during mid-hard throttle (while driving or in neutral) there is a terrible screeching sound coming from the top/rear of the engine. when this sound occurs, the engine loses power immediately and will hesitate/buck.
the ECM threw a code 45 Oxygen Sensor Rich.
several people have suggested a vacuum leak. so here's what i've ruled out while looking for the vacuum leaks: NOT belt squeal NOT a bad alternator NOT a clogged/noisy PCV valve NOT a bad distributor NOT related to fuel pressure (fuel pressure reads fine and fluctuates as it should during throttle)
still can't find a vacuum leak, so i'm wondering if anyone has any input. am i just going to have to replace all of the vacuum lines?
Sounds like a vacuum leak. Try spraying carb cleaner around the upper and lower intake area and see if the idle changes. A length of clear tubing could be used like a stethoscope, stick one end in your ear and the other by the engine, keep moving it around til you hear the squeal real loud. If you have a gasket partially sucked in, it can act like a reed in an instrument and make a squeal noise. I had an exhaust manifold gasket leak on my 8100 Chev pickup engine that squealed real loud on accell, I would assume a vacuum leak in the intake somewhere could do the same thing. You get a rich code because the vacuum leak is causing a lean condition and the ECM is dumping in fuel to compensate.
[This message has been edited by seajai (edited 06-20-2014).]
What does the volt meter do when the squeal occurs?
If you hold the throttle at a higher RPM does the screech stay or does it stop?
the volt meter stays constant. and throttle held open, the sound will either dissipate or stay constant (depending on the throttle position).
I'm going to keep looking for leaks today. i may have to take off the upper plenum to check its gaskets too. does spraying carb cleaner leave a mess over the engine, though?
Originally posted by Enix: NOT belt squeal NOT a bad alternator
These things were likley to me, how did you rule them out? Bearings in something the belt is connected too. Does you car have AC, and does it do it with it turned off?
I woudlnt call any air leak a screech, but maybe someone else would.
[This message has been edited by 2.5 (edited 06-20-2014).]
These things were likley to me, how did you rule them out? Bearings in something the belt is connected too. Does you car have AC, and does it do it with it turned off?
I woudlnt call any air leak a screech, but maybe someone else would.
i don't have AC. all i did was take the belt off and drive the car around the block off the battery. which means the water pump and alternator were inoperable. the symptoms were still there. =/
[This message has been edited by Enix (edited 06-20-2014).]
Is your warm engine idle around 950? If so, there is no vacuum leak. Now that may change at a higher RPM, and a crack in the EGR tube, or loose connections on either end, may be able to produce a 'screech'.
Is your warm engine idle around 950? If so, there is no vacuum leak. Now that may change at a higher RPM, and a crack in the EGR tube, or loose connections on either end, may be able to produce a 'screech'.
yeah, my idle is just below 1k. in addition, i removed the EGR flex tube from the upper plenum and blocked the hole... the engine still screeched and stumbled with throttle. =[
i've eliminated any suspicion of the EGR vacuum line, the FPR vacuum line, the vapor canister vacuum line, the PCV vacuum line, and the tiny MAP vacuum line.
oddly enough, i'm now unable to reproduce the screech sound when the car is being revved in neutral. it only occurs while driving.
neutral or driving, however, it stumbles and hesitates so much that it won't rev past 4.8k
I think if an air leak is so big that it runs lean it could hesitate and buck. But I still dont know about a screech sound, or why an O2 rich code would show up..
If a cat us plugging could it cause this symptom?
[This message has been edited by 2.5 (edited 06-20-2014).]
Has it always been like this? Anything replaced or repaired lately?
my friend and i just rebuilt the entire engine back to stock. : block was hot tanked and measured : 20-thousandth bore job with new oversized pistons and rings to match : ground crank with new oversized bearings to match : new cam bearings, lifters, valve stem seals, and head job : professionally cleaned fuel injectors with all new o-rings and seals : new oil and water pump : newer gear reduction starter, reman distributor, and CS style alternator : all new seals and gaskets of course : new temp sensors and oil pressure sender
that was about a month ago. I just put on the first 600 "break-in" miles on it and it ran beautifully! now it just started having these problems last week. =[
it's a manual so there's not much to go wrong there... i also laid under the trans while a friend revved the engine and the sound is definitely coming from the top, engine side.
as for injectors, i was curious about that too. people say to use carb cleaner when looking for vacuum leaks and not brake cleaner, because brake cleaner is bad for EFI components... well, when we did the rebuild i cleaned the injector filters (those little conical basket screens) and the fuel rail with brake cleaner. i wonder if i messed something up. =/ i used brake cleaner because my friend said he'd used it before on injectors and has never had a problem.
as for the article, i like they're comparison to a screeching reed induced by air, like a high-pitched duck call. that's exactly what i was hearing. but he doesn't mention power loss with it. =/
as for the article, i like they're comparison to a screeching reed induced by air, like a high-pitched duck call. that's exactly what i was hearing. but he doesn't mention power loss with it. =/
Maybe something with that much power it might go less noticed. It could be just one. I dont know alot about injectors, but its a thought.
a bad throw out bearing can screech too, but dont think it would affect power ... maybe let the clutch slip though. Seems like you checked all the obvious possibilities. Ive never heard any kind of vacuum leak screech. A pulley or something could be rubbing, but you said it also did it with belts off. Maybe pull off the valve cover and see if the tops getting enough oil. A burned out cam bearing can squeal, but your sounds higher up. Lots of other suspension stuff could screech but you said it does it setting still with engine running. You might try spraying some silicone around and see if you can make it stop to narrow down what your looking for. You got me stumped otherwise. My first guesses would have been alternator belt or AC belt.
Listening closer to the audio, maybe its an air leak where the air cleaner boot goes to the throttle body or filter canister. Seems to do it when you accelerate, but dont think that would affect performance either.
[This message has been edited by rogergarrison (edited 06-20-2014).]
From what I am seeing it is happening when you are moving the throttle open. So that means it isn't happening when the vacuum is highest. It seems somewhat coordinated with when the airflow is higher. A piece of garden hose to listen through might help in finding what area of the engine the noise is coming from. Also taking off the intake snorkel and seeing how that affects things would help.
So if taking off the intake snorkel makes no difference then I would look at bearings.
Any chance that sound is coming from the distributor? It's been a while since I had a 2.8 but I seem to recall a bearing or shaft problem with the 2.8's distributor.
A piece of garden hose to listen through might help in finding what area of the engine the noise is coming from. Also taking off the intake snorkel and seeing how that affects things would help.
So if taking off the intake snorkel makes no difference then I would look at bearings.
i tried using hose to find the sound, but the sound is so airborne that i can't track it down. i took the snorkel off and it became so loud that i couldn't hear the screech, but the engine still stumbled and hesitated. i don't think it's bearings because each and every internal bearing only has 600 miles on it. that, and i don't think a bad bearing would cripple the entire engine like that. =/
quote
Originally posted by Purple86GT:
Any chance that sound is coming from the distributor? It's been a while since I had a 2.8 but I seem to recall a bearing or shaft problem with the 2.8's distributor.
i actually swapped distributors with a friend's working one and the screeching and hesitation still appeared. so i've ruled that out too.
i've also just swapped the MAP sensor with my friend's working one and the symptoms are STILL there.
You goosed it pretty good one day, got a screeching sound and loss of power at higher rpm?
Sound is coming from the rear of the engine? I'm not sure if it is to the right or left..
Can we get a sound clip or video?
A bearing failing will often happen early in it's service life. Usually screeching is a bearing, hissing is vacuum (or boost).
What about timing chain components? I assume this was changed during the rebuild? If the cam is slightly out of time, it could result in loss of power at higher RPM and loss of compression through the intake or exhaust (making some sort of sound I'm sure).
At this point we need to systematically eliminate everything until the problem is identified. Ma favorite that will give you a good idea of the condition of the engine is a compression test.
if its a fresh rebuild, change the oil (you need to anyways for the break in) and examine the oil for anything shiny or fuel odor.
remove the alternator and go have it tested. (most auto parts places do this for free) they will spin it up and make sure the bearings are ok.
A bearing failing will often happen early in it's service life. Usually screeching is a bearing, hissing is vacuum (or boost).
What about timing chain components? I assume this was changed during the rebuild? If the cam is slightly out of time, it could result in loss of power at higher RPM and loss of compression through the intake or exhaust (making some sort of sound I'm sure).
Good luck, keep us posted! Cheers!
As much as everyone knows how much I hate agreeing with engineers Having worked at a GM assembly plant and being a utility repairman I was asked to take a new car home many times, at least once a month and if they had a hair across their asses about a mechanical problem they had me take one home every week along with a lot of the other repairmen. And these were cars we couldn't drive more than 80 miles total from the plant home and back, because they could still sell them as new if they had under 100 miles on them.
You wouldn't believe the amount of brand new parts that failed, like bearings, belts, hoses, mechanical and electrical parts. Any moving part is something that can fail and we had more than our fair share in the mid 80s at GM. for the life of me I can't remember all of them as it was a long time ago and during my fuzzy years but do remember a few that were lots, a full load and we are talking a train car load of parts at a time. So don't discount it being a bearing internal in the engine because it is brand new. Not saying it has to be that but don't discount it because it is a brand new bearing.
And oh ya don't forget to do a dry and wet compression test when doing that, that can help track the problem down.
Steve ------------------ Technology is great when it works, and one big pain in the ass when it doesn't
Detroit iron rules all the rest are just toys.
[This message has been edited by 84fiero123 (edited 06-21-2014).]
does spraying carb cleaner leave a mess over the engine, though?
It can damage plastic and painted surfaces.
If you have a small LP tank with torch, you can test for leaks with it. Open the valve just slightly and without lighting it, slowly pass the tip along vacuum lines and around manifold joints. The engine will gain speed as you pass over a leak. You can slip a rubber hose over the tip so you can get underneath the manifold or in areas where the torch tip won't bend and reach.
Cam, crank, and rod bearings a bathed in a film of oil so they can't make that noise. If something happened where they were starved of oil they woud either knock or quickly gall up and seize. In the video, the noise is perfectly synced with the opening of the throttle, if it was a bearing, the noise would remain briefly after the throttle is closed as the engine RPM's come back to idle speed. My money is on a vacuum or pressure leak.
Once a bearing starts screeching, it will never stop until it locks up. That sounds like either a vacuum or exhaust leak. The tube under the TB is manifold vacuum and will cause a high idle or squeal at idle (when manifold vacuum is at its highest).
Watch the vide and listen for the whistly squeak sound. This was on my 3.4 DOHC swap. I used a 10" flexible exhaust pipe in the crossover, and the convoluted tubing inside the pipe was causing the sound. Drove me nuts for several weeks .
Just pointing out that sometimes its not what you think...
------------------ 1986 SE Aero coupe.
3.4 DOHC swap is complete and running, now just have to finish the rest of the car...
Once a bearing starts screeching, it will never stop until it locks up. That sounds like either a vacuum or exhaust leak. The tube under the TB is manifold vacuum and will cause a high idle or squeal at idle (when manifold vacuum is at its highest).
Watch the vide and listen for the whistly squeak sound. This was on my 3.4 DOHC swap. I used a 10" flexible exhaust pipe in the crossover, and the convoluted tubing inside the pipe was causing the sound. Drove me nuts for several weeks .
Just pointing out that sometimes its not what you think...
A bearing can squeal when exposed to lateral thrust and then be practically silent when not loaded. But that is besides the point.
If it was a vacuum leak, it would be most apparent during idle. My understanding is there is a "screeching" sound, under load and higher RPM.
Someone else mentioned it was timed to the opening and closing of the TB?
The sound is coming from the back of the engine. Can we clarify this? Is this the back as in the Fiero trunk side or the back as in behind the driver?
With the new evidence, (sound and power loss timed to the opening of the TB under load) I would perhaps suspect the fuel pump.. I have not heard the noise and to be honest never heard a fuel pump "screech" but it at WOT the fuel flow is the highest and if the pump can't keep up there would be a power loss.
Can the OP edit his original post and give us all the details in one area? I'm trying hard to get all the clues together and I feel we are chasing our tails with missing info.
BTW according to Bosch 02 sensor instructions you shouldn't use 'carb' cleaner on a fuel injected engine because the silicone is bad for the O2 sensor. In fact there is 'throttle body' cleaner for that reason. I also cringe when I hear 'move around the engine with an unlit torch or other propane source'. What could go wrong?
Can the OP edit his original post and give us all the details in one area? I'm trying hard to get all the clues together and I feel we are chasing our tails with missing info.
figured I would recap in chronological order with better explanations and results:
Phase 1: i completed a rebuild on the stock 2.8 that included the following (and more): : block was hot tanked and measured : 20-thousandth bore job with new oversized pistons and rings to match : ground crank with new oversized bearings to match : new cam bearings, lifters, valve stem seals, and head job : professionally cleaned fuel injectors with all new o-rings and seals : new oil pump, water pump, timing chain and sprockets : newer gear reduction starter, reman distributor, and CS style alternator : all new seals and gaskets of course : new temp sensors and oil pressure sender
Phase 2: just finished putting on the first 600 "break-in" miles and it developed the following symptoms: : during mid-hard throttle and high revs (while driving) there is a terrible screeching sound accompanied by immediate power loss (aka, engine gets louder but the car don't go) : if you ever-so-carefully ease into the throttle (while driving), you can get the car to accelerate with minimal screeching. however, speeds above 40 are impossible to attain : if you quickly rev the engine (in neutral) the screech will occur momentarily (see video). if you keep the engine revved (in neutral) the screech becomes more prominent and it will refuse to rev any higher than 4.8k (almost like a rev limiter, it will stumble and bounce around 4.8k but it won't go any higher) : the ECM threw a code 45 Oxygen Sensor Rich.
Phase 3: i have ruled out the following and the symptoms still occured: : NOT belt squeal, alternator squeal, or water pump bearing squeal (i drove the car around the block without the belt) : NOT a clogged/noisy PCV valve (disconnected the line and capped the vacuum source) : NOT a bad EGR flex tube (disconnected the line and capped the plenum vacuum) : NOT a bad EGR vacuum line (disconnected the line and capped the vacuum source) : NOT a bad brake booster vacuum line (disconnected the line and capped the vacuum source) : NOT a bad vapor canister vacuum line (disconnected the line and capped the vacuum source) : NOT a bad distributor (replaced it with a friend's working one) : NOT a bad fuel pressure regulator vacuum line (disconnected the line and capped the vacuum source) : NOT a bad fuel pressure regulator (using a gauge on the fuel rail valve, fuel pressure reads fine and fluctuates as it should during throttle) : NOT a bad MAP sensor (replaced with a friend's working one)
Does it still do the sound with the intake disconnected? if it does, can you try swapping the throttle body?
From the sound, it seems there is a restriction in the intake somewhere. The engine is not getting enough AIR at high RPM. The hissing sound in the video is air leaking in from around the intake or near the TB.
I would be looking for some sort of restriction in the intake or a problem with the TB. If you can't see anything, check inside the plenum with a bore scope.
From the sound, it seems there is a restriction in the intake somewhere. The engine is not getting enough AIR at high RPM. The hissing sound in the video is air leaking in from around the intake or near the TB.
I would be looking for some sort of restriction in the intake or a problem with the TB. If you can't see anything, check inside the plenum with a bore scope.
BTW according to Bosch 02 sensor instructions you shouldn't use 'carb' cleaner on a fuel injected engine because the silicone is bad for the O2 sensor. In fact there is 'throttle body' cleaner for that reason. I also cringe when I hear 'move around the engine with an unlit torch or other propane source'. What could go wrong?
Don't turn it on full blast. Just crack the valve enough to get the propane flowing. If you get an ignition from a faulty spark plug wire, it wouldn't do any damage.
Have someone feel the exhaust while you rev the engine enough to make the noise. If the exhaust flow decreases, you have something loose in the exhaust (most likely the catalytic converter) that is moving under exhaust pressure to plug the system when you rev the engine.
Yes, you could have mice who took up residence in the air intake box/baffle. I didnt notice, did you replace the air filter too ? Ive seen them soaked with injested water and they swell up cutting off most of the air even after they dry out.
am i just going to have to replace all of the vacuum lines?
Having worked at a GM assembly plant and being a utility repairman I was asked to take a new car home many times, at least once a month and if they had a hair across their asses about a mechanical problem they had me take one home every week along with a lot of the other repairmen. And these were cars we couldn't drive more than 80 miles total from the plant home and back, because they could still sell them as new if they had under 100 miles on them. 
