so my OBD cable is on the way and I plan to be getting my pressures in spec soon, ideally with a small (1") sensor lift. I've looked through a few threads and I haven't quite found a step by step guide on what to do. Here's what I have so far, would the knowledgeable folks in here let me know if this is correct? I've put some questions in line as well.
1) Park vehicle on a flat surface. Measure from fender to center cap and make sure the left and right side are the same (or close to). If not, crank the torsion bars in opposite directions until the car is even.
Q: Is this done with the vehicle off? Do I have to do this in the rear? If so, what do I adjust? Do the AHC height sensors come into play here at all?
2) Plug in OBD cable and fire up techstream. Have the vehicle in Normal height and check the pressures. Adjust both torsion bars equal amounts until pressure is in spec.
Q: do you do this right after raising it up from Low mode? Vehicle on or off?
3) after front is in spec, if rear pressure is out of spec, either replace springs with OEM, or add spacers, or add King 79 springs for added weight
Am I missing any important details?
Also, where does getting a slight lift fit into all of this?
1. Good. Should be close to 19.75” both sides. Vehicle off. Back just is what it is, nothing to adjust. Maybe drive around the block once it’s set just to make sure it’s still good but likely you won’t have to even adjust it at all to begin with.
2. Vehicle on. Go to L. Raise to N and watch pressures shift as it moves. Once it lands in N, pressures will settle. Note what they are. Do this maybe three times and get an average/consistent reading. TURN OFF TRUCK and crank bars. Repeat.
3. Yes.
Two approaches to lift: Method 1. Do the above, find rear pressures still high. Install King Springs and repeat, find rear pressures low. Raise height sensors and repeat above steps until pressures raise back to spec. Method 2. Start by raising height sensors. Then do the above three steps. Replace rear springs, add spacers, etc. as necessary.
**Read @DirtDawg AHC lift thread.**
Here is a cheat sheet I pilfered from @PADDO various posts:
PADDO says:
First, on flat ground check and adjust front cross level, you should be able to easily get in within 1/4". One turn on one torsion bar bolt will lift/lower that corner approximately 1/8". Engine doesn't need to be on for cross level check/adjustment. Wheels on the ground, if the TB bolts are really tight you can raise to H to take some preload off. Use penetrating oil liberally if they haven't been adjusted in a while. Breaker bar doesn't hurt either.
Second, measure all four corner heights at N with engine running and AHC settled. If you have 19.75F and 20.5R hub center to fender bottom you are very close to stock spec height. Adjust height sensors if necessary, engine off, to avoid potential injury.
Lastly, hook up techstream and check pressures, same number of CW turns on both TB bolts to lower pressure, one turn (on both bolts) will lower pressure about 0.2MPa (CCW to raise pressures). Target front pressure is 6.8 - 6.9MPa. All you can do for the rear pressure is to ensure you aren't physically too high and then you may need to add 30mm spacers to get the pressure down a reasonable amount or ideally, new AHC coils AND spacers to get the pressure down to the lower end of its design range of 5.6 - 6.7 MPa.
Expect a small variance in the front height sensor height values, if they fall within say 0.3" from 0 there isn't any need to tweak them. Best just to see how it all plays out. Additionally, lowering the front pressures also has a positive effect on the rear, and vice versa.
I know the FSM says to adjust pressures with full tank of gas etc etc well lately I've been adjusting pressures with the vehicle set up how I normally drive it and that's with 2nd and 3rd row seats out, 1/2 tank gas and my tool box, myself in the drivers seat. I just think it makes better sense that way. If I'm loading up for a trip I readjust TBs as necessary, it only takes a minute.
Finally, I use these numbers as my guide to predict necessary pressure adjustments:
Front:
1 turn: -0.2 MPa
1” height: +2.2 MPa
Rear:
King Springs: -3 MPa
1” height: +0.6 MPa (stock springs)
210lbs over axle: +1 MPa (stock springs)
