Blue_Thunder

iTrader: (1)

I have an 86 Iroc-Z that has a 1974 CMJ 350 Block with the TPI setup on it. Since the block doesn't have a plave for a knock sensor since its a 74 block do I really need one?. I always put premium in my car too. I know there is the saftey issue with not having a knock sensor but my car is not knocking. A master tech at my work who knows how to work on everything from 1936 and up told me that on alot of chevy trucks from the 80's had there knock sensors and electronic spark control modules removed since they had so many problems with them. He has showed me how to remove mine and bypass it. And since I have no place for a knock sensor do I really need the esc module?

By the way I was not the person who swaped engines I am fixing someone elses mistakes.

Sonix

iTrader: (1)

I thought the knock sensor just goes in the plug in the bottom of the water jackets? Aren't those holes in all blocks? It's in my 1977 350 block.
If you can bypass the knock sensor in your TPI programming setup then you might as well. People with carbs don't have knock sensors...
Then again, how does TPI set up your timing curve? Isn't it based on knock sensor input?

Dens71TA

iTrader: (5)

The knock sensor just goes where the block coolant drain plug is normally installed. GM never changed the engine block casting to add the knock sensor.

According to the factory service manual, with the knock sensor disconnected the engine will always run with normal timing advance as if no spark knock is detected. If the ESC module is unpluged or faulty the ECM will set timing at full retard and a diagnostic code 43.

Sonix, people with carbs DO have knock sensors. The 305 HO, '85-87 base LG4 305, and the truck version of the 305 HO all had 9.3/9.5:1 compression and used a knock sensor.

nascar2496

iTrader: (2)

not be a jerk or anything, but i think sonix was refering to people with aftermarket carbs? ie holley or eddys but yes most if not all the computer controlled carbs did have them.

sofakingdom

iTrader: (1)

AFAIK you NEED the knock sensor for TPI; without it, the ECM will run the timing at the minimum ("safe") spec, nearly limp-home mode, and maybe set a code.

ALL SBCs have had the knock sensor place since 1955. The wisdom of those engineers.... they somehow KNEW that 30 years later, after they were all retired and gone, that a place to put that thing would be needed; so they designed it in. They cleverly disguised it as the "coolant drain plug hole", so that way the value planning project engineers (who aren't issued near as powerful crystal *****, and therefore couldn't see as clearly into the future) wouldn't mark it as an unnecssary cost and eliminate it from the design. Smart guys, those.

So yeah, forget about all that "bypass" business, and just put one in there like it belongs, and enjoy having a car that runs right. Just don't overtighten it: that makes it SUPER sensitive, and it will pull timing out MUCH too enthusiastically. About 12-15 ft-lbs is all it needs; enough to keep the water from falling out.

Sonix

iTrader: (1)

Yea, I was referring to the non-cc-carbs. I meant the guys who convert these cars (from TBI, TPI, or cc-qjet) to holley or Edelbrock, or my non-cc-Qjet. Old school stuff.

Blue_Thunder

iTrader: (1)

I have no trouble codes right now. And according to michel on demand all the Electronic Spark Control Module does is amplify the signal from the knock sensor when the knock sensor picks up a knock and it also has a set retard spec in case it goes bad. So if there is no knock dectected then the car ecm will not retard the timing. So as long as my car is not knocking than when I set my timing and fix my exhaust leak it should run fine. I also checked another 3rd gen an 87 Camaro and the scantool data for the knock sensor listed Knock Sensor: No Signal

This is exactly what my scan data says for my car.
I also run premuim in my car only.

Damon

Hmmmmm..... odd. Every time I've disconnected the KS the ECM threw a code. I've bypassed it on several occasions by installing a 3900 ohm resistor in it's place but never gotten away with simply unplugging it.

bunkie21

This is funny timing, and I dont mean to hijack this thread but I am looking at the same thing. I installed long tubes and I believe that my knock sensor is picking up my loud exhaust and headers and retarding my timing.

So if I uplug it, it will just sit at base timing right? I have heard that you can relocate it to the drivers side but I would like to check if its the sensor or not. I run 91 in it and am not real worried about knock on a test basis if I uplug the sensor.

Toehead

The knock sensor in our cars is connected to a module that conditions the signal and outputs 10 volts when no knock is occurring. When knock occurs, te signal is pulled low.

Disconnecting the KS should not throw a code. I know some cars advance the timing a ton for a split second and listen for knock. If the knock sensor doesnt respond, then it throws a code. I am not sure if our cars do this, however.

Blue_Thunder

iTrader: (1)

What does all your 3rd gens say on the scantool when looking at the knock sensor? And I looked for my knock sensor everywhere on my engine and I don't have one. I can't find the wiring for it either. And I don't know anything on 91 camaros but as far as I know unplugging the knock sensor wont do anything except that the ecm will not be able the detect a engine knock. And if you look at your list of trouble code definitions there is no code for the knock sesnor. There is one for the spark control module. The wiring for the knock sensor is as folllows. One wire knock sensor goes to spark control module which then goes to the ecm. But I think everyone is forgetting something about 3rd gen cars. The cumputers in our cars are not that advanced. It won't detect a lot of problems because it is a basic obd1 system. Case in point my blms are at 150-160 contsantly. Yet I have no codes because the lean condition code works off my o2 sensor and my o2 sensor swings from 200 to 800 millivolts. So my ecm thinks the car is running fine even though its not.

ljnowell

You will not have the proper timing if you do not have a knock sensor. The unplug it and forget it stuff is off base. If you want it to run properly you need the knock sensor. Even an OBD I system does, if it didnt it wouldnt be there. The manufacture wouldnt put something that cost them more to produce on a car if it wasnt needed.

Guest

Ford didnt use them.

I've had mine disconnected (unintentionally) and it didnt set any codes.

rgarcia63

Isn't emissions the ECM's priority? fuel air ratio is the only parameter it needs to minimize emissions, as long as the O2 signal is within the specified range the ECM can't complain.

IMHO knock a bad thing even if you can't hear it, personally I would use whatever is available to minimize, or eliminate it.

ljnowell

When an ECM controls timing also, it must have some method of feedback. Otherwise it could destroy itself with too much advance. Seems most of the poeple who say "my knock sensor is disconnected and it runs fine" would be most surprised if they had it operating properly and realized how much better it ran. Without a knock sensor you will not have the proper amount of ign adv, and it will not make optimum power.
I just replaced both knock sensors on a 2000 lexus rs300 at work the other day(they suck, under lower intake plenum). Because one of them was bad the PCM would only allow 15 degrees total advance. If you didnt know better you would say it ran ok. When repaired it ran night and day difference.

Blue_Thunder

iTrader: (1)

Yeah but is our ecms in our third gens that advanced. That and I just set my base timing. I put it at 7 or 8 degrees advanced. Then I checked it with the est plugged in and it was oh id say around 20 degrees advanced or so. Can't be too sure since my timing mark plate only goes up to 12* advanced and 12* retard. And also that was a 2000 lexus. OBDII, not OBDI from 1986. There is a big defference. OBDI in the 80's was very very basic.

On a side note I also discovered while checking my timing at high rpms that I must have an intake valve that is not sealing correctly because my car backfired through the intake. I heard the familar backfire bang but it came from the intake air duct. So I still have major problems.

Guest

No our ecm isnt that good, and neither is the one in a Lexus or any other production car. The only thing the knock sensor will do is try to keep the engine from detonating under load. It doesnt have the slightest clue what the power output is and where it makes the most power.

I'd use one if the wiring was available. You have the hole in the block, not much question about that. But if its not and doesnt detonate, it'll be ok. Fix the other problems first.

Blue_Thunder

iTrader: (1)

It only backfired through the intake twice while setting the timing. I checked my base timing yesterday and I must have bumped the distributor when I retighted it. The timing was running retarted. So I reset the timing to 8* advanced and it did not backfire anymore so I guess I just goofed up and misadjusted my timing.

Still runs like crap even though timing is correct. But on a plus side I don't see anymore small puffs of bluish grey smoke from my tailpipes which is good.

sofakingdom

iTrader: (1)

Now that you've learned how the system works and learned of the knock sensor's importance and installed one, what other missing or otherwise defective parts are there?

Guest

Good point. He might have one of those "3-wire" TPI harnesses.

1990 truck

I put headers on my 90 and it is doing the same thing how do I truck the computer
My knock sensor is through a 43 code

OrangeBird

iTrader: (1)

So you name is "1990 truck" and you want to know how to "truck the computer" ?

You may not get a lot of answers here because this is a forum dedicated exclusively to 1982 through 1992 Chevy Camaro / Pontiac Firebird cars only .
(The Third Generation of the GM F body car , hence the name "Third Gen . Org" )
If you meant "trick" the computer a truck forum may be more helpful for you if no one answers your question here .

Tuned Performance

iTrader: (92)

This is a 1227747 ecm, you can desensitized the knock sensor with a 1/4 npt street elbow.
or do a custom tune. This is $42 mask. The knock sensor is enabled at 58c . This value can be maxed to delete the use of the knock sensor. I would keep it in place for added protection but if you do want to delete it check your base timing.

GeneralDisorder

iTrader: (1)

The knock sensor is a piezo electric microphone - if you disconnect it the result depends on the ECU being used. Some (that use external ESC modules) have no way to detect this so they happily continue running as if there is no knock being detected - the ESC module may "know" but has no way to communicate this to the ECM. I'm fairly certain the ESC module does not pull the ECM signal low if the knock sensor is not connected as that would be stupid. Others that have the knock control built-in may use a bias voltage to detect that it's not connected and revert to a "safer" timing level and throw a code.

GD

ASE doc

My experience is that any fault in the knock sensor circuit, including a disconnected sensor, causes the ECM to set code 43 and default to full knock retard. GM did this to safeguard against detonation when the ESC system can't detect it. Can't say I've paid that much attention to which vehicles had separated ESC modules and which didn't. I just have come to associate any OBDI GM knock sensor fault with a likely loss of power due to knock retard. Perhaps the systems that used the separate module don't set a code or default to full retard if the sensor is disconnected, but I don't remember this being the case.

Installing a brass fitting between the sensor and the engine block is an effective means for reducing sensitivity. I've had to do this in cases where an aggressive cam or other significant engine mods have been done. It's a cheat and I would warn it only be done in cases where the timing curve is tuned, either mechanically or through software, to fit the motor's current needs. Premium grade fuel is a given with any high performance engine. Of course, if you can tune the timing curve of an EFI motor, you can disable ESC.

FRMULA88

The knock sensor simply tells the ECM engine knock was detected and the ECM will retard timing using the time retard programmed into it until the knocking stops.
no knock detected means ECM uses the default timing tables programmed into it

GM installed the knock sensor so the car could run on mid-grade or even unleaded regular (knowing that a lot of people would use cheaper gas) cheaper to put in a knock sensor then replace a whole engine under warranty.

it's cheap insurance and nice to preserve the car's originality, if it's numbers matching car, and a safety net that could save the engine. Is it needed for the engine to function properly, not really just understand if you are too aggressive with your timing and tune you have no safety net

sofakingdom

iTrader: (1)

IMO "originality" and "numbers matching" is a pretty lame excuse to completely install the entire engine control system. "Function properly" is the operative concept here and should be elevated to the highest priority.

It is true that SOME (not ALL) of the CC carb cars came without one. It's important to remember though, that the ONLY ones that didn't have them, were the early LG4s, which had such low compression that yerbasic local stray tomcat could walk up to your car missing its gas cap (because, you know, lawn ornament...) and pee in it, and the car would run on it. The LU5 and L69 cars, and AFAIK ALL FI ones however mighty or lowly, needed it, because the ECM had enough brains programmed into it to "hear" the knock signal by whatever means it was presented to it, and pull out timing to make it go away; thereby allowing the car to run off of the aforementioned tomcat body fluid, without detonating and damaging the motor. If the ECM (or whatever other part is charged with this task) fails to detect its presence, the whole system goes to the most conservative timing chart possible, to avoid engine destruction in case the tomcat did his thing. It does not "retard timing using the time retard programmed into it until the knocking stops"; it simply goes into a particular variety of limp-home mode, with ALL of the normal advance pulled out. It's an emergency "red alert" kind of mode, not a delicate "slight adjustment" applied gently with the minimum interference required to get below a threshold. It is BRUTAL and heavy-handed.

Bottom line is, remains, and shall ALWAYS be, if your car came from the factory equipped with one, INSTALL IT, and keep it working properly, so that it (a) provides the safety function in the event of the cat, and (b) prevents the ECM from adopting a dysfunctional ignition timing curve except when ABSOLUTELY UNAVOIDABLY necessary.

GeneralDisorder

iTrader: (1)

If the car is 100% stock, then yes put one on.

If it has the first, and most important upgrade - headers and y-pipe. It's probably not going to function worth a damn due to noise and may need to be tuned out. Mine is much too sensitive and essentially useless with just a few mods - headers and 1.6 roller tip rockers.

If you have mods please get your car dyno tuned. Your tuner can easily tell what to place the timing at based on the power output. It's quite easy - increase timing till your HP peaks and then back it down a degree or two for safety.

GD

Fast355

iTrader: (2)

Headers and quality 1.6 rockers have never caused false knock retard on any GM I have messed with.

However a loose body heat shield vibrating on a header tube and exhaust pipe contacting the trans cross member both caused knock retard.