You probably have cleaned the cables at the battery,now clean the other ends (starter and engine nlock)<br />Does this help?<br />DHP

 

[fireship1]

Re: 85 Mercruiser 170 runs bad when warm

Hello, Clean up everything like DHP suggested. When you turned on the blower and the pump you said the volts at the coil dropped to 3.5. What did the volts at the battery drop to? If all the conections are clean and tight I would suspect the voltage regulator. Don't just look at the battery cables at both ends and dismiss them as OK if they just LOOK clean. Take them apart and make sure. The greenies tend to creep in between terminals and connections. Also make sure all of the wiring at the regulator is all clean and tight. Let us know how it goes.

 

[cgreen5760]

Re: 85 Mercruiser 170 runs bad when warm

Everything was cleaned up when I first noticed this problem but thanks for the suggestions.I don't know what else to try. I guess I will have to replace the voltage regulator I don't have enough room to put the alternator conversion kit in my engine compartment.I will let you know what happens thank you.

 

[cgreen5760]

Re: 85 Mercruiser 170 runs bad when warm

Does anyone know where I can get a cheaper voltage regulator than from Mercruiser.

 

[Dunaruna]

Re: 85 Mercruiser 170 runs bad when warm

Cris, firship1 suggested replacing the resistance wire (also my first thought). Your follow up post said that you did that but it reads as though you replaced the coil lead (coil to distributor cap centre post). <br /><br />Did you replace the ballast resistor? This is what supplies 8-9 volts to the positive side of the coil.<br /><br />I think the 16v problem is a seperate issue. <br /><br />I may have misread, if so ignore this post.<br /><br />Good luck.<br /><br />Aldo

 

[cgreen5760]

Re: 85 Mercruiser 170 runs bad when warm

The resistor wire I replaced was the one that goes to the positve side of the coil but thank you anyway. Could I tell if the Voltage reg. is really if I unhook the regulator and try to run off the battery for a while?

 

[kcole683]

Re: 85 Mercruiser 170 runs bad when warm

For all of your 3.7 liter Mercruiser problems go to : Breezeworks 470 mercruiser forum<br /><br />This link is for the 470 3.7 Merc. only<br /><br />The host sells used and aftermarket voltage regulators.<br />You can also find out how to troubleshoot the one you have.<br /><br />It still sounds like you have a bad connection somewhere to me.<br />If you have 16 volts then you are charging for sure. You should get 14 to 16 volts cycling on a voltmeter as the regulator turns on and off during operation.

 

[cgreen5760]

Re: 85 Mercruiser 170 runs bad when warm

Does anyone know a good boat mechanic that can diagnose my problem in Michigan near Oakland,Wayne, or Machomb counties?