engine miss firing

[drpete3]

I got gas at a crappy gas station and the miss started after that. this is Rebuilt engine with less that 10 hrs on it. Ill go along and then the Rpms drop about 2-300 then they will come back up and so on and so on. First thought was bad gas. I still put a bottle of water remover in it and put 15 gal of good gas in it. this jump in rps occurs at any speed. I removed the water seperator and dumped it into a bottle and didnt see any water. Help

[MOBILEMERCMAN]

Careful the ethenol and dry gas absorbs the water so the motor can pass it. It lowers the octane and leans it at the same time. When you looked at the fuel was it clear or cloudy? Cloudy fuel is water laden and bad news. Could you hear it pinging?

[Ratickle]

I just got off the phone with Chris. The filter type you replace. In a pinch, out on the water, you can pull them and slap the crap out of them and about 80% of the water will come out.

But change them if they have water in them when you get back to shore.

The water will not mix in the poly seperator, it will show as little beads/droplets.

Think I got it right.

[Chris]

If I thought I had bad gas, I'd suck every drop of it out of the tank and fuel system. Engines are expensive. Bad gas destroys them.

[Sean Stinson]

I got gas at a crappy gas station and the miss started after that. this is Rebuilt engine with less that 10 hrs on it. Ill go along and then the Rpms drop about 2-300 then they will come back up and so on and so on. First thought was bad gas. I still put a bottle of water remover in it and put 15 gal of good gas in it. this jump in rps occurs at any speed. I removed the water seperator and dumped it into a bottle and didnt see any water. Help

Do yourself a favor drain it and start over with new gas preferably some without ethanol!!!!

[Sean Stinson]

when is the last time you did plugs and wires and such

[Sean Stinson]

pull #1 and #6 plugs and see what they look like on the motor that is missing!!!

[drpete3]

Thanks guys. when i dumped the gas into a empty dry water bottle it was ceal but was more yellow than I expected. Looked like diluted Mt dew. I guess Ive never look at gas in a clear container so that surprised me a little.

This is a new(rebuilt) engine so all the plugs and wires are new.

What should ilook for on the 1 and 6 plug?

No it wasnt pinging. sounds fine to me other than the rpms droping and jumping up. It goes in maybe 10 sec intervals. Normal 10 sec then dropps for about 10 sec over and over.

I was thinking this type of water serarator was just a replacment type.

i only run 87 octane normally (420 Hp 454) and when I filled it after the problem I used 91 from a reputable Marathon station.

any more thoughts?

[MOBILEMERCMAN]

Check your fuel pressure and check for an obstruction or air leak in the fuel supply . Surging like you described can be costly. Don't let it do that. If its surging because its lean it is damaging the motor.

I don't put 87 in anything with a carb.

[Ratickle]

No it wasnt pinging.

i only run 87 octane normally (420 Hp 454) and when I filled it after the problem I used 91 from a reputable Marathon station.

any more thoughts?

Sounds more like fuel starvation than electrical issues.

Unless you know exactly what they did to the engine, assume they may have surfaced the heads and block and your compression was increased so 89 is no longer enough octane.

Float levels possibly guys?
Fuel pressure?
Fuel Filters?

What else?

[drpete3]

Check your fuel pressure and check for an obstruction or air leak in the fuel supply . Surging like you described can be costly. Don't let it do that. If its surging because its lean it is damaging the motor.

I don't put 87 in anything with a carb.

What kind of pressure should it be? I ran the boat fine for the firt 8 hrs or so after the rebuild. then this started. I was going to a differnt lake than normal so as I got close I found a Bp staion in a tiny little town and decided I sould get gas. I ran it for maybe 45 min then we sat for a few hours. I ran it fine for about 10 min on the way back to the dock and then this started. I was about 500 yrd s from the doock and took the boat out. didnt think much of it then. the next day I went out again and ran it maybe a half hour and the problem started right away and never stopped. It seems mild like about 200 rpm even at WOT. ANd when it drops its sounds like its bogging and I can feel the loss of power. actually the feeling is more drmatic than the rpms show.

So I should drain the gas
check fuel pressure
check for fuel obstruction
check for fuel line leak...air entering

I think the first thing I shoudl do is run it again since I ve put dry gas into the system. if the surging is gone then i would assume bad gas. then take appropriate measures to get it out..Right?

[drpete3]

Sounds more like fuel starvation than electrical issues.
Unless you know exactly what they did to the engine, assume they may have surfaced the heads and block and your compression was increased so 89 is no longer enough octane.

Float levels possibly guys?
Fuel pressure?
Fuel Filters?

What else?
I think they wanted to get about 9.25:1 comp

they put in 2.25 and 2" valves
they didnt touch the carb to my knowledge. Quadrajet carb. all new filters

My theory was the the water serarator filled up with water then I started having troubles.

[Ratickle]

Was it almost empty when you put new gas in?

Jim's worried the motor is starving for fuel, running lean, and that will definitely damage a moter.

[drpete3]

its was at about 1/4 tank and I remember putting in 30 gal.

What sdo the plugs look like if its running lean? Why would it run lean? from the gas?

[Ratickle]

its was at about 1/4 tank and I remember putting in 30 gal.

What sdo the plugs look like if its running lean? Why would it run lean? from the gas?

http://www.spark-plugs.co.uk/pages/technical/diagnosis.htm


http://www.gnttype.org/techarea/engine/plugs.html


Detonation/erosion/overheating

[MOBILEMERCMAN]

Any easy first test would be to run it on an outboard tank. Determine whether it is in the supply or the motor. It is also easy to check the float level. The fuel pick up cracking and obstructions in the supply are random misfortune. How many hours is irrelevant. A cracked pick up allows air in the line and only acts up at half tank or less.

[Ratickle]

its was at about 1/4 tank and I remember putting in 30 gal.

What sdo the plugs look like if its running lean? Why would it run lean? from the gas?

How big is your tank?

[drpete3]

http://www.spark-plugs.co.uk/pages/technical/diagnosis.htm


http://www.gnttype.org/techarea/engine/plugs.html


Detonation/erosion/overheating

so do you think Ill see this even if Ive only run it 45 min in this condition?

[drpete3]

Ok i took the boat out now that I added dry gas and still had the problem....prob not bad gas. BTW it was no longer surging it was just plain missing.

So this moring I pulled all the plugs and found one not very tight when taking it out. Put te plugs back in and fired it up on the hose and sounded good again. so I took it down to the lake. Ran strong for about 5 min then started up again. So i figured i either tepmrarily fixxed the problem or this is a warm engin prob. So I pulled all the plugs agian. I broke an insulator on one of the plugs this time. Maybe it was cracked and i didnt notice it before. Put in a new spare plug checked all of the plug wires and boom. the boat ran great all day today. FEWWWWW! i am so relieved that i got it fixxed

[MOBILEMERCMAN]

Nice

[drpete3]

Nice What i meant to say was Thank you to all you guys that shared their knowledge. Really Thank you very much.

I am heading to lake st clair next weekend and have been planning this trip for 3 months and its going to be my biggest hoooraaa of the summer. So I am so glad I can still attend. Great job guys!

Also I was concerned about somthing worse like losing a lobe on my cam or somthing really bad.

[Ratickle]

Ok i took the boat out now that I added dry gas and still had the problem....prob not bad gas. BTW it was no longer surging it was just plain missing.

So this moring I pulled all the plugs and found one not very tight when taking it out. Put te plugs back in and fired it up on the hose and sounded good again. so I took it down to the lake. Ran strong for about 5 min then started up again. So i figured i either tepmrarily fixxed the problem or this is a warm engin prob. So I pulled all the plugs agian. I broke an insulator on one of the plugs this time. Maybe it was cracked and i didnt notice it before. Put in a new spare plug checked all of the plug wires and boom. the boat ran great all day today. FEWWWWW! i am so relieved that i got it fixxed


Nice

Curious Jim, root cause bad/loose plugs? Why would it take time to appear?

[drpete3]

Im not sure it was the lose plug. what about a bad insulator? maybe even a wire not on tight. as I look at the engine it was the left side with a lose plug 2nd from the back and the 4th from the back on the left seemed to not be on good.

the broken plug was on the right side and was the 3rd from the back.

Sorry i dont know which cylinder is which 1-8

[Ratickle]

Im not sure it was the lose plug. what about a bad insulator? maybe even a wire not on tight. as I look at the engine it was the left side with a lose plug 2nd from the back and the 4th from the back on the left seemed to not be on good.

the broken plug was on the right side and was the 3rd from the back.

Sorry i dont know which cylinder is which 1-8

That's okay, I'd have to look it up too.


Just trying to figure out root cause so if someone else asks with the same type of issue we can steer them correctly as one of the possibilities.

[drpete3]

also, all of the plugs looked light brown or tanish.

one thing I noted was 2 plugs on the left side (front 2) had droplets of some liquid on the center electrode when the were first pulled. not sure if that means anything.

[Ratickle]

also, all of the plugs looked light brown or tanish.

one thing I noted was 2 plugs on the left side (front 2) had droplets of some liquid on the center electrode when the were first pulled. not sure if that means anything.

This was the very first time out this year, correct?

[drpete3]

This was the very first time out this year, correct?
No I have put about 9 hours on it before these symptoms started. Remember this was a rebuilt engine. I got it in the water over memorial day and been out a few times since then. Then you know the story. Started surging then I m pretty sure was just running on 7 cyl. All in all prob took abou tan hour of run time to go from surging to just missing.

Fyi, Jim I put in 89 oct today figured it cost me about an extra $1.50 for 15 gal to top it off.

[MOBILEMERCMAN]

Since you mentioned unknown liquid on plug I would suggest you check the plugs again since you have run it.. Make sure the exhaust isn't leaking. Water from a leaking exhaust will make it miss. It will show up on the plug with water drops or rust spots.

The loose plug will make it miss. A loose wire will fall off. Broken insulator can be from installation, lean, or water leaking.

[MOBILEMERCMAN]

When the motor was redone did you check your exhaust and/or change your riser gaskets?

[Ratickle]

Since you mentioned unknown liquid on plug I would suggest you check the plugs again since you have run it.. Make sure the exhaust isn't leaking. Water from a leaking exhaust will make it miss. It will show up on the plug with water drops or rust spots.

The loose plug will make it miss. A loose wire will fall off. Broken insulator can be from installation, lean, or water leaking.


When the motor was redone did you check your exhaust and/or change your riser gaskets?

Why the surge though?

[MOBILEMERCMAN]

Why the surge though?

I don't know. It is hard to interpret others descriptions some times..

Liquid on the plugs is more clear. I wonder why was motor redone?

[drpete3]

The only time I had a liquid on the plugs was the first time I pulled them. the second time they were all dry.

The reason i needed a new engine was becasuse it had a cylinder failure on the old block. It was a cylinder that had been sleeved. I dont know why the sleeve didnt hold up though. So in onther words I dont know why I had a failure. was it just the sleeve failed or was it some other factor. So what I really got was a long block the used my old parts to build the new engine.

I am sure the guy that rebuilt the engine used new gaskets on the manifolds but the risers hmmm not sure. Probably not. I have stock exhaust/not high performance.

Now what?

[Chris]

The first rule in racing is never trust a new part. Put it on and make sure it works, then put it away until you need it.

I've seen plenty of bad-out-of-the-box parts. And beyond that, if something has a defect, it's going to show up quick.

[drpete3]

The first rule in racing is never trust a new part. Put it on and make sure it works, then put it away until you need it.

I've seen plenty of bad-out-of-the-box parts. And beyond that, if something has a defect, it's going to show up quick.

Chris Im not sure what your referencing here. Or are you saying just the whole situation in general.

[drpete3]

I spoke to my engine builder and he said with out looking at it he wasnt sure either. The more i think aobut the liquid on the electrode the more i think it was water. It was beaded up on the electrode but these dropletts were tiny. Very tiny and only a few of them. He said it could have been condensation from sitting outside and a cool night.

[Chris]

Yes- as a general rule.

I just bought all new ignition stuff for my son's Tahoe. Put it all on and no start. Made me nuts for a full day of poking around. Finally, I started backing up one piece at a time. Put the old distributor cap on and it fired right up. Returned the first one and put the new one on- no start. Returned that one and put a 3rd one on- stared and ran poorly. Finally bought another brand and it ran fine.

[MOBILEMERCMAN]

I spoke to my engine builder and he said with out looking at it he wasnt sure either. The more i think aobut the liquid on the electrode the more i think it was water. It was beaded up on the electrode but these dropletts were tiny. Very tiny and only a few of them. He said it could have been condensation from sitting outside and a cool night.

Riser gaskets on stock exhaust need to be changed every 3 or 4 seasons in fresh water and every other season in salt. They do a lot of work separating exhaust from water in a small area. As time passes the gasket begins to weep water into exhaust.. At first it is hard to recognize. Soon it will begin to miss on a long idle but, clear as you rev it past 2k for a moment. Eventually it starts to leak some much the starter sounds like it is going bad when you try to start it.

I don't know if it is your problem but, it is a common service item that often gets overlooked.

[drpete3]

Riser gaskets on stock exhaust need to be changed every 3 or 4 seasons in fresh water and every other season in salt. They do a lot of work separating exhaust from water in a small area. As time passes the gasket begins to weep water into exhaust.. At first it is hard to recognize. Soon it will begin to miss on a long idle but, clear as you rev it past 2k for a moment. Eventually it starts to leak some much the starter sounds like it is going bad when you try to start it.

I don't know if it is your problem but, it is a common service item that often gets overlooked.
good point. Ive only owned this boat since aug of 2007 and I know I havnet replaced the gaskets on the risers so I shouold look into this. Actually what I would like to do is find some take offs(manifolds and risers )and get rid of the stock exhaust

[MOBILEMERCMAN]

Stock exhaust on stock motors work well. The riser gasket change is about an hour each. Pretty easy and inexpensive. In fresh water the manifolds and risers last a long time.

[drpete3]

Stock exhaust on stock motors work well. The riser gasket change is about an hour each. Pretty easy and inexpensive. In fresh water the manifolds and risers last a long time.
got any part diagrams to see what I would be pulling off and replacing. I know its somthing I can do just never done it before. Like you said it may not be a problem but if its semi routine maintenance then I should jus tdo it before I have a problem.

[MOBILEMERCMAN]

http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=804807%2099&ivar=images/COMMON/20114.png&inbr=4854&bnbr=120&bdesc=Exhaust+Manifold+and+Exhaust+Elbow

Install gasket with permatex aviation sealant on both sides. It has a brush in the cap. Scrape and clean surface. Drain manifold first. When you have removed riser you should see no signs of water or rust in center exhaust area. Tighten evenly to 30lbs.

[MOBILEMERCMAN]

Old thread on subject

http://www.seriousoffshore.com/forums/showthread.php?t=3188

[drpete3]

http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=804807%2099&ivar=images/COMMON/20114.png&inbr=4854&bnbr=120&bdesc=Exhaust+Manifold+and+Exhaust+Elbow

Install gasket with permatex aviation sealant on both sides. It has a brush in the cap. Scrape and clean surface. Drain manifold first. When you have removed riser you should see no signs of water or rust in center exhaust area. Tighten evenly to 30lbs.
So this looks like an easy job. Where would you suggest I get the permatex sealant and also the gaskets? Looks like I have the cast type.

[CAPM KURT]

Good advice m.m.m. That's what I've used before is the Permatex. Just this week I've ben talking to Loctite just to try and get the best sealer I can as I'm fixin to change mine on my 3 year old 5.7liter that are leaking on the outside.

The Permatex is good to 400 degrees. I'm sure the exhaust gases are way up there but the actual metal surfaces are much lower, who knows exactly-maybe over 400 right on the edge of the exh side but way less on the water side.

I bought some Loctite Hi Temp Gasket Maker part # 30558, (good to 600F.) Put a bead out just to look at it-looks thicker like the old #2Permatex form-a-gasket but different smell and dried much quicker than Permatex so it's not just a similar product. Looks like it would work even better. It's non-hardening also. I'm going to try it next week or so.

Volvo Penta has just gone to thin metal gaskets with a crimped ridge in them. Cannot get the old paper type for my 5.7L from Volvo. I think I'll try one of the metal type with the Loctite 30558(even though they strictly say to put the metal one on completely dry) and one paper type aftermarket gasket. I'm just not sure about the metal type!

Do you have any experience using a gasket maker hitemp silicone on the elbows?? Loctite suggested it may work also(Loctite # 5920). Just have to make sure its a sensor safe one. But they aren't any higher temp than the 30558 - 600 degrees. Never heard of anyone using silicone. Probably not any better than the Perma or Loctite.

thanks for any advice

[MOBILEMERCMAN]

The permatex aviation is brown has the brush in the cap and is the equivalent to Mercurys Perfect seal. You should be able to find it in any well stocked supply house. I would not use silicone or any RTV.

[MOBILEMERCMAN]

http://www.smallparts.com/Permatex-Aviation-Gasket-Bottle-GROUND/dp/B00137FW4S

[MOBILEMERCMAN]

Respectfully guys, I have witnessed the various gasket types, aluminum and stainless risers on cast iron manifolds over the years. You need to protect the metal around the gasket. Dry metal hazes and corrodes faster than protected metal. The foil gaskets were developed for SS risers on cast manifolds. They were just a band aid for poor engineering decisions.

I have been using perfect seal {aviation sealer} since 1983. There is nothing better.

It is just your engine at stake. Go ahead and experiment with something new.:(