Well guys, I installed a set of Jet-Hot LTs w/emissions on my car and everything is running fine except the PCM is throwing the dreaded "P0400 - EGR Recirculation failure" DTC code, which illuminates the SES (MIL) light. No other codes are being thrown. I've checked and double checked for exhaust leaks and everything is leak free. Also, this code is only thrown after cruising for a few minutes in 5th or 6th gear and not while driving in town or at lower speeds. I was not getting any codes prior to the LT install.

I did some searching on here and found out that this is not an uncommon issue to occur after high-flow headers are installed, because such headers reduce backpressure and prevent the EGR from functioning at an acceptable flow; at least a flow rate that is acceptable to the EGR diagnostics program in the PCM. Aside from disabling the EGR completely, which I'd like to avoid, is there anything that can be done to enable the EGR system to function at this lower capacity without the PCM throwing the SES, pulling timing or otherwise affecting performance/driveability? I guess my question is, can the PCM be reprogramed to accept this low-flow condition without disabling or otherwise removing the EGR function entirely?



As an exercise in ignorant speculation...it's my opinion that the real issue is actually related to EGR-to-header connection placement. In the factory manifold configuration, the EGR is connected at a location where all 4 exhaust pulses are already merged into the manifold channel thus EGR flow is "normalized" as far as the PCM thinks. When a set of emissions capable LTs are installed the EGR-to-header connection is on the #8 primary only, thus the pressure is roughly 1/4 of what it was when the manifolds were present. Now, I would never do this, but this leads me to think that if the EGR connection were at the LT collector then the pressure would be sufficient enough to power the EGR without the PCM complaining about EGR flow.

EDIT: Better yet, an EGR connection on each primary, all connected to a single tube that runs to the back of the intake manifold. I think I've seen other emissions capable headers that have this setup.

Just a thought.

 

Have you ever replaced the EGR valve? On my 96 Formula, the valve developed pinhole leaks in the diaphragm and I also got the PO400 code. The dealer will replace it free of charge, because there's a bulletin out for 96-97 LT1s. It sits on the back of the intake manifold, so it's a bit tricky to reach.

 

I highly doubt they'll honor that EGR valve replacement when based off of LT headers

 

I also have that code and it did come up when I put in the new headers I did eliminate the air pump and just plan to do the same with the egr. Though I think it will still throw the code.

 

And another vote for that code... '97 using Random/AZS&M headers and cats I get P0400 when cruising at part throttle only in 6th gear. Not 5th, nor anywhere else.

So I don't believe it's a broken EGR, and I'd be more than a little reluctant to spend 50 bucks guessing.

But if anyone has any ideas on how to get rid of it, I'd love to know too.

 

I also got the P0400 when I did the FLP LT headers. The EGR needs a certain amount of back pressure to work. Whn you do headers, you will lose alot of back pressure. My fix was to do a !EGR and had the code programmed out.

 

I had the same problem...made my own EGR simulator to trick the computer into thinking it's working. If anyone is interested in making their own...just email me, I will try to help out. Its an easy fix...and can be returned to stock in a minute if needed. No more SES light!

 

I got the same code when I installed my SLP shorties. Have no idea what is causing it or how to fix it.

 

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.