Puzzled, need suggestions not running all 8 cylinders.

[Wvgdutchboy]

So, I purchased my first searay 340 Amberjack 3 months ago with mercruiser 8.1 L horizons 2002
Seller had a problem with with starboard engine not running right and said he would have it fixed for sea trial.
At sea trial both engines ran 4200 rpm and ran smooth idle. He said he had changed low fuel pressure pump (not original OEM) sea trial was completed with minor repairs needed so we purchased the boat. After using it a few times the starboard engine started running rough idle and could not get it up to no more then 3200 rpm.
Found an experienced mechanic from a friend and we did the following. He said theae engines are notorious eating up plugs and that's probably the problem.
Hooked up diagnostic computer did not show any codes for concern.
Checked compression all came back 180, changed spark plugs first with AC Delco 41-983. No luck. Checked full pressure was normal at 42. Pulled all fuel injectors showed dirt had them cleaned and tested, changed fuel filters, checked for spark, changed out computer from port engine no difference. Change sparkplug wires. After all that we noticed that cylinder number 8 new sparkplug was dry and black for as little as we ran it just for test runs. Did not change out coils since we had spark on all cylinders. Engine still sounds like not firing on all cylinders. I am suspicious the low pressure full pump is junk since it is a cheap one. My mechanic wants to try different spark plugs. We both are puzzled and think it's probably something stupid. We take any suggestions at this point. I really like to get this engine running right again.

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[techmitch]

For starters, if 4200 rpms was your WOT on the sea trial, I don't know the spec, but that sounds low.
The right diag. computer should be able to do a cylinder balance test at idle, when running at cruise and WOT.
I would base line it with whatever the correct spark plug that Mercruiser recommends.
Is 42 the correct fuel pressure at idle and under load?

 

[Wvgdutchboy]

I thought 4200 rpms was also on the low end but the surveyor said it was acceptable. However both engines at that time ran at 4200 now the starboard is only doing 3200 rpm. The fuel pressure is 42 at idle which I think my mechanic said is the correct pressure. His opinion is that there is no reason to go out and push the engine at higher rpms if we can't get the engine to run smooth on 8 cylinders at idle. I agree with him on that. We are trying different spark plugs on Monday if that doesn't work I am hoping I get some other suggestions.
Thanks.

 

[Korkie]

Not sure if your engines have the individual col packs or not. I had this same issue and it turned out to be one of plug wires at the connection to the coil pack was arcing and grounding out against the engine as it is quite tight around the coil packs. Tere was aloso a post on here about the same thing. That post stated it was arcing to the valve cover. Found ours by closing down the engine hatch to create dark bilge and running engine. There she was bright as ever, the arc coming from the #8 cylinder to the vave cover. Checked the brand new plug wires and found a small slit. Replaced wires with High Performance wires and problem gone. These coil packs send out like 40,000 volts, so doesn't take much for one to stray. Not sure this is your issue. We had done all the troubleshoting you mentioned in you post and came up with same results. Everything normal. Compare your findings to the other motor. We have 13,500 hours on our motors and WOT is around 44,000 with light load (people, fuel, etc)

 

[techmitch]

Not sure if your engines have the individual col packs or not. I had this same issue and it turned out to be one of plug wires at the connection to the coil pack was arcing and grounding out against the engine as it is quite tight around the coil packs. Tere was aloso a post on here about the same thing. That post stated it was arcing to the valve cover. Found ours by closing down the engine hatch to create dark bilge and running engine. There she was bright as ever, the arc coming from the #8 cylinder to the vave cover. Checked the brand new plug wires and found a small slit. Replaced wires with High Performance wires and problem gone. These coil packs send out like 40,000 volts, so doesn't take much for one to stray. Not sure this is your issue. We had done all the troubleshoting you mentioned in you post and came up with same results. Everything normal. Compare your findings to the other motor. We have 13,500 hours on our motors and WOT is around 44,000 with light load (people, fuel, etc)

Yep, 40KV and it will find the path of least resistance to ground.

 

[atrick]

Wait till night then start the engine with no lights on you'll see if the wires are arcing anywhere, that's how I found my bad wires.

 

[DaveDep]

I had a similar problem this summer. Turned out that a wire harness was resting on the motor (not sure exactly were) and burned through to cause an arch. Shop repaired it and it seemed ok for the short time we ran the boat before winter haul out. But while looking for the problem we learned about a prior service bulletin on these motors were the cool fuel system's internal paint finishes deteriorate over time and clog the high pressure fuel pump and the injectors. I'll be following up on that this spring since my fuel pump was full of gunk (replaced). I'm thinking we'll have the injectors cleaned (and replace the other pump) as preventative measures. I'm interested in any other advice on this topic.

 

[Wvgdutchboy]

Wait till night then start the engine with no lights on you'll see if the wires are arcing anywhere, that's how I found my bad wires.

Lol, I thought you were joking first but that sounds like a good trick. Thanks.

 

[Scott215]

Definitely sounds like a spark issue

 

[boatrboy]

We have 13,500 hours on our motors and WOT is around 44,000 with light load (people, fuel, etc)

Assuming a sticky keyboard . I’m guessing you have 1,350 hrs. And hit 4,400 rpm’s

 

[Wvgdutchboy]

Lol, i figured , yes I have about the same amount of hours on mine 1375 on both engines.
I tried the dark late tonight to check engine for arcing. All clear didn't see any arcing, however my mechanic did change all plug wiring when he was here last. He thought it was still running not on all cylinders however I thought tonight it was. He did also mention when shift boat in forward the engine makes a knocking sound and in reverse it does not. I noticed that also tonight but I think it is not related. So tomorrow I am going to see if it runs better and reaches 4200 + rpm. If it does I have another problem but switching out the plug wires might have done the job. If it doesn't I will post a update tomorrow.
Thanks for all the info so far.

 

[Wvgdutchboy]

Wait till night then start the engine with no lights on you'll see if the wires are arcing anywhere, that's how I found my bad wires.

Tried it tonight, thanks for that but no arcing

 

[Wvgdutchboy]

I had a similar problem this summer. Turned out that a wire harness was resting on the motor (not sure exactly were) and burned through to cause an arch. Shop repaired it and it seemed ok for the short time we ran the boat before winter haul out. But while looking for the problem we learned about a prior service bulletin on these motors were the cool fuel system's internal paint finishes deteriorate over time and clog the high pressure fuel pump and the injectors. I'll be following up on that this spring since my fuel pump was full of gunk (replaced). I'm thinking we'll have the injectors cleaned (and replace the other pump) as preventative measures. I'm interested in any other advice on this topic.

I think but I am not a mechanic that if your engine is running good there shouldn't be any need to clean your injectors. However from what I learned and I guess common sense I would replace the fuel filters. I was told poor them out in a clear glass end see if any debris or water in them . Once you take them off replace them don't put the old one back on even if it shows clear. It's not worth it just replace.

 

[Wvgdutchboy]

I had a similar problem this summer. Turned out that a wire harness was resting on the motor (not sure exactly were) and burned through to cause an arch. Shop repaired it and it seemed ok for the short time we ran the boat before winter haul out. But while looking for the problem we learned about a prior service bulletin on these motors were the cool fuel system's internal paint finishes deteriorate over time and clog the high pressure fuel pump and the injectors. I'll be following up on that this spring since my fuel pump was full of gunk (replaced). I'm thinking we'll have the injectors cleaned (and replace the other pump) as preventative measures. I'm interested in any other advice on this topic.

I think but I am not a mechanic that if your engine is running good there shouldn't be any need to clean your injectors. However from what I learned and I guess common sense I would replace the fuel filters. I was told poor them out in a clear glass end see if any debris or water in them . Once you take them off replace them don't put the old one back on even if it shows clear. It's not worth it just replace.

 

[Korkie]

Assuming a sticky keyboard . I’m guessing you have 1,350 hrs. And hit 4,400 rpm’s

Yes a sticky keyboard and you are correct. Hopefully Santa is going to address that keyboard in a few days.

 

[Korkie]

If yo are satisfied it isn't a fuel problem, the next thing I would consider is to swap coil packs between the motors and see if problem moves to port side.

 

[Wvgdutchboy]

If yo are satisfied it isn't a fuel problem, the next thing I would consider is to swap coil packs between the motors and see if problem moves to port side.

Hi, to everyone, I have tried all you guys recommended. We pulled the fuel.injectors again after trying different plugs. After pulling the fuel injects we are pretty sure we found the problem. (Please see picture.) We pulled everything fuel flows through from injectors to the tank to clean and today we are have the tank fuel tank drained and cleaned . This hopefully will fix it. My mechanic said he's never seen this much junk in the fuel lines

 

[Scott215]

Yeah that's incredible man I hope that fixes it

 

[Korkie]

Not sure which cool fuel module you have on the 2002. On our 2006 we have the Cool Fuel 3 and it had the "paint issue". Mercruiser paid to have BOTH of my engines fuel system replaced from and including the complete fuel module to the injectors along with having the injectors professionally cleaned, tested and certified. Merc supplied the parts and I paid the labor for removing, cleaning and reinstalling what original parts went back on. Basically the fuel lines from the cool fuel and the fuel tree. Basically a totally new system. Cost to me: $425.00

 

[boatrboy]

Hi, to everyone, I have tried all you guys recommended. We pulled the fuel.injectors again after trying different plugs. After pulling the fuel injects we are pretty sure we found the problem. (Please see picture.) We pulled everything fuel flows through from injectors to the tank to clean and today we are have the tank fuel tank drained and cleaned . This hopefully will fix it. My mechanic said he's never seen this much junk in the fuel lines

Wow - I’m surprised how much crap is in there. Like Korkie I had my fuel pumps and injectors replaced by Merc (parts only), but I’m guessing you have the spin on filters and not the cool3 set up.
I am hoping while you are that deep you are replacing the files lines themselves with the proper marine ethanol rated fuel lines.

You may/should be sending the injectors out for professional cleaning/testing as well..

Good luck getting back to smooth running.

btw- you sig says 8.1 then 496 with straight drive- may want to clarify - if 8.1 I’m guessing it has v-drives from your first post. And 496 has bravo 3’s? Not important here but may help in the future if we know exactly what drive train you have.