Semopar Forum

**Redtruck-VA** · 04-14-2011, 05:36 PM

Well folks I finally got the trans LP gauge installed. It is pretty much confirming what I thought, but to a even greater degree. That being we need a lot more LP pressure. First the LP pressure is constantly changing. It is very sensitive to MAP/TPS input. Sitting at a light it reads about 120psi, step into it it may go as high as 165psi. But cruising it is only 45psi. Now it is easy to see a big torque motor will hurt the trans if it doesn't raise quick enough. I pulled the resistor (transgo style) to do initial testing. And will start testing after I get a better feel for what is happening. One thing I am very confident in saying is tuning the MAP signal to change pulse width has a very big influence on the transmission LP.

ORT · 04-14-2011, 06:03 PM

When are going to put the resistor back in? I would be curious to hear how much the lp increases due to the resistor. Too bad you don't have a Sonnax bc a comparison between the two would be great info to have.

**Redtruck-VA** · 04-14-2011, 07:00 PM

Actually, I'm interested in a hybrid of the two. I'm thinking of using the Sonnax style to raise the pressure across the board and then add a Transgo style resistor to add pressure less aggressively at the higher levels. I would be happy seeing my pressure range between 120psi and 185psi. Just thinking out loud, what really surprised me was how it is constantly fluctuating and the low cruise pressure.

ORT · 04-14-2011, 07:58 PM

That is pretty cool how it fluctuates based on the load placed on the drivetrain.

**Redtruck-VA** · 04-14-2011, 09:19 PM

Originally Posted by ORT

That is pretty cool how it fluctuates based on the load placed on the drivetrain.

Or maybe not so good, if you have pulled fuel to cleanup a idle and also are pulling LP at the same time.

**Redtruck-VA** · 05-06-2011, 10:20 PM

Well got to thinking about this some more today, waiting for the delivery truck to show. Anyway, what I think I'll try is using two adjustable rheostats mounted on the dash, wired into the LP signal wires. One will represent the Sonnax and the other the Transgo. This will require four wires cable spliced in as the Transgo is parallel to the sensor and the Sonnax is in series. The idea is that I can make adjustments as I'm driving and when I find what I feel is optimum pressure I will measure the resistance of the rheostats and either make some kits and/or post the values.

**Redtruck-VA** · 05-21-2011, 01:34 PM

Post cam install, found cruising the LP is running at around 33-35 PSI, but steps up quickly when leaned on. I'm thinking this improves fuel mileage but at what cost when playing with other mods. Went out to the shop and looked at what I had for resistors, 4.7k, 2.2k and 220 ohm. I think the 220 ohm is the resitor used in the IAT mod 2.2k I have no idea and the 4.7K is the transgo resistor. Here is the numbers: the LP sensor is 7.8k resistance with no pressure applied. If you parallel the 7.8k with a 4.7K you have 12.5k divided by 2 which equals 6.25K. So the base value is 6.25K instead of 7.8K this difference transulates to about 90 psi. So instead of cruising at 35 psi you are now cruising at 125psi. Everything still rolls up as it should. I actually ran this setup for a few years but wasn't setup to read the actual pressures. I'm going to play with this some more and use a Sonnax resistor of less value to see if I can get my pressure to base a little higher. There is a couple of ways to do this, Sonnax is a 5 ohm resistor, so if I install that in line after the parrallel resistor already installed it will directly raise the base without affecting the other values. I think I want something like 150 psi for cruise.

**4XLGator** · 05-21-2011, 01:47 PM

Ever think about writing tech manuals, Greg?

**Redtruck-VA** · 05-21-2011, 05:25 PM

[QUOTE=4XLGATOR;25436]Ever think about writing tech manuals, Greg?

Shipboard maintenance and repair procedures.

**Redtruck-VA** · 06-05-2011, 03:28 PM

Well the LP sensor I installed to read the LP pressures has crapped out so my readings are inaccurate. I'm removing the sensor and going to install an analog gauge. I finally actually bought a Sonnax line booster and found the resistance to be 380 ohms. It has been posted many times that the resistance was 5 ohms. BS! The Sonnax folks are a little sneaky as they used a resistive wire instead of a resistor. Longer the wire the more resistance. But this would simplify manufacturing, making it cheaper and less identifiable. I'll get back testing as soon as I get the new setup installed. On a side note I was experimenting with my tune and several things happened that surprised me. As I started to aggressively pull fuel, the shifting became harsh and clunky. I would have really liked to see what the LP was doing. Pulling fuel seriously affects the transmission., just be aware of that. I also started getting crank and camshaft sensor missmatch codes. I have to try to figure this out, how does pulling fuel cause sensor codes?? Will update later.