ahickman

Stopped for a bite to eat tonight before going on duty. Got back in my truck and fired it up. Noticed something was not quite right as I pulled out, seemed like the engine wanted to shut off in between shifting gears. Got to the squad house and pushed the clutch in. The engine started sputtering and almost died out. Looked at the gauges and everthing seemed normall so I mashed down the gas to get the RPMs up. At higher RPM's it runs well enough. Let off the gas and it stumbles. Shorted TEI and T1. Diag codes 41 and 42 were received. No visible/audible vaccum leaks. Sound like the TPS out of alignment?

iamsuperbleeder

hmmm, 41 and 42... lemme flip through the book here...



TPS could be maladjusted, broke, or even rattle unplugged if the clip is damaged.

You've looked at the TPS yet?

42 may be a result of 41 coming on; you know, one sensor throws another one off... that's why I like working on old American cars most of the time; only electronics are the alt, starter, coil and dist, lol

ahickman

Yeah, I pulled the TPS connector off and started it. Ran a little rougher, but not significantly.

thook

Is your speedo or cruise control working right? Do you have cruise control?

The speed sensor will be on the same circuit as the TPS for ECU input.

On my '92 with an A/T, when the speed sensor went south, the speedo started acting up and CC would not work. Plus, the tranny would drop out of high gears under load. The TPS and speed sensor input regulates A/T shifting. Exactly how it works on a 5spd, I don't know. Might just be for speedo and cruise control.

Anyway, it does sound like the TPS is bad or out of adjustment. The spd sensor wouldn't affect the idle.

ahickman

Thook. Thanks. I will look at the TPS with an Ohm meter tonight after work. Now that I think about it, over the last few weeks I have felt a little "bumping" as I drive along, especially after startup. Seemed to go away more or less after warmed up (thinking ECT sensor), but was getting worse. Symptomatic of a TPS sensor going bad, or do they just drop out? BTW, on another thread, you and Ganoid walked me through ordering new shims for a 3.0 I am rebuilding. Got them measured and ordered. Thanks.

thook

"Bumping"? I'm guessing you mean a slight miss or hesitation in the motor? Yes, that could be signs of the TPS going bad. The tracks in there wear over time, so the signal gets worse as that happens. It would be unusual for a TPS to just go out all of a sudden. Though, I suppose it could from a major jolt/trauma....but, typically not. It may just seem like that.

Sometimes electrical issues can smooth out as the engine warms. Once it has reached operating temperature, the ECU, ECT, and O2 sensors are running things more optimally as they all affect ignition timing. And, so does the TPS...but, it's not temperature regulated. So, TPS symptoms could be "masked", as a result.

Check the TPS thoroughly making sure to also test the VTA range:

From 4crawler's website....

"One final test, not listed in the FSM, would be to run the TPS shaft from idle to WOT and watch the VTA-E2 resistance and make sure it increases monotonically, no drop outs or dead spots. If you observe abrupt resistance changes, the TPS could have a burned area on one of the current tracks."

All about TPS...
http://www.4crawler.com/4x4/CheapTri...roubleshooting

ahickman

Thook, or anyone else....any suggestions on brands of TPS sensors to stay away from? I looked at prices on NAPA's website and see that they range from $95 to $300 or so. Assuming as always that you get what you pay for and should stay away from the cheaper options?

thook

I really can't tell you anything from experience on that specifically. I've only bought ND/OEM throttle sensors. I do remember a thread from a couple of years ago where the fellow used one he bought from O'Reilly and it worked fine. For how long, I don't know.....he never posted back on long term results.

Probably the brand you'll see at NAPA is Beck-Arnley.??? I've used a B/A ECT sensor.....still do...and it seems to work fine. I've even tested it with my meter and it worked just like one should.

abecedarian

Bought mine at autozone for 85 bucks out the door with their limited lifetime warrantee schpiel. Seems to be fine.

ahickman

Tested the TPS and thought I had identified a bad unit. Took off the TPS and the throttle body to clean and measured the VTA-E2 and IDL-E2 again. With the TPS off the throttle body, everything checked out fine. So I put it all back together and adjusted the TPS according to FSM. Started it up and it still idles like poop, misfires and is blowing smoke at the exhaust. The code 41 and 42 are no longer reported. I thought maybe the O2 sensor may be bad so I disconnected it and did not hear any change in idle or response at throttle. With no codes to go on now, I am aimless. Could this be caused by a bad O2 sensor?

abecedarian

set the timing and idle speed then see what happens.

ahickman

Checked the timing and it is good. Took the plugs out and found them wet with fuel. Seems like it is running horribly rich.

iamsuperbleeder

I wander if your cold start valve sticking open...

Unplug it and see what happens.

If it still does it, try unbolting it off the manifold, place a glass jar over it, plug the hole on the manifold, and try to start the truck (all that may be easier with 2 people, lol). The valve should shut off if the trucks warm and running; you shouldn't get a hole lot of gas out of it.

It just puts in a little extra fuel at first startup since us FI guys don't have a choke, it just adds more fuel instead of taking away air; same principal there, just different ways or working

Edit: I'm not sure why this would throw those codes though, lol

thook

Well, the downside of EFI vehicles is the electronics....hard to say what's giving you the problem without testing. As always, it could be mechanically related, but when a problem pops up out of the blue it's usually just electrical.....and it could be one or more of several things.

That being said, I have to correct myself. After thinking more about how speed sensors work (memory starts flooding in) the speed sensor could actually be the problem given the other symptoms aside from idling. The code may have disappeared for the time being, but sometimes after tinkering they come back. First, find out if you have one. Then, find out where your speed sensor is located. Should be on the tail end of the transmission, pass. side, and close to the output shaft.

ahickman

Alright, just came in from fussing with it. I do have a speed sensor, but can't find and troubleshooting steps in the FSM. While in diagnostic mode looking for new codes, I noticed that the the fuel rail was pretty noisy and don't recall the noise before. It sounds like fuel (engine is off, but key on) is passing from the fuel rail through the fuel pressure regulator. Is this normal? I took off the vaccum line on the regulator and applied pressure and vacuum. Very litte change in pitch. Shouldn't the regulator close up with either pressure of vacuum applied? I also check the 02 sensor and it comes in at 7 ohms as expected. An expensive part to aimlessly replace, but I am rather stumped.

jeopardy98

I'd bet money that it's still the TPS. I just went through this with my brother in laws 97 taco. Exact same symptoms. We went to Pep Boys and auto zone for one but they both wanted like $165 and they had to order. I called the dealer and they had one in stock for $60. We put it in and it runs like a new truck.

ahickman

Did you test the TPS with an ohm meter? Did it show bad tracks? I too mine off and it ohmed out fine, put it back on and was able to adjust it back to factory specs. Stuck between bad 02 sensor, bad TPS sensor, bad speed sensor (?) and bad injector(s). Getting spark and gas makes me think it has to be one of these sensors. Uggh! Sure would be nice find at least one of them bad rather than keep testing out OK.

jeopardy98

I did not test the TPS. I was confident from driving the truck that was the culprit. Sorry.

thook

Well, I don't know exactly how your fuel rail noise sounds, but I can tell you the fuel pump should not run any longer than one or two seconds after you turn the key on. Hate to say it, but that points the ECM. Maybe even the AFM. Not sure, though. I know there's a switch in there that signals the OCR to activate when the key is turned on. I'd have to varify being a culprit in that case, though.

Anyway, about the sound..... I bet it kind sounds like a vibrating, rumbling like the fuel line may explode? That would be normal. Pressure is just building up in the system with nowhere for fuel to go. My '86 does that when I have the key on because I have the COR switch permanently jumped and so the fuel pump stays on with the key to ignition. My switch went bad from corrosion, so it was cheap and easy fix.

When I tested the spd sensor, I just took it off and hooked the meter to the terminals. Then, I turned the driven gear to watch for deflection and it was very erratic. Compared to testing a brand new spd sensor, it should deflect smoothly and evenly......monotonically. So, give that a shot. It's not hard to pull it out and put back in, but that's what you'll have to do because....if it's positioned like mine....you can't reach the terminals with the meter probes.

Next thing I'd look at is the AFM, if the spd sensor checks okay.

Oh, btw....have you tried running the vehicle with the TPS disconnected? I mean, take it for a drive so the ECM can adjust itself without TPS input.

ahickman

Ouch! ECM is pretty expensive. Scary to think about getting another one and swapping it out only to have it damaged again. No returns on electronics

I have not driven it with the TPS off, but will do so today. Also will take out the speed sensor and AFM and test them. Thanks.