AFR for towing
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On The Tree
Joined: Feb 2014
Posts: 157
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AFR for towing I have a 68 Chevy pickup that I have swapped in a 2002 5.3 L59 into.
It has a 700r4 with all the upgrades and a 3.42 posi rear gear. I tow a 4500 pound travel trailer and a car trailer regularly. Empty, the truck gets average 16.5 MPG empty. I just completed a 500 mile trip with the trailer and got about 12 or so.
My question is: How lean can I put Stoich value at and stay safe?
I believe I am leaving a lot on the table with power and MPG on the table.
Any suggestions are welcome.
Thanks in advance!
It has a 700r4 with all the upgrades and a 3.42 posi rear gear. I tow a 4500 pound travel trailer and a car trailer regularly. Empty, the truck gets average 16.5 MPG empty. I just completed a 500 mile trip with the trailer and got about 12 or so.
My question is: How lean can I put Stoich value at and stay safe?
I believe I am leaving a lot on the table with power and MPG on the table.
Any suggestions are welcome.
Thanks in advance!
With an ECM in closed loop it will adjust fuel trims to maintain stoichiometric AFR. For gasoline that is 14.7 air/fuel ratio or 1.0 lambda. You aren't going to change that by simply adjusting a stoich value. If you truly want to run your truck above 1.0 lambda (lean) you will have to force it into open loop by setting the ECT required for open loop higher than normal operating temperature.
I've street driven my Nova in the 16s AFR but that isn't pulling a load and it's only 9½:1 static compression. You might be able to handle low 15s pulling a load, but keep an eye on engine temp and signs of detonation. Is it worth a broken piston from detonation?
I've street driven my Nova in the 16s AFR but that isn't pulling a load and it's only 9½:1 static compression. You might be able to handle low 15s pulling a load, but keep an eye on engine temp and signs of detonation. Is it worth a broken piston from detonation?
There is very little to gain by leaning out the A/F ratio during cruise from 14.5->16.0
It is not recommended for novice tuners to attempt either.
Your primary gainers for fuel economy are:
1. lightweight drivetrain parts (parts that turn, make them lighter, i.e. wheels, driveshaft, flywheel, crankshaft accessories, etc)
2. reduced rolling resistance (same effect as #1) grease the wheel bearings, reduce brake drag, reduce wind resistance, perfect the alignment.
3. and finally, sometimes ignition timing could use a bump, but this is more advanced and may require an EGT gauge to determine accurately, i.e. you drive the vehicle fully loaded up, and gradually reduce timing until the EGT climbs significantly to find the "ledge" then add timing back until diminishing returns occurs for EGT vs timing (as you advance the timing, EGT drops a little, then a little less, then a little less, until it barely drops at all, and depending where the EGT sensor is, you make a judgement call based on this and other factors such as octane, compression ratio, are there any hills, condition of the engine(mileage/oil quality), etc))
4. often overlooked is the state of the various filters and PCV components, you need to use a super clean air filter, replace the pcv valve, check for leaks, use a lightweight synthetic motor oil, do a tune-up, fuel filter, coils, plugs, check the compression, look for signs of oil on plugs or in the intake manifold, basically you want to make the engine as "new" as possible by cleaning it and changing worn out components.
It is not recommended for novice tuners to attempt either.
Your primary gainers for fuel economy are:
1. lightweight drivetrain parts (parts that turn, make them lighter, i.e. wheels, driveshaft, flywheel, crankshaft accessories, etc)
2. reduced rolling resistance (same effect as #1) grease the wheel bearings, reduce brake drag, reduce wind resistance, perfect the alignment.
3. and finally, sometimes ignition timing could use a bump, but this is more advanced and may require an EGT gauge to determine accurately, i.e. you drive the vehicle fully loaded up, and gradually reduce timing until the EGT climbs significantly to find the "ledge" then add timing back until diminishing returns occurs for EGT vs timing (as you advance the timing, EGT drops a little, then a little less, then a little less, until it barely drops at all, and depending where the EGT sensor is, you make a judgement call based on this and other factors such as octane, compression ratio, are there any hills, condition of the engine(mileage/oil quality), etc))
4. often overlooked is the state of the various filters and PCV components, you need to use a super clean air filter, replace the pcv valve, check for leaks, use a lightweight synthetic motor oil, do a tune-up, fuel filter, coils, plugs, check the compression, look for signs of oil on plugs or in the intake manifold, basically you want to make the engine as "new" as possible by cleaning it and changing worn out components.
