hello, i'm new to this so;

Six months ago i had a "crank but not start issue" so I replaced the FPDM and it started fine until recently. It was intermittent and i could not find a pattern. Sometimes it would start right up and other times up to 4-5 start attempts. I could hear when the fuel pump was energizing. Once it was started it would run fine with no stalling at all. The following is what i've done so far to try to fix the problem. i changed out the battery, i found some wiring diagrams and had to decipher the right one for my truck. i then thought to see if there was voltage at the inertia switch in the passenger kick plate. I was not getting voltage to the switch when i turned the key to "ON" as i should have to energize the pump prior to starting. Turned the key off and tried again, this time i would get 12v, truck would start and i would see 14.6v so i knew the alternator was working. That lead me to the PCM relay(s) in the fuse panel under the steering wheel. the relays were clicking when i turned the key to "ON" but truck wouldn't start. I swapped the two relays OEM 5C3T-14B192-AA and truck started 4 times in a row. Boy i hope all i need is a new relay, any suggestions?

 

First off have you tried replacing the fuel filter that is on the frame rail? It may have been clogged up with junk, it is cheap to replace I would check that and then give it a try.

Then I would go and grab some starting fluid spray Take it and squirt the fluid into the intake and crank the motor. If she fires and the truck runs,the problem is in the fuel system So onto the next step

I would check the Fuel pump control module which is also on the frame rail, water can run off the frame rail and drip down on to the wires at that module and cause corrosion which could be causing it to have a case of the green nasties or a short Need to have a look at it and make sure everything is all good there and there are no short or green nasties that may be giving you intermittent issues

Next up after that is to have someone go under the truck with a rubber mallet while you try to start on it and have them hit the bottom of the furl tank while you try and start it at the same time and see if it turns over and runs, if it turns over and runs your furl pump is on the way out and its time to replace it.

Try those and see if that helps you any you can always report back with what happens. Hope this gives you a few more places to check

And another member in a different thread mentioned this as well:

 

so, i installed a 12v light at the inertia switch so i could see when the fuel pump was being "told" to energize, and found it was not lighting everytime. traced the wire back to the plug on the back of the CJB(under dash drivers side). using a test light found that there was intermittent power coming from the CJB. i took a chance and bought a used panel off of Ebay(1 year warranty) and changed out the CJB. have not had any problems since. yay me

 

Great to hear!

 

Nice work Rob on digging deep to track the issue down. I have never heard of that being the cause but could be it has been seen by folks but they just haven't got on a place like FTE to share it. Appreciate you sharing the info and what you did to check out what was going on.

You never know when the next person is going to run into an issue like you did and this will be one more thing for others to have a look at before they haul it somewhere and get whacked with a big repair bill.

Nice work on tracking it down and good job on getting your rig back up and running

 

FYI, on this generation of truck (SD starting in 02 until whenever), the fuel pump relay is soldered onto the circuit board of the Central Junction Box (CJB).

This is not an uncommon failure. The troubleshooting method that Rob used is to be commended as it quickly slip the circuit in half and allowed him to focus on the correct half of the circuit instead of just guessing that maybe it was the fuel pump , inertial switch, relay, etc.