Smarty pants, I really could use your help! 350 Mag trouble SOLVED?? MAJOR UPDATE

212rowboat

Wildboating said:

Haven't been able to swap sensors yet, needed did socket.

However, I just discovered the good motor at idle holds a steady 14 degree advance at idle.  The trouble motor however is jumping from 10 degrees to 14 very erratically.  Could this be related. 

get a can of ether and carefully spray around the intake manifold in very short bursts... avoid the air hat- try not to get any in the path of the intended intake... 

if you find a spot that when hit with the ether/starting fluid revs the engine higher, you've found your vacuum leak.

that is what this sounds precisely like- a slight vacuum leak... 

you said the engine was new?  it may have an unmarried surface, which likes to happen at the corners of the intake manifold on SBC's, if care isn't taken while seating the intake on the heads.  

Wildboating

The problem was there before replacing the long block as well.  The long block had a knock coming from the bottom end which i was told to be a spun rod bearing.   I will check to see if i can find a vacuum leak.  Thanks
@212rowboat

Wildboating

I was able to record some new runs.  Notice on the starboard motor from 60% throttle to 99% there is very little change in rpm.  However the port motor in that same range will significantly increase rpm and you can FEEL the boat lurch forward when applying the extra throttle.  The port motor runs about 45% to keep the same rpm as wide open on the starboard motor.

Wildboating

Starboard Motor>  https://youtu.be/rDX63u_aygs

Wildboating

Port Motor> https://youtu.be/Yk4ZohcX0So

212rowboat

watch your MAP in both runs.... 

the barometric is of value here because the MAP value is expressed in PSI- so, deduct the baro from the PSI to express vacuum.  You're pulling a fine vacuum on the second clip even when you're coming up on plane and loading the engine- at idle, the vacuum signal is about what would be expected with a marine profile cam.  You're actually pressurizing the manifold on the starboard clip at times (higher in the RPM range).  

the timing jumping indicates an unregulated air source, too.  

look around the throttle body carefully for unplugged fittings... swap IAC's between engines... do the ether thing... if that checks out, do a compression test and a leak down test.  

get a vacuum gauge and find a port to use it on both engines.... I'll come back and edit this post (again) with what to look for.... with the exception of a computer and sensor monitoring, there is no better tool to diagnose an engine. 

actually, just check out this webpage and use the flash... 

212rowboat

CHART OF VACUUM READINGS
Engine Speed	Reading	Indication of Engine Condition
Smooth and steady idle (800 to 1200 RPM)	Between 17 to 21 inches	Engine is in Good Condition, but perform next test to be sure.
Open and close throttle quickly	Jumps from 2 to about 25 inches	Engine is in Good Condition.
Smooth and steady idle	Steady, but lower than normal reading	Worn rings, but perform next test to be sure.
Open and close throttle quickly	Jumps from 0 to 22 inches	Confirms worn rings.
Steady idle	Intermittent dropping back 3 or 5 divisions and returns to normal	Sticky Valves. If injection of penetrating oil into intake manifold temporarily stops pointer from dropping back, it's certain the valves are sticking.
Steady 3000 RPM	Pointer fluctuates rapidly, faster engine speed causes more pointer swing	Weak valve springs.
Steady idle	Fast fluctuation between 14 to 19 points	Worn intake valve stem guides. Excessive pointer vibration at all speeds indicates a leaky head gasket.
Steady idle	Constant drop	Burnt valve or insufficient tappet clearance holding valve partly open or a spark plug occasionally miss firing.
Steady idle	Steady 8 to 14 inches	Incorrect valve timing. It must also be remembered that vacuum leaks and/or poor compression can result in a low vacuum reading.
Steady idle	Steady 14 to 16 inches	Incorrect ignition timing.
Steady idle	Drifting from 14 to 16 inches	Plug gaps too close or points not synchronized..
Steady idle	Drifting 5 to 19 inches	Compression leak between cylinders.
Steady idle	Steady below 5 inches	Leaky manifold or carburetor gasket, or stuck manifold heat control valve.
Steady idle	Floats slowly between 12 and 16 inches	Carburetor out of adjustment.
Blipping engine speed	Quick drop to zero then return to normal reading	Muffler is clear.
Blipping engine speed	Slow drop of pointer then slow return to normal reading	Muffler is choked or blocked.

Dream_Inn

Nice little chart there Drew!

Wildboating

Wow, Thanks Drew - 212..    So, if the MAP is less than the Baro we are pressuring the manifold?  Did i understand that correctly? 

212rowboat

opposite... I think I may have misrepresented that above... your baro is your baseline- say, 14.7 @ sea level on a perfect day... if you're @ 12.7psi, you're pulling two psi of vacuum... if you're @ 16.7, you're pressurizing the manifold 2psi... I don't know the equation off my head that translates psi to bar or inches of merc... 

it's a lot easier (for our brains) to use inches or bars than it is to reconcile pressure in psi against barometric pressure in psi, but doing it the way the computer does reconciles against barometric which is pretty important. 

point is, with your engines, there is a difference... it may be a vacuum leak.. it may be load (due to gearing)... it may be a valve train out of adjustment... it may be non-seated rings (new engine, right?), it may be worn rings, but- it's something, though... 

212rowboat

does your valve train make ANY noise whatsoever? 

it should, but just a tiny percussion- nothing that can be heard from a few steps away... 

if a single valve rocker is too tight, it can be leaving the intake valve slightly open which can cause the pressurized manifold- hence, the rising ABOVE barometric pressure in the first clip.  (expressed in psi and on the MAP reading).... other than silly blow by (which usually happens in crank case and not intake manifold) that's pretty much the only way to get pressure in your intake manifold... equilibrium, yes, pressure? hard to do without there being valve train issues.

so.... get 'yern redneck stethoscope in hand (piece of water hose, long screwdriver, piece of pipe- something to place your ear on one side and the other on an area- creating isolation)....

fire the engine...

now this is scientific, so stay with me here:  listen for the woofwoof.... as you move the end of your 'sound isolation' device across the valve covers, from one end to the other, and comparing sounds- listen for the one going woofwoof...

my guess is this is your issue...

a new engine, it may not have been dialed other than initial....

to adjust.... this is a messy job... warm engine... remove valve cover (one side at a time).. get a towel...  lay towel over other rockers tight enough that it won't get grabbed by the actuating rockers, and get your ratchet and socket ready (that matches the rocker arms mount).  

move from intake to intake valve/rocker (use runner feeds on intake manifold to identify which is which)... you simply loosen the nut until you hear decided popping as the rocker makes a gap between it and the push rod.. tighten the bolt until it's just barely audible... then, turn it 1/8th more... JUST ONE EIGHTH... move to the next one... when they're done, go ahead and do the exhaust ones on that bank... button that side up and move to the other side and do the same thing.... as a finished product, you're going to want to hear just the faintest series of slight slaps from that valve train.  you want the lifters charged with oil, and you want them to just slightly depress as the engine runs- slightly, like, .05 or thereabouts... sound, and feel is just as good as any other method, and the one I just described- though messy- is the best.

having the valve rockers too tight wears on cams, and RPM's charge up the lifters and they'll lift more than they will on a resting engine, meaning a valve may be ever so slightly open, disallowing full compression to take place...

betcha betcha....

oh- spray the engine room/bilge with simple green or purple power PRIOR to making this adjustment... it makes clean up a breeze..   

Wildboating

212rowboat

break out your hose and use it like a stethoscope, and compare it to the strong engine.   you're definitely pressurizing that intake manifold, and that needs to be explained.  it can account for your timing bounce for certain, and it can account for the engine not developing power for certain.   

Wildboating

Drew,  In the first clip labeled Starboard Motor you are saying you see the MAP exceed the Barometric pressure of 14.36?  I am not seeing this ever happen.

Wildboating

On it.  Heading to boat.  Thanks so much!!!

212rowboat

Wildboating said:

Drew,  In the first clip labeled Starboard Motor you are saying you see the MAP exceed the Barometric pressure of 14.36?  I am not seeing this ever happen.

you're right- it didn't break barometric... but it came dang close and hovered above 14 at times... the other engine didn't struggle near as much...  it's not using that air efficiently... let's hope it's a simple valve adjustment or a easily discovered vacuum leak... let's vote against bad compression.. 

Wildboating

Using my mechanic scope, i hear NOTHING, nothing at all along the valve covers of the new motor.  I did notice a difference in the tick of the injectors however if that adds anything.

212rowboat

it may be as Al is indicating, then... a fuel contribution/balance thing...  

Robs_232

I recently had an engine issue with my 2004 Yukon Xl with 5.3L making strange noise. I bought a mechanics stethoscope at O'Rielly's auto for $10. Well worth the money as it makes listening to engine noises, like valve train or injectors, much easier. In the past I used a hose in the ear. The stethoscope helped me narrow the noise down to valve train noise in number 1 and number 7 cylinders. Injector clicking was consistent.

I ended up having 2 rollers on those lifters (Vortec engine) that were galled or burred and damaged camshaft. Ended up replacing engine with a reman. long block.

Wildboating

Thanks Rob, fortunately it all sounds good. New motor but chasing low rpm issue that existed with former engine.   

Wildboating

Crossing fingers, just put new injectors in.  Fuel pressure primed to about 50psi then rest at 45psi.   Blipping throttle in neutral psi stays above 40.  Going to check under load. 

reneechris14

Good luck

Black_Diamond

This is rather vexing. If the gear ratio was off, that engine should sound like it is lugging. 

Injectors are pretty reliable fellas. Unless plugged up or bad electrical connection. I'd think it would run bad, not just rpm limited?

212rowboat

it ought not drop 5psi off idle without load- or drop 5psi at all so far as that goes... the pressure is a constant no matter the volume... it's why you get larger injectors in the first place, and when they consume and request more fuel than available at the relative timing sync.

this kinda lands your issues directly on a fuel pump, a clogged filter, an obstruction, or an unvented source.... I'd lean toward pump seeing as how the pressure dropped while unloaded.  there is no excuse for that other than clogged filter or bad pump...   

Wildboating

Injectors didn't help

Wildboating

At idle 16 in vacuum.
1700 rpm blip drops to 10 then jumps to 23
2700 rpm steady raises to 19in then pull off throttle jumps to 24 quickly. 

Wildboating

2000 rpm driving 11in vaccum
getting on plane about 0 in vacuum 
3500 rpm cruising 0 in vacuum 

Wildboating

Good motor 
1700 rpm blip drops to 4in then jumps to 21
2700 rpm steady in neutral  drops to 10in then raises to 20 then raises to 24 when dropping throttle

Wildboating

2000 rpm driving  bouncing between 10 and 14 in.
Getting on plane bouncing between 1-4in
Cruising 3500 rpm bouncing between 3-8 psi

Wildboating

@212rowboat @Alswagg