I have the original BOSCH MAF and I purchased an aftermarket Delphi maf. Both supply the same grams and throw no codes.

 

It's not a wideband, it should be oscillating. The feedback from The O2 sensor controls the BLMs. A single snapshot of a narrow band 02 is meaningless. Cross counts and BLMs tell you what the computer is reading from the O2.

Anyways, Checking for a vacuum leak is cheap and you have the indicators of it.

Could it be a bad O2, sure could be. It will be expensive to buy another one, and you still have other possibilities.

Could it be a bad MAF, yup sure could be. It's even more expensive to buy and toss in there to see if it fixes the problem.

Could be a dead injector.


Its free to confirm no vacuum leaks, and I would pull the plugs and see if they show a lean or rich burn before I put more money in it. I had very similar issues with my IROC, replaced O2, data logged, swapped MAFs, it was a vacuum leak. Nipple under TB that supplied the EGR had came off. O2 sensor probably needed replaced anyway, went back to the MAF that was on it and put the other one on the shelf as a spare.

 

i appreciate the response. I tried posting the video I took on my phone but it wouldn’t upload. It was a 30 second video and the o2 sensor bounces from 700-738 and only dips to 450/550 once or twice in the whole video.

ive checked all vacuum lines. Haven’t done smoke test but I suppose that’s in Order to see if any gaskets are leaking.

I’m just confused on what the BLMs are calculated off of. How can the BLM show an extreme lean condition while the o2 sensor shows rich at .7 basically the whole time.

Where does the ecm get its block learn from? It obviously can’t be the o2 bc that is showing rich the whole time..

 

Another good suggestion. I agree if you have low fuel pressure the BLMs will increase because the engine is needing longer pulse widths to get the fuel it needs. Another quick and free check before you buy more parts. If you don't have a fuel pressure gage, you should always have one around working with Fuel Injected engines.

I have seen 160BLMs before with no codes. The one word of caution I will give you about resetting the computer. It has learned and compensated for your lean condition. Resetting it will remove the added fuel until it re-learns it. It may be almost impossible to keep running until it adjust again. I would do some other checks before doing this step, but it is a valid consideration to watch the BLM and INT build up again.

The only thing feeding Rich/Lean back to the computer is the 02 sensor. The BLMs have to be calculated off of it. I am not sure of the actual algorithm or formula that is in the computer to calculate this. It may take TPS/MAF/02/Load/RPM all into consideration as it calculates the value, but the 02 sensor is certainly part of it.

 

I guess this depends on what you consider significant. I was able to have a vacuum nipple come off the port that feeds the EGR on my IROC. Mind you, I think it was this condition since I bought it. Always had high BLMs, but the IAC counts were not at 0. Were around 20. I believe this to be because the throttle stop screw had been adjusted to compensate. It was so hidden, I didn't find this until I had the intake off for another reason - hence why I think it was that way from the time I bought it. I had no significant change in behavior one day, but also never had healthy scan data since I bought it. I bet I will next season.

Every time I re-set the computer, the car ran like crap for about 30-45 minutes of run time before things would get back in-line. I was also fighting a Code 36 at the time due to a thin film MAF not returning a spoof voltage to the computer when it called for the burn off function.

 

I’m working on getting the scanner back from my buddy.

however, I was able to disconnect the battery to re set the ecm. And it start and runs the exact same.

 

That is somewhat good news, but doesn't rule out any possibilities unfortunately. Hopefully once you get the scanner back, you can do the same thing. I would be checking the Fuel Pressure, all vacuum connections, and any potential leaks around any of the gaskets and intake tubing before buying more parts. Then if you don't fine anything I would go back to the 02. When you get your scanner back, also look at the oscillations and make sure the 02 is going back and forth.

Pulling the plugs could also confirm if the burn is actually rich. Again, another free check before spending more money. Unless while you have them out you just put new back in. Which is what I usually do if I have a reason to pull them. Just too cheap to do the work and put old parts back in.

 

These are my spark plugs. FYI should be able to post data tonight or tomorrow morning.

also. The o2 does move around. It just stays above 700. Like 700-730

 

Another question I have is

why would o2 sensor read rich but BLM and integrator the long and short fuel trims read lean?

 

If logic doesn't seem to solve anything, the prom chip is the logic/algorithm calculator. You might have a bad chip.

 

Your plugs look used and slightly rich, not bad. Certainly not soot filled(rich) or a glazy white(lean). A slightly brown look with no build up is what you want to see. So your saying it moves between 700-730 only? Does you scan tool give you cross counts? Has the BLMs went back to 160 after the reset?

 

Finally able to attach the video. The quality dropped. The line under the white line is the o2. You can see it Changes but stays over 700 except for a few times.

also the integrator stays at 130 almost the whole time as well..

I haven’t been able to get the scanner on it to see what the blms are. I’ll have it in the morning.

 

Is that a wideband? I have never seen a narrow band so steady???? Where is your old O2 sensor? Did it do the exact same thing?

 

this is just a regular ac Delco o2 sensor part number AFS21. Old o2 was broken while trying to get it out. It was the Original o2 from 85...

 

You have an O2 sensor that indicates on the rich side. The BLM is at 160 which is just about as much as it can go. Did you check BLM at 3000 rpm?
Just curious....if you disconnect the coolant temp sensor, does it go into open loop, what does O2 and BLM read? You should also trip a fault code.
Let's see what the ECM does.

 

That oxygen sensor is definitely not behaving correctly.

 

What everyone has to remember what you're seeing is what the computer is telling the scan tool. Is it correct?
Since there';s a conflict of data, ;let's not condemn that O2 sensor at this time.

 

I'll try this shortly,

however, i know when i plug the scanner in the car goes into "field service mode" and the rpms go to 1000 ish. im not sure if this allows the car to go into open or closed loop?

 

Based on your scanner, it says closed loop. I wouldn't worry about the rpms. That should not affect the BLM and O2 output. I'm curious as to what the ECM is seeing, and if that's true.

 

That is one of the points I was trying to make! The oxygen sensor can cause the car to run rich or lean when they are faulty. With a meter connected to the output from the O2 you should see the numbers jumping from .1 to .9. It oscillates very quickly and is hard to see without the right equipment.

I still think that your issues are because of a Faulty Oxygen Sensor but you need to fix the EGR to get the "most" out of your Corvette. I found mine had failed at a exhaust emissions testing station where it failed due to high NOX levels indicating a failed EGR. The EGR is a device that many folks are afraid of and frequently try to disable and or remove from the engine. Without the EGR your engine will run hotter combustion temperatures and this will lead to detonation in a 9.5-1 compression ratio engine designed for 87 octane fuel. It can really add up if you ignore it. We hear lots of complaints regarding detonation and frequently the EGR is the cause. People frequently just use premium grade fuel to quiet it down and the problems get worse. There are passageways that fill with carbon and can be a real PIA to clean out. Premium gasoline gets expensive after a while, I am glad my C4 works just fine on 87 octane.

I would fix it like I did on my 1988 C4 and let it work as the GM engineers had intended. Your performance and economy will be there best when the EGR is functioning. I will be honest, it is not the easiest thing to fix as there is a good deal of dis-assembly that needs to be done and then cleaning the passageways out afterwards can be challenging. When I replaced mine I did the EGR vacuum solenoid as well and it was tough as nobody had the one I needed. I finally found one and hooked it back up. The EGR Vacuum solenoid is power by a PWM signal so don't be surprised if the meter doesn't show anything. The EGR system is an important subsystem on your engine, keep it working properly and you will enjoy better performance and economy with your Corvette. The fact that you are seeing Knock counts shows that the engine is starting to detonate. Knock sensors should be tested every now and then as well. With the engine running you can tap a metal wrench or hammer on the engine block and the idle should drop right away indicating the knock sensor is working. Knock sensors can go bad so it is worth checking it when you get a chance as well.

If you don't want to keep the EGR you will need to remove it and re-program it out of the software so a new chip is needed to do it properly. It is against Federal laws to remove them so don't expect a mechanic to help you unless they are willing to take the risk.

The Coolant Temp Sensor suggested it was 217*F in that last picture of the Snap On tool reading. Is that accurate? Can you verify it is accurate? Wacky temperature sensors will make the fuel system do weird things. Higher temperatures usually make the mixture leaner so the CTS is likely okay as long as it is accurate. If the sensor was indicating a colder than actual temperature it would en-richen the fuel mixture and make it run too rich. That is why I was interested in your CTS and asked about it.

For now though you need to STOP ANY vacuum leaks, Period. Block off any open vacuum lines on the engine. If you replaced your MAF sensor that is good, you should be all set. Did you replace both relays associated with the MAF system? I tell people to always replace the relays with the MAF. The MAF would have failed if the Burn-Off relay was not operational. The Burn-off function is to cleanse the 1/10 of a mm wire of any contaminants that have stuck or attached themselves to the tiny wire. After shut down the car should activate the burn-off relay and this cleans the MAF sensor and keeps it accurate. The MAF sensor measures the volume of air going into the combustion process, when they fail and your car will bog or miss under heavy loads.

Best regards,
Chris

P.S. I believe that my EGR Vacuum Solenoid was the culprit behind my EGR failing and getting all plugged up. It has to start someplace and when the EGR solenoid fails so does the entire EGR system. Kind of like when the MAF Burn-off relay fails the MAF goes next and it is expensive to replace. make sure your air tube is well secured between the throttle body and MAF to avoid any leaks. I have one of the Non-Corrugated "Performance" air tubes with nice smooth airflow feeding the air into my throttle body and those can slip off if you are not really careful installing them allowing a major air leak.