Mercruiser missing at around 2000 - 3000 rpm (350 mag mpi 2004)

[benchircop26]

Hi,

A few weeks ago when I put the boat at sea, engine wasn't getting enough power (revs) but by time after some minutes working it starts to accelerate. I changed distributor cap and plugs and engine worked perfectly.

Next time I used the boat, it started to work very bad from revs 1700/2000 up to 3000 (missing really badly) once you pass the 3000 rpm it works fine but sometimes it misfires. I changed high tension leads, tried a new coil, plugs, tried another distributor cap + rotor, tried other injectors, checked fuel pressure and everything remained the same. I also did compression test and all cylinders are fine.

Can you please help me maybe you had a simlar problem and advise what I can do.

Thanks in advance

 

[alldodge]

What's the motor serial number?

What was the fuel pressure readings from idle thru WOT?

 

[alldodge]

Can anyone help with thunderbolt v ignition problem, getting no spark at plugs, getting spark at coil, done troubleshooting guide and it pointed to ignition sensor which I changed but still no spark at plugs HELP PLEASD
5.7 V8

Jazzy, not cool, your hyjacking anothers thread. Start one of your own and we will answer

 

[Jazzy357]

Sorry new to this I'll try figure out how to start one so sorry

 

[Jazzy357]

How do I start a thread

 

[alldodge]

Good Grief
Select the Mercruiser section (Because your talking about a Mercruiser problem)
Near the top left of the Merc section is a button labeled "+ New Topic"
Select the button
Then fill in Title and your trouble and questions

Select this link to take you to the Merc section
Hey GA_Boater

https://forums.iboats.com/forum/eng...ance/mercruiser-i-o-inboard-engines-outdrives

 

[benchircop26]

Hi, sorry for my late message. Fuel pressure was good according to mechanic (35-40).

 

[alldodge]

Need a serial number to help best

If your motor has the flat distributor cap (HVS) I would replace it and the rotor even if it looks good. The caps are known to go out and cause misfires and other issues and go out without warning. If it doesn't fix it, keep the cap for the future when it does go out

 

[benchircop26]

OW061587

I did buy a new distributor cap + tried another one just in case and also replaced rotor. This week we changed the crank sensor but it's still the same.

 

[alldodge]

Thanks, the fuel pressure should be 43 psi from 1800 rpm and up

It would be good to connect a fuel pressure gauge on the fuel rail and leave it there as the boat goes from idle thru WOT

Can also need to place a scanner on and see what things are changing.

You mentioned that other injectors where tired. Your saying the fuel rail was removed and another set of 8 where installed?

 

[QBhoy]

How’s the fuel ? When you say misfire...is it a missfire or a popping lean noise.

 

[benchircop26]

Thanks, the fuel pressure should be 43 psi from 1800 rpm and up

It would be good to connect a fuel pressure gauge on the fuel rail and leave it there as the boat goes from idle thru WOT

Can also need to place a scanner on and see what things are changing.

You mentioned that other injectors where tired. Your saying the fuel rail was removed and another set of 8 where installed?

Hi, sorry for not replying back... I’m still with the same issue.... we did change the injectors not the fuel rail. Changed the throttle position sensor and also crank sensor.

 

[benchircop26]

How’s the fuel ? When you say misfire...is it a missfire or a popping lean noise

Within those revs it’s missfire (like the power is coming and going).

 

[alldodge]

Here is a bulletin for the HVS misfire

 

[benchircop26]

No Luck yet

 

[alldodge]

Have you scanned the motor?

 

[benchircop26]

Have you scanned the motor?

Yes, mechanic said everything looks fine (no errors) … they also changed harness, injectors, plugs, high tension leads, crank sensor, tps, distributor cap, rotor, coil … checked compression, fuel pressure

 

[alldodge]

Your parts changer (so called mechanic) is costing you a lot. Appears there not even doing any testing, just changing parts.

If the injectors came from ebay, there most likely junk. If they are Merc injectors then Ouch, that cost a lot.

I changed distributor cap and plugs and engine worked perfectly.

This is the puzzler. Changed cap and plugs and runs great. Next time it has problems again

If the motor is sound (meaning compression is within range , spark timing is correct) then it has to be fuel. The issue, is your not doing the work and your getting only the info the parts changer is saying

Which plugs are installed?

 

[Garybly]

Your parts changer (so called mechanic) is costing you a lot. Appears there not even doing any testing, just changing parts.

If the injectors came from ebay, there most likely junk. If they are Merc injectors then Ouch, that cost a lot.



This is the puzzler. Changed cap and plugs and runs great. Next time it has problems again

If the motor is sound (meaning compression is within range , spark timing is correct) then it has to be fuel. The issue, is your not doing the work and your getting only the info the parts changer is saying

Which plugs are installed?

They are Bosch injectors, why pay the money for Merc parts, they do not make them Bosch does Part number 0280156081?