Help: TPS wiring! How to (code p0122)

[discslinger]

98 sl2, DOHC, auto tranny. Throwing code p0122.... runs good cold in open loop then crappy in closed loop/warmed up.

I just replaced TPS sensor. Still throwing the code.

I haven't backprobed yet because I first checked the connector looks very clean - no corrosion, however I jiggled wire, unplugged and replugged... idle varied and jumped to 1200.

I suspect wiring. (Haven't ruled out bad TPS however from Autozone, made n Japan supposedly).

Never messed with wiring to PCM or wiring except for battery cables and rather obvious macro stuff. How do I go about fixing this?

THANKS!

[OldNuc]

Take the TPS off the throttle body and check the resistance pins a-c and then measure resistance between a-b for a smooth continuous sweep of resistance as you rotate the TPS through its range. A-Black+ground, C-Gray=+5V, B-Dk Blue=variable output depending on position. 0.4v->4.7v full closed to WOT smooths sweep. Lay off of probing the connector unless you really want to be replacing it. Poke a straight pin through the Black and Dk Blu wires and monitor the voltage as you sweep the throttle Key ON engine off. The tolerance on full closed and WOT is 0.2v. Aftermarket TPS=mostly junk. OEM from a 97 or 98 at the pick and pull is a better bet.

[discslinger]

OldNuc... thanks; and here's what I did.

I used safety pins to poke through the two wires as suggested... AND it works perfectly to poke the multi-tester leads through the hole at the circular end of the safety pins and then crimp 'em tight.

I took pictures but couldn't upload them for some reason. I'll get that done later. But I attached pics to help anyone else who needs to visualize this. If anyone (like me) didn't know what back probing meant... you will now - with photos, so you don't have wreck a wire harness.

So with ignition in on position, TPS on wire harness not attached to throttle body I measured .2 v at idle. Rotated the inner part of the sensor and measured just over 4.6v on WOT.

At any rate... I take it this means both the TPS and the wiring is fine.

Now... why do I still start running crappy in closed loop/warmed up but not open loop/cold.

Is this because of low compression. (Which I have in Clyinder 2,) but would this not make the car run crappy immediately? Or does the PCM make adjustments that "screw up" the fuel mixture due to the low compression in cylinder 2?

I'm going to retest compression cold and hot... and retest compression with a bit of oil added - as suggested in order to distinguish between rings or valves.

But why am I still getting a code p0122 if the TPS and wire harness check out OK? Thanks again for your insight!


What I've done so far

ECTS replaced with brass version.
New plugs, gapped at .040"
Swapped plug wires (less than year old off my 95 SC2)
Tested Coil wires: 9.2K ohms cold - 9.6 hot, cleaned ignition module
replaced crankshaft position sensor
cleaned throttle body
swapped cylinder 1 & 2 fuel injector. No change in code read. Then I finally tested compression for Misfire on Cyl. 2 - read considerably lower than the other cylinders (all other three same) I don't trust the numbers so not using them.


AS POINTED OUT BY TD1238

Odd that it would run smoothly at first, and then misfire once warm, but it does run a bit richer when cold, which might cover up the leaky cylinder.

Does the temperature gauge deflect normally? The ECTS can look good and still malfunction, though they usually crack open when they go bad.

ECTS is fine.

and so now that I've ruled out TPS and harness (But still throwing the code) I'll try the "add oil" to cylinder suggestion and as TD1234 asked and suggested:

Does compression go up greatly when oil is added to the low cylinder? Add a tablespoon or so. If it does not increase greatly, you may have a burned valve. If it does, you may have sticking or worn rings. You can soak them with Marvel Mystery Oil, SeaFoam Oil, or a good throttle body cleaner like B-12 Chemtool. I like this last product a lot because it contains very strong solvents. Some of them evaporate rather quickly, so it's best to do piston soaks in 2 hour intervals. Reinstall the spark plugs while the pistons soak, so-as to reduce the evaporation of the product. Pour a liberal amount into each cylinder, perhaps about a handful. Keep strong solvents away from paint and lettering. It will remove the clear coat from the Saturn emblem on your valve cover.

[OldNuc]

Install the TPS and check the voltage A-B as you go from closed to open throttle. Also measure the voltage from C-A.

This is an aftermarket sensor or is it a TPS from a 97-98 SOHC/DOHC J/Y car? They are different than the generic or 91-97 design.

How low is low compression?

What type of plug wires are you using? The resistance is incorrect.

[discslinger]

Aftermarket. But car runs fine now... as I'll get to shortly! That was variable voltage I was reading - I assume potentiometer reading from idle to WOT. Wasn't sure about reading resistance... I'll practice that just to learn it.

However... lightening has struck. Runs fine in closed loop now AND the codes cleared. Here's what I did.

I used 2 nickels to plug the EGR. Let the car warm up til temp gauge reached nearly the 1/2 mark and went for drive. Drove for approx 10 miles... fan kicked on as it should have around 5/5 mark... and never was acceleration hampered either entering freeway or from stop to 30 mph on side streets. SES light was still on, but....

... after I took a iced coffee break, took another test run, the SES light went off after reaching closed loop/warmed up mode. No problems again.

I was not satisfied thinking that just because I swapped EGR's from one car to the other that this necessarily meant the EGR wasn't the problem... even though the 95SC2 ran fine with the EGR from my 98SL2.

HOWEVER... I have not fixed the low compression issue. It's bad... around 115 or 120 PSI. I get a rattle once it's warmed up.

So I still have that looming. I did the 'add' tablespoon of oil and the compression went up about 20 or 30 PSI from 90 on an earlier read. Is this significant enought to indicate a ring problem or point to valves?

[OldNuc]

It is valves. The DOHC will burn valves very rapidly if operated at high RPM with any fuel problem. For that much oil you should see just about what you saw if the problem was valves and not rings.

[discslinger]

Fan kicked on at 5/8.

[discslinger]

Valves. Dang.

I'll be reading about that next.

I'd like to possibly tackle it myself... gotta look at what it takes.

Thanks again for the insight.

[OldNuc]

You buy a rebuilt head from a reputable source and swap heads.