No throttle response and running rough?

Tiny
DUCKSHOOTER
  • MEMBER
  • 2000 JEEP GRAND CHEROKEE
  • 4.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 130,000 MILES
Running rough no throttle response.
Saturday, March 6th, 2021 AT 7:23 PM

10 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,133 POSTS
Hi,

Is there any change in the RPMs when you press the accelerator? What you are describing sounds like it is related to the throttle position sensor (TPS).

Is the check engine light staying on when running? If it is, we need to scan the computer for codes. If we don't, it becomes a guessing game.

Here is a video showing how it is done:

https://youtu.be/bEcxOoD1-9Y

If you don't have a scan tool, most parts stores will lend or rent one to you. If you can't have this done, let me know.

Take care and God Bless,

Joe
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Saturday, March 6th, 2021 AT 8:41 PM
Tiny
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I do have a scanner. I’m going to make a video of how it sounds on start up and while running. I will also get video of scanner. Thanks for your reply.
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Sunday, March 7th, 2021 AT 2:46 AM
Tiny
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Also, I was a little vague with my question. Let me explain the vehicle had been started about five times in the last seven years. I decided to get it on the road but it wouldn’t start thought it was the fuel pump so I replaced it but guess what it was a fuse dumb mistake number one. Didn’t drain gas while had tank out dumb mistake number two. So put new gas with old gas and fuel treatment seemed to be running great drove it to the car wash started it every day for about two weeks. Then one day for no apparent reason within about one second the engine started shaking violently like it was a bucking bull And making all kinds of noise thought maybe it spun a bearing or something so I shut it off and tried to restart it and it started and kinda smoothed out but still making lots of noise so I shut it off thinking the worst I dropped the oil pan and checked out the bearings best I could seemed to be okay as far as I could tell. But the oil was filled with gas but there was no metal shavings in the oil good sign right. Put new oil in it and tried starting it again it started but it smelled like gas really bad so I figure something with the injectors then I kind of figured I had flooded it with gas while trying to start it. So anyway I tried diagnosing it as best I could scanner give me a trans sensor code and that was it. Anyway It came down to the crankshaft position sensor so I was trying to change it got frustrated and called mobile mechanic asked him to change it and went to my house he called me about five minutes later talked to him he said it was bad gas and to put new gas in it with octane boost tried that and it didn’t work still ran the same.. So it sat for about a month until I finally drained the tank put new fuel filter in it premium gas new plugs witch bye the way were really bad can’t believe it ran at all. New oil lots of mistakes can you tell I’m not a real good mechanic anyway tried starting it it backfired three or four times then started it will set and idle but it almost sounds like it’s starving for fuel when you step on the gas. I’m just tired of guessing. So that’s my story. I will do what I said in my first reply but if you can think of anything else anything would be helpful. Thanks for your time.
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Sunday, March 7th, 2021 AT 3:32 AM
Tiny
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Started pretty quick code po500 says it’s a speed sensor and no check engine light.
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Sunday, March 7th, 2021 AT 9:59 AM
Tiny
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Second video.
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Sunday, March 7th, 2021 AT 10:15 AM
Tiny
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Hi,

I was unable to see the data stream on the scan tool. At first, I saw fuel trims in the negatives. That usually indicates a rich fuel mixture. You mentioned the fuel smell, so I think that is the direction we need to go. The engine sounds like it has a dead misfire, so I have a feeling one of the injectors is stuck and dumping fuel causing the smell, misfire, and the rough idle. It is likely a result of the old fuel and work that has been done.

Since there are no codes, we can't focus on one specific cylinder. You can pull one injector wire off at a time to see if there is one that doesn't change the way it runs. Or you could pull the plugs and see if one is wet.

Also, I realize you replaced the fuel pump. Have you checked the fuel pressure to confirm it is within the manufacturer's specs? There could be an issue with the fuel pressure regulator allowing too much pressure. If you haven't, I would check it. Here is a link that shows how it's done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

I attached a pic below showing the test port location. I realize you may not have a fuel pressure gauge, but oftentimes a parts store will lend you one.

Here are the manufacturer's specs for pressure:

2000 Jeep Truck Grand Cherokee 4WD L6-4.0L VIN S
Pressure
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Pump Fuel Pressure Specifications Pressure, Vacuum and Temperature Pressure
PRESSURE

Fuel System Pressure

Fuel System Operating Pressure 339 kpa +/- 34 kpa (49.2 +/- 5 psi) psi
Fuel Pump Capacity 1/4 liter in seconds L

__________________________

Check this if possible. Also, check the engine oil to see if there is a fuel smell again.

Take care and let me know what you find.

Joe

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Sunday, March 7th, 2021 AT 6:09 PM
Tiny
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Thanks for getting back to me. It may take a couple of days for me to let you know but I will check those things. I appreciate your help thanks again for your time.
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Sunday, March 7th, 2021 AT 7:22 PM
Tiny
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You are very welcome. Let me know the results. Don't worry about the time it takes. I'll be here.

Take care.

Joe
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Sunday, March 7th, 2021 AT 8:22 PM
Tiny
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Hey Joe, this is what I found the dirty ones were the one that changed the idle when I unplugged them the clean ones no change in idle. But when I pulled out the whole rail and turned the key on I didn’t get any gas so I turned it over and still didn’t get any gas I’m confused. Anyway the damper is filthy would that have something to do with the way it is running should I replace all of them or can I clean the four up and by two new ones? Also the throttle body is filthy should I pull it off and clean it up what is the best way to do that? Also the oil does have gas in it again does that mean my rings are shot or am I just getting to much fuel I’m getting discouraged anyway let me know what you think and thanks again for your time and help.
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Sunday, March 14th, 2021 AT 1:18 PM
Tiny
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Hi,

The smell of fuel could be due to one of the injectors being stuck open and then the cylinder not firing. I would try cleaning the good ones and replace the ones that made no difference when the engine was running. If there was no difference, they likely weren't working.

Here is a link explaining how to service the throttle body. The second link explains how to test the injectors.

https://www.2carpros.com/articles/throttle-actuator-service

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Let me know.

Joe
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Sunday, March 14th, 2021 AT 6:58 PM

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