Knock sensors

Hello, '94 S10, 4.3, it has the two knock sensors in the heads. Could someone tell me how it is that I am able to make this engine knock with timing setting, shouldn't the knock sensors just retard the timing when they sense knock? Is there a range that I am out of? Slightly confused. Thanks to all.

-- David Algie Algie Composite Aircraft

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Reply to
David Algie
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The ECM can only do so much. Are you still trying to set the timing on that thing? never found that little brown wire? If all else fails, retard it 'till the ping goes away......Be sure to listen close on the highway, high gear, and slight acceleration.

Reply to
Scott M

If you get the base timing wrong the engine will be running it's pre-set spark curve but with the wrong setting. Let's say it calls for 15* of advance under X driving condition, and your base timing is supposed to be TDC. If you have it set @ 6* BTDC it'll end up running 21* advanced at condition X and might ping as a result. The ECM can only retard the spark so far, and if the offset in base timing exceeds this limited range, she'll be a-pingin'.

Doc

Reply to
"Doc"

Well, I found the little timing wire, disconnected it, I had earlier filled the crank damper mark with white paint so I'm sure it was visible, but when hooking up a timing light, the mark wasn't anywhere near. I guess my concern is that the distributor is nowhere where it used to be, I was very careful to set the engine on TDC, on the right cycle, before pulling it out, I did a lot of engine mods to the thing including port work, a new Crane cam, new high flow exhaust system, etc. but when I put the dist. back in the exact original place, with the engine still on the correct cycle, it was waay off, like I had to turn it about 40 degrees to make the pinging go away and make it idle happily. Everything points to the engine having much better flow with better filling capacity so it can't run the same spark advance it once did. Hmmm.

Reply to
David Algie

"David Algie" wrote

Have you checked the harmonic balancer closely? The 4.3 engine often had two slots in the harmonic balancer. It's possible you could have marked the wrong one.

Ian

Reply to
shiden_kai

probably wont idle at the lower speed because the ECM has had its power taken away and it needs to reset itself. Try holding the throttle open just a bit and look for the correct mark with the wire unplugged. Then if you find it, set it there. Then plug it back it and see if she'll idle/and run good. Bottom line: you are using the distributor to set the idle speed, thats a no-no. :) p.s. where did you find that little pesky brown wire?

Reply to
Scott M

Well, I have set the timing by ear, I keep retarding it until all pinging, or knock is gone, under high loads and speeds usually. The engine idles well at this setting and shows no signs of otherwise abnormal running. So Doc, what you are saying is that the engine has a set spark curve that I may be out of, and was, and now maybe it's close with the knock gone. Still, the knock sensors don't seem to be doing anything, they should reduce the advance when knock is sensed, and aren't doing that. Do they get old, or fail in anyway that you know? I am 100% sure about the timing mark setting when I had the engine apart, it was also confirmed with the cam timing marks as well, these lined up when the damper TDC was on it's mark (After I put it back on!), and the engine was at TDC. Strange.

Reply to
David Algie

From: "Scott M" Subject: Re: Knock sensors Date: Saturday, October 18, 2003 10:58 AM

probably wont idle at the lower speed because the ECM has had its power taken away and it needs to reset itself. Try holding the throttle open just a bit and look for the correct mark with the wire unplugged. Then if you find it, set it there. Then plug it back it and see if she'll idle/and run good. Bottom line: you are using the distributor to set the idle speed, thats a no-no. :) p.s. where did you find that little pesky brown wire?

Reply to
Scott M

First, I'm pretty sure your motor only has one knock sensor, either located in the bottom of the passenger side cylinder head (just beside the starter) or on the back of the intake manifold behind the dizzy.

Your KS is working or you'd have a code 43 when the ESC module ran it's self test, which is does each and every time you fire her up. So, no SES light means the KS is working fine. Unless you have a scanner hooked up to the ALDL and actually watch the timing advance you would have no way of "telling" that the KS was actually working (which it is). When the KS detects a knock, it sends a signal to the ESC which in turn tells the ECM to back off the timing a little bit. The ECM can only back it off so far, and of base timning is incorrect it'll still ping.

You need a timing light bud. You may be off a tooth on the dizzy.

If the timing is in fact set correctly and it still runs like ass, you may need an updated PROM with your cam and head specs.

Doc

Reply to
"Doc"

This truck has the VCM, as Mitchell software calls it, the one with the ECU under the hood, the wire was located among the harness among the ECU wires, with the big plugs connecting to it. The thing idles well, and has great power, and in fact I now get 32 MPG @ 75 mph, so it all seems good BUT the timing mark still baffles me, and I know that the inertia ring on the damper hasn't slipped because the mark was right on at TDC, noting that I could check TDC with the heads off, it was the #1 cylinder, the truck's left front cylinder. The idle is being set with the IAC because no matter where I set the timing now it always idles at 850 rpm. Doc noted that this truck should have one knock sensor, I may be mistaken but it seems like the same thing on both heads, a large diameter sensor with one wire coming off it, the left head has two sensors, one below the knock sensor, which I think is the gauge sensor.

Reply to
David Algie

well be one on each side. So you have any idea where you have the timing set at now? Maybe it just slipped a little fooling you into thinking it didnt slip at all. I guess if it runs cool, good and no pinging you are OK. When you say left side you do mean drivers side correct? Is your truck the newer Vortec with the "real" port injection, not the CPI? What mods did you do? I've been thinking about doing some on my Sonoma. Mine is a '94 but is the CPI (the one with the goofy single injector with pop-offs)- OBD1- 4.3 L Vortec. Does it seem to have more low-end power after the mods?

Reply to
Scott M

Scott, Mine's a TBI, I have the Edelbrock intake manifold and Crane cam's best "Computer compatible" cam (There is only two to chose from). It actually lost some low end power, or at least it's the same, it's just that the mid range is so much better that you never notice it, and now, as mine's a 5 speed, it's not like a Kenworth in that you have to shift constantly because the engine has about 800 rpm usable power, 1500 to 2300 like it did when stock. Now it revs on up and makes good power while doing it. MUCH better engine. It needs less throttle opening at 75 mph than 55 mph because the cam is in it's power there and not in it at 55! Yes, left side is driver's side. I was very careful before pulling the dist. out, I marked the forward position of the dist. body and where the rotor was pointing to. Other mods, increased fuel pressure by making the regulator adjustable,

100% stainless exhaust, ported iron manifolds, 2.25" primaries into a Magnaflow muffler, 3" single outlet all the way to the rear bumper, MSD coil, heads were ported, nice valve job with blended seats, decked 0.025", high flow air intake, edelbrock manifold was ported and matched to the heads. it could use a new chip to improve the fuel mapping (it's not lean, causing the knocking I don't think), but generally runs very well, fun to drive now.

Reply to
David Algie

adjustable,

Boy, you've been busy...All sounds good.

Reply to
Scott M

. Today we attempt... to fix an idle prob and low-end drivabilty symptom....on a computer controlled vehical that has engine mods.... . . you need to take Doc's advice on the computer.

you're working with a puter that's programmed for OEM systems.......you have altered the parameters with your engine mods....so now you "should" bring the puter system in-line with what the engine needs......timing mods.. fuel mods..firing mods......and the only way to do it is to get the computer to do it.

Take The Docs advice.

scrib abell ~:~

Reply to
Scrib Abell

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