Plug-Coil-MPG Conundrum (1 Viewer)

[kennedymil]

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:

• 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!

 

[NickSonoma]

H

 

[bigredmachine]

Did you at least eyeball the gap to make sure the new ones weren’t way off from what you removed?

thats not really going to help much, its normal for the gap to open up as the plug wares. you would want to use a gap gauge on the new ones, they should come pre gapped so they should be good to go.

 

[NickSonoma]

thats not really going to help much, its normal for the gap to open up as the plug wares. you would want to use a gap gauge on the new ones, they should come pre gapped so they should be good to go.

yes, but things happen. Gravity happens. You start with the simple solutions.

 

[kennedymil]

Thank you! I’ll pull it back apart and do a spot check on a few plug gaps.

Are there any Techstream metrics that might provide a clue?

 

[suprarx7nut]

First off, is there a chance this is just a perception issue?

The calculated instant MPG readings are of minimal value unless you're a savant and can run an integrated total in your head while driving.

Run a few tanks and see what the real world mileage is.

Techstream can show bank1 vs bank 2. If the banks are notably different, that might be a clue.

However, if it runs well and your only concern is that you think the instant MPG calcs in the infotainment seem low.... I'd not worry.

 

[kennedymil]

@suprarx7nut- I’ll definitely look at bank1 vs bank 2numbers.

For MPG I’m looking at the trip averages and the tank-since-fill average. The ScanGauge tank average agrees with the built-in display, so I think the numbers are accurate. I’ve also noticed the fuel needle dropping much more quickly.

 

[abuck99]

Replacing plugs & coils is also a good time to clean MAF sensor since ECU will be working from the previous values of old plug & coil combination. Your truck may need to go through a series of run cycles to adapt to new parameters before you notice any difference in mileage.

 

[kennedymil]

Cleaned MAF today, which looked good pre-clean. Now it’s extra clean.

I also pulled a plug (#2) to inspect and check gap. New plugs are Denso Iridium IK20TT.

To my surprise (?) the plug gap was 0.85-0.90mm, not 1.0 mm as spec’d on the Denso site. Some were as low as 0.80 mm. Could this be part of the issue? I bought them at AutoZone, so am confident they are genuine.

AutoZone has guarantee - -maybe I pull all 8 and return them for a fresh set? I’m wondering if I should go back to SK20R11 that were in there before.

Boroscoped the cylinders while I was in there. They are very clean.

 

[04UZJ100]

Cleaned MAF today, which looked good pre-clean. Now it’s extra clean.

I also pulled a plug (#2) to inspect and check gap. New plugs are Denso Iridium IK20TT.

To my surprise (?) the plug gap was 0.85-0.90mm, not 1.0 mm as spec’d on the Denso site. Some were as low as 0.80 mm. Could this be part of the issue? I bought them at AutoZone, so am confident they are genuine.

AutoZone has guarantee - -maybe I pull all 8 and return them for a fresh set? I’m wondering if I should go back to SK20R11 that were in there before.

Boroscoped the cylinders while I was in there. They are very clean.

The SK20R11s are OEM - they’re in my 2UZs and 3URs. The IK20TT are not.

 

[kennedymil]

The SK20R11s are OEM - they’re in my 2UZs and 3URs. The IK20TT are not.

Denso spec’s the IK20TT as compatible (at least from their website and automotive stores). A number of guys are putting them in 2UZs and reporting good performance. I thought I’d try ‘em, but am now second-guessing that decision.

 

[04UZJ100]

Denso spec’s the IK20TT as compatible (at least from their website and automotive stores). A number of guys are putting them in 2UZs and reporting good performance. I thought I’d try ‘em, but am now second-guessing that decision.

700,000 miles on Toyota V8s and I only ever use SKs……Toyota doesn’t list the TT.

They list one Denso plug and one NGK plug for nearly every car/engine they manufacture.

 

[kennedymil]

Update: I went back to SK20R11s. Issue solved. I’m back at 13 mph in city traffic driving and 15 mpg in the burbs. 19 mpg at 70 mph cruising.

 

[04UZJ100]

Update: I went back to SK20R11s. Issue solved. I’m back at 13 mph in city traffic driving and 15 mpg in the burbs. 19 mpg at 70 mph cruising.

Something something you so......

 

[2001LC]

Drop in MPG by just install of TT spark plugs. Indicates something wrong with those parts store plugs. To often I got bad plugs from parts store (Advance Auto). I found a minimum of 1 in pack of 4 (SK or TT), either bent electrodes ground, gap off or someone replaced (returned) with replacing with bootlegs! I also found some with plastic and some with cardboard shipping protectors.

I stopped buying plugs from parts store like Advanced Auto, ebay or Amazon. I now buy only directly from Denso wholesale approved supplier or Toyota dealership.
In over 100 TT spark plugs form Denso wholesale. All have had plastic shipping protector covers and all gaps perfect at 1.0mm for TT, +-0.05mm.

TT is designation for the supper thin 0.4mm electrode (China ASAIK can't bootleg, "yet"). The IK20TT are interchangeable with the SK20R11, which are both compatible with our 4.7L 2UZ-fe. Both are Iridium-tipped.

NGK discontinued the IFR6A11, which Toyota has list in the 98-07 FSM, so no longer sold at Toyota. They sub over to the IFR6T11 NGK.

I found NGK BKR6E1X-11 in one 2000 LX470. It ran strong with very good acceleration, once I torque in all the plugs. Funny thing: Owner complained of sluggish acceleration. I found all plugs loose. Crush washer not even crushed..DUH!

 

[kennedymil]

Drop in MPG by just install of TT spark plugs. Indicates something wrong with those parts store plugs. To often I got bad plugs from parts store (Advance Auto). I found a minimum of 1 in pack of 4 (SK or TT), either bent electrodes ground, gap off or someone replaced (returned) with replacing with bootlegs! I also found some with plastic and some with cardboard shipping protectors.

I stopped buying plugs from parts store like Advanced Auto, ebay or Amazon. I now buy only directly from Denso wholesale approved supplier or Toyota dealership.
In over 100 TT spark plugs form Denso wholesale. All have had plastic shipping protector covers and all gaps perfect at 1.0mm for TT, +-0.05mm.

TT is designation for the supper thin 0.4mm electrode (China ASAIK can't bootleg, "yet"). The IK20TT are interchangeable with the SK20R11, which are both compatible with our 4.7L 2UZ-fe. Both are Iridium-tipped.

NGK discontinued the IFR6A11, which Toyota has list in the 98-07 FSM, so no longer sold at Toyota. They sub over to the IFR6T11 NGK.

I found NGK BKR6E1X-11 in one 2000 LX470. It ran strong with very good acceleration, once I torque in all the plugs. Funny thing: Owner complained of sluggish acceleration. I found all plugs loose. Crush washer not even crushed..DUH!

Was definitely something wonky with TT plugs. The gaps were clearly off, as noted above.

Exchanging the TTs for SKs (from the same Advance Auto), fixed it. Gaps on the SKs were right on.

TT packaging looked OEM, no paper electrode covers or anything like that. Appeared to be exactly like pictured on Denso website. But I’m definitely not a plug expert.

Word to the wise - double check gaps before install

 

[dbleon]

Genuine Toyota plugs only for me.. not much cost difference

 

[2001LC]

Was definitely something wonky with TT plugs. The gaps were clearly off, as noted above.

Exchanging the TTs for SKs (from the same Advance Auto), fixed it. Gaps on the SKs were right on.

TT packaging looked OEM, no paper electrode covers or anything like that. Appeared to be exactly like pictured on Denso website. But I’m definitely not a plug expert.

Word to the wise - double check gaps before install

Always check gap, and with care to not put force on electrode!