OBD-II Programming
Thread Starter
Registered User
Joined: Dec 1999
Posts: 1,697
From: Petersham, MA
OBD-II Programming
OK, I have LT1 Edit for my OBD-II car. Here in Massachusetts, they scan your ALDL port to ensure that all OBD functions are ready. Is there a way that I can eliminate my car from throwing a code (AIR and EGR delete) using LT1 Edit, but still have my PCM show them as ready when my car is scanned at inspection time? I know I can turn off the hardware verification, but that would probably cause me to fail inspection. Any ideas?
Registered User
Joined: Jul 2003
Posts: 700
From: Upstate New York
SlickBlack Z may have an answer for the egr part of your problem.
SlickBlack Z
Member
Registered: Feb 2001
Location: NJ, USA
Posts: 242
BitCypher has the right idea...the code is set off because the backpressure is not as strong as with the stock manifold, due to the placement of the EGR tube on the single header pipe with longtubes. It seems to be an OBD2 specific problem on cars with headers, probably because the EGR is more sensitive than OBD1.
Here is why the code is set off: the PCM commands the EGR valve to open, then the MAP sensor takes a reading of manifold pressure. It measures this rise in pressure as a low rise in voltage...but if the pressure hasnt risen enough, the voltage reading is too low and a P0400 code is issued.
Here is what I did to trick the computer: Unplug the 2 wire weatherpak going to the EGR solenoid, and splice it onto a relay. From there...off the other side of the relay, one wire gets spliced onto the rear wire of the MAP, and another wire gets spliced onto the center wire of the MAP, with a 75 ohm resistor. The front MAP wire stays as it was. Now when the PCM tells the EGR to open, it is actually energizing the relay, then sending the properly tuned voltage (because of the resistor) onto the MAP circuit and the computer thinks the manifold pressure has risen. The result? No more SES light.
I made all of these connections using weatherpak connectors I got at NAPA...from their AC delco catalog. It just plugged right in. Otherwise...you would have to cut into the wires and it wouldnt be easy to put it back to stock if needed.
And thats the easiest cure for the P0400 code
SlickBlack Z
Member
Registered: Feb 2001
Location: NJ, USA
Posts: 242
BitCypher has the right idea...the code is set off because the backpressure is not as strong as with the stock manifold, due to the placement of the EGR tube on the single header pipe with longtubes. It seems to be an OBD2 specific problem on cars with headers, probably because the EGR is more sensitive than OBD1.
Here is why the code is set off: the PCM commands the EGR valve to open, then the MAP sensor takes a reading of manifold pressure. It measures this rise in pressure as a low rise in voltage...but if the pressure hasnt risen enough, the voltage reading is too low and a P0400 code is issued.
Here is what I did to trick the computer: Unplug the 2 wire weatherpak going to the EGR solenoid, and splice it onto a relay. From there...off the other side of the relay, one wire gets spliced onto the rear wire of the MAP, and another wire gets spliced onto the center wire of the MAP, with a 75 ohm resistor. The front MAP wire stays as it was. Now when the PCM tells the EGR to open, it is actually energizing the relay, then sending the properly tuned voltage (because of the resistor) onto the MAP circuit and the computer thinks the manifold pressure has risen. The result? No more SES light.
I made all of these connections using weatherpak connectors I got at NAPA...from their AC delco catalog. It just plugged right in. Otherwise...you would have to cut into the wires and it wouldnt be easy to put it back to stock if needed.
And thats the easiest cure for the P0400 code
Registered User
Joined: Jul 2003
Posts: 700
From: Upstate New York
Since the circiut goes through the relay instead of the EGR valve this should work even if you have deleted your EGR and haven't deleted it in the computer.
I welded in emissions fittings onto my TPiS longtubes so I don't have any tricks for the AIR.
Maybe you should put AIR fittings in. 7/16 fine thread nuts will do.
Could probably do it on the car if you're careful.
I welded in emissions fittings onto my TPiS longtubes so I don't have any tricks for the AIR.
Maybe you should put AIR fittings in. 7/16 fine thread nuts will do.
Could probably do it on the car if you're careful.
Thread
Thread Starter
Forum
Replies
Last Post
PFYC
Supporting Vendor Group Purchases and Sales
0
Aug 7, 2015 08:52 AM