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Fuel rail high pressure P088 Grand cherokee wk2 crd

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22 Nov 2019 12:02 #35215 by Guv
Hi,
Newbie and DIYer...eek:-)

Keep finding scannerdanner youtube videos to help me and thought it was time to join so hi guys and girls from the UK.

Background...Recovered home after car threw up the throttle body icon (lighting strike between to vertical lines in red) , misfiring and sligth rattle and smoke from exhaust. RAC (Recovery) could not diagnose problem! No codes.

I've just replaced No1 cylinder injector which I diagnosed as faulty with the Power probe tool. Had the injector tested and it was defective.
For some unexplicable reason the car will not accept the IQA code so I'm also working on that problem as well.
Car started fine in idle mode but when gently accelerating a slight knocking noise which I believe to be the injector and then a puff of smoke again and the car stopped dead and the throttle body icon illuminating again. The car would not start again and threw a P0088 code High fuel pressure.

My thoughts are the following:
1. Find a way of coding injector (Bosch)
2. Test fuel pressure.
3. Test fuel pressure sensor and/or regulator.
4. Change fuel filters as a matter of course.

My question :
Has anyone experienced any of the above and confirm that I have covered everything or not as the case may be please?
Am I missing something obvious?
Any guidnace on how to test and locate the above components greatley appreciated.

Thank you
Gary

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23 Nov 2019 04:00 - 23 Nov 2019 04:05 #35224 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Fuel rail high pressure P088 Grand cherokee wk2 crd
Hi I have moved your question to the problems section where it will get more attention.

In the Bosch CRD systems the high pressure side of the fuel system is computer controlled using two components on the engine
(1) The high pressure sensor on the fuel rail
(2) The pressure regulator valve on the high pressure pump.

If the engine has any kind of black box tuning mod on it should be disconnected and engine put back to standard until the fault is diagnosed. These black boxes sit between the sensors on the engine especially the fuel rail high pressure sensor and the engine computer and alter the signal.
Working with basic tools a multimeter and a test light
The fuel rail pressure sensor is a 3 wire pressure sensor (istr centre wire is signal wire) the signal range works from 0.5v to 4.5v Normally at key on engine off it should show just above 0.5v this should increase to about 1.2 volts at idle and anything up to 4.5 when the engine is working hard on the highway. If you see much above 0.5v at key on engine off there is a problem with the sensor or short in its wiring.

The pressure regulator on the pump is controlled by pulse width modulation of the ground side of the solenoid. The supply voltage side of the solenoid is full 12 to 15v battery voltage. In normal operation supply side should show a constant battery voltage but the comtrolled ground should be pulled down to somewhere below this.
The operation of the PRV is not so easy to check with just a meter especially with a non-start fault.

If the fuel rail pressure sensor dose't show too much above 0.5v at key on engine off I would be inclined to go straight for the PRV on the high pressure pump, do a basic visual check on the wiring and connector + power and controlled ground but the odds are the PRV has stuck,

" Welcome to the 21st"


Last edit: 23 Nov 2019 04:05 by Andy.MacFadyen.

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23 Nov 2019 06:06 #35225 by Landroverman1958
Replied by Landroverman1958 on topic Fuel rail high pressure P088 Grand cherokee wk2 crd
Good morning,the engine ecu will not sometimes accept the code as the ignition has to be cycled after coding or it wont remember the code,lol if you can do a leak back check using clear tubing,washer jet tubing and old soft drink bottles,clamp off the return,crank over and note the return rates,also disconnect injectors at electrical connectors,disconnect inlet metering valve crank and watch pressure rise on voltmeter if it has min max button set it on max and crank over,it will give you an idea of the rail pressure the pump can produce, you may have another injector that is faulty,leaking back too much.

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23 Nov 2019 06:21 #35227 by Guv
Thank you Andy.
Very much appreciare the guidance.
Gary

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23 Nov 2019 06:23 #35228 by Guv
Hi Landroverman,
Thank you for your guidance. I was looking at doing a leak back test due to the mileage and the relacement of 1 injector probaly means the other 5 are not far behind.
Thanks again
Gary

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24 Nov 2019 06:46 #35274 by Guv
Update :
Rail sensor test was ok.
PRV - Tested on bench with 12v supply and it works. (Opens and closes)
PRV - Ohms test across terminal = 2.8 ohms.

PRV Electrical connector removed from High Pressure Pump(HP) Igniton on engine off :
Green / Brown wire (GB) 11.48V
Blue/ Brown wire (BB) 3.4V

PRV electrical connector connected to HP Ignition on engine off:
Green / Brown wire (GB) 11.44V
Blue/ Brown wire (BB) 11.45V

Does anyone know if these readings are within parameters as I cannot find anything online...in fact the information for these jeeps is pretty sparce?
Thank you
Gary

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24 Nov 2019 09:35 - 24 Nov 2019 09:38 #35279 by Deltron
I'm by no means an expert on that system, but your last voltage reading indicates a problem to me. Your signal voltage(the low unplugged voltage) is equivalent to sensor source voltage when plugged in, and that indicates internal short.

edit: actually forget all that. I thought PRV was a sensor but it sounds like's its a duty cycle solenoid, in which case your voltages are proper.
Last edit: 24 Nov 2019 09:38 by Deltron.

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24 Nov 2019 09:39 #35281 by Guv
Hi Deltron
Yes I agree..I thought it strange that the readings were nearly identical with no indicated resistance, hence the request for more clarification from you wonderful people :-)

Thank you.

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24 Nov 2019 09:42 #35283 by Guv
Soory Deltron I've just read your reply again and apologies as I thought you were referring to the voltage reading from the connecter wires when connected.
As you can tell I'm also less of an expert than you with electrical components!

Trouble is there does not appear to be any easily sourced parameters for the grand cherokee for comparison.
Thanks though.

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25 Nov 2019 15:28 #35312 by Guv
I've noticed that my jeep has the Omron extrenal fuel relay modification.
Does anyone know how to test the external relay as I'm kinda getting the feeling that the fuel pump isn't working...just a hunch at the mo.
Thanks

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