2014 GMC Sierra misfire

svan78 · March 31, 2015

i could use some advice....

I bought a 2014 GMC Sierra crew cab z71 4x4 and my check engine light flashes so i take it to the dealer. Truck has 5k miles on it. Dealer says it is a misfire on cylinder 8. They tell me it had a loose clip on the spark plug.

500 miles later the check engine light flashes again. Go to the dealer again its a misfire on cylinder 8. They replace the plug and the wire. Said it was a bad plug.

500 miles later the light flashes again. I call the dealer and they tell me they will have to teardown the enging to cylinder 8 to see what the problem is.

Does this sound right for an engine with less than 7k miles to need a teardown to cylinder 8? What does that all consist of anyways i ask? The serive guy never gave me a straight answer and wouldnt tell me what the compression was on that cylinder.

I dont like the sounds of teardown a new engine and asked for that coil pack to be replaced and was told no.

Anyways anyone had any problems similar to this and could offer some adive or tell me what a teardown to cylinder 8 consist of?

Thanks

LongrangeLauber · April 1, 2015

Well its pretty time consuming to pull a head.

If they won't even try a new coil pack before pulling the head then there is something wrong with them. Try the easy things first. Go to a different dealer and tell em the entire story and see what they can do for you. I know I would have started with the plug and wire, then moved onto coil pack, then check the wiring harness that runs all the way to that coil pack. If all is good, then check the injector flow rate. I couldn't imagine needing to pull a head or even more for a misfire

svan78 · April 1, 2015

My point exactly...why pull the head before you tried the coil pack? I was hoping someone with a similar problem could tell what fixed their 2014. but thanks for the reply

LongrangeLauber · April 1, 2015

sounds like a rare case IMO

pm26 · April 1, 2015

A misfire could be the result of an ignition problem or fuel problem (malfunctioning fuel injector. A dealer should have the ability to diagnose the system to see if it is fuel related. if not, then replacing the suspect ignition component(s) is in order. This is ridiculous.

svan78 · April 1, 2015

Is that the dealer protocol

pm26 · April 1, 2015

I am speaking from experience. I had a misfire code on my Mazda 626 some time ago. Te local dealer tech first checked the ignition, even swapped the spark plugs, which did not help. The car has a single ignition coil with 6 ports, so this was not a suspect. Then the tech connected his breakout box to the engine ECM (computer unit) and it showed him clearly which injector was misfiring. Therefore it seems to me that GM should have a similar procedure to diagnose cylinder misfire problems. In case of individual coils per plug, they should also swap out the coil from another cylinder to eliminate/identify if this is an ignition related issue.

BTW, it took 325k miles of driving for this car's engine to throw its first misfire code. And even a very good experienced tech could not determine at a glance whether the problem was ignition or fuel system related without proper test procedure.

Edited April 1, 2015 by pm26

redwngr · April 2, 2015

Connector with poor connection in harness to #8 injector?

Let'em do their thing. that's what warranty is for (but I'm betting service advisor is not correct about the next step in the 'diagnostic list')

Edited April 2, 2015 by redwngr

DeePa · April 2, 2015

I had a cyl 6 misfire...they replaced the injector. It had 5800 miles and no issues since. Fuel pressure was low on that cylinder.

pm26 · April 2, 2015

Connector with poor connection in harness to #8 injector?

Let'em do their thing. that's what warranty is for (but I'm betting service advisor is not correct about the next step in the 'diagnostic list')

You mean the "NORMAL" step?

Silverado915 · April 5, 2015

Why not swap #8 coil to #6 cylinder and see if the misfire follows? If it does you have a bad coil. If it doesn't you probably have a bad injector. I'm leaning towards the injector personally though.

Gmc sierra guy · April 22, 2021

I have a 2014 gmc sierra 5.3 the code reads a misfire on cylinder 7 which is a cylinder that kicks it into 4 cylinder mode, before this when j start mh truck it sounds like a dry lifter until the oil gets to it and it quiets down! My buddy said it is most likely the lifter giving out! Does this sound accutate to anyone?