Ok when I hit the accelerator hard wether from a stop or while I'm moving the engine will knock for about 1 second then stop. Is the computer bad or is it the knock sensor? I have an '87 IROC-Z with the LG4(the very big and very fast engine ).

It will also knock more before the car warms up. And just out of curiosity what is the normal operating temp of the LG4? Thanks in advance.

P.S. I forgot. another problem that has started recently is also when I hit the accelerator hard there is a big thump between the front seats under the console. Any ideas what this is?

 

Step #1 is to check your ignition timing. If it's okay, then there are a couple of other possibilities.

The EGR helps avoid pinging. The ignition advance curve built into the computer assumes the EGR is working. If the passages are plugged up (they were in my original manifold), then you'll get more pinging (and I did). Or if the EGR isn't working for some other reason, more pinging.

Normal operating temp is 195. Personally I run a 180 thermostat and prefer that. Also helps to suppress pinging.

The thump you're hearing is a broken transmission mount.

 

bare with me. How do you check the ignition timing and the EGR?

 

Ghig,

You'll need a timing light to check/set the base ignition timing. You can get a basic inductive pickup timing light for around $25. Make sure you get the inductive pickup type.

The engine should be at normal operating temperature, at the specified idle speed, and with the EST system bypassed. On some cars that involves disconnecting and electrical connector, and on some older models you may have to install a jumper in the ALDL connector under the dash. Check the label under your hood for specific instructions and the correct idle speed to check timing. It should also list the factory preferred timing setting.

Connect the timing light power leads to the battery, and clip the trigger pickup lead around the spark plug wire for the #1 cylinder (front left). Once everything is connected and the engine is idling at the correct speed, aim the light at the timing marks on the harmonic balancer (crankshaft pulley outer ring) on the driver's side. When you squeeze the trigger of the timing light, it should flash every time the #1 spark plug fires. This should illuminate the timing marks so that you can see the line on the balancer ring in relation to the timing tab on the front of the engine. If you cannot see any marks, shut off the engine, check to make sure the timing light pickup is around the #1 plug wire, and clean off the timing marks on the balancer hub.

Once you can see the timing marks, note the relative position. The tab is marked in two-degree increments, and the largest (deepest) 'V' in the tab is the 0° or Top Dead Center mark. All timing references are taken from that point. If your base timing is off the specification, loosen the distributor clamp bolt and slightly turn the distributor while observing the timing marks. Adjust the distributor position until you achieve the correct base timing. Shut off the engine, tighten the distributor clamp bolt, and recheck the timing to make sure it didn't move when the distributor was tightened.

You're all set to go.

EDIT: When you get that far, we'll get into EGR diagnosis.

 

your going to think this very funny.....I don't have any stickers under the hood with the exception of the hood's part #. and my repair manual doesn't tell me what the timing should be.