Engine cranks but will not start

I just want to clarify what is happening. First can we check for spark just to ensure this is not a crank sensor issue as that is what it sounds like.

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

If it has spark when it is not starting then we need to go back to a fuel issue as it should not be dropping to 20 and then 0 like that. Clearly the engine cannot run on 20 PSI so that sounds like the issue.

Also, just to check and make sure I understand the fuel pressure side of it. It was 50 when it was running then did it slowly drop or was it immediate to 20 and it stalled?

If this is the case, then it sounds like a pump issue but if you replaced it twice then we need to check power to the pump when this happens.

https://www.2carpros.com/articles/how-to-check-wiring

Below you will find the wiring diagram that comes from the relay. If we are losing power before it shuts down then we need to check the relay and then make sure the PCM is not removing the ground which closes the relay.

You should have 12 volts on the pump when the key is on so we need to verify this.

Hi,

I realize the crankshaft position sensor is new. However, is it an OEM part? Also, the ASD will shut down fuel and ignition. Have you checked the relay?

If you look below, I highlighted the ASD relay in the underhood fuse/relay box. Switch it with a known good one with the same part number to see if it makes a difference.

If there isn't one with the same part number, here is a link that explains how to test one:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know what you find. Also, please let me know if you lose spark when it won't start.

Take care,

Joe

See pic below.

First of all; thank you both for replying as i'm at wits end here, lol.
Joe and Kasekenny1, crank sensor was replaced approximately 3-4 weeks ago and came from Advanced Autoparts so i doubt that it's OEM. The fuel pressure dropped pretty fast and the relay is new also and can hear it click when key is turned on. I will check the ASD relay and all other questions tomorrow. the truck is at my work so I will check for spark and answer back tomorrow around 5:00 pm. thanks again guys.

Interestingly, per the request of a customer, I installed an inexpensive crank sensor about two weeks ago. Originally, the vehicle would run for about ten minutes before it shut down and lost spark. The new sensor made it better. It would run for about twenty minutes before it lost spark. LOL I replaced it with an OEM Chrysler part and haven't seen the customer for two weeks.

Honestly, I have been getting so many bad parts lately. Ugh!!!.

Take care and let us know what you find. We're interested in knowing.

Joe

Okay guys, sorry it took so long... truck does have spark when trying to start but zero fuel pressure. I ordered and installed oem crankshaft and camshaft sensors, nothing changed. Crank but won’t start. I also checked the ASD relay in the fuel pump relay also switch them with once it has same number and no change. They both click once when key is turned on , then 3 seconds later they click again. Checking to see if there is power going to fuel pump.
Now (green/white wires).

Okay, i have posted a pic of the so you can see the wires/colors... 1st wire(green with white stripe) when key is on, 0 volts. When trying to start, 10.66 volts.
2nd wire (light blue) when key is on, bounces between 10-12 volts.
Hope this tells you something...

Hi,

The green wire is the one of interest. That provides 12v to the fuel pump. With the key on engine off, you should see power for about 2 seconds when the key is first turned on. When cranking (voltage drops due to the starter) so the 10.66 isn't bad. If there is power to the pump (10.66v) and it has ground, it should run.

What I think is there is no ground for the pump or the pump is bad. Does it prime or do anything when the key is first turned on?

The light blue wire is for the gauge.

Let me know.

Joe

Well, i have already installed 2 new fuel pumps. when i tested for power to the green/white wire with the key on, engine off, i got nothing. While i tried to start it is when i got the 10.66v. I also noticed that my gas gauge didn't move,it normally bounces up after 2-3 seconds… how can i test to check to make sure ground is good?

Hi,

When you get the 10.66v, does the pump turn on? What is confusing me is how the system is designed to work and what it's doing. For the first second or two when the key is first turned on, the pump should prime. You should see power at that time and then it should turn off. When the computer recognizes engine ignition, that is when the pump is repowered.

If you look at the pic below, I highlighted the black wire which is the ground path at the fuel pump connector. I also circled a splice in the wire that could be bad. Using a multimeter, see if there is continuity to ground via that black wire. Simply disconnect the connector, put one probe into the black wire pin, and the other probe to a known good ground. The meter should be set to read ohms. There should be minimal resistance.

Or, take a long wire from the negative on the battery and attach it to the black wire on the connector to provide a ground direct. See if that makes things work.

Let me know if you have other questions or need help.

Take care,

Joe

See pic below.