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Discussion Starter · #1 ·
Alrighty everyone, picked up a 2003 GMC last weekend. The truck has 316,000 miles on it, but you'd never guess that by looking at the interior, and the exterior looks great except the rust in the usual spots. I think the injectors might need changed. First off, the truck has some kind of annoying tapping noise. It's very faint at idle, and you can only hear it under load. It sounds like an exhaust leak, but I've checked and can't find one anywhere. Its not a ticking sound, its more of a tapping noise. Did a cylinder cutout test- although you could tell an injector was shut off (engine would miss a little) couldn't seem to get the noise to go away completely, so it might be something else other than an injector.

No smoke at idle, not even a haze. The only smoke is when you step on it real hard and it'll blow a little bit of black smoke.

I did a paper towel test. Looked like there might be fuel in the oil, but not sure. wasn't much separation, and even then, the previous guy had an additive in the oil who who knows. Changed it today and will be getting an analysis done by blackstone.

It feels like its not as powerful off the line as it should be. I've got a buddy with a similar truck, and he could beat me in a race. Actual and desired fuel rail pressure are very close- about 1-200 psi difference, so I know thats not an issue.

Finally, I checked the balance rates. Need to do the math and correct them according to the thread, but as it sits right now, we're looking at:

#1: -0.143
#2: 3.664
#3:-2.118
#4: 1.992
#5: -0.055
#6: -4.149
#7: -2.711
#8: 4.164
calculated fuel rate is 9.

What do you guys think? Is there anything else I should try?
 
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2007 Klassic CCSB 2500HD. Six-gun w/speedloader, iDash, and EFILive.
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Well, if you are really, really bored you can do a compression test, and do the bottle test to see if a lot of fuel is being returned, but I don't think that's it. If you can make what... 26k psi (been flying for two days solid and can't think straight), and it only puffs a little black from the go, that's pretty normal.

I'd be more curious about the OA. Wrist pin, bearding, broken lifter guide screw, stuck lifter etc.

Sounds like valvetrain to me. Rare, but it happens. Try and localize it with a Mechanic's stethoscope. Then you can at least narrow it down to one side and pull the cover...if you're the adventurous type. It's tedious but not difficult. Any idea when injectors WERE replaced?
 

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Discussion Starter · #3 ·
I’ve tried to localize the sound. Definitely sounds like it’s coming from the back of the engine, and from the middle. Doesn’t really sound like it’s coming from a particular side. However, if you get under there while it’s running it’s more noticeable from the passenger side. I think I’ll try to go in and adjust the valves and see if that does anything.
 

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I’ve tried to localize the sound. Definitely sounds like it’s coming from the back of the engine, and from the middle. Doesn’t really sound like it’s coming from a particular side. However, if you get under there while it’s running it’s more noticeable from the passenger side. I think I’ll try to go in and adjust the valves and see if that does anything.
It very well could be an injector or two knocking. Your balance rates are off on a few injectors.
As roswell mentions, I would perform a bottle test next and go from there
 

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Discussion Starter · #5 · (Edited)
Alright so I haven’t yet gotten around to bottle testing anything yet, but I’ve been driving it and ran a full tank through it with a strong dose of power service white. Definitely helped a little- slight power increase, and slightly quieter. The sound comes and goes in that it gets louder at times and then quieter. Also, I did hookup and check the Balance rates again. This time, I’d just gotten done driving so it was at full operating temp.

here are the rates in drive, foot on the brake. Cyl. 2 is definitely off. After a while it climbed all the way up to 8.
Grille Automotive tire Textile Mesh Line



Here’s the command values in drive. I’ve heard that they should be close to 35 milliseconds.
Grille Mesh Wood Textile Grey

Here’s the values in park: (balance rates in attachments for some reason)

Grille Product Mesh Textile Wood
 

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Discussion Starter · #7 ·
yes I changed it right away after I got it. The one that was there looked pretty new, but you know how that goes...
 

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2007 Klassic CCSB 2500HD. Six-gun w/speedloader, iDash, and EFILive.
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Indeed I do. You should probably change it again after you get done. You just never know what can flush loose. That got me once!
 

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Discussion Starter · #9 ·
Indeed I do. You should probably change it again after you get done. You just never know what can flush loose. That got me once!
Ill definitely change it again soon. I'll probably run a couple more tanks with the power service and then change it, or if I do injectors. Based on the pictures I posted above, do you think an injector issue is likely?

One thing I forgot to add earlier- I did individual cylinder deactivations on the ones that had the worst balance rates (2, 6, and 8). It didn't really like it much when I did those, except number 2, which didn't do much to change the behavior of the engine. I sent off an oil sample this afternoon so hopefully they'll get that turned around quickly.
 

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I'm the wrong person to answer this. The only reason I ever replacey the injectors in my LB7 was because it was smoking at idle, and there was a 67 stingray parked next to us in traffic that had to roll up their windows. Guilted me right into it. I'm generally a math guy, but I've never learned about the balance rates. Haven't had to yet.
 

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Discussion Starter · #11 ·
Alright so a little update. Bottle tested the whole system by disconnecting the return line at the tank (side note: heard somewhere theres supposed to be a fuel cooler there. Is that true? because mine doesn't). Had just driven to the hardware store and back so it was warmed up. Anyhow, results as follows.

At 15 seconds of cranking, I got just over 50mL of fuel in the container. However, I also measured with the engine running. At 15 seconds, I had exactly 8oz, which according to the google machine is 236.5 mL. I ran out of time to mess with doing the individual banks.
 

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Discussion Starter · #13 ·
Does the "ticking" sound like a typewriter (I know, exposing my age here) - https://static.nhtsa.gov/odi/tsbs/2016/MC-10137981-9999.pdf
No it’s definitely not typewriter tick. It’s more of a tapping noise. Not a clunking like a bad rod bearing, and it’s different than valve tick, although I’m sure it wouldnt hurt to adjust the valves. Sometimes it pretty much goes away, others it’s pretty noticeable.
 

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Discussion Starter · #14 ·
Just found this video. Sounds just like this.
 

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I would run a bottle of the old GM injector cleaner before replacing the injectors. My injectors get out of whack every now and then, run a bottle of this about every 50,000 miles and rates are back to near perfect. Don't recall the part number off hand, perhaps someone else has the number handy, but it cures a multitude of sins.
Mix with 64oz of clean non bio fuel, tie in your lines at the quick disconnect at the firewall, takes about an hour to an hour and a half of idling, but you will see a definite improvement in you balance rates. Do NOT put this in your fuel tank.
 

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Discussion Starter · #16 ·
Alright guys update for y’all. Not yet sure if the noise is gone yet, but I have confirmed that the injectors are well and truly done for.

I decided to tear into it see if I could find anything. Due to the fact that the injector history is unknown, and the balance rates are a little off, I ordered up a set of reman Bosch from Lincoln, and I’m glad I did. Got those a couple days ago and started on the change today.

Pulled everything apart on the passenger side without issue. Went to pull the injectors- I started by turning the injector side to side in the bore as much as I could to help break it from the cup. No matter what I did, I couldn’t pull them by hand alone- I had to use two pry bars to wiggle them up and out of the bore. I was immediately dismayed to see the massive amount of burned oil covering the injector. The nozzles were caked. I have no idea how this truck was running. Must be Chevy tough.


Wood Font Metal Auto part Fashion accessory

Every single o ring was either cut or crimped. One of them was badly frayed. I could tell by looking that the oil had been entering from these o ring issues because of large burned trail of oil starting at the bad part.

I also pulled the cups (side note: the harbor freight blind bearing puller with slide hammer works great for this. Did have to make an arbor with a pulling bolt for number 7. Pic below) they cleaned up nicely with an acetone bath and drill powered spiral brush, so they will be ready to drop back in with new orings and locktite.

here is the arbor I made. Excuse the crappy welds.
Motor vehicle Automotive tire Vehicle Hood Wheel
 
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About four months ago I had to replace mine with only 78k miles. Mine were somewhat carbon up also which was disappointing as I had use additives since the truck was new. Good news is once finished the truck runs new.
 

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Discussion Starter · #18 ·
Man that drivers side rear injector cup is a real beatch to get out. Of course that injector was carboned up so the cup had to come out for cleaning. Finally got it out though. Two of the injectors on the drivers side were just fine- no carbon coating and the orings were intact. So whoever put them in had a 2/8 success rate 🤣. Pretty happy all around because I only had to extract 2 valve cover bolts in total. Got a bunch of new ones at the hardware store and will throw out any that even started to strip.

Here’s a pic of an old injector next to a new one;

Handheld power drill Gas Auto part Drill Machine
 
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