xjtrailrider Posted June 4, 2011 Share Posted June 4, 2011 I need to get this thing running. Its a 89, 4.0, AW4 I have zero fuel pressure while the engine is cranking. when the key is released to "run" I have plenty of pressure. If I prime the TB it will start fine until it runs out of fuel then it shuts off(then it gets fuel pressure). I suspect the starter relay(having trouble finding one) but why do I only have pressure in run? I have good spark, the synch sensor is good, the CPS is good, the grounds are clean, the TB is clean, I have injector pulse on all six, I have good compression, all of the relays are tested and good, I have not checked the starter relay yet. I've owned RENIX XJ's for a while and thought I had them figured out but this one has me stumped! Come on RENIX gurus help a man out! Link to comment Share on other sites More sharing options...
NewfieMJ Posted June 4, 2011 Share Posted June 4, 2011 That is a wierd one . Only got one thing for you to try . Turn the key to "run" , jump it off the starter to see if it starts . If it does , I'd suspect the ignition itself . Link to comment Share on other sites More sharing options...
xjtrailrider Posted June 4, 2011 Author Share Posted June 4, 2011 That is a wierd one . Only got one thing for you to try . Turn the key to "run" , jump it off the starter to see if it starts . If it does , I'd suspect the ignition itself . I'll try it! Link to comment Share on other sites More sharing options...
maddzz1 Posted June 4, 2011 Share Posted June 4, 2011 Possibly the ballist resistor. Doesnt it cause the voltage to the fuel pump drop once the truck starts? Maybe its dropping too much because of the ballist resistor goin bad? Link to comment Share on other sites More sharing options...
Automan2164 Posted June 4, 2011 Share Posted June 4, 2011 Possibly the ballist resistor. Doesnt it cause the voltage to the fuel pump drop once the truck starts? Maybe its dropping too much because of the ballist resistor goin bad? IIRC, the ballast resistor only comes into play in RUN. IN start, it is bypassed. So if the ballast resistor was bad, the problem would be opposite, no? Rob Link to comment Share on other sites More sharing options...
maddzz1 Posted June 4, 2011 Share Posted June 4, 2011 Possibly the ballist resistor. Doesnt it cause the voltage to the fuel pump drop once the truck starts? Maybe its dropping too much because of the ballist resistor goin bad? IIRC, the ballast resistor only comes into play in RUN. IN start, it is bypassed. So if the ballast resistor was bad, the problem would be opposite, no? Rob I'm actually a little confused now, because when I turn the key to run I hear the pump prime (pump is loud, which is the reason for the BR) but once I start the truck it quiets down but then the keys turns back to run and it remains quiet. :dunno: So now I'm not sure Link to comment Share on other sites More sharing options...
xjtrailrider Posted June 4, 2011 Author Share Posted June 4, 2011 I forgot to add, I have bypassed the ballast resistor. I don't mind hearing the pump run and its just another thing to go bad Link to comment Share on other sites More sharing options...
Eagle Posted June 4, 2011 Share Posted June 4, 2011 You have bypassed the ballast resistor, I assume, by just jumpering the two wires at the resistor location on the inner fender, right? But the START circuit still has its bypass that directs full 12 volts to the fuel pump when the engine is cranking on the starter motor. That bypasses the whole ballast resistor portion of the circuit, so I would suspect a break somewhere in that START bypass circuit. Link to comment Share on other sites More sharing options...
xjtrailrider Posted June 4, 2011 Author Share Posted June 4, 2011 You have bypassed the ballast resistor, I assume, by just jumpering the two wires at the resistor location on the inner fender, right? Correct But the START circuit still has its bypass that directs full 12 volts to the fuel pump when the engine is cranking on the starter motor. That bypasses the whole ballast resistor portion of the circuit, so I would suspect a break somewhere in that START bypass circuit. Thats what I suspect. Doesn't the starter relay take part in that in some way? Link to comment Share on other sites More sharing options...
JeffN Posted June 4, 2011 Share Posted June 4, 2011 Suspect bad ignition switch Link to comment Share on other sites More sharing options...
xjtrailrider Posted June 4, 2011 Author Share Posted June 4, 2011 Suspect bad ignition switch That would be nice! Cheap easy fix :clapping: Link to comment Share on other sites More sharing options...
xjtrailrider Posted June 5, 2011 Author Share Posted June 5, 2011 Two words-fuel pump It has 0 pressure even though it is running. When the key goes to start, the amp draw from the starter actually cuts the pump out Thank you for everyones replies and help Link to comment Share on other sites More sharing options...
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