Hi - I have a '03 LC with 182,000. As part of PM, I did a full coil (Denso 6731303) and plug (Denso Iridium TT, IK20TT) replacement for all 8 cylinders.
The engine starts up and runs beautifully. Purrs like a kitten. No noises or oddities whatsoever.
However, my "city" gas mileage has fallen dramatically based on ScanGauge readings. For a short city trip with a few lights, 20-40 MPH, I now get ~ 10 MPG. Used to be ~15 MPG. In heavier traffic, it can be as low as 8 MPG (used to be ~12-14). Other than plugs/coils, I did not do any other work to the truck.
Here's the really odd thing: my highway mileage does NOT appear to be affected. At 65mph cruise control, before and after readings are consistent at ~ 18-20 MPG.
Here's what I've troubleshot so far:
The only thing I didn't check is the plug gaps. From my understanding, the plugs should just go straight in, no adjustment necessary.
I read the entire Spark Plugs Alert Alert Alert thread (super informative) but didn't see the issue raised.
Is there a ScanGauge or Techstream metric/reading that might provide more info as to what's going on?
Thanks in advance!! With gas in Chicago north of $6/gallon, a 25-50% hit on city MPG adds up quick!
The engine starts up and runs beautifully. Purrs like a kitten. No noises or oddities whatsoever.
However, my "city" gas mileage has fallen dramatically based on ScanGauge readings. For a short city trip with a few lights, 20-40 MPH, I now get ~ 10 MPG. Used to be ~15 MPG. In heavier traffic, it can be as low as 8 MPG (used to be ~12-14). Other than plugs/coils, I did not do any other work to the truck.
Here's the really odd thing: my highway mileage does NOT appear to be affected. At 65mph cruise control, before and after readings are consistent at ~ 18-20 MPG.
Here's what I've troubleshot so far:
- Confirmed plugs torqued to 17 ft-lb (higher than manual, but recommended in this thread to avoid plugs backing out.)
- No anti-seize or other lubricant applied to plug threads. All went in cleanly.
- Ignition coil tubes were clean, no evidence of oil or fouling
- All vac hoses reconnected to air box and double checked
- Connections from air filter to manifold double checked, tight, no obstructions
- Battery terminals disconnected, then reconnected to flash ECU
- No fuel odor or other evidence of a rich mixture
- Same tank of fuel pre- and post-change
- ~ 150 miles driven since coil/plug change. Lower MPG noticed immediately, has been consistent.
- No new codes (have had an intermittent charcoal canister code, but nothing new)
The only thing I didn't check is the plug gaps. From my understanding, the plugs should just go straight in, no adjustment necessary.
I read the entire Spark Plugs Alert Alert Alert thread (super informative) but didn't see the issue raised.
Is there a ScanGauge or Techstream metric/reading that might provide more info as to what's going on?
Thanks in advance!! With gas in Chicago north of $6/gallon, a 25-50% hit on city MPG adds up quick!