Code 41

[89turbosupraman]

Hope this is the right place to post this...

The TPS was replaced at the end of last Fall because it felt like the original has developed a flat spot at the 20-25% throttle spot then it got parked for the winter.
I don't remember getting a 41 last year but the car had driveability issues before and after replacing the TPS.
The car has most of the same symptoms this year so the TPS adjustment procedure is done again just to be sure and still the 41 appears. (the EFI fuse has been pulled to clear so many times after driving or starting the car)
I was under the impression that a bad/failing TPS shouldn't cause huge driveability issues so I disconnected the TPS connector and took the car for a drive and it drives with nearly identical symptoms.

Symptoms are: high idle/ hunting idle/ wandering AFR's at idle/wandering AFR's at cruise/stumbling under accel and decel/jerky on and off throttle with the TPS connected.
If I unplug the the TPS, symptoms are: normal idle with little hunting/wandering Afr's at idle and cruise/less stumbling under accel and decel and less jerky on/off throttle.
WOT is intermittent - sometimes it will pull like hell right through to redline and sometimes it will miss/skip like I'm taking my foot off the pedal and then stomping it to the floor.

The throttle linkage has been adjusted for no slack and code 51 is not present. I tested the voltage at the ecu and am seeing just under 1 volt with the throttle closed and about 3.85 volts WOT. I verified that the voltage steps up smoothly as the throttled is cracked slowly.
I checked the resistance on IDL and E2 pins on the TPS and it's well under 2000 ohms.
To verify wiring, I disconnected the TPS and got the 51 then jumped the bottom 2 pins on the TPS plug (IDL and E2) and 51 went away.

This an 89turbo 5speed with 142,000 miles, LexAFM, 550 injectors, Walbro fuel pump, TMS downpipe, no cats, full 3 inch, MHG, upgraded Ct, and a whole bunch of other crap to fill a folder 4 inches thick.
It is NOT throwing any other codes.

I thought perhaps the ecu let some expensive smoke out so I pulled it out and removed the cover and all the caps appear to my eyes to be ok (no leaky caps) and no cracks in any solder points/lines.
I assume testing with another ecu should be in order unless anybody can point to something else.
I also think I will be replacing the Stock 02 sensor as it doesn't owe me anything at this point as it hasn't been replaced in almost 8 years.

Sorry for the boring read guys...

 

[jetjock]

I wish all posts were as "boring".


Do you get 51 with the TPS connected and throttle cracked?

Other than a bad ECU there are only three conditions that will set 41:

1) VTA more than 4.8 vdc (open circuit).

2) VTA less than 100 mv (short circuit).

3) VTA exceeds 1.5 vdc with IDL low.

The last condition will result in rpm cut. Other than that you're correct a faulty TPS will not cause huge driveability issues.

 

[89turbosupraman]

Thanks for the response Jetjock.

To answer your question,
Yes, I do believe it will throw 51 if I crack the throttle but to be completely sure, I will test it again if the weather holds and report back if it's any different.

The 3 conditions you detailed:

1) VTA more than 4.8 vdc (open circuit). My WOT 3.85 volts measurement falls within the expected voltage?

2) VTA less than 100 mv (short circuit). My closed throttle measurement of just shy of 1 volt is to be expected?

3) VTA exceeds 1.5 vdc with IDL low. My monday fog is thick right now - I interpret this as if I took the closed throttle measurement and found it to be as high as 1.5 volts I would see the rpm cut at 2000rpm?

 

[jetjock]

My WOT 3.85 volts measurement falls within the expected voltage?

It's less than 4.8 volts isn't it? Appx 3.6 is typical for WOT so what you're seeing is normal.

My closed throttle measurement of just shy of 1 volt is to be expected?

No, it's too high. Should be around 200-300 mv. Recal the TPS using the proper feelers.

My monday fog is thick right now - I interpret this as if I took the closed throttle measurement and found it to be as high as 1.5 volts I would see the rpm cut at 2000rpm?

When IDL remains at or near zero vdc and VTA crosses 1.5 vdc code 41 is set. The high VTA isn't what triggers rpm cut though. It's the idle signal coupled with increasing airflow and rpm. Since to the ECU that's an illogical condition suggesting possible runaway it halts fuel injection.

 

[89turbosupraman]

I tested for 51 by cracking the throttle and I did get a 51. As soon as I closed the throttle I got the 41 instead.
I tested VTA again and this time I had 2.35 volts with the throttle closed and at WOT had 3.50 volts. Now I'm getting intermittent voltages on VTA???
When I tested it the other day it was under 1 volt with the throttle closed and ramped up nicely to 3.5 at WOT and I have not adjusted/touched the TPS since the last measurements.
The only thing I did since checking the voltages from my 1st post above was to remove the ecu itself and give it and the soldering/caps a visual inspection. Today, I plugged it back in to confirm jetjock's comments. It hasn't been started or driven and it has been sitting with the ecu out.

With IDL low and 2.35 volts on VTA that would surely cause driveability issues - As you described it IS an illogical condition. (now I'm wondering if I have been fighting intermittent fuel cut because of wandering voltage on VTA)
Measuring IDL to E2 on the ECU I get no voltage with the ignition on or off which is to be expected - Correct?
I will see battery voltage at the TPS with the ignition switched on I believe.

Does this mean a) an improperly adjusted TPS can cause a voltage as high and as low as I have measured or b) removing and reinstalling a bad ECU can vary the voltage to that extent or c) both a+b are in play

 

[jetjock]

Again, cal the TPS per the TSRM. Make sure the throttle is not being held open by the linkage or dashpot. If necessary remove the TPS from the TB and check it. Use voltage, resistance, or both. If it fails the checks replace it. It's nothing more than a potentiometer and a switch. When the switch is closed (at idle) it connects IDL to E2, pulling the input low to ground. When off idle the signal gets pulled high to +5 by a resistor internal to the ECU. If you're getting 51 that's happening.

 

[akito]

If I put an ohm meter to idl n e2 at the tps (off throttle body) and no reading shows up on my gauge is it safe to say that the tps Is dead? Also, nothing comes up between e2 n any of the prongs actually.

 

[89turbosupraman]

Again, cal the TPS per the TSRM. Make sure the throttle is not being held open by the linkage or dashpot. If necessary remove the TPS from the TB and check it. Use voltage, resistance, or both. If it fails the checks replace it. It's nothing more than a potentiometer and a switch. When the switch is closed (at idle) it connects IDL to E2, pulling the input low to ground. When off idle the signal gets pulled high to +5 by a resistor internal to the ECU. If you're getting 51 that's happening.

Ok, I calibrated the TPS per the TSRM and verified the linkage and dashpot aren't holding the throttle open. I rechecked the new TPS and it falls within all specs in the TSRM. Everything verifies ok.
When I measure VTA I still get around 2.35 volts at the ECU with the throttle closed and just over 3.5 WOT. If I measure VTA at the sensor itself and ground to the battery's negative terminal, I then see about 500mv throttle closed (which is alot closer to the 200-300 you mentioned earlier) and the same just over 3.5volts WOT.
Is it me or am I looking at replacing some bad wiring for the TPS?

 

[jetjock]

"VTA exceeds 1.5 vdc with IDL low."


Can't fix it. Not there. Can only tell you what the problem is...

 

[89turbosupraman]

"VTA exceeds 1.5 vdc with IDL low."


Can't fix it. Not there. Can only tell you what the problem is...

I know, I know - Thanks again for your input and patience with a putz. My head is just not in it as I'm in the process of buying a house. I thought at one point in my life I was really sharp with this crap. My 76 Z was a wiring hackjob nightmare when I bought it.
I think I'm on to something (I might slap my forehead so hard if this turns out to be the issue) but ran out of daylight and got sick and tired of trying to hold the flashlight with my chin. I'll do some further testing tomorrow and give an update.

 

[3p141592654]

I'm not there either, but find a way to check continuity on the 4 TPS wires (E2, VTA, IDL, VC). If you've got 500mV at the TPS, and 2.3V at the ECU it seems like a wiring problem to me.

 

[89turbosupraman]

UPDATE: This is now resolved.

I had the light bulb in my head flicker the other night and wanted to be sure to test my theories thoroughly before providing an update.
Turns out the issue was with the data logging feature of my PLX wideband. The TPS, MAF, CTS, and stock O2 signals had been tapped to do data logging. I think that part of the PLX went up in smoke.
I pulled the tap off the TPS wire near the ECU and the code was gone and measuring VTA at the ECU got me back down to 500 millivolts. I also pulled the taps off the MAF and CTS wires to test. The car drove much better.
I did have lean idle and cruise while testing for a few days but AFR's were rich as always under boost.
Finally, I pulled the tap off the stock O2 and idle and cruise are near stoich as they were before these problems started last year.
I think the wideband is still accurate as the numbers are identical to post install numbers a few years back.
Lesson learned - Never assume a piece of electronics that worked before still works properly.
Anyways, THANKS again for all input.

 

[3p141592654]

I would never recommend tapping the O2 signal. That is a very sensitive signal that is easy to mess up.

 

[jetjock]

^ This. And even when tapped the device needs to have a high impedance input. > 10 meg.

Maybe I missed it but I don't recall the OP saying he'd tapped into anything. Not exactly a minor detail...