78 P.C. L-82 Strange Engine Noises

[Stuart F.]

Last night my son picked up his 4th 78 Pace Car, an L-82 Automatic. The previous owner had a lot of work done on the engine (R & R), ringing up a large bill. He claimed it just was not running right, so he took it to a shop that specializes mostly in exotic foreign sports cars. They replaced the entire valve train (cam, lifters, timing chain and sprockets, etc), and rebuilt the carb, distributor and alternator, including the transmission - some $9k worth of work - eek!

My son had driven the car before he bought it and said that after it was warmed up, it ran fine (has newly rebuilt brakes too). When I first heard it during loading, and again when we got it home and drove it, standing next to it it sounds like a Diesel!

Now I admit, I don't have much experience with 70's/80's emission Vettes, so I thought I'd throw it out there for some advice from the C-3 experts. Being as how the work was done by some Ferrari mechanic, I have concerns for the following:

- Exhaust leaks at the packings and/or heat riser valve

- Operation of the air pump system

- Operation of the EGR

- Distributor and valve timing/positioning

Mind you these are from my first observations on a dark street at night. We'll be looking at it closer when time permits. The car has a lot of redeeming qualities, i.e. 8000 miles on it since bought from Pro-Team in 2000 (42 miles on it then), it is all mostly original and in pretty good condition in, out and under, and the price was right.

Any thoughts appreciated, and I'm sure he or I will post more about it - specially if he decides to "cherry" it up for judging.

Stu fox

[Paul J.]

Re: 78 P.C. L-82 Strange Engine Noises

Stu, I think you've named the four areas where it could be. My 78 L82 was notorious for noise from the EGR, and GM had several issues with these in the late 70's and early 80's. However, if it sounds more like a diesel, it could be timing related.

Why was so much work done on a low mileage motor?

Paul

[William C.]

Re: 78 P.C. L-82 Strange Engine Noises

If it still has one, anybody check for a clogged cat converter?

[Stuart F.]

Re: 78 P.C. L-82 Strange Engine Noises

Paul;

Thanks for your reply. Good question. The previous owner is a P.I. Attorney, and perhaps they saw him coming and decided to exact some revenge, we don't know. Practically, we surmised that it may not have been driven or even started for a long time (typical low mileage P.C.) and when he did try to start it he had a very rough runner with bad gas and possilby some clicking hydraulic lifters and fouled plugs, etc. He then took it to a friend (?) near his home and left him a blank check.

When it is warm, it runs strong, but hesitates and even popped through the carb once during warm up. The engine was repainted and detailed very nicely - same with the tranny. It really is a decent car that just needs some attention. I'm sure we'll get it sorted out, but hope not to have to open it up again. Looking at all that plumbing makes me appreciate my 63 all that much more.

Stu fox

[Stuart F.]

Re: 78 P.C. L-82 Strange Engine Noises

Thanks Bill. Yes, it still has the original cat converter. Good thought.

Stu Fox

[Edward J.]

Re: 78 P.C. L-82 Strange Engine Noises

Stu,Its tuff being a TDB mechanic, There are many moving parts in a running engine. Some of the things that are common with the L82 engines were wrist pin noises. this type of noise generally goes away after the engine warms and does kind of sound like a diesel engine when cold. This problem really would not harm anything,The engine can last for many years, if not for its life. If you can maybe do a video of the engine started when cold. Its been done here before and you may get some good results. Ed

[Tom R.]

Re: 78 P.C. L-82 Strange Engine Noises

When I first heard it during loading, and again when we got it home and drove it, standing next to it it sounds like a Diesel!

Being as how the work was done by some Ferrari mechanic, I have concerns for the following:

- Exhaust leaks at the packings and/or heat riser valve

- Operation of the air pump system

- Operation of the EGR

- Distributor and valve timing/positioning

Stu

I've been around 78s and have had to troubleshoot many issues. Also have played with the devices in your list and cannot believe they would cause engine diesling except the Distributor and valve timing/positioning. My 78 PC had issues when I first got it. It was a mechanically neglected 56k mile vehicle. Troubleshooting, emission hoses were routed incorrectly, timing was off, some devices not connected at including the EGR. Rebuilding the carb finally cleared up the remaining issues. If I were to bet, I would guess the distributor position.

[Stuart F.]

Re: 78 P.C. L-82 Strange Engine Noises

Ed and Tom;

Thanks for your responses. The wrist pins is a new one for me, but we'll keep it in mind as we sort this L-82 out. I will recommend to my son (Brian), that we start by reviewing all the service and repair receipts he got with the car to determine where they may lead us, i.e. just how far down this engine went (heads, cam or short block). I've only owned about 3 GM cars of that era and they were all new, so I didn't get into them too deep as, for one thing, they were all still under warranty.

One item I believe I read about had to do with the air pump. As I recall, control of it during warm up diverted the air through a muffler of some sort, so that will probably be one of the first items we check. I've dealt with a number of distributor issues including ones being a tooth off, and cams that were also a tooth off. They were HP engines (Chevy 348 and a Poncho 389 that was bored and stroked. In either of those cases, the engines would wind up to 5000+ RPM real fast and then shut down (go flat) as if they had a governor. The Chevy probably was experiencing valve to piston contact as it bent the push rods.

Thanks again for your input. I'm sure either I or Brian will be posting again if we run into any stumpers.

Stu Fox

[Clem Z.]

Re: 78 P.C. L-82 Strange Engine Noises

Ed and Tom;

Thanks for your responses. The wrist pins is a new one for me, but we'll keep it in mind as we sort this L-82 out. I will recommend to my son (Brian), that we start by reviewing all the service and repair receipts he got with the car to determine where they may lead us, i.e. just how far down this engine went (heads, cam or short block). I've only owned about 3 GM cars of that era and they were all new, so I didn't get into them too deep as, for one thing, they were all still under warranty.

One item I believe I read about had to do with the air pump. As I recall, control of it during warm up diverted the air through a muffler of some sort, so that will probably be one of the first items we check. I've dealt with a number of distributor issues including ones being a tooth off, and cams that were also a tooth off. They were HP engines (Chevy 348 and a Poncho 389 that was bored and stroked. In either of those cases, the engines would wind up to 5000+ RPM real fast and then shut down (go flat) as if they had a governor. The Chevy probably was experiencing valve to piston contact as it bent the push rods.

Thanks again for your input. I'm sure either I or Brian will be posting again if we run into any stumpers.

Stu Fox

remove all the belts and start the engine and see if the noise goes away. that will tell you if it is internal or external

[Stuart F.]

Re: 78 P.C. L-82 Strange Engine Noises

Clem;

Thanks. Sounds like a good approach.

Stu Fox

[Stuart F.]

Re: 78 P.C. L-82 Strange Engine Noises

Yesterday, my son and I spent some time trouble shooting this 78 P.C.. With a stethoscope, the diesel like sounds are present everywhere I listened; i.e. block, heads, valve covers, intake manifold, etc. Vacuum gauge showed a steady 16" hg at a 600 idle speed.

We found the EFE was disconnected and capped off, so the heat riser valve (although free) was inoperable. The vacuum hose from the temp valve on the thermo housing was instead routed to the air cleaner. We corrected that and ran a new hose from the proper base connection on the carb to the air cleaner using a tee. Both of the vacuum motors on the air cleaner seemed to work fine. We also found the choke spring was not properly engaged to the link in the housing. The carb did look like a recent rebuild. Owing to the missing bolts and improper routing of various hoses and wires, it apperas that indeed the hood and radiator had been removed to make a cam change (as noted in the receipts). It is obvious that the shop that did the work was not familiar with "emission Corvettes", and were generally sloppy about tagging and bagging hardware.

Believe we made some improvement in the engine operation, but the diesel sound is still quite present and concerning. I'm not that familiar with the L-82's of that era. My son says he recalls the other ones he had had similar characteristics, but not so pronounced. Wish I could spend more time in diagnostics of this beast, but my son doesn't seem too concerned or motivated.

Stu Fox

[Clem Z.]

Re: 78 P.C. L-82 Strange Engine Noises

did you try readjusting the valves ??

[Edward J.]

Re: 78 P.C. L-82 Strange Engine Noises

Believe we made some improvement in the engine operation, but the diesel sound is still quite present and concerning. I'm not that familiar with the L-82's of that era. My son says he recalls the other ones he had had similar characteristics, but not so pronounced. Wish I could spend more time in diagnostics of this beast, but my son doesn't seem too concerned or motivated.


Stu, Thers nothing thats different about the L82 engine than you 63 engine, its just a emisson motor for that era. it should sound the same as any other small block, with the exception of the A.I.R. system maybe make a little noise while listening to it run with the hood open.When listening to if running if theres a lifter making noise it sounds like a ticking noise, as I explain the noise. wrist pin noises do sound like a diesel engine when the engine is cold and generally go away after 3 or 4 minutes of running. if the noise is constant it may be something with the rotating assy.(crankshaft)

[Stuart F.]

Re: 78 P.C. L-82 Strange Engine Noises

I tend to agree about "tappet" noise from my experience, but it has been so long since I had a Chevy engine with hydraulic lifters - like maybe 1956. I can't find any evidence that they dug into the short block and, with only 8000 miles on it, I tend to doubt/hope against that.

Clem; what could they have done so wrong to make so much hard knocking sounds in the valve train? The engine seems to run smooth, pulls good steady vacuum, starts well, and runs good tremperature and pressure. The noise is a very metallic rattle and it is present throughout the engine, i.e. every cylinder - so we'll see. Thanks for the input.

Stu Fox

[William C.]

Re: 78 P.C. L-82 Strange Engine Noises

Is the sound constant across all the rocker arms? If you run the engine with a valve cover off can you feel it in the pushrod/rockers? If you load the engine with the brakes locked does the sound change (more/less noise)