loss of power?
 

I have a 502 MPI MAG with a M-3 sc ProCharger running 5-6 lbs boost, ECU and headwork done by Precision Marine. I have an extreme loss of power on takeoff with a popping (backfire?) noise on the port side. I am down 800 rpm, from 5200 rpm at wot to 4400 rpm! I have replaced the dist. cap, rotor button, plugs and wires and get the same. The oil looks fine.. no milk. What should I look for next? I have not checked timing or compression yet.

Re: loss of power?
 

anyone?

Re: loss of power?
 

Your next step is to pull the valve covers and look for valvetrain problems,especially on the offending side. If you find nothing a leakdown test might show something but i bet you'll find something in the valvetrain if youv'e already checked the ignition. I had problems early in the season with comp cams rocker nuts cracking and backing off,everyone tells me i must be overtightening them BUT,never had that problem before on MANY motors i have built and the new arp rocker nuts haven't given me any grief. When the nut cracked and backed off the pushrod bent then rocker fell off valve,motor sounded seriously hurt,was POPPING and making metallic noises from intake valve letting mixture in ,firing with no way out,Smitty

Re: loss of power?
 

Pull plug wires and make sure you didn't drop a cylinder. Check fuel pressure and make sure there is no fuel restrictions. The popping sounds like a fuel problem.

Re: loss of power?
 

I installed a fuel pressure gauge in the dash when the ProCharger was added, fuel pressure is fine. I am leaning towards a blown Felpro head gasket between the cylinders, to lose 800 rpm that would have to be at least two cylinders down, do you guys agree with that?

Re: loss of power?
 

i would be willing to bet on a bent or tuliped valve or bent push rod

Re: loss of power?
 

I agree,my motor also has a m-3 procharger and like i mentioned earlier a valve train problem 1 month ago gave me exact same symptoms,Smitty

Re: loss of power?
 

pop followed by big loss of power= something broke. like smitty said you most likely have valve train problems. At worst it's probably a sucked valve, is your fuel old or poor quality ? this is the most common cuase of tulliped valves in a marine engine especially a force fead engine. You can either start by pulling the valve covers or doing a compression test, I'd start with the compression test so you can be sure of which side needs to come apart but I'm sure youll find the problem in the valvetrain.

Re: loss of power?
 

No procharger here but I had a loss of rpm recently (~800rpm too). Pulled it apart and found a couple of bent pushrods and the valvetrain wasn't lashed correctly.

Tim

Re: loss of power?
 

I too have the same problem,( no procharger) and not sure what it is. Did you notice noise in the valve train from the bent push rods?
Did the motor constantly pop through the carb.? I only sometimes here a pop through the carb. Any help is greatly appreciated.
Thanks!

Re: loss of power?
 

Unfortunately I'm having the same issue...I go to get on plain and the Port motor backfires.
I don't want to hurt the motor or blower(10-71)trying to figure out the problem by anymore trial and error.
We have changed/new plugs, wires, cap, rotor, air filters, ignition box, fuel pump, exhaust system, new dist gear, checked timing, float levels and even took apart the carbs for a cleaning with new power valves.
A comp check (twice), with 120psi on all 8 cylinders.
The only other things we can think of is air maybe getting sucked into the fuel line...the mech gauge at the pump fluctuates from 7.5-6psi sometimes.
Or a valve train issue...broken/weak springs, bent rods or a bad lashing?
1/4 to 1/2 a turn should be within limits for a hyd. roller cam, no?
We are at our wits end on this one...time to pull the valve covers. :(

Re: loss of power?
 

Ttt :(

Re: loss of power?
 

I have not had the time to check into my problem, hopefully this weekend.

Re: loss of power?
 

Burnt or tuliped valve my guess too. Exact same thing happened to me in early summer. M1 w/ 5lbs boost. Been there and done that $$$$$
Time for a compression check. check #5 and # 7 first

Re: loss of power?
 

Did a compression check and #2 & #4 were about 125 lbs and all others were around 145 lbs, pulled the head and found that the intake and exhaust valves were leaking! Sent the head to have it checked, hopefully its just the valve seats. All the valves looked good. I should have it back in a few days.

Re: loss of power?
 

Glad to hear you found it...now its my turn to find my hic-up.

Re: loss of power?
 

They found a few valve seats leaking and had to deck the head a little, so I put it back on and got 175lbs compression on starboard, checked port side again and got 155 lbs. Ran the engine at the marina on the trailer under a load and still got the inconsistent popping through the intake, took it back to the shop, pulled the port valve cover to find one of the rocker arms had a lot of play so we relashed it and turned the engine over and saw that the rocker had less than half the travel of the others! So it looks like the lobe on the cam is gone... anybody got a suggestion on what cam to go back with? The one I have is the stock cam and this time I will use a roller cam and lifters, I want to be a little more aggessive but am worried about reversion since the silent choice is still on.

Re: loss of power?
 

need more info on your motor to make a cam guess...

Re: loss of power?
 

96 502 EFI with stock bottom end, heads have five angle valve job, large intake valves w/ incolnel exhaust vaves both are Ferrea, Crane gold roller rockers and either Comp or Isky springs... cant remember, Felpro 1047 gaskets, ARP head bolts, Stainless Marine exhaust, ProCharger M3sc stage II @ 5-6 lbs boost and ecu reprogrammed. I forgot to mention the cause of this whole problem was due to sucking up some sand and pebbles, I left from a beach area and within a mile or so the engine went into power reduction mode first and as soon as I looked down at the dash the buzzer went off and the temp was pegged, got towed in and the next morining took the hose of at the seawater pump and ProCharger's fuel cooler, flushed all the debris out and fired it up and everthing appeared to be ok so I took it to the marina ( about 5 miles) and had no issues on the ride over but the next time I used the boat is when all the problems started.

Re: loss of power?
 

Take a look at the ISKY #696275/284 Hyd. roller(228/238-.553/.578)...and have them grind it on a 114 lobe center. :cool:
http://www.iskycams.com/onlinecatalog.html

BTW....We might have found our problem being that the MSD caps we have are not of the vented type causing corosion and rust inside the dist.