Been throwing off a code 42 for weeks now and can't find out why. Read somewhere that a bad TPS could cause code. Can't seem to adjust the TPS. Voltage jumps all over the place and does not want to settle down. Is it defective or is something causing it to flake out. Know how to adjust but not working. Have a replacement in hand and also an ACDelco ignition module. Tired of other brands that I think are crap. Comments.

 

Done some google reading and it seems as if a bad tps could be causing just the problems I am experiencing. Runs rough. Terrible gas mileage. Louder exhaust - like its on open loop. Will replace tonight and see. Do ignition module this weekend when motor will be cooler to work on. 100* temps in Houston make for hot work.

 

Been a loooooong time since I have had to trouble shoot the old GM systems that predate OBD2.

I seem to remember most that grounds always wound up being an issue in 80% of the problems as time went on and the cars got older.

I don't think the TPS is causing the problem but that fact that your are getting a whacky reading tells me you maybe having issues else where. The TPS should be pretty solid to setup and the sweep of voltage should be very consistent if not then the TPS is bad.

I believe the MAP and CTS help the computer determine EST. I once had a corroded contact on a CTS that would make and engine think it was like -50 out every so often and it would flood the engine due to the high resistance the computer saw. Cleaned the CTS and I never had it again.

Remember that the computer is pretty ignorant of extenuating circumstances. It only tries to make changes based off of what it sees through its sensors. So many times sensors are bad but more often than not its bad connections or something upstream of that sensor preventing if from reading the condition as it exists.

Find your grounds clean them up. Check and re-seat the usual connector suspects. Re-seat the ECM connector. Then start with the sensors that are responsible for the type of error code and check them with a meter. DON'T just swap parts unless you don't care about the money but beware swapping parts can also induce other problems. Hold on to all the old parts and note when you changed them.

I also remember a wire used to bypass the EST so you could set the timing. Not sure if you have that but make sure its not grounded all the time.

Your ignition module could be bad or worse the ECM. But I'm betting on a bad connection or ground.

Figure out whats up with the TPS and if that's working ok and you still have the 42 I would probably try the ignition module. Of course after checking the grounds and connectors on the entire system.

 

Going to replace the tps first. It was not expensive from Rock Auto.

Have checked the est wire but will check again first. At least I think I did. There are so many dang wires under the 82 hood in that area. Will just follow it back from the distributor to the firewall. Will find the connector somewhere along there.

 

Sounds like you have messed around with the TPS so you will have to set it right. How are you doing it? Shouldn't jump around. I had one owner put it in cockeyed so the arm from the TBI was on the wrong side. Make sure you go it on right first off.

Here is how I have done it and it took me a while to figure it out. Get two paper clips and straighten them. Do not disconnect the connector. Just insert the paper clips in to the connector. Get two clips. Attach each probe of the meter to the paperclips with the clips. Or tape them. Place the meter somewhere that youcn see it and not hit it. Set the meter to read to the third decimal point ".000". Ignition turned to on. Undo the screws that hold the TPS but level them snug enough so it does not slide off your adjusted setting. Move the TPS up or down until you get as close to .525 as possible. Remember thats 3 decimal places...not 5.25 which is two.

Here is the pain in the *** part. Three decimal places is real sensitive a hair could throw it off. So you get your .525...great....then you go a head and tighten the bolts and the reading changes to .550....everytime you try it it changes. Here is the trick. Lets say when you tighten it it goes from .525 to .550. Lets say it jumps .025 but it couldbe anyting. Undo the screw again and set the TPS to .500....the .025 varience. Now go ahead and tighten the screw as it changes it should settle at or near .525.

Once you have it set and still have the meter on there. Move the arm of the TPS to wide open. You should get a smooth rise to 4.5 Volts. Try it also with the throttle linkage. Again you should get a smooth rise to 4.5 volts.

See how the engine runs after that.

If your code 42 is random I would check the wires just inside the distributor. Mine were melted.

You may also want to go ahead and change the module.

Jim

 

Replaced the TPS and set it close to .525v.

Checked the EST connection and it it tight. Wiggled it around to bust any corrosion. Probly will disconnect this weekend clean up.

Then replace the ignition module - anyway.

Its just too hot in Houston to work on a car in the evening.

 

Don't forget to put the lithium grease on the rear of the module and where it sits. Most likely your problem.

As for you request for comments. Anything but OEM is $hit. I have a few aftermarket TPS and Modules....none really worked right. I actually have an assortment of aftermarket parts....all $hit.

First thing i do is call the dealer. Second is good used. Third is aftermarket.

Jim

 

Replaced the TPS and set it at spec. Check engine light gone. Will prolly do ignition module anyway since I already have it. Wher!

 

Had a hard time getting the right voltage. As described above, would get close and then tighten and off, sometimes way to much. Finally got within tolerance.

Then replaced the ignition module with a "genuine" acdelco module. Buttoned up the distributor and went to start it and would not fire. WTF? Got out of car and saw rotor still on the ground. FORGOT to put the rotor in. How dumb is that. Only excuse if its very hot and humid in Houston and working outside.

Got it all back together and starts nicely. Then the check engine light comes on!

To make a very long story short, I knocked off the MAP hose from the driver TBI and had a very big vacuum leak. Back on and runs like a charm.

Have another O2 sensor coming from Rock Auto. Last one was replaces way over 100K miles ago, so why not. I don't think I can screw that one up.

 

LOL....were you drinking? Been there done that!!

Don't drop the friggin car on you when changing the O2!!!

Jim

 

Ah! Yeah. It's just we're putting new coversheets on all the TPS reports before they go out now. So if you could go ahead and try to remember to do that from now on, that'd be great. All right!


Scott

 

I drank 3 glasses of wine afterwards at 11 in the morning.

O2 will be this weekend early. Two jackstands.