Ok, lets make this short and sweet...i usually fill up with 91 octane, today i tried some good ol 87, now i can here this knocking from the engine bay when my car is idling. I can hear it from inside the cabin...only faintly though...My car is an 86 SE V6 Auto with about 182,000km on it. Could this be the knock sensor...someone mentioned this in another thread...but if it is can i repair the sensor, or adjust it or do i have to replace it completely? and better yet....where is the damn thing?

thanks eh

-Phil

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86 SE V6 under constuction
Please rate me if i am of any assistance, thank you...

Our cars didn't come with a knock sensor, only provisions for one on certain years. Anyway a knock sensor would not make any noise. If the knocking goes up with engine rpms, you might have lost a crank bearing. Edit:Make that a rod bearing.

[This message has been edited by avengador1 (edited 02-27-2004).]

Yep, no Fiero came with a knock sensor. The lower octane would tend to create predetonation (pinging) at part and full throttle, not at idle. With the high mileage on the engine my guess would be a failing rod bearing. If the rod bearing is replaced now before the crank is damaged it will save a couple of hundred bucks over buying a reground crank later.

JazzMan

quote Originally posted by JazzMan: With the high mileage on the engine my guess would be a failing rod bearing. JazzMan

Wouldn't i hear the knocking all the time then at idle, not only when i fill it with 87 octane?

thanks though
-Phil

Bump!

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86 SE V6 under constuction
Please rate me if i am of any assistance, thank you...

quote Originally posted by Phil86SE: Wouldn't i hear the knocking all the time then at idle, not only when i fill it with 87 octane? thanks though -Phil

Not neccesarily. Rod knocking is most pronounced under load, so when you're idling there's no load on the engine. As the rod bearing continues disintegrating and the rod bearing journal grinds away the knocking will become louder and louder, eventually such that it will knock at all engine loads and speeds. Without being there to hear the actual sound it's hard to guess what it may actually be.

JazzMan

some thing to think about is if there is carbon in the coumbustion cambers it could be that it is rasing the grade of gas you need(9 to 1 is stock i think the g.m manul said to only use 91 so if there is carbon in there it don't take much to bump the ratio up ) .i had this same thing happen in my 6000 with 250,000 or more miles i had to use 91 or 93 .When the trans. went out i took the head off so my buddy could have them and there was A TON OF CARBON. don't know if that is what is going on with your but i think so because you ONLY hear it when you use cheap gas (or so it is called )

[This message has been edited by fierobrian (edited 02-28-2004).]

Presuming that the carbon may be contributing, you might want to try the decarbonizing kit from Ed Parks. I've used it on my duke & had amazing results.

If it doesn't help, next time you hear it knock, go back tothe engine bay with a mechanic's stethoscope (or a long 3/8" drive extension), place the end on the block & your ear on the other end & listen, as it could be a rod end or crank bearing. If it is, looks like it's time for a rebuild...

quote Originally posted by fierobrian: some thing to think about is if there is carbon in the coumbustion cambers it could be that it is rasing the grade of gas you need(9 to 1 is stock i think the g.m manul said to only use 91 so if there is carbon in there it don't take much to bump the ratio up ) .i had this same thing happen in my 6000 with 250,000 or more miles i had to use 91 or 93 .When the trans. went out i took the head off so my buddy could have them and there was A TON OF CARBON. don't know if that is what is going on with your but i think so because you ONLY hear it when you use cheap gas (or so it is called )

ATTENTION ED PARKS!

i need your carnon pacakage thingy!
does anyone have his web site addy?

thanks to everyone!

-Phil

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86 SE V6 under constuction
Please rate me if i am of any assistance, thank you...

I don't think that Ed reads here, though Jeremy does. Here's his site, you can get his phone number from there. He's a really nice guy to deal with.

http://www.thefierofactory.com

JazzMan

Hey I had this and it was a rod bearing, quick check, pull one cable from distributor(start with 1, chances are its 4-6)... start car, give it a little gas... if sound goes away as you check each cylinder... YOU WIN.... well no win. but a chance to put in a 4.9

Carbon would possibly glow red, igniting the gas as soon as it got in the cylinder. That would cause spark knock..
just a thought

quote Originally posted by headhunter: Hey I had this and it was a rod bearing, quick check, pull one cable from distributor(start with 1, chances are its 4-6)... start car, give it a little gas... if sound goes away as you check each cylinder... YOU WIN.... well no win. but a chance to put in a 4.9

Yeah, 2.8's aren't very strong in the lower end. Was a Pontiac dealer.....we put in 3 diff engines in the Fiero demo!

Phil

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87 FIERO GT 2.8 5spd

GM auto tech for 27 years. Specializing in electrical and computer problems. Now on workers comp. and it looks like I will be unable to return to work as a tech.

Hmmmm, weird...i have a new throttle body on the way so today i went and set my idle alittle lower it was at about 2000spm at start up and 1500 at idle so i set it down to 1500 at start up and about 1000/900 at idle...and the knocking has seemingly gone away...
i will check for the rod bear though!

thanks eh!

-Phil

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86 SE V6 under constuction
Please rate me if i am of any assistance, thank you...

If you are adjusting the throttle blade stop screw to change your idle, you'll need to fix whatever problem is causing the high idle and then go back and set the stop using a scan tool or Winaldl. That throttle stop is not the idle adjustment, the idle is controlled by the ECM using the Idle Air Control valve, or IAC. The stop screw is not supposed to be tampered with.

JazzMan

Thanks Jazzman, i was already aware of this but i know that my throttle body does not seal anymore as the bushings in it are shot and there is always air getting through. I just had my IAC and my TPS and my Timming set by a local shop and so i know they are good. I have a new throttle body on the way that should be here any day now so i will just install that one and see if my idle problem has to do with the throttle plate not sealing correctly on my old throttle body. If not then i will go buy a vacuum pump and test every damn little vacuum line i can find. I just adjusted the throttle plate screw to temperaraly fix my idle problem as i wait for the new throttle body.

thanks for the insight though
and thanks to everyone who has helped me out here

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86 SE V6 under constuction
Please rate me if i am of any assistance, thank you...

I agree with "Headhunter". At idle pull off plug wire one at a time. If knock goes away.."Bingo" thats your cylinder with the problem. Drop the pan and replace the rod bearings and oil pump. Not sure about pan to cradle clearance.
ps: I like your idea about the knock sensor.. If only it could be that easy.

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I realize this may be a long shot, but here goes my knock story...

Years ago, as a cost saving measure, I decided to switch to 87 octane, after 4 years of always using 91 or better. It was now over 100,000 miles, too. The next thing I noticed was the nasty rotten-egg smell, which I assumed was the catalytic converter dealing with bad gas (pun intended). I went back to hi-test again, but I soon noticed a knocking sound, really noticeable at idle. Only when I had the exhaust system off for a clutch job, did I notice the knocking sound from the cat. I dumped about 1/2 cup of sandy stuff from the head pipe, which I assume was catalyst material from a damaged catalyst brick. I replaced the cat, and no more knock. It's been over 7 years and 70,000 miles since, and the knock hasn't returned.