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Jeep Tech
Jeep Tech, Technician
Category: Jeep
Satisfied Customers: 72
Experience:  Work on Dodge & Jeep Products for 30 years.
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I recently purchased a 2005 Jeep Grand Cherokee Laredo, 4.7

Customer Question

I recently purchased a 2005 Jeep Grand Cherokee Laredo, 4.7 L V8. I have had an issue since the first day that the local Jeep dealership has been unable to fix. The issue is a surging or hesitation that is most noticeable at engine speed of 1200-1700 RPM as a low frequence surging (1-2 times per second) when driving in 4th or 5th gear on uphill grade at 40-45 mph, partial throttle. The hesitation is present at higher engine speeds and in other gears, but the entire vehicle surges forward most noticeably at low rpms. It feels like an engine misfire, but the ECM is not showing any codes. So far the spark plugs have been replaced, chamber cleaning performed, TPS sensor replaced, ECM flashed / reprogrammed, heads removed and valves replaced and ground, and torque converter replaced. None of these actions has changed the symptoms. Please help! This is a very nice vehicle otherwise, but I am quickly loosing confidence in the local Jeep's service dept.
Submitted: 5 years ago.
Category: Jeep
Expert:  Jeep Tech replied 5 years ago.

Hi

 

Customer: replied 5 years ago.
hi
Customer: replied 5 years ago.
how are you?
Expert:  Jeep Tech replied 5 years ago.

Did you hear what the fuel adaptives were reading on the compter, was it possible a neg high number like 25 or 30. This is the reason most of the time for this type of problem. And what cause this is the pcm is getting a bad reading from a sensor that is leaning the engine out and causing it to misfire. I am going to give you some information on what can cause this problem. Thanks Ken.

 

Solution NumberNNN-NN-NNNN/p>

Case NumberNNN-NN-NNNN/p>

Vehicle Issue Runs rough Erratic idle negative adaptives | Explanation of

possible causes for a HIGH NEGATIVE ADAPTIVE CONDITION.

Year 2005, 2004, 2003, 2002, 2001, 2000, 1999, 1998, 1997, 1996,

1995, 1994, 1993, 1992

Model AA - Acclaim, LeBaron, LeBaron Landau, Spirit, AB - Ram

Van/Wagon, AC - Dynasty, New Yorker Landau, New Yorker

Salon, AD - Ram Pickup, Ramcharger, Ram Cab and Chassis,

AG - Daytona, Pacifica, Shelby, IROC, Chrysler GS,Laser, AJ -

LeBaron, AN - Dakota, AP - Shadow, Sundance, Shadow

Convertible, AS - Caravan, Voyager, Town and Country, AY -

Imperial/New Yorker, AY - Fifth Avenue, Imperial, BE - Ram

Pickup/Quad Cab, BR - Ram Pickup, DN - Durango, FJ -

Avenger, Sebring, FJ - (IMPORT) Talon, JA - Breeze, JA -

Cirrus, JA - Stratus, JR - Sebring/Stratus Sedan, JR - Sebring

Convertible, JX - Sebring JX, Sebring JXi, LH - New Yorker, LH -

Vision, LH - LHS, LH - Intrepid, LH - Concorde, LH - 300M, NS -

Caravan, Voyager, Town and Country, PL - Neon, PR - Prowler,

PT - Chrysler Cruiser, RS - Caravan, Voyager, Town and

Country, SR - Viper Coupe/Roadster, ST - Sebring/Stratus

Coupe, TJ - Wrangler, WJ - Grand Cherokee, XJ - Cherokee, YJ

- Wrangler, ZJ - Grand Cherokee

Category Customer Concern (No DTCs)

System or

Component

Group 18 - Vehicle Performance / Driveability

Symptom Engine Performance, Idle Concern, Rough / Unstable / Erratic

Idle, Noise, Vibration, Odor Issues

Case Verification Prior to replacing parts, please review the explanation below in

the recommendation field.

Recommendation Explanation of possible cause for a HIGH NEGATIVE ADAPTIVE

CONDITION The adaptives become negative when the PCM

decreases the injector pulse width in an attempt to make the

oxygen sensor switch uniformly about the PCM's oxygen sensor

goal voltage. This means that the oxygen sensor is producing a

voltage that is close to one volt ( 1.0v ) consistently indicating a

low oxygen (rich) state in the exhaust. The causes of the oxygen

sensor reading a higher voltage usually falls into three main

categories: 1) Excessive amount of fuel, 2) Not enough air, and

3) The PCM is being provided with the improper information.

THE FOLLOWING IS A GENXXXXX XXXXXST OF POSSIBLE

CAUSES. THE LIST IS PROVIDED AS AN EXAMPLE OF

POSSIBILITIES. SOME OF THESE MAY NOT APPLY TO

YOUR SPECIFIC VEHICLE. IT IS YOUR RESPONSIBILITY TO

DECIDE WHICH COULD APPLY. THIS IS NOT A

COMPREHENSIVE LIST: MERELY THE MORE COMMON

CAUSES. 1) EXCESSIVE AMOUNT OF FUEL -- there is such an

abundance of fuel that there is no left over oxygen in the exhaust

after combustion. -- This additional fuel could be caused by any

of the following: TOO HIGH OF FUEL PRESSURE WRONG

FUEL INJECTOR LEAKING OR WORN INJECTORS LEAKING

INJECTOR O-RINGS CONTAMINATED CHARCOAL

CANNISTER (liquid fuel) DEFECTIVE PURGE SYSTEM

PRESSURE REGULATOR WITH A HOLE IN THE DIAPHRAM

(vacuum compensated type ) CRANKCASE CONTAMINATED

WITH FUEL (fuel contaminated with fuel other than gasoline

such as diesel will wash past the piston rings and end up in the

crankcase,) 2) NOT ENOUGH AIR- For some reason the

cylinders are not filling with the proper amount of air. The amount

of oxygen in the combustion chamber is low . This condition

could be cause by any of the following: CAM TIMING-(including

loose timing chain, sheared cam dowel pins, keyways, or skipped

teeth) WORN CAM LOBES OTHER VALVETRAIN PROBLEMS

RESTRICTED EXHAUST EXCESSIVE EGR FLOW FOR

CONDITION- (Be sure to verify that the vacuum hoses to the

EGR vacuum transducer are routed correctly. If the vacuum lines

are reversed the EGR valve will open and stay open until the

engine is shut off.) 3) PCM IS BEING PROVIDED IMPROPER

INFORMATION- If the PCM does not receive proper sensor

readings it will not deliver the proper injector pulse width for

conditions. The following is a list of sensor problems that could

cause short and long term adaptives to be highly negative:

COOLANT SENSOR CALIBRATION (sensor is reading much

colder than the actual engine temperature). OXYGEN SENSOR

CIRCUIT PROBLEM- (this includes O2 sensor heater, grounds,

signal wire problems, heater operation. Once the O2 sensor

reaches operating temperature the voltage should never exceed

1.02v) MAP SENSOR CALIBRATION--One of the most important

readings for testing a MAP sensor is the voltage reading

obtained with the DRBIII with the ignition on and the engine off.

This voltage reading is important because the PCM uses this for

calculating barometric pressure. If the PCM does not "know" the

correct air density from the MAP sensor (baro. reading) it will

have to drastically change the fuel curve through the adaptives to

get the proper response from the oxygen sensor. Below is a

chart of key on MAP sensor readings for a given elevation. You

should get to know what is normal for your area. Elevation (feet)

Baro Reading (in.-hg.) MAP voltage 0 (sea level) 29.92 4.6v

29.67 500 29.42 29.17 1000 28.92 28.67 4.4v 1500 28.42 28.17

2000 27.92 27.67 2500 27.42 4.2v 27.17 3000 26.92 26.67 3500

26.42 26.17 4.0v 4000 25.92 25.67 4500 25.42 25.17 5000 24.92

3.8v VOLTAGE SENSE-- The PCM compensates the injector

pulsewidth based upon charging system voltage. The higher the

voltage => the stronger the magnetic field opening the pintle

valve in the injector. The PCM compensates for this condition. If

the PCM sense a lower voltage than is applied to the injectors

the Adaptives will become negative.

Case Created By T6270ML

Last Modified By T6270ML

Creation Date 12/31/03 5:00 AM

Modification Date 11/18/04 1:44 PM

Review Approved

Distribution USA

Escalation Group Driveability

Customer: replied 5 years ago.
As I understand, that concern is for a rough or erratic idle. My idle is smooth 90% of the time, the hesitation is most noticable when the engine is under a load (uphill grade at low rpm, constant 1/2 throttle). The tech who diagnosed the misfire drove the vehicle with the Star computer attached found no out of normal conditions. That is why it was first diagnosed as an internal engine issue and the valves were replaced.
Expert:  Jeep Tech replied 5 years ago.
I still like to see what the fuel adaptives are saying when this occurs. Possible if you go by autozone and possible they will read the fuel adaptives when this problem is occuring and tell you. Are there any codes ? If there is the information will be on the freeze frame data that is saved with the code. Let me know.

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