2003 5.0 MPI engine flooding/backfiring??

jcc2823

so on rare occasion one of my engines decides it ain't gonna start. Once it was the port engine which I always have to give a little throttle to start when cold (had it checked out and they couldn't find anything wrong on computer etc), but today it was the starboard which generally fires right up.  I turned the key and at first it's just like it won't start- turns and turns and turns but never starts. So then I gave it a little throttle, but still won't start. I turn it over and over for probably too long and pump the throttle little bit. Still no starting. Once it's gotten to that point it ain't gonna start, but I keep trying and the only physical observation is that it seems like it sort of backfires through the flame arrestor- like a little puff sound, but no smoke or anything. Just like a "puff". 

Last tume this happened i went back next day and it fired right up- no problem. I hope the same happens tomorrow, but anyone with any ideas why this happens?

Dream_Inn

hmmm, first thing that comes to mind is the IAC valve.  But with that it typically starts with throttle, just won't stay running.  I'd say take 10 minutes and switch the IAC with the other engine.  I had issues with them on my prior boat (2002 310 with 5.0 MPIs). 

Black_Diamond

++ with Dream. IAC valve 

jcc2823

Thanks guys. I'm not very skill in these things but I'll give it a shot as soon as I can get back down to boat. I forgot to mention that when I turn this engine's key to the on position to left the fuel pump run before starting it beeps twice instead of the normal solid beep. 

jcc2823

I found a mercruiser PDF online giving cause for two beeps- says either a sensor or open short in circuits. 

jcc2823

Okay so I went down today and switched the IAC values between working engine and non working engine. No change in problem. Also I put IAC from non starting engine onto starting engine and that one still starts so I don't think any things wrong with IAC valves.  

Symptoms are: engine will turn over but won't start. I can crank and crank for what seems like forever but not starting. The only things that do happen are:
a random puff of air back through the flame arrestor/air filter. At one point while trying to crank there was a puff of very light colored smoke- almost vapor like almost clear. No smell to the smoke either. Other weird thing when it does do this 'puff' like backfire (don't know what else to call it) it's enough to pop a little hose that runs from the left hand valve cover to just behind the air intake off its fitting that is just behind the air intake.  I can easily pop back on but that didn't change anything. 

Strangely today the warning beep was back to normal single beep when you turn key. 

Thoughts anyone?

Black_Diamond

Sounds like the PCV valve hose is popping off?  

Have you started with the basics: check cap/rotor, plug wires?  

reneechris14

Try to switch battery to emergency start.mpi have to spin real good.pull one plug to see if you get spark.computer won't throw spark until it spins good.

jcc2823

Hi:

so i found a pic on line (it's not my engine and I don't have those fancy chrome fuel injectors lol). The hose connector that's popping off when the engines puffs or backfires through the flame arrestor is connected to that little metal tube (in my case the tube pops out of the metal hole) in the pics below that is directly behind the air intake (in the first pic zoomed in it's between the two dotted lines).  I can easily push it back in- only comes out when that puff of air is released. 

I didn't try emergency start setting- I don't really know what that does. :-). The batteries are brand new- literally like 1 month old. It does seem sluggish when I try to start though- when I'm cranking and watching the belts turn it's almost like they are going too slow to get the engine moving. I sort of see that same thing on the port engine which does start okay but I always have to give it a little throttle to get it going when it's cold. 

I forgot to checked the cap/rotor and wires today although it was just serviced with all that replaced about 3 months ago. What am I checking on the cap and rotor?    I have to go out of town so I may not be able to get back down there for a week or two. 

jcc2823

The biggest part I don't understand is why is it backfiring through the air filter?

Robs_232

Did this problem occur before wires, cap, and rotor or after? There have been many issues with caps, rotors, and wires even though new. I personally have had issues with new cap and wires. Did the caps get replaced with Mercruiser brand or other brand. Caps can have internal cracks (even new ones) and spray spark inside cap to other terminals causing misfire. 212rowboat hopefully share his experience with this also.

Robs_232

It could also be fuel related. If fuel pressure at fuel rail isn't high enough or filters are plugged you could also see similar issues. Fuel pressure at the fuel rail can be checked at the Schrader valve right above where your hose is blowing off in the picture. It looks like a tire pressure cap on the fuel rail. Also EFI fuel systems are sensitive to voltage. Just some more thoughts.

jcc2823

After, but months after. It was perfectly fine 2 weeks ago. I assume they are mercruiser caps- I took it to a mercruiser dealer, but who knows. All filters were replaced when it was service same time as the caps, etc. although I realize that prob doesn't mean much. Lol

thanks for your help and ideas- I feel
like I know just enough to be dangerous. ;-)

im going to call a mechanic to come take a look on Monday. I'll update the post once I find out the problem- hopefully nothing expensive as this boat is draining me. 

212rowboat

sounds timing related.  i'm guessing you're saying the hose pops off that nipple on the manifold, right?  it shouldn't... it should have some pretty firm vacuum- but if it's backfiring through the throttle body then that means it's positive pressure in the manifold- which can only be had by bad ignition timing or a valve not seating.  

your timing is off- either the chain skipped a tooth or two, or your CKPS or CPS is giving wonky data.  

jcc2823

Thanks rowboat. I had read one other vague post on a mercruiser site about a valve sticking causing backfire. Unfortunately this looks beyond my skills so will call mechanic on Monday. 

Cheers and thanks

Dream_Inn

Please post when you find the cause.  I know I am very curious and I'm sure at some point it will help others out as well. (& happy new year)

212rowboat

by the way... i doubt your timing has jumped at the sprocket (valve event timing) or your CPS or CKPS is goofy (ignition timing).... but what I DO wager?  you've got a bad dizzy cap or wires.  it causes spark to spray in the cap and charges plugs that otherwise should be cold- boom... backfire through the intake manifold when the spark plug gets charged on a cylinder entering its intake stroke.  

rasbury

changing that you can do yourself and not that expensive, chances are needs to be done anyway....and the first thing the mechanic will do at $100 bucks an hour. I do the things I can do, without hopefully making it worse, before I go to the mechanic. I live and learn as @212rowboat will attest! These are pretty good motors, I would sure start there and then if no luck call- like I said if you don't know when that was last done, probably the first thing they will do anyway!

captpaul

do you have cool fuel module?

jcc2823

Captpaul i do have a cool fuel module-  I'm pretty sure at least. 

jcc2823

Hi guys mechanic is coming either Monday or Tuesday. Will post once I find out. Only other thing I can add is while I'm trying to crank the engine it never sputters or even attempts to run. It's like you're just cranking and cranking a dead motor....  

captpaul

open up cool fuel and take out filters. see if paint flaking or black paint visible. if yes, it could be all thru the fuel system pump and injectors.

jcc2823

Well guess what...  I went down to boat and engine started right up, like there had never been a problem. Ugh. I mean I'm glad it started but wth???  This kinda makes me wonder if a valve is sticking...  only difference between when it wouldn't start and today was 1.change in weather from 80 to 45 degrees- yes it was 80 a week ago here in TX, and before I started it I gave it a little throttle and turned the battery bank from on to emergency start. 

jcc2823

Additionally today I learned that my port engine power steering pump 1. Leaks and 2 isn't connected to the power steering. Only the starboard engine is....  is that normal?  Not the leaking lol. 

reneechris14

Yes that's normal,it's just there for the ride.like spare part.hay that way it is the same belt.

jcc2823

Well engine back to not starting. Waiting on mechanic to come. :-/

Nygroove

I had similar problem.For me it was moisture in distributor cap.Distributor vents not enough had to remove them was a bulletin on this.

jcc2823

Ended up being two bad cylinders. Had to replace engine. :-/

Robs_232

What was the cause? Valves or pistons and rings, cracked block?

jcc2823

The first mechanic wasn't sure- the spark plugs were completely destroyed so he said it was probably surface detonation. I decided to just swap out the motors with brand new so they didn't tear apart the old one to be sure. 

rasbury

wow- how could it run at all with a two bad cylinders? Sorry for your luck on that one.....yikes.