Trying to improve mileage - what have I missed?
03-11-2021, 04:31 AM
#61
CF Veteran
Kinda? The discussion started with the premise that a hot intake manifold heat-soaks the IAT sensor and screws up the numbers. Which is overall a false premise given how IAT sensors are built and function. And your observation generally backs that up. If I read you correctly, OAT < Intake Manifold Temp < IAT Reading. If the IAT reading is higher than anything else it can't be heat soaked...and suggests a weird algorithm/correction/calibration in the ECU. The problem with all of these approaches is that they aren't proving that the IAT sensor isn't wrong. They are just proving that you can move it to a different location and read a different temperature. You can't say the IAT is measuring properly without a secondary known truth source measuring the air temperature at the same location. Everything else is just using circular logic on the IAT sensor.
The PCM uses [IAT] to calculate the following:
• Injector pulse-width
• Adjustment of spark timing (to help prevent spark knock with high intake manifold air-charge temperatures)
• Injector pulse-width
• Adjustment of spark timing (to help prevent spark knock with high intake manifold air-charge temperatures)
1. Heat soak exists; and
2. Inappropriate changes to engine performance occur because of it.
I have to tow a load that's nearly maximum, in 3rd gear, up a few hills. The engine temperature increases during the hill challenges, so I'll watch IAT and timing during the challenge.
03-11-2021, 04:45 AM
#62
CF Veteran
Meanwhile, I need somebody in the North to prove to me that moving IAT to the airbox does anything good to the engine when you tell it the intake air is 20 degrees instead of 162.
03-11-2021, 04:56 AM
#63
CF Veteran
Also, since
ya have to wonder even if IAT is completely engulfed in flames how much difference it really makes in the overall algorithm.
The PCM adjusts ignition timing based upon inputs it receives from sensors that react to: engine rpm, manifold absolute pressure, engine coolant temperature, throttle position, transmission gear selection (automatic transmission), vehicle speed, ...and the brake switch.
03-11-2021, 05:19 AM
#64
CF Veteran
03-11-2021, 06:23 AM
#65
CF Veteran
If they let Death Wobble slide why is it a stretch they found it easier to put the IAT in the manifold than the air box. Coffee sure is good this morning.
Ill go further, why didn't they put 60mm throttle body on if it works better. Why didn't they use better pistons that don't develop slap. How about some bigger brakes? Why not the 2 downpipe exhaust manifold, or one that doesn't crack? 120A alternator? Copper nickle brake lines? Well they could have..
Ill go further, why didn't they put 60mm throttle body on if it works better. Why didn't they use better pistons that don't develop slap. How about some bigger brakes? Why not the 2 downpipe exhaust manifold, or one that doesn't crack? 120A alternator? Copper nickle brake lines? Well they could have..
Last edited by 97grand4.0; 03-11-2021 at 06:29 AM.
03-11-2021, 06:54 AM
#67
CF Veteran
Guys come up here looking for suggestions to improve performance, you give them one, and they try to rip it to pieces. Have a nice day.
03-11-2021, 12:38 PM
#68
CF Veteran
I gotta stick with "kinda" till I see one more thing but yeah IMO moving the IAT is (mostly) a perpetuated internet myth.
So now I have to drive around to try to prove that:
1. Heat soak exists; and
2. Inappropriate changes to engine performance occur because of it.
I have to tow a load that's nearly maximum, in 3rd gear, up a few hills. The engine temperature increases during the hill challenges, so I'll watch IAT and timing during the challenge.
So now I have to drive around to try to prove that:
1. Heat soak exists; and
2. Inappropriate changes to engine performance occur because of it.
I have to tow a load that's nearly maximum, in 3rd gear, up a few hills. The engine temperature increases during the hill challenges, so I'll watch IAT and timing during the challenge.
03-11-2021, 01:37 PM
#69
CF Veteran
Nope!
AAMOF the only enhancement I have is the Crown Heavy Duty Leaf Set (782s in the front to level it out).
I tow during off hours to avoid traffic, travel on days when the temp is ~50, and as noted, use 3rd gear the entire way. Rolling hills of New England, nothing really long or steep.
AAMOF the only enhancement I have is the Crown Heavy Duty Leaf Set (782s in the front to level it out).
I tow during off hours to avoid traffic, travel on days when the temp is ~50, and as noted, use 3rd gear the entire way. Rolling hills of New England, nothing really long or steep.
03-11-2021, 02:53 PM
#70
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Year: 95
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How is the incoming air charges temperature raised from ambient to 162F in the time and distance it takes to travel from the throttle body to the IAT ?
03-11-2021, 03:41 PM
#71
CF Veteran
03-11-2021, 03:51 PM
#72
CF Veteran
Or...
"Ambient" is relative. The engine compartment gets pretty hot. I tossed the house thermometer in front of the airbox intake and the temperature got to 110. The intake is too hot to touch. Gotta get a therm gun and see what the temperature of the intake manifold is to see what it's contribution is-- yet that still wouldn't provide proof. Somebody's gotta drill a hole...
"Ambient" is relative. The engine compartment gets pretty hot. I tossed the house thermometer in front of the airbox intake and the temperature got to 110. The intake is too hot to touch. Gotta get a therm gun and see what the temperature of the intake manifold is to see what it's contribution is-- yet that still wouldn't provide proof. Somebody's gotta drill a hole...
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NM-XJ (03-11-2021)
03-11-2021, 03:58 PM
#73
CF Veteran
...but even THAT wouldn't provide proof because we don't know what the algorithm is.
And besides, does the temperature really matter? It's just a number. I can envision the engineers with a 4.0 on the dyno saying "Hmm, @5000 ohms we get more torque if we increase the injector time to 5 mS instead of 4."
And besides, does the temperature really matter? It's just a number. I can envision the engineers with a 4.0 on the dyno saying "Hmm, @5000 ohms we get more torque if we increase the injector time to 5 mS instead of 4."
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doublechaz (03-11-2021)
03-11-2021, 07:36 PM
#74
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Join Date: Oct 2019
Location: Current XJ is
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Year: 95
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Or...
"Ambient" is relative. The engine compartment gets pretty hot. I tossed the house thermometer in front of the airbox intake and the temperature got to 110. The intake is too hot to touch. Gotta get a therm gun and see what the temperature of the intake manifold is to see what it's contribution is-- yet that still wouldn't provide proof. Somebody's gotta drill a hole...
"Ambient" is relative. The engine compartment gets pretty hot. I tossed the house thermometer in front of the airbox intake and the temperature got to 110. The intake is too hot to touch. Gotta get a therm gun and see what the temperature of the intake manifold is to see what it's contribution is-- yet that still wouldn't provide proof. Somebody's gotta drill a hole...