'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
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
Thank you for your input. Just trying to help out my mechanic, he's doing a lot of work locally but with older cars there's always some stuff to learn for everybody, especially in american cars out here in these times.
Measuring oil pressure with a real gauge is on it's way as I was told. I'll let you know what the results are. The engine was rebuilt by a trusted machine shop and I delivered the engine myself and got it back myself and delivered it to my mechanic to have it installed. The rebuild consisted of: new crank bearings (lowest possible oversize), polished crank to fit those, new pistons (largest available from Enginetech or Sealed Power, can't remember now - due to excessive cylinder wall scoring, but I calculated the displacement pretty much rose roughly from 2.5 to 2.6 because of this), new piston rings for the new pistons, new pushrods, new valve stem seals, new camshaft with new lifters (roller), new cam bearings, new cam gears. Adding to that cylinder honing, block and head surfacing, block and head pressure checked, valve polishing, new head gasket, bolts and head torqued down according to service manual specs. I remember the shop calling me that the valves are good and there wasn't any need for ordering those new. Got all the old parts back so I guess the job was done right. They did engine rebuilds before for me and I haven't had any complaints.
So we're still looking unfrotunately but can't rule anything out.
A cracked exhaust might be in play since pretty much anything outside the engine was left stock apart from gaskets, etc. Will make sure it's checked and see if there's something suspect there.
[This message has been edited by cebix (edited 01-21-2021).]
A cracked exhaust might be in play since pretty much anything outside the engine was left stock apart from gaskets, etc. Will make sure it's checked and see if there's something suspect there.
Look for scorch marks around the exhaust manifold and gasket. Could appear grayest in color or black if you're running a bit rich.. When my 2.8 manifold leaked I could put the back of my hand (more sensitive than palm) near the manifold and feel the pulsing of the leak.
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
Still don't know what is knocking however the shop measured the oil pressure with an external gauge and it was over 4 bar at 2000 rpm. That's almost twice what the service manual says it should be. They cleaned the oil pump and now it drifted down to 2,5 bar so there was something wrong either with the pressure regulator valve(?) or some dirt got stuck in it.
However they say it still has that slight knock/tick sometimes. They checked those lifters and pushrods and they didn't notice any wear so far. They're gonna change the oil and see what's in the pan.
A quick update. The problem seems to be resolved. Drove 200 miles today and yesterday with no knocking whatsover.
It was probably indeed the high oil pressure. Probably the pressure regulator valve thing in the oil pump got stuck. The shop adjusted the pump, changed the oil and all seems ok for now. The conclusion was that the high oil pressure probably starved a lifter or more of them of oil and caused the lash to be excessive. But that's just a theory.
Another thing I think I didn't mention was that for some days before the knock appeared my oil pressure gauge was pegged far right. After some reading I concluded there's no chance it's that high and it's probably a cut wire or the sensor failed or the gauge itself. Now the gauge states the correct oil pressure - about 1/4 of the scale on hot idle and about 3/4 of the scale driving highway speeds. So there's a high chance it did indeed show the correct oil pressure.
Another thing I think I didn't mention was that for some days before the knock appeared my oil pressure gauge was pegged far right. After some reading I concluded there's no chance it's that high and it's probably a cut wire or the sensor failed or the gauge itself.
If that was the case, then the high oil pressure readings would've still been indicated with the key ON and the engine not running. From what you've now informed us about the oil pump, I suspect that was not the situation.
I can't say for sure but that's what the shop told me. One thing is for sure that they definitely didn't change any lifters or other engine parts since these are unobtainum here. They read the oil pressure with an external meter, not the dash gauge.
EDIT: I can't remember 100% if the gauge read high on ignition on engine off.
[This message has been edited by cebix (edited 03-01-2021).]
No idea what the hell is it. Oil pressure gauge works and shows the pressure correctly. The knocking just comes and goes unrelated to anything as far as I can tell. Sounds like a lifter to me but what do I know.
If the tick came back its probably a hung valve lifter. Lifters should be easy to find in Europe as they were used on a large number of different vehicles. As for the Duke 4 engine; it is far easier to work on that engine, than on most all Japanese engines. Lifters are usually very inexpensive parts but if you order them they will ask for your engine code.
------------------ " 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 "
Another observation... Your oil pressure was reading really high, but started reading normally after the oil pump was removed, cleaned, and replaced. The oil pressure is measured right after the oil pump. That leads me to believe the something may have been restricting the oil flow, downstream of (after) the pump. Once the pump was removed, whatever may have been restricting the flow may have fallen out, when the oil flowed back out. It's possible that there may be something else in there that is restricting oil to one or more of the lifters. Not too difficult to imagine, since it's a fresh build. Now... how to deal with that is an entirely different question. If I was doing the work, I might be inclined to take all the lifters out, and crank the engine over until it flowed enough oil to push out whatever might be in there.
