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Unread 06-30-2013, 06:21 PM   #1
RamboPants
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1987 XJ Cherokee 
 
Join Date: Jan 2007
Location: Roanoke, VA
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Fuel pressure regulator bad?

My jeep has been running kinda weak, like it wants to stall. With the AC on its worse. I noticed when i pull the vac. hose off the regulator there is no change at all in the way the jeep runs. Would that mean the regulator is bad?

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Unread 06-30-2013, 07:57 PM   #2
tjwalker
It's the crank sensor!
 
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1999 XJ Cherokee 
 
Join Date: Nov 2007
Location: Central Minnesota, MN
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You'll need a fuel pressure gauge to properly test your regulator. Can be rented from some parts stores; call around.

First, get baseline fuel pressure. For your 87, you should have approximately 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Also check to see if there is raw fuel in the vacuum line; that would show that your regulator has a ruptured diaphragm.
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Unread 06-30-2013, 09:13 PM   #3
RamboPants
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Ok thanks also I just noticed my egr will not stay compressed when I block the vac line hole with my thumb. Does that mean it bad?
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Unread 07-01-2013, 05:49 AM   #4
tjwalker
It's the crank sensor!
 
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Join Date: Nov 2007
Location: Central Minnesota, MN
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TESTING THE EGR VALVE FOR 87-90 4.0 ENGINE

Valve Opening Test

1) With engine at normal operating temperature and at idle,
rapidly open and close throttle. Open throttle sufficiently to obtain
at least 1500 RPM. Movement should be noticed in EGR diaphragm.
2) If diaphragm does not move, probable causes are: faulty
vacuum signal to EGR, defective EGR diaphragm or defective
backpressure sensor diaphragm (if equipped), or leaks in vacuum lines
or connections.

Valve Closing Test

1) With engine at normal operating temperature and at idle,
manually depress EGR valve diaphragm. RPM should immediately drop,
indicating that EGR valve is not leaking and had been properly cutting
off exhaust gas flow at idle.
2) If there is no change in RPM and engine is idling
properly, exhaust gases are not reaching combustion chamber. Check for
plugged passage between EGR valve and intake manifold.
3) If engine idles poorly and RPM is not greatly affected by
manually moving diaphragm up, EGR valve is not closing off exhaust gas
flow. Check for carbon between pintle, leaking EGR valve gasket or bad
EGR valve.
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99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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Unread 07-02-2013, 04:54 PM   #5
RamboPants
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EGR was bad, ordered a new one. Thanks for your help.
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Unread 07-05-2013, 06:31 PM   #6
RamboPants
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OK finally tested my fuel pressure since the new egr didn't seem to take care of the problem. Its 39 with the fuel pressure reg. hose removed. Around 31 at idle the needle kinda jumps around though. Also the jeep kinda misses around 55 - 65 mph but not constantly. Any ideas?
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