Rod Bender

Is their a diagnostic device you can attach to the dashboard.that alerts you to preignition. My hearing can tell me if I am getting preignition at low rpms, but there is so much engine and exhaust sound at higher revs I would like to know if I am getting it.

Injuneer

Your engine has a knock sensor to detect detonation. When it senses knock the PCM retards timing. It is so sensitive that it "hears" the knock and eliminates it before you can hear it. If you ran scan software like AutoTap, you could constantly monitor knock retard. You can also monitor knock retard with the ScanMaster LT1, but I'm not sure if that is still being made:

http://www.injuneer.com/images/photo.../DCP04287a.jpg

Rod Bender

Injuneer, thanks for the reply. However, my car has a PCM Tune For Less and an LT4 knock sensor. I get the rattle can sound when I load the engine under 2000 rpm. I use 93 octane Shell. I am thinking of sending my pcm back and having them re-program it for 89 octane. Or maybe the knock sensor is not working. What do you think?

Injuneer

You can't have an "LT4 knock sensor" because there is no such thing. I suspect you have an LT4 knock module. That's just a noise filter for the Crane Gold full roller rockers used in the LT4 engine.

In stock configuration the PCM can pull up to 15-deg of timing in response to detected knock. But tuners sometimes reduce the limit. If you are hearing it, you are risking damage to your engine. I'd check with the tuner to see what he did with the knock parameters.

But I don't see anything in your setup that would cause the engine to be prone to knock (different than pre-ignition, but pre-ignition is seldom the problem) on 93 octane. You need to find out why its happening, in addition to checking to see if the tune has seriously limited the ability of the PCM to respond to knock.

Is it possible its got heavy carbon buildup in the combustion chambers? Is the coolant temp excessively high? Is it possible its running lean? Are you lugging it in 6th gear under 2,000 RPM? Is the EGR system functioning properly - it will help reduce the chances of detonation when lugging the engine at low RPM?

Rod Bender

Injuneer, thanks for the input. I can't say whether there is heavy carbon buildup. How would I check, compression test? Coolant temp is not over 160 by my dash guage and when the PCM was recalibrated the thermostat was set to open at 160. Other than that I do not know how PCM For Less adjusted it. I think rather conservatively. Running lean? How do I tell, how white the plugs are? EGR system functioning properly? How is that tested? Nope, not lugging it in 6th at 2000 rpm. But third gear, yes.

01Z

Checking for a carbon buildup without some engine tear down would require a Borescope.

Generally your dash temperature gauge is adequate to check for overheating but a hot engine that causes detonation is obvious to the senses. Your coolant temperature will exceed 160F but generally shouldn't go beyond 220 with a 160 thermostat and cooling fan adjustment from your mail order tune. My LT1 will run about 185 in normal weather and driving conditions but can go beyond 210 in heavy traffic.

Checking for a lean condition requires a wideband oxygen sensor connected to a wideband controller and a way to record and / or visually monitor the sensor - many on the market and in speed shop tuning. Reading plug color is not going to be something you can (easily) or want to do with your engine.

Your PCM will report a faulty EGR system unless the mail order tune disabled the testing; a distinct possibility.

You need to contact the mail order tuner and explain your situation. If you have detonation now but didn't have it before the tune, your problem and solution is probably limited to that direction but not exclusively. Things / coincidences happen.

Rod Bender

Thanks for the reply 01Z. I do not think my coolant temperature is the problem, at least my gauge registers just above the 160 level and what I perceive to be pre-ignition happens even before reaching operating temperature. I do not get any codes. I would imagine a monitor to be expensive.I think I will send the pcm back to have the programming checked as you suggest.

01Z

Please post the results.

BTW, great screen name!