I have a 1990 Vert with the following mods..
-Magnaflow catback
-Catco cat. convertor
-precats eliminated
-air filter cover opened
-frisbee removed
-March u/drive pullies
-throttle body bypass
-air foil (yes I know)
-Performance Resource e-prom calibrationl
-24# Accel "silver top" injectors
-AFPR= 37# @ idle; 47# @ WOT
The two readings that have me confused are;
Total advance= 36.4*
Knock sensor =235....(max is 255)
Cant seen to find in my FSM if the 2 above readings are of CONCERN..
Im running a bit rich on my BLM's.
Can someone help me determine if the 2 readings are out and if so what should I be reading as a correct spec?????
Thanks

 

You sure that isn't the knock count, not knock sensor? The count continues to increment and will roll over after the max. On some cars there will be hundreds or thousands of "events" from starting it up. A high number doesn't mean anything. Though if you continue to have knock events while driving, that might be of concern or at least worth investigating.

Total advance, is this ignition timing? Does the value change over time/throttle/rpm/etc? Or is it just 36.4 all the time? Are you sure "Total advance" is the parameter name in the scan tool?

 

It does display "Knock Sensor" but your description is EXACTLY the same as the manual terminology.
It does display "Spark Advance" it states"the amount of spark advance or timing from the ignition module. Displayed in crankshaft degrees."
Will this information now better help to analyze my concern. Im just not used to some of this terminology and want to understand it more fully.
thanks again....

 

What is the concern exactly? Just seeing those two numbers and having no idea how they are changing, etc, I'm not sure what anyone can say?

If the knock count increases when you floor it, etc, perhaps you have a problem. Otherwise, the number 235 doesn't mean much.

The 36 degrees of spark advance, depends on the situation. On light throttle or if you let off, sometimes the advance can be crazy high, but it's normal. I don't know what kind of timing an LT1 normally has at WOT, so I can't say too much about that either.

Maybe you can explain what exactly you are concerned about?

 

I scanned the numbers at 60 mph. My confusion so to speak is that this data is strange to me and was concerned at possibly being high. I just wanted some clarification that this was okay so to speak for a L98 engine. I thought that there was a total advance number not to be exceeded and this is where my lack of knowledge on this subject comes into play.

 

I am curious about the knock count too... does it clear when you clear codes?
AND.... the timing advance, what should it be under normal situations at say, half throttle and full throttle?

 

Indeed knock counts is called "Knock Sensor" in the AX manual. After each startup the ECM advances the timing till a knock is detected in order to test the operation of the knock sensor. This causes that knock count to increase even if no knock under driving condition.

How rich is it running at part throttle (what BLM values)?
What do the O2 sensor values look like during a WOT burst in Monitor Mode?

I like to tune so my O2 values are in the low 900mV range over the WOT burst.

If yours are higher you could back off fuel pressure a little to lower the BLM & Int values at part throttle.

 

Will check it out today and record my findings. Ive just recently retired and want to get this right and understand more.
thanks
Bill

 

Here are my findings:

AT START Up - PART THROTTLE - WOT
- (55 mph-198*F) - (76 mph-193.5*F)
2758 rpm - 4428 rpm

O2 Sensor - 400mV - 456mV 752mV
Blk. Learn - 118 - 114 - 128
Integrator - 128 - 128 - 128
Spk Advance - 24.5* - 23.1* - 25.5*
Knock Sensor - 4 - 149 - 165

One thing that I have noticed in the past 2 weeks....when engine is cold; it hunts for a gear and I have no power as if the engine is very sluggish with no real power but when the engine warms up it is fine. I bought my Vette last year and has just turned only 14,000 miles. When I got it; I replaced all fluids and changed the fuel filter. Had a fuel injector go right after I got it (Multec) probably due to the fuel injector cleaner(lots) I put in the tank. I replaced them with the Accel 24#(silver tops) ones plus a AFPR as these were the the only ones from Summit that apparently would fit. Hurt my back in the process(old age) but was determined to finish the install myself.
Can you help me understand the above documentation ...is it normal...if not is it contributing to the above problem????
Any help would be appreciated.
thanks
Bill

 

The injectors are the wrong ones for your car(too big) and the lower number at start up means rich. At WOT the cells lock @128 which is what you should be seeing in an ideal situation.You might try bringing the AFPR down a touch and run another set to see what happens.Your O2 values are showing lean (lower=leaner opposite of BLM) too should be above 800. Your Knock is fine and I can't say about the advance but will guess it is OK.

You may have issues with bigger injectors as you turn down the fuel pressure they are not as efficient. If may have something to do with the prom. You should not need a reprogram and larger injectors with your mods.It may be tricky getting it right as you already have the pressure down quite a bit.

 

Thanks for your imput.. The best I can reduce fuel pressure on the AFPR is 36# at idle; and 46# at WOT. Dont want to go lower as the screw(adjuster) may come loose. Will try later....need to snap open a FEW cold ones!!!! Enough for one day for this OL retired guy

 

FYI, lower O2 values indicate a leaner mixture, not richer.

To the OP, since you mention the car runs better when warm, you can use your scanner to see if in fact it runs better when it goes into closed loop. Perhaps with bigger injectors, it doesn't do well in open loop when it is guessing at the fueling, and guessing based on a smaller expected injector. Just a guess.

 

 

Once the O2 sensor has warmed up the O2 readings should cycle between low & hi numbers in closed loop mode.
To look at A/F with O2 readings do a WOT burst on the highway in Monitor Mode.
I like to let the AX advance to the Trigger point and then go to WOT through the 1-2 shift up to around 60-70mph. This gives will let you see a number of engine parameters from idle through the WOT shift points. Here I make sure the ECM is in Closed Loop mode before starting this "testing".

After you do the WOT run look at knock counts and knock retard as well as O2 readings.

For some insight into the meaning of the sensor readings and EFI operation in general I suggest:
"Chevy TPI Fuel Injection Swapper's Guide" by John Baechtel
"How to Tune & Modify Chevrolet Fuel Injection" by Ben Watson
The 1st volume gives a brief overview with troubleshooting guide; the latter is a little more in depth on theory. Both are available through Amazon for around $15 each.

 

There is also a bunch of info in the FSM. For 1990 see 6E-9, 6E3-A-12, 6E3-C1 and C2 pretty much the whole sections, but especially the first parts.

 

I have an 5000 model and the readings are pretty confusing. It's not fast enough to pick up the low-high readings on the O2. Find somebody with a Snap-On scanner and the reading will make a lot more sense.

 

Never heard this before. Can you quote a source?

 

A quote from Datamaster help section
"This is the measured voltage (in Millivolts, mV) generated by the O2 (Oxygen) sensor. Will typically range from 100 mV (lean) to 900 mV(rich). For SFI systems, this is divided into left and right side " OOps you guys were right had BLMs on the brain.

"Formally called the Block Learn Mode (BLM), this is the long term fuel correction factor that the PCM is using. This is displayed in percent deviation from the nominal value of 128 counts. Negative values indicate that the AFR is rich, and if this exceeds 2% the display will turn red. Conversely, positive values indicate the AFR is lean, and if this exceeds 2% the display will turn green. For SFI systems, this is divided into left and right side values."

 

I have read that before but never verified it but knock occurs on start up most of the time anyway.

Another Datamaster quote
"This is a cumulative count of the number of knocks that have been detected. Will count from 0 to 65,535 then start over again from 0. Note that it is normal to see the knock count number jump by 100 or more units at a time; and when the vehicle is first started the count may increment several thousand!"

I never saw several thousand knocks on start up but a few hundred so I thought the timing thing might be true at least in a LT1 anyway.

 

Re '88 Vette FSM, pp 6E3-A-52 ECS Circuit "Circuit Description":