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  #1  
Old 10-02-2016, 04:33 PM
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no throttle response

Hi,
I have a 2000 grand Cherokee with inline 6. I was driving and slowed to turn and the engine start to run rough. When I tried to accelerate there was no response with the pedal to the floor. I made it across the intersection then turned off the car and it restarted. I made it home. It threw a P0172 code.
The exhaust does not smell rich but it does idle like it is misfiring.

I replaced the air filter and fuel injectors a month ago because a code was thrown indicating missing cylinder and lack of fuel
A search indicated that injector 3 tends to coke up due to heat.
Any ideas where to start the search?
Thanks
Brad Miller

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  #2  
Old 10-03-2016, 12:47 AM
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Re: no throttle response

Welcome J
P0172 is 'system too rich'
Poss sources are:
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Faulty Mass Air Flow (MAF) sensor


The 'no throttle response' is a worry and could suggest lack of fuel pressure. Are you able to check the fuel pressure? Spec is 49 psi (+ /- 5 psi). Low FP could reflect impaired fuel filter. Too high could be fuel pressure reg. Note: she's 16 years old now and many oem parts are at or past their usable life. Plugs / leads OK? Episodic nature of your problem (doesn't run /run) suggests some thing is 'failing' and moving towards 'failed'. Fuel delivery seems the likely candidate so far.
How far has the JGC travelled? Good luck--keep us posted!
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Old 10-03-2016, 06:51 AM
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Re: no throttle response

Thanks for your reply. Yes, she's getting old, 186k. The problem had only happened twice but the idle is pretty rough now. When warm you can feel a miss every few seconds.
Would a faulty O2 sensor throw a code also? I only have the P0172.
I don't have a pressure gauge to check fuel pressure but I was gonna borrow one from advanced if I got figure out where to tap in to the fuel line.
I replaced all of the injectors back in August and it was running fine then this happened Labor Day weekend and again Saturday. Although I guess I could have gotten bad a injector.

Thanks for your help.
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Old 10-03-2016, 12:38 PM
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Re: no throttle response

I would first check the wiring from the bank 1 O2 sensor for damaged isolation (melted against exhaust). If the O2 sensor or wiring is the culprit, it could for example sense a rich mixture, while in fact it is not. The PCM will downtrim the fuel injected. This can go until a point that the mixture doesnt burn well. Do you have a scanner to check the O2 sensor voltage and the 1-1 fuel trim figure?
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Old 10-03-2016, 01:29 PM
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Re: no throttle response

I checked the O2 wiring on the forward sensor and it is intact. I don't have a scanner to check the fuel trim condition. I do have a volt meter.
Is it worth replacing the upstream O2 sensor even though there is no code for this?

Thanks for your help.
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Old 10-03-2016, 06:01 PM
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Re: no throttle response

Hey J
use your DMM to check resistance on plug leads to ensure they are in spec,too. Plugs ok? If Advance will lend a fuel pressure reader, p'haps they'll lend a scan tool with 'live' data read. Here's a link for examining the O2 sensor although your embedded code does not indicate the O2 is a fault.
Part 1 -How to Test the Oxygen Sensor (O2S11) Bank 1 Sensor 1 (Jeep 4.0L)


Can you work out which cyl is misfiring? if you kept the old FI's, p'haps insert one on the troublesome cyl to see if the 'new' FI is faulty. Bonne chance! Keep us posted!
ATB!
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Old 10-03-2016, 08:08 PM
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Re: no throttle response

If you have a smart phone, then you can have your own scan tool, just by buying a bluetooth or wifi dongle and downloading the free torque app. With this app you can read and errase fault codes and see many live data.
If there is a real misfire, then the PCM should set a fault code for that (P030X, where the X is showing the cylinder number, or a 0 for multiple cylinder misfire)
I had the fuel pump going out some time ago and was getting a lean mixture code. Looking at the live data showed a fuel trim figure of +25 on both banks. Measuring the fuel pressure showed less then 20 psi, while 49 psi +-5 is the standard.
Monitoring the live data can many times point towards a faulty component, or at least help during the trouble shooting. In your case, with a rich mixture code, i would first look at the 1-1 sensor voltage. With a rich mixture, the O2 voltage is high (between 0.5 and 0.9V). Normally the 1-1 sensor voltage should bounch up and down between 0.2 and 0.8V every few seconds. If the voltage is fixed, then there is a good change that the O2 sensor is bad. There are however other sensors who could be the problem. If the MAP sensor reads faulty for example, then it could get too much fuel injected. But then the fuel trim should show -20 (or more) for both banks. Since you didnīt smell any raw fuel from the exhaust, i would not expect this to be the problem however.
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Old 10-05-2016, 06:46 PM
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Re: no throttle response

So I made a check around the engine just in case there was a vacuum leak there was a cracked pcv breather hose connection so I changed the front and back rubber hoses. Then the fun started
i disconnected the battery to reset the codes and stsrted her up ran ok cold. Idled without missing so i went for a spin.
The engine pinged during acceleration but after 3 miles, the engine was warm and when i came to the stoplight, the engine died. Restarted the engine and when turning at the light i had almost no power and the engine was missing. No codes.
The pedal was to the floor, she was picking up speed then i heard several backfires. Still no codes but the warning chimes to check my gauges went off. The lak of acceleration felt like the accelerator pump was bad... if she had one.
For the mile, every time I took my foot off the gas pedal she tried to stall.
I'm turning to head home and no power. eventually i wuld get up to speed but it took tens of seconds. i found that manually downshifting to first help get the engine running a little better. then upshifting at 40 had more power.
As I turned into the neighborhood the warming chime went off again. still no codes.
Any thoughts out there as to where to look next?
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Old 10-05-2016, 11:21 PM
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Re: no throttle response

Did you try to get a scanner?
On a cold engine, the fuel system runs in open loop mode and the O2 sensor input is not used by the PCM for trimming. After a short warm up time, it goes into closed loop and the O2 sensor input is used. If you canīt get a scanner, you can simply disconnect both upstream O2 sensor connectors. In this way it will continue to run in open loop mode and only a pre set fuel schedule in the PCM will be used. If it then runs fine, then the problem must be with the O2 sensor(s).
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  #10  
Old 10-06-2016, 02:58 AM
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Re: no throttle response

Wow J!
Don't you love those driving episodes like this when your hear rate zooms and you're not sure if you're gonna make it home and its a coin toss if you will or call the flat bed?
Hopefully, Franks idea gets you back on the trail!


I'm thinking outside the bun here and have an idea your ignition switch is failing/faulty--the chimes and dash lights and stall die out are the drivers for this.


Ignition switches get a lot of abuse-hope you don't have 40 keys on the ring or a heavy pendant (HD or Alma Mater or similar) as the guts of the ignition switch (IS)aren't meant for that and do wear out over time.


Try this to 'see' if the IS is letting go:
Turn key to 'on' and then continue to 'start'
Just as things power up in the 'start' position, let the key return to 'on' (run) -NOTE: [Don't actually start the engine]


Here, what you need to look for is the activation of the various 'warning' lights (oil, brake, charging) as these will not be visible at key click one (on /run).


If these warning light 'activate' when you turn key to 'start' and then go out when you allow the key to revert to on/run, then your switch is faulty and all the above symptoms you dealt with can be expected.


I've heard of some using compressed air to clean the units as all that junk in our pockets (dust, thread, fuzz) can get wound around the keys and then placed in the switch inadvertently. I think there's a release tab for the key/cylinder on your Jeep which can be accessed from the 6 'clock position on the trim piece below the key on the steering wheel assembly if you want to start with cleaning that first.


Keep us posted! Bonne chance!


Here's a vid of how to swap out the old for a new IS. You'll need Torx bits.
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Old 10-06-2016, 06:43 AM
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Re: no throttle response

I tried the ignition switch test and all of the lights stay on. I did this before I left to work and after I got to work. All lights stayed on.

What was interesting on the ride in was that after idling at a stoplight when I accelerated the car fell on its face. I had to feather the gas pedal to keep accelerating. Albeit slowly. It behaved like a carborated engine. Once above 1500 rpm I was able to run normally. Even at reduced rpms.
Still no codes. I'm gonna to try disconnecting the O2 sensor tonight on my way home

Thanks for the help.
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  #12  
Old 10-06-2016, 10:15 AM
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Re: no throttle response

Be sure to secure the wire ends to a save spot, so that the wiring will not touch the hot exhaust and melt.
What about a scanner?
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