I've noticed that while driveing my '88 N/A 'vert with the 2 LED ECU error checker that the boost/Pressure sensor error is lighting. One long followed by 2 short flashes of LED 1. It only happens when I'm cruising at greater than 3700 RPM and I let my foot off the accelerator. It just flashes the error code once or twice.
Does anyone know what exactly is the significance of this?

 

The ECU is expecting a very low voltage (very high vacuum reading) from the sensor when the throttle plate being closed all the way is sensed. I would do a vacuum check on the engine, when closing the throttle at 3000 rpm you should see greater than 20 inches of vacuum. If you are not, you have a vacuum leak, find and fix. If you have the vacuum, check the hose going from the engine to the sensor for any cracks/leaks. If it is ok, check the sensor for proper grounding. If ok, check for the correct signal as per the tech manual. If ok, replace ECU, otherwise replace pressure sensor. Good luck!

Irv, Keith's dad

 

Does it really make that much of a difference to warrent all that troubleshooting? The engine seems to run fine.

 

Good question. There are 2 theories on this. One theory is, the boost sensor only controls retard under boost. If this is so, it is probably not worth worrying about. The other theory is that the boost sensor in combination with RPM determine fuel supplied to the engine, as well as retard. I believe this theory, since I have personally verified that the AFM is way past it's usefull range WOT, so the ECU has to use some other way to determine fuel requirements. Now, if this second theory is correct, you may very well be running lean under boost, and, since this could cause a blown engine, I would certainly check this out further. You can find an article on the TeamFC3S site on how to build your own FCD which includes a voltage versus boost graph that you can use for comparison purposes with actual readings from your sensor.

Irv, Keith's dad