f100 need help please bad missfire

[slipery8700]

Hey i have a 1999 yamaha f100 4 stroke that is giving me hell this year. I am an ase certified automotive tech and maybe im just over thinking this. started out this yr doing regular maint changed all fuel filters all oe changed plugs and oil nothing major all oe parts. ok when i run the boat it would take off full power no problems and after running wot for about 5 min would cut down from 6000rpm to around 4800 and lose power. then come back to idle and it would have a missfire for about a min then run smooth and take off agian and same problem occars no matter what. so i started testing things. in the process of testing i found the batt would charge then not charge then over charge so after checking everything found the rectifier to be burent and bad and replaced it with new oe replacement. also in that process the tach quit working it is a digital gauge with trim temp and oil it will light up and alarm works just no tach and no tach after replacing rectifer. ok so it seemed like fuel and fuel pumps tested ok tank is good took everything apart replaced fuel line from tank to filter and cleaned carbs. then went to retest and started eng to find a bad missfire. only #4 cyl seems to be firing good took plugs out and are white tiped. checked compression all was good at 190psi across. all the coils have spark but on a tester seems faint to me. this thing is driving me crazy and the manual i have does not help much beacuse nothing seems to match up when testing with my dvom. in my opinion it seems like the cdi might have gotten fried from the over charging but as expensive as it is i need to be sure anyone that can help please lend me a hand from mechinic to mechinic i can tell u anything about a car but this has got me stumpped thanks

[99yam40]

As a mechanic you should know that a proper manual and the proper test equipment is needed to troubleshoot modern motors, whether they are marine or automotive.

You need to find out if you have any codes being throw, monitor fuel pressure, input and out out of the CDI or ECU, and probably a lot more

[200090tlry]

Lol but are you a good tech?

BMW guy's know there stuff. 190 comp test holly roller, mines 95 at pretty good altitude. Being a car guy you have positive and negative cables tight right. Rod knows cars and outboards! He will help you

[rodbolt17]

however rod also knows when to break out the manual, borrow or buy the tools needed to PROPERLY test the machine I am working on OR trade my service for anothers.
small case point.
I am also currently certified for volvo and mercruiser.
the volvo sx style ,and the old cobra drives had an issue with commercial use.
the lower gimbal ring swivel pin wipes out 3 to 5 times a year.
the bracket assy now costs 297 dollars.
today the owner of a local machine/welding shop needed his carbs done on a 2001 F50.
I did it, traded labor for him to build me 10 swivil pins out of some scrap 1" prop shaft.
I will drill and tap the lower bracket,set screw the pin in place and sell it installed with a new bushing for 225.
I have 7 lined up so far.
mechanic to mechanic?
dont call yourself a mechanic until you understand a multimeter and nderstand how your system works.
then and ONLY then start wrenching.
its NOT a car motor,similar but not.
uses NOTHING you ever saw for ign production.
Ill save the altenator thing ,,, for a bit

[slipery8700]

thanks

ok guys thanks for the scarscam. first off this is a carb f100 no codes to pull. i did have a correct manual but got an oe yamaha one to be sure. I have a fluke 88 and a snapon modis so i did all the testing on the stator and pickup coils and the cdi unit and secondary ignition coils. just wanted a little advise beacuse spending money on parts is not easy with kids. anyways everything tested good and im really stumpped. good wave form from stator and pickup coils or lighiting coils and voltages were in spec. ign coils ohm out good and i doubt two coils would both go out at the same time. also like i said no tach signal and all this seemed to start when the rectifer went bad and voltage did go high. it has a new rectifer now oe yamaha and charging system is fine. tach signal comes directly from cdi and everything points to cdi being bad. so if any of yall real mechinics have a real answer please let me know if not i will figure it out on my oun.

[99yam40]

Can you post the readings you got with the " snapon modis" and tell me what that is?
All I know is that if you do not have the peak reading voltmeter for these motors you need a DVA adapter to get the readings to compare to manual.

Your first post said the readings did not match up and you are not giving us much info, just all looked good. We can all guess at it or you can give us something to go by

If the charge coils and pulsar coil inputs are good and the CDI out puts are good then the CDI is good in my thoughts, but I have no real thoughts on the CDI feeding tach as I have not seen that on any of my motors.

[rodbolt17]

tach signal is generated by the CDI on that model.
has nothing to do with the rectifier.
yes if the rectifier smokes,usually due to loose cables, it can burn up the CDI thats mounted just above it.
that system fires 1 and 4 and 2 and 3 all the time.
if 1 fires then four fires on its exhaust stroke,
its a 12V transistor controled ign system and uses waste spark.
dunno what a snop on modis is.
if its capeable of reading PEAK volts NOT volts RMS but PEAK, and automotive doesnt use voltage PEAK, then it will work.
if not your readings will be low.
consistant but low.

[slipery8700]

more info

Ok lets see if anyone can help. here is an update and more info. I replaced the cdi unit and my tach works now. But the missfire is still there and it gets worse as the eng warms up. the rectifer did not completly burn up i noticed charging problems and had no missfire took it off and found a small spot on it to be burent so i changed it. took the boat out it ran fine other than the origonal bog problem at wot after running it for about five min. anyhow took it home and cranked it a few days later and the dead miss is there. I have changed almoust everything and completly checked all grounds and ohmed them all aou as well as almoust every wire on the eng. has new batteries and cables. I replaced both ign coils, plug wires and plugs. agian changed the cdi . I also changed the stator and pickup coils. still got a miss. only thing i havent changed is the dang flywheel. here are some readings im getting. from the rectifer red wire at 1500 voltage is 14.7 and at 3500 stays at 14.8 not much change. my manual says it should be 18v at 3500. cdi output to coils is at 400rpm 46v, at 1500 64v and at 3500 at 111v. It is hard to say out of the water but it does seem to get better at high rpm or the miss seems to go away but it is hard to tell. also im not sure but to me the spark from the coild appears to be weak. not sure if it is just the system but it is a blue spark just not that hot. i do kinda understand how this system works with the waste spark but i dont see how the stator or rectifer has anything to do with the ign since the pickup coils feed the cdi and the cdi feeds the coils, but a am no marine experct thats why im asking. also i did ohm out the stator and pickup and both were in spec. to me the only thing left is the flywheel but i hate to waste more money if i caint deterime it as a pos im just gonna take it to a local shop.

[rodbolt17]

what model multimeter are you using?
what DVA adapter are you using?
that engine does NOT use the charging system to produce spark.
spark is transistor switched 12V.

[slipery8700]

i have several diffrent meters but i dont think it is giving me a corect reading as you are saying. i have an old fluke auto range dvom, and a new fluke 88 dvom. but i dont think im getting peak readings out of them.

[rodbolt17]

neither one of those meters reads peak voltage, but the 88 can use a DVA adapter.

[ddaschbach]

i have a similar issue with my F100

I have a similar issue with my 2002 F100 with similar repair history. Have you been able to resolve your misfires?

[mercurypro]

f100 withsame problem also..

hey did he find the problem... omg i have simular problem ..
hell somebody call me.. 920-493-1002 ken..mine is definetly eletrical.. but dont know if its a pulser coil or cdi... mine starts miss firing at 2400 and then nothing comletly at around 3500... but only on 2-4 cylinder.. its not the coil..i swaped it with the other one and same thing happend..now what>>???..

[lucky lachi]

Hi

Hi I just got the same problem with my outboard f100 have you find what was the problem in yours?

[boscoe99]

Lucky, you are riding on a four year old post. The main player is long gone.

Best to start a new thread of your own. State the complete model identity, what the symptoms are, and what, if anything, that you have done.

What is it doing and when is it doing it?