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Author Topic: '99 GC 4.0, hesitation on acceleration when first starting.  (Read 1100 times)

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rfoster

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'99 GC 4.0, hesitation on acceleration when first starting.
« on: September 20, 2011, 03:30:02 PM »
Afternoon all, I'm new to this forum so be gentle! Have just bought my second Grand Cherokee, 1999 4.0 LTD in wonderful condition. Previously had a '96 model a few years ago which was brilliant.

The car is in excellent condition with all the electric & air con working perfectly. However, when I first start the car and drive away, the engine is not very reponsive. It struggles to get above 1,500 rpm, stutters and I can hear popping from the exhaust (which I guess would mean the fuel is too rich?). Anyway, the problem clears itself after 30 seconds or so and then the car runs perfectly smoothly.

I'm not particularly mechanically minded, but I'd guess that it's a sensor of some sort that's sending some incorrect information to the ECU regarding temp / fuelling. But before I start tearing the car apart to get to the bottom of the problem, I wondered if anyone had a similar experience and what the outcome was! Any help is greatly appreciated.

Cheers in advance.
Richard.
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Bishops Finger

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Re: '99 GC 4.0, hesitation on acceleration when first starting.
« Reply #1 on: September 20, 2011, 03:41:47 PM »
Possibly o2 sensor..
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Panic mechanic!

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Re: '99 GC 4.0, hesitation on acceleration when first starting.
« Reply #2 on: September 20, 2011, 04:05:33 PM »
Sounds like it could do with a good service first and then I would think  if it still persists then it may be an o2 sensor.
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rfoster

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Re: '99 GC 4.0, hesitation on acceleration when first starting.
« Reply #3 on: September 20, 2011, 04:32:47 PM »
Thanks very much - it was last services about 3,000 miles ago but it was also last year. So I'll definitely get that looked to. Don't these vehicles have quite a few O2 sensors? Wonder if they would throw up a fault code if they were faulty.
Cheers,
Richard.
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Panic mechanic!

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Re: '99 GC 4.0, hesitation on acceleration when first starting.
« Reply #4 on: September 20, 2011, 04:46:37 PM »
they don't always throw up a fault code, we have a vw beetle that eats o2 sensors and never throws up an error code or warning light!
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bigjeepzj

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Re: '99 GC 4.0, hesitation on acceleration when first starting.
« Reply #5 on: September 20, 2011, 05:03:16 PM »
 :iagree: Fault codes for sensors are only report by the ECU if the sensor is not connected or broken completely.
If the sensor faulty in a way that is basically  lying to the ECU no code will be reported and the engine will not run correctly
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Jonny Jeep

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Re: '99 GC 4.0, hesitation on acceleration when first starting.
« Reply #6 on: September 20, 2011, 07:18:51 PM »
It's defo the upstream O2 sensor. The heater circuit has gone bad. No cure other than replacement.
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Tank

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Re: '99 GC 4.0, hesitation on acceleration when first starting.
« Reply #7 on: September 20, 2011, 10:00:42 PM »
The bag o shite astra i just got rid of was the same. Disconnect the O2 sensor then start it up from cold,see if it runs normal.If does then theres your fault. The astra would be very lumpy until it warmed,i disconnected the sensor and it would idle and rev normally.Wouldnt leave it disconnected though as i dont know what it might do damage wise
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