mspennyhughes

I am the original owner of a 2002 Z28 with 120,000 mi. There was a knocking noise from the engine and I took to Chevy dealer, who came back with a diagnosis of collapsed lifters. Quoted 20 hours labor + $1700 in parts for a total estimate of $4200. I've put a lot of money in my beloved car over the years, but this knocked me over. Anybody have any suggestions? Of course the dealer is always horrendously expensive. But is a collapsed lifter job something I could take to another mechanic. In other words--is it a big, complicated job better left to a dealer?
Any suggestions are welcomed.

Injuneer

I'm going to move this to "LS1 Based Engine Tech". Better chance of responses there. "Drivetrain" is only for everything from the clutch or torque converter on back.

mspennyhughes

Thanks!

Fatdog2

I had a similar experience with a dealer with a rough idle and they wanted $2000. for new injectors and they said that was the problem.Then I went to a real mechanic and he said the car checked out ok and that my injectors fired fine with no leaks,or anything he could find but maybe clean the throttle body and run injector cleaner though a few times.Anyway,on the LS1 engine it has the metal sleeve in the aluminum block and previous posts have heard what they thought was a knock at startup only to be what they call piston slap and that it wasn't really bad at start up.Did you drive the car in and out of the dealer?What I'm getting at I don't know how a car could be driveable with a broken valve train.Sorry for the long post.Hope this helps.I'd get a second opinion.

mspennyhughes

The engine knock that I hear, occasionally, is not usually on start-up. It's generally after the car has been driving a few minutes and it's been around for a few years. Yes, I drove the car in the dealer and as the service advisor was checking the battery connection and we were standing there talking, the knock started. I agreed to let them check it out since I was having the oil changed.
On the way home from the dealer (only 2 miles) the engine did not knock. I drove it 5 miles yesterday (after I got over my fear of "destroying" the engine, as I was warned at the dealer) and the engine did not knock. That isn't to say it won't start knocking again, just hasn't so far.
I am absolutely getting a second opinion because in the VERY least, 20 hours labor is crazy. $1700 for parts is also a jaw dropper because lifters and related parts are nowhere near that costly, even if they mark them up 3 X!
Thanks so much for commenting. I really appreciate it.

shoebox

It's the labor, because I am pretty sure the heads have to come off to replace the lifters.

Fatdog2

I'm sure the oil level has been checked but I was wondering if this could be an oil distribution problem maybe with too light an oil vis. or something somewhere where the oil is clogged up somewhere and not getting up to the heads at idle.Do the cheap stuff first.Hope this helps.Let the board know of the results.

mspennyhughes

I use the synthetic oil recommended by the dealer. When I turned down the $4200 estimate I told them to go ahead and change the oil and honestly, they resisted because even though it had not been changed in almost a year, I had only driven 750 miles. But I insisted and as if to prove a point, the advisor said as I paid for it, that the mechanic had mentioned the oil was clear. I said, I know but it's been sitting in there a long time.
One thing I did not mention is that from time to time, I get the service engine soon light. I no longer panic and I don;t run to a mechanic. Instead I have it checked and its usually P0172 and 175, which are about the same thing.
A couple people suggested using a fuel injector cleaner, but here's the thing--the light goes out after I let it sit overnight. The last time it came on and I read the code was February. I don't guess it's related, but it is something that puzzles me.
I drove the car again today and it's not knocking. When I got home, I let it idle in the driveway for 10 minutes and again, nothing. It puzzles me. I am going to get a second opinion but it's REALLY hard to find someone who is trustworthy. I've been through a few mechanics (I had a great guy who had his own Camaros and Vettes, but he had a falling out with the shop owner and left the area) and have a few suggestions I am going to check out.
Thanks for the idea about the oil distribution. It's worth checking out.

Fatdog2

I went online with your codes and the result I think it might be (if the car runs great now)is either your mass air sensor at the intake needs a little spraying(ever so lightly)or you might have a gas filter clogged and or old gas.The ethenol in gas causes a lot of problems with a car that sits a lot.(Ask Jay Leno)You could run a couple of bottles of techron fuel injector cleaner,I did,the cleaning of the mass sensor and the fuel filter change can't hurt especially if it's been sitting alot.And a fresh tank of gas.Hope this helps.Do the cheap stuff first.My02

mspennyhughes

I have been thinking about using the fuel injector cleaner. I went to Auto Zone and talked to a few people there and they all said the same thing. But I wasn't sure I could trust their opinion.
However, I DID make the effort to run up enough miles to go through that tank of gas and I let it run way down and filled it up about 4 weeks ago.
The car runs great, other than the knocking that only happens occasionally and doesn't seemed to be triggered by anything obvious. It doesn't do it when I start it up and every so often, I hear it and it often just goes away. I wasn't too worried about it until the dealer hit me with a $4200 estimate.
Now, of course, I am worried.

Injuneer

When you hear the knocking sound, is the oil pressure unusually low? A collapsed lifter is going to cause a loose rocker arm to valve clearance. Probably sound like a "click", not a "knock" if mild, or a "clatter" if severe.

Does the onset of the "knock" possibly correlate to the A/C operating?

P0172 and P0175 are the "same" only by telling you a bank of the engine is running rich. But one code is for the left bank and the other is for the right bank. That tells you the source of the problem is something that affects both sides of the engine. Have you checked the fuel pressure? Higher than specified fuel pressure could cause it to run rich. Have you checked the MAF sensor, possibly cleaned it. An MAF sensor reporting higher than actual air flow can cause it to run rich. Could possibly be the MAF sensor installed facing in the wrong direction.

Those codes should clear as "active" only after the engine has been operated three times without the same problem.

Now.... possible connection between running rich and collapsed lifters. Running rich could lead to gasoline bypassing the piston rings, getting in the engine oil and diluting it, causing the oil viscosity to thin out. Lifters won't be happy with thin oil, low oil pressure. Pull the oil dipstick and see if the oil smells like gasoline.

mspennyhughes

I have never noticed a change in my oil pressure when the knock happens. Let's put it this way, if the pressure dropped it never went so low as to cause the Check Gauges light to come on. I pay pretty close attention to the gauges because I had to replace the water pump TWICE in the space of a year, so I probably look at them more than most people when I drive. But I am going to write down any changes when I drive, to see if anything unusual is happening.
I will pull the dipstick today and see if it smells like gasoline. I did see that the 2 codes could be linked to MAF sensor, so I think I'll have that looked it. Again, the codes come and go with no pattern.
I thought about the AC connection. I actually tried to tell myself that was the problem and rarely use it. The AC was not on the other day when it started knocking at the dealer and I had not used it (the AC I mean, not the car) in 2 weeks or more. I don't think there is a connection.

Injuneer

The Check Gages (GM spelling for some reason) light doesn't come on until the pressure drops to 6 PSI. Don't rely on that to tell you the pressure is low. What is the oil pressure at hot idle?

MachinistOne

Mix in some marvel mystery oil and run it for a while, if your lifters have varnished up inside due to poor oil quality or long change intervals that has a good chance of clearing it up and fixing the problem. Just mix in a whole can and drive it easy for a couple hours...then do an oil change with some good 10w-40 due to the age and see how it does.

Fatdog2

I think your oil pump is semi clogged.The oil pump has a screen on it.If you car has sat for years,I think it may be clogged up with old oil.New oil has detergents in it.New oil's detergent's last about 200mi.I would change the oil again and inspect the old oil filter.Cut it open and take a look.I've changed my oil 8 times since I picked it up 2 years ago.Now the oil is clean like new.My money is on a simi clogged oil pump screen.Hope this helps.My02.