e-man

What is the better way to do this? Wrapping 2 wraps of teflon tape around the threads or not torqueing it in all the way? I know changing it in the prom is the right way.

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89 350 TPI,comp cam,edelbrock intake base,SLP headers,highflo cats,flomaster cat back,accel 300+ ign,ported plenum and runners,ported maf,auto w/shiftkit,cold air induction,AFPR,Ed wright chip,3.23 posie best ET 14.011@98.72mph without cam/New best 13.926@98.27mph

Vader

E-man,

Install a brass/bronze adapter in the block, then install the detonation sensor into the adapter. If you can't find a single-piece adapter, use a ¼ NPT close nipple and hex coupling to make one. Obviously, the sensor is going to mount farther from the cylinder case, so if you have an interference problem with headers or the starter, you might want to find a 45° adapter to make space and kill the sensor even more.

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Later,
Vader
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"Let the bodies hit the floor!"
Adobe Acrobat Reader

e-man

vader or any body else, before I do this what is the best way to find out why the ecm is pulling timing out? I have my base timing at 4 dbtc and still get about 12-16deg at WOT pulled out, total timing is only 29deg. I think its false knock because if I give it a good rev in park my scanner says it pulling 8-12deg at only about 2500rpm's and it feels like the exhust is vibrating a little. What do you think

Guest

I think something on your drivetrain is loose or is hitting the car. I have heard of loose accessory brackets causing false knock before, you may wanna find out if the exhaust is hitting the car somewhere.

89BlueTA

Has anyone tried running with the knock sensor just unplugged? I wonder if the computer would just automatically pull ou timimg. I had an 85 TPI and I always ran it with the knock sensor unplugged and never got a ckeck engine light or any codes. I am wondering whether I should do this with my 89
or not, I think I am going to check it out at the Dragway. Well if anyone has any ideas let me know, Thanks

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14.48@93.72mph

e-man

I was thinking of disconnecting it at the block and connecting a new knock sensor to the connection then running a ground wire to the new sensor so the ecm still see's it is there,then tape the hell out of it so it wont get any vibrations.Then go for a drive and listen for pinging if its really there? Or if there is a easier way let me know!

MikeH

iTrader: (10)

Just put in a 3900 ohm resistor and run it to ground. You will never have to worry about it pulling out timing again. And It will throw no codes. You can even run a switch to were you can have it working or not.



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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!

okfoz

I have a friend whos father had a mid- 90's Full size Chevy Truck and he had a loose bracket on the front of his engine that caused the Knock sensor to get a false reading.

it would actually retard the timing so far it would stall.



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87 Formula 5.1 converted to TPI Yellow/Black
SLP cam, headers, cat-back exhaust
Ported & polished TPI intake
Gil Younger (no yo-yo) Shift Kit
Aluminum Driveshaft
3.73 Posi gear
Baer 12" brakes 4 wheels
KYB AGX Adjustable Shocks & struts
Hotchkis strut tower brace
South side machine frame connecters
Custom reinforced control arms and pan hard bar.
Custom Leather interior
CUSTOM Yellow Gauge Faces

87 Formula TPI (5 Speed) Yellow/Gray STOCK

1967 Buick Riviera 430hp Turns high 14's (Not bad for 4300 lbs)

83 Camaro (Parts)
83 T/A (parts)

http://www.3rdgenformula.com

BLOWN85/TA

iTrader: (2)

OLD knock sensors can become very sensitive also. You might just need a new one?

P J Moran

This is very interesting. I had never heard this before. Is anyone else of this same opinion?

I have battled this problem, too. I have installed a "desensitizing circuit" ahead of my sensor, but it doesn't seem to have much effect. My sensor is the original, but my engine is only a year old. I don't mind swapping it out, but I don't like throwing parts at problems without knowing that they will actually fix them.



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'87 IROC 5.7l TPI - original owner!

e-man

I noticed some thing when I tap the block with a hammer and a extendion the scaner says there is knock count but no knock retard is this right? Now the question is get a new sensor from autozone or gm?

Grim Reaper

I have done a lot of testing of my knock sensor etc, while burning my eprom. First, controling the knock sensor's sensitivity via the attack rate, decay rate and capping the maximums @ various rpms inside the eprom is the best method. This way you can limit the amount of retard it pulls out while still leaving it functioning ... just in case.

Second, there may be some truth to the knock sensor being more sensitive as it gets older or possibly when the engine is cold. I have noticed that I get far more incidences on knock counts when the engine is first started cold. But if I turn off the engine and restart it within 5 minutes, it is definitely less sensitive.

The knock sensor has almost 200,000 miles on it. I plan to replace the knock sensor shortly, to see if this still occurs.

89gta383

iTrader: (5)

You have to find out the cause of your knock first. I had the same problem, and tried a new sensor wrapped with tape, no change.

You need to check your initial timing first.

The only way I found it was by recording runs down the dragstrip with a scanner. I was getting too much advance on each gear change.

You need to find out why you are getting retard. Getting rid of the sensor can hurt your motor. If you really want to desensitize it, go to radio shack and get a 1/4 watt 4.7k ohm resistor,(pack of 5 for .99) and wire it in before your knock sensor. It is the white wire in your wire harness running along your passenger side injectors. The resistor will send the signal back to the ESC module that everything is functioning properly, and will eliminate the computer retarding timing. You will hear audible knok though, so you can still hurt your motor. Borrow a scanner and record some runs, and play with your inital timing. That should help some.

JakeJr

I'm interested in trying this fix to cure what I've determined to be 'false knock' (forged pistons, roller lifters and rockers, etc.

I went to Radio Shack and bought the resistors you recommended, but when I looked in my 86 GM Corvette Service Manual, I don't see a white wire identified.

I did find four wires that plug into the ESC Control Module which is mounted in the engine compartment, passenger side close to the firewall.

Can I use one of these wires and, if so, which one.

Also, can you give me the details on grounding the resistor and any other info you can think of to help me out.

Thanks,

Jake



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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

TunedPort350

Jake,

For what it's worth I also have TRW forged pistons, Crane 1.5 roller rockers, and roller lifters and I don't receive any false knocks. Even when it's cold I don't receive any (pistons). Just thought I would mention this because your false knocks (if you are POSITIVE they are false) may be coming from somewhere else...


[This message has been edited by TunedPort350 (edited June 17, 2001).]

89gta383

iTrader: (5)

I would look in your service manual for the wiring schematic and look for the color of the wires coming out of the esc module. Trace your wire from your knock sensor up into your wiring harness. Mine is a white wire that runs from the knock sensor, in back of the ac compressor, and up into the fat wiring harness that holds the same wires for my passenger side injectors. The same wiring color that is going into your sensor should run all the way up into the esc module, at least it does on mine.

I used simple male-female electrical connectors to tie the resistor into a wire that I ran to ground. You want to hook up the resistor in the circuit between the esc module and the knock sensor, but instead of running the wire to the sensor, take it to ground.

I left my original wire hooked up to my knock sensor and grabbed the wire in the injector wiring harness to make things easy. I ran my ground wire to the firewall and it is just sitting there. I still have the resistor hooked up in between the esc-knock sensor wiring. All I do when I want to hook it up thru the resistor is unhook it and hook in into the wire going to the firewall.

Did you try playing with your inital timing?

JakeJr

Thanks for the info.

Yea, I've played with the initial timing trying everything from Zero to 12 degrees; EST wire disconnected and ECM code cleared after each adjustment.

I've even tried 4 different PROMS, three of them custom burned.

I now believe that the timing curve is too fast (aggressive) since Diacom reports that it's all in at 2100 RPM.

I thought of just disabling the sensor, but the GM manual says the ECM reverts to retarded timing and the resultant poor performance when it doesn't receive the correct signal from the knock sensor through ESC module. The manual also recommends that sensor be wrapped in tape (teflon), which I've done and it's torqued to 14 lbs as per the manual's instructions.

Plugs and power are excellent but the engine is noisey when cold (.065 piston to wall) and the rockers do tick no matter what the lifter preload is (I've tried everything from 1/4 turn to 1-1/4 turn in 1/4 turn increments).

So I bought three sets of resistors yesterday, 2k on each side of 4.7K, all 1/4 watt and want to give the resistor approach a try now.


So if I've got this straight:

What I'd be doing is:

1. Locating the wire that goes between the knock sensor and the ESC module.

2. Cutting that wire and install the resistor to the end of the wire that goes to the ESC module

3. Ground the other end of the resistor

4. Leave the wire that comes off the knock sensor disconnected

If I understand this correctly, the knock sensor will then be effectively disconnected from the ESC module and the resistor will be supplying the signal the ESC module is looking for.

Am I right on this? Electrical stuff has never been my strong suit.

Thanks for all the advice.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

JakeJr

Well, it worked!

I found that the Vette wire controlling the knock sensor is blue.

I disconnected the ESC module and cut the blue wire about 6 inches from the module connector. I then spliced in a 4.7K ohm resistor and grounded the other end of the resistor at a spot just above the module. I first tested the spot with a 12V test light to make sure it was a good ground.

Slid a 5/16 piece of black rubber hose over the wire and cable-tied it to a metal support located right at the ground spot.

Fired the engine and no code and no knock count.

Took the car out on the interstate with Diacom running to test my handy-work under different trans gear settings and throttle positions, listening for knock or ping.

Under certain conditions I could hear very slight ping, so I pulled over, popped the hood and, using my timing light, lowered the advance two degrees. Naturally I disconnected the EST plug first and disconnected the battery afterwards.

Back on the interstate and more experimenting. Had to drop it another two until no trace of ping was left under all conditions. Seemingly no loss in performance either.

BTW, found out my timing pointer isn't accurate too. My damper is a special externally balanced road race damper measuring 6-1/4 inches in diameter, and I haven't been able to locate a pointer that is made for that diameter yet. Closest I could find was a 7" tab from Mr. Gasket so whatever the timing light is showing me isn't correct. One day I'll get around to tracking down the right one.

If anyone knows of a tab made for a SBC 6-1/4" damper I'd love to hear about it.

Thanks guys for the advice.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

[This message has been edited by JakeJr (edited June 17, 2001).]

[This message has been edited by JakeJr (edited June 18, 2001).]

JakeJr

BTW, in researching the knock sensor wiring color in my 86 GM Service Manual I found that it says it's 'IMPORTANT'(GM's word) to wrap the threads of the sensor with tape. If that's the case, then the number of wraps won't make any difference.

I read on another site that the sensor gets its input through the coolant and that using a different ratio other than the 50/50 ratio of antifreeze/water effects the sensor's accuracy.

When I posted a question about that most of the responses said "that's wrong/crazy", but the info supposedly came from a GM engineer involved in designing the system.

Since GM stresses the use of tape on the threads, it appears the sensor does not have to be grounded to the block via the threads.

Amazing how much conflicting info you can get on issues like this.

Hope this helps and doesn't confuse matters more.

Jake



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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

89gta383

iTrader: (5)

Jake:

Glad it worked for you. I'm also in the 'timing tab not correct for balancer' club. That was part of my problem. What is interesting is that I made my experiments at the track, and the more timing I pulled out, the slower the car got. My rockers make noise also, and can't get rid of it.

Hey Jake, were you the one with the friend who had his miniram intake cut in half and ported in order to get 400 cfm out of it? If so, do you know what the flow numbers were of the miniram when it was stock, and the name and number of the guy who ported it?

Thanks.

JakeJr

Dupe.

[This message has been edited by JakeJr (edited June 17, 2001).]

JakeJr

[QUOTE]Originally posted by JakeJr:
[B]

The target was 340 cfm with the manifold bolted to the heads. Bob said that was the flow needed to make 600 HP.

If memory serves, the miniram flowed 310 cfm @ 28" of water in stock form and at that point a lot of turbulance developed which prevented it flowing more. The manifold was then sectioned and the short turn radius was blended and that removed the turbulance and the flow increased to 320 cfm.

After that it was opened up again and more porting was done and the final numbers were in the 400 range. Bob explained there is a math formula that determines how much the manifold must flow based on the head flow.

This, in effect resulted in no restriction to the heads at all, so they were able to flow to their full potential. Prior to that the manifold was the bottle-neck and restricted the head flow quite a bit.

The final results were 340 cfm with the manifold bolted to the heads on the flow bench.

Took a long time to work out the kinks, but the final results were worth it. The heads started out being All Pros that were supposed to flow a ton, but the guy Steve bought them from had them milled a lot - I'm guessing to increase the compression for the combo he was planning to run. This made it impossible for Bob - the porter - to get the flow back even though he welded up the ports and redid them. The radius just became too short with the decks cut so much.

We ended up using a set of Brodix heads modified by Gerate. He's a well known roundy-round guy and I believe he buys the castings from Brodix and then works them the way he wants.

Bob use to work for Extrude Hone and has ported and flowed about everybody's stuff and he's got a lot of stories on how some of the big name companys fudge their numbers.

He'd done minirams before, but never to the extent he did on Steve's.

Interesting thing he told Steve too was that the manifold has to be able to flow a lot more than the max flow of the heads so as not to present a restriction to the head flow.

I had thought that if your manifold flowed, say 320 and your heads flowed the same they'd be a matched set. Ain't so. The manifold needs to flow a lot more than the heads.

So when you see flow numbers from a head company or in one of the mags, that doesn't mean it'll flow nearly that much if the manifold isn't up to snuff.

He also had to weld up and re-port the intake opening so that they'd match the raised runner heads.

If can email you the final flow numbers if you'd like; let me know.

His name is Bob Jones 1-562-923-6774

Take care,

Jake



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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

e-man

OK the resistance of the knock sensor is 101K ohms and I back probed the ECS module and getting 1.9v with the everything connected so the knock sensor is dead! Is the 1.9v at the ECS module OK or is the ECS dead too?

JakeJr

My service manual is for a Vette, so the circuits and wire colors may be different, but it says that:

Disconnect ESC module. Check voltage from ESC connector term B to ground. Should read battery voltage.

If Okay: Check for open or short to ground in CKT 457 (which is probably a different # circuit on the "F" body). If not open or shorted to ground, it is a faulty ESC connector or ESC module. Unfortunately I couldn't find 457.

If below battery voltage: Repair open in circuit 439 (probably different # again). BTW, 439 is the pnk/blk wire that goes from the ESC module to the instrument panel (IP CONN)connector through the ECM/IGN switch to the ignition. It also branches at the IP CONN (still Pnk/Blk) and goes to A6 on the ECM.

Now remember, these wire colors and circuit numbers are for an 86 Vette so yours will probably be different, but, hopefully, this info can point you in the right direction.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

e-man

What about the knock sensor should I get a GM one or a autozone one?

89gta383

iTrader: (5)

Get it from GM, mine was like $45 bucks.

e-man

Is the 90 and up knock sensor less sensive than the 89 sensor?