I bought a 2005 LQ4 from a buddy of mine, planning on a full overhaul and I was told the ECM had the VATS deleted and had the MAF delete, I've got zero experience with tuning and extremely green with engine building. It's a N/A mild build, BTR stage 1 truck cam going in a 1985 GMC K10, running SM465 transmission for now, eventually NV4500.

I live in a place where winters get down to -40°C/F, and as high as 32°C/90°F, and I go from 800 feet to 2100 feet elevation. That being said would it be better to go back to a MAF sensor and tune, or leave the MAF deleted and run the IAT?

If I run the intake air sensor, how does that connect in with the harness, and do I just leave the MAF connector alone? Again totally green so just looking for some feedback, thanks!

 

My experience with Gen 3 motors/ECU's (never had a Gen 4 or 5) is they tend to run better with the MAF enabled especially at very low rpm near idle. The boosted folks disable the MAF because you can easily max it out under boost and go lean. For an NA application, I would run a MAF and do. So it depends on what you plan to do with the LQ4.

That being said, if you plan to tune it yourself, you need to read a lot before tackling that project. It's not hard, it just takes significant understanding of what to change in the tuning software then being easy on the motor while confirming the changes are doing what you think they are doing.

 

It'll probably be better for me to reenable the MAF, I don't rev my engine very high, I don't know if I've even revved over 4000 in my 350, so this engine would be living its life in the lower range. I planned on building it all up, swapping the old out, firing it up and driving carefully to have someone tune it for me properly.

It should be a stock tune, enough to make it to a tuner, he had plans for a turbo build hence the MAF delete, thank you for the info!

 

I think you've answered your own question. Go back to the MAF. I've been told by more than one in-the-know tune guy that you should run a MAF system whenever possible, and only go to speed density when using the MAF setup will no longer work for your application/combo. Best of luck, and hope this helps you somewhat.......

 

I know there are 2 schools of thoughts on this. Some say they run better in SD but I don't know if I have ever seen anyone actually explain why.

SD or VE is a calculation of airflow. MAF actually reads the airflow.

MAF will be easier to tune.

 

My guess is that most people form their opinions based on the quality (or lack of quality) of a tune they had, attributing the good or bad results to the software itself rather than to the person who tuned the software. And the tuner matters a lot more than the software. They both have pros and cons but the one thing I know for sure is that people are superstitious as ****. MAF is easier and that probably leads a lot of people to think that MAF is better.

I gotta take issue with "MAF actually reads the airflow" though. MAF actually reads a voltage or a frequency from a sensor, and uses that signal as the input to a table that models how the voltage or frequency varies with airflow, and uses that model to come up with a grams-per-second value based on the voltage or frequency. Then divide by RPM to get grams-per-intake-stroke.

Whereas SD measures pressure, temperature, and engine speed and feeds those into a table that models how much air the engine inhales under those conditions... and uses that model to come up with a grams-per-intake-stroke value.

Either way, there's calculations involved, and either way the important part is to get the model right.

 

keep the maf if your na and you drive it in those temps , also i think you can make the maf work under like 3k and then off above it . I thought i recall my tuner mentioning it , i thought maybe a cts v2 does it that way .
Look into this .

 

I do enjoy how the community tends to pit the two methods against each other like its actually a competition between them lol. The real competition is between the performance that might be gained from improved measurement method versus the extra money it will cost the manufacturer on every vehicle that has the hardware to do it. Some manufacturers are admittedly more concerned about profit margins than others.

As far as the physics is concerned, each method has its pros and cons. There's no single winner. A MAF may need less effort to dial in under some nominal conditions, put it in a big intake tube in front of an engine with a large camshaft at low RPM and the output will be garbage. Intake reversion exposes the weakness of a MAF. Not to mention the need for smooth, uniform airflow across the sensor. Speed density presents difficulty as well, in the form of inaccurate fuel delivery during conditions like exhaust scavenging and in setups where the IAT measurement is far from the intake valve. If you've chased different fuel trims in the afternoon versus the morning in SD, chances are you're chasing that IAT/ECT blend issue.

So there's clearly no winner. It depends on the hardware and how much you care about the accuracy, or lack thereof. There are situations that are still better served by Alpha-N. Or ask Japan about their love affair with karman vortex flow measurement lol. In the end, if an OEM had the vehicle you're working on and needed to meet startability/drive/emissions/other requirements, it would receive custom software. I've made engine controller software changes for far less exotic mods than a lumpy camshaft. The aftermarket is stuck with the software they've got in whatever specific OS part number they're running, so you have to make the best of what you've got

 

Please run the MAF for something like that. I will never recommend SD on these old PCMs unless there is a good reason, and that mild of a setup is not a good reason.

 

I would still temporarily disable the MAF to properly tune for SD with an aftermarket cam. On my old Whippled work truck 4.8 I have the proper 2 bar sensor and SD tune, but also have the factory MAF, since it is not maxed out on the low boost 4.8. It takes time to do it right, but I like having the factory redundancy operable whenever possible.

 

My plan was to rebuild the engine, then when I get the chance to do the swap, I was going to fire it up on the existing tune and just bring it straight to the shop to get it properly tuned, I feel like I'm already in over my head with rebuilding the engine and doing a swap haha

 

My understanding is the MAF is a heated wire that sends signal to the PCM as air flows across it. As the wire heats and cools the signal changes. Seems the easiest way to determine temp and elevation change as well as airflow for a street car or truck.

I think the SD tune is more for track only cars that have a dialed in combo.

 

That's just a normal part of tuning since it will always "blend" the MAF with the VE table on transients, etc. SD is a backup mode for these old controllers and you lose certain features when running it which is why I don't recommend it unless there is a good reason.

 

How does the ecm decide & transition between the two? Is speed density open loop?

 

Speed density can be open or closed loop, as can MAF or Alpha N. The GM computers have several tables that determine what to use. In most of these vehicles, SD is used exclusively for idle and MAF is used exclusively for over around 3000 to 3500 rpm, depending on the model. These tables are all "mostly all" able to be tuned to your desire with HPT or EFIlive. The exact nature of how the inputs are blended during the transition rpms is at least partially tunable with some software, but the short version is that fast throttle transients are biased toward SD, while steady state is biased toward MAF.