Rough Idle - Suspect Throttle System

[Scottydoggs]

check the temps at the manifolds, the cat, and a foot or so past the cat, if after the cats is a lot cooler its not getting proper flow through the cat.

when cold you can also hit the cats with the palm of your hand, listen for rattling inside them. some times a few hammer blows will clear the blockage up, till you floor it again then the chunks pile up. but id not go smacking them unless you hear loose stuff inside with a palm hit.

that misfire could also be a dead injector, you can try swapping it with the one next to it seeing if the misfire moves with the injector to a new cylinder.

lub up the o rings and dont loose the o ring in the cross over pipe rail to rail. here those dumb o rings cost like 35 bucks.

lube the o rings on the injectors when you put them back in to keep from tearing or rolling one out of place. oil works or petroleum jelly.

 

[HiHoeSilver]

When were the plugs/ wires last changed?

 

[Rocket Man]

I still say it’s the cats. It’s acting just like mine when they were restricted. You can have them tested at a shop, mine tested as 60 & 40% restricted.

 

[Justinj360]

I just got a call from my mechanic and he said ignition coils 1 and 2 were bad and it could use new wires. It didn't take him very long at all to diagnose it so who knows how far he actually got into it. I told him I'd take care of the work myself and pay him for the diagnosis. Any idea how the coils are numbered or which ones are 1 and 2? I'm assuming they correspond to cylinder numbers. Would it be wise to just do all the coils at once or maybe one whole side of coils since it has so many miles? (230k)

Also, shouldn't the wires still be good after about 25k miles? Unless he was talking about the wires for the coils themselves? He asked if I had been through salt, which I had been through the rust belt during the drive to GA. I haven't had a chance to clean the engine bay since.

 

[Rocket Man]

Having 2 coils go bad at once is suspect to me. And yes, they correspond to cylinder numbers so he’s talking the front ones on each side. If he didn’t damage the wires pulling them off then I don’t see how they could be bad at 25k. Did he do a restriction test on the cats? Anyway, I would put 2 new coils on and see if it fixes it. I wouldn’t worry about the rest, they usually last about forever.

 

[Justinj360]

Having 2 coils go bad at once is suspect to me. And yes, they correspond to cylinder numbers so he’s talking the front ones on each side. If he didn’t damage the wires pulling them off then I don’t see how they could be bad at 25k. Did he do a restriction test on the cats? Anyway, I would put 2 new coils on and see if it fixes it. I wouldn’t worry about the rest, they usually last about forever.

He made it sound like one is bad and another is going bad. What makes them go bad, just age? He didn't mention any other test so I'm guessing he didn't get too far. Should I stick with ACDelco coils or does it matter?
Is it common to get a pending misfire code for cylinder 8 in the back of the engine but have 2 bad front coils on the opposite end of the engine?

 

[Rocket Man]

He made it sound like one is bad and another is going bad. What makes them go bad, just age? He didn't mention any other test so I'm guessing he didn't get too far. Should I stick with ACDelco coils or does it matter?
Is it common to get a pending misfire code for cylinder 8 in the back of the engine but have 2 bad front coils on the opposite end of the engine?

The reason I’m questioning his diagnosis is that clogged cats can cause misfires, misfire codes, MAF codes, etc. Pretty much anything that involves air coming in or going out. Coils going bad Isn’t all that common so to have 2 go out at once is pretty rare. And now you’re talking misfires on #8? Hmmmm. If you’re seeing misfire codes for a particular cylinder I would try swapping coils with a cylinder that isn’t showing misfires, clear the old codes, and see if the codes follow the coil. Too bad you don’t have a Tech2.

 

[Doubeleive]

if he didn't do a backpressure test I would have him do one.
I have had multiple coils die around the same time on 2 different trucks, in both cases I replaced them all I bought the herko ones off of ebay and had no problems from what I understand they get them from the same manufacture as oem and they are much cheaper.

 

[Justinj360]

The reason I’m questioning his diagnosis is that clogged cats can cause misfires, misfire codes, MAF codes, etc. Pretty much anything that involves air coming in or going out. Coils going bad Isn’t all that common so to have 2 go out at once is pretty rare. And now you’re talking misfires on #8? Hmmmm. If you’re seeing misfire codes for a particular cylinder I would try swapping coils with a cylinder that isn’t showing misfires, clear the old codes, and see if the codes follow the coil. Too bad you don’t have a Tech2.

This is the first time I've been to this shop so I don't know how reliable it is. Maybe he or his tech got the numbering mixed up, who knows... Is it possible that a bad coil or 2 could throw the whole system out of wack and make the computer think the misfire is in a different cylinder completely? Well I've only seen a pending code once for #8 so there's nothing to clear yet. Yeah I'd love to have a Tech2.

 

[Justinj360]

if he didn't do a backpressure test I would have him do one.
I have had multiple coils die around the same time on 2 different trucks, in both cases I replaced them all I bought the herko ones off of ebay and had no problems from what I understand they get them from the same manufacture as oem and they are much cheaper.

I probably should've just asked the shop to test the exhaust in the first place. I'll give him a call back and see if he can do the back pressure test while it's in. Good to know that multiple coils can sometimes die around the same time.