TOPIC: 1998 chev suburban

Finally did mod to wife's suburban. We are both pleased with results! Pre-mod city 12 MPG, Hwy 17 MPG. Post-mod city 15 MPG, Hwy 20 Mpg. Approx. 173,000 miles on car and been running with drilled and gapped spark plugs for couple years now. Seems to have increased pre-ignition knock significantly. Mileage gains were results of checking numbers on first couple tanks of gas. Hopefully not losing gains as we speak. Seems like knocking is either not as extreme as it was or grey matter ecu just tuning it out. I'll have to check with my bride to see if mileage numbers are maintaining gains.

Congratulations on your first Groove!

To correct for the spark knock, what I have found assists the sluggish ECU's is to do some short power surges. In other words, slam on the gas pedal and hold it until the knock appears, then release. Let the vehicle slow, then slam it again.

After a few of these (five or six) the ECU generally adapts the timing, and will further reduce the fuel delivery...

IMHO that is!

Give 'er a shot and let us know how that works for you!

Further, increasing the spark gap will further reduce that nasty knock as it delays the spark a very slight degree. Of course, it also helps with the mileage!

Ron

Just a common-sense guess on my part--how old are the O2 sensors? If a scan tool could be plugged in to the OBD2 port under the dash, it could be seen if the O2 sensors voltage is going up/down, with a warmed-up engine. If the O2's are very old, they might be sluggish or dead...? TracyG