# [SOLVED] Chevy truck 4.3 motor failed emission test



## major41 (Nov 29, 2007)

Hi guys
I have a problem and would like come suggestion on how to fix it.
I have a 1988 Chevy truck with a 4.3 motor and I swaped it out for another 4.3 motor because the other one was no good . I had to take it for a emission test but before I did I changed the oil 'oil filter replaced the plugs' rotor and cap and then took it for the test and it failed.
Here's the reading of the test.

ASM 2525 Curb Idle
Limit Reading Result Limit Reading Result
HC ppm 83 190 FAIL 200 419 FAIL
CO% 0.46 0.95 FAIL 1.00 1.99 FAIL
NO ppm 893 203 PASS N/A N/A N/A
RPM 1296 VALID RPM 582 VALID
Dilution 14.8 VALID Dilution 14.8 VALID 

OVERALL TEST RESULTS : FAIL

IT FAILED : So I brought it back home and I took of the EGR valve and checked the ports to make sure they where not cloged and they where clean and I cleaned the EGR valve put it back on. I checked the vacuum line on the EGR valve to make sure it was opening right after idle and checked all other vacuum lines for leaks.I dumped some good throttle body ' valve and combustion chanber cleaner down it and let it site . Then I started it and boy did it ever smoke. I changed the plug wires air filter and pcv valve and took it for another test. 

ASM 2525 Curb Idle
Limit Reading Result Limit Reading Result
HC ppm 83 191 FAIL 200 313 FAIL
CO% 0.47 0.58 FAIL 1.00 0.52 PASS
NO ppm 893 172 PASS N/A N/A N/A
RPM 1321 VALID RPM 563 VALID
Dilution 13.4 VALID Dilution 13.2 VALID
OVERALL TEST RESULTS : FAIL

Can anyone give me a suggestion on what to do next.
I checked the timing but I wasn't sure what the timing is suppose to be. I looked in my book but it did not say and I looked on my truck but nothing.
Anyhow I read in the book that the ignition timing cannot be abjusted on 1996 and later SFI engines on a 4.3L v6 engines because it is electronic controled. So what can I do to bring the HC and CO down to make it pass.
Thanks in advance for any HELP.
PS: and I changed the catalytic converter 2 years ago ' I put a universal cat on it and now someone told me that they only last one to two years ' Is that true. :4-dontkno


----------



## qldit (Mar 26, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

Good Afternoon major41, that is an interesting problem, I am not familiar with that vehicle but the symptom appears to be the engine is running rich.

As you would be aware the electronic system monitors all the parameters of the engine but in the main it operates off oxygen sensed in the exhaust system and calls for more fuel etc. until the oxygen presence is minimal.
This uses a preset fuel schedule for the engine that the computer is designed for.

You have replaced the motor with a definite same type motor so that should not be a factor.

The next thing could be understanding that some systems purposely run a little rich to provide the catalytic converter with more substance to allow it to cook properly and provide better overall operation.

So it may well be that the catalytic converter has a problem.

Although you say you have replaced it, it is possible that a sick engine could have prematurely adversely affected it's operation.

if you decide to replace it, run a tankful of pure unleaded petrol with some injector cleaner added to that fuel and ensure the best circumstance is present before going further.

Injector cleaner residual may affect readings, so ensure the tank is used and refilled with pure petrol (not blended fuel) before proceeding with converter replacement and another test.

So my guess would be the converter may well be the problem.

But that is a guess, others will have different ideas.

Cheers, qldit.


----------



## major41 (Nov 29, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

Thanks for your reply gldit
I have about a half a tank of pure petrol in it when I took it for it's last test.
I was told by a mechanic to add a can of SeaFoam Auto Marine to the throttle body to clean the system out and then add a can to the gas tank and it would help the emission test.
Here's what the can said on it :
Motor Treatment 
. Injector Cleaner
. Carburetor Cleaner
. Carbon Cleaner
. Fuel Stabilizer
. Frees Lifters & Rings
. De-Icer Anti Gel
. Upper Cylinder Lube
. Dries Oil and Fuels
. Cures Hesitations ' Pings and Rough Idles
. Helps Pass Emissions Test

And I had that in the tanks on the last test to and it still FAILED.
Any other suggestions before I have to change the converter.
Thanks again to anyone that reply's to my ad.
PS: I for got to mention that my sticker has run out and I can't drive it around to much to use anything up that is in the gas tank.


----------



## qldit (Mar 26, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

Good Morning major41, I really don't know that if that kind of substance added to fuel will actually reduce emissions while it is present in the fuel being used, it is a hydrocarbon substance and probably also contains other wax type material in low percentage.

You might contact the manufacturer for information, but I would expect anything apart from pure fuel will have effect and possibly produce residue in the exhaust.

I feel that mention of "helps pass emission tests" would refer to after it has all been used and replaced with normal fuel, I suspect it would be a slight exaggeration as it reads, somewhat!

If the catalytic converter were diminished in function these substances could possibly increase exhaust emissions.

Any presence of lead in fuel can destroy a catalytic converter in short order, is there any chance you may have run leaded fuel at any time?

I think I would be inclined to drain that tank if you can't take it for a long run, and replace it with pure premium or standard unleaded, then consider another catalytic converter before any further testing.

But this only my idea, others may have different opinions. 

Cheers, qldit.


----------



## major41 (Nov 29, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

Thanks for your reply again gldit
They don't sell leaded fuel a round here any more ' It is just unleaded or higher so no lead in it.
I think I will have to change the catalytic converter but I did not want to unless I had to because I put one on two years ago. I was hoping it was something else I could do to it instead of changing that. I changed just about everything else.


----------



## qldit (Mar 26, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

Good Morning major41, yes it is a problem, I can't really suggest anything else apart from checking the engine timing but although that is supposed to be preset there should be some specs you can observe using a timing light to confirm it is correct.

These things these days are all really designed to be placed on engine analysers and display all the parameters on screen, so there is not all that much you can do with general tools. 

Sorry no positive help.

Cheers, qldit.


----------



## major41 (Nov 29, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

Good Morning to you qldit But it's night time here for me.
I checked the timing but I wasn't sure what the timing is suppose to be. I looked in my book but it did not say and I looked on my truck and can't see anything on it tell me what it is suppose to be. Do you know what to set the timing at on a 1988 4.3 motor and what the idle speed is suppose to be. The motor I put in the truck I think is around the same year ' Would it make a difference if it was a little newer or older.


----------



## Midnight Tech (Dec 31, 2001)

*Re: Chevy truck 4.3 motor failed emission test*

Major, if you have to replace the cat, try to get a direct-fit Ultra converter from someone like Walker.
These have an increased catalyst loading which may help your situation.


----------



## major41 (Nov 29, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

Thanks Midnight Tech
I will remember that if I go to change the cat.


----------



## major41 (Nov 29, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

Can anyone tell me what the timing should be set at on this 4.3 motor and what the RPM should be at idle speed.
Thanks


----------



## qldit (Mar 26, 2007)

*Re: Chevy truck 4.3 motor failed emission test*



major41 said:


> Good Morning to you qldit But it's night time here for me.
> I checked the timing but I wasn't sure what the timing is suppose to be. I looked in my book but it did not say and I looked on my truck and can't see anything on it tell me what it is suppose to be. Do you know what to set the timing at on a 1988 4.3 motor and what the idle speed is suppose to be. The motor I put in the truck I think is around the same year ' Would it make a difference if it was a little newer or older.


Good Afternoon Major, sorry can't help with timing setting checks, but it is possible that motor may have a different cam which could have effect.

It may be an idea to confirm that it is in fact an identical motor.

I have no idea how you would do that.

I haven't fitted any hi-tech motors that were not exactly identical.

You may get a clue by checking the computer part numbers if there is any possible year difference, and memcals if they have different adaptions or use them.

As a matter of interest, how hot is that cat running after a prolonged stiff idle?
As in can you touch it with your hand?

I would expect it to be pretty hot! 

Is there any evidence of "rotten egg" gas smell at the exhaust?

Cheers, qldit.


----------



## major41 (Nov 29, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

I checked the timing and it looks like it is set about 3 between 4 degrees and I think it is suppose to be 0 but not sure " Is it true.
The truck is a little sluggish at start of pickup so I was wondering if the timing is off or not.
I also changed the 02 sensor today
Thanks.:4-dontkno


----------



## major41 (Nov 29, 2007)

*Re: Chevy truck 4.3 motor failed emission test*



major41 said:


> I checked the timing and it looks like it is set about 3 between 4 degrees and I think it is suppose to be 0 but not sure " Is it true.
> The truck is a little sluggish at start of pickup so I was wondering if the timing is off or not.
> I also changed the 02 sensor today
> Thanks.:4-dontkno


Here's an update 


Here's the problem " I have a 1988 chevy truck with a 4.3 motor and it failed the Emission Test 4 times now ' Everything passed except the C0% ASM 2525 limit 0.46 Reading 1.10 
Here's what I have changed .
Oil & Filter' Plugs & Wires 'Rotor & Cap 'Air Filter ' PVC ' 02 Sensor ' Catalytic Converter and Set Timing to 0 degrees.
I ended up change everything I can think of and it still won't pass .
Any ideas what to look at now .


----------



## Midnight Tech (Dec 31, 2001)

*Re: Chevy truck 4.3 motor failed emission test*

Are you getting a "check engine" light?


----------



## major41 (Nov 29, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

NO "check engine" light
I jumped the data link to see if there was any trouble code and there was no codes


----------



## major41 (Nov 29, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

You can Close this post now.
Thanks to everyone that tried to help me on my problem with my chevy truck .
I found a small leak under the 02 sensor and I changed the throttle body and it passed the emissions test.
So thanks again. :wave: :wave: :wave:


----------



## qldit (Mar 26, 2007)

*Re: Chevy truck 4.3 motor failed emission test*

Good Afternoon major41, well done, You had me stumped!
(not that it takes much to do that!)

Cheers, qldit.


----------



## Midnight Tech (Dec 31, 2001)

*Re: Chevy truck 4.3 motor failed emission test*

Wow...I still can't believe it hadn't set any trouble codes.
Marking this one Resolved...if you need it reopened, just give me a shout.


----------

