Fuel supply, injector or control module issue?

[Onin96]

Just completed installing lower intake gasket. ("fun")
Now, rough start and idle, narrowed down to cyl 4 and 6. (Drivers side front and back)
No change in RPM when 4 and 6 plug wire caps pulled off distributor, all other cylinders have huge drop in RPM.
Both have good spark. Confirmed spark to plugs. Changed plugs.
Tore out all injectors, cleaned, inspected, ohm tested all are at 15.3 ohms +/- 0.1
Replaced all injectors on driver's side with what came out of my 1996 engine after testing and cleaning them too. (I replaced my 96 4.0L with 97 4.0L because cyl 1 blew a rod.)
Put it back together and have same issue on same cylinders. So at least I reproduced the issue LOL.
Any suggestions what I could check next? thx

 

[pentode]

I'm guessing you're getting misfire codes on those cylinders? Any other codes? I really don't want to ask "any chance you have intake leaks at those corners?"

 

[Onin96]

I'm guessing you're getting misfire codes on those cylinders? Any other codes? I really don't want to ask "any chance you have intake leaks at those corners?"

Only code is P1445 Evap emission sys purge flow sensor. How would I test for an intake leak?

 

[pentode]

Only code is P1445 Evap emission sys purge flow sensor. How would I test for an intake leak?

The classic way is to spray flammable brake cleaner (last can I bought said it wasn't flammable ) around suspect areas and listen for changes in how the engine is running. If it's sucking large amounts of excess air in that might be enough to cause misfires - you might find adding extra fuel (brake cleaner) might cause it to fire... Or some other change that might help diagnosis.
I'm puzzled though as to how it's not reporting those misfires if it's running that rough. Maybe someone who knows that 4.0 better than me will have info about that.

 

[Onin96]

The classic way is to spray flammable brake cleaner (last can I bought said it wasn't flammable ) around suspect areas and listen for changes in how the engine is running. If it's sucking large amounts of excess air in that might be enough to cause misfires - you might find adding extra fuel (brake cleaner) might cause it to fire... Or some other change that might help diagnosis.
I'm puzzled though as to how it's not reporting those misfires if it's running that rough. Maybe someone who knows that 4.0 better than me will have info about that.

Thanks. I sprayed starting fluid all over. No change in engine rpm.

 

[pentode]

When you swapped the injectors on that back the dead cylinders stayed the same and nothing changed at all?

 

[Onin96]

update changed plugs. Smoother now but 4&6 now have slight change in rpm, not as comparable to other cyls.
Next I guess is plug wires?... have not compression tested.

Also 3 observations:
(1) suction at the oil cap. Is that normal? It's not huge but it's there.
(2) acceleration is not what it should be and at higher rpm in 2nd gear I get a ping here and there from down below which I assume is unburned gas in the CAT.. idk
(3) just realized tube from oil filler needs to be connected to air intake... trying that next

 

[Blmpkn]

The classic way is to spray flammable brake cleaner (last can I bought said it wasn't flammable )

 

[Onin96]

Now I have P0174 lean on bank 2
Snapping sound here and there, not consistent, at 3600rpm in 2nd gear. No snaps in 1st gear same rpm.

 

[Onin96]

When you swapped the injectors on that back the dead cylinders stayed the same and nothing changed at all?

Correct. I swapped all 3 on driver's side.

 

[pentode]

Well that seems to rule out quite a few things at least. Have you looked over the harness in that area? Any chance something got pinched or cut in the process?

Edit: oops missed a post or two. Snapping sound really sounds like damaged plug wires or something like that.
Suction at oil filter doesn't sound normal to me at all. Something screwy with the PC setup?

 

[Onin96]

I'm guessing you're getting misfire codes on those cylinders? Any other codes? I really don't want to ask "any chance you have intake leaks at those corners?"

P0174 bank 2

 

[pentode]

And lean code starting to sound like vacuum leak again. I'm assuming cylinders 4-5-6 are bank 2 as well, so at least the symptoms are starting to make sense

 

[pentode]

Another easy test you could do is swap the plug wires for each companion pair on the coil pack and see if the misfires stay on 4 and 6. At this point it sounds like they probably will.

 

[Onin96]

Well that seems to rule out quite a few things at least. Have you looked over the harness in that area? Any chance something got pinched or cut in the process?

Edit: oops missed a post or two. Snapping sound really sounds like damaged plug wires or something like that.
Suction at oil filter doesn't sound normal to me at all. Something screwy with the PC setup?

Thanks. It's more of a popping than snapping from plug wire, I'm guessing unburned fuel? Only here when driving... not sure if its backfire into manifold or what... it sounds more in the engine area than under the cab like I'd expect for CAT but IDK if a CAT would do that... I'm thinking underburned fuel getting through. If an older vehicle with a rotary distributor I'd say timing was off.