No ping when very humid?


Denisefwd93

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That's the question I had the other day! the humidity has been in the high 80 to Almost 100% here for the past week and I just happened to notice I could not get the engine to Ping like it always does even on light acceleration,.
so what's up on that? I just know Ron has the answer LOL
 


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Dirtman

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You want the engine to ping :icon_confused:

But anyway... Hot humid air is less dense, less o2 per volume so engines run richer. Rich mixtures don't knock/ping as much as lean mixtures because rich mixes have cooler combustion chamber temps.
 

Denisefwd93

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I kind of believed it was humidity related density of air and all that but it just really struck me as odd because the truck pings at all speeds & ranges except flat roads & light gas pedal. And not something I even addressed yet,
 

Dirtman

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Flat roads with a light foot means less engine load which again means lower combustion chamber temps so less likely to ping. Once you get those combustion chamber temps up it can start turning carbon buildup into "glow plugs". The red hot carbon ignites the fuel instead of the spark plug and it will continue pinging until the temps drop.
 
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RonD

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Yes, I would agree with Dirtman

Humidity actually makes air less dense, I know that sounds bassackwards, lol.
But the water molecules in a volume of air displace the "air" molecules, so less air

MAF sensor uses a heated wire to determine air density, the faster it cools the wire the denser the air, so while there is less "air" the MAF is "tricked" by the humidity.
So computer uses same amount of fuel in the mix which has less "air", which causes a slightly Richer mix and less likely to ping under load


Pinging under load can be a few things, since the humidity thing seems to help it could be IAT(intake air temp) sensor or MAF is slightly off, causing computer to run leaner mix that it should, normally the O2 sensors should adjust that, but while they are good for feedback they are not always Prefect, lol.
 
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Dirtman

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Back in the days of carburetors when we had to take a vehicle for an emissions test you NEVER went on a hot, humid day because the engines ran richer and you were more likely to fail. We always waited for the coldest driest day. I had a printout showing 2 tests done on a 73 chevy c-10. One test on the nastiest day of summer and one in the middle of January. The difference in emissions was amazing. Modern fuel injection compensates for this but like Ron mentioned, only to a certain point. Sensors can only do so much.
 

Denisefwd93

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Just to follow up on this. The other day I tried out my new Harbor Freight tamper-proof Torx on the MAF screws, that sure made it easy!


Took the MAF out and sprayed it really really well with MAF cleaner at least three times, put it back in let it set for half an hour plugged it back in started it all was well. Started driving the truck yesterday no ping and it's warm out driving around again today no ping. I'm impressed and just confirms what I always say always seek out and fix the little things first!
 

RonD

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Denisefwd93

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Thanks Ron I apparently trying to clean the MAF from inside the air intake tube isn't effective.

The 2000 RPM burst at startup is back, sigh
 

Denisefwd93

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Day 3 it was really even warmer today, no ping! even with the AC on!
 

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Denisefwd93

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Thinking I'll give this thread a ping since it's about pinging 🤣 no mistake it's been humid all week and there's hardly ping coming from my 4.0!

it's hard to believe, im retired and I can't find time to do things. 🤔
I will clean the MAF again and connect up some kind of duct to take air from outside the engine compartment where it's as hot as an oven! Not quite ready to get into taking the intake and valve covers gasket replacement. 😨
 


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