My Envoy is approaching 170000 miles and has developed an engine noise like a rod bearing knocking. I have my OTC mechanical oil pressure gauge installed. At a cold startup, I see 80 pounds of pressure on the gauge and have no engine noise at idle. Driving down the road, the oil pressure gets close to 95 lbs at approximately 2000 rpm then drops back to 80lbs when the transmission shifts into second gear. After everything warms up to operating temperature, cruising at 65 mph, I'm seeing 70lbs on the pressure gauge. I hear no noise driving down the road. When I come to a stop with the engine at idle in gear i have 26 to 28 lbs of oil pressure, and the engine is quiet. When you take off again at about 2000 rpm, just about the time the transmission changes gears, it sounds like a rod knocking . In park after the engine is at operating temperature, if I bring the rpm up to 2000 rpm, it sounds like it is knocking. When the engine was cold, I pulled the spark plugs and brought each individual piston up to top dead center, starting on the down stroke, I took a wooden dowel and tried to push each piston down to check for a bad rod bearing and didn't find any. I again brought the engine up to operating temperature and using my Tech2 scanner, I did a cylinder balance test at 2000 rpm. Each cylinder dropped the same rpm but the knocking noise never changed. I'm at my wits end here. I have access to another low mileage engine but I'm unable to perform the swap myself, so before I spend the money to have it swapped, I'm looking for suggestions.
2002 Envoy 4.2 engine noise need help!
- Thread starter francerichard
- Start date
I'm using Valvoline 5w30 semi synthetic. 5.5 quarts of oil and 1. 5 quarts Lucas oil stabilizer. It is finally a warm day here so I just got back from doing about 90 mile round trip drive. Mostly 70 mph. I kicked it into passing gear several times up to 6000 rpm. I pulled off to the side of the road and it was quiet. Oil pressure at 70mph was 68psi. When I came to a stop, it idled in gear at 24psi.
I have always used Lucas. My Bonneville that I bought with 30,000 miles on it, alwasys got 1 quart of Lucas with 4 quarts of Valvoline. It had over 400,000 miles on it and still running strong when the rear suspension rusted out from under it.
Mooseman
Moderator
Lucas has the tendency to increase viscosity since it is as thick as honey so I would do an oil change and avoid adding it. This engine does run on higher oil pressures compared to others like the V8 but this may be a bit too high.
I am currently using Lucas in my Av because it is having low pressure issues. It did bring it back up along with 10w40 diesel oil. I will be replacing the oil pump and dumping this stuff out. I have heard that Lucas aerates the oil causing foaming.
I am currently using Lucas in my Av because it is having low pressure issues. It did bring it back up along with 10w40 diesel oil. I will be replacing the oil pump and dumping this stuff out. I have heard that Lucas aerates the oil causing foaming.
I have only had this Envoy for a short time. I bought it from the original owner and he had always had it serviced at the GM dealer. He had just had the oil changed there before I bought it. I put 4000 miles on that oil change. I had been experiencing the issues I listed above for about 3000 of the 4000 miles on that oil change. I changed the oil myself and added the Lucas with no difference in the noise that I'm hearing. When I first started hearing the noise, I had only put a little over a thousand miles on it. That is when I installed my mechanical oil pressure gauge. I had the same pressures then as I do now with the Lucas. I'm just not sure what to do next.
Okay. I changed the oil and filter using Valvoline 5w30 and an AC filter. My oil pressure is the same as before. My noise that i am hearing is the same as before. I put my Envoy up on jack stands and started it up. I had my son hold the rpm at 2000 while I was under it listening for the noise. It was very loud and sharp sounding only at the transmission bell housing. I noticed the flex plate was not running true, it had a wobble in it. I shut the engine off, marked one of the lugs on the torque converter and the corresponding spot on the flex plate, then removed all of the converter bolts. I pushed the converter back in as far as it would go and had my son start it back up while I was watching the flex plate. Just as soon as the engine started, there was a terrible noise and the converter turned. Shut the engine off immediately. The converter was still in as far as it would go and I could turn it without binding or touching the flex plate. Could I have a broken flex plate causing all of this? Wanting thoughts before I pull the transmission to check.
Mooseman
Moderator
Yes, it does happen and sure looks and sounds like it is that.
gmtnation.com
<FIXED> Lifter noise & dull knocking (bottom end?) troubleshooting
And I also forgot to mention, there's a second crack opposite of the one... @Sparky will do man, may end up asking Brandon's father to borrow his extra truck until I can install the flex plate next weekend. It'll arrive Wednesday apparently. Kinda nervous now seeing how it has two cracks. Also...
gmtnation.com
Mooseman
Moderator
And here's a post that indicates that the engine and tranny mounts may be at fault and should be replaced.
gmtnation.com
Truck took a few tries to start, now have knock/tapping noise?
Went to start my truck after it sat a day, turned key and got nothing. Similar to as if you had a low battery. On some tries though it felt like the starter was getting caught up possibly. Well several tries later I heard and felt a loud thud noise and it started, idled roughly with gray smoke...
gmtnation.com
Mooseman
Moderator
And this post has info regarding the R&R of the tranny.
gmtnation.com
Removing Trans for main seal leak.
So I'm removing my transmission so I can replace the main seal and main cover gasket. Any tips for removing trans? Never pulled the transmission out of a trailblazer before
gmtnation.com
gmcman
Member
- Dec 12, 2011
- 4,656
Coincidentally after I installed my oil temp/pressure gauge, I would see similar reading when cold. Idling hot oil pressure over 20 PSI is pretty good for the I6.
I went through the same diagnostic steps trying to figure out the noise in my engine, turned out to be worn rod bearings but I also had some other issues going on with carbon deposits from a clogged oil catch can..(long story)
Usually when a rod bearing is near it's end, the motor will be quiet at idle when cold and as the oil heats up the bearing will show it's face.
A wrist pin would make a noise when transitioning from a high idle to normal idle, ie, raising idle to about 2000 RPM then right when you release the gas it will rap a few times, but at a higher pitch.
The water pump has been known to make some shrilling knocking noises but at a more random pace, not at 6 per second at idle.
I would drain the oil and see if you have any gold glitter. Perhaps even cut open the oil filter.
I will see maybe 80 tops on mine when cold. But never have I seen 95 lbs at 2000 rpm at any temperature, but then mine has over 284xxx miles on it.
somebody posted here or somewhere ... i do not remember, that the oil pressure gauge on the TB's are a Joke, what he means ( and explained ) that is not a real pressure sensor, it is something tied to the RPM so when you rev the engine the needle moves aka simulating more oil pressure, so you can be low on oil and the needle "measure normal" as you rev up
there is the LOW OIL red light that lights up when the level is too low
but to my taste i think there is some damage on the engine or at least much extra wear and tear from running it on low oil condition
Can somebody confirm this.
Found IT !!!
so the bulb ( i replaced it on mine also it was leaking ) only reads too low pressure and trips the
RED light on the dashboard, but not at actual PSI pressure, the PCM fakes as your REV the engine
the needle moves up.
see the below video
there is the LOW OIL red light that lights up when the level is too low
but to my taste i think there is some damage on the engine or at least much extra wear and tear from running it on low oil condition
Can somebody confirm this.
Found IT !!!
so the bulb ( i replaced it on mine also it was leaking ) only reads too low pressure and trips the
RED light on the dashboard, but not at actual PSI pressure, the PCM fakes as your REV the engine
the needle moves up.
see the below video
Last edited:
Mooseman
Moderator
And it will be one of life's great mysteries why the engineers went this route. Like it wouldn't have been that difficult for them to put a real sensor (same as LS engines) and have the PCM translate that into real pressure readings.
So this song is dedicated to that fake gauge:
So this song is dedicated to that fake gauge: