Renix mileage issue / fix

I thought since gas mileage is such a hot topic around here now, I would post a tidbit that may help any of you having poor gas mileage on a Renix based system. There is a sensor very few people ever think about. It is the MAT or manifold air temp sensor. They are out of tolerance on many older vehicles and can cause a significant swing in your mixture. You can easily check it with a ohmmeter without taking off of the vehicle.

old_man said:

They are out of tolerance on many older vehicles and can cause a significant swing in your mixture.

Click to expand...

Hey old_man thanks for the tip, but I have a question about the quote above.

Are you saying they are out of tolerance due to age (if not replaced) or are you saying that some of the older ones were just defective?

I'd say age. Anything that responds to the environment is going to lose response over time.

I'd say to change IAT/MAP/HEGO at a minimum at about 200K or so - they all get old. I've got to do mine sometime soon...

5-90

No, they just go bad in many cases. You can easily check it by unpluging it before you start the engine and proble the connector. The chart should show you what the reading should be at any given temp. I originally found a bad one on my 4.0L after I stroked it and took it into the state to get their blessing. I passed emissions, but the guy like to play with his toys so we shot the breeze and he hooke up his SnapOn scanner and gave me a complete readout on all my sensors and their readings. After changing the bad sensor, it definately had a change in power and mileage. It was running way too rich.

Is this a renix only sensor?

-looking for improved milage on an HO

I'm not a real HO guru, so maybe someone else can help out here, but my memory says they don't have the sensor.

had to go take a look- there are four holes (for lack of a better term) on that side of the intake manifold.
from front to rear:
1. ccv output from valve cover
2. vacume line to brakes
3. sensor (IAT I assume)
4. something else-too cold to look for where it goes

so did the Intake air temp replace the MAT?

Like everything else inside the renix intake manifold the sensor end of the MAT gets covered in sludge eventually.
Unless my memory is slipping (again) the Engine temp. sender (lower left block) and the MAT have the same resistance values at the same temperature.
I've tested both, using an electronic thermometer, an ohm meter and a table lamp to raise the temp. some in a controlled way. Cleaning the crust off of my MAT sensor did help some.
As rich as mine was running this morning (first frost of the year), it's probably time to clean it and test it again.
Thanx for the reminder Old_Man.

Mine broke off in the manifold, now its plugged and the sensor is zip tied to the firewall. It doesnt seem to have altered mileage even though its probably cooler being in the engine bay. Maybe hit it with some penetrant before you try to remove it.

old_man said:

I thought since gas mileage is such a hot topic around here now, I would post a tidbit that may help any of you having poor gas mileage on a Renix based system. There is a sensor very few people ever think about. It is the MAT or manifold air temp sensor. They are out of tolerance on many older vehicles and can cause a significant swing in your mixture. You can easily check it with a ohmmeter without taking off of the vehicle.

Click to expand...

Thanks Tom... I will be checking that tomorrow on both my 250+ trail rig, and the 175K mile DD, 89,90 respectively..