Alexr54

Started after doing a tune up. Was running rough before the tune up, but after it’s much worse. Ran codes and it says all the fuel injector circuits are open, 1-6.

I've gotten the ECM looked at, and it came back ok.
Replaced the spark plug cables again just to be sure.
Changed the IAC and TPS sensors.

Same issue...
engine runs and starts fine. Soon as it goes into Drive or Reverse it starts jumping and wants to stall. Then when the gas is pressed sometimes it does stall. Sometimes when the gas is pressed it sounds like it’s starving for gas and it keeps misfiring.

Any ideas on what what else I should look at?

Noah911

It started after doing a tune-up? A tune-up is supposed to improve running performance!

How so was it running rough.. prior to performing the recent tune-up? Was it just running rough always only when you were on the gas, and/or when in gear pressing on the accelorator? Never a bad idle?

What made you decide to replace your TPS sensor? Was something wrong with it? Did you replace the TPS sensor with another MOPAR TPS sensor?

If everything is all cleaned up, and your IAC valve is new now, it should not be a likely source of how you describe the problem.

Before : After...
Having done this tune-up it got worse. Is this maybe related?

Alexr54

It was hesitating on acceleration and seemed like it was misfiring, this is why I did the tune up to begin with.
The tune up did not make it any better. It made it worse in the end.
Before it was running rough but didn’t stall or lose power in acceleration. Now it does.

Just looking for advice on what what else I should look at with the symptoms I described and the error codes I get on the diagnostic tool.

Noah911

P0201 means that the PCM detected a fault in the injector or the wiring to the injector. It is a OBDII generic code.

The PCM watches the voltage at the injectors. It sees the difference between when the injectors fire vs when the injectors are switched off. The PCM expects to see near battery voltage at an injector when the injector is switched off. An injector is supposed to have a correct resistance reading. If the resistance is off, the injector needs replacing...

All SIX of your injectors happen at the same time? You can check for battery voltage and resistance at an injector to see.

Also, I would visually inspect along the injectors wiring leading into at the main harness too, for anything gone bad here at the wiring to and with the injectors.

Unless, the injector fault code to all six injectors is being picked up and thrown, and it is related to a different issue elsewhere?

Alexr54

Yea all 6 codes for all injectors are showing on the diagnostic tool at the same time.
I have cleared all codes and the same 6 codes (p0201 to p0206) all came back right away.

I guess I should get a Noid light test kit. I doubt all 6 injectors went bad at the same time... I do need to check the wiring.

About a year ago I replaced, and soldered on the 3 plugs to the wiring harness which plugs into the ECM. It’s been working fine until now.
I can always find replacement plugs from a upick yard if needed.
It is very strange this would happen after a tune up. Although I can’t see how these symptoms point to that.
Maybe while i was putting in the new spark plugs, cables, distributor cap, and air filter I moved some wires inadvertently and caused it to fail somehow.

Noah911

P0206 code means the PCM has detected either voltage or resistance that is out of specification in the fuel injector circuit for cylinder 6.

You could check for voltage and resistance at the fuel injector of cylinder 6. I would do that since I see that code is specific to this cylinder.

Also, the P0201 is a diagnostic trouble code DTC for "Injector Circuit Malfunction - Cylinder 1"

I would check the fuel injectors at Cylinder 1 & 6 for voltage and resistance right now.

(Edited to add):
I just saw what you wrote about the scanner showing all six of the injector codes all at once at one time. That seems unusual and unlikely to be all of the injectors like that at the same time you know. Maybe check at the main harness? That would show up in the readings obtained at the injectors too though, and lead back to at the harness...

Alexr54

I am getting this code for all cylinders.
p0201
p0202
p0203
p0204
p0205
p0206

So it seems it’s either pointing to a wiring issue or an issue with the ECM itself.
Its highly unlikely all 6 injectors are suddenly bad at the same time. Although I wish it was that simple.

I do have 2 ECMs. One as a spare.
One was rebuilt by an online place that does that. Sent my core and they sent me a working replacement for about $200 (programmed with my VIN)

The other was pulled from a junked 1997 with the same makeup. It’s oem.
I have not gotten the 1997 ECM programmed with my VIN/Mileage yet. I will probably get that done next week just to have a backup. This ECM came from a 1997 and mine is a 1998 but the 1997 had the same engine and transmission. So figured it should work fine (if it’s functional).

I did plug in the 1997 ECM and the jeep started fine, speedometer worked. But had the same issue with the injector codes and ran really rough, backfired eventually, and sometimes stalled.

I have the Noid Light test kit on order. Without the right tools I don’t think I can get to the bottom of this.
Wish I had a way to test and program the ECM myself but I don’t think the cost of those tools are worth it.

Noah911

That is supposed to mean the PCM is not liking the voltage and/or resistance it sees at each of the individual fuel injectors. Maybe you will trace down a lack of proper electricity happening here in this pathway?

If not a problem with the injectors or at the wiring to the injectors. I would have to say it kind of sounds like a TPS problem maybe by the way you describe the running symptoms. I would think to recommend testing here at the TPS sensor to see. It is not hard to do and is easy to test the TPS. I would test it.

Alexr54

But wouldn’t the TPS sensor throw a different code?
I did replace the TPS since it was readily available and not very expensive. It made no difference.
Also replaced the IAC sensor. Just to be thorough. Same results.

Noah911

It may? Of course, sometimes codes do not get thrown.. and you have to find the issue. The TPS can malfunction in many different ways each a little different.

You sound like outside of the injector codes, exactly all of them at once, your running symptoms are stemming from what could be ultimately a lean condition of the air/fuel mixture. An engine that hesitates, stumbles or misfires when accelerating or when it is under load, is an engine that is either sucking too much air, not getting enough fuel, or misfiring. The misfiring could be the result of sucking too much air or not getting enough fuel? Or, misfiring could be weak or no spark related to something like a weak malfunctioning ignition coil for instance.

If there are no misfire codes, a common cause of acceleration stumble is a bad throttle position sensor (TPS). The TPS tells the computer how far the throttle is open. The computer uses this information to determine how much fuel is needed to maintain the correct air/fuel mixture and when extra fuel is needed if the throttle suddenly opens wide. A bad malfunctioning TPS could make the stumbling and stalling symptoms happen that you describe, and I think it is worth testing it.. Even a new TPS. Especially, if it is a cheap non-Mopar one. That would definitely make me question it even more!

Alexr54

I did replace it with a cheapo TPS from amazon.
i will look up how to test it, if I remember correctly it’s with a multi meter?

I really appreciate all your input.

Noah911

Index

I. How to Test a Throttle Position Sensor

A. Is Your TPS Connected to Ground?

B. Is Your TPS Connected to Reference Voltage?

C. Is Your TPS Producing the Correct Signal Voltage?

I. How to Test a Throttle Position Sensor


The most common TPS test is to measure for resistance (ohms) or voltage at the various positions, including throttle plate closed, half open and fully open. We'll use voltage to test the TPS here.

1. Open the hood and remove the air cleaner assembly where it connects with the throttle body.

2. Inspect the throttle plate and the walls of the throttle body surrounding the throttle plate.

* If you see carbon buildup around the walls and under the throttle plate, spray some carburetor cleaner on a clean shop rag and wipe the buildup with it until the surface is completely clean. Carbon buildup can prevent the throttle plate from closing properly and moving freely.

3. Locate the TPS mounted on the side of the throttle body. The TPS is a small plastic block with a three wire connector.


A. Is Your TPS Connected to Ground?B. Is Your TPS Connected to Reference Voltage?

1. Now connect the black test lead from your DMM to the ground terminal on the TPS connector you just identified.

2. Turn the ignition key to the ON position, but don't start the engine.

3. Connect the red test lead to each of the other two terminals.

4. One of the terminals should read 5 volts, or pretty close to it. That terminal is providing the reference voltage to the TPS to produce the voltage signal. Make a note of the color of the wire connected to this terminal. The third wire corresponds to the signal voltage or signal wire.

* If you don't get 5 volts from any of the two terminals, there's a problem in the circuit you need to fix because there's no reference voltage going to the TPS. Check the circuit for bad terminals, loose, dirty or damage wires.

5. Turn the ignition key OFF.

6. Plug back in the electrical connector to the TPS.


C. Is Your TPS Producing the Correct Signal Voltage?

1. Now backprobe the signal and ground terminals on the TPS electrical connector. If necessary, use a couple of pins to backprobe the wires.

2. Connect the positive (red) test lead from your DMM to the signal wire and the black negative (black) test lead from your DMM to the ground wire.

3. Turn the ignition key ON but don't start the engine.

4. Make sure the throttle plate is fully closed.

5. Your DMM should read around 0.2 up to 1.5 Volts or close to it, depending on your particular model. If the readout on your meters shows only a zero, make sure you're at a low setting—usually at the 10 or 20 Volts setting. If your meter still reads zero, continue with this test anyway.

6. While watching the readout on your DMM, gradually open the throttle plate until is fully opened (or have an assistant gradually depress the gas pedal to the floor).

* Your DMM should read 5 volts or close to it when the throttle plate is fully opened.

* Also, make sure that the voltage increases smoothly as you gradually open the throttle plate.

* If you notice the voltage skipping or stuck at a certain voltage value, as you gradually open the throttle plate, your TPS is not working properly and you need to replace it.

* Also, if your TPS doesn't reach 5 volts, or close to it (up to 3.5V on some models), when the throttle plate is fully opened, replace the TPS.

7. Repeat step 6, only this time use the handle of a screwdriver to lightly tap on the position sensor as you open and close the throttle plate. If the voltage skips as you tap the sensor, replace it.



Note: TPS is directly involved with transmission shifting characteristics too...

Noah911

You could also try swapping injectors around too. Move either, or both, the fuel injectors from the number 1 or 6 cylinder to a different cylinder.. Swap cylinder 2 injector with cylinder 1 injector, and follow to see if the code(s) change staying at, or moving to something different from the current p0201 and p0206 codes that stuck around on your scanner?

These generic OBDII codes may honestly just simply mean a lean condition is being picked up by the PCM. It does not have to be bad readings, or a bad voltage or resistance at the injectors, or the injectors wiring... It could be dirty clogged injector(s) is a possibility to set these codes too.

Does your scanner read high and low fuel trims?

Alexr54

After changing the spark plugs again but with iridium plugs, this issue went away.
now I just have a rough idle. But it does not stall anymore and runs fine.

Alexr54

It was better for a short while and started again.
tested TPS and the Injector plugs. All came back good.
next thing to do is change our all injectors.