Tech2 readings on engine data 1

[Danneman]

Ok, so I invested in a tech2 scanner, and thanks to this forum I have the service manual for the 1998 (mine is a 1999 yukon with 5.7). Took a look at my Engine Data 1 and compared this to what the Specs section shows as the "typical values." I tested under the recommended conditions: i.e. engine at operating temp, engine idling in closed loop, closed throttle, in park, and accessories off.

I see several differences between "typical" and actual, but I exercised what I think is some reasonable judgment in what appeared to be different ENOUGH to maybe question it.

The ones that I'm wondering most about are:

• MAF typically 4.6 g/s, I'm showing 6 g/s
• Knock Sensor activity typically none, I'm showing 154 counts
• LT FT Bank 1 typically 127 counts and 0%, I'm showing 121 counts and -5%
• LT FT Bank 2 typically 127 counts and 0%, I'm showing 120 counts and -6%
• Spark typically 21 degrees, I'm showing variable between 22-25 degrees
• Spark control typically Retard, I'm showing Advanced
• CMP retard typically 0-2 degrees, I'm showing 4 degrees

For those very familiar with these readings, can you help me interpret? Are these deviations worrisome? Knowing absolutely nothing about anything, it looks to me like 1) I'm getting too much air and the computer is dropping fuel in order to maintain proper ratio, and 2) I've got some funkiness in my timing.

 

[Sean James]

Mine shows very similar to yours. I was kinda concerned about all the advance at idle! But I'm new to this as well, and the 99 yukon 4x 5.7 runs perfect. Only mod is flowmaster 44. Previous owner had a CAI on it, and said he had a "tune" installed. I put stock filter assy back on and wonder if things are less than optimal. Guess we both have A LOT to learn. I do know that the DLC cable wont plug in upside down, anyway back to studying tech manuals.

 

[Danneman]

Yes, I'm being careful not to pretend I know what I'm doing. There's data and there's proper interpretation of that data. Further searching on the CMP Retard suggests that the reading isn't any good until RPMs are over 1000, and that from there you rotate distributor (clockwise or counter depending on whether offset is + or -) until you get to get it to 0 +/-2, again at +1000RPM.

The problem I'm trying to solve for is covered under a separate thread, "Bucking." But that thread kind of died and so now I'm just trying to focus on scan tool readings and what they might mean.

The Spark, I am led to believe, is not something that can be set. Just the cam offset.

And I misspoke about the air/fuel thing. The LT FT is showing negative, so it's reducing fuel in response to what it thinks is reduced air. The typical value shown in the service manual is 4.6 and I was showing 6.0, but there's nothing in the manual that I can see about true "spec" - so I probably shouldn't assume I'm showing low air, especially if the fuel trim is doing what it's doing.

I replaced the MAF sensor altogether a year or so ago, but I do use a K&N filter and I've never felt like I was being scientific with the amount of oil I use so perhaps I've soiled the sensor a bit. Will see what a cleaning does.

 

[dkknaebel]

I have been chasing an electrical gremlin and fuel/spark issue and started experiencing bucking. Turns out one of my bolts came loose from the exhaust manifold where it connects to the exhaust. My truck was sucking air and confusing the computer with the 02 sensor. Replaced that bolt and viola, no more bucking. The final nail in the electrical gremlin is that I need a new distributor, mine has a dead spot on it.

 

[Big Mama]

Get @swathdiver to chime in he’s got a good bit of experience with the Tech2
Preach to ‘em James.

 

[swathdiver]

Get @swathdiver to chime in he’s got a good bit of experience with the Tech2
Preach to ‘em James.

Ok, I saw this the other night and was waiting to hear back on how the cleaning of the MAF went and checking out the K&N air filter for too much oil.

Dan's computer system reads different than what I'm used to and I do not have a manual for his truck to consult. Never seen the counts associated with the LTFTs but think that if the difference is more than a specified value, it would either set a code or be out of spec.

 

[Danneman]

Ok, so MAF cleaning did seem to result in some mild power increase but didn't resolve the main problem. And I was preparing a good response to all of the above, concerning my Tech2 readings and interpretations, etc., when I stumbled upon something in the service manual that seems to give me issue a name (a transmission "chuggle"). So, I've followed up on that other thread, and I'll leave everyone alone on this one for now - will come back if we need to. I AM still curious about a few things with this tool but one thing at a time I guess. Thanks all for staying with me!