1996 Impala SS LT1 (Intake backfire) PART 2 live graph of the 02 sensors.

Today I tried to learn how to use my Autel ms906 to help with my intake back fire issue..

PS all 4 sensors are new Bosch units

See Images below of codes in history after scan.

Bank one sensor two looks like its stuck lean however your temp gauge suggests its not warmed up to operating temp. You may need to check the bias/supply voltage at pcm and at o2 sensor to see if its dropping at some point in harness. Also make sure its warmed up as the rear o2s need it warmed up to function as designed.

Thanks for reply

I think coolant temp was around 88c during video
I would think system is warm enough for o2 to be fully running . But will try again with more warm up time to see what goes on .

Let’s say the same could you explain more the testing I should do to B1S2

Thanks again your tips are a big help .

you could check reaction time for a lean (create a vacuum leak) or rich (add fuel like propane to intake) condition and see if it reacts and how fast as well as re-stabilization time. It should react very quickly for upstream and downstream should react a little after that.

I did try pulling vac line I saw my fuel trim go up to 25 and then back down to 10ish when i reconnected

I see many talk about propane how do you do it?

do you connect a vac line from propane into a intake port?

You can add it through throttle body just make sure torch is not ignited. Or attach a larger hose then step it down to fit a smaller vac line.

thank you I think I have a step down brass adapter that should work . I will give it a try. thanks

I took car for a drive today and I am seeing that bank 2 sensor 2 disappear from graph.

I tried holding at 2000 pm at a stop and it does not match the graph like bank 1 sensor 2.

something fishy with bank 2 sensor 2

I would say that sensor is dead then also from the graph might need a upstream sensor on bank 2 as well. But replace b2s2 first then graph them to see if upstream improves.

All 4 sensors are new when this intake backfire started, I thought to get all 4 replaced with Bosch parts since they are pretty cheap .

I am going to try to get under the car and back probe connector to confirm I got power and ground and see from there


edit
today I was able to mess around with the car. I warmed up very well and i was watching graph on trims and o2 operation.

upstream sensors both banks up and down like they should 100-900ish
downstream sensors bank 1 ok
bank 2 as you know low but it is working
(its funny that sometimes after reving etc I see a flip in reading S2B1 now would show low and S2S2 reading middle of graph).

idle/2000 rpm
fuel trims

stft bank 1 and 2 around 0%
ltft bank 1 and 3 around 3%-5%

I created a vacuum leak and I noticed fuel trim spike right away which is good
2-3% on stft and ltft maxed out at 24

when I corrected leak it went back to normal which i was happy with .

I then used same port to feed propane with a silicone line. I opened up propane slowly then full i was only getting a bit rich reading change but when i turned off the propane I did see o2 lean so they are working fine in my eyes.

ok that is good to hear in a sense. i take it your car has a true dual exhaust?... what kind of condition is the catalytic converter in for the effected bank?

Today I wanted to play around with the propane trick. I was not having much luck with it , I think it did not have enough pressure to make a difference into intake.

so then I tried with brake cleaner and that was great I can see on scan tool everything I wanted.

What I saw with brake cleaner added
STFT B1 -21
B2 -15
LTFT B1. -15
B2. -15

I was able to get her very rich.
All 4 o2 sensors shot up rich (900mv)

then when I stopped adding brake cleaner I saw system shoot to very lean and then it corrected its self afterwards.

Once settled I saw (no brake cleaner)
STFT B1 3
STFT B2. 3
LTFT B1 -3
LTFT B2. 0

(on graph see picture)
upstream sensors working up and down
B1S2 was around 104mv steady
B2S2 was around 399mv

see what I mean sometimes B1 is around 400-500 and B2 is at 104

interesting ...........

moving forward to your question regarding cats

only test I have done is remove all 4 o2's and stick scope camera inside to see if comb is damaged. They were mint.

Any suggestions on checking them more?

Few notes:
-I am reading trims and graph much better compared to when I first made this post on scannerdanner. I am thinking better since I used scan tool to clear old history. Not sure if thats true or not but thats what I noticed.
-regarding intake back fire. Also yesterday I had to try really hard to get it to pop..
before all these test and history clearing it would pop so easily and super violent if I didn't let off the pedal.
Now I find it less violent of a sound and not always going to do it.

**just a reminder the intake back fire is only if the car is at a complete idle and I hammer gas pedal.**

thanks for your help

With that info i would say to put the scope camera down the intake and see if there is carbon buildup on the intake valves.

The way to check for a cat problem ie plugged/restricted cats is to take upstream sensor out and thread in an adapter hooked to a low pressure gauge 20 psi or less with a vac hose or a piece of brake line . These gauges are in a carborated fuel pressure test kit plus they have a vac readout on them as well and they are not expensive as well. Then once its hooked up start the car and see what reading is at idle then at higher rpm. The pressure should not exceed 2-3psi if it goes over that then cat is restricted. Repeat test for each side. Let me know if you have any issues etc.

Great information thank you for helping me out.

I actually have the otc vac/pressure gauge it goes up to 15psi so I think it will be perfect for this test

Just need to think of fitting to use into cat.

Ps my autel says my knock count is 6000 perhaps that sensor is finished ? Maybe related to my issue

I would look at sensor and wiring for it if wiring is good and not crisp then swap out sensor.

  I was finally able to get car on the hoist I wanted to do exhaust back pressure test like you advised.

I checked both banks at idle and 3000rpm

Reading came back fine
0-1 psi 

 

Ok that's a good thing cats are not cheap. Now I also noticed in the pics you provided that your knock sensor counts were around 6000 as well as codes for intake air temp and coolant temp sensor as well as both downstream sensors have codes for the heater circuit. I would say to focus on the iat and ECT sensors as those will cause a rich and or lean condition so be sure to check wiring for proper voltage on vref. also check ground for less than 200 MV with key on engine off. Then the signal wire should read low mv when cold and increase in voltage as it warms up. You will also want to do a resistance test with a ohm meter and see what the resistance is compared to temperature of air (iat) and coolant(ect).

Once again thank you for helping me it’s been such a long time I have not had this car fixed 

the codes you see where most likely when I first tested my new autel and messing around unplugging things to see if it ran better etc 

as of now under current codes there are none after I did a clear codes and test drive 

ps there is another tab on autel called addition codes which I don’t understand what they are since they can’t be deleted 

so as I have been getting more tested so far 

fuel pressure is correct 
exhaust good 
I confirmed spark plug wires where installed correct and they are 

the knock count is fishy thou it does not move from there 

I removed both knock sensors and tested on bench with scope and meter and both were in gm
spec 

plus voltage at pig tail at KS is to spec to so why it’s shows that knock count and why its not going up and down as it should is confusing 
 

Oh also did you check base timing and inspect the timing chain slop?

Interesting that you brought that up. I am thinking that might be something I have to check.

Car had low km of 124000 KM and it was mature 1 owner car when I bought it. I didn't think these cars with LT! could have this issue already but I have to check.

I have to research how to do it. I am hoping I don't have to remove water pump and Opti-spark once again to get access.

I think before I dive into timing I like to see whats up with the knock sensor system showing that high number on scanner.

this is what i am trying to fix on car. darn intake backfire 



 

What about a bad head gasket, leaking between two cylinders?or maybe a broken valve spring