What Thermostat and Eprom gives best mileage?

[sad-lumina-owner]

As you can see, many of the operating parameters depend upon the coolant reaching 176ºF. Particularly interesting is the acceleration enrichment, which starts to fall off above 220ºF. That curve alone, along with the injector PW versus CS is why the engine "feels" better at lower coolant temperatures. It also wastes fuel and doesn't burn as cleanly.

If you take a lesson from NASCAR crews, you'd run the coolant around 235-240ºF, just like they do. That gets the peak power (and therefore, mileage) out of every drop of fuel. They are restricted in displacement, valve lift, and often in throttle bore size, so they have to make the most power from what they are given. That's why they run the temps higher. The factory has been doing this for at least 20 years. Thermodynamics don't take a rest and don't cut any breaks for people who don't understand them. They apply no matter if the car is a 120HP grocery getter or 850 HP normally aspirated race engine.

If you want to go further, you can enable the factory Highway Fuel and Spark modes at cruise. This programming has been included in factory binaries since the '80s, but never enabled because it might affect how the car reacts on the emissions treadmill (too lean means too much NOx) and potentially risks warranty coverage. If you car is out of warranty, and you don;t need to meet emissions requirements, you can enable the HFSM and get over 30 MPG with a 1980s V-8. If your cat converter is robust enough and the EGR is working properly, you'll still meet emissions standards. I can point you to several documented examples of where this has been done with success, including my programming and others'.

The above quote was taken out of this thread here:
http://www.automotiveforums.com/vbul...d.php?t=901856

Okay I'm trying to understand this thread (where can I get a crash course in ECM programming?).

I have a couple of patience-taxing questions:

(1) Can I increase the mileage I am getting out of my /94 3.4L v6 DOHC engine ? Right now, its running on a replacement ECM taken from a /95 Monte Carlo, if the markings on that are any indication. It doesn't look like anyone burned a special eprom for it.

(2) I know everyone else wants to have 'fun', but I strictly want the BEST MPG: I am spit-poor and can hardly afford to keep this thing running as it is by doing my own mechanic work.

(3) It seemed to be somewhat self-contradictory in the discussion above: How can you be getting maximum practical power (by clinical experience) while at the same time be wasting fuel with incomplete burning? According to person A, running cool gives more power, but according to person B, max power and mileage is given when running hot! How can you have it both ways?

(4) If you can get over 30 mpg out of v8, why can't I get that out of 3.4L v6? Shouldn't I be able to get something like 40 mpg or more?

(5) Is my car running at peak MPG efficiency now, or can I, should I get a new thermostat/custom eprom kit? Could you write an eprom that would kick MPG ass? and give me an extra 10-15 mpg?

(6) if I don't know what thermostat is in my car now, how can I find out? Its already had at least one new waterpump job, but I wasn't paying attention back then, because I didn't have a clue anyway. What thermostat should I be using for maximum MPG?

[Blue Bowtie]

Not in any particular order:

(1) The PCM in your car should probably be a 16196401 sine you have the LQ1 engine. The 16196401 was also used in the 1995 model year on the same engines. That particular PCM used a 256Kb UV EPROM. Typical broadcast codes (BCC) for the software are BCFD, BFRS, BHZW, BHLJ, BKLK, BKLL, BPCJ, BPCK, and BSBH. This PCM used a MEMCAL, which can be converted to include a socket to facilitate easy EPROM exchange. You can also use a Moates Prominator to eliminate the EPROM and change the program on-the-fly.

(2) Was there a question there?

(3) With stock programming, fuel is enriched when the coolant is below the threshold, which is programmed at a point below the intended thermostat setting. Conversely, as coolant temperature increases, the factory programming will start to lean the mixture for peak economy and emissions.

Maximum performance engines (those intended to run for hours at a time at peak power, not top fuel engines) are run hot to provide maximum efficiency. They are also set up (whether via carburetor adjustment or injector adjustment) to maintain a richer mixture even though the engine and coolant are hotter. Their tuners aren't concerned over emissions, warranty, or longevity past 500-600 miles. Peak power with gasoline is typically made at about a 12:1 AFR or slightly less, which is considerably more rich than most factory programming, even in power enrichment mode. If you program yourself, you can get closer to both.

(4) The highway MPG of a particular vehicle has less to do with engine displacement than you might think. A 400+ CID engine will need to make 30 HP to keep a given car moving at 60 MPH. That same car equipped with a 100 CID 4 cylinder would still need 30 HP to maintain 60 MPH. With proper tuning, the V-8 will used the same amount of fuel to make 30 HP as a 4 cylinder. It will also be working a lot less to accomplish that. That's why a 2003 Camaro Z-28 with a LS1 and T56 gets 27 MPG on the highway, just like the same car with the 3.8L V-6. Modern engines and fuel systems are a lot more efficient at metering fuel and managing ignition, thus the fuel efficiency of large engines at road speed. Overall mileage will likely slightly favor the smaller engine, since it will use less fuel to accelerate the vehicle, although it will work harder to get it there.

(5) No one but you can determine that. What is your current average MPG? Even with the correct thermostat, a working EGR, and everyting in stock condition, there might be improvements to be had. Most factory programming includes Highway Fuel and Spark modes which can increase ignition timing to nearly 50º BTC and air/fuel mixture rates to 17:1. However, this programming is usually disabled because running at those levels can increase NOx emissions and may cause overheating. A typical driver would probably not detect these conditions and would likely not understand what to do to prevent engine damage as a result. The EPA would also not allow anything which would put the vehicle out of compliance.

(6) You can either remove the thermostat and read the temperature rating, or measure the temperature at which the coolant stabilizes. A 195º thermostat will usually maintain about a 205ºF coolant temperature at highway speeds with ambients under 85ºF. Much of that will depend upon the cleanliness of the cooling system and effectiveness of the water pump. Contamination, wear, and corrosion will adversely affect the system's cooling ability.

[sad-lumina-owner]

Originally Posted by Blue Bowtie

Not in any particular order:

(1) The PCM in your car should probably be a 16196401 sine you have the LQ1 engine. The 16196401 was also used in the 1995 model year on the same engines. That particular PCM used a 256Kb UV EPROM. Typical broadcast codes (BCC) for the software are BCFD, BFRS, BHZW, BHLJ, BKLK, BKLL, BPCJ, BPCK, and BSBH. This PCM used a MEMCAL, which can be converted to include a socket to facilitate easy EPROM exchange. You can also use a Moates Prominator to eliminate the EPROM and change the program on-the-fly.

(2) Was there a question there?

(3) With stock programming, fuel is enriched when the coolant is below the threshold, which is programmed at a point below the intended thermostat setting. Conversely, as coolant temperature increases, the factory programming will start to lean the mixture for peak economy and emissions.

Maximum performance engines (those intended to run for hours at a time at peak power, not top fuel engines) are run hot to provide maximum efficiency. They are also set up (whether via carburetor adjustment or injector adjustment) to maintain a richer mixture even though the engine and coolant are hotter. Their tuners aren't concerned over emissions, warranty, or longevity past 500-600 miles. Peak power with gasoline is typically made at about a 12:1 AFR or slightly less, which is considerably more rich than most factory programming, even in power enrichment mode. If you program yourself, you can get closer to both.

(4) The highway MPG of a particular vehicle has less to do with engine displacement than you might think. A 400+ CID engine will need to make 30 HP to keep a given car moving at 60 MPH. That same car equipped with a 100 CID 4 cylinder would still need 30 HP to maintain 60 MPH. With proper tuning, the V-8 will used the same amount of fuel to make 30 HP as a 4 cylinder. It will also be working a lot less to accomplish that. That's why a 2003 Camaro Z-28 with a LS1 and T56 gets 27 MPG on the highway, just like the same car with the 3.8L V-6. Modern engines and fuel systems are a lot more efficient at metering fuel and managing ignition, thus the fuel efficiency of large engines at road speed. Overall mileage will likely slightly favor the smaller engine, since it will use less fuel to accelerate the vehicle, although it will work harder to get it there.

(5) No one but you can determine that. What is your current average MPG? Even with the correct thermostat, a working EGR, and everyting in stock condition, there might be improvements to be had. Most factory programming includes Highway Fuel and Spark modes which can increase ignition timing to nearly 50º BTC and air/fuel mixture rates to 17:1. However, this programming is usually disabled because running at those levels can increase NOx emissions and may cause overheating. A typical driver would probably not detect these conditions and would likely not understand what to do to prevent engine damage as a result. The EPA would also not allow anything which would put the vehicle out of compliance.

(6) You can either remove the thermostat and read the temperature rating, or measure the temperature at which the coolant stabilizes. A 195º thermostat will usually maintain about a 205ºF coolant temperature at highway speeds with ambients under 85ºF. Much of that will depend upon the cleanliness of the cooling system and effectiveness of the water pump. Contamination, wear, and corrosion will adversely affect the system's cooling ability.

I meant to thank you for this wealth of information. I had no immediate use for it, since I had to (and must continue to) study these issues to understand them better.

Your info on the ECM/PCM was spot on: I found the same (more obscure) version here:

16196401
16173300

Application:1994-95 3.4 DOHC V6 PFI “X” LQ1MEMCAL IDs:BCFD, BFRS, BHZW, BHLJ, BKLK, BKLL, BPCJ, BPCK, BSBHEPROM type:27C256









http://www.cruzers.com/~ludis/p4xref.html#16196401

Here is their crossreference and pinout page:
http://www.cruzers.com/~ludis/
http://www.makinterface.de/index_e.p...e=/aldl_e.php3

These people also have links to free diagnostic software (that runs on a PC clone/laptop), which others may be interested in:
http://www.aldlcable.com/

[travelair]

NASCAR actually super cools the coolant prior to qualifying. That is one reason for the faster times. Of course this isn't so helpful in a race, but I saw it being done at Bristol and that was the answer I was given by the (very busy) crew chief who got us our pit passes.