Corsica 95, 3.1L: EGR valve seems not activated
 

I am trying to figure out at what condition my Corsica 95, 3.1L, EGR valve starts activated. Valve has 3 solenoids and at park position I increase RPM to 2000 and using oscilloscope do not see any solenoid to be energized.
Currently trying to solve hi NOx problem, engine is after rebuild works
smooth.

So it won't pass emissions because of Nox?If so, what are the CO's in ppm? The egr might just need cleaned. The egr might come on with exhaust gas temp.

CO is equal to = 0, HC is equal to = 8 : NO is 1390 (three times bigger than limit) - this is at 1900RPM, Catalist is new: Magnaflow #93505 - Universal converter. Diagnostic data shows no engine errors at all.

I have figured out that it works only when car drives. EGR works but "NOx" is still high. Mechanic says engine can run lean - Can fuel injectors cause this?
Fuel pressure at injectors rail is around 35 psi

Well, nox, and co's are a function of temperature. I'd think if it were too lean, you have higher co's, and lower nox. However with the unburned hydrocarbon, interesting.

only 35 PSI?!
that fuel rail is supposed to have 40-45 PSI at least!!

We had an issue like this before, the car was getting extra gas because the pressure regulator ruptured and gas was going into the intake through the vacuum line...lol

Also low fuel pressure can cause it to run lean or wrong as well...

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So basically, it can be a number of things.
Please check in this order:

1) Check for defective fuel pressure regulator. Or replace to test and make sure its not the problem.
2) Check fuel pressure with engine off after running fuel pump a few times, pressure should go up to 40-45 PSI. (Check with both old and new pressure regulators.)
3)Check to make sure you do not have leaking or dirty injectors stuck "open."


It can either be one of 3 things:
1) Improperly functioning Pressure regulator.
2) Weak fuel pump.
3) Stuck open injector. (these need replaced, cleaning won't do anything).

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My 3.1L MPFI v6 reads 43 PSI average.
My 3100L SFI v6 reads about 44 PSI average.

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That EGR is actually 3 motors that open and close a plug.
Chances are it is working correctly.

But yah, that fuel pressure is low.
Does it have trouble at higher RPM's? sometimes low fuel pressure can cause this.

Also, inspect vacuum lines and check PCV valve for proper operation.

Please let me know what you find, or if you have other questions/comments. :)
Also, this is the same issue, try not to post other threads for this same vehicle & problem, it helps others with this issue and it also helps us help you.
And moderators do not like it, they get mad at that. lol :P

I have done the following:
1)replaced the fuel's pump motor (with -ACDELCO #EP313 - from RockAuto) - but not assembly
2)replaced fuel filter
3)replaced fuel regulator

When turn ignition ON (no crank) fuel pump starts work for couple of seconds and pressure rise maximum to 40-41 PSI. Pressure gauge is connected to injectors rail test port
When engine is run on idle the fuel pressure is around 35 PSI.
I think on idle the pressure cannot phisically be higher that 40PSI due to pressure regulator is rated for 40PSI
Also I put OBD2 catalitic convertor - please let me know if it is going to work on this type of car. This car has sticker with: EGR/HO2S/TWC/SFI
---TWC means that catalyst is three way
Please let me know how engine works in case of wrong timing.
As I understand it easy to see visually and listen
Currently looking for emission appointment, will let you know

Additionally to my previous:
1) each injector I have tested individually and cleaned with LUCAS inj cleaner an Gas (50/50% mixture under pressure)
2) after turn ignition ON (no crank) the gas ressure rise to 40-41Psi and stay for a lonf time - this means that all injectors are holding pressure - no stuck open case

hm...

You borderline on emissions or you failing miserably?


**(That still seems low to me for fuel pressure, but if thats how it is, I guess we can leave it...)**

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did you put a new catalytic or a used one?

Maybe the wrong kind of converter is installed, or its plugged up, maybe someone punched a hole in it?

However, there have been cases where some people installed a converter and it did not work properly on the given vehicle.

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I totally forgot this part:

Did you change the spark plugs?
Surprisingly bad plugs, cheap plugs, or improperly gaped plugs can cause this.

With the 3.1L MPFI engine you had better be using the AC delco (standard or platinum) single prong plugs with the proper gap, anything else is BAD with this engine.

If you do not have the proper plugs, get them out.
Especially Bosch plugs, they WILL warp the heads because they burn too darn hot, I learned the hard way 2 times with bosch plugs and warped heads.
And then I learned the hard way with cheap plugs before, they just do not work correctly.

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The last thing I can think of is disconnect that ECM for maybe 30 minutes, then see if there is a difference.
Those older EPROM block learning designs will learn, then their "learning" seems to get old after some time.

I usually reset mine before winter, then before summer simply because the drastic weather change really makes it confuzzled. lol

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Other than that, I'm simply lost.
Its hard to help sometimes with issues like this when the vehicle is not right in front of you...

EDIT: Maybe you got bad gas?
My old 2.8L v6 was borderline in emissions testing before, I had 5-6 gallons of gas, so I stuck 10 gallons or more worth of that alcohol based injector cleaner to help it pass, it worked for me, but it is not recommended. lol

Finally emission is fine. The summary is below:
1) replaced fuel filter, fuel regulator and fuel pump motor - after this fuel pressure at rail did not change too much: 40PSI when ignition is ON and 36PSI when engine is at idle run. Initially I suspected a poor gas supply/lean mixrure due to low pressure. It is easy to verify without replacing the above mentioned. There is return fuel line rubber hose under hood - so that when engine is in idle - just press it with pliers - and watch fuel pressure - if jumps over 40PSI - means that pump is performing well
2)Cleaned EGR, cleaned pipe from exhaust to EGR. Also cleaned passage from EGR flange to intake. Seems to me it was partially clogged
3) Replaced Catalytic converter with used OBD2, from Oldsmobile 2000, 3.5L, 200K milage. Put it close to exhaust. Looks like my previous universal Magnaflow 93505 was too far from exhaust flange
Did not touch sparks - but think to replace with original from dealer
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Also I have checked all places for vacuum. As I have noticed this type of engine could have clogged passage from EGR to intake manifold as the result error code:
EGR-3 will be stored

EGR3 - error
 

After all work done, plus spark plugs where replaced with original from GM dealer, I have observed the following:
On highway when accelerating at speed over 120Km, when release gas pedal the check engine lamp goes on. Code reader says: EGR3 error. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
But EGR valve works fine – I verified all wire, verified valve each solenoid by connecting 12V and observed valves movement, also verified valve solenoids during drive – connecting LED’s to each solenoid wire – all solenoids are operational from engine control module.<o:p></o:p>
EGR passages are not clogged and fine – one from exhaust the second in intake. <o:p></o:p>
As I have mentioned vacuum and fuel pressure are fine. One thing is unusual: on Idle when engine is hot when press and release the gas pedal the engine makes high rpm to low rpm several times like bouncing – trying to find idling point. At cold engine - this is not happens

The high and low RPM movement sounds to me like Hunting at idle.

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Of the following, sometimes just 1, or just 2, and sometimes both can occur:

1) Hunting at idle is usually caused by an O2 sensor becoming Pluged up.

2) A plugged up O2 sensor usually causes to high emissions output from the engine. This is because when it becomes plugged, it reads less, so then the engine is commanded to output more (usually fuel) to compensate with this.

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I suggest checking the O2 sensor readings on the ECM monitor and comparing them with the factory readings it should be getting.

Also, It might be wise to consider replacing the O2 sensor if the hunting continues.

When you changed the plugs, how did they look? Were they dark/black?
Usually a Pluged O2 sensor causes extra fuel to be dumped, then the exas fuel mixture is not completely burning, then coming back through the EGR and thus probably causing an EGR fault code because the EGR is probably open more than usual to try to compensate the exes emissions.

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Now I forget what you have as far as O2 sensors. But being a 1992, I believe you only have one O2 sensor and it is behind the engine on the exhaust manifold.

If you have 2 O2 sensors, then the second one will be down the exhaust pipe some place right after the catalytic converter.

I believe you only have the single wire O2 sensor, these are usually 20-30 dollars a piece and can be found at places like advanced auto parts and auto zone. (I personally buy Bosch when I replace my O2 sensor).

If you have the 3-4 wire O2 sensor, then you will probably have to pay around 40-60 dollars on a replacement. Same stores. (I also buy Bosch brand with these too, but you can buy different if you chose).

The downstream O2 sensor after the catalytic converter will probably be a 3-4 wire version if it does exist.
Being a 1992, like I said above, you might just have one O2 sensor on the exhaust manifold and it is probably just a single wire.

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If you replace the O2 sensor I suggest adding Something like Anti-Seize or some form of thread lube (NOT thread locker) to help it keep from rusting together and so it helps make it easier to remove later. Be careful not to get it inside the sensors breather holes. Usually the come with this, I like to add a little extra myself.

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I hope this helps, I'm interested in seeing the outcome and in helping you get this car working. Seeiing (from my viewpoint) that you put this much money and effort into it, its worth the extra effort, the money parts your domain...lol :P

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EDIT:
The forums were glitched for some reason. They were not properly operating. So I had to attempt to delete and repost a couple times to effective post this reply.

Sorry if this caused any incontinence to anyone, and sorry if the previous posts still show up, if they do I will edit them out. Hopefully they are gone.

I have only 1 heated sensor, 4 wire. Before this emission story happened
I have replaced sensor and it got around 30000 km. Visually looks clean and no deposits. I got it from dealer, but they changed the design - sensor does not look like old types. What I can see from diagnostic and oscilloscope - the sensor voltage is slowly changing during idle, from 400 to 800 millivolts with new type of sensor. I have tried to use original used old sensor AFS-75 and voltage does the same, but a little bit lower 300-600 millivolts. Probabbly current sensor is fine. But spark plugs looked very dark with small gray color spot on the top. Plugs were new from CHAMPION, when replaced it was max 500 km milage. As I have mentioned before I have replaced them with AC DELCO platinum from dealer. Also I have to mention that engine was rebuild - so that all my trials were done with rebuild engine. But what is suprising - that EGR#3 error happened in exactly the same pattern as for old engine.

Sorry this is a long post, but I left everything so you can se my train of thought.

I did not realize it but your fuel pressure should be over 40 PSI at all RPM ranges of the engine. Please read on and tell me what you think.

This is my thought process, I suggest you verify everything else you did first before looking into replacing a fuel pump as they are expensive and its not an easy job. And it involves lots of gas and gas fumes sometimes.


Did you replace the EGR? idk if you did.

I'm at a loss anymore. Sorry I can not be of any more help other than tossing around different thoughts.

Did you get the same code with the old O2 sensor?
If the sensor is different, it might be possible the slight difference in voltage is causing the issue.

Because you only have the one O2 sensor, that means the converter is not causing the problem.

You said all injectors are checked and proper?
all engine sensors are correct? Wires are correct? etc?

I'm going to say this; Maybe the EGR has a sensor built into it to monitor its movement? Its possible. If I'm right, there are 5 wires. Maybe everything working correctly, but the Computer thinks otherwise.

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Before we get into that. What is the error code itself? should be something like P0000 or something like that listed on the scanner.
example: P0314 P0101, etc...

"EGR #3 error code" This is useless to me, sorry. :P
I probably should have asked this sooner.

Also, I will need to know if it is the stored error code, or if it is the real time error code.
and did you disconnect the battery for at least an hour? Did the code show back up? Did any sensor readings look odd when it showed back up?

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looking back on your other posts, I'm seeing 35 PSI.
And you have high NOx. Which right there shows you have to much air, not enough fuel. And Maybe the EGR error is showing up because the EGR is at full open?

Or maybe, the engine thinks the EGR is not proper opening, and causing the high NOx, but really its because of not enough fuel.

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If you have a factory service manual, I suggest you find out what the fuel rail should be reading.

Because I have both the 3.1L MPFI v6 and the 3100 SFI v6, and they both run at around 45 PSI fuel pressure.

The reason I'm coming back to this is because the sensors work, the EGR works, the O2 seems to be reading properly, its not the converter. Ignition system is correct, MAP sensor is correct, etc...

It leads back to fuel & air ratio in my mind.
And knowing what my engines run at, I'm thinking the lack of fuel pressure is causing the engine to get a little less gasoline per injection.
Yes the ECM should compensate, but its running based on a preset that the fuel pressure is in a set range.

here is a link to an Ehow that confirms what my shop manual says for both my V6 engines:
Fuel Pressure Requirements for a GM 3.1L | eHow.com

I suggest checking the regulator, and fuel pump.
But I think you said you checked the regulator. So I'm thinking you might want to test the fuel pump somehow.
When they fail, the fail in two ways: 1) they get weak and then just do not make pressure; 2) they just stop turning.

If anything, I'm still certain that you lack proper fuel pressure.
Because although our vehicles are different, the engines are not. The engines still need the same fuel pressure.

If I was you I would go to the dealership and have them open a shop manual and look at what the secs should be for you.