'85 duke auto w/AC. Engine rebuilt a year and a half ago.
Amidst other problems this car has there seems to have occured something more severe this time.
After doing about 200 miles straight I noticed a slight knock coming and going from the engine. It started off quiet with low rpm, disappeared for a few seconds at higher revs and came back with lower, etc. More like ticking actually than knocking. The next day I started it cold and the knock was HUGE not going away. Getting worse with higher rpm. After about a minute of running it disappeared altogether. Drove about 5 miles and the ticking/knocking was coming and going.
My immediate guess was one of the lifters has gone bad. Those were all new from Enginetech. However my mechanic got around to them and said they were fine, not one is soft and they are all good. Still don't have a diagnosis and looking for clues.
Anyone? I've been reading about piston slap, could this be a possibility?
Piston slap usually occurs more often when the engine is cold. If the sound is more a tick then its likely a lifter or loose rocker arm.. If the sound comes and goes then my guess would be the valvetrain. Have you checked for clearance/adjustment ? Mark harmonic balancer with a chalk mark. Rotate 1/4 turn check by trying to lift each pushrod with your fingers for any looseness. Rotate 1/4 turn try again and keep doing this for two complete rotations. If you can rattle any pushrod by feeling excessive up-down clearance, there is your problem.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Piston slap usually occurs more often when the engine is cold. If the sound is more a tick then its likely a lifter or loose rocker arm.. If the sound comes and goes then my guess would be the valvetrain. Have you checked for clearance/adjustment ? Mark harmonic balancer with a chalk mark. Rotate 1/4 turn check by trying to lift each pushrod with your fingers for any looseness. Rotate 1/4 turn try again and keep doing this for two complete rotations. If you can rattle any pushrod by feeling excessive up-down clearance, there is your problem.
Yeah when cold it was ticking/knocking very loud, like obnoxiously loud - something I heard on another engine when a valve burned out. However with that engine with revs it became happy. The Fiero with revs was ticking/knocking louder. A minute after running cold it just disappeared but came back quietly when hot under different conditions and went out again.
Yeah when cold it was ticking/knocking very loud, like obnoxiously loud - something I heard on another engine when a valve burned out. However with that engine with revs it became happy. The Fiero with revs was ticking/knocking louder. A minute after running cold it just disappeared but came back quietly when hot under different conditions and went out again.
Its not going to get fixed by guessing. You will need to go through the checks to diagnose the problem.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Its not going to get fixed by guessing. You will need to go through the checks to diagnose the problem.
Yes, working on it with my mechanic, was just looking for some ideas since he ruled out the hydraulic lifters. Maybe these engines have something in common that cause this, that's why the topic came about.
...working on it with my mechanic, was just looking for some ideas since he ruled out the hydraulic lifters.
Just how did he rule them out?
Why don't you shoot some video with your phone and upload it to YouTube for us to see. We're more interested in the audio, so get the phone in close to various parts of the engine while it's running and ticking/knocking. Just be careful around moving belts and pulleys!
Why don't you shoot some video with your phone and upload it to YouTube for us to see. We're more interested in the audio, so get the phone in close to various parts of the engine while it's running and ticking/knocking. Just be careful around moving belts and pulleys!
Well he said none are collapsed or soft and he's 100% sure it's not the lifters. Shooting a video is gonna be troublesome now since the car is ~200 miles away. I can say however that from youtube videos it sounds like those bad lifter and piston slap videos. Definitely not a rod or crank bearing sound, not that metallic kind. Wish I recorded a video when it started first but didn't think the diagnosis would take this long.
You can make your own "Stethoscope" with a piece of 1/2" Heater hose....
Just another possibility; On my CVX-20 Jet BOAT 460 engine I had a loud ticking sound- like two wrenches clanging together...Turned out to be an exhaust leak thru one of the smog pump ports at the end of the head- in the enclosed engine compartment it sounded mechanical, not like a typical exhaust leak.
Although this applies to my BOAT with a completely enclosed engine compartment, I have never heard what an exhaust leak may sound like on a Fiero...especially considering where it may be located on the engine....
Yes, a cracked exhaust manifold can certainly make some strange "ticking" noises, especially if the crack is located next to an individual port. And it can come and go as well, depending on metal expansion/contraction from heat.
[This message has been edited by Patrick (edited 01-20-2021).]
Sorry for your situation. If the knock is as loud as you described and it got better without doing some work, I doubt it's a rod knock. With the exception of someone adding 90 wt gear oil to the crankcase I've never heard of one getting better on its own. Excessive rod bearing clearance is not like a lifter tap where the slack can be taken up with oil pressure. Have you checked your oil pressure with a real pressure gauge connected to the engine? Let us know.
On the other hand I would be curious why a 2 yr old engine rebuild would develop an engine knock. Just the words "engine rebuild" leaves a lot of open areas such as what was included. Even an honest mechanic may have to depend on a trustworthy machine shop to do some of the work. My neighbor had a valve job done and still had problems afterwards. I took a look and discovered a valve job could miraculously be done without removing the head from the block and the new head gasket came with the factory color already on it. Lesson learned it doesn't hurt to ask for the old parts even if you're not sure what you're looking at.
Keep us posted. Maybe it's just a cracked exhaust manifold. They can expand and contract due to temperature changes and make various sounds depending on the size of the fracture.
Spoon
------------------ "Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut
