1984 Jeep CJ7 Fuel Injection

Tiny
JTVETER
  • MEMBER
  • 1984 JEEP CJ7
  • 6 CYL
  • 4WD
  • MANUAL
  • 120,000 MILES
Hi I bought a Jeep that was built for rock crawling. Everything was working fine. Now it wont start with out giving it a little gas down the trottle body. After it starts it runs fine. The cumputer is working fine. Is there a rely or something I am missing? I also wanted to add this injection system is out of a late 80 - early 90 v6 GMC - Chevy. I have look at the injectors and they do do spray any fuel when you turn the engin over, but after you add a little fuel and it fires up they start to work fine.
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Thursday, March 5th, 2009 AT 10:58 AM

5 Replies

Tiny
JAMES W.
  • MEMBER
First question, is this a throttle body or ported injection system? When you turn the key to on, not start, the fuel pump should run for a few seconds to pressurize the fuel system. Crack the fuel line at the pressure regulator and see if you are getting fuel, being very careful, we don't want a fire. That would turn a simple fuel test into a bad day. If no fuel at "key on", check flow with "key crank". If no fuel at key crank, I'll need to know more closely what year system we're dealing with if possible. The ECM sends the signal to the pump relay which turns on the pump. Please advise.
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Thursday, March 5th, 2009 AT 5:50 PM
Tiny
JTVETER
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For the first question it has a injection system. We have tested the fuel line pressure. The pressure is good before and after cranking the motor.
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Friday, March 6th, 2009 AT 8:30 AM
Tiny
JAMES W.
  • MEMBER
OK, next you need to check injector pulse on "key crank". If you have, or have access to, a set of "noid lights", these will plug into the injector connector and flash if you have injector pulse. Or, you can use a regular incandescent test light to accomplish the same thing. If you have a throttle body system, you should be able to see the fuel spray. If it's a ported system, you will need a light. Keep in mind, the injectors are feed 12 volts with key on. The ECM "grounds" the injector to make it fire.
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Friday, March 6th, 2009 AT 12:31 PM
Tiny
JTVETER
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No fuel is sprayed when you turn key on or any time while turning over but if you add a little fuel it will start up and the injectors will start working
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Friday, March 6th, 2009 AT 1:04 PM
Tiny
JAMES W.
  • MEMBER
Well, not knowing for sure what ECM system you have, I can only guess. It must be the ECM isn't processing the "cranking" signal to the injection circuit. The ignition module must be sendind the cranking signal to the ECM, or you wouldn't have spark either. The run circuit out of the ECM has to be OK, or you wouldn't get any fuel at all. I wopuld change ECMs.
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Friday, March 6th, 2009 AT 2:30 PM

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