mercruiser 454
 

Hi, i'm new on this forum and after searching and looking for answers for my problem wihtout luck i'm now asking directly.
here it goes.
I have reacently bougth an old cigarette 21 with an 454 mercruiser mid 90's engine and bravo one drive.
It has an enourmous powerloss and is chugging on the left side exhaust, constantly and when reving over half throttle it backfires and shoots up the carburator.
what i've don until now.
1. changed sparkplugs
2. compressiontested it (on cold engine so it's not the real readings i know but it was about 120 psi on all cyl. so nothing really popped out as an answer there...)
3. tried several distributors and set the timing.
4. changed the carburator. edelbrock 1410 (the old one was cracked anyway)

The previous owner said that he reacently had the heads overhauled with new valves and sealings. because of some burned valves.

i really hopes that somebody can give me som clues of what's going on...... :)

sorry for poor english

Svein Ronningen a Norwegian in need

A couple of initial thoughts;

1. when you set the timing was it steady or bouncing around?
2. are you sure you set the timing correctly and to correct setting?
3. Could be as simple as crossed or bad spark plug wires. Did you validate the firing order and insure right plugs wires in right socket of distributor and on right spark plug?
4. make sure the valves were set correctly. Pull off valve covers and reset rocker arm preload
5. if all the above checks out could be very lean which would cause backfire through the carburetor? Try richening up the carburetor.

Along with the above suggestions, make sure no valves are hung up in their guides and check for proper rocker movement (could have wiped some lobes off the camshaft).

I have a 1994 Merc. Mag. Had similar issues. Carb, get it re-done. and change the coil. I bet a case of heiny. it's the coil.

Also be sure to start at tdc on #1 and make sure rotor is sitting correct. Then check firing order.

It could be a lifter problem or the lifter not moving freely in the lifter bore.

120psi on ALL cylinders tells me everything in the valve train is working . Popping back through the carb and the ignition timing was checked , leads me to diagnose a cam missing some lobes . I doubt it would show that kind of compression numbers with a valve hanging open .

thanks for answering. :)

1. when i tried to set the timing i could'nt really set it correctly, when it got down to 10* and close to 8* it just dropped down and the scale was not possible to read.
but it was chuggin in the left exhaust nomather what the timing was, i also took of one and one wire on the left side but the symptoms where the same.
2.i re routed the wires just to be sure, and i used the firing order on the intake manifold, which was the same as the order on the distributor cap.
3. all the plugwires are also new.
4. i'l try to adjust the valves tomorrow, i was told to loosen on rocker at the tim until it starts to make noise and then tighten til it's quiet again and a quarter after that. Is that corect?
5. the carburator is brand new and opened for inspection. it is an Edelbrock 1410 750 cfm, identical to the originale weber that was on before.
6. the cyl's weren't exactly 120psi more like 115-124 psi all eavenly spread in that range.
7. i have not changed the coil my self but the previous owner said that he did with no luck.
8. can the distributor have been put down at the wrong spot by the previous owner?

Thanks again

Svein Rønningen :) :)

Answer to # 4 . Not really the correct way but will work .
Answer to 1 and 8 . Most definitely yes . Bring number 1 piston to top dead center on compression cycle and verify that your distributor rotor is pointing at #1 spark plug wire in your cap . If not , pull distributor and adjust . Pull #1 spark plug and place finger over hole , bump engine over a little at a time till you feel compression pressure blow on your finger , then set on TDC . Easy way to find compression stroke .

what type of ignition module you have on engine ?
if you have thunderbolt 5 , to set up timing you need to ground purple-white cable (two locations possible for that cable , by the thermostat housing or by distributor )

thanks again :) didn't get anything done today, pouring down outside :/
i do not know what igition system it is but it looks like it is the originale. and on metal thing between the rockers it says "mark v" if that can tell anybody what year or ignition system it is?

:)

Svein

find ignition module on the engine and see what is written on it , can be mounted on distributor or port side exhaust elbow
thunderbolt IV is a single module no special procedure for timing
thunderbolt V usualy two modules mounted on distributor , needs purple white wire connected to ground to set timing and carb adjustment

Gen 5 a mid ninties is probably a tbolt 5 ign. The purple/white wire that you need to ground runs between the ig module and knock sensor module and has a pigtail to ground, often with a rubber plug in it that you remove when grounding.

Ignition or kill switch?????

hi again :) it is finally sun again and i've don a little on the boat. it is a TBV ignition on it i think, it has the two modules on the distributor.
i pulled the valve cover and all the rockers were tigthend almost all the way in :O when i adjusted them the chugging was gone :D but i saw that one of the pushrods where sligthly bendt. :/
on full thottle she still backfires but i have not adjusted the timing with the white purple wire grounded yet. i hope i got time for that tomorrow.
any thougts? :)

best regards.

Svein Rønningen

You better find out what bent that pushrod. Still could be a cam lobe.Replace and check that each lifter has same amount of movement.

that is a heavy boat, but a nice one. spend a few bucks. pull the heads and get a valve job done, install a roller cam, and msd ignition.... they are heavy and need a strong engine to wake em up!

if it's not helping with an adjust of the timing tomorow is it only cam or coil left that can be wrong? if so what brand type is the one to choose? engine parts are extremely pricy here so i would prefer to have something reliable but not too pricy.

best regards

svein rønningen :)

If the rockers were adjusted to tight, could have started to round the lobes on the cam..

set up a paypal account and buy the stuff on ebay in the states. figure a way to get it shipped to you before you buy. the good thing with roller cams is used ones work fine unlike a flat tappet cam. a msd blaster 2 coil is cheap and produce a h3ll of a hot spark, get someone that knows these engine to set the heads up properly for the cam you buy, the correct spring pressure is very important. i would buy a set of good valve springs to go with the cam. you can make a lot better hp and tq with a roller cam, they open the valve much more quickly, so it is at maximum lift much longer... that is a killer boat. post up some pics...rm

I think it is worth mentioning that you should check/replace the fuel filter/ water separator filter, you could be getting bad gasoline (water in the fuel)

well, i ordered a new pushrod today and the msd blaster 2, so i will have them in a few days :) i don't know how to upload pictures, don't have a pic site.....
when i took out the pushrod today i noticed the rockers were extremely loose, are they supposed to be that when the engine is not running? :confused:
and the fuelfilter is new :)

the procedure for adjusting them is on the internet, google it. its very easy to do. there should be zero clatter once they are adjusted properly. you can loosen them on at a time with the engine running, then adjust them til they stop clattering. rm

Toylux,

Setting valve lash/preload accurately requires that each lifter be on the base circle of the camshaft to ensure the valve is fully closed when you adjust the lash/preload. The foolproof method is to remember "EO/IC", which stands for Exhaust Opening/Intake Closing. Run one cylinder at a time. First rotate the engine observing the exhaust valve. When the exhaust valve just begins to open, stop cranking and adjust the lash/preload on that cylinder's intake valve. Then, rotate the engine again, observing the intake valve of the same cylinder. As the intake valve moves past peak lift and begins closing, stop and adjust the exhaust valve on that cylinder. Repeat on each of the remaining cylinders.

If you are lashing a solid lifter cam use a go/no-go on your desired lash setting. Setting the preload on a hydraulic camshaft requires tightening the rocker adjustment slowly while rotating the pushrod between your thumb and forefinger. When you begin to feel the pushrod tighten, add the required preload to the plunger. Be cautious to not preset any rockers prior to adjustment. As you rotate the engine to adjust the current cylinder, it may compress the adjacent (yet to be adjusted cylinders) plungers, purging the checking fluid /oil in that lifter making it difficult to determine when the pushrod and cup are at zero preload.

Bob

^^^^^^This is the gentleman you need to talk to about a new roller cam and ALL related valve train components . Great prices and a wealth of knowledge . He is by far the very very best . :thankyouthankyou:

hi' thanks for your post rmbuilder :) i have adjusted when running as mentioned, but i know that is not very accurate but it can't be that far off? it seems like my lifters bleed dry over night because there were much slack when i took the cover of again, but when i started up again they looked fine.. but i don't really know what's normal :P i'm a scania mechanic so i only wrench on v8 diesels :P
i'm still waiting for the pushrod so i don't know if it will solve the problem, but can you recomend a complete cam,lifter,rocker and spring set rmbuilder?
and to all, i really appreciate all the help i get :)

thanks again.
Svein

You set the lifters when the engine is not running for best results now days.

Been a long time now. The engine is teared down and many problems are found :p
does anyone know of shops in texas that sells mercruiser, comp cams and msd parts?
my cousin stays there some days too and from his work in the gulf.
thanks again
svein

Get with rmbuilder. He will get you the right stuff. Have it shipped to your cousins office with his name on it.

He just stays in a hotell, his office is on the ship :p

Yeah I run supply boats out in the gulf. Have his next flight go through NY, he can grab it from Bob there. Lol. Bob might be able to just ship it to you.

Hehe yea if it was that easy :p pretty long way too travel and he just get the ticket i think. To get thing shiped is not the biggest problem. But the costs of shipping and the customs :p