I just noticed what I think might be a light knock in my gta(90 model,5.7) It only makes this noise under light throttle. If I really get on it I do not hear a thing wrong. My guestion is if this noise is a knock would the computer throw up a engine code? I'm kinda new at computers and fuel injection. I haven't checked for codes yet but the check engine doesn't come on except when the car is started. I could really use your help guys and gals.

thanks,andy

 

Slayer,

The ECM uses the detonation sensor to detect preignition and detonation "knock" and adjusts the ignition timing accordingly. You may be hearing one or two "knocks" before the ECM and ESC can react, but then the timing is retarded to prevent engine damage.

Typical causes of detonation are base ignition timing that is advanced too far, excessive carbon buildup in the combustion chambers, excessively hot cylinder heads from poor cooling, inoperative EGR system, lean fuel mixture, and low octane fuel.

Check all those, and use fuel that is rated at least 91 road octane.

 

thanks vader,

does this sound like detonation? I've had a few engines with rods that knocked but this doesn't sound quite the same. I will check what you suggested and repost when I finish. One more thing though, I thought that the L98 was relatively low compression(9.3-1). does it really need premium? Anyway I'll ceck it out and let you know. thanks again man. I really appreciate the help.

andy

 

You will have to experiment with your car to find out which octane fuel it needs, the lower octane the better.

I have to run 93, I have the timing set at 12-13 deg and have disabled the knock sensor.

If the knock goes away with better fuel then it is detonation.

 

Slayer,

The static compresion ratio is likely more on the order of 9.5:1, but close enough. The L98 gets extra charging from the TPI system and thus extra compression pressure than it would get with a more conventional intake.

If you have a copy of your owner's manual, it probably details the fuel requirement for your engine. I believe that was 90 or above, but I'm not positive. And that was with a new engine with all the systems working at 100%, and no carbon buildup.

If you're detonating, the extra octane won't hurt a thing for now. Do a survey and see what everyone is using with the modifications they have, or stock. I use 93 or better since my 305 is base timed at a little over 10° BTC.

 

thanks guys,

I'm using 89 octane right now. I just bought this car(90 GTA) and I haven't had time to do much to it. I did see a hypertech sticker on the door so I don't know if that really means anything or not. I'm going to check the timing today and I'll get a bottle of octane boost and see if that helps. As for carbon deposits any ideas how to clean them off? I always heard that running 3000 or so rpm for 20 or 30 miles could get them hot enough to burn off but is there a chemical cleaner that can do this?

 

misting water into the throttle body will help clean carbon off the tops of the pistons. just make sure its a MIST. the water will "steam" clean the deposits right off. If you think this is just a myth, take the heads off an engine with a blown headgasket and the pistons where the coolant was getting into the cylinders will be significantly cleaner than the rest. i had a detonation problem with my old LG4 formula firebird, and i misted water into the carb for a little while and it really helped.

 

if you think you are hearing a pinging heres how the gol durned system works and then i will excuse you for however long it takes to fill up with premium fuel-even if it oxygenated-and also to procure a can of gm top end cleaner, which you will use according to the instructions-and then be amazed at the poop jetting out the tailpipe. ready? ecm will verify esc (not est) readiness and verify circuit and component integrity by actually over increasing the timing once, shortly after start up, till it actually hears the knocking itself (yeah,like its alive or something) at which time the esc module on early tpi (maf) or the chip backs timing down and the self test is over. code 43 (again a best guess, feel free to doublecheck me, i would if i was me)sets if no knocking is heard. how come sometimes certain words are bracketed with asterisks-examples --- *always* *guess* *know* *naked pictures of your mommie* why?




:rockon: thin lizzy

 

I'll try to get the top end cleaner tomorrow. Is this a dealer only item? Redfirebird, I've heard of the water trick but I'm too chicken to try it. Knowing my luck I'd blow the engine, but thanks for the suggestion. I was still wondering if the computer would store a code if it detects detonation? Unfortunatly the weather here took a nosedive so I didn't get a chance to do anything today. I hopefully will get to do some work tomorrow so I'll post anything new I learn then.

 

no code is stored if "too much"detonation is heard. thats is one of the reasons why your butt is plunked in the drivers seat.

 

Is your base time set, I have no idea if your care has a distributor or DIS. Your sensor may not be properly torqued to the block, they have to be torqued to spec to work right. If you have acess to an oscilloscope you can hook it up to the sensor and tap the housing lightly and check the Ac output for voltage signal. The sensor has one wire so you just ground to the housing.

 

o-scope? nah hows about a dvom set on ac volts-what wire are you telling him to ground out? ks signal wire? why? you are scarin me!

 

Knock sensors have a piezo crystal that creates an AC voltage that is sent to the ECM when the base of the housing is moved or the shape of it is changed by vibrations sent thru the engine block when the cylinders fire. A dvom doesnt react to the voltage soon enough to gather the full spike it makes, you have to run a o-scope at a 10millisecond scale to capture the wave. You ground the common (black) on the o-scope to the sensor housing, and run the B+(red) to the backside of the connector to capture the signal. I do it all the time, I am a tech for a Porsche, Jaguar, Audi dealer and have a 1993 Suburban with a TBI 350 that had the same problem.:nono:

 

yo daddio-i got the science-im talking the way to fix it. if you are going thru all that just hook up a scanner and drive it. couple that with the knowlege that the early sensors get picky over time-guess what maybe its time to replace it. or if its an esc module equipped year monitor the 6v from term C the ecm likes to monitor so it can make timing decisions based on the knock counts. i mean your the man and all but o-scopes really dont have to come out to repair most all gm driveability problems till the obd2. as long as we are throwing credentials around, like the mean something, i have been in this trade-fixing automobiles since 1978 with 5 years out for active military i have owned my shop for almost 5 years and i know guys like you and it aint flying with me. you want to help-help, dont try to impress with your techno-babble cuz it aint helpin-i have made 200 posts and never have thrown credentials around. and im pissed im doin it now-you throw your work experience out too soon-it dont make you nothin-if you was bad *** you would be posting at iatn-if you belong. try that "im a so and so" horsecrap over there, yeah right, directly into the sh-tcan you would go.

 

:hail: they call him grumpygreasape folks!:hail:

 

Sorry grumpy!

 

lol.. I agree the oscilloscope is a bit much there, but it's got my curiosity piqued and I'm gonna try it sometime anyway just for my own curiosity. I like playing with them anyway.

 

you may all rise now :lala: :rockon:

 

hey grumpy

I got a can of gm top engine cleaner pn 1050002. But The stuff that the dealer had is supposed to be poured into the carb. There doesn't seem to be any way to use it with TPI. Is there something that I've missed?

 

I've seen people suck it up through the PVC valve.

 

hello there -in front of me i have an aerosol spray can gm X66-A part #12302498 13 oz. power brake booster line works nicely warm it up and spray till it almost chokes on the stuff when the can is almost empty choke it off till it stalls-actually can take off the intake duct-(yes, maf and all) run it and spray thru t-body-best way also the longer it sets the more is removed-overnite works ****. later and when ya start it back up you really got to hammer the feces out of it. drive it hard like you stole it, and the chunks will spew forth from the tailpipe- over, out. till later