Running rich after changing spark plugs

Just changed the spark plugs on my 95. I replaced with the dual electrode ngks iridiums (

$6 BKR5EKB-11 NGK Spark Plug Stock # 3967

BKR5EKB-11) and although the RPMs are where I’d expect them the truck now smells like its running rich and it never had before.

I didn’t gap them because these supposedly come pregapped but now I’m second guessing that decision. I coated the outside part of the plugs lightly with dielectric grease and just cleaned the MAF sensor but besides that nothing else has been touched. No codes or anything.

Any idea what might be contributing other than the gap?

 

What did you clean the MAF sensor with? I'd focus on that as if it's not reading accurately it will throw off your fuel/air ratio.

 

I cleaned it with the CRC MAF sensor cleaner I picked up from autozone. Thanks for the tip- I’ll look into troubleshooting the MAF since I don’t really know much about it.

 

I'd double check them double plugs.
Could it be gunk got in the throttle body?

Seafoam er'!

 

Yeah I was wondering about the TB, too. I’ll clean that out and see what there is to see. Thanks for the ideas. With regard to the plugs, should I be gapping them myself despite that they say they’re pregapped with some fancy laser technology?

 

Always good to check the gap to make sure it's right.

 

Did you reset the ECU?

 

Definitely! You don't need to change the gap, just insert various feeler gauges until you know what "pre gapped" means to that manufacturer. Also the ground electrode could be pushed in during shipping/handling but often there will be a protective cylinder over the threaded end to prevent this.

This was going to be my suggestion -- disconnect the battery overnight. Also, nearly all vehicles will "smell rich" during the warm up cycle (open loop). Once the cats and everything gets up to temp, the unburned fuel smell goes away... usually.

 

Probably the ecu calibrating itself for the clean sensor and the new plugs are probably burning better.

 

I'm a pretty firm believer that 'magic plugs' don't do anything but lighten your wallet. Have only seen advertisement 'evidence' that shows otherwise.

The OE brand/rating plugs work just fine.

Regardless, checking the gap is a must do.

How does that happen if he hasn't reset the ECU?

If they are 'better' that would mean more complete fuel burn, right? But his complaint is smelling rich. As in un-burnt fuel.

@Bend_corners, I have no idea if your '95 even has a learning ECU. My mid 90's Mazda I did a bit of racing with did not. Of course that doesn't mean your truck doesn't. So, regardless of it being learning or not, a 'reset' via pulling the negative battery cable for 10 minutes or so won't hurt anything either way.

 

Man y’all are awesome. So when I cleaned the MAF, I pulled the negative terminal and it was out for a good 30 minutes or so. When I powered the truck back up, I let it idle for ~10 minutes and the RPMs dropped steadily during that time, settling out around 700/min. Because of this, I assumed that the ECU had reset. But maybe it needs longer than 30 min to reset?

I guess I need to gap the plugs, despite the fact that they had a protective cardboard cylinder around the grounding electrode. Seems like a rookie mistake, but when I checked with a standard autozone gapping coin it was tough to fit the coin in without pushing hard even at the shortest gap on the coin. That was a consistent finding on all 12grounding electrodes, so I figured this was because the grounding electrodes were scalloped in the middle. Not sure if that makes sense in the abstract, but now I’m thinking the plugs are massively under the recommended gap.

 

they are probably over gaped now if you forced the flat single electrode gaping tool between the center electrode and the grounding points. You need a round plug gaper similar to this https://www.sears.com/kd-tools-spar...rId=Tool Shack&prdNo=7&blockNo=7&blockType=G7.

As to your thinking it is running rich there is only one way to tell and that is with a decent OBDII scan tool that will give you live data, specifically grams per second reading off the MAF and fuel trims both long and short term.

 

When you are gapping plugs, try not to touch the center (hot) electrode very much. Changing the plug gap should be done by tweaking the ground (strap) electrode ONLY.

 

I bought my dual-strap Denso OEM plugs from the dealer. Pre-gapped means they are "pre-gapped" to the wrong spec. I had to adjust ALL of them to spec.