I found the issue with the MX+ and am once again able to get reliable data from it. I then brushed up on short term and long term fuel behavior and captured a CSV file. The only thing I see is the long term fuel at idle is running around -10%, and goes to zero above idle. The fuel pressure reads a bit high at 65Lbs. I replaced the pressure regulator when I started to debug this issue and there was no improvement so I moved on. Perhaps a leaky injector, but does not seem severe enough to cause this issue. The short term and O2 sensors seem to be behaving as would be expected with the O2 sensors going between .1 and .9V and the short term averaging around 0. so nothing I can see there with my limited knowledge.
I contacted Monmouth Auto Diagnostic, and the told me to try a performance shop, so I would be interested in any suggestions to hel with this diagnosis.

 

I can't believe a diagnostic shop told you to take it to a "performance" shop...they should be able to diagnose this whether it's your Corvette or a Honda !!...long terms that are negative at idle that go positive under load is either the O2 sensor is receiving a rich command...the O2 sensor will be well above 450 Mv's...if they switch from 200-800 Mv you are good...it can be high fuel pressure but 65 psi should be OK...a dirty air filter can cause these negative fuel trims as well as an "over reporting" MAF sensor...what does your scan tool show at idle ??...should be roughly the liter displacement of the engine so 6.0-6.5 grams/second are good numbers I normally see ...8 or 9 grams/second not good...are you seeing negative fuel trims on BOTH banks...a dirty MAF will cause this over reporting...has it been cleaned lately and is your air filter clean ??...if the MAF is suspected you can disconnect it on now run on speed density using the MAP sensor for an input...see what the long terms now look like at idle !!..below is screenshot of my 01 at idle with my scan tool.

 

C5 Diag,
Yes it suprised me too. I guess they don't need the business. I will keep looking at this until I can find someone to scope it.
I will try to address your questions. These readings are taken from a 10 minute run I made. They are taken from the csv file where it was at idle:
The long term fuel trim is -8.6 on both banks. It dipped to -10.16 on bank 1 and -9.38 on bank 2, but that may have been on deceleration
Both bank O2 sensors are swinging from 60 to 800mv.
I just cleaned the air filter, but it probably should be replaced.
The MAF is reading 6.7 grams/sec.
MAP is 6.85 inhg - a bit low
At idle the secondary O2 sensors on both banks were above 700mv

I will try removing the MAF and see what numbers come up. Will the ECU automatically use the MAF when that happens?
Thanks again for your help.

 

Just check those fuel trims at idle once the engine warms up and if they are still negative but go positive it’s like I mentioned either a dirty air filter or a MAF issue…your O2’s look fine !!…the PCM will use the MAP sensor for its fueling strategy when the MAF is disconnected…I was in NJ last month to visit family and give some scope training to a friend and his employees at his shop for a few hours…could have stopped by if you had this issue back then !!

 

Just check those fuel trims at idle once the engine warms up and if they are still negative but go positive it’s like I mentioned either a dirty air filter or a MAF issue which it doesn’t look like !!…this may also be a bad MAP sensor…what does the MAP read key on engine off ??…should be around 103 Kpa or 29.8 InHg or 29.8 BARO !!…your O2’s look fine !!…the PCM will use the MAP sensor for its fueling strategy when the MAF is disconnected…I was in NJ last month to visit family and give some scope training to a friend and his employees at his shop for a few hours…could have stopped by with some of my diagnostic equipment if you had this issue back then !!

 

Mine was a coil pack went bad

 

I unplugged the MAF and the behavior did not change.
I checked the MAP with the engine off and it went to 30inhg so it is behaving as expected.
The air filter is a vararam. I cleaned it and it seems OK but I ordered a new one anyhow since it will not hurt to change it.
The only other thing I see in the data from the last drive is if I go to wide open throttle, the spark advance for #1 cylinder goes from 40 degrees to 0 degrees. It bounces between 0 and 6 degrees while the throttle is at 99%. While it is at wide open throttle the car hesitates, misses and looses power until I come off of the throttle. It will then respond normally.
I still have not found a diagnostic shop. I have however looked at oscilloscopes on line and am suprised at how reasonable they are. Since everything seems to be behaving as expected except perhaps the spark advance I am wondering if buying a scope may be worth it. I am a retired EE so I am familiar with how to use them. I used to borrow one from work to debug the ignition on a chevy small block. How difficult would it be to use one to try to determine a mechanical issue which I am starting to suspect.

 

Unless the engine is "knocking" the timing should not be retarded below WOT which you are seeing...spark timing is controlled by engine load, RPM and temp which I believe is IAT (intake air temp) so maybe you should look at IAT with your scan tool...which scan tool are you using BTW ??...you really couldn't use a scope to look at timing. If you want to look at something mechanical using a scope you would need an in cylinder pressure transducer which the training has a STEEP learning curve...now this is my car at idle using the pressure transducer...I've inserted a blue line which would represent a synced ignition firing event which is about 10-15 degrees BTDC and each hump represents TDC...if you had a pressure transducer and snapped the throttle you could see where the blue line would now be...a lot further to the left or advanced under WOT. Since you are seeing loss of power and hesitation etc. I would look at "live data" to include RPM, load, fuel trims, O2 sensors, MAP, MAF...I would also with a scope look at the crank sensor waveform with an ignition sync to see the relationship between the CKP and ignition...I don't know of any other shops so I would call around to see who uses a scope...if they don't look elsewhere!!

 

The scan tool is an OBDLink MX+. Other then issues syncing with my iphone at times it seems to be pretty reliable. I have the csv file with the live data capture of that trip so I can look at the IAT. Thanks for the input on the scope. The engine is not knocking that I can hear although I am still getting the P0332 code even after replacing the knock sensors and the wiring harness for them. Since this code appeared long after I started getting the P0300 I assumed it was a seperate problem and would have expected replacing the sensors would have fixed it as it has in the past. I should have tried testing them before putting the manifold back on. I am not even sure how to do that but I do have the shop manual so that is the next step for testing that. That reminds me of how my old football coach broke down the word "assume."

 

You can try disconnecting the knock sensor connector and see what happens as in the video…the sensor produces an AC signal so a hammer and a multimeter (scope is better) set to a low AC voltage setting may help as shown !!

 

Another video !!

 

Thanks for the videos on knock sensor testing. It is still tempting me to get a scope. Are the under $200 scopes available worth buying?
I looked at the shop manual for the P332 and it is saying that the PCM is failing to read the number 2 knock sensor. Out of curiosity I tested the old sensors, and they both had the correct resistance and showed up to 900mV in the voltmeter when I tapped them. The old harness also tested good. That being the case I am going to check continuity and voltages at the PCM connector before I take the manifold off again.

 

Always best to check the entire circuit…don’t think a scope under $200.00 is any good…I use the Picoscope 4425A and it’s my best diagnostic tool hands down…if you have the money you could get a 2 channel Pico 4225…you might find one on eBay…has a lot of tests preloaded you can do with it…you’ll also need to invest in AMP clamps and other accessories.

 

At that milage could the timing chain be very loose and ready to skip a tooth or more?

 

Thanks again for the scope input. The 4225 is way out of my price range since I would only be using it to diagnose my own cars.
At 351K miles I suppose anything is possible, but the behavior seems too inconsistant to be mechanical. For instance under smooth acceleration it runs smoothly, but WOT it stumbles completely. I would expect a timing chain that is already tensioned not to bounce around on acceleration. I may be wrong, but I want to exhaust all possibilities before looking into mechanical issues.

 

Has the fuel pressure been checked when you go to WOT…pressure should not drop…what about your fuel filter/pressure regulator ??…was an AC Delco used ??…I’ve seen bad new filters on here !!

 

I changed the pressure regulator with the AC Delco regulator and the filter with a WICS filter about a year ago. I am not sure how to check the pressure at WOT since the tester I have requires an under hood inspection. The scanner checks for fuel pressure, but the PCM does not seem to report it.
I looked at the live data comparing throttle with the spark advance and when you did a rapid acceleration, the spark advance would go to 5 degrees and since this was the only reading that was abnormal I decided it must most likely be the knock sensor. I checked it at the PCM and sure enough one of the sensor lines had no reading.
I tracked it back to the connection between the sensor and the harness. I put it all back together checking as I went and the car is running much better and not showing any codes yet. I will have to run it for a while to see if the P0300 comes back, but it is sure a big improvement from what it was.
The moral of the story is this extra work could have been avoided if I would have checked my repair before putting everything back together.
I thank everyone for their help and comments. I learned a lot about using the scanner in the process.