IainM

On a 30 yr old car, vacuum leaks have to be high on the list. When warmed up, spay carb cleaner around the vacuum line and air intake and see if revs pick up

tosha

I see @Steve Weiner-Rennsport Systems posted that the likeliest way to tell that it was chipped is by seeing if it was replaced - so if my ECU only has 900 hours, it likely was replaced. Question is - to stock? I need to look at the part number I suppose. If it was previously chipped before it was sold, what components may be lurking that needed the previous ECU? Exhaust bits are all stock. Anything relate to fuel injection or air intake that could have been changed?

IainM

After you’ve done the quick and easy vacuum test you can pull the drivers seat and see if the security screws on the ECU have been removed

LimeyBoy

Intake or exhaust parts may have been modified if the ecu was - to take advantage of a new ecu tune. But first I'd verify the ecu - per Iain above. Post a photo to start - showing part number and exterior ecu condition.

LimeyBoy

You have a condition now where you feel performance is down (may be the ecu pulling timing).
So add octane booster and see if that known condition changes.

Ie. Using octane booster stops the loss of power feeling you previously noted.
Ok, now you have a piece of the puzzle: Octane changes the situation.

95_993

+1 for LimeyBoys recommendation. In addition, please share a little more if ie- what gear, rpm, speed are experiencing the pinging? Does the pinging subside after a sec or does it stay constant as long as you hold the throttle down?

systemsc

A typical mod of a '96 DME ECM;

the wanderer

Would it not be a good idea to test the DD
ensure it's working as it should?
TJ

wellcraft290

Check the distributor as well. I had a 964 that pinged under hard acceleration and ended up being the twin distributor belt snapped. Wouldn’t realize otherwise.