mercruiser 5.7 spark plug reading result

[bolo78910]

hi again guys, well today i took out the spark plugs, on the merc 5.7 rochester carb, the reading result is 7 plugs seems to be burning great , on number 8 cilinder that spakr plug ,the whitr thing at the tip is white as milk as if it did not burn,. the carb is new but it smell rich . my mechanic said it is not water hitting that plug but he said i might be running lean. so as we all know this is the go to forum, what could cause that one plug to be clean.

thanks

 

[MikDee]

Re: mercruiser 5.7 spark plug reading result

If it looks clean, or washed, I'm guessing it's water intrusion, or take a compression reading, could also be no compression. The intake valve could be broken, cracked, or hung open too?

 

[Maclin]

Re: mercruiser 5.7 spark plug reading result

Good pics will help.

 

[180shabah]

Re: mercruiser 5.7 spark plug reading result

Ditto - pics are great.

Do you have spark on THAT cylinder?

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

thanks for the come guys, last week i was away so i ask the mechanic to do a compression for me, he stated that all cilinder was up to speck . but who knows i am going to do one myself, also i just learn i cant do a plug reading with the boat idling in my slip a lot, i need to take it for a run then shut it off and check them. maybe thats why i am only getting 4000 rpm wot, probbly only hitting on 7 cilinders.

 

[snoski]

Re: mercruiser 5.7 spark plug reading result

If it was not firing on that cylinder, the plug would be black and wet with gas and not clean.

 

[snoski]

Re: mercruiser 5.7 spark plug reading result

and if it looks like a brand new plug (clean) then maybe the intake valve is stuck closed or worse, a broken push rod on the intake rocker assy.

 

[krisnowicki]

Re: mercruiser 5.7 spark plug reading result

4000 rpms at wot would be tough on 7 of 8. How does it respond getting you out of the hole?

 

[MikDee]

Re: mercruiser 5.7 spark plug reading result

Just thought of something else, a broken intake valve spring leaving the intake valve open a tiny bit, could let a lot of the fuel mixture escape, (but not all) Because piston compression would tend to close it, and hold it closed on the power stroke, causing a lean condition! With loss of power, and no other symptoms. This may, or may not, show up on a compression test.

 

[wca_tim]

Re: mercruiser 5.7 spark plug reading result

If it's clean as in spotless, then water intrustion likely as mentioned.

if white as in leaned out, that can be caused by a small intake manifold leak...

If the latter is the case, it won't effect the compression test much if any...

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

thanks guys i did not take the boat out as yet , i install new MR43T gap at 035 today, got dark so i stay put . now about the #8 cilinder plug that is clean, only the little white thing is real white like new, but the outer edge has that black sooth, there is no water in the oil so far. now about how it get up out of the hole, man for a 26 foot carver montego heavy boat with four guys on board it jump on plane real quick and hall ***, but it just go to 4000 rpm and stuck there . even if i give it more throttle it goes no faster. i will post the next run in the morn.

 

[Mkos1980]

Re: mercruiser 5.7 spark plug reading result

Before I did my head swap, my plugs looked they they were removed from the Box and never ran. Thats how clean they were. No water no nothing. Just a perfect burn. They were not even a light tan... Had the new Edelbrock 1409 on there and timing set to 10*. I did make a ton of WOT runs though. Maybe that helped keep them spotless.

 

[wca_tim]

Re: mercruiser 5.7 spark plug reading result

picture would help an awful lot...

what was referring to on the intake is that if the gasket has a bit of a leak right next to the runner for your odd cylinder, could be outside or inside... may only be enough to lean it out at lower rpm's.

As to not running over 4000 rpms, what prop, gear ratio and how fast? Has it ever rin faster with the same combo?

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

this is my first season with this boat, so i dont know how it sopose to perform . i know i can drop down at least a 15 pitch right now i an running a 4 blade aluminum, i call carver to find out what prop was on these models from day one, but they did not call back as promise. i got my trim tabs working good today, so with proper drive trim. and the tab i will post the result.

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

ok gentlemen up date on todays run, with my trim tabs finally working good i took of the four blade aluminum prop and install the a mercury mirage plus 15x17 three blades. trim all the way out ect i get 28 knots at 4200 rpm gps, i then come to a full stop shut the engine off pull the # 8 spark plug it did not wet with gas or water, . after that i went home and give carver a call simply because i want to know when this boat new what size prop was install with the merc 5.7 alpha one drive, he told me they has install a 15x17 prop but the boat never go mush over 4000 rpm , so he would suggest that i install a 15x15 prop and be happy with what it gives. this boat is 5,300 lbs dry weight when it was new, with so old now i know it probably weight more now. so what y'all think guys ? what else. thanks for all the help.

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

i realy wants to close these on going threads on my engine problems, but i have one last question for everyone.

today i take a good look at my intake manifold and it seem something is not right, the firine order on it is totally diffrent from my engine. in the middle of the manifold it has what seems like a egr valve hole that is plug off with a plug. so will the wrong intake kill my horse power ect thanks and with these i will put a rest to the thread.

 

[MikDee]

Re: mercruiser 5.7 spark plug reading result

i realy wants to close these on going threads on my engine problems, but i have one last question for everyone.

today i take a good look at my intake manifold and it seem something is not right, the firine order on it is totally diffrent from my engine. in the middle of the manifold it has what seems like a egr valve hole that is plug off with a plug. so will the wrong intake kill my horse power ect thanks and with these i will put a rest to the thread.

There should be no egr valve or port on a marine manifold! We need pics to see if that's what it actually is?

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

thanks i will realy get a camera in the morning and take some pic

today i show it to my mechanic and he said he never seen something like that.

 

[bolo78910]

Re: mercruiser 5.7 spark plug reading result

up date here guys, as i stated before i install new spark plugs, took the boat fishing on a 25 miles round trip to the reef with four guys on board, i could only get 3600 rpm with speed up and down roughly 13 14 15 miles per on gps. carb symptom running rich smell, now here is the bad part, i went back today pull all the spark plugs, 7 plugs burning great, and again #8 cilinder that plug is white/clean plug , now i have my compression tester this time i was arm today lol. this is the result 7 cilinder read 130 psi dry # 8 cylinder only got 120 psi i put some oil in that cylinder and it goes up to about 140 psi i then give all the other cylinder some oil and re test they all stay at 130 they did not go up. so i know #8 cylinder has problem. ???? is it water, is it too much fuel, is it head gasket, does the head need to be re tork , and last with a new long block dont i sopose to be getting more compression at least 150 psi?? 130 seems a little too low,

wen i first launch the boat this season i was getting more speed, the engine seems stronger, ad at 3500 rpm i was getting 25 or 26 miles per hour with four guys on board.

you will as me what did i do wrong , all i did so far was adjust the rocker/valves and change the fuel pump, did i mess up the valve lash?? i let the engine idle loose the rockers antill it rattle then i re tighten until it stop, then i give it a halh turn tight.

HELP I REALY NEED HELP HERE thanks guys ha ha

 

[BaileysBoat]

Re: mercruiser 5.7 spark plug reading result

This is a "new" motor right? Long block? Came with heads(new cam, lifters, guides, valves etc)? How many hours? Kind of funny about the EGR passage, as was previously stated shouldn't be on a marine engine. Was the intake changed?
The compression readings are a lot lower than I would expect (150-160) with a "new" engine. Are you checking the compression with a warm engine and the throttle wide open? The difference between # 8 and the other seven is not significant, but the generally low readings bother me.
Now, you said you adjusted the valves. Why? I'm a licensed auto tech and run a big car shop (wish it was marine), and providing the initial setup was done correctly valve adjustment is not normally required on a Chevy small block (same thing right?). Were you getting noise?
The correct adjustment is done with the engine off, zero valve lash plus specified number of turns ???. I don't have a Mercruiser spec, but 1/4 turn seems a little light, I would expect at least 1-1/4. Someone else in the forum can answer that.
Is the idle ok? What does a vacuum gauge show at idle and high idle? Steady at 16-18 (normal), regular downtick of 4 hg will indicate valve not opening correctly (worn cam or valve lash incorrect) or burnt valve. Rapid /vibration at higher rpm indicates weak valve springs. Fluctuating at idle but going away with higher rpm is valve guides.
Regarding the plug, I would be looking closely at a lean condition on #8. Pop the valve cover and check if the intake valve is opening. If its not could be a bent pushrod caused by improper valve adjustment or cam lobe worn off. Verify the exhaust valve as well.
If this looks ok go ahead and verify the valve adjustment. Considering the valve cover is off you might as well do all 8on that side. When I do this adjustment the engine is off as the manual states (But I'm a car guy). Try it running if you like, but it's not as exact and messy.
If all is well to this point, look at the intake manifold. A long block comes without an intake. Was the Intake checked & cleaned? Usually it has to be machined to match the new block. It could be the gasket is out of position. We use a plumbers propane torch with a small diameter vacuum hose attached, and with a low flow through the hose look for an rpm increase as it is passed over the suspect area. Not a good idea on an inboard so don't try it, but you can get the same effect by spraying a little bit of WD40 around the intake runner. If the idle jumps up or changes you've nailed it.