Emission HELP Please!

Hello to all!
I have a serious problem with a 95 Tahoe. I have changed the EGR valve and the O2 sensor. With each change the results are worse when having it checked at our local smog station. Here is what I have:
HC (PPM) max allowed 83, measured at 200 @ 15 MPH.
NO (PPM) Max allowed 477. Measured 1621 ppm @ 15 mph

HC (PPM) max allowed 48ppm. Measured 190ppm @ 25 mph
NO (PPM) max allowed 730ppm. Measured 1516ppm @ 25mph.

I have no clue why it has gotten worse after changing the key sensors and parts. Could it be the CAT(s)?

Any help or information is appreciated by myslef and brother in law. (his truck)

Blessings to all in attendance!
Chuck aka ulremember:banghead:

If this helps, the truck does not smoke. It actually runs very good!
It is not a "smoker" :)
Blessings to all
Chuck aka ulremember

Go for a good old fashion basic tune up.
If that does not do it get out the fuel pressure gauge a nd a engine capable scanner.
Get codes and rear out data and complete fuel pressure check.
Post back codes and fuel pressure and out of spec data /sensor reading.
MT

Pull All plugs and do not mix them up. Which one is the most sooty? Could be an injector hanging up in that cylinder giving off that much NO/HC.

Air cleaner clean/dirty? Try with zero air cleaner installed. Let the air unrestricted so there is more air than fuel gulping.

Hello to all!
I have a serious problem with a 95 Tahoe. I have changed the EGR valve and the O2 sensor. With each change the results are worse when having it checked at our local smog station. Here is what I have:
HC (PPM) max allowed 83, measured at 200 @ 15 MPH.
NO (PPM) Max allowed 477. Measured 1621 ppm @ 15 mph

HC (PPM) max allowed 48ppm. Measured 190ppm @ 25 mph
NO (PPM) max allowed 730ppm. Measured 1516ppm @ 25mph.

I have no clue why it has gotten worse after changing the key sensors and parts. Could it be the CAT(s)?

Any help or information is appreciated by myslef and brother in law. (his truck)

Blessings to all in attendance!
Chuck aka ulremember:banghead:



MAP sensor...check the voltage output at idle should be around 1.5volts dc. also make sure PCV is replaced and hoses to it are in excellent shape...


If the cat was bad it would not cause those very high readings..

Thank yous to all that replied. Will get on it! I forgot about the MAP. Worked on a car a long time ago, it was the MAP and BARO!
Blessings to all
Chuck aka ulremember

One question. How do I check the MAP sensor with it on the car. Do I go to ground with my meter, or do I jump across two of the three leads?
Thank you in advance!
I tried from ground to each wire. The highest voltage I got was 1.2 I think on the green lead in the middle

One question. How do I check the MAP sensor with it on the car. Do I go to ground with my meter, or do I jump across two of the three leads?
Thank you in advance!
I tried from ground to each wire. The highest voltage I got was 1.2 I think on the green lead in the middle

the wires should be ground,5volts d.c. , and the MAP output...3 wires correct... a reading of 1.2 volts dc sounds good..remove the MAP and make sure that the intake rubber gasket is in good shape...

Hello to all!
I have a serious problem with a 95 Tahoe. I have changed the EGR valve and the O2 sensor. With each change the results are worse when having it

since the MAP appears to read in the normal area now you must check that the EGR passageways are clear ....many times I have had to do this on my now retired vehicles...

usually the intake passageway gets plugged with carbon....as you probably know exhaust gas is sent to the intake manifold by the EGR valve...If this is not done the combuston chambers will get too hot and this then causes high N.O. readings as well as pinging....pre-ignition...

let me know what you found or if you have more questions..

Thank s j cAT! I really appreciate this. SMOG PROS were gonna charge him 700 dollars for the repairs. Get this, NO REPORT THAT THEY CHECK ANYTHING> Charged him 90 dollars and RECOMMENDED the fix of: CAT EGR (new) (checked with vacuum pump. instructions say do not test with), and possible theromostat missing or stuck open (OH YEAH, they said it would not get to operating temp so they blocked the radiator) Low coolant I found but I know that did not cause it. Sorry to run on, but I thought about the temp. Now back to the blockage. :) I will check. I put the egr on and did not notice the common build. But I am thinking the intake area to the heads? Maybe you think let me know and thank you VERY much!
Blessings
Chuck aka ulremember

Thank s j cAT! I really appreciate this. SMOG PROS were gonna charge him 700 dollars for the repairs. Get this, NO REPORT THAT THEY CHECK ANYTHING> Charged him 90 dollars and RECOMMENDED the fix of: CAT EGR (new) (checked with vacuum pump. instructions say do not test with), and possible theromostat missing or stuck open (OH YEAH, they said it would not get to operating temp so they blocked the radiator) Low coolant I found but I know that did not cause it. Sorry to run on, but I thought about the temp. Now back to the blockage. :) I will check. I put the egr on and did not notice the common build. But I am thinking the intake area to the heads? Maybe you think let me know and thank you VERY much!
Blessings
Chuck aka ulremember

a quick test is to manually force open the EGR with your fingers with engine at idle this should cause the engine to stall...this will indicate if passageways are blocked..


another test is place a vacuum guage in line of the EGR control vacuum line and with a long enough hose take a ride you should see 7-10 inches of vacuum when increasing spend..this ensures that there is vacuum to open the EGR...

this will give you help as to whats bad..

Hello! j cAT, I just opened the egr with finger, and it stumbled pretty good. I also hooked up the vacuum line straight to the egr. It does pull it open a bit. I also hooked it back up to the control solenoid, and it open slightly when I raise the r's. Could it be the temp sending unit? I otice that the te,p gauge does not show that the temp of the engine is not as hot as it should be. I would say that it is showing about 152 degrees ( line on gauge between 100 and 210).
Well I want to thank everyone that has replied so far, and I hope that I get more sugesstions.
Blessings to all
Chuck aka ulremember

Hello! j cAT, I just opened the egr with finger, and it stumbled pretty good. I also hooked up the vacuum line straight to the egr. It does pull it open a bit. I also hooked it back up to the control solenoid, and it open slightly when I raise the r's. Could it be the temp sending unit? I otice that the te,p gauge does not show that the temp of the engine is not as hot as it should be. I would say that it is showing about 152 degrees ( line on gauge between 100 and 210).
Well I want to thank everyone that has replied so far, and I hope that I get more sugesstions.
Blessings to all
Chuck aka ulremember

that engine temp sender could very well be the problem as the engine management thinks the engine is still warming up and not providing the correct idle air mixtures too rich...and it can also prevent EGR operation... ECT sender unit replace it..should be 190deg f

Bless you! I will have brother in law invest in the ECT. It is the one on the side of the head? correct?
Blessings
Chuck aka ulremember

Bless you! I will have brother in law invest in the ECT. It is the one on the side of the head? correct?
Blessings
Chuck aka ulremember

the ECT on the driverside of engine near #1 plug is the computer ect....on a 5.3l engine ....the 5.7l engine it is near the thermostat..the resistance at 75-80deg should be around 2800ohms and at operating temp 275 ohms...

The ECT for the computer is in the intake manifold near the tstat housing. The one in the drivers side head is for the gauge on TBI engines.

//2000CAYukon

Thank yous! I will check the resistance on the ECT at the intake manifold! Stay tuned!
Blessings to all
Chuck aka ulremember

j cAT I, back. Just now checking my vehicle. 95 GMC Burb 454cid 2500rated with I think the same problem. I just pulled my thermostat and found that it is rated at 180. I am checking the ECT now. At 74 degrees I got 2700 ohms. started falling as it warmed up I assuming. Now I am going to warm it up to 210 degrees and see. Now, I have two sensors for temp I believe. There is one in each head. Is this the case? I am checing the ect right under the tstat

Checked it with thermometer in boiling water to about 208-210. Ohm reading dropped to 174 ohms. Does this suggest that it is bad? Well I am on my way to Auto Zone and get one. Along with a tstat and water neck, Mine was sooooo badly eroded my hose was popping off. Not good at all!
Well I will be waiting to hear from you with a reply that I really appreciate.
Thank you's again.
Blessings!
Chuck aka ulremember

jcAT, I think that did it. Just put it back together. Idled at 1200 while cold, dropped to about 1000 r's. Idles sooooo much better. I still have a miss at 1200-2000 r's with no load. When I put it in gear at idle, soooooooo much better! Thank you for the advice. Now on to the brother in laws and a good friend with a 454 duelie. We are all having the same problem!
God's speedy Blessings to you and yours!
Untill next time!
Chuck aka ulremember

jcAT, I think that did it. Just put it back together. Idled at 1200 while cold, dropped to about 1000 r's. Idles sooooo much better. I still have a miss at 1200-2000 r's with no load. When I put it in gear at idle, soooooooo much better! Thank you for the advice. Now on to the brother in laws and a good friend with a 454 duelie. We are all having the same problem!
God's speedy Blessings to you and yours!
Untill next time!
Chuck aka ulremember

hi I thought you did all this last month..any way the 75degF at 2800 ohms is perfect...at 212deg f boiling water at sea level this is also correct 175 ohms... so that ect/temp sensor is correct...remember that these parts are the same... temp sender and ect so test both.....

Dang. I thought you said 275 @ 210. Oh well. It must have been the thermo. Baby is running SOOOOOOOOOO much better. No gas odor at the tpipe, better idle under load (still misses a bit a idle. thinking plugs from fouling sooooo long.) Gas needle lowers, does not FALL. :) Temp gauge reading from 200 - 190.
Another question: what are the symptoms of a bad speed sensor? When I come to a stop, I notice the engine stumbles just a bit and the speedo needle jumps with the stumble/miss. Could this be a problem also. Tranny question (okay two questions). My R's are about 2500@65 mph. When I take my foot off of the gas pedal, the r's drop about 500 rpms. When I BARELY press down on the pedal, the r's shoot up the 500 rpms and you can feel the "tranny" engage. When I touch the brake pedal, the r's go up a little ( i believe that is the lockup?) Could my convertor be in lock up and raising the r's, or is it put of lock up and needs to be. ( As you can probably tell convertor issues are not my forte'. (It has been explained, but ooh.) i know bolts and compression and stuff like that.

Thank you for the information jcAT!!!
Blessings !
Chuck aka ulremember

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Thank you for the information jcAT!!!
Blessings !
Chuck aka ulremember

I'm glad that its running better... the sensor connector contacts may have been corroded and as a result tricked the computer into thinking the engine temp was much lower, causing a rich runing condition... on this type of vehicle , after repairing a rich condition, replacement of the plugs, and also the resistance check of the spark plug wires is suggested..

this should stop the idle /miss issues...

alot of transmission shift problems are caused by damaged trans fluid ...replacement of fluid and filter every 30-40,ooomi is what I do and this keeps the shifting quick and solid....also under torque converter lock up it is common to get wierd transmission action with plugs not working properly..


I hope this will get those vehicles running better for you and you associates good luck

The 500 rpm blips are the TC locking and unlocking as you press and release the gas pedal, respectively.

When you are coasting with foot off the gas pedal, the TC unlocks and lets the engine spin free (sort of) of the tranny, but it is still in gear so the spinning drivetrain side of the TC still causes the engine side to spin as well, giving you that engine-braking effect.

When you depress the pedal, the engine and ECM rev up to match the drivetrain rpm and then locks the TC.

TCs are interesting little "black boxes" but put simply it is like causing one fan to spin using the wind of another fan, except in a fluid versus air.

Usually problems with worn fluid are shown as shuddering or hard shifts, not an inability to obtain TC lockup which is a solenoid issue. Brown, opaque, and burned-smelling fluid is definitely overdue for changing. But DO NOT opt for a tranny flush in the hopes of reversing any damage. Too many times I've read of people doing this and ending up ruining their tranny. If you're way overdue, I'd suggest doing a regular fluid & filter change, then do a second fluid change about 1,000 to 5,000 miles later. This way, all the bad fluid is removed or very diluted and any harmful deposits can be caught by the filter. Hope this helps!

Dang. I thought you said 275 @ 210. Oh well. It must have been the thermo. Baby is running SOOOOOOOOOO much better. No gas odor at the tpipe, better idle under load (still misses a bit a idle. thinking plugs from fouling sooooo long.) Gas needle lowers, does not FALL. :) Temp gauge reading from 200 - 190.
Another question: what are the symptoms of a bad speed sensor? When I come to a stop, I notice the engine stumbles just a bit and the speedo needle jumps with the stumble/miss. Could this be a problem also. Tranny question (okay two questions). My R's are about 2500@65 mph. When I take my foot off of the gas pedal, the r's drop about 500 rpms. When I BARELY press down on the pedal, the r's shoot up the 500 rpms and you can feel the "tranny" engage. When I touch the brake pedal, the r's go up a little ( i believe that is the lockup?) Could my convertor be in lock up and raising the r's, or is it put of lock up and needs to be. ( As you can probably tell convertor issues are not my forte'. (It has been explained, but ooh.) i know bolts and compression and stuff like that.

Thank you for the information jcAT!!!
Blessings !
Chuck aka ulremember

No problem with your tranny. jdm was dead on.

Engine stumble is likely a vacuum leak. Test:
Loping idle is vacuum leak. 30 year old lawnmower, or a new car on the lot. If it sucks air where it ain't supposed to, it lopes.

Brick on pedal, block TB arm, anything to get a STEADY idle. 1200rpms or so... Feed starting fluid spray, A LITTLE AT A TIME, EVERYWHERE. Rev increase is the leak.

In a tough spot to pinpoint? Light a book of matches, blow it out while the heads are burnin', and feed the smoke to the leak.

Thank you for the replies. I will get on it. The stumble/miss only happens when I come to a stop though. I see the speedo needle "jump" with the miss. I will check for the leak as instructed :)
Thank yous to all who have helped me!
Blessings!
Chuck aka ulremember