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sertac

Grand Cherokee 4.0 Sluggish Performance

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At Last Intermediate drive i felt something highly wrong with the car. I remember the time we went to Sweihan before Covid, car was climbing everywhere super easy. At the last drive it was like max 100hp car not a 200hp. So after that i checked my fuel pressure, i am getting 49PSI which is normal. Than we clean the thortle body and it wasnt that dirty anyway. Than last i changed the air filter today. Spark plugs changed 6 month 15.000km ago. Spark plugs and air filter original Mopar product.

Today after the new air filter i made a 0-100km acceleration test with GPS application. I got 23 seconds. Factory data is 10.5 seconds. What could cause this? My mechanic already things i am crazy and he gave up. He is saying most probably something wrong with the gearbox it is not transferring the power properly and he said what you excepting from 20 years old car it is running good enough for its age. 

I feel like i am giving up on the car and i will just sell it and get something max 6-7 years old and low km. Is there any last thing i should check before i totally give up?  

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Shoot that Mechanic....

I've heard the same excuse from incompetent mechanics so many times before. If they can't find it they just start throwing excuses around.

There are many possible reason for sluggish behavior. Did you try with another MAF sensor, or just unplugging it to see if there is any difference ? It will throw a Check Engine Light when you unplug it, but should reset itself when you put it back.

I do not believe his story about the transmission. You should try to find a guy who is willing to spend a day going through all possibilities. 0-100 in 23 seconds is indeed an issue.

In my particular case of sluggish engine, it was the timing that was slightly off, which resulted in good mileage but horrible performance. Since i got that sorted the car has been fine and plenty powerful for a little 3.0

Other things that rob power is the AC or clutch fan if it's fully engaged, the CAT that might be blocked, faulty sensor throwing wrong data to the ECU, clogged injectors, faulty spark wires or coil pack....

 

 

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"Go as far as you can see; once you get there, you'll be able to see further."

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@Frederic I will try to remove the MAF sensor tonight. I have a OBD2 reader and i can take real time data from car. Anything i should check there at the data? Also currently i have no code. 

I find the transmission issue logical because I rebuilt the transmission 1 year ago and i dont think they did a great job. Lately car start shifting at 2500rpm even if i give full gas. When i am cruising 80km and i am start giving full gas it will not lower the gear it will try to accelerate at 4th gear. Just a note, while i am making the acceleration test i shifted manually. If i let the car shift it will shift the 4th gear at 80kmh and it will take 2 years to reach 100km. I remember 6 months ago when i give full gas car would take the gear to 2th and it will run like crazy till the redline.

Also any shop advise to take this car. Many places are not interested to put their hands on old cars. I have a Jeep specialist at Sharjah, i went 2 years ago. He is only working for at 4.0 Jeeps but Sharjah is too far now. Also after many bad experiences over years with bad mechanics i fell like i want to buy a most newer and most low km Xterra possible and call it a day. I am really confused these days. 

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I couldn't wait and I removed the sensor. It immediately gave the check engine light. Than I took a test drive but car was stalling at 3000rpm. I am attaching a video. This is also how slow car is pulling at 2th gear 

Another video gear is at D position and even tought I am giving full gas it is up shifting at 2500rpm

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Did you check fuel pressure at idle and under load?

Also look at AFM gm/s and compare it with factory data or a known good engine. More accurate than just unplugging it and seeing what happens  

Check exhaust sensor data and look at fuel trims. 

How is the general condition and wear in the engine? Are you getting any blow by? Pull the dipstick and see if you can feel any air pulsing. 
 

If you can’t get a mechanic to sort it, bring it by and I’ll have a look. 

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7 minutes ago, Barry said:

Did you check fuel pressure at idle and under load?

Also look at AFM gm/s and compare it with factory data or a known good engine. More accurate than just unplugging it and seeing what happens  

Check exhaust sensor data and look at fuel trims. 

How is the general condition and wear in the engine? Are you getting any blow by? Pull the dipstick and see if you can feel any air pulsing. 
 

If you can’t get a mechanic to sort it, bring it by and I’ll have a look. 

Hi Barry. They checked the fuel pressure at idle. 

Am i able to see these data with my MaxiScan MS509(if i am not mistaking you know this scanner)? 

I will check the dipstick but engine is not burning big amount of oil(half liter at every 5000km) so i am guessing it is in good condition. 

If i cant sort myself looks like it is time to leave it to you. 

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I used to have the MS509. Nice little tool. You should be able to read all the data you need on it. 

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@sertac donot think buying a relatively newer used car will sort your issues, because it is still a used one and you will have to get some things sorted.

What I have seen with mechanics,  as per my limited experience is that they start telling "it's an old car anything can break and not work", when they are not able to pin point to a specific problem.

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@Barry I am getting 47kpa Map reading at idle. When I raise the rpm it is getting lower. Is this normal? I am unable get data from O2 sensor. It is not reading it. 

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It does seem pretty high. What are you getting on the airflow meter?

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