Here are a few examples of what I got in this week.


Case 1
Dead TPS, Misadjusted IAC

http://www.pcmforless.com/images/dat...adjustment.JPG

The blue line in the graph is the TPS sensor %. As you can see the car thinks its at 100% throttle the entire time at a idle. This is quite obviously a bad sensor or possibly bad ECM.

Also, you can see at the end of the file (where the cursor is posistioned) that the idle is fluctuating hard, desired idle is 1100 rpm (pretty big cam) and IAC position is at 160. This means that the IAC is opened completely trying to hit the desired idle, its not enough so the car is bouncing around off the stall saver. GM reccomends around 25 counts at a fully warmed idle.

Case 2

Bad ECT sensor.

http://www.pcmforless.com/images/dat...ECTscrewed.JPG

This car is bouncing around between 130 and 140 degrees reported at a fully warmed idle. This is a pretty good indication of a bad sensor or high resistance in the wiring to/from the sensor. This car also tripped a LOW TPS code and woulnd't read higher than 14% TPS so it had some other issues also.




Case 3

Lazy/Dead 02's

http://www.pcmforless.com/images/datalog/deado2.JPG

This guy just installed a set of pacesetter coated long tubes. Its quite typical for the new coating to burning off and fouling the O2 sensors with this type of header (and others really). As you can see the 02's are not fluctuating at all on one bank and is really lazy on the other.



Case 4

Bad IAT sensor

IAT, ECT, MAT, TPS, O2, MAP, MAF, and probally a few others I'm forgetting are extremely important to fuel calculations. They cannot be removed.. This customer removed his IAT/MAT sensor because he believed that the sensors only function was for EGR. He didn't mention that to me until we where welll underway with diagnosing this thing. The car ran terribly and fouled plugs.

 

I noticed 2 of those datalogs had lots of knocks . Sensor related ??

 

Thanks for sharing Alvin.
Hank

 

No, if you look at the black line you'll see that they might get .2 degrees once in the entire log (probally noise related) I keep knock retard graphed all the time to keep an eye on it. The knock counter in the 93's rolls over constantly.. If you turn the key on but engine off the knock counter will roll at a rate of probally 20,000 counts per minute for example. Knock counts <> actual knock. Knock retard = actual knock (or noise)

 

Couldn't the lazy O2 sensors be from the location of the sensor in the new long tube headers? Not enough heat for them? Are they heated?

 

They get a hair bit slower with long tubes but look at the graph of that 02's output.. Its barely moving at all. It is a dead o2..


Crap I had another one today I could have posted but didn't take a snapshot of it. Guy came and complained of the car throwing lean codes.. I scanned it and the o2 was sitting on .002 mv's What does that tell you?

 

Did you post the right charts? Monitoring O2 voltage during open loop operation can be misleading. I've used it to monitor warmup and with a heated sensor, expected it to start developing a voltage sooner, rather than later.

A lot of so called fouled O2's (assuming it hasn't been slathered in antiseize) can be cleared with heat - from the air pump or applying a little (to a lot of) throttle. I've always considered "lazy" as a Bosch marketing term - (there has never been an emissions recall or TSB for any production vehicle over failed, slow or what have you O2 sensors - I think that says more about their durability then anything you might be seeing by logging the signal - absent a code of course).

There are plenty of other causes for what's in your logs and hard codes generally don't take much logging (if any) to figure out. I'm not saying that it isn't helpful, but to say that any one of your examples points to a specific cause, even though the reason may have been applicable to the vehicle you're working on - can be misleading to those who don't know any better. And for performance mods, far better to use the log in conjunction with EGT's, though obviously, that's fairly difficult for most of us.

 

The reason why the car stayed in Open loop is because of insuffecent switching.. I see it all the time with pacesetter headers especially and LS1 cars. If you can't look at the graph of those O2's and come to the concluesion that they are dead than I don't know what to tell you.. The car is fully warmed up it bounces in and out of open and closed loop (because of insuffecient switching) and the O2mvs do not fluctuate one one o2 and is damn irratic on the other.

I don't know what your trying to say here? That its impossible for these sensors to get fouled unless they have been dipped in antiseize? theres lots of reasons for a O2 to go bad. 1. Age, 2. ceramic Coating "breaking in", 3. Silicone poisining, 4. Heat burning up harness.

No offense to how you do things but I would never reccomend someone cleaning up a O2 with heat. I would rather the guys use a fresh set of Delco 02's. I've had too many problems first hand with bosch to reccomend them. I'd rather do things absoulutely 100% clean and right than to try to skimp out and save a few bucks.


Yes, but with my experience I have spelled out the problems with these cars and the sensors responsible. If you don't agree with me thats fine.. And your dead wrong about hard codes.. The car with the bad TPS (sitting at 100% the entire log) never tripped a code.. Neither did the o2' problem cars.. Hell neither did the car with the IAT unplugged.

The point in my thread was to never underestimate the power of a good datalog in the hands of someone who has experience w/ these cars.

For example I have people swear up and down to me that thier chips are bad or whatever only to find out with a datalog that the IAT sensor was left unplugged the last time they worked on it.. Now, In a perfect world the car would have tripped a code and the guy woudl have found it.. but I'm hear to tell you that it hardley ever works that way. Think I'm pulling this out my rear? Well, unplug a IAT sensor, or a O2 sensor and take a ride around the block. I think you'll be quite suprized in the hundreds of miles you might have to put on the car before it trips a code.

 

I don't disagree with you, except to the extent there are other causes.

Yes I've removed harnesses from sensors plenty of times to see if it will trip a code - that's a quick and clean ECM test - disconnect the TPS and see if it will set a 22. If it doesn't, suspect the ECM or suspect something else.

Some sensors - EGR in particular - aren't going to do anything until commanded by the ECM. Disconnecting the EGR harness on idling car doesn't mean very much. Driving it around the block before it's warmed up is the same. OB2 makes it a lot simpler since there are readiness codes. Monitoring open loop operation, for the most part, doesn't always help but at least you can see how some of the sensors are reponding, so that's why I asked if you had the right chart for your O2 test. On the face of it, I see an engine that's been running long enough to get close to the thermostat and I would expect some voltages soon - just not enough there for me to draw the conclusion you did.

Yes there are faulty O2's - my experience is from slopply installations - I'm sure you've seen some of the tools individuals have fashioned or relied upon to install them - ditto for too much antiseize. Ditto for leaking headers sucking air, though more readily picked up by monitoring Block Learn (at least for me).

As to the O2, the air pump was designed to make it work faster - that afterburn gets it up to speed, along with the CAT. So does exhaust, especially if it's non heated. I wouldn't replace one without verifying that the former was working and I'd monitor a non heated sensor while applying a little bit of throttle.

Again I'm not knocking it - there are other causes and for those who datalog, they need to follow the Trouble Charts to cover all of them - or at least post their data for help when they're not sure.

 

Another problem found with datalogs

http://forums.corvetteforum.com/show...35&forum_id=48

 

quick question, how do you get datamaster to graph

 

Its at the vary bottom.. Double click the item and it brings up a list for you to change to.

You can also drag boxes over what you want to look at in detail with the right mouse button.

 

AH HA!!! Thanks!

 

The thing I like about the the logs and the description of the problem is it's educational for folks that don't do it everyday.

I understood the problem was found and fixed and the logs definitely matched the problem.
There's no end all/be all for troubleshooting. The problem must be analyzed a step at a time and the post by Alvin and SunCr describes the process that that a LOT of people take years to learn.

I throughly enjoyed reading the description of the problem, looking at the data logs and seeing the logic that was used to find the problem.
Hindsight is 20/20 and I like to see how other folks think about problem solving.
Particularly by someone that sees these problems everyday.

SunCr I've enjoyed a lot of your post, much so in the realm of AC diagnostics.

Alvin , thanks for taking the time to post your info and logs.

Folks, this is how you can learn at someone's else's expense and someone else's experience.

A great big to both of you.
Alvin since this is your thread a super thanks to you.

 

Alvin, this is EXCELLENT! Thank you very much!

PLEASE consider, no, I FULLY ENCOURAGE you to continue making such posts so folks like me can learn more!! Great work sir!

 

DITTO that

 

I got 2 more in this week..

A EGR related spark knock issue and a TPS low.. (.40 v idle less then 4 v at wide open)

 

links?

 

On a related note: I think my datalogs point to a bad lifter. Has anyone else seen this behavior

http://forums.corvetteforum.com/show...24&forum_id=48

 

Alvin,

I really enjoy seeing-learnig what somebody with your experience has to say about datalogs (and PCM tuning), the low knowledge I have about the subject is thanks to people like you.

Thanks for share with us!