Today on my way to work I decided to datalog my car on the way to work to see how everything was doing. I was particularly concerned with thevknock count as I want to advance my base timing to either 8 or 10* engine permitting.

I brought the laptop, hooked it up and went to the spark count page on WinALDL. Right away it started recording knock at idle. It went from 3 to 4 and then 5 before I gave it some gas and held it at 1600RPM. Within about 5 seconds, it recorded 254 knocks at this RPM and this number jumped to 5xx another 5 -10 seconds later. As soon as I let off the gas, the 5 knocks that had been recorded at idle changed to 2xx knocks.

Is my knock sensor bad? How is this even possible? My base timing is currently at 4* BTW which is a 2* retard from stock.

 

Common to get some knock counts at start up from the noise of the starter engaging.

As for the other counts, good possibility that it is false knock. Any noise that isn't common to the engine will do it. Exhaust rattle, bad bearing in an accessory, bracket loose or broken, bad rod bearing, cracked flex-plate, and so on.

RBob.

 

Where do you think the false knock could be originating from? As for the previously mentioned possibilities, I can tell you that all the front end accessories have been removed except the waterpump, steering pump and alternator. Steering pump doesn't seem to be making any noise and the alternator/waterpump are new. The motor only has 15k on it with no noises and I can't hear any sort of rattling or vibrating parts.

Might it be worth it to try replacing the sensor, or do these rarely go out? What I can tell youis that it is the ONLY stock sensor still remaining and has somewhere around 170 k on it

 

New engine: compression ratio higher? Different cam? Forged pistons with some clearance? Knock sensor too tight? (11 - 14 ft/lb torque spec).

Pull some plugs and look for signs of detonation.

RBob.

 

It's the autozone stock rebuild. If anything, the compression would be LOWER than stock, but it says rebuilt to stock specs.

I did try hooking up WinALDL again. What I can tell you this time now I paid closer attention is I believe some of the knock counts are actually detonation. It counted somewhere around 10 - 14 at 1000RPM and I could hear it from the engine. It didn't sound like a traditional knock. It was something like a misfire but this sounded different. It almost sounded like muffled popcorn was cooking in the block. It does not do this without the WinALDL cable plugged in (I have the ECM that requires the 10K resistor thus disabling spark knock retard while datalogging).

Something isn't right. What would be causing this? I'm on 87 octane right now and the next fill-up I'll try premium. Something else I can tell you is that the base timing is also not correct. The shop that installed the engine set it at 4* advanced. I know 2* isn't all that much especially since It's retarded by 2* instead of advanced by 2*, but thought it would be worth mentioning. Any input?

 

Seriously, only 11-14 ft./lbs.? Didn't know that when I installed one recently.

If the sensor was tightened more, let's say to 25 ft./lbs., how would that adversley affect knock counts?

 

That 10K resistor can also tell the ECM to add timing. Not sure on the '85 TPI ECM, but it does for the majority of the others of this era.

RBob.

 

Makes the knock sensor more sensitive. Which can mean more false knock is reported.

RBob.

 

Really? Do you have any documentation on this? If this is what it's doing, that's just stupid and going to be the last straw to make me do an ECM swap. I already hate the 165 ECM enough.

 

with WINALDL it will show ALDL mode in the flag data tab. zero that value out in the bin

 

The OEM ECM has been swapped for a '7165 ECM? If so which code mask are you running ($32 or $6E)? Easy enough to zero out the calibration parameter for the added SA.

For the stock '85 ECM ('6870) I don't know of a hac for it. So I can't help much with it.

RBob.

 

Sorry I got my wires crossed. Right now the car is equipped with the stock 870 ECM.

I did however score an ECM from the junkyard today from a totaled '86 Z28 TPI. I still cannot for the life of me figure out why they had about 10 thirdgen birds out there, a couple TBI and the rest V6's, and the one TPI thirdgen they had I had to get them to lift 2 cars off the top of it in order to pick it apart. They crushed the car after I left

I was going to thoroughly molest the motor but it turned out to be 100% stock. All the parts were still there too except the driver side valve cover.

 

What would you look for on a plug for signs of detonation?

 

Usually you use a magnifying glass to inspect the insulator porcelain. If you can see tiny metallic specs, that means that cylinder has been detonating. Those specs are actually small metal particles that get blasted off the piston as that cylinder detonates. In more extreme cases, the insulator porcelain can be cracked or broken.

 

Would the specs be shiny or dull when you shine a light on it? I've got a 20x eye loupe with a small LED light attached to it.

 

I would assume a tad dull since there is combustion going on in the cylinder, probably won't be spitshined. I'll wait for someone else to chime in on this.