smallblock87

A couple days ago the car started having issues reving past 2000rpm after a half hour of driving around town. Limped back home and the TPS voltage reads 5.1V continuously with the car off via my ALDLDroid app and using a Solus Pro. When ON it will read 5.1V and DECREASE with pedal input down to ~3.5V. When running it shows the same signal. I reset the idle and TPS and now running in the driveway it revs no problem but runs extremely rich.

Continuity checks on the old and a new TPS sensor are checking out with relatively the same resistance range. Measuring the voltage at the sensor when installed is showing .54(ish) to 3.87V when cycling the throttle body (with a dying battery). Plan on getting a new battery tomorrow.

Of course I'm getting code 21. I've done a couple Google and CF searches but haven't seen anyone with this kind of high voltage issue sustained. So, has anybody seen this? Got any ideas on what it could be? Hoping its not an ECM fault...

Thanks for any help!

Kevova

I would look at ground circuit. You can use a 12v bulb and socket to load test circuit.

smallblock87

Thanks for the suggestion. Got to looking through the FSM a little deeper and it looks like the ground circuit goes back to the ECM. Code 21 troubleshooting seems to suggest the same course of action. I'll trace it back tomorrow morning and see what I can find.

It also seems to show the ground circuit branch out and is shared with the manifold air temp sensor and coolant temp sensor. Could one of those mess with the TPS reference and cause this issue?

Cliff Harris

The 5 volt reference on the TPS comes OUT of the ECM. If that voltage is wrong, then there is a problem in the wiring or the ECM is bad.

smallblock87

I was referring to this. Looks like the ECM provides the ground path as well.

smallblock87

Added some clarification to my original post above. Also, I had some time to go out and do some continuity checks this morning. Here's what I got:

ECM and TPS connectors both unplugged
D2 to C13 = open
C14 to C13 = open
C14 to D2 = open
C to B = open
C to A = open
B to A = open

ECM connector unplugged with TPS connector plugged in
D2 to C13 = 3 kOhm
C14 to C13 = 11 kOhm
C14 to D2 = 8 kOhm

TPS connector unplugged with ECM connector plugged in
C to B = 2-20 MOhm never could get a constant reading
C to A = open
B to A = 190 kOhm

Also checked TPS connector voltages with the ignition ON. All values were nominal according to the FSM.
C to B = 4.36V
C to A = 5V
B to A = 0.559V

Does this mean what I think it does (ECM is busted)? Does this prove anything else? Thanks again for any help.

JimLentz

The resistance measurements don't make sense. C14 to D2 should be the highest resistance. Even if the measurements for the bottome 2 are mixed up the math doesn't work.

5 volts X 3 K / 11K = 1.36 volts from B to A.

smallblock87

Hmm, thats with a brand new TPS. I just swapped the old one back in and it read roughly the same values:
D2 to C13 = 3.6 kOhm
C14 to C13 = 8.8 kOhm
C14 to D2 = 6.5 kOhm

Even weirder is that now (after all of the plugging, unplugging, and swapping TPS) the ALDL datalink is reading TPS voltage of 2.49V at rest. As I depress the pedal voltage goes down then back up to ~4.5V. Improvement, right?!

Voltage readings with the multimeter at the TPS sensor still read 0.54V to >4V as I cycle the throttle body. Oddly enough, right as I get to WOT the meter reads open loop . This happens with both the new and old TPS.

kael

If you have probes, I think you should check voltage C13 - D2 at the ECM with ignition on, that will tell you exactly what it sees. And check ALDL is telling you the right thing too. Put probes in before ignition! This should match TPS, it not, got a resistance problem in the wire.

Matter of fact, if my TPS goes bad again, that's what I'll check. I made the adjustment, worked great for one night and then bleah, accelerator hosed again the next day. Cleaned contacts today and added from electric grease, drive after that was good. Ah darn, I'll have to drive again tomorrow.

smallblock87

Thanks for the suggestion. Next chance I get I'll see if i can find something small enough to probe the back of those pin connections. I've taken the ALDL data with two separate phones and a Solus Pro so I'm pretty confident its accurate.

kael

Grab something like these:

JimLentz

I bet the ECM has some level of load (resistance) that allows these resistance measurements to make sense.

smallblock87

NAPA had an ECM for $105 so I snagged it. Should be coming in next week so we'll see if that is the issue or not. Fingers crossed!

ctmccloskey

Have you ever tried a Power Probe on your Corvette? This tool is the one device I used in finding all my voltage drops and bad grounds. It almost makes it easy to find the problems. I have the model 3 and the newer model 4. The model four is the very best yet. You can test everything from the injectors to the tail lights.

Here is the link:
https://www.powerprobe.com/pp401as-page/

This is one tool I would recommend to all Corvette Owners who work on their own cars. I use mine regularly around the garage, yesterday it used it to help fix one of my power seat tracks. It has far more capabilities than I know how to use it for. I bought the Master Kit when I bought my model 3, it has saved my butt more times than I car to talk about. It has all the accessories in the one box and it was about $150. It is a bargain price for what it can do for you. My Power Probe 4 was $135 on sale.

I hope you have a great day with your Corvette!

smallblock87

Just thought I'd update for some closure. Installed the ECM and everything works great now. TPS voltage on the data link reads exactly as it should. Looks like it solved some other smaller gremlins I had been chasing as well. Thanks for all of the suggestions.

castlefrank

I've been looking at getting mine rebuilt. Never thought about NAPA. Got one for 145