Yeah, I have to run 91 octane or my truck pings real bad. But then again, I get better gas mileage than with 87, so I'm not actually spending any extra money (the two cancel each other out).

You might want to look into a full ISR mod, lots of threads and ideas. It's shown to improve performance and gas mileage slightly as it allows more air in faster. And yes, also cleans up the engine bay. Your truck will be a little bit noisier though, if that bothers you.

 

Im gonna bump mine up once Im finished putting her back together, i really think the engine likes it advanced a bit...

 

I look up the isr mod to seewhat i can learn, i cut out the bottom of the air box mainly because i like the way it sounds, im assuming the full mod intails removing the little elbow box.

 

i pulled my plugs today after finaly getting truck together and running and they are black but not ashy. i know it means rich condition and so the only thing i can think of to do is adjust the vafm so i guess my question is do i turn it clockwise or lift the lock pin and turn it counter clockwise

 

For leaner, you turn it so it tightens the spring, which is clockwise. Tighter spring => less deflection for the same air flow => the ECU thinks less air is coming in => ECU reduces the fuel flow. Voila, leaner mixture.

Best way to get it right is to run a pair of wires from your diag port to inside the cab to a voltmeter. Connect the + lead to the VF1 terminal, and the - lead to E1 (ground). Then drive around and monitor the voltmeter. If the system is set right, you should see 2.5 volts during normal cruising around, when the ECU is in closed loop operation. The voltage will go to 0V at idle and at WOT, because then the system is in open loop mode.

If the closed loop signal is bouncing between 0V and 1 volt, you're running rich. If it's up around 3.75-5 volts, you're running lean.

 

thank you and i should have looked around more because i found what i was looking for minutes after i posted that and then lost power so i couldnt get back on. i adjusted it 3 clicks and seems to have a ton of midrange then loses top and bottom end. im going to pull the plugs and see what they look like. maybe advancing the timing slightly will give me what i want. there seems to be a slight ping from the engine when under a hard load or hard acceleration.

 

Ok, lets beat this dead horse. My 93 T100 with the 3vze is running very rich. I've had the heads reworked and put headers a hollow cat with stock muffler, and a"cold air intake" lol. I removed egr and pair junk and no matter what adjustment I make it still runs rich and can't get any better than 13.5 mpg. Ideas?

 

Have you run the tests described by RJR? As you know, the VAF has very little to do with mixture in closed loop, so the cause of your running rich and low mileage will be found elsewhere.

 

I haven't done the tests with a meter yet but have adjusted the afm 4 notches clockwise and seemed to get worse mpg. Even smelled like raw fuel was running out the tail pipe. Every where I read it says clockwise is to go lean.

 

Forgot to mention that I was getting 17 mpg before I tore it down to do the heads and gaskets etc.. Yesterday for some reason a hose I had from the valve cover to the intake pipe kept popping off. So I put the breather that came with the cold air kit on the cover and blocked off the port on the tube. Still feels like I have a bed load of rock or mulch or something. Feels like it should have more power.