chasing mis-fires...fun fun fun

[griehl]

hey guys, first post on here - so, to offer a little back story, I bought a 1997 GP GTP, it was running like cr*p when I bought it...and I got it on the cheap so no worries there. So, I started out replacing a vacuum line and it helped alot, but it was still surging real bad. Found it was sucking air in through the SC manifold gasket and the SC was making noise anyway (play in the unit), so, I managed to find a used on at the pull your part, and installed it along with a new gasket and also replaced the TB gasket, now, when I block air flow it does right out, so, no vacuum leaks. yay! So, the motor is quiet and runs better but it is still missing....so, I get cly 3 misfire codes and I clear them and then I get generic misfire codes the next time the CEL comes back on. I have spark at the coils, wires are good, plugs are good, I have swapped injectors and I turned the motor with the fuel rail out and then injectors are shooting..I have not run a compression test....I am wondering this: is there something common I am missing? Any help would be great....Any more info you need let me know and I can check it and report back

thanks!!

[Russosaur]

Have you checked the coils? I think you can swap them around and see if the missfire moves cylinders. Other thing I can think of is possibly the ICM.

Sent from the Milky Way

[griehl]

I've tried all that.....I guess I can't figure out why it goes from a cyl 3 code to a general misfire....thoughts?

[Kejross]

You do the LIM gaskets when you did the SC swap? Sprayed it to check for vac leaks? I'd do the compression check cause its free and is good peace of mind. Maybe pull valve covers and see if there's any obvious valvetrain issues.

I hate to say it but kinda sounds like why I'm pulling the engine outta my GTO right now. Had misfire on cyl 6 would reset and get random then cyl 5 then 6.... I did all the common stuff to diagnose it like you have plus swapped a few parts that I had extras of just to rule out faulty sensors. I'd checked it several times with a stethoscope already but decided to do it again and found one tiny sweet spot leaning across from driver side with it on pass side head I could hear the tick. After taking the head off and pulling the lifters on 6 one had chunks missing outta the roller tip and looks like matching chunks out of cam. Ran perfect, never missed a beat and wasn't nearly enough metal from the couple tiny spots to worry about bearings. But I'm pulling it to swap a 5.3 iron block just cause it's cheaper than repairing my LS1 and I wanted iron block for turbos down the road.


Not trying to scare you, but get your stethoscope out and poke and prod that thing everywhere...

[griehl]

Well I didn't do the manifold gaskets .... But when I cut off air flow it dies flat on its face so I'm fairly certain I have no vacuum leaks....I'm going to fault trace a little more but I am afraid I have internal engine issues

[tomtom123]

You do the LIM gaskets when you did the SC swap? Sprayed it to check for vac leaks? I'd do the compression check cause its free and is good peace of mind. Maybe pull valve covers and see if there's any obvious valvetrain issues.

I hate to say it but kinda sounds like why I'm pulling the engine outta my GTO right now. Had misfire on cyl 6 would reset and get random then cyl 5 then 6.... I did all the common stuff to diagnose it like you have plus swapped a few parts that I had extras of just to rule out faulty sensors. I'd checked it several times with a stethoscope already but decided to do it again and found one tiny sweet spot leaning across from driver side with it on pass side head I could hear the tick. After taking the head off and pulling the lifters on 6 one had chunks missing outta the roller tip and looks like matching chunks out of cam. Ran perfect, never missed a beat and wasn't nearly enough metal from the couple tiny spots to worry about bearings. But I'm pulling it to swap a 5.3 iron block just cause it's cheaper than repairing my LS1 and I wanted iron block for turbos down the road.


Not trying to scare you, but get your stethoscope out and poke and prod that thing everywhere...

^ Just gotta say... Love the amount if 'Merican man in that picture. Car parts, beer, and bullets. Hoorah

Sent from my SM-N900P using Tapatalk

[Russosaur]

#3 plug wasn't bent or damaged at all was it? I can't remember if a chipped piston could cause a missfire but if you have access to a borescope you could take a look.

Sent from the Milky Way

[Kejross]

Well I didn't do the manifold gaskets .... But when I cut off air flow it dies flat on its face so I'm fairly certain I have no vacuum leaks....I'm going to fault trace a little more but I am afraid I have internal engine issues

Almost forgot... There is an overlooked common issue! Check the egr tube that goes in under the TB, those are prone to cracking which creates vac leaks. If your not loosing coolant then I doubt the LIM gaskets would be bad enough for a vac leak there. But if you pull it again, don't bother with a supercharger gasket, just use rtv in the pattern of the gasket. Sure you gotta wait for it to dry before you run it but it's cheaper if you have it apart often.

^ Just gotta say... Love the amount if 'Merican man in that picture. Car parts, beer, and bullets. Hoorah

Sent from my SM-N900P using Tapatalk

That wasn't staged at all... Just what happen to be on my desk when I came inside pissed and wanting to rant about my lifter to the GTO guys lol.

[griehl]

That's the thing. Plugs are all good. When I unplug the #3 injector I can hear the cyl drop. I tried a junkyard ICM.....when they fail can the failure change based on the car being warm or cold?

[Kejross]

Or just rip the EGR off completely and put some pennies/dimes(can't recall which) in the holes with RTV and toss that sucker.

[97gtpjoe]

Or just rip the EGR off completely and put some pennies/dimes(can't recall which) in the holes with RTV and toss that sucker.

^^ dimes

[Kejross]

That's the thing. Plugs are all good. When I unplug the #3 injector I can hear the cyl drop. I tried a junkyard ICM.....when they fail can the failure change based on the car being warm or cold?

Almost all the ones I've replaced have either worked fully or been dead fully. One ICM had stopped power to just 1 coil. But you gotta figure it would be 2 cyl if a coil was bad. Also autozone has all the crap to plug an ICM in and run a series of diagnostics on it.

[Kejross]

^^ dimes

I welded mine shut and never actually use the coins... I know you can file a bit off the edge of a dime to block the coolant ports in the LIM that go to the TB too lol. Best use of pocket change! LOL

[griehl]

whoa, good call!!!!! I think I heard air being sucked in from that area a few days ago when I was working in it but I didnt check that!!!! I got frustrated and left it....ok, so i need to check it of course but is there a way to block it, or fix it without removing the SC again and without spending alot (or any!) money? So the tube that bolts in cracks? Is that right?

[Kejross]

whoa, good call!!!!! I think I heard air being sucked in from that area a few days ago when I was working in it but I didnt check that!!!! I got frustrated and left it....ok, so i need to check it of course but is there a way to block it, or fix it without removing the SC again and without spending alot (or any!) money? So the tube that bolts in cracks? Is that right?

No need to remove anything but the bolt for that hose. And that's what we were talking about the dimes for, you rip that tube outta the flange that bolts it down, put a dime with rtv in the groove and bolt that flange back down.

[griehl]

Ok got it. I will do it tomorrow and will report back!!!!! I have high hopes!!!!!!!

[Kejross]

^^ dimes

I tried finding a how to with pics but couldn't. Most post mentioned pennies though instead of dimes. So to OP just see which one fits better I guess.

Ok got it. I will do it tomorrow and will report back!!!!! I have high hopes!!!!!!!

Keep in mind deleting the EGR will set a code that won't go away unless tuned out of the PCM. But you can plug it temporarily til you can find a new hose or whatever your gonna do. I just hate when a code stays on that means nothing, but then other codes set and your not aware because the light is always on now. And get the copper rtv, so it won't melt once exhaust is good an hot.

[griehl]

Ok cool. Good direction guys I'll report tomorrow!