RossyHusker

Attached are pics from my first data log at idle after already running a few minutes on my 90 vert. It looks like my O2 sensor is bad based on a reading of 663. The AFR shows red at 14.73, not sure what that means? Is anything else I should be taking note of?

Unfortunately I stopped logging so I don't have the reading but as I ran the RPM's up a little to 2,000 I noticed in the spark advance numbers went to red?

Thanks in advance for any guidance and input.

Cliff Harris

Your TPS voltage is high. It should be around 0.54 volts. Do a minimum idle adjustment:

http://forums.corvetteforum.com/1570563689-post1.html

The oxygen sensor output varies between about 200 mV and 800mV, so 663 is OK (as long as it doesn't stay there). It should bounce back and forth between about 200 and about 800 without staying in between. The O2 cross counts look OK, so it is switching. The count increments by one every time the O2 sensor switches between the extremes. When the count reaches 255 it resets to zero and starts over. The main thing to watch for is that it is increasing. It should increment by one about every second or two.

The BLM of 108 is at the low limit. You're very rich. You can see that in the Switches window under "O2 Rich/Lean Status". Why you're in cell 4 is sort of mysterious. You'll usually be in cell zero at idle with the engine warm. I don't know how the BLM cells are arranged in MAP cars. Mine is RPM vs. air flow, but MAP cars might be RPM vs. MAP -- I don't know.

The IAC motor position of 57 is a little on the high side, but not bad. Do the minimum idle adjustment and see how that affects it. The main thing to watch for is to make sure it doesn't go all the way down to zero. That means that the ECM has lost control of the engine.

Your spark advance looks low to me. My car idles at 20°. Check the timing and make sure the timing constant is the same as whatever you set the timing to (it should be 6° but many "experts" recommend more -- I don't). Maybe that's the "Spark Adv Rel. to Ref Pulse"?

vetteoz

" will stay in cell 4 if sitting in neutral or if the ECM doesn't see any vehicle speed or doesn't see the car has warmed up"

Also related to CCP operation
http://www.thirdgen.org/techboard/po...07-post14.html

JackDidley

The TPS looks ok to me. In 90 cars its not adjustable. ECM sets itself to 0% on start up. The O2 numbers should be junping up and down all the time. There is no correct O2 number at idle . What looks wrong to me, is the Int and BLM. Both are rich.

MrWillys

Your TPS is fine for speed density vs mass air where they're adjustable.

As Cliff mentioned your BLM of 108 is the rich wall. 128 is optimum blm, 108 is taking away as much fuel as possible, and 160 is adding as much as possible. Your 108 can be caused by a larger cam which creates lack of vacuum signal at idle. A larger than 22.1 lb injector was installed, or fuel pressure has been turned up. Because you've only posted a single snapshot only you know which is the cause. Your idle looks appropriate for a manual trans car, so no minimum idle air adjustment is required if a manual car. Cross counts look like it is going rich to lean, so the .663 is normal.
Biggest issue is why is it rich, and what BCC are you using, and has it been modified?

RossyHusker

Thanks for the feedback. My O2 is bouncing while running. I rewatched the log and the range of was 150 to 860, but mostly in the 500 to 600 range. It sounds like my O2 sensor is probably working ok. My spark advance was also changing while idling. I attached a couple of pics of the two common readings while idling. I have not checked my timing since I purchased the car last fall. I have changed the plugs, cap, and rotor. I have new cables to install also. I will check timing and see what I get.

RossyHusker

Thanks. I rewatched my log and the Int ranged from 114 to 124, but mostly sat around 117 or 118. The BLM never seemed to change from 108. The PO installed Accel 24lb injectors and the FSM calls for 22lb, I have the original injectors, the 24lb injectors may be causing this reading?

RossyHusker

Thanks for the thoughts. The PO installed Accel 24lb injectors so maybe that is why the BLM is high? It is a manual transmission so sounds like I am in good shape with idle. I have not looked at the BCC, I believe it is the original but I will have to check it. The PO didn't mention it had been changed.

RossyHusker

I found a spot in the file while playing where I revved to above 2,000 rpm, so I paused it and took clips. Maybe these readings may help shed more light on my data above?

Cliff Harris

To clarify the TPS reading: The ECM reads the TPS when the ignition is first turned on. Whatever value it sees it records as "throttle closed" and uses that afterwards. The ECM calculates the TPS value as a percentage, so the initial TPS value is zero percent (which is what the datalog in post #1 showed).

INT is an instantaneous value. It is calculated many times per second -- that would depend on how the ECM is programmed and the ECM clock speed. I don't remember the number offhand. I have graphed it from a datalog and it jumps all over the place depending on what is going on with the engine. Because of all that, I don't consider it to be a valid way of determining anything useful.

What INT is used for is modifying the BLMs. The ECM compares the INT to the current BLM and if the INT is higher it increases the BLM. If it's lower then it decreases the BLM. My recollection is that the ECM uses a lag filter on the INT. For an article on how this works see this link:

http://home.earthlink.net/~cliff_har...nks/747lag.txt

MrWillys

A BLM of 108 is too rich. You need to reset flowrate to 24 lbs (assuming fuel pressure is 43 to 44 psi with vacuum disconnected) to get blm's closer to 128.

JackDidley

MrWillys is correct. If you cant adjust the injector constan, you could probably lower the fuel pressure to get it better. IF you have an adjustable regulator.

RossyHusker

Thanks

RossyHusker

Thanks. I don't know how to reset, assuming a different chip to tune? I am leaning towards replacing with 22lb injectors?

RossyHusker

Thanks. I don't know if my regulator is adjustable, I will try to figure that out. I am leaning towards replacing with 22lb injectors?

Cliff Harris

It's a parameter in the ECM. The ECM uses it to calculate the injector pulse width. If the parameter doesn't match the actual flow rate of the injectors then the calculation will be wrong and you'll be rich or lean.

It will be called something similar to "Injector flow rate" or "Injector flow constant".

You will need to burn a new EPROM to change it.

RossyHusker

Thanks Cliff