Insight needed, 2012 Ram 5.7L Hemi #8 misfire diagnostics

[clinebarger]

This is from a shop that has put in 3 different reman Engines from LKQ, New OE Mopar #8 Injector, New OE #8 Coil, New NGK plugs, Different PCM, Engine harness from a wreaking yard, Intake manifold & Fuel Rail changed twice.
All 3 engines misfire on #8

I haven't had a lot of time to mess with it as I'm slammed with good cash flow work. The mechanic that worked on it is a pretty good R&R guy (Wish he was my employee).

First I made sure that #8 is in fact misfiring & all others are hitting, #8 is the offending cylinder. Clear Flood cranked it & it doesn't have a open hole/Even compression per the ear anyway.

Back probed the Injector & Coil....They both have control & collapsing magnetic fields.

The next day I did some quick in cylinder pressure testing on #8 & #3.....Relatively new to this & would to integrate it into my diag procedure more often. Besides the max pressure.....I don't see any other anomalies in the waveform, It was driven here with the injector plugged in washing #8 with fuel & has NEVER hit on a newly machined engine.

I plan on running more channels to get some "sync's".....Cam, Crank, Coil, Pressure Tranducer.

Thoughts??

 

[panthermike]

Has cylinder 8 misfire been the issue on all three of the engines? These can sometimes be the rocker/lifter but I would be quite surprised if it was on all 3 engines (unless mfg issue). Is the motor running? Curious how it sounds/runs.

 

[The_Eric]

Why was the engine replaced to begin with? Was #8 misfiring before this saga began or did it only start happening after engine replacement?

 

[iCurious]

Injector on time is 3.8 ms? What about the other injectors?

What happens to the waveform when you do a snap test? Compare it with the known good.

I would also sync up the cam and crank.

 

[OVERKILL]

So, I assume engine #1 was replaced because of the misfire and they probably thought it ate a cam/lifter (common for 2011/2012) but then the replacement engine didn't fix it, so they swapped in two more engines? And then an ECM and harness?

Is this a 1500 or 2500/3500?

 

[clinebarger]

Engine runs & hits on all cylinders besides #8, This is a 1500 with a 66RFE.

*Supposedly the original engine missed on #5, They verified a lifter/cam failure by pulling the valve cover.
*All 3 subsequent engines have missed on #8.
*The PCM, Injector, Coil was swapped after the first replacement engine.
*The Harness, Intake was swapped after the 2nd engine.
*After the 3rd engine didn't fix it....They threw in the towel & brought it to me.

These do not snap throttle very well because the electronic throttle control, But will attempt it once I get back on it.

 

[clinebarger]

Injector on time is 3.8 ms? What about the other injectors?

Can do that easy enough, Though Injector duty cycle is bank to bank not single cylinder.

 

[wtd]

I can see one problem right now with your in-cylinder waveform. Your vacuum pocket on the expansion stroke and the intake stroke should be roughly the same. Yours is not. Your intake stroke vacuum is deeper than your expansion stroke. Was the in-cylinder waveform taken at cranking or idle?
Here is a good article on in cylinder waveform analysis. There is also a part 2.
https://automotivetestsolutions.com...ction-to-in-cylinder-pressure-testing-part-1/
This is a good video on the same subject.

 

[clinebarger]

This engine has VVT, Which I believe can cause that in the waveform. #3 has the same phenomenon.
All waveforms are at idle.

 

[OVERKILL]

Not sure how it impacts the operation (you'd know better than me) but with the dual ignition, have you actually verified, beyond with the scope, that you have spark at the plugs in #8? I ask because you mentioned "washing down the cylinder" as it was driven there, which implies that you know beyond injector cycling that fuel is making it into the cylinder.

 

[The_Eric]

Not sure how it impacts the operation (you'd know better than me) but with the dual ignition, have you actually verified, beyond with the scope, that you have spark at the plugs in #8? I ask because you mentioned "washing down the cylinder" as it was driven there, which implies that you know beyond injector cycling that fuel is making it into the cylinder.

Agreed. Compression, fuel, air and spark at the right time and she should be hitting.

As many engines as this thing has seen, it's bound to have had, at least at one time or another air and compression. It sounds like it's got fuel so I guess that leaves spark eh?

 

[clinebarger]

Not sure how it impacts the operation (you'd know better than me) but with the dual ignition, have you actually verified, beyond with the scope, that you have spark at the plugs in #8? I ask because you mentioned "washing down the cylinder" as it was driven there, which implies that you know beyond injector cycling that fuel is making it into the cylinder.

The mechanic that's been trying to diag this said the plugs are wet......Trust but verify still applies here!, However I didn't verify this 'til I removed one of the #8 plugs to get a pressure waveform.

You can see the slight oscillation in the firing/burn line between jumping the 2nd plug gap......