So I am having a no power to the fuel pump on my 97 tj. Just purchased jeep. Jeep sat for 7 years got it home and started checking it out. I've repaired all broken/chewed wiring and removed the p/o alarm system checked/swapped relays and checked the crank sensor. I can bypass the fuel pump relay and get good 12 volts to the back connector but when the relay is plugged back in it does not work. Not really sure where to go from here. Any thoughts?
No power to fuel pump
- Thread starter Joeyt
- Start date
When are you measuring? The fuel pump only receives 12 volts for 1.8 seconds after the ignition switch is turned on if the engine doesn't start.
Yes checking for power as soon as ignition is turned on. I have bypassed fuel pump relay and get 12 volts. Wiring is good from the pump to the relay. For some reason sorting is telling the relay to not work. I've swapped the asd relay as well.
So the fuel pump relay inside the PDC is not energizing right? Have you unbolted the PDC from the fender well yet to check out the condition of its wiring?
Check the TJ resources on the forum for a downloadable PDF of the Factory Service Manual for your year TJ.
Look in section 8W-30-15 for schematics of the fuel pump circuit.
https://wranglertjforum.com/attachments/1997-jeep-wrangler-service-manual-pdf.308365/
FUEL PUMP RELAY When the ignition switch is in either the START or RUN positions, it connects circuit A1 from fuse 3 in the Power Distribution Center (PDC) to circuit A21. Circuit A21 feeds circuit F12 through fuse 11 in the fuse block. Circuit F12 powers the coil side of the fuel pump relay. The Powertrain Control Module (PCM) provides ground for the relay on circuit K31. Circuit K31 connects to cavity C19 of the PCM. When the PCM grounds the fuel pump relay, contacts inside the relay close and connect circuit A61 from fuse 16 in the PDC to circuit A141. Circuit A141 powers the fuel pump motor (part of the in-tank fuel pump module).
Look in section 8W-30-15 for schematics of the fuel pump circuit.
https://wranglertjforum.com/attachments/1997-jeep-wrangler-service-manual-pdf.308365/
FUEL PUMP RELAY When the ignition switch is in either the START or RUN positions, it connects circuit A1 from fuse 3 in the Power Distribution Center (PDC) to circuit A21. Circuit A21 feeds circuit F12 through fuse 11 in the fuse block. Circuit F12 powers the coil side of the fuel pump relay. The Powertrain Control Module (PCM) provides ground for the relay on circuit K31. Circuit K31 connects to cavity C19 of the PCM. When the PCM grounds the fuel pump relay, contacts inside the relay close and connect circuit A61 from fuse 16 in the PDC to circuit A141. Circuit A141 powers the fuel pump motor (part of the in-tank fuel pump module).
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So I ran a separate ground wire to the ground lug on the relay and now I have power to the fuel pump. Does this mean the pcm is not working for that function. The engine will start on either.
Read post #5 above.
With the ignition switch in the RUN position (fuel pump should be commanded by PCM to run); use a multi meter on Ohms (conductivity) and measure from Cavity C19 of the PCM to chassis ground. IF you donot read conductivity between Cavity C19 of the PCM and chassis ground; then the PCM either has a problem OR it is not commanding the fuel pump to run.
With the ignition switch in the RUN position (fuel pump should be commanded by PCM to run); use a multi meter on Ohms (conductivity) and measure from Cavity C19 of the PCM to chassis ground. IF you donot read conductivity between Cavity C19 of the PCM and chassis ground; then the PCM either has a problem OR it is not commanding the fuel pump to run.
So an update on the no power issue. Figured the pcm was bad, ordered a reman from flagship and installed it this evening. Fuel pump now runs and oil pressure guage and voltmeter now work, but still won't start. Took out a spark plug and tested for spark and getting no spark. Any ideas where to go from here?
First, Flagship1 has an abysmal reputation for their PCMs. I'd be more trusting the PCM was good if it had come from Wrangerfix.com.
Then, how did you test the crankshaft position sensor?
Then, how did you test the crankshaft position sensor?
Have not tested crank sensor. But pcm was dead. Voltmeter works now and oil pressure shows and fuel pump now runs at ignition on.
Sounds like the OP had a bad, new PCM from Flagship. Not surprising since the prevailing wisdom for replacement PCMs is WranglerFix.com.
That being said...have you checked your fuses, relays and continuity tested your wires?
Have you checked fuel pressure at the rail? I assume you did and that's how you came to discover no voltage at the connector.
FSMs and wiring diagrams are in the resources section.
-Mac
It further sounds like he had additional problems since the new computer still resulted in a crank/no-start condition. in my experience, it is very very often the wiring at/near the cam & crank sensors that cause this. Replacing the sensors often does the trick although often (again, in my experience) it wasn't the sensor but rather the wiring at the pigtail. I would start by inspecting the wiring at the sensor plugs. Then I would check fuel pressure, simply because it's easy. And then either a noid light or other redneck check for spark.
Lastly, or maybe firstly, spraying starter fluid down the throttle body can tell you if it's a fuel or spark problem. If the fuel pump relay kicks on with the key, then 99% you've got a spark problem caused by a sensor/wiring.
p.s. starting a new thread with your specific year, symptoms, and what you've done to troubleshoot will likely be more productive than bumping somebody else's ancient thread.
Lastly, or maybe firstly, spraying starter fluid down the throttle body can tell you if it's a fuel or spark problem. If the fuel pump relay kicks on with the key, then 99% you've got a spark problem caused by a sensor/wiring.
p.s. starting a new thread with your specific year, symptoms, and what you've done to troubleshoot will likely be more productive than bumping somebody else's ancient thread.
Brand new member here.
How can I find the service manual for a 1999?
Thanks in advance
EDIT A little more digging and I found it.
Thibodaux, Louisiana, eh? I once new a cat who lived about 45 minutes southeast of there.
Guys be sure to check the condition of the relay box, I thought that I was having the same issues for a very long time, however after going through several different relays I realized that I was not getting a secure connection up underneath the fuel pump relay circuit to do this you have clips that will take your fuse box that's up underneath your hood halfway off so then you can blow it out and you can check the condition of the wires ...I ran a switch engaging my fuel pump to work for about a month via the relay circuit until I figured this out, it's a trail Jeep and it was dirty, after that I ran like a champ and it had great fuel pressure.
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