Mercruiser 7.4 top end issues

[Glastron Fisher]

Does anyone have or know where i could get a digital download of the service manual?

 

[Glastron Fisher]

So i found a service manual and determined that i have MEFI3 which means the codes i thought i had are not what i thought they were, here is what i have currently

 

[alldodge]

MEFI 3 is better then the 1 and 2 by far, but still does not go very far to help. Is starting to look like a ground or corrosion issue

 

[Glastron Fisher]

So i think i fixed the codes issue, ran the flow chart for TPS and MAT sensors and both tests came up with bad sensors but i had tested the sensors themselves and there was no issues. Went on to test the coolant temp sensor and found the 5V reference wire was halfway in the connector. Popped it back in and codes went away, i figured it was good to go so we took her out for fireworks last night and same thing, get up on plane and she won’t go over 4,000 RPMS. Looks like my fuel pressure stabilized after fixing the codes but when i put her on a load the pressure dropped to like 35-38. I’m going to pull the pump and check the regulator and clean everything and see if pressure comes back up but if not I’ll get a new pump. Does anyone know if the pressure is supposed to stay at 43 when key on? Mine drops instantly to 25 and stays there so I’m hoping that’s the issue and the pump just can’t keep up with the pressure lose under load

 

[Scott Danforth]

its supposed to be solid at 43psi

 

[alldodge]

Agree and will add, the fuel pressure can drop off but should be slowly
The manual indicates 43 with engine running

 

[Glastron Fisher]

I pulled the pump and regulator to try and clean it and bench test it, starts to bleed off at 25PSI and i think it’s just a little too much for the pump to keep it up and that’s why it fluctuates. I’m hoping the pump isn’t getting weak and i figured the regulator leaking off that much would eventually overwork the pump anyways. Does anyone know anywhere to get a regulator without spending 150$? I tried to reference the part number and find something in the automotive world but couldn’t find anything

 

[alldodge]

Assuming your looking for 861126A1 Cool Fuel Gen 2 (43 psi) which is also Mallory 9-33206

They do cost

 

[Glastron Fisher]

Ok so i pinched the fuel return line and pressure went over 100 PSI so i know the pump is working. Found an old adjustable fuel pressure regulator from one of my old turbo Honda’s and it was the same style so i slapped that on there and adjusted it to 45PSI, took her out on the lake and same thing, won’t go over 3K and Boggs then when it’s on plane maxes out at 4K, i pulled a few of the plugs and still super lean, turned fuel pressure up to 80PSI, still bogging and once again plugs were super lean. No more trouble codes thrown either. I’m at a loss with this and I’m about to light a match and call the insurance company. Anybody got any other truck or tips as to what it could be? Compressions good, could a camshaft that’s worn down cause a lean issue? It’s got a pretty significant tick to her as well so valve covers are coming off tomorrow to see if i can see anything. Hard to determine if it’s a lifter tick or engine knock but I’ve put probably 2-3 hours on it so far and the noise isn’t getting worse.

 

[Glastron Fisher]

Ok so i pinched the fuel return line and pressure went over 100 PSI so i know the pump is working. Found an old adjustable fuel pressure regulator from one of my old turbo Honda’s and it was the same style so i slapped that on there and adjusted it to 45PSI, took her out on the lake and same thing, won’t go over 3K and Boggs then when it’s on plane maxes out at 4K, i pulled a few of the plugs and still super lean, turned fuel pressure up to 80PSI, still bogging and once again plugs were super lean. No more trouble codes thrown either. I’m at a loss with this and I’m about to light a match and call the insurance company. Anybody got any other truck or tips as to what it could be? Compressions good, could a camshaft that’s worn down cause a lean issue? It’s got a pretty significant tick to her as well so valve covers are coming off tomorrow to see if i can see anything. Hard to determine if it’s a lifter tick or engine knock but I’ve put probably 2-3 hours on it so far and the noise isn’t getting worse.theres only one other factor i haven’t messed with yet and that’s timing, i set base timing and it’s spot on but didn’t think that maybe the distributor is off a tooth and the timing advance under throttle might be maxing out. Does anyone know what the timing should be at at 4,000RPMS? I’m going to look into it tomorrow. The only other thing that makes sense

 

[QBhoy]

When it bogs is there any sign of black smoke out the exhaust at the time ?

 

[Glastron Fisher]

When it bogs is there any sign of black smoke out the exhaust at the time ?

No and spark plugs are white as a ghost

 

[alldodge]

The cam has nothing to do with fuel mix, and running lean and your tick could very well be the motor eating itself with detonation. Fuel mix is controlled by the ECM using the MAP, TPS and MAT/IAT

If the motor is detonating I would wonder why there is not a knock sensor is not setting a code 43 and retarding timing, or code 44 because knock sensor not detected.

Could also be an issue (even though slim) that 7 injectors have a problem, and one does not

What Honda part number is the regulator?

 

[Glastron Fisher]

The cam has nothing to do with fuel mix, and running lean and your tick could very well be the motor eating itself with detonation. Fuel mix is controlled by the ECM using the MAP, TPS and MAT/IAT

If the motor is detonating I would wonder why there is not a knock sensor is not setting a code 43 and retarding timing, or code 44 because knock sensor not detected.

Could also be an issue (even though slim) that 7 injectors have a problem, and one does not

What Honda part number is the regulator?

The regulator is an aftermarket regulator, I’ll see if i can find it online but I’ve had it for over 7 years sitting in a box, i still have no codes so i would imagine the knock sensors are doing their job. I’m going to check timing at higher RPM to see what it’s doing. I have no idea where to go from here haha

 

[QBhoy]

No and spark plugs are white as a ghost

Ok. Would suggest it’s maybe a fuel issue right enough. If it was getting suitable fuel and it was caused by an ignition issue for example...you’d imagine you’d get a sign of unburnt (almost like what an old carb does when under choke) fuel black foggy smoke maybe ?

 

[Glastron Fisher]

Ok. Would suggest it’s maybe a fuel issue right enough. If it was getting suitable fuel and it was caused by an ignition issue for example...you’d imagine you’d get a sign of unburnt (almost like what an old carb does when under choke) fuel black foggy smoke maybe ?

That’s what i was assuming and that was why i didn’t look at ignition, but since codes are now fixed and fuel pressure is more than enough I’m wondering what else could cause it, doesn’t hesitate and low RPM or idle so doesn’t sound like clogged injectors to me

 

[QBhoy]

That’s what i was assuming and that was why i didn’t look at ignition, but since codes are now fixed and fuel pressure is more than enough I’m wondering what else could cause it, doesn’t hesitate and low RPM or idle so doesn’t sound like clogged injectors to me

Yeah. Doesn’t sound like blocked injectors. You’d need to be hellish unlucky enough for them all to Be blocked unless it’s at the fuel rail entry itself. I’m honestly not familiar with this big block MPI Engine but does it have fuel rails like mine (the small block mpi) and with a test/bleed nipple ? Assume it has if you have mayne used that to put a gauge on ? No chance it’s drawing air Somewhere on the LP side ?

 

[Glastron Fisher]

so i was looking at timing last night and i spun my distributor a tooth to see what it would do, reset timing and took her out tonight, 8* is what i set it to and it drops to just about 0 or a little after TDC when taken out of service mode, revved to 3000 RPMS and it looks like she right about 30-34* so it should be working properly right? She seemed to get up on plane easier than before but still had a hard time hitting 4K RPMS and not sure why, after we were out for a while and watched fireworks i once again had to throw someone up in the bow to get it on plane so i’m not thinking i got anywhere since the last time we took it out. What else can i possibly look at before i start ripping valve covers and lower intake off to check the cam? Could it be possible that the timing chain is off a tooth when i rebuilt it? Could that possibly cause this issue without running like crap at idle?

 

[alldodge]

Got a new used engine with forged internals

Your original engine was a 385HP motor which had 502 heads. I don't think the truck motor would have the same setup, or did it?

 

[Glastron Fisher]

Your original engine was a 385HP motor which had 502 heads. I don't think the truck motor would have the same setup, or did it?

Old engine had cast crank and rods so i’m assuming it was the 325 or 310 HP one, gen 5 or 6 454 block according to casting numbers and the new one was a gen 6 454 from summit that was used in CNG generators. Forged crank and what looks like cast rods but had a different number on them. So i would assume everything is exactly the same. Same bore and stroke so even if i had 502 heads the computer was setup for them