PCM 6.0L Engine "Pulsing"

[mlange]

I also posted this on PN.

2012 SN 200 ZR 4 6.0L. 600 hrs

Just starting to troubleshoot an issue and plan to throw parts at it if it's part of regular maintenance (or they are cheap) before getting a dealer involved.

Very first time out this year when running up/down the lake the boat would have a very quick (and very, very short) drop of, say, 200 RPMs. It was so short I couldn't even hear it, but it almost felt like there was suddenly a bit of resistance to moving forward if that makes sense. Sort of like if you were driving a car and just for a very split second you let your foot off the accelerator and then put it right back on. Perhaps said another way, instead of being pinned into the driver seat from the force of moving forward, just for a split second you wouldn't feel pinned. The problem went away by the time I was out next time around so I wrote it off as bad gas.

This weekend the problem reoccurred. My driver said he also heard a few "pops" from the engine. My driver isn't a mechanic, but he's not a moron either and very specifically didn't call it a backfire. From the rope end I didn't hear (or feel) anything odd. I hopped in and drove it. It is a bit rough out of the hole and at various RPMs (20 mph, 34mph, 36 mph) it's doing that same thing from the first time out. I didn't hear any "pops" again, though.

FCC filter and water/fuel separater are 3 yrs old. Plugs have 150 hrs on them. I drained the FCC and didn't find any water. Running at the right temperature. Run 89 reformulated non-ethanol. ZO on/off makes no difference. Over the last two years I have had a few codes thrown for the throttle position sensor, but only when I'm idling in/out of gear. I've delayed replacing it so far since the ECM needs to be flashed for a new one.

I'm going to focus first on fuel, then ignition, then other stuff. If you guys have any other things to add to my list it would be much appreciated.

Fuel/Air

• Replace FCC filter
• Replace spin on filter
• Clean flame arrestor
• Replace MAT sensor
• Add injector cleaner to tank
• Add fuel dry to tank
• Switch to 91 non-ethanol

Ignition

• Replace plug wires

Other

• Replace throttle position sensor

Any other things to add to the list?

Edited July 24, 2023 by mlange

[jpwhit]

I assume you've checked for Engine Codes via the LINC screen. 

[skihacker]

Does it have a distributor?? Sort of wonder what the cap looks like, 

[jpwhit]

ZR4 doesn't have a distributor

[chrislandy]

To me, it sounds like a coil breaking down.

 

Grab a multimeter and check that each coil pack is OK (search the coil number for the diagnostic sequence and expected resistances), run the engine up and get it nice and toasty then check the temperature of each coilpack to see if there is one that's hotter/cooler than the others. If you can't find a diagram, then just work out a test sequence where the resistance between each pin is tested against the other, earth and the king lead(s) and compare results.

Then check for shorts on the trigger wires for the coils, then check for loose terminal and earth connections

[mlange]

@jpwhit  No diagnostic codes in LINC.  I'd expect if there was a miss it would throw a code.  Somewhat wishing it was so I could zero in faster.

@chrislandy  Thanks for the idea on the coil pack.  I've got the PCM Diagnostic Manual so I'll need to look at how to check each one.  Checking the temp of each should be eazy peazy so if the fuel/air stuff I'm doing this week doesn't fix it I'll move on to the coils/plugs/wires.

[DW]

I would add a couple items to the list:

1. Verify throttle signal is not dropping

2. at some point a leak down test to verify nothing amiss in combustion chamber.

[mlange]

Thanks @DW  

I've got a tech that does side jobs with access to Diacom so if my initial list doesn't do the trick we're just going to hook it up and go for a spin.

I'll post back the results after I get it all behind me.

[jpwhit]

I would offer more input, but this is the kind of issue that's nearly impossible to be of much help remotely. There could be a lot of things that would cause this, but I wouldn't rule out water in the tank. Especially if you always run non-ethanol gas. We had a similar issue with our 2012 Nautique 200 club boat building up water in the bottom of the tank when we ran non-ethanol gas. It happened twice actually. Now we run ethanol gas except over any winter storage and haven't had any more problems. Our club boat doesn't get much time off, so there's not a lot of winter storage. FCC will separate out some water, but not if there is standing water in the bottom of the tank, when it gets up to the level of the fuel pickup, you start getting a steady stream of water mixed in the fuel that causes random misfires. Fuel additives won't get out that much water either. 

The misfire detection in the ECM won't detect this either. It really can only detect a consistent misfire in one cylinder that happens in a consistent pattern. It looks for patterns of inconsistencies in the rotational velocity data from the CPS. 

I have a separate outboard motor style gas tank I use to help diagnose issues like this. It even has its own electric fuel pump, adjustable pressure regulator, and pressure gauge to make it pretty universal. But you actually don't need all that on a Nautique since it doesn't have an in-tank fuel pump and pressure regulator. Just connect an auxiliary tank to the input of the low-pressure fuel pump. 

I also have Rhinda Diacom, and I've recorded a lot of reference files for most of the key sensors for the boats I work on regularly. That way I have something to compare against when something starts acting up. It can be useful to just look at the sensor reading w/o having references, but it just makes it even easier having them.  

When things get really deep, I also have a digital storage scope for all my electronics work. I have HV clamp on probes for that that can monitor each spark plug to look for misses. And I have fuel and cylinder pressure transducers I can hook up as well. 

Not sure this will be all that useful for you....good luck, this is the type of problem that can be pretty challenging to diagnose. 

[mlange]

Appreciate the response.

After replacing both filters went out again last night and behavior is the same.  I guess the good news is that it's consistent and even stumbles every 5-10 seconds at idle.  I was starting to think high pressure fuel pump, but wouldn't expect that at idle.  I did get another TCP trouble code again last night. 

Have a new TCP coming today.  A tech is coming out tonight to flash it.  If that doesn't do the trick we'll see if Diacom catches anything.  And if that doesn't catch anything I plan to do to plugs/wires tomorrow and then dig into the coils.

[mlange]

New TCP on and flashed, but we think PCM gave us the wrong firmware because the command vs. actual throttle percentages aren't matching and results in a serious hesitation out of the hole.

As for the "pulsing"... even though LINC wasn't showing a code Diacom was showing that there were a few thousand misfires on cylinder #2.  We put an inline spark tester on and are seeing good spark so we think the coil and wires are ok.  Despite that I'm putting new plugs/wires on tonight and we'll see how things go after another flash of the ECM.

If plugs/wires don't do the trick thinking injector.

Edited July 28, 2023 by mlange

[gmut]

@mlangeI don't know if your engine has knock sensors but my 5.7 pcm 2009 nautique 196 does and after going thru pretty much what you have I discovered that I needed a new knock sensor and that cured the surge problem' I  have 2 knock sensors one on each side of the engine block. You have to remove them to drain the engine block. You have to make sure that the single wire lead going into each one is plugged in properly. Hope this helps.

[RAWSki]

Had what seemed like a similar issue on a 6L ProStar last year, afterreplacing all the injectors cured the problem.

[mlange]

Replaced plugs and wires and runs better than ever. 

It was cylinder #2 showing the misfires.  I numbered the old plugs when I pulled them and that plug had a .044 gap.  Ever other one had a .040 gap.  Aside from that gap every plug looked exactly the same and the electrode on that .044 gapped plug looked ok.  

Think I need to buy Diacom.  It showed a misfire count on that cylinder that never popped up on LINC as a trouble code.

Thanks for the input everyone.

 

[DW]

@mlange - .044” gap or .004” gap difference from the ‘good’ ones should not be enough for a misfire.  Would be worth measuring resistance on old (and new) plug wires to see and confirm that’s the gremlin.  Automotive plugs can fire reliably with .065” gaps with similar ignition components.

One can never have enough tools 😁

[mlange]

Ugh.  Already threw them out.  I agree that the gap shouldn't have been a difference maker here.