427 $0D MAF Tuning - Third Generation F-Body Message Boards

92K2500 · 11-02-2009, 07:59 PM

I have performed a MAF Swap in my 92 Chevy K2500. I have worked out the electrical and ads stuff with the with Dimented24x7. I am including my bin and the adx file for TunerPro.

Here are the specs on my setup:
4 Bolt Main 400 Bored .60 over=413
ProComp Aluminum 190cc Intake 64cc Combustion Chamber 2.02 intake/1.60 exhaust
Full Roller Rockers 1.6 ratio
Holley Pro-Jection Throttle Body Injection Manifold
COMP Cams Xtreme Energy 12-262-4 – 114 LSA, .464 intake lift, .470 exhaust. With the 1.6 rockers the final lift at the valve is .495 intake/.501 exhaust
Bored Out GM Small Block Throttle Body flows 750 cfm
90hr/lb 454 Injectors @ 21 PSI
NV4500 5 Speed Manual
255gph fuel pump
New GM Distributor
Headers
COMP 981 Valve Springs
COMP .080 7.2 Pushrods
SCAT 400SBC Cast Crank
ProComp 5.7 I-Beam Rods rated at 550 HP
9.5:1 .60 over SpeedPro Pistons
EGR Disabled and 160 thermostat
Heated NB 02 and Wide Band 02

This is my first tuning adventure and it is kickin my butt. I am messing with stuff but there are some problems that are killin me.

1st My idle goes up to 1500 like clockwork when I push in the clutch until the vehicle comes to a stop. If I am coasting long enough the idle will start moving between 1500 and 900. It hangs up there until I have been at a stop for about 4 seconds.

2nd The AFR's aren't where they are supposed to be I think. At idle they are showing 11-13. As soon as I touch the gas they bump up to 13.5-15. Even cruising yields 14.3-15.4. When I floor the truck it goes up to about 17/18 and after about a second they come down to about 14.3. I can't get them to richen up anymore than that.

It has decent power but not what it should I think. The truck in 5th wont break 96 on a flat highway but put it in 4th and it will accelerate.

Anyone at all I am all ears as I don't know what I am doing but I want to get this thing running right before winter really comes on.

Thanks everyone

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rocko350 · 11-03-2009, 10:50 PM

You need to command open loop by setting the minimum coolant temp to 200 and then set the open loop afr table from 44degreesc and up to 12.8 across the board and log idle and a short low gear drive. make sure the wideband mirrors the commanded ratio. The spark table looks like its a table from a 305, you will need to hand edit them. But for now, the closed throttle spark advance needs to be smoothed out in the kpa areas that your engine idles at to corrall the hunting idle. Make sure the MAF table is the correct one. a b body lt1 maf is smaller than the f body lt version and ls models are all there own. the table looks to be one from an f body. Some stuff to check and focus on. HTH Essentially, you have to correctly "calibrate" the system so you can tune.

Chris

dimented24x7 · 11-03-2009, 11:12 PM

All the stock codes based on the $0D all do that with manuals. My vortec PCM (also based on the $0D/0E, etc.) did that as well before I patched it. The idle will hang until it hits closed loop idle when you come to a stop. I added tables to allow for the idle to touch down smoothly when a stick is in use. These basically decay out the added idle speed/throttle follower airflow so the idle smoothly comes down rather than hangs and suddenly drops.

As for the second issue, it sounds like the MAF tables are mis-calibrated to the sensor. GM has a whole butt-load of different sensors, so the table may need to be re-calibrated. Its not hard to do, and only has to be done once.

Later, I'll post up details on how to fix these.

dimented24x7 · 11-04-2009, 01:18 AM

I took a look at your bin, and it looks like you do not have the throttle follower reduction enabled. Go to the min closed throttle follower IAC TPS reduction table and try the values I have shown in the table attached. This should reduce the T/F action as you come to a stop.

dimented24x7 · 11-04-2009, 01:35 AM

Now, the way to tune the MAF is as follows. You need to run the truck at varying loads so you get a broad range of airflow rates and AFRs. The key is to make sure the engine has a chance to stabilize at each load and reach steady state, or the results will be meaningless.

For example: you might start off by just driving at a constant 30 MPH. Hypothetically, the MAF could read 4500 Hz, and the actual AFR could be 16:1. If your desired AFR is 14.7, this means that the MAF is underreporting the airflow by about 8.8% in this example.

To correct this portion of the table, you would then go to the cell or cells closest to 4500 Hz. Say that cell currently has 25 grams per second in it. From the test results, the actual AFR was 16:1 while your desired AFR was 14.7:1. In this case, you would multiply the entry at 4500 Hz by 16/14.7, or 1.088. The new airflow at 4500 Hz would then be 1.088 x 25 grams/sec = 27.2 grams/sec.

You continue this way by running the engine at low to increasingly high loads and observing the reported AFR in the datalog to determine if the MAF is reporting the airflow correctly. You then apply the corrections to the corresponding entries in the MAF table and then smooth the curve back out again. After that, repeat until the AFR is within a few percent of your desired AFR. When you are done, the finalized MAF flow curve in tunerpro should be a smooth parabolic shape regardless of the corrections made. If it has kinks or humps/bumps in it, then there is some other effect throwing the fueling off.

Remember, in order for your results to be valid, the engine must be allowed to reach steady state for at least a few seconds. If the load is varying rapidly, then your also having the fueling dynamics coming into play as well, which will throw everything off. The MAF MUST be tuned under steady state or as close to steady state as possible. You must also know both the actual reported AFR and desired AFR, and the AFR must be steady. When your tuning, you may want to set the entire open loop AFR table to 14.7:1 at the higher cool temps and also set the PE table to a constant AFR across the board, like 12:1 or so. Or, you could set the open loop AFR and PE AFR to 12.5:1 at all cell entries. Both will work. This way the AFR is steady under normal driving and in PE. Lastly, you must also lock the BLMs at 128 and disable closed loop when tuning the MAF with a wideband so the PCM does not try to apply corrections. Locking the BLMs can be done by setting the upper allowed limit and lower allowed limit for stored BLMs to 128. This will reset all the BLMs on the next restart.

Lastly, if you have the wideband hooked up to the PCM, the wideband calibration table must be set up to match the widebands output, or the reported AFR will be off. I can give you some help with this if you need it.

dimented24x7 · 11-04-2009, 01:41 AM

Also, which MAF sensor are you using? The entries in your MAF table look kinda low, which would explain the lack of power (running lean).