New Day, New Ignition problems with TB IV systems

[chrismurr1]

ok, here is the skinny. Dual Merc 5.0 (230 HP) straight inboards. had it out 2 weekends ago, 6.5 hour cruise, no issues. took it out yesterday, 1.5 hours into the cruise... i started having ignition problems.... looking for advise and help and i know the experts here have the knowledge.

Each engine has its own unique issue :/

Port: engine runs fine under 2000 RPM (when hot) when i take it over 2000 it will be fine for like 2 minutes max and then start cutting out (no backfire) just feels/sounds like its missing on half the cylinders. once it starts it will bounce around, run fine for a few moments then start missing for a few seconds then go back to being fine... if i drop the RPMs back down to just 1850, its fine... TB IV system has newer pickup in the dist. this engine is running an ACCEL coil (suspect yes but looking to get concensus). I am thinking the coil just isnt giving up the spark properly but i suppose it could be the pickup too. will be doing the troubleshooting chart tonight.

Starboard: Engine runs fine at any RPM but just shuts down like the key was turned off. the more i try to restart and run with it, the worse it gets till it just wouldn't run at all. First time it happened, it started right back up and i ran another 10 minutes, it dies and after a restart runs for a few more minutes and dies... got to the point that it wouldn't start at all and hobbled in on the port engine. This system has a new dist pickup installed but is running a rather old Merc coil. again, running the troubleshooting chart tonight. I did notice that the ignition amp mounted to the riser was really hot, hotter than the riser itself....

both engine have new wires and plugs (plugs are gapless bosch platinum 4s) the cap and rotors look really good so i cleaned up the contacts with emery cloth and reassembled. timing is right on at 8 degrees BTDC @ 700 PRM.

during yesterday's run on our way out, we both engines running @ 3000 RPM with not so much as a hiccup for a good 20 minutes before we had to bring them down for slow speed zone, when we came out of the zone, the port engine started acting a fool.... we mozy'd the rest of the way out picnic island and hung out for a couple hours. on our way back, the port continued to act a fool and then 30 minutes into the return the starboard started acting as described.... sorry for the long winded but i know more is better when asking for assistance.

Chris

 

[Don S]

Re: New Day, New Ignition problems with TB IV systems

It sounds a lot like a fuel delivery problem from the tank. I would sure run the tests on the fuel system from this thread.
http://forums.iboats.com/showthread.php?t=283269

I would also go back to the proper spark plugs and coil for your engine.

For more specific info, I need to know what the engine serial numbers of the engines are. The 230's didn't come out until 1981 and were used until 1995. Lot of different ignition and fuel system changes in there.

 

[chrismurr1]

Re: New Day, New Ignition problems with TB IV systems

Thanks for the quick reply Don. i will run through the list you gave me for fuel while im out there and i will get the serial numbers too. I did switch fuels yesterday for the first time. We usually go to the yacht basin and get the 90 octane unleaded but yesterday, i decided to use the marina's fuel dock instead which has ValvTect unleaded (the only valvtect fuel supplier in the area). Since i don't run addatives in my regular fuel, could this new fuel have caused these symptoms?

also, I agree with the coil change and will be doing that this week, but the spark plugs.... do you really think these premium plugs could be a problem in this engine? I will change em if they really are the problem but man they are expensive...

 

[Don S]

Re: New Day, New Ignition problems with TB IV systems

but the spark plugs.... do you really think these premium plugs could be a problem in this engine?

They may be premium plugs, but they are also not what is called for. Can they be the problem, Yes, are they? Who knows without putting in the right AC or NGK spark plug for your engine.

 

[wca_tim]

Re: New Day, New Ignition problems with TB IV systems

a fuel problem - like mixing incompatible additive packages, adding ethanol free fuel to wet fuel with ethanol in it or vice versa, etc... can cause all sorts of strange things... "sludge" partly clogging tank screen or fuel water seperator, etc...

I recently had a fuel issue from similar mistake and the boat would run fine for short spurts, then crap out. soon the needle was also sticking open and so nit was loading up at idle, etc... turned out I mixed good, ethanol free premium in with a little bit of gas that had 10% ethanol and was saturated with water... had additive in the tank, but there wasn't enough ethanol to solubilize the water and it phase separated and clogged the fuel filter, and I found chunks of jellow looking stuff in the carb and everything... I filled my corvette up from the same gas pump so that's all I can think of...


Hope you figure it out whatever it is... I would think if an ignition problem, that it would not have effected both engines in the same time frame...

 

[chrismurr1]

Re: New Day, New Ignition problems with TB IV systems

ok, here are the serial numbers. looking at them now, the port has to be a different year from the SB, just guessing though.

Port: 6206067
SB: A371115

let me know if these bring up any more suggestions. I tried to reproduce the problems in the slip last night but was unsucessful. i wont be able to get that marine coil installed till the weekend and will also get the right plugs... looks like i can get autolite's AP145 which is a direct cross reference to the AC plugs the manual i have says i should be using. let me know if the serial numbers tells you any different. i didnt have time to do the fuel system checks yet either... gonna have to wait till the weekend i think when i have more time.

thanks again for the help

 

[chrismurr1]

Re: New Day, New Ignition problems with TB IV systems

See that was my thought too. i usually get my fuel from the yacht basin which sells 90 octane marine fuel with no additives or anything and definitely no ethanol. Sunday, i purchased fuel at my marina because i didn't have enough to make it to the basin (50 cent difference per gal. is what makes me go to the basin). My marina only carries ValvTech fuel which is premixed with additives.....

i had the tanks flushed back in November and have only used marine grade fuel in them since, they are fiberglass tanks so don't need the ethanol eating them while my new SS tanks are being fabricated.

 

[chrismurr1]

Re: New Day, New Ignition problems with TB IV systems

ok, finally had a chance to do some additional testing and whatnot. Fuel system is fine now (had to replace the pre-pump filters as they were full of crap and a little water). fuel pressure is spot on, 5.5-6. no air in the lines. took it out for a 1 hour run to push it and see if i could recreate the problems i encountered last time out and while i was not out nearly as long as i was when i had the problems, i still couldnt recreate the problem. Max'd out the RPMs at a still weak 3500 RPM but i suspect that is due to growth right now, its due for a scrubbing and these engines are rated WOT @ 4000-4400 so im sure once i clean the bottom i can get that last 500 RPM and get fully on plane.

Starboard engine seems to run just fine now and didnt die on me at all so im guessing that the filter on that side was just too junked up to deliver the proper amount of fuel.

Port engine didnt exhibit the stumbling that i experienced but it is really running rough, especially around the 2500 RPM area. if you stand between the engines while running, place a hand on each riser, you can feel the port engine vibration is really rough and the starboard is nice and smooth. I double checked all my wires to make sure it was not mis-wired when i changed them. Checked the voltage at the coil both while engine was on but not running, after i started and again at 3000 RPM, 11.9 volts every time.

Here is what i did notice on the port side. at idle (800 RPM out of gear) im at 8 degrees BTDC, when i put it in gear RPMs drop to 700 and timing drops to 6 degrees...... starboard side doesnt do that, its at 8 degrees in and out of gear when idle.

the other observation i made with the timing is that out of gear, at idle, the timing jumps from time to time, between 6 and 8. it spends most of its time at 8 but drops to 6 momenarily and then back up to 8.... timing chain? bad ignition module? i still need to replace my plugs on that side with the Autolite AP145 plugs i crossreferenced out the other day. doing that tonight.

Any thoughts? Don, were you able to look up my serial numbers? i could not look them up on the sites i had access too :/

 

[Don S]

Re: New Day, New Ignition problems with TB IV systems

Neither of your numbers worked, are you sure they are correct?
If your water separating fuel filter had a lot of stuff in it, it may have bypassed some to the carb. Check the filter on the carb inlet, and you may even have water, dirt and corrosion inside the carb.

 

[chrismurr1]

Re: New Day, New Ignition problems with TB IV systems

thanks, i will check that out tonight as well, i have spare filters for the carb too so wont hurt to change those out either. as for the numbers... its right off the tag on the block.... valve cover labels match :/ what did i get a pair of imitation mercs LOL

 

[chrismurr1]

Re: New Day, New Ignition problems with TB IV systems

ok, so..... discovered that my fuel pressure gauge was hosed and bought a new compound and low and behold, 2 lbs of pressure.. so i put a new Holley red label marine electric pump on and now i have good steady 6 lbs of pressure and when the carb demands more fuel, it only drops to 4 for a second. replaced the coil and and spark plugs with Merc spec or direct cross reference.. still the same thing. the timing issue i mentioned above i dont think is worn gears or chains, it sounds like its lean missing, because it spends most of its time where i set it at 8 Degrees. so back to fuel delivery.

is it possible that if the float is off just a smidge, that it would cause the condition i am experiencing. i rechecked everything for timing to make sure i was on... brought the engine down to 700 rpm and made sure the timing was at 8 degrees... engine sounds like it wants to die, running on maybe 6 of 8.. (that is what is sounds like). I have to bring the idle up to 950-1000 out of gear to get it to idle in gear at 700ish and when i put it in gear, its weak, tach shows it drops to 550-600 at first and then it struggles up to 700ish... lean mix? not getting enough fuel maybe? I am thinking that the float is set too low but i would like second or even third opinions before i go back down there today to yank the carb and recheck and reset that float...

anyone?

 

[chrismurr1]

Re: New Day, New Ignition problems with TB IV systems

Thoughts?

 

[Stamey]

Re: New Day, New Ignition problems with TB IV systems

brought the engine down to 700 rpm and made sure the timing was at 8 degrees... engine sounds like it wants to die, running on maybe 6 of 8.. (that is what is sounds like). I have to bring the idle up to 950-1000 out of gear to get it to idle in gear at 700ish and when i put it in gear, its weak, tach shows it drops to 550-600 at first and then it struggles up to 700ish... lean mix? not getting enough fuel maybe? I am thinking that the float is set too low but i would like second or even third opinions before i go back down there today to yank the carb and recheck and reset that float...

anyone?

Have you checked for a vacuum leak around the carb? That'll definitely contribute to a lean condition. Typically this is done with carb cleaner, squirting it in small shots at small areas to narrow it down. As I have been messing with the Q-jet on my 83 MCM228 I found that my throttle shaft had worn to the point it was a major vacuum leak, and I could not get the idle below 1000 RPM. I have now fixed that throttle shaft issue and it idles where it should, smooth as silk, now.

Chris

 

[chrismurr1]

Re: New Day, New Ignition problems with TB IV systems

thanks for that one and its the first thing i thought of and i have sprayed all over the place on that thing trying to find a leak if there was one, even spraying around the intake where it meets the heads to make sure nothing went bad with the intake gaskets... its just plain baffeling, carb cleaner squirt in the flame arrestor and i get a boost (just to make sure) any where else and I am just cleaning parts :/ the carbs were remaned in Nov. and i dont even think i have 20 hours on them yet......

 

[Stamey]

Re: New Day, New Ignition problems with TB IV systems

Do you have Q-jets? I understand that they can have internal vacuum leaks. I do not quite understand this, and do not know how to determine if that is the culprit, but I did read someplace that one of the bowl screws that comes in from the bottom can get loose and cause a vacuum leak. The recommended procedure is to tighten it back up and put silicone sealer in the recessed hole where the screw is. I would think some loctite on the threads would be a good idea too.
I was researching vacuum leaks on my carb when I ran across that. When I pulled it off I found that the throttle plate my rebuilder put on was not a marine throttle plate and had a 1/2" vacuum port unplugged, that I couldn't see because it was directly under the fuel inlet. No wonder mine revved like crazy when I sprayed carb cleaner anywhere around the front of the carb. I don't fault him though, as he was just trying to find a throttle shaft that wasn't worn out, and he didn't charge me much to do the rebuild.

Chris

 

[Toypirate]

Re: New Day, New Ignition problems with TB IV systems

Try the timing light on all the wires, look for missed flash or moved flash at the balance, could be a bad cap. Also the rotor and distributor shaft should not rotate much, if it does it could be the 2 deg timing change, check the distributor bushings, also do a compression test as this misfire can cause the loose rotor to change the timing, I hope your problem isn't this bad, good luck.
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