Fuel Pressure Testing- how you doin it?

[Shellbird01]

The FP sensor on a 3.6 JL is in the fuel feed line about 2ft from the connection to the rail. I don't believe you'll see a pressure drop in that distance, if it's not pinched. The live data page on JSCAN shows fuel pressure.

Would you mind sniping a pic of Jscan? What year, mines an 18?

Sponsored

 

[roaniecowpony]

Im a 2018. This is from the JL demo page. I can get a screenshot of real live data, but I'd have to install the bypass and dongle.

 

[alphawolff]

How are you guys testing without a valve in the line or on the rail?

I thought about putting in a small tee? Maybe someone makes one?

I pop the line and try to start the vehicle. If it sprays out it's got fuel pressure. I have a vacuum line I just snug onto the line and lead it to a bottle.

I think I've had to pull a fuel pressure gauge maybe thrice in my entire career. Getting accurate fuel pressure isn't something you need often. You either have it or you don't. Can sometimes use scan tool data if needed, but it usually isn't the most accurate

3.6 - trouble shooting, the engine is hunting (reving) at idle. Using the obdII I now think it’s when the purge valve opens. It started after I swapped the fuel pump, but also repaired the pinched Evap line.

Just trying to rule out the fuel pump.

Annnd this is where you'd probably want an accurate reading, but seeing as the issue began ocurring after the pump replacement you probably have your cause already. So long as there isn't some type of vacuum leak before the purge solenoid the EVAP repair shouldn't be related.

 

[roaniecowpony]

This is the type of line tap you would need. But I can't find the correct one for the JL in this website for Mopar tools. I've bought from them in the past for other things, so I think you'd be able to purchase directly from them if they had it.

6539A, Adapter, Fuel Pressure Tester - Mopar Essential Tools and Service Equipment

 

[roaniecowpony]

I just measured the fuel feed line I have laying around and it's 5/16" at the push connector.

Here's a T-tap for the fuel line. A little pricey.
00-01811-5/16 Nitrous Outlet Universal 5/16" Inline EFI Fuel Rail Adapter Feed | eBay

Or this Amazon gauge set
Amazon.com: BETOOLL Fuel Pressure Test Kit 0-100PSI with 9.49,7.89,6.30 Fuel Line Fittings : Automotive

 

[Shellbird01]

Interesting, put in some 91 today, fuel trims were very different, thru p0443,p0113, p0461, cleared them and didn’t come back.
No noticeable surging, Commanded Evap never moved from 0 on a 3 hr drive. Is 91 that stable it or I have some gremlins?

Man it purred like a kitten. I’t seems to run so much better when purge solenoid doesn’t open?

 

[roaniecowpony]

Interesting, put in some 91 today, fuel trims were very different, thru p0443,p0113, p0461, cleared them and didn’t come back.
No noticeable surging, Commanded Evap never moved from 0 on a 3 hr drive. Is 91 that stable it or I have some gremlins?

Man it purred like a kitten. I’t seems to run so much better when purge solenoid doesn’t open?

Water in the tank?

Had an airplane engine quit shortly after takeoff. Deadsticked in, then it was running fine. Water.

 

[roaniecowpony]

That's about 10% low. Might have an effect.

 

[dstevens]

You seem to have a logger so have a look at the fuel trims. And lambda if you can (does the JL V6 finally get a wideband o2?) And also the secondary o2 sensors. And ignition timing.

What has happened is that something has upset the PID control loop for idle speed with an input going outside the expected range. If the JL has a fuel pressure sensor then it is not that because the PCM can compensate. It could be injectors, o2 sensors, catalysts. Or even just the throttle body. I'm presuming no DTCs. You seem to have eliminated air leaks.

 

[mwilk012]

Fuel pressure isn’t going to be the answer.

 

[dstevens]

Yep, fuel trims look ok. Doesn't look like Stelantis has widebands on the V6 yet.

 

[mwilk012]

Yep, fuel trims look ok. Doesn't look like Stelantis has widebands on the V6 yet.

I don’t like the difference in B1/B2. Suspicious. Would like to know how it looks live if it hovers up and down from zero or if it hangs out around 5 like shown.

 

[Shellbird01]

I don’t like the difference in B1/B2. Suspicious. Would like to know how it looks live if it hovers up and down from zero or if it hangs out around 5 like shown.

You want at idle any other rpm or driving?

 

[mwilk012]

Idle, especially if that’s where you’re having the surge.

My thoughts are: you just did a hunch of work and now it’s doing something new. Prove it wasn’t something you caused.

 

[alphawolff]

I don’t like the difference in B1/B2. Suspicious. Would like to know how it looks live if it hovers up and down from zero or if it hangs out around 5 like shown.

Assuming that graph is right something is up there. Downstream o2s should remain steady, if it jumps to meet the upstream it's a bad cat (right side in this case). That or the left side o2 has failed. Hard to say without more graph data, but it's definitely an issue. Its been awhile since I diagnosed a cat from o2 voltages but I swear both down streams should be near the same voltage and not have such a difference like we're seeing here

You want at idle any other rpm or driving?

Monitor all 4 o2s and go cruise around a bit. Both down streams should remain consistent and not jump around.

Sponsored