John McGraw

Can anybody please explain the throttle control sequence on a LS2 with ETC?
I have searched high and low for a description of how the sequence works, without any success. In particular, what the relationship should be between the Sensor D and Sensor E. At full throttle on my LS2, the sensor E reads 88%, but my sensor D reads 44%. I have had real problems getting my engine to perform at high throttle positions, but after messing with the throttle pedal this afternoon, it really came alive. When I first started the engine, I got a code on the sensor E, and the Throttle body would operate at all. After unplugging and then re-plugging the connector to the pedal, it started working. Every problem I have been having seems to be somehow related to the pedal assembly, and I just need to understand the logic of how it controls the ETC, and what functions the D and E sensor perform.


Thanks, John McGraw

edcmat-l1

iTrader: (10)

They are redundant sensors. Potentiometers.
One operates high to low as the pedal transitions from closed to open. The other operates form low to high as the pedal transitions from closed to open.
They both do the same thing, just opposite each other.
The throttle body has 2 sensors also. That operate exactly the same way. One goes one way, the other, the other way.
If any of the four fail, and they can fail independently of each other, the PCM will go into reduced power mode.

John McGraw

That is what I had figured, but do all faults that cause the ECM go into the reduced power mode set a code? Also, should the D sensor and the E sensor read the same relative position? When I logged the position of these 2 sensors against each other, when the E sensor was 88%, the D sensor was only 44%. It was only after playing around with the connections on the pedal that the car started running good, but it had never set a code.


Thanks, John McGraw

edcmat-l1

iTrader: (10)

Thats very odd.
I'm not familiar with logging them for percent. I use a scope and look at the raw waveform.
Seems to me, they should have the same percentage. And yes, they should all set codes. Usually, when you have a problem with one, you get no throttle. Not sluggish, NONE. Havent seen one yet that had a sensor issue/code, that would drive, but not drive normal.
I will say though, that my knowledge and experience with these problems have been all with Vettes. None with the Goats. They may have slightly different strategies when dealing with a throttle pedal sensor failure.

John McGraw

The percent reading may be a function of the AutoTap software that I am using. They are both shown, and the percentage is dramatically different, but no codes set. Only after messing with the throttle pedal did the engine really come to life. When I started the engine for the first time, the E sensor set a code and the throttle did not work at all. I checked the resistance and range of both sensors, and all looked good, so I just plugged the connector back in and the throttle started working. I have a sneaking suspicion that the pedal is the source of all my problems, but I will wait for it to crap out again before I can properly troubleshoot it. When the engine went from running crappy to running good, the O2 sensors showed that the F/A went from very lean to slightly rich at WOT. The LTFT's settled down and did not dramatically reset every time the throttle was opened. Given this, it would seem that for some reason, the throttle enrichment program was not working correctly, but It does not make sense.


Thanks, John McGraw

John McGraw

OK, here is the straight poop! As expected, the engine was back to it's old ways as soon as I started it up tonight. Ran it for 15 minutes, and it ran lean and with poor throttle response for the entire time.

Turned the engine off, and stepped on the throttle pedal a little before starting, and the engine came to life! Repeated this test 10 times, and every time it did the same thing. If you start the engine with your foot off the throttle, it runs very poorly, but if you give it just a little throttle befrore starting the engine, It runs like it is supposed to! I don't see any differences in any of the parameters when logged in both modes, except for the fact that the O2 Sensors are extremely lean in the full throttl position when it is runnung poorly. This does not make any sense to me, but hopefully someone can tell me where to go from here!

Thanks, John McGraw

edcmat-l1

iTrader: (10)

At "key up" the PCM updates the learned minimum pedal value. At the same time it updates the learned TP value.
I would venture to say, that if you were to use a scope, or volt meter, you would have different readings at "key up", or KOEO (key on engine off), foot on versus foot off, yet on the scanner, you would have no change in %. Only because the PCM is "learning" the pedal position with your foot on it, as zero.
I know this doesnt explain the difference in performance, but at least it explains why the scanner values dont change.
It may be, though, that the minimum value, without your foot on it, is out of range, but not bad enough to set a code. Just hypothetical. I would break out the volt meter and start probing.

John McGraw

Thanks,

I was pretty much thinking that it has got to be either the pedal, or the TPS in the throttle body. I am going to try replacing the pedal first, and if that does not fix it, then I will try a new throttle body. John Spears is sending me a new pedal, and I am hoping that that fixes it. I hate to buy a new TB just to find out if that is it, but maybe I can find a friend who has one I can "borrow" for a few minutes.

Last resort, will be to pull the ECM and send it back to John to have it re-flashed. It sure sounds like the ECM is fine, it just sounds like it is getting bad info.

The really strange thing is, that you do not have to have your foot on the pedal to make it run fine. You just have to turn the key on and then press the throttle a little before starting it. You can let you foot off the pedal before starting it, and it runs fine. The only time it runs crappy is when you go from off to start without touching the pedal. It makes absoultely no sense at all, but I don't know what the control logic is for the ETC. The problem is absoultely 100% repeatable, and is absolutely 100% cured by hitting the throttle with the key on befrore starting the engine.


Regards, John McGraw

edcmat-l1

iTrader: (10)

That is very bizarre. Make sure you post up the final out come.

John McGraw

I will do that!

John McGraw

Well, the throttle pedal arrived from Speartech today, but that did not fix the problem. Time to try a new throttle body.


Regards, John McGraw

John McGraw

Update,

I borrowed a brand new throttle body today, but it did not cure the problem either! I will pull the ECM out and send it back for a re-flash. I will post an update when I get the ECM back from Speartech.


Regards, John McGraw

John McGraw

Update,

The ECM came back from Speartech last night, and the problem is gone. John re-flashed the computer, and car runs great now. What a head-scratcher!
I chased my tail for days on the asumption that I had a wiring or hardware problem, but it turned out to be a software issue.


Regards, John McGraw

edcmat-l1

iTrader: (10)

Great to hear.