Where is the vapor canister vent valve located?

Thanks AL. Your help is important. Even though I am a beginner mechanic and went to school, I do remember some things I learned in school. I learned that getting the code P0420 doesn’t always mean the catalytic converter is bad. It can also mean a lean o2 sensor. Many shops made that mistake by dropping in cats and the code came back. It turned out to be a 02 sensor sometimes.

The vehicle runs fine, and acceleration is smooth. But sometimes it delays when stepping on the gas pedal like it’s hard to accelerate at first. I don’t smell any rotten eggs like I smelled before. So, I am hoping the purge valve fixed that.

I just have that one little problem with the rpm surging. It still surges at idle and when you are slowing down the vehicle. What it does is, when you drive it cold it doesn’t surge and it’s easy to step on the gas pedal. But when it reaches operating engine temperature and the engine is hot, say driving it for 35 mins to longer it’s when the rpm begins to surge. Usually at cold starts RPMs surge for a couple of seconds. But it drops and is fine for a while when driving.

At this point, I wouldn’t say it’s sluggish, just a delay in acceleration stepping down on the gas pedal at first. I just don't like it when I am at a green light and have to accelerate again. Feels like the pedal hesitates to go to the floor. It feels like it’s hard and you can barely get the car to move forward at first. It takes some effort at first because all cars usually are smooth like butter soon as you step on the gas to accelerate.

I will have to check the MAF sensor on the scanner and let you know. Is that rule of thumb for the MAF the same range for any car or truck or specs are different?

Between, is there any idea I can check the cat without any special scan tools? Like what do I need to notice after I remove the top o2 sensor from the manifold? Someone said you can check with a meter?

Okay, so all that stuff about removing the o2 sensor and checking the voltage readings cannot be done with a meter. It has to be seen on a scanner.

I have a craftsman scanner I paid $55 for. I can view graphs and see what some of the sensors are doing in freeze frame. Today I checked the MAF sensor and got around 4g% at idle. Today the idle was smooth and I was able to accelerate fine. But like I said you have to be driving the car longer and further for it to do what it does with the rpm surging. At idle I did notice the engine feels like it still surges but only slightly, nothing erratic or anything kind of like a minor misfire, if I had to describe it.

I did not notice any RPM surging today because I didn't drive that far. I did look at the fuel trims at cold to operating temperature. Long term fuel trims still is lean at idle and rich at acceleration. But I didn't see anywhere near -17% this time at acceleration when it went that lean last time.

First at idle it's at 0.0%. Then I accelerate and it gets rich. Around +3% to +6%
I make a complete stop at a red light and back to idle again. The vehicle decreases to -5% down to -0.3% at idle.

These are just the ranges I am seeing. When I receive around -17% lean at acceleration that was before the exhaust was leaking. But so far after the exhaust has been repaired these are the current trims. It looks stable than before. But I am still seeing always lean at idle and rich at accel.

Yesterday I looked at the fuel trims and o2 sensor readings when engine was hot and being driven for a long period of time. 02 sensor for front Bank 1 sensor 1 is all over the place. It doesn't give me steady readings. 02 sensor for rear near cat Bank 1 sensor 2 is reading around 600-800v. I remember you said for the rear 02 sensor, if it was reading from 200-800 and it wasn't staying steady there would be a problem with the cat working. But the second 02 sensor looks fine because it's staying around 700v for the most part. 02 sensor bank 1 sensor 1 is going from 0.90v to 800v. It's never staying at one reading. Now from the readings below you'll see what the issue is. When it's lean and when it's rich and when it stays lean and when it stays rich. I also have a pic of a graph of the 02 sensor bank 1 sensor 1 when engine reach temp and was at idle. It starts out normal and has some resistance in the middle.

IDLE READINGS
SHORT TERM FUEL TRIM (AT IDLE) AT ENGINE TEMP
READS BELOW -10 BUT STILL AT LEAN
LONG TERM FUEL TRIM (AT IDLE) AT ENGINE TEMP
READS BELOW -10 BUT STILL AT LEAN

ACCELERATION READINGS
SHORT TERM FUEL TRIM (AT ACEL)
READS BELOW +10 BUT STILL RICH
LONG TERM FUEL TRIM (AT ACEL)
READS BELOW +10 BUT STILL RICH

Now here's where it acts up. This is when the rpm needle starts to surge

Acceleration to deceleration readings
When you let off the gas pedal to decel on brake pedal the rpm needle will continue to rise to 1000 rpms making the engine surge after making a complete stop to oncoming intersection, red light, ect

Short term fuel trim (acel to decel) at engine temp
Reads higher lean counts and higher rich counts. Somewhere between -9 to -20 and adds more fuel +10 to +20. But only does it when you decel and the rpm needle surges. If the rpm doesn't surge the fuel trims are fine. The shor term fuel trims are making the engine lean because air is getting inside the engine and it's putting a heavy load on it when you decel

Long term fuel trim (acel to decel) at engine temp
This was the fuel trim that was reading higher lean and higher rich before at decel before the exhaust was repaired. Short term trims were reading fine before. Now exhaust is repair and short term is reading higher lean and rich counts.

*important info*
Mention before but will mention again because it's important
Before the exhaust was repaired it was the complete opposite. Short term fuel term trims would be normal and long term fuel trims would be higher counts of lean and rich at (acel to decel) at engine temp.

But as you can see now with exhaust repair, short term fuel trim counts only go higher at decel when the rpms surge. I would say every couple of mins the rpms surges when the engine has been driven for a long period of time and short term fuel trim counts get really lean than back to really rich adding all that fuel. When you begin to wide open throttle to accelerate the vehicle the numbers go back to rich again but not too rich and everything smooths out again.

I know I keep repeating myself but it's very important that you know when the fuel trims change and when they do it at what times.

So the real deal here is when you step on acel pedal to acel the short term fuel trims move to lower rich counts until you decel and short term trims move higher lean to higher rich again. I feel if there was large vacuum leak when the engine surges or the cat was clogged it would create back pressure at wide open throttle and you would not be able to floor the gas pedal at wide open throttle or even acel smooth down the road. The gas pedal is able to acel, but when you let off the gas pedal to decel you feel the engine surge and rpms jump. That is when the short term trims go crazy. I wouldn’t say it does it constant at decel, but if the engine is hot and driven long periods that is when the engine and cat gets really hot and rpms will make short fuel trims go higher than normal at decel causing it to go really lean and really rich.

What we are dealing with here is not acceleration issues, it happens at decel when you are slowing down.

0xygen sensor voltage readings: at idle, acel and decel
O2s bank 1 sensor 1- swinging from 0.95v to 840v
02s bank 1 sensor 2 - does not reach below 600v, it can go as high as 850 but stays around 700.

Here is the graph I attach also of the o2 sensor bank 1- sensor 1
You see how the current changes in the middle? That is when the rpm needle surges at idle.

Here is how the engine is breathing also.

Yes, the idle on the brake pedal when you decel is when idle surges with the RPMs. The RPMs also surge when you are in park. That only happens when you start the vehicle every single time and RPMs jump from 1,000 to 2,000 RPMs. It used to do it constantly last year. But it has to whine down.

When you say, “You have to re-prime the system in between injector pulses” you don’t mean disconnect the fuel pump relay? The car has to be at idle to test each injector right? I was thinking you had to disable the fuel system to test each injector while using this tool. I recall something like that when I was in school. We had to do a injector balance test and they cranked the vehicle to check engine injector pulse. But they said don’t flood the engine so only crank for 5 seconds. Maybe I forgot and got it confused with the compression test we done. Please refresh my memory how this tool works.

How long will it take to have it run at idle until the fuel clears out until you can do the balance test one more time?

Also, I don’t have an oscilloscope and probably will not be able to afford one if it’s over $50.00 at the moment because I have to save for more parts for the Chevy and my classic car.

So, if the injector balance test will save me that would be great... Just in case I will need to put $100.00 some dollars for injectors. I am waiting for the tool to get here. So, I should be able to check them out next week. I know checking resistance and hearing them click isn’t a confirmation test. Just lets you know they are working but not official if they are still bad or not.

As for the smoke test, no shops want to seem to do it. I have been telling the one shop I took it to smoke test it and they said it’s not necessary because there isn’t a large vacuum leak present. If it was misfiring like crazy they would do it. They keep telling there isn’t a need for it. Plus, I can’t afford a smoke machine yet either. Still starting out saving money for the more expensive tools. But I want to work on my car myself because 1. I am a mechanic and 2. I can’t keep putting money out for labor when they do nothing for the things they have more tools with to complete the job. So I have been for the most part getting some info from experts like you guys to lead me in the right direction to diagnose it myself. Nobody around here knows what they are doing. The guy I take it too doesn’t have a famous idea why it does this at idle. You were the first person who was able to guide me in the right direction who actually listens to my questions and finds the right answers. Around here every shop just wants to charge you lots of money and it’s not fixed the first time.

But it wouldn’t hurt to replace the intake manifold gasket if the injectors are ok. First, I am crossing my fingers the injectors is the problem.

I will keep an eye out on the injecting testing and if all is good with that, I will replace the intake manifold gasket. It has 77,000 on it. So, I might as well replace it if injectors aren’t the issue. They last between 50,000-60,000 mostly. But I will keep you posted on the injector testing.

As for letting the vehicle idle to get all the fuel out before doing the test again, it would probably take about 5 minutes or so until I can redo the test, right?

Okay, I have a question here. I put the injector balance tool on pulse four to test the injectors. Is that fine? After I did that, I noticed it dropped from 50 PSI to 46 PSI on one cylinder. But something is going on with my harbor freight fuel pressure tester gauge. When I start the vehicle to check fuel pressure it goes to 55 PSI and then the needle starts to jump like crazy not giving me a steady reading anymore. Could it be the gauge is going bad? The car starts fine and seems to give me a good reading at first, but when I was disconnecting each injector on each cylinder the fuel pressure tester gauge would not go back to 50 PSI when I cycle key off and on. It’s supposed to go back to normal pressure after each injector test when you prime the system back to specs, to do the test again, but it just stays at 46 PSI it doesn’t go back to where it should be. I have to keep freeing the pressure back to 0 to get a good reading again and sometimes with key on engine off the pressure is at 49 PSI. When checking fuel pressure, the actuate reading is at idle, doesn’t seem to want to give me normal pressure at key on.

I connected it again and fuel pressure started dropping at key on. Then I start the car and it’s at 55 then keeps shaking the needle. It stays actuate, then it doesn’t. I also notice the Schrader valve is not in the hose anymore you attach to the gauge, so it looks like it took a shit. Harbor freight is cheap. I was looking at ones on Amazon. What are the best gauges to get with good quality hoses and Schrader valves?

Okay, disregard those questions. I just figured out why I am having so much trouble. You can't have the key turned on when using this tester. After you get fuel pressure with key on, it has to be turned off and you can start testing. Then do pressure testing over again with key on, until it's at specs and test other injectors with key off. There is a lot of bad worded info out there. So, I had to research more.

I was so confused because I didn't know that you need to have another pig tail connected to the pig tail wire, they given you to connect to the injector. You did not mention that but no problem it's fine. I got to find another pig tail that will connect to the pig tail they given me so I can connect it to the fuel injector. Otherwise, the pulse will not work.

They give you two pins, red and black. But I was only able to fit the black connection on the fuel injectors pins and it wouldn’t test it because you need to use both pins if that makes any sense. Is there any tool out there that you don’t need to change the pins? The connections on the tool I have will not connect both pins to the injector. I have seen a lot of videos with people adding their own pins to the ones on the tool. But I don’t want to solder them. What about this tool? Would both connections red and black, connect to the fuel injector pins without having to do customize the connections to work ? https://www.amazon.com/Injector-Professional-Ignition-Powerful-Burnt-out/dp/B08XJZCT82/ref=pd_lpo_2?pd_rd_i=B08XJZCT82&th=1

Go to 8:30 in the video and you’ll see what I mean. He talks about the female connectors. That’s what I didn’t want to do. I just want a simple tool that tests the fuel injectors. Not having to customize it. https://youtu.be/VUEDycxyJ0Q

What are you referring to? Tool I post from Amazon or one in the YouTube video? All I am looking for is a tool you don't have to customize the female connectors.