P0400 EGR flow Code - Page 2 - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

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post #16 of 24 (permalink) Old 04-26-2010, 04:26 PM
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Disconnect both terminals on your battery and touch them together for about 10 seconds (don't touch the battery when you are doing this). This discharges any capacitors in the system. Then hook your battery back up, and your PCM will default back to factory settings. Over time they learn driving habits and other crucial info from their environment for better performance. I recommend doing this when buying a used OBDII vehicle and when moving so your PCM can adapt to its new home/driver.
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post #17 of 24 (permalink) Old 04-26-2010, 05:19 PM Thread Starter
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Quote:
Originally Posted by 97Trans-AM View Post
Disconnect both terminals on your battery and touch them together for about 10 seconds (don't touch the battery when you are doing this). This discharges any capacitors in the system. Then hook your battery back up, and your PCM will default back to factory settings. Over time they learn driving habits and other crucial info from their environment for better performance. I recommend doing this when buying a used OBDII vehicle and when moving so your PCM can adapt to its new home/driver.
ok I will give it a try, to I need to leave it unplugged for an extended period? or just touch them and hook it back up?

97 Trans Am WS6, LT1 factory 4bolt freak, M6, FLP LTs, Cutouts, Flowmaster catback, Accel 300+wires, Jet Airfoil, K&N air filter, Ferco Bellows, MSD Opti and Coil, Beehive Springs, CAT 1.65 Steel Full Roller Rockers
68 Firebird 400, YC 400, Hbeam rods, ported 670 heads (2.11i, 1.77e valves), 1.65 RRs, Torker 2 intake, Nodular Crank, Eaton Limited Slip, 3.55 gears, M20 M4
65 Impala SS 327 Camelhump Heads, 650 carb, M20 M4 12 bolt 3.73 gears
91 Jeep XJ 2 door. 4X4 NP 231 TC, AX15 M5
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post #18 of 24 (permalink) Old 02-26-2013, 07:04 PM
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Thread necro.

I am having the same problem on my 96 Firebird formula. I can't seem to figure out what is causing this flow issue. Can I just put my hand over the top part of the EGR valve where the tube connects, to check for vacuum?

I also have longtube headers. They have a bung and everything but we are having a pinch issue with the tube that comes off of there.
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post #19 of 24 (permalink) Old 05-20-2013, 11:42 AM Thread Starter
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Quote:
Originally Posted by Bennylava View Post
Thread necro.

I am having the same problem on my 96 Firebird formula. I can't seem to figure out what is causing this flow issue. Can I just put my hand over the top part of the EGR valve where the tube connects, to check for vacuum?

I also have longtube headers. They have a bung and everything but we are having a pinch issue with the tube that comes off of there.
I still havent fixed this, I was rebuilding my exhaust system (im thinking that my cutouts were causing back pressure problems in the primary where the EGR connects and causing the computer to think the EGR was acting up.)

BUT while I was working on this my OPTI took a crap, and since I just moved and was remodeling the new house, I hadnt had any time to work on it, now that the garage is not filled with boxes and furniture, I have started to work on it again.

I really think there is a leak which is causing the code

97 Trans Am WS6, LT1 factory 4bolt freak, M6, FLP LTs, Cutouts, Flowmaster catback, Accel 300+wires, Jet Airfoil, K&N air filter, Ferco Bellows, MSD Opti and Coil, Beehive Springs, CAT 1.65 Steel Full Roller Rockers
68 Firebird 400, YC 400, Hbeam rods, ported 670 heads (2.11i, 1.77e valves), 1.65 RRs, Torker 2 intake, Nodular Crank, Eaton Limited Slip, 3.55 gears, M20 M4
65 Impala SS 327 Camelhump Heads, 650 carb, M20 M4 12 bolt 3.73 gears
91 Jeep XJ 2 door. 4X4 NP 231 TC, AX15 M5
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post #20 of 24 (permalink) Old 08-07-2014, 04:45 PM
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Any update on this? I'm having the same issue, only mod is a flowmaster muffler, everything else is oem, I put 1100 miles on from when i bought it and no issues, car has sat at a body shop for about 7 weeks, did a cpl short trips around town everything was fine, first trip on thruway light came on with this code, I can clear it and it comes back on after on highway for 3/4 miles,


any thoughts?


96 WS6 #689 shoulda kept it!

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post #21 of 24 (permalink) Old 08-08-2014, 10:36 AM
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DTC says MAP did not increase more than 1 Kpa (vacuum drop) when the EGR was commanded on. EGR opening should open the pipe from the exhaust manifold. That should cause the vacuum to drop due to CO2 and exhaust pressure entering manifold with the TB at a constant position (+/- 1% see test conditions below). I'm thinking maybe the due to Negative Backpressure EGR valve operation. Normally in a stock setup the exhaust backpressure can be up to 1 PSI . But you have a freeflow exhaust. Could be not enough exhaust pressure to correctly move the valve. Here's some reading ref shbox.com 4th Gen LT1 F-body EGR . And following that just for info I added the GM mode6 (diagnostic test) writeup for DTC P0400.

1997 5.7L (LT1) F-car ENGINE DIAGNOSTIC PARAMETERS

Test Description:

MAP change > 1 Kpa.
A change in EGR flow
results in a change in
MAP.

Malfunction Criteria:

The EGR valve is closed for 1.5
seconds, and the peak change in
MAP is recorded.
A filtered value of expected vs.
actual MAP change is compared
to the fail limit.

Test Conditions:

No MAP DTC’s
No IAT, ECT, or Throttle position DTC’s
No EGR solenoid control circuit DTC’s
MAP > 24 KPa
ECT > 20C
Vehicle Speed > 19 MPH
BARO > 60 KPa
Engine Speed > 500 rpm
Delta Idle Control < 3 steps
Delta MAP < 1 KPa before test start
The vehicle must meet stable operation criteria
for 1.0 - 2.0 seconds.
CRUISE:
Throttle position > 5% but < 20%
Delta Throttle < 1%
Compensated MAP > 20 KPa but < 60 Kpa
Stabilization before and during the test is
required. Duration 1.5 seconds.

I'm Bob.. 1994 Z28, A4, Stall, CAI, Cam, RR's, 342 rear, LT's , CatBack, Tuned

Last edited by bobdec; 08-08-2014 at 10:38 AM.
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post #22 of 24 (permalink) Old 08-11-2014, 10:13 AM
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I'm confused lol, could this bye chance be caused bye a small exhaust leak? the did take off my muffler and tail pipes, maybe I have a small leak somewhere


96 WS6 #689 shoulda kept it!

Looking for 98-02 T/A
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post #23 of 24 (permalink) Old 08-13-2014, 05:47 PM
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so I still find its odd that after my car was in the shop I have this engine light, I found they had to cut off the exhaust to do some work to the rear, it has been clamped where it comes from the front and into the muffler, there is a exhaust leak there not sure how bad but some soapy water shows me bubbles, could this cause this code?
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96 WS6 #689 shoulda kept it!

Looking for 98-02 T/A
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post #24 of 24 (permalink) Old 09-28-2015, 04:55 PM
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Necro-thread part II... OBD-II... oh, man am I funny.
I've been fighting this code for about 6 months.
My kid got a 97 z28 - 170k on the clock now.
EGR - new
EGR solenoid - new
Vacuum lines from egr to solenoid - new
Don't see any other leaks, but i'll look again. No other codes on the scanner. Car seems to run fine. Could get better MPG, but doubtful.
Anyway, does anyone have any other advice? Actuating the EGR manually, instantly kills the car, so according to what I've read this is NOT a clogged passage issue.
Do I keep looking under the hood or do I start looking at exhaust?
Your advice, or at least moral support is appreciated before I lose what's left of my hair.
-d
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