Chevy Silverado and GMC Sierra Forum banner

Couple of questions

1K views 21 replies 9 participants last post by  PennStateGuy 
#1 ·
Hello everybody. Longtime reader of the site. Have gotten tons of useful information and questions answered all without ever needing to post just by reading through the archives. I do have a couple of questions that have been danced around before, but never really to my exact situation. Forgive me if anyone feels the answers have already been given. If they were, I simply missed them.

Anyways…

2001 Silverado Extended cab with a 4.8 with 149,000 miles. Had an event to attend this weekend. Drove from central PA to Cincinnati, OH. Roughly about 450 miles one way/900 round trip.

Question 1: On way out, cruising between 65-75MPH check engine light would flash and then quit (from what I understand this means a misfire was detected). It did this 3 or 4 times (not consecutively- there was some time between each time it did it), and eventually just stayed lit. We stopped for a restroom break or two and once for gas and light stayed on each time engine was restarted. When we got to Cincy and drove around there at city traffic speed the light went off. Was off the next day-again just city driving. Left there Monday morning and on the way home, same thing as before. When I got home, I read the code and it was P0300. From reading here, I gather it could be plugs, wires, coil packs or more severe causes like compression issues, leaking intake manifold, bad injectors. I got 19.7MPG on the highway with three full size adults and luggage, so I don't think it's possible that it's one of the more severe issues or it would show up in the mileage, right? I'm going to put new plugs (Delco Platinum 41-962) and wires (Delco 9748HH) on this weekend. I replaced both about 6 or 7 years ago. I think when I bought the wires, I got the shorter 9748GG because that's what the sales clerk gave me and they're stretched pretty tight. I didn't know at that time that there were two different wire sets that only varied in length at that time. Could this be an issue (or the issue)? In you guys' opinion, it this a worthwhile thing to try?

Question 2: When driving, when the engine gets to the 2000RPM area, I get an extremely loud tapping sound. From the cab, or even standing outside of the truck it sounds almost like an exhaust leak- that tell tell ticking sound. Thing is, it only does it from around 1800-2200 or 2300RPM. Above that or below that RPM range, the engine just purrs like a kitten. When you open the hood and rev the engine, you can tell that it's not an exhaust leak. It almost sounds like something in the top end. If it was a valve or lifter or something else in the top end, it wouldn't quiet down at the higher RPM would it? Also, if it was something in the top end of the engine, I wouldn't be getting almost 20MPG highway would I? Let me add that this isn't the piston slap issue that occurs when the engine is cold that I've read so many posts here about. It does that too, but that goes away when the engine warms up- this tapping occurs when engine is at normal operating range.

Question 3: Could Question 2 be related to the issue in Question 1????

Any help or comments would be greatly appreciated!!!
 
See less See more
#2 ·
Well p0300 just tells you you have a unknown misfire. The big thing to look at is if the history misfire counters can narrow that to one specific cylinder. Do yourself a favor and hold off on changing the plugs and wires until you determine the root cause of failure. Don't introduce variables you don't need to. This is best looked at using the scientific method. Determine the question , research, create a hypotosis, conduct experiment, gather data, come to a conclusion, then retest you theory. The taping noise and how you describe it really sounds like an exhaust leak to me. Are all the bolts still in the manifold?? To stay on task with this you need to determine which cylinder misfired the most.
 
#3 ·
Thank you for your reply Mike.

My understanding was that the computer would throw a code P0301 for cylinder 1 up to P0308 for cylinder #8. Why wouldn't it throw those codes instead of the generic P0300?? I used an Actron CP9145 scanner to pull the code. It doesn't go into the level of detail it sounds like you're suggesting to diagnose problems. And, to add insult to injury, I cleared the error code after I pulled it so I'm afraid I might've lost the data you speak of. Stupid me.

It really sounds like an exhaust leak to me too, but when the hood is opened, the noise isn't coming from the area of either manifold, rather it seems to be higher up. Additionally, there's no trace of the carbon you'd expect to see if there was an exhaust leak anywhere around the manifold. Wouldn't one expect an exhaust leak to get even louder the higher the RPM? I wouldn't think it would go away entirely.
 
#4 ·
Well p0300 sets with x amount of total misfires then you have the cylinder specific codes such as p0301-2-3-4-5-6-7-8. They need X amount and way more to be generated by the ECM. The misfire diagnostic can be effected by multiple different factors. Good question but trust me when I say that p0300 is just a generic way of saying look at the history misfire counters. At this point let's stick with diagnosing failure codes and then address the noise. My guess is they are related. Your scanner probably has a data screen. Scroll through it and see if you have a misfire counter?
 
#5 · (Edited by Moderator)
Ok Mike,

Scrolled through the data screen. Nothing mentioning anything related to a misfire other than on the I/M readiness screen. (Attached screenshot)
IMG_1502.JPG


Also included a screenshot of the code screen.
IMG_1501.JPG
Note that it currently is a pending code, but before I cleared the codes yesterday, the code had matured.

I also noticed when I was out reading these codes that the engine was idling a little rougher than it normally does.
 

Attachments

#6 ·
Have you ever cleaned off the MAF sensor?
I would take a can of MAF and spray it down out of the vehicle. As well as clean the throttle body. That way you don't have to throw money at parts to diagnose it.
Dirty MAF can cause a random misfire causing the truck to run too lean/rich.

Change your air filter recently? Was it dirty?

It can be something as simple as this although if the problem persists then do as Mike says. He knows best! :mrgreen:
 
#7 ·
Air filter changed last summer. Looks fairly clean, and for what it's worth, the little indicator GM has attached to it doesn't indicate it needs changed (although I always wondered if those things worked anyway :mrgreen: ) I have trouble believing it's anything extremely serious because of the mileage I'm getting. From what I've read on here, I'm getting excellent mileage (compared to some others with the same engine) and something serious one would think would exhibit itself in horrible mileage.

Mike seems like a knowledgeable fellow, I plan on trying everything he suggests!
 
#8 ·
I had a p0300 on my 01 and I was never able to find the issue. It had high misfire counts on cylinders 5, 7, and 8 (if I recall correctly). I did all the normal stuff like plugs and wires (was due anyway) cleaned the maf and throttle body and checked for intake leaks. I eventually just said screw it and gave up trying to find the cause. I couldn't feel it and it didn't do it all the time. Only at highway speed for a period of time. And even then it didn't always do it.

The p0300 can be tricky to diagnose sometimes. But other than the usually lifter tap when cold started, I didn't have any engine noise out of the ordinary.
 
#9 ·
This has the lifter tap when cold (don't they all?), but it goes away once the engine warms up. I'll try to get a video tomorrow and see if the noise I was referring is clear. It has to be as loud as it seems from inside.
 
#11 ·
OK Mike,

I know you said that we'd tackle the noise issue after we took care of the misfire issue, but it was quick and easy for me to get a buddy help me make a video this morning. I had him start the truck and left it run briefly so you can hear what it sounds like normally and then about 16 seconds into the video I had him rev it up to 2000RPM. The noise I am referring to come through pretty clear, however you will need to take my word for it that it seems much more sinister sounding in person!



Forgive me for the video being a link. I can't figure out how to embed the video in the post
 
#12 ·
Does the noice continue above 2000rpm or is it just at the rpm range? you could possibly have a slight blockage in the oils pathway to a lifter or two. so basically when the engine idling it has enough oil and is silent. when you increase the rpms it will require a bit more oil and if youve got a slight blockage in the oils path it may not be getting enough oil. this is very unlikely but it would make sense if the tick persists above 2000rpm.
 
#15 ·
stocksilverado25 said:
does it only happen to a cold motor or at all times
This would be the second question asked that was already answered earlier in the thread.
 
#16 ·
Related question Mike,

If I do need to go the replace the plugs/wires route, which plug in your opinion is better:

41-962 Platinum

or

41-110 Iridium?

Does one have advantages over the other? I know I'm to disregard to .060 gap the sticker under the hood tells me. Just curious if there's any real big difference between the two. This Iridium are actually almost $7 cheaper for 8 vs the Platinum.
 
#19 ·
Gm updated the gap to .045".

I didn't even bother setting the gap on the ones I've done. They come pre set. And if your not careful when checking or setting the gap, you'll break the tip off the electrode, which is why Gm says not to gap them and that they come pre set
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top