New Cam, Jeep will only run without TPS

Its running without the Throttle Position Sensor. The motor will not run at all with Crankshaft position sensor disconnected, I found that out the hard way.

L.W.(Bill) Hughes III wrote:

TPS = "Throttle Position Sensor"

Still, ¿wtf?

Earle

First thing that came to my mind is that you may have the distributor indexed incorrectly.

With cyl. 1 at TDC, the trailing edge of the ign. rotor should be about .020" PAST the #1 post in the distributor cap.

With the TPS disconnected, the PCM may not be advancing the timing and that may be enough for it to 'fire' the correct post.

In other words, the rotor isn't pointing in the right direction when the PCM fires the coil.

TPS and CPS must be the keyboard again, he he, Coasty

That's a good point, could you have put the wires on the distributor cap one position off? I've done that and the engine will run, but sounds off and backfires when revved.

Jeff DeWitt

bllsht wrote:

It seems at least as likely as the thing running with the TPS unplugged! THAT one I don't understand at all.

Jeff DeWitt

bllsht wrote:

The TPS is not a critical doodad. If it goes missing the computer will adjust based on the O2 sensor.

What you do loose is the WOT (Wide Open Trottle) signal.

My 93 will run without the TPS. I know this because I left the darn thing disconnected. :] heh. oops.

Wonder how the engine runs with the WOT signal on all the time?

The OP said the sensor was replaced, but maybe the new one was bad or wrong? Is it possible to connect the sensor wrong?

Jeff DeWitt

DougW wrote:

There is a big difference between not being able to compute the optimal fuel and timing demands (no TPS signal), and having spark in the wrong cylinder and no spark in the right cylinder.

You d>It seems at least as likely as the thing running with the TPS unplugged!

At least on the ZJ it's possible. :) The shaft and tangs have to be lined up. Thing is, if they arn't the throttle simply won't open. (or at least that's how the ZJ acts) Some vehicles require the TPS to be indexed by watching the voltage.

In all cases it's a good idea to reset the computer and reprogram the range. Simply pull the battery off (or pull the fuses), have lunch, put the battery back on. turn the key to on, (engine not running) and slowly move the throttle between closed and wide open about five or six times. Holding it at the limits for a few seconds. Then turn the key off, start the car, and let it idle, drive it normally, and eventually hit the highway.

Easy enough to test the TPS sensor. Just takes a volt meter. (backprobe. i.e. don't pierce the wires, just slide a pin/paperclip up the back of the connector)

with ignition on, engine not running. Measure across the two outer wires. Should have 5 volts. Measure between the ground wire and the center wire. Throttle closed >200 milliVolts Throttle wide open

I went through this a while back after replacing a distributor cap, it was driving me nuts because the engine started fine and while it seemed a bit off it only ran a little rough until I gave it some gas and brought the revs up, then it started spitting, backfiring and raising a fuss. As first I thought it was a vacuum leak but it turned out to be the wires were one position off.

If the TPS isn't functioning how does the FI system know how much fuel to deliver? With a carburatorated engine the vacuum naturally would pull more fuel out of the jets, but with FI something has to tell the computer.

Will the computer figure something out from the 02 sensor telling it the engine is running too lean?

Jeff DeWitt

bllsht wrote:

MAP sensor.

With no TPS it's gonna be in open loop, using a pre programmed strategy. The PCM is ignoring the O2 at this point.

the pcm has top go into closed loop before it can start learning tps and other sensors values after a reset is done some vehicles atke as much as

DougW wrote: