UPDATE: Foul exhaust smell

[blazer94]

Just wanted to post results / interesting observation. ( 94 4.3 L, CPI exhaust is smelling bad.( rotten/ sulpher) I checked usual suspects: no washing of nut kit or spider, no rattling of the cat, ( cat was replaced in Nov. 04 ) new O2 sensors, (also Nov. 04) cleaned air filter, switched gas stations. I know we have additives in our winter gas, but my other vehicles do not exhibit this problem. Any other suggestions? Full tune up ( plugs, cap, rotor, ) also Nov. 04. No MAF sensor in CPI, so I'm running out of ideas. No codes either.)
After checking / resetting time, and then running a couple days, still had odor and same gas mileage. I stopped at the Chevy dealer last Tuesday to order a rear window striker plate, and was talking to one of the mechanics. He asked what plugs was I running, and I told him AC Delco Plats. He told me to get rid of them, and run the regular AC Delco CR43TSM, and I would be amazed at the difference. As of yesterday, my idle is much smoother, and picked up almost 3 MPG and no smell. I would not have expected that much difference.

[BlazerLT]

So the upper inside plenum was completely black with carbon?

Also, did you check fuel pressure?

[blazer94]

Yes, I pulled the plenum prior to my original post. I have had to deal with regulator/ spider / nut kits before, so i knew what I was looking for. ( no washing) Fuel pressure @ the schrader valve on key on start / engine not running was 61 psi.( fuel pump was replaced 10/04)
What I found most interesting about this is when I initially checked the timing as you suggested, the base timing ( with ecm shunt disconnected) was 4 deg advanced. I reset to 0 deg., and did notice some improvement. After changing the plugs, I checked the timing with shunt attached, it was hunting between 3-4 deg. advanced. I disconnected the shunt, getting a reading of 0 deg. I cleared the ecm, re-connected the shunt, and when i checked the timing again, it was solid 4 deg. advanced, no hunting. The plugs I took out all were coated with the light grey ash common to short trip driving, and they were gapped correctly. Is it the plugs? Seems like it could be, although I am not an engineer, I am pleased with the outcome. Thanks

[BlazerLT]

Originally Posted by blazer94

Yes, I pulled the plenum prior to my original post. I have had to deal with regulator/ spider / nut kits before, so i knew what I was looking for. ( no washing) Fuel pressure @ the schrader valve on key on start / engine not running was 61 psi.( fuel pump was replaced 10/04)
What I found most interesting about this is when I initially checked the timing as you suggested, the base timing ( with ecm shunt disconnected) was 4 deg advanced. I reset to 0 deg., and did notice some improvement. After changing the plugs, I checked the timing with shunt attached, it was hunting between 3-4 deg. advanced. I disconnected the shunt, getting a reading of 0 deg. I cleared the ecm, re-connected the shunt, and when i checked the timing again, it was solid 4 deg. advanced, no hunting. The plugs I took out all were coated with the light grey ash common to short trip driving, and they were gapped correctly. Is it the plugs? Seems like it could be, although I am not an engineer, I am pleased with the outcome. Thanks

The shunt is supposed to advance the timing 4 degrees after it has been reconnected after timing the base timing to zero.

What you saw was perfectly normal. It is the timing advance.

What plugs are you using? How old are they?

Have you checked for vacuum leaks? I just found one on my engine.

When was the last time you did a tuneup?

[blazer94]

Originally Posted by BlazerLT

The shunt is supposed to advance the timing 4 degrees after it has been reconnected after timing the base timing to zero.

What you saw was perfectly normal. It is the timing advance.

What plugs are you using? How old are they?

Have you checked for vacuum leaks? I just found one on my engine.

When was the last time you did a tuneup?

Yes, I know the timing is supposed to be advanced. If you re-read my post, it was advanced w/ the shunt disconnected Also, the timing is not supposed to hunt up and down if everything is is connected and all sensors are functioning. I am now using the AC Delco CR43TSM, I was using the AC Delco platinums (they were only 4 months / 2800miles old.) I checked for vacumn leaks (using a vac hose and plain old hunting ) when beginning this procedure, and full tune was done in 11/04. Note that at this point, as stated earlier, my mpg is up 3mpg. Average of 2 tanks last week and during the weekend was 15.6 (mostly city) and 17.2 city/highway. The exhaust odor is gone, too.

[BlazerLT]

good.

[blazer94]

Originally Posted by BlazerLT

good.

I appreciate the help and advice, LT. Thanks

[BlazerLT]

Originally Posted by blazer94

I appreciate the help and advice, LT. Thanks

You are very welcome.