GTSSportCoupe
2LTE abuser
As most 2LTE owners know, the ECU goes into fuel cut when it sees more than about 14psi at the boost sensor. Once intercooled, its desirable to run more than 14psi. I've found personally the motor really comes alive around 17-19psi. In order to achieve those boost numbers, the computer has to be tricked in some way (along with a manual boost controller, and turning up the fuel at the spill control valve).
For years I've used a bleed valve that @pradocruzer came up with. In fact he sent me the valve I was using. The theory behind it was it lowered the entire boost curve as seen by the ECU by bleeding off air before the boost sensor. It was adjustable, so could be adapted to the range of boost I was running. Well, recently my trusty bleed valve crapped out.
So I installed a cheap Chinese Ebay one that I'd bought quite a while ago. ASC-08 off ebay. Well, it turned out to be a total piece of garbage. In about 1/16" of a turn It went from no boost to full over boost as seen by the ECU. So it was nearly impossible to adjust. Not sure why. I guess you get what you pay for. Now I know why a number of you have struggled tuning your motors with these.
So, I rememebered @Waikato Willy mentioning he'd used a 4.3V zener diode to clamp the Boost sensor output to 4.3V. He had measured the boost signal voltage output to see at what level the ECU went into fuel cut. So I tried the same zener diode today that Willy had used. It's a 1N4731. On my engine, it dropped the boost signal way more than the 4.3V rating. After a bunch of testing, I realized the zener diode was loading the map sensor output. The 1N4731 begins reverse conducting significant current long before it gets to the 4.3V rated voltage.
So, back to the drawing board. I looked more in our inventory at work, and found another 4.3V zener diode that had less reverse leakage and thus should load the map sensor less. It's a 1N749A. Installed that sucker, and voila! I could hit my old boost levels again with no over boost issues. Tons of power with no pissing around adjusting a bleed valve etc.
I connected the 1N749A between the MAP sensor output (Yellow wire) to ground (Brown wire). I'll make a little schematic at some point and post it up here along with ordering information for the part incase anyone else would like to do the same.
Now keep in mind, I've only been running this setup a couple hours now. I will report back and let you guys know how it goes in the long run though. Once concern I have is that when the zener diode is reverse conducting at 4.3V, it does still load the map sensor output. In theory I should have a limiting resistor at the sensor output to keep from damaging it.... However I think Willy's sensor is still working ok after months of this?
For years I've used a bleed valve that @pradocruzer came up with. In fact he sent me the valve I was using. The theory behind it was it lowered the entire boost curve as seen by the ECU by bleeding off air before the boost sensor. It was adjustable, so could be adapted to the range of boost I was running. Well, recently my trusty bleed valve crapped out.
So I installed a cheap Chinese Ebay one that I'd bought quite a while ago. ASC-08 off ebay. Well, it turned out to be a total piece of garbage. In about 1/16" of a turn It went from no boost to full over boost as seen by the ECU. So it was nearly impossible to adjust. Not sure why. I guess you get what you pay for. Now I know why a number of you have struggled tuning your motors with these.
So, I rememebered @Waikato Willy mentioning he'd used a 4.3V zener diode to clamp the Boost sensor output to 4.3V. He had measured the boost signal voltage output to see at what level the ECU went into fuel cut. So I tried the same zener diode today that Willy had used. It's a 1N4731. On my engine, it dropped the boost signal way more than the 4.3V rating. After a bunch of testing, I realized the zener diode was loading the map sensor output. The 1N4731 begins reverse conducting significant current long before it gets to the 4.3V rated voltage.
So, back to the drawing board. I looked more in our inventory at work, and found another 4.3V zener diode that had less reverse leakage and thus should load the map sensor less. It's a 1N749A. Installed that sucker, and voila! I could hit my old boost levels again with no over boost issues. Tons of power with no pissing around adjusting a bleed valve etc.
I connected the 1N749A between the MAP sensor output (Yellow wire) to ground (Brown wire). I'll make a little schematic at some point and post it up here along with ordering information for the part incase anyone else would like to do the same.
Now keep in mind, I've only been running this setup a couple hours now. I will report back and let you guys know how it goes in the long run though. Once concern I have is that when the zener diode is reverse conducting at 4.3V, it does still load the map sensor output. In theory I should have a limiting resistor at the sensor output to keep from damaging it.... However I think Willy's sensor is still working ok after months of this?
Last edited:
