Problem With 454 Mags
 

:( long story hate typing so here it is:
twins: just rebuilt 1 works fine. i change the elctronic module in distributor on one, guess which one i'm having problems with.
it will pop when i give it throttle pass 3500 rpm it is missing on number 7 cylinder (i pulled spark plug wire while it was running
no change
i've checked valve lash and these are new cams and lifters in engine.
herer is what i replaced so far either by taking it off good engine or new?
carb
cap and rotor
modules (electronic and the one on riser)
plugs
wires
i have timing set @ 10 intial 24 module
checked push rods on #7 cylinder (this is the one that seems to be the problem)
boatfix.com (george) great guy by the way has helped me out alot, says to try putting timming light on sparkplug wire where problem is, which i will try this weekend.
here is what i think might be happening possible water in cylinder after it is running. maybe a head gasket?
anyone have this problem? i sure would like to talk to you.

thanks in advance to all motorheads that are going to try to help me

Re: Problem With 454 Mags
 

You might want to check firing order, cap can be wired for left or right rotation.

Re: Problem With 454 Mags
 

bin there done that (about 15 times)
i'm also going to change distributors from running engine

Re: Problem With 454 Mags
 

Could be a weak or broken inner valve spring---doesn't matter if the springs are new, you may have a "dud"...they usually start popping/causing trouble right around 3000-3500rpm or so.

FYI, I was having a intermitent miss this summer right around 3000-3500rpm or so as well, but it wasn't because of a broken spring.....did a compression check, changed the plugs, checked the cap/rotor, changed pulg wires....it was water in my fuel---I hadn't inspected the fuel/water seperators in a while and they were full of water. Once I emptied them out the miss still didn't go away until about 30 more miles of boating---then it finally disappeared.

Re: Problem With 454 Mags
 

you maybe right i will check fuel too
if motors are using same tank won't they both have problems?
oh yea have 165lbs compession in that hole too.

Re: Problem With 454 Mags
 

I have dual/seperate tanks, but the other fuel/water sep was pretty close to being full too---but was just happening with one engine. I have the KE coalesant (spelling?) fuel filters.

Do you have the Merc 454cid Mag 365hp engines with the old Rochester carbs??? It's been a very long time since I have had a Rochester carb in my hands, but if I remember correctly don't they have the fuel filters that are located within the carb itself? If I am right, then those should probably be inspected/replaced as well.

Re: Problem With 454 Mags
 

Did you crank the engine while you checked the push rods? Mine acted like that with new cam, lifters and rockers. I had a rounded cam lobe.

Re: Problem With 454 Mags
 

changed carb from one side to the other, so its no change there. i watched push rods too, this rebuild has been a nightmare (3) times my machineshop guys are clueless
i might get another set of valve springs and put them in if nothing else works. i got to say this that if i could have found big block chysler exhaust for the boat,,,i would have put 2 blown 440 in it.

Re: Problem With 454 Mags
 

What does the tach do when this popping starts?

Is it popping out the intake or exhaust or both?

The engine with power steering generally has a deeper fuel pickup, so it will get all the water first when you have a water in fuel issue.

BT :cool:

Re: Problem With 454 Mags
 

My Other Engine Has Ps Pump
Tach Bounces All Over The Place

Re: Problem With 454 Mags
 

Probably not water in fuel then. I would start the engine and while someone is watch the tach go over the engine wiggling wires. See if you can get the tach to bounce or the engine to stumble. If the wire to the tach has an intermittant short to ground the tach will freak and the engine will pop and fart. You never said is it out the exhaust intake or both?

Make sure you wiggle the ignition ground wire coming out of the tbolt ignition module and the wires on the back of the distributor. When this happened to me though the short was under all the black tape at the front of the engine where the harness runs down to the breaker. I got lucky and spotted it doing the wiggle test.

BT :cool:

Re: Problem With 454 Mags
 

I Think It Is Out Of Exhaust Not Sure About That Yet
We Have Done The Wire Test Alredy And The Problem Seems Like #7 Cylinder. Motor Only Has 4hrs On It.
Carbs Were New Exhaust Manifolds Are New Too
I Bought A Hei Distribtor Which Will By Bass All Electronic In Boat This Weekend. I Will Also Do Aleak Down Test Too.
Thanks For Help So Far Ideas Help Me Figure Things Out

Re: Problem With 454 Mags
 

Tryme, I wasn't talking plug wires, I was talking primary and tach ignition wires. Particularly the purple and grey ones that come off the coil and to the back of the distributor. Also the tbolt wires and ground. Follow them and wiggle them with the engine running. I don't think a miss in just number 7 will make the tach go nutz.

BT

Re: Problem With 454 Mags
 

WE HAVE WIGGLED EVERYTHING TRYING TO MAKE IT MISS
I HAVE PICKED UP HEI DISTRIBUTOR..THAT WILL BYPASS ALL "BOAT STUFF" TO TRY TO FIND PROBLEM.
DO YOU KNOW IF THERE IS A BUILT IN REV LIMITOR ON MODULES? AFTER READING OTHER THREADS I'M LEANING TO WATER IN CYLINDER FROM EXHAST GASKET. I'M LEAVING WORK EARLY TOMMORROW GOING TO RAYSTOWN AND WORKING ON BOAT....I HAVE BEER COME ON UP :rolleyes:

Re: Problem With 454 Mags
 

Did you try the main pigtail? Had mine loosen up on two different Merc motors. Pulled it apart, cleaned up both sides and coated the connections with dialectric grease. Problem solved.

Re: Problem With 454 Mags
 

No rev limit built into the TB IV modules.

Re: Problem With 454 Mags
 

well here's update
i went to lake friday after reading everything i could during week on this website
it seems i had several grimlins
1st gasket (riser) was replaced and that solved my miss problem
2nd we found loose pigtail and that sovled my tach problem
popping still continue thru carb when you throttle it
so i put my "old carb" back on and it made most of it go away so i think i'm heading down the right path.
she got to 4300 rpms still shy of 4800 i had before rebuild
but i'm happy just going down the lake until...i feel the need for speed :rolleyes:
still need some help thou
need crank pulley for 454 and i need to know the sizes if metering rod that should be stock for 1991 454 mag(rochester carb qjet)