Ok, cool deal, I can see the live time Cylinder 3 miscount total. I can see it totalizing the misfire count.

I've done a lot of scans on our cars and I have theorized a generic misfire is triggered when the Engine Ecm detects a stumble in the engine.
I think it detects this stumble when calculating the time between ignition pulses as triggered by the crank shaft sensor.
(Technicality, the crank sensor sends an analog waveform on our cars that the Engine Ecm uses to calculate degrees of rotation. Crank sensor doesn't directly control or trigger spark.)

Another words, as the engine is running, the Engine Ecm can predict how long before the crank sensor should trigger the next timing pulse.


An engine stumble/misfire can happen for many different reasons including mechinical problems like valves, compression etc AND electrical problems such as bad wiring, weak spark(from coil or plug), etc.

That's a badd azz scanner and I'm sorry I had to google it and it says it has a built in scope, might have to break that bad boy out if the misfire turns into a more extreme diagnosis, -if they scanner actually has that feature- . lol

PS- it sounds like that buffet of codes in post #1 may have cleared up somehow but I fear they will come back if the problem is not found. And, Murphys Law, the previous owner may have allowed a few issues to manifest due to " delayed maintenance". lol

>>PS, how did that cylinder 3 plug look? Any signs that can indicate a bad fuel injector?

 

Cyl 3 plug looked better than the 2,4,6 which were more carbonized. It was bit wet, bit oily on the threads. If you look at the 1 st pic even the cyl 1 n cyl 2 shows misfire momentarily then got corrected. I am still wondering if this is a harness issue.

 

I guess there should be a way to check continuity at the questionable cyl 3 coil harness.

 

I don't fully understand how that live data works on your scanner but I think cylinder 1 & 2 look like a misfire but I don't think they really are.
Only because the glitch on both cylinders is at exactly the same time, I think? and if so, it can't be right because of the firing order, -only one plug firing at a time.

Also, it didn't totalize misfires for those cylinders, only cylinder 3.

However,,, that glitch as seen on cylinder 1 & 2, could that be an ecm hiccup due to a bad ground or harness somewhere?
OMG, what if that's a clue.

Have you dropped the glove box and unplugged the harness cables(battery disconnected) on the Engine ECM to inspect for corrosion at the connectors, etc?

For anyone following along, our Engine ECM is behind the glove box.

Next post, I'm working on continuity test as you requested for coils, If I understand correctly.

 

Will check the connectors at ECM tomorrow.

 

This is the scan that had me questioning the misfires.
I may not fully understand what the live data on this scanner shows but...





Where are we at on this car and what do we know for sure?
Are you saying there is only one persistent code now and it' for a cylinder 3 misfire?

If so, it looks like you made some progress friend.

 

Here is the info on the spark plug coil connectors.

About:
(1): power wire(+B) is common to all coils

(2): ground wire is common to all coils

(3): IGF wire is common to all coils. This wire sends a feedback pulse to the Engine Ecm when the coil fires and it is on a common wire shared by all coils because no two coils fire at the same time on our car- so only one wire is needed.
*Note- this wire can be scoped to see all the feedback pulses for the coils.
*note- if the Engine Ecm does not get it's expected feedback pulse it will trigger a code like P035N, where "N" is the number of the cylinder.

(4): IGT wire is the only wire that is not common to all coils. This is the coil trigger wire that powers the coil's primary winding. Each coil has it's own IGT wire that goes directly back to the Engine Ecm.
*note- these wires can be scoped.





My thoughts so far:
If no wiring damage is found.
If there's no ground wires in the engine left unhooked by the last guy who worked on it.
If the fuel injector is good.
If the coil and spark plug is good.

Only thing I know is a compression test and maybe a boroscope on cylinder #3 before going any further.

That's only if the cylinder #3 code is the only code showing after driving it around for a bit to see what happens.

 

A badly misfiring cylinder can affect other cylinders, due to ECM changing fuel mixtures, and if a bad valve then manifold pressures are affected. In my case, no compression on #4, caused misfires on #2 and #1, which was odd since #1 is on different bank, but seems similar.

 

I will check the compression on the cyl, but as you said if any ground wire is loose of left hanging would it not cause a total NO start rather than just one cyl.?

 

Thank you @Mesquite77 .

I was hoping others would jump in and help.

I totally forgot, wouldn't a vacuum gauge show a blipping needle for a bad valve or compression issue?

Won't tell which cylinder of course but maybe a visual confirmation?
​
A ground left dangling and arcing can do all kinds of wierd stuff.
Probably not the issue at hand but just being thorough..

I am just stressing the point of going over all the wiring and looking for anything that doesn't look right.

The reason why is because you bought the car like this and we don't know what the last guy did to it before selling it.

Also, I dug thru the wiring and the codes listed in post #1 are completely unrelated and share no common wiring. Could be someone was scoping and probing pins at the ecm and crossed pins and triggered codes, who knows, that's the problem, codes make no sense but hint that someone has been inside this engine poking around, maybe, just a guess.

PS, I work on electronics and very often another company already tried to fix it and failed before I get it. On every job I have to do a thorough inspection first and fix the last guys mistakes(if any) before I begin the actual repair. Lol

 

I forgot about our friend, the vacuum gauge
I have the same one and bought it at harbor freight, dirt cheap.

For doing some checks without pulling the plenum, for anyone following along.

 

Thats a great video Thanks.

 

Just did the compression on all cylinders, 1-200, 2- 195, 3- 85, 4-189, 5-208, 6-191. So cyl 3 really had only 85psi i checked twice. What could that be ?

 

Oh man.
Today is a sad day.

I was hoping for ANYTHING but this, dammit.
You found your cylinder #3 misfire.

I'm not sure where to go from here.
Compression leaks can come from bad valves, stuck cylinder rings, head gasket, etc.

Hopefully others can join in with ideas.

PS, now I'm even more convinced someone else was probing and pulling plugs trying to diagnose this car before you got it -hence- triggering the weird unrelated extra ghost codes in post #1.

 

Yeah i didnt expect to see it myself, How bad can it be to work on this, i mean to check the lifters, valve seats, head gaskets on that cyl & repack that engine bank. Also do you know if these 190-208 psi are expected avg for these engines with 146xxx miles.?