383 Stroker High RPM Lean Out
 

This is a brand new MC 383 with about 22 hours... In the break in period I have run the motor passed 4000 rpms with no problem.

Last weekend while out I ran it up from idle to 4k the motor pulled strong all the way then a 4k it started popping. It sounded like a hi speed lean out and not a rev limiter sound. I tried it a few more times during the weekend and same thing every time.

We were on a trip so when running at 27-32 rpm the thing ran great no bells or whistles going off. All systems checked out. However every time I took it up at 4k pop pop and then I had to back down.

Today I pulled the water sep filter and the gas was real clean and no sediment.

Any thoughts? Thanks in advance!

fuel pump?

You need to hook up a fuel pressure gauge, a Snap on, type. If the fuel pressure is dropping off and this is a new package someone did not pre fill the filter with fuel. That should be in the canister which holds the fuel pump also.

I guess I don't understand your reply...for the 1st 20 hours I could run this thing up to redline. No problems...now it still pulls strong until 4000 rpm. So would not the problem show up before?

Your fuel pump might have been fine before. SOMETHING is not right now since you have a problem NOW. Just because it worked yesterday doesn't mean it is working today. Hook up a fuel pressure gauge and see if the pressure( fuel delivery) is keeping up.

Don't get me wrong I was not questioning the fuel pressure gauge hook up... it was the part that it was not pre filled, and that would that take 20 hours before something would show up.

Hooking up a FPG makes a good first choice.

Once the pump gets damaged, it will start dropping fuel pressure down to the point you have now. My point of using a gauge, is to keep it simple. You have a fuel issue from what you stated, so start with that. This my not be the issue, if not the pump has been eliminated.

Heck of a deal...picked up from Auto Zone a FPG testing kit. Just put a deposit down and when I return the kit, I get all the deposit back. Tomorrow we will try it out and see what gives.

Ok good luck!

Did the fgp thing today and everything is OK and within specs. Pulled all plugs just in case a plug was bad. They all looked good, same grey tan color. ??? Now I am wondering if it is time to take it in and let them do the hunting down of the problem.

When you pressure tested the fuel system was it under load? If it wasn't, when you turned the key off did you have a very fast decline in pressure? I had a fuel pressure regulator go out, gave me symptoms of the fuel pump only so I change the pump. Problem not solved. I then pressure tested the other engine and the pressure held after pump stopped running, motor with issue would drop pressure very fast so I change regulator and bingo.

need to ck fuel pressure running when issue comes in..what pressure at that point..you could have plenty of pressure up to a point you have a flow issue that drops of the pressure..

Did u test it with a load on it past 4000rpm?

No I did not check it under load... However when I get it back in the water I will do that, knowing how easy it is to do, and that I can get the gauge for zero cost.

Ignition on no start...42-44
Running at idle ...36
Ignition off ...34

At wot your fp should be in the neighborhood of what it is ign on no start (or idle with regulator vacuum hose disconnected and plugged).

Noted!

check timing, I have had this problem. it wound up being distributor drive gear. look at fuel pressure at load to ensure it is not that. worn gear acts like stretched timing chain, no load snap throttle it will bounce timing a lot.

I called Mercury Tech support...before I read your post and they told me the same thing...Check timing, and that they were issuing a service bulletin that after a break in period the timing gear might wear slightly and that you should turn the distributor 1/4 inch left or right to fix the problem. When boat is back in the water I will check it out.

Problem Fixed "Sorta"
 

A little review... the engine would start popping after 4k rpms.
The trouble shooting was done in this order. Checked fuel pressure not under load and on trailer...OK
Changed plugs and then did load run, still popping...now at 3.8k.
PU FP gauge from the Zone and did a run under load every thing OK pressure wise.
Loosened up distributor and turned the cap approx. 1/2 inch counter clockwise (if looking at the transom) pulled hard all the way up to 4.5k.

The "Sorta" part is it use to pull hard all the way up to 5k. Now the bottom was a little dirty and maybe more fuel in the tank. So I will work on those variables after it get back in the water again.

Thanks for the update, I hate it when a thread stops with no results!!! = )

I had a bit of higher RPM sputtering when a fuel pump relay started going bad. Just a thought… Good luck.

I am not experienced with small blocks but turning the dist CCW will advance the timing? It ran better? Looks like a timing issue?? Did you get a timing light on it and set it to spec? I would not be running this thing anywhere near full throttle without getting the timing dialed in properly. If this is an EFI motor than than the base timing needs to be set. Check for full advance as the engine is revved and make sure it is also to spec. Maybe the knock sensors are retarding the timing? Bad gas? Could be a million things causing this. Get a tech or a friend with some diagnostic stuff to check everything out.......

Don't risk frying your motor bud......

Good information. Now that it is back on the trailer I can do some checking. Needed to check what Mercury said made an sense. It does not seem like the correct way to do it. Motor still under warranty and most likely will go back to the dealer.

Timing light is critical. I don't guess at timing. Asking for problems.

I Agree...since this is a efi motor, there really is nothing more that I can do, without proper tools. Not like the old days where I could slap a timing light on and turn it over....:whistle:

Sure ya can. Distributor less ignition is a different story. Still a timing light and twist of a distributor. Might have to add a jumper somewhere for true time but not that difficult.

?? There is no timing mark, and no specs on what the timing should be...All it says is that the timing can not be adjusted.

Learn something new everyday. If yours is efi it is adjustable. If mpi it needs to be done at a dealer.

http://www.justanswer.com/boat/3ie76...-1-efi-at.html

Really my fault for spouting off letters that are wrong...for some reason I always want to use the EFI moniker for anything that is injected.

My motor is a MPI...:lolhit:

When you move the distributor on that engine you are not adjusting the timing. The timing is fixed, and referenced from the reluctor wheel on the front of the crank, and the curve is in the calibration. The distributor needs to be properly phased so that when the Ecu tells it to spark, the rotor is close enough to the correct terminal in the cap. As load and rpm increase, the distance between the rotor and post in the cap can become too far apart for the spark to jump, and it acts kinda like a rev limiter dropping spark. They usually run best when cranked ccw until the mounting boss for the cap contacts the back of the intake. (About as far as you can go) :)

Thanks...your explanation now confirms what Mercury tech support was talking about. They were saying the distributor gear (?) wears a little in break in and may have a little slop and needs to be adjusted slightly like you have indicated.

Makes me feel better that I am not hurting anything.