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No Start on a '89 XJ 4.0

WillParker

NAXJA Forum User
Location
Birmingham, AL
ok here is the run down.

New CPS, Fuel Filter, Fuel Pump, Cap and Rotor, plugs and plug wires. It will crank, but not start. It will start how ever if I pour gas in the thottle Body. I pulled a spark plug and cranked it. The plug did spark, but it was a wimpy orange spark. I also have tested the fuel rail and I have great fuel PSI. I pulled the electrical connection on an injector and put a test light on it and it does nothing when I crank it. I put a meter on it as well and I don't see any voltage at the injector. I tested most of the sensors and all of them that I tested get 5v to them. So, What would cause the injectors to not get power?
 
Follow the injector harness back towards the firewall, there is a known bad splice in there, I think it is were the wires take off to the distributor synch sensor.
 
Can't find any bad wiring and the CPS test correctly. Any other ideas? I should mention I do not have a top on my XJ and it has set for a long time (about a year without running.) Although it ran when I parked it. I wonder if moisture killed my computer? Also could it be the ignition coil?
 
How good is the battery? Had it load tested? Might be amp enough for cranking but voltage under 9v and no electronics. Check all the grounds--dipstick, back of head, fenderwell (starter relay), and to the block, all very important Renix.

Main concern is the lack of power to the injectors.
 
Brand new Red Top Optima Battery, so I have 1000 CCA at 12v. It seems like all the grounds are ok. I can't tell what wire at the starter relay or the Coil powers the injectors. I think I am going to pick up a new coil today and put it in. The one I have is OE from '89. I just can't get it out of my head if the computer is ok. If I have 5v at the sensors does that mean the computer is good or could it still be bad even though I get power to the sensors? I am great at the mechanical stuff, the electrical stuff is still a grey area for me. Funny though seeing how I build smart homes, and Home AV systems :)
 
Short answer - no, doesn't give a definitive answer either way.

Long answer: The sensor power indicates that the voltage regulator powering the sensors (and possibly the computer internals, I'm not sure if they split rails on that) inside the ECU is still OK, but it doesn't mean the rest of the ECU is OK. A better indication of the computer at least not being completely braindead is if you can connect to it with an OBD I reader or Renix equivalent (I'm not so good with that end of things...) and read failure codes / information. That still won't rule out all forms of damage though, the analog end of the computer that interfaces with the engine could be toast.
 
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