Sudden P1120, P1220 and P1516 at start attempt

[bson]

Hi,
I have been struggling with this problem for weeks and it is driving me nuts. First clearing fault codes and with ignition on (engine off) the throttle blade follows the pedal as it should. No fault codes at this stage. The TPS voltages are verified and runs from .6 to 4.3V and vice versa for sensor #2. I have replaced the TAC module with a new, but no change. The throttle body is new and the car has been running fine until a few weeks ago. No changes made since. I have measured all involved wires in the harness all the way from TB to TAC module and from accelerator pedal to TAC.

I would pay anything (well not anything, but some...) for having this solved. I have attached a log file showing involved sensors in a graph. The log contains two slow push and release of accelerator pedal with ignition only and a few start attempts (where the first probably sets the DTC's. The engine start but dies immediately. I have checked cabling, groundings etc. The car is always indoor in a dry and warm garage.

[5FDP]

Not sure on the TB never swapped them before, sorry I can't help there.

But your temp sensor is unplugged, IAT are -38. Just thought I'd give ya the heads up.

[bson]

Thanks for your observation, but I don't have any IAT sensor.

All involved sensor has been carefully measured and seems to be within specified limits:
TPS1 0.62 - 4.3V, TPS2 4.32 - 0.64V
APP1 0.6 - 2.95V, APP2 4.3 - 1.9V, APP3 4.0 - 2.55V

[dermotw]

It surely won't run or function properly with the IAT stuck at -38?? I know mine was horrible to drive and only just kept running when the sensor connector broke and it went intermittent! Eventually it would go to some sort of limp mode and ran & idled, but not nice. You would need the temp sensor to be fooled to read e.g. 35C or something with a resistor?

[5FDP]

He would need a IAT if he ever want accurate tuning, the computer needs to know temps for SD and MAF tuning.

[dermotw]

...and some VATS issue maybe...?

[bson]

Thank you all for your feedback. The reason for not having the IAT sensor is that I have eliminated the MAF sensor to run in SD mode. Now I have added a 2.2 kOhm resistor which gives 30C IAT. This however didn't make any difference to the problem I'm fighting right now. The strange thing is that it ran ok two weeks ago with this setup. However, as soon as I made a WOT it immediately sets P1120 and P1516 which indicates some mismatch between TPS and expected throttle blade position and the engine entered reduced power mode. The problem did go away if I turned off the ignition and started again. But as soon as I pushed WOT it entered "limp home mode" again.

The problem I see right now is that the engine starts but shuts down immediately within a second and now I get the fault codes P1120, P1220 and P1516. Previously I could start it but in reduced power mode. Attached a new log with 30C IAT and a few start attempts.

I have two questions regarding the HP scanner:
1) Is there a way to detect what is causing the immediate shutdown using the scanner?
2) Is there a way to expose DTC's in the graph in order to spot exactly when they are set?

PS
All TPS and APP sensors are measured and ok and the wiring all the way to the TAC module is verified.
All relevant groundings ans cabling is checked.
Fuel pressure at fuel rail is measured to just below 60 psi.
TAC module is replaced.
DS

Any hint of where to go next?

160902-1.hpl

[dermotw]

Hi,

Well, DTC's are read on demand, so I think no to both. "I'm no expert" though. I don't use a servo throttle myself, however there are tables and expected behaviour, if your setup goes outside those rules (i.e. whatever throttle body/ECM/flash tune combination you have doesn't "match") then thats what I'd expect to happen... you'd have to edit (presumably) the diagnostics values (Engine Diag) to suit whatever it is that you have. (As well as it being setup properly, obviously).

I also see (looking in my own tune, you didn't post yours) a bunch of warnings about altering tables related to the ETC...

FYI, SD or not, Air Temp is still one of the critical things, you would surely be much better off with an IAT. My own temp varies from whatever ambient is, up to +65C on a hot day, idling.. However, a static value is at least better than nothing!

[bson]

Thank you dermotw for your feedback. I see your point and will for sure add a IAT sensor soon, but first of all I just want to figure out what causing it to immediately shut down. I have attached my tune here. force-sd-2016-09-02.hpt

[bson]

The values under Engine Diag is TPS High Fail and TPS Low Fail which are 4.9 and 0.15V. My highest/lowest TPS values are 4.32 and 0.62V. I have also checked the 5V ref with oscilloscope to find any unexpected transients, but nothing.

Just pushing and releasing accelerator pedal (engine not running) shows the throttle blade first flipping down to idle position and then follows the desired value.
Screen Shot 2016-09-02 at 15.21.56.png

This shows what happens when starting the engine. The throttle blade never flips down to idle position and therefore never meets the desired value. I'm guessing this is the reason for setting DTC's and maybe "limp home mode". But shouldn't the engine start and run with reduced power at least!!!??? Could it be something else than this keeping my engine from running?
Screen Shot 2016-09-02 at 15.24.11.png

[dermotw]

Well, there are a couple of flags you can see from the scanner, ENGINE RUNNING and COLD START;

Capture.JPG

It would seem to me that the ECU perhaps doesn't realise you are trying to start the engine.. hence it doesn't shift the blade from rest and it stalls (if it fires at all)..? One faulty sensor is not enough to stop it running as far as I know, GM designed it with many failsafes, and even with eg. a faulty cam sensor it would start & run.

The VATS security (if its not disabled) will stop it, but only after running a a few seconds I believe.

EDIT; Just looked at your tune, the P0101/2/3 DTCs <must> be at MIL ON FIRST ERROR, nothing else will do! If they are not, you won't goto SD...
Also, I see you have VATS off, so it's not that.
You have quite a lot of DTCs off, I would have them on wherever possible. If they are off then even if the ECU could correct for some fault it detects, it won't.







-D

[bson]

Thank you dermotw for your valuable feedback. I really appreciate that you take your time to look at my tune. I'm new to HP Tuners and LS1 engines (as you probably have noticed) but I'm a quick learner ;-).

I read somewhere on the net that by setting MAF Frequency Fail to 0Hz and P0103 to SES Enabled and No MIL Light would force it to SD mode. I thought these setting meant that the error is reported to the ECU but the lamp on the dash didn't came on. I must admit I'm not sure how these different setting really work. This is what I read: https://www.hptuners.com/help/index....ngdiag_dtc.htm

Anyhow, I had some break through yesterday. I measured the TPS level for rest and idle position on a stock LS1 tb. These levels were 1V and .4V while the 87mm tb had 1.5 and .68V. I pulled down TP1 against ground (low ref) and TP2 against +5V ref with two 4.7kOhm resistor to imitate the stock tb. And boom, it started and ran right away!

One observation I did (before putting in the resistors) was that TPS at rest was as high as 29% and between 15 and 18% at idle pos. There is a parameter Max Idle Pos which is set to 19.55%. Could that possibly have anything to do with this?

The resistors is not a solution but rather an interesting test. Now I realized that this 87mm truck tb is simply not compatible with the Corvette -98 TAC module. I've been in contact with Torque Rush regarding their X-Link product and they confirmed that this incompatibility is true and that they at the moment don't have any solution for this setup. So next step would be to build an interface emulating the TPS levels I have from an LS1 tb.

[dermotw]

Hi, thanks for the comments, wasn't so long ago I was new too... Anyway, you can set the MIL light on or off as you like, but not the test, it has to be that way, if you search you'll find many cases of it being set to something other than 1st error and causing people odd problems.. and yes, set MAF freq to 0.

I don't think the maxidle pos will be it, although again, it's a sanity check that in your case it might fail, I expect it's there just to make sure the throttle isn't opened a silly amount by the idle controls, but if you have a non-standard TB (cable like mine) it's typical to have to adjust the TPS position, and aftermarket cable TB's are often slotted so that you can rotate the TPS sensor a little, to get within the "sanity check" values of the ECU... those sanity check values are adjustable, but it's only TPS1 in your case I suppose(?) Typically the TPS is at about .45-.55v at idle...also, could you not just goto a cable throttle? I'm assuming your car is a 98-era Corvette, the others in that era, like mine, are cable anyway...I guess things like the wiring might be a pain...

BTW, on cable cars there is something called the "idle relearn procedure", which allows the ECU to learn where physically the "shut throttle" position is, and it has to be run if you change the position of the throttle blade at idle by more than a small amount. -But I have no idea if the same or a similar procedure is needed on a ETC car! If you search the forum(s) you should find it 'tho. On a cable throttle car, you just disconnect the TPS, turn on ign, count to 10 slowly , turn it back off, then plug TPS back in, thats all. Next time you turn on ign, it reads/stores the throttle blade position.

[bson]

Hmm, I'm a bit confused here. You can either set MIL on First Error or No MIL Light. Does SES Enable unchecked prevent MIL light from turning on? When I read the text below quoted from the HP Tuners help file I understand that a MAF failure will affect the behavior of the ECU in the same way independently of these settings.

"Diagnostic Trouble Code (DTC)
This tab controls the setting of the MIL and SES lamps and the reporting of the various DTC codes (Pxxx). Note: It does not disable the actual tests. eg. disabling the MAF DTCs will not affect the behavior of the engine if the MAF fails. ie. it will still revert to backup mode, set maximum knock learn etc.


Diagnostic Trouble Code (DTC) Error Mode

0 - MIL on First Error: Emissions related. Illuminates MIL the first time DTC sets.
1 - MIL on Second Error: Emissions related. Illuminates MIL if fault is active for 2 consecutive driving cycles.
2 - No MIL Light: Non-emissions related. Does not illuminate MIL, but will illuminate SERVICE light.
3 - No Error Reported: Non-emissions related. Does not illuminate MIL or SERVICE light.


Diagnostic Trouble Code (DTC) SES Enabled

SES Enable (Checked): Enable SES/Check Engine/Service Vehicle Soon lamp/display for this DTC
SES Enable (Unchecked): Disable SES/Check Engine/Service Vehicle Soon lamp/display for this DTC"

[dermotw]

Sorry, should have been clearer: SES Enabled/Disabled = the dash light operates (or not). That one doesn't affect the ECU, just whether the light comes on or not. And the other should be MIL on 1st error. Despite what it says in HPT, the ECU behaviour IS affected depending which setting you make, at least for the MAF DTCs, and possibly many others.
Not all cars have an actual MIL light...

Ok?

D.

[bson]

Ok, I get it. Thank you very much for yor tips and info!

[Earwax]

Iam no expert,but I think that these parts will correct your problem. You can also run a truck or Corvette T/B.This worked for me using the 8 pin truck T/B or the 6 pin Corvette T/B (with X-link adapter).
http://www.wholesalegmpartsonline.co.../12588923.html
http://www.wholesalegmpartsonline.co.../89059124.html
https://www.summitracing.com/parts/a...3153/overview/
https://www.summitracing.com/parts/a...2422/overview/

[bson]

After being in contact with Torque Rush they confirmed that my problem was a compatibility issue. They also said they didn't have any X-Link product for my setup (97mm truck tb and Corvette 1998 TAC/ECU) so I ended up building my own interface emulating the LS1 tb TPS signal levels.
IMG_2012.JPG
If anyone is interested I have all the details documented here on my blog.

[Earwax]

GREAT WORK. THANKS FOR SHARING. Let us know if it sets any codes.

[bson]

Just returned from a 30 min test drive. Works perfect and no DTC codes.