Occasional P0400 Code

Glas1700 · 11-30-2012, 02:28 PM

My P0400 has been still cropping up sporadically. Sometimes I can drive a 40-50 mile round trip on the freeway and it doesn't throw a code, other times it does. Driving on local streets, it does the same thing, sometimes a code, other times nothing.

I've cleaned the EGR valve (it was actually pretty clean initially) and of course checked for correct live functioning, cleaned the ports in the head, including the port running into the plenum. All of the ports, with the exception of the opening right at the plenum, were reasonably clean, with nothing completely plugged.

Now I figure that I may have to remove the exhaust manifold to do a final cleaning, but I'd like to know if there's any way around this. The nuts, of course, are rusty and I'd rather not risk breaking a stud unless it's absolutely necessary to get the EGR system functioning again. I barely passed the last emission test and won't need another test for about a year, so at least there's no hurry to get it done.

CR88Ranger · 11-30-2012, 08:58 PM

There are a lot of posts about this, and for some reason some people can't get that code to go away no matter what they do. We had the same code for a while, and after a really good cleansing with Throttle Body/Intake cleaner and some flexible wire, it finally went away. We practically drowned the thing in intake cleaner, which I think is what helped the most. The long tube on the passenger side of the engine bay goes up to a 90 degree elbow in the intake manifold, so that part is particularly tricky to clean. I'd spray the crap out of that from both sides (egr tube and behind throttle plate) and make sure nothing is clogged in there. Seems to be the most common issue, and is what fixed it for us.

xxx · 12-01-2012, 03:43 AM

400s can be easy or hard.
q1: do you need it to pass a smog test?
sounds like your reseting? or is it self clearing?
it also does not run the test ,until you drive correctly, fooling
some in to thinking the tests passes.
the test takes a moving fast but steady foot , to do the 1st
then a fast moving then coasting down test, (like exiting a freeway)
then coasting down and exit ramp,
do the PORT 1 is cleaned out to 11mm?
these test pass:
1: hand operated EGR main stalls or almost stalls motor? (i use vacuum hand tool so no burns)
2: if you suspect the intake "S" turn or exh #4 , you can start
the engine with the eGR main, removed, with far right port plugged
i call this the bark test. must be a strong bark.
3: The Live test passes? real wheels spinning?
4 ;Both EGR VSV pass bench testing?
5: keep in mind , air leaks in the induction can cause EGR to fail and its AOK.
6: does the LTFT in the full scan too show huge + % readings at hot idle? if yes, look for #5 intake leaks.
like here
http://www.fixkick.com/ECU/Authority...OBD2_scan.html

7: last and not least the freeze frame will show which test failed, test A or B EGR. cut fuel EGR test, is cut fuel mode test.

keep in mind 3 paths can fail
exh flow
electrical
Vacuum.

The live test usually proves electrical and vacuum.

on 97
the Hole #1 , must not be reduced !
the sidewinder sst tube must not be reduced,it love do that mid way....
non sticking main.
strong bark tests.

see gen 3, here (plug the right hole with a cork or I use rubber corks, for the bark test, then start it up)
EGR-problems?

Bex · 12-01-2012, 04:23 AM

I have been 'maintaining' my car with bottles of Techron, and mostly using Texaco (Chevron) gas that has this additive in it. It cleaned my engine out really well, and doesn't hurt to try.

xxx · 12-01-2012, 08:37 AM

the above carbon pile ,was a victim
of
exhaust #4 cracked, 02 failures. and running rich from many years.

if the exhaust , burns clean, the EGR lasts far longer.

if PO had a scan tool, he'd have seen the closedloop failures.... and took action.

Glas1700 · 12-01-2012, 11:38 AM

Have to pass Calif. smog test. NOx limit is 577 @ 15mph, measured was 551. NOx limit is 830 @ 25mph, measured was 414, both with new O2 sensor and new CAT. ECU goes into closed loop very quickly. HC and CO passed easily although HC was slightly higher than norm, limit 65, average 9, measured 16.

I use a Scangauge to clear the code after it sets, it's not self clearing.
Haven't tried "bark" test yet, but will as soon as rain stops and will do live test again to make sure EGR is working. Vacuum operation of EGR causes engine to almost stall. Haven't tested either VSV on bench yet, but will.

Will report back after making further tests.

Bex, I've used Techron in other vehicles and will try a bottle, can't hurt.

Bex · 12-01-2012, 01:13 PM

Check carefully for any exhaust leaks upstream of the catalytic converter, as any extra air coming in will cause a raised NOX value.

xxx · 12-01-2012, 02:10 PM

i do not understand your post, why not just post the smog tag.?
you post shows a passing car, or are you doing pre tests and just worried
that its so close to failing.???????? my guess is are doing the California fandango, were by pretest , avoid being flagged a Gro

did you do 5 gas or just 5.
5 adds oxygen , and is vastly better for diagnosis..

id say the EGR is failing
what is LTFT? it idle.?
what we dont know is what is EGR flow. (at HOLE #1)
we do know the EGR test is not fibbing now... it's one dirty bugger.

the EGR does not stop all NOX.
it only reduces to about 200-300 at exhaust ports (pre CAT)
then goes real low past the 3way cat TWC (can be even as low is 5 or less)

WHY NOT post a photo of the SMOG TAG.?
my tag is a HC failure. (air leaks into the cat, are not making nox. sorry, bex , that take 2000 degrees) (but not sure her track there...????)

Quote:

as any extra air coming in will cause a raised NOX value.

<< no idea what that means. not me....

A working cat, will have nox at the tail like 24 below (your cat is good but EGR is Dead)!
in fact an air leak here, will hit the 02 and cause huge rich and NO NOX AT ALL ,rich motors do zero nox

the air is mostly nitrogen 79%, and pass right thru the engine, un changed, but
if the combustion chamber is too hot, makes NOX (a deadly gas) all engines do this, and the EGR greatly reduces that NOX.
the cat , catalyses the remainder. most of it. your motor is filty.
so a leak here actually helps 1way , the cat uses 0xygen to combine NOX. so leaks up stream are bad only for the 02 sensor. and never NOX/
"It uses semi-precious metals to absorb oxygen and then recombine the oxygen with the NOx to create harmless gases."

if the 02 is in closed loop at the 15mph (high NOX) then its not running lean. (its a new sensor) LEAN AFR MAKES NOX HUGE !
what is LTFT at 15mph? +20% would show huge air leak in the plenum .
if the o2 sees an air leak (crack near by) the ECU then goes rich and rich KILLS all NOX. Rich motors run cold and NOX ends.

example1 (btw 2, the cat needs to be roasting hot before any test !!!) NO TAG cant see if it was..... why make us blind?

xxx · 12-01-2012, 02:59 PM

when doing the live test, use 2 persons.
use my gen3 tests, live, with links to full FSM on that topic. i didnt make it up.;
car on rear strands
person1 accelerates to 15mph
person 2 feels or watched (bummer they put it near impossible to see)
and see that it opens off idle and increase that open, as you add power to the
rear axle. (no kids near car , please)
the fsm live test fails to check rates. it only checks the the eGR wakes up.
if not its bad, but still dont prove flow
as you know the electric side can be perfect.
and the vacuum
but if the exh path is blocked, then it fails.
50% reductions will cause 400s... seen it.
and more NOX.

the bark test if good, i then go clean hole one ,the sidewinder then the 90 port
on top of the sidewinder. tube.
if the bark fails, then time for that path to be cleaned. (exh is easiest. (if lucky)
you can clean #4 tube then head tunnel in one step.
leaving only the intake S bend from H3LL.

its all here those spots
last 4 frames are not yours.
1995.5 to 1998 EGR carbon path failures. - Page 1 of 1

FLOW !
hole 1 is bad here.
http://www.fixkick.com/sensors/EGR/b...-Perfecto1.jpg
now cleaned
http://www.fixkick.com/sensors/EGR/EGR-HOLE1clean1w.JPG
do not do this, its just to show the packup , clean from, under.
http://www.fixkick.com/sensors/EGR/97egr-tube-end.jpg

then this (these are all easy to do, not hard work at all, like intake and exh)
http://www.fixkick.com/sensors/EGR/9...e96clean1a.jpg

all this is on my gen 3 page. every photo and always , easy to do hard order..
http://www.fixkick.com/EGR-Gen3.html

if the live test shows action, (main opens) and it shows signs of moving open more as you load engine.
then the exhaust flow is blocked,,
(assumes running STOICH "closed loop" at 15mph cruise thus proving flow is bad)

Glas1700 · 12-01-2012, 04:01 PM

It didn't fail the smog test, but came close to failing. If it throws a code just before or during the test it will fail. I need to get to the bottom of it and get the EGR to function normally.

I just connected the scangauge and found two codes, P0400 as expected and P1530 (ignition timing adjustment switch circuit). First time I've see a P1530, but I did adjust the timing a couple of days ago and that could have caused the code.

No 5 gas test was done. Scangauge shows open loop at an idle and closed loop at ~2K rpm and ignition timing @ 5 deg BTDC. IAT is 64 deg, as expected and coolant temp is 185 deg.

I plan to do other tests, such as LTFT, later today.