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Username Post: 93 Silverado NOx code 13        (Topic#257734)
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
02-17-11 01:33 PM - Post#2047984    

My 93 Silverado is putting out 3600 PPM NOx. It starts fine, runs fine, idles fine.
I see no missing or damaged EGR hoses. I do not have a vacuum pump to test the EGR valve.
The OBD flashes 13, and the check engine light comes on and off during driving.

Question #1: Could a bad 02 sensor cause 3600 PPM NOx?

Questopn #2: How do I determine which o2 sensor is setting the fault code?

Question #3: Should I expect any better performance or gas mileage after I get this NOx problem fixed?

Thanks in advance!

Edited by adam75dfw on 02-17-11 01:38 PM. Reason for edit: No reason given.

 
Auzivision 
Forum Newbie
Posts: 57
Auzivision
Reg: 01-11-11
02-17-11 01:54 PM - Post#2048000    
    In response to adam75dfw

Not sure about your NOx, but NOx is a product of an engine running lean of stoich. For the most part lean means better fuel economy, but can cause other problems like detonation and heat.

Anyhow, Code 13 appears to be O2 sensor and I'm pretty sure the 93 only has one.

CODE 13

Trouble Code 13 indicates that the exhaust stream oxygen content sensor (O2 sensor) is not responding as expected. When cold, the sensor is 'biased' by the ECM to about 450 millivolts. Before it warms to at least 600 deg F (315 deg C) it acts as an open circuit and when the ECM reads it, it reads the 450 mV bias. The ECM expects the sensor to warm in a short period of time and begin sending its own voltages.

The conditions for setting this code are:

engine running at least 40 seconds and
no code 21 or 22 (TPS errors) present, and
coolant temperature is at least 118 deg F (48 deg C), and
O2 sensor voltage not fluctuating (i.e. steady between 350 and 557 mV), and
TPS signal indicates above idle (over 6%), and
all the above conditions met for more than 8 seconds

Typical causes for this code include:

1) Defective or degraded O2 sensor
2) Deposit contaminated O2 sensor (running leaded fuel, RTV silicone deposits etc.)
3) Corroded/defective O2 sensor connection
4) Defective sensor ground circuit
5) Defective connection at ECM
6) Defective ECM

Looks like this:




There are different wiring types... mine has one and it's a 92.

1992 GMC C1500 Sierra SLE w/ 5.7L T.B.I


Edited by Auzivision on 02-17-11 01:56 PM. Reason for edit: No reason given.

 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
02-17-11 02:12 PM - Post#2048010    
    In response to Auzivision

Okay, that simplifies which o2 sensor is bad. I thought all v8 (or v6) had 4 o2 sensors.

Has anyone reading this ever seen an o2 sensor cause super-high NOx?

Does OBD1 set a fault for a bad EGR?

 
Auzivision 
Forum Newbie
Posts: 57
Auzivision
Reg: 01-11-11
02-17-11 02:30 PM - Post#2048018    
    In response to adam75dfw

CODE 32
Trouble Code 32 indicates that the Exhaust Gas Recirculation (EGR) system has detected a fault. There are two types, the older integrated electronic EGR contains a voltage regulator which converts the ECM signal to provide different amounts of EGR flow by regulating the current to the solenoid. The ECM controls EGR flow with a pulse width modulated signal (turns "ON" and "OFF" many times a second) based on airflow, TPS, and RPM. This system also contains a pintle position sensor which works similar to a TPS sensor, and as EGR flow is increased, the sensor output also increases. The other type is a digital 3-level EGR used in newer engines. Code 32 will get set when:
? (Integrated EGR) Coolant temperature above the specified amount, EGR should be on.
? (Integrated EGR) EGR pintle position does not match duty cycle.
? (Digital EGR) Failure of EGR system.

Possible causes include:
1. Faulty EGR valve-to-ECM connection
2. Plugged EGR passages and/or sticking EGR valve
3. Defective EGR valve
4. Defective ECM
Check the shop manual for details on vehicle specific EGR valve applications.


I supose it's possible the ECM thinks the engine is running rich due to a faulty O2 reading and leaning it out too much... but I don't knwo for sure.
1992 GMC C1500 Sierra SLE w/ 5.7L T.B.I


Edited by Auzivision on 02-17-11 02:31 PM. Reason for edit: No reason given.

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 2962

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
02-17-11 03:42 PM - Post#2048038    
    In response to adam75dfw

Depending on how the vehicle is used, some people don’t do driving that allows the system to run a self test of the EGR.

The EGR may not be working and it may not set a code for some time.

Here is the first test I want you to do.

Testing
Most vacuum operated EGR valves that are the GM original equipment valve have large openings below the diaphragm area. If you lift the EGR diaphragm with your fingers, with the engine idling, (being careful not to burn yourself or get your fingers caught in the EGR valve) you should hear a definite difference in the way it runs and the engine will most likely stall. If there is no difference you should look for plugged passages.

There are multiple types of EGR valves and to help you test it I need to know which kind of EGR it has.

TBI trucks are generally Negative pressure EGR or Port EGR systems, except California emission 4.3 TBI trucks had Linear EGR valves.

Negative pressure EGR valves - Should have an “N” after the last numbers on the valve. The pressure in the exhaust system effects (modulates) how much the valve opens.

Port EGR Valves – The EGR solenoid pulses like a mixture control solenoid/fuel injector to control vacuum supply. Port valves have no “P” or “N” and it is blank after the last numbers on the valve.

Both port EGR valves and Negative backpressure EGR valves should open if vacuum is applied to them with a hand vacuum pump with the engine not running.

This is a site that has a photo and an illustration about EGR vale numbers which should help you determine which type of valve your vehicle has.

http://shbox.com/1/EGR_ID.jpg

High combustion chamber temps cause high NOx readings. The EGR is there to lower combustion temps.

Is the vehicle running hot?
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
02-17-11 05:00 PM - Post#2048060    
    In response to Chevytech

I changed out the o2 sensor since it was setting a light anyway. The NOx went from 3700 at low speed to 2800, and 3998 to 3700 at high speed. (I quoted the 3600PPM from memory before. Now I have the papers in front of me. The standard is 905 and 990.) HC and CO went up, but they are still waaay lower than the standard.

I don't drive my vehicles very hard, except my bike. This truck has been sitting undriven since October, though, due to a tranny leak they I got around to fixing a couple days ago.

According to the gauge, it runs about 200-210F.

I will test the EGR tomorrow since the sun is going down now.



 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
02-18-11 02:24 PM - Post#2048480    
    In response to adam75dfw

I tested the EGR valve, and the engine choked instantly. The PIN is (was) on a printed sticker, but it's blank now. Apparently it operates on negative pressure.

Then I checked for vacuum on the EGR side of the EGR solenoid valve. None was there.

Then I tested the intake manifold side of the solenoid (I went ahead and bought a MightyVac.). It gets lots of vacuum from the manifold, and the solenoid holds vacuum pressure from the hand pump.

1) Should there be vacuum from the EGR valve side of the solenoid immediately at cold start, or does it not kick in until normal operating temp?

2) On the EGR side of the solenoid, there are 2 holes. One obviously is supposed to have the EGR valve hose on it. The other is just flat - no knurl to seal with the inside of a hose. Neither hole has any vacuum through the solenoid. Is the 2nd hole supposed to have a cap on it, or is it just supposed to be open to air?


Edited by adam75dfw on 02-18-11 02:35 PM. Reason for edit: No reason given.

 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
02-18-11 03:35 PM - Post#2048523    
    In response to adam75dfw

questions already answered:

someotherguy
Moderator
Posts: 17865
someotherguy
Age: 40
Loc: Corpus Christi TX
Reg: 08-01-03
07-13-10 06:43 AM - Post#1944651
In response to 355Cheyenne

You generally need a vacuum tester (like a Mityvac) to effectively test your EGR valve. Pushing it with your fingers to see if the engine stumbles only proves that the passage is not blocked.

Connect the vacuum tester to the EGR and pull vacuum, with the engine off, and see if it holds. If it does not, it's bad. With the engine running, it should bleed the vacuum off immediately.

This test is good for the majority of EGR valves used on the TBI engines, which tend to be negative pressure (as indicated by an N at the end of the part #).

As far as determining which port is the vent and which is vacuum on the solenoid, the vent does not have a barb on it to retain a hose; the vacuum does.

You can test the EGR solenoid by connecting the vacuum tester to the "output" side of the solenoid, engine running, and tweak the throttle to see if it energizes. At idle, there should be no vacuum coming from it.

Richard
This space reserved for something really witty.
Truck Shop Projects

 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
02-18-11 03:46 PM - Post#2048528    
    In response to adam75dfw

I revved the engine with the mityvac hooked up to the EGR side of the EGR solenoid and got no reading of vacuum on my mityvac. My understanding is that I should have gotten some amount of vacuum from the EGR side, so the part is faulty. Is this correct?

There was constant vacuum on the intake side of the solenoid. The engine was not at normal operating temp. Is EGR solenoid open-loop at cold start?

Edited by adam75dfw on 02-18-11 03:50 PM. Reason for edit: No reason given.

 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
02-18-11 05:02 PM - Post#2048563    
    In response to adam75dfw

The test below says "apply battery voltage." Does that mean straight from the car battery? I would think that would fry the part...

EGR Solenoid Test:

1. Mark vacuum hoses on EGR Solenoid for reference, then disconnect and plug.
2. Connect a vacuum pump to the solenoid nipple that previously had the vacuum line that went to the throttle body.
3. Disconnect the EGR Solenoid valve electrical connector, and apply battery voltage to one of the solenoid terminals. Attach a jumper wire from ground to the other pin of the EGR Solenoid.
4. Using the previously attached vacuum pump, apply vacuum.
5. Verify that with voltage applied to the solenoid, vacuum holds, and with no voltage applied, vacuum does not hold. The solenoid should also make a "clicking" noise when voltage is applied and when voltage is taken away.
6. Remove battery voltage and jumper, and check the resistance of the EGR Solenoid.
7. If solenoid fails any of the previous steps, it is defective and needs to be replaced.

 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
02-18-11 06:26 PM - Post#2048595    
    In response to adam75dfw

I found a tear in the boot of the EGR vacuum line. I think that the reason there was no vacuum from the solenoid is that the engine was not up to normal operating temp. I took the truck back to be retested, and the NOx went down to 232!

Unfortunately, the HC went up from 115 to 250, so it still failed the emissions test.

It also seems to hesitate/surge from a red light, which I never noticed before. The coolant stays around 215 when driving, but gets halfway from the center line (210) to the red on the gauge when it runs stationary on the dyno.

The EGR valve works, but is not OEM. The holes on the underside aren't big enough to stick a pencil through.

Any thoughts or suggestions would be appreciated.

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 2962

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
02-18-11 06:38 PM - Post#2048600    
    In response to adam75dfw

The high temp will cause NOx problems but should clean up the other readings. It could just be a poor dash gauge too.

The hesitation you feel could be the EGR opening, and that is why you did not notice it before.

Too much EGR can cause a misfire which will raise the HC reading.

If it is a negative backpressure system, the EGR valve modulates its movement.These TBI truck are very picky about the EGR valve operation.

Here is a site with a good illustration of a negative backpressure EGR valve.
http://shbox.com/1/EGR_valve.jpg

I would put an OEM EGR valve on it. Being that it ran cleaner HC numbers with no EGR, it may be all it takes to pass the emission testing.
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
02-18-11 07:07 PM - Post#2048617    
    In response to Chevytech

What's the normal operating temp? 185?

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 2962

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
02-18-11 07:21 PM - Post#2048629    
    In response to adam75dfw

It should have a 195 degree thermostat in it.

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
02-18-11 07:44 PM - Post#2048640    
    In response to Chevytech

If it's a 195 degree thermo, then something is falling short...


Edited by adam75dfw on 02-18-11 08:10 PM. Reason for edit: No reason given.

 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
03-03-11 12:54 PM - Post#2055241    
    In response to adam75dfw

Okay, I got a GM EGR valve. Unfortunately, it comes with a set of about 30 different orifices and says to choose the orifice according to the number on the original EGR. I do not have the original EGR. How do I know which orifice to use?


 
someotherguy 
Moderator
Posts: 25470
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
03-03-11 01:04 PM - Post#2055249    
    In response to adam75dfw

You got a "GM" EGR and it came with orifices to swap around? Where did this valve come from? That's parts-house stuff.

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
03-03-11 01:09 PM - Post#2055251    
    In response to someotherguy

It came from a GM dealership. The valve has a size 20 orifice already in it, but it also comes with a bag of other sizes and says to match it with the original.

 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
03-03-11 01:11 PM - Post#2055253    
    In response to adam75dfw

Should I just assume that the 20 is correct? I have a history of bad luck with assumptions, which is why I'm asking instead of just putting it on with the 20.

 
someotherguy 
Moderator
Posts: 25470
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
03-03-11 01:21 PM - Post#2055260    
    In response to adam75dfw

I'd like to see a picture of this valve and hopefully the box it came from, too. If GM has begun selling one-size-fits-many EGR valves, I'm going to have to quit recommending people go to the dealer for this part.

They should have supplied you a direct replacement, no sack of different orifices to try.

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
03-03-11 01:49 PM - Post#2055275    
    In response to someotherguy

Richard,

When I went to get the EGR for my 88 I went to the local dealer a friend works at and all he had was off brand parts house options. In fact they resell as a "auto value" reseller. He used his GM inventory system and insisted the generic part was correct and was a direct match. It worked but it wasn't a universal unit. Initially he offered that up and I declined which meant paying a little more but in the end it worked and then I sold the truck.

Long story short, yeah a GM dealer gave me my only option as being a cheap off brand china crap.
98 Silverado k1500 4x4 350


 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
03-03-11 02:11 PM - Post#2055285    
    In response to 355Cheyenne

Yeah, dealerships aren't known for their great prices or fair business. It passed, though, so now I can move on to the other million problems with the truck. Or I can sell it. Heh...

 
someotherguy 
Moderator
Posts: 25470
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
03-03-11 02:31 PM - Post#2055295    
    In response to adam75dfw

I did notice when at the GM dealer buying some megabuck gear oil for the NV4500, they had some TMC "glo-brite" taillight boards on the counter - one of the aftermarket replacements for the GMT400 taillight boards. I asked what they were doing there and the guy said they sold those too. At least those claim to be US-made, dunno if it's true, though I'm not impressed by the quality. The bulbs fit kind of loosely in them.

Back to the EGR, glad to hear it worked with that particular orifice installed - that's the one you say was already in it, yeah?

I'd really like to know what brand, any kind of markings, were on the part and/or the box.

I do know some dealers for a while just didn't have any of the valves in stock at all, they'd obsoleted them as is their right under federal law. From what I understand the parts stock is floor-planned to the dealership just like cars are, so it's a financial liability for them to keep all that stuff in stock. I just worry about what not only the immediate, but distant, future holds for replacement parts on our trucks. Some things you can find good in the salvage yard, others are entirely consumable and not a good bet when used.

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
someotherguy 
Moderator
Posts: 25470
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
03-03-11 02:38 PM - Post#2055299    
    In response to someotherguy

Right now NAPA lists 3 different valves available for your '93 (assuming 1500 or 2500LD and 5.7 engine) -

"Mileage Plus" (a cheapo brand I always avoid) list $61.59 but this is also a positive backpressure valve, which I think is uncommon on our trucks - they're almost always a negative backpressure valve. Anyway it has the appearance of a universal type but I guess you don't know until you open the package.

Echlin (a NAPA brand) list $134 with no details, and the one pic provided appears same as an OEM valve.

Delphi list $88 and appears to be exact OEM, even has OEM style part #'s stamped into the top cover. This would be my choice, given the dealer trying to slip me an aftermarket unit.



In fact, I'm going to go update my freshly-written EGR testing write-up to mention this...

I'll confess to having an EGR on my truck that I pulled used out of my old inventory. It tested good, and was OEM, so I threw it on. No more code 32 and the engine runs well, so it must be working! Passed smog with flying colors, too, but it also had a nearly-new converter.

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
adam75dfw 
Forum Newbie
Posts: 21

Reg: 02-17-11
03-09-11 03:07 PM - Post#2058624    
    In response to someotherguy

The EGR that I removed had no orifice ring.

The EGR I got from the dealership retails for $140. I got it cheaper because I know people who work at the dealership.

The box was just plain white. It is most likely not an actual GM part.

 
someotherguy 
Moderator
Posts: 25470
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
03-09-11 04:48 PM - Post#2058689    
    In response to adam75dfw

Definitely not a GM part.

That Delphi valve I pictured in my previous reply can be had off Amazon for as little as $54. It lists at NAPA for $88, and can probably be had a little cheaper for a walk-in customer...and probably a little cheaper other places that carry Delphi.

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
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