Ok in open loop it knocks if I try to take the engine above 2000 rpms and in closed loop it pings a little just before the shift into either 2nd, 3rd or possibly overdrive on hard accelaration. any ideas? timing is at 0*, new knock sensor(which helped with the problem). it is an LG4. Thanks in advance.

 

Inoperative EGR valve or carbon-plugged EGR ports.

For me, it was the latter.

 

First off, 0` is not where your initial timing should be, 6` is and most cars can get away with way more than that. I realize doing this might decrease the severity of your knock, but retarding your ignition is just masking the problem at hand instead of fixing it.

Second off, how do you know you have knock? Is it audible or did you notice it with a scanner?

 

ok some people keep saying for an LG4 the stock timing is 0* while everyone else says its 6*. I can hear the knock. I even took it to a shop and they set it to 0*. So I don't know about the timing anymore I'm just leaving it at 0*.

 

My factory-recommended base timing was 0 degrees. When I bumped it up to 6 degrees, my pinging problems started unless I used mid-grade gas.

I had a coolant leak around the intake, so in taking it off I discovered the plugged EGR passages. I put the intake in my sig back on at that time, and 6 degrees was no problem. I'm running 10 degrees now, no pinging on regular unleaded.

Carboned-up combustion chambers will also cause pinging.

 

I assume your iroc is either engine code 8, F or G (this is the 8th vin digit), and if that is the case 6` BTDC is factory spec. You can trust me on this one, I even cracked open my Motor's manual to double check. If your engine code is a H, 0` is factory spec, but I don't thik you could get that engine in a '87 iroc. Like 57kid said, most people can get away with way more than factory spec, I have my car at a conservative 10`.

If your knock is bad enough to hear, there is something really wrong, and I would tend to agree with 57kid's train of thought. It is time to verify the operation of your egr system, and that's not going to be easy.

Good Luck!

 

so whats all involved in checking the EGR system? What should I be checking?

 

According to https://www.thirdgen.org/newdesign/tech/techdb.shtml, the LG4 was available in an '87 IROC.

The easiest way to check the EGR valve itself is to attach a vacuum source directly to the valve. At an idle, the engine should stumble or die when the valve is opened. If it doesn't, you either have a bad valve, or plugged passages.

If that works, then the solenoid is suspect. Put a vacuum gauge on the line going between the solenoid and valve. It should show vacuum at part throttle (might have to check this while driving, I've never done it on a CC car).

 

I can vouch for EGR causing knock. My first car was an 87camaro with an lg4. I went nuts trying to make it quit knocking. Finally, I had the intake off one time (other repairs), and say the EGR passages were 100% blocked with black carbon deposits.

Is this knock at about a mid-throttle acceleration? If it's knocking at WOT, then EGR is not the problem. EGR isn't supposed to operate at WOT.

After I cleaned my EGR passages out, I was able to advance timing above stock spec. IIRC, 0 deg was the spec for the LG4 engine.

 

before closed loop its more mid-throttle but in closed loop its more at low throttle acceleration and for a very very short time at WOT.

 

My problem is the EGR ports too. I took my car to the mechanic in town to have the plugs and wires changed (didn't have time to do it myself) and he checked the timing to and said it was dead on. Did some tests on the EGR valve and said that it was barely working at all and I'd have to take the intake off to clean it enough to make a difference. Having an open element air cleaner and running premium fuel makes my pinging go away. The mechanic recommended I just keep doing that until I have time to fix it.