Long crank on cold start

[B1Toad]

I noticed my crank time is slightly long on the first start of the day, not really long but longer than I am used to (although I've been driving diesels for a few years). I would say it takes about 10 revolutions and maybe 3-4 seconds. Is this normal for a 4.0? Also the idle is not perfectly smooth although not really missing and no misfire codes, just a little rough but I thought that may just be normal or should it purr? Is any of this pointing to a possible crank sensor? The 7.3 Powerstroke guys all carry a spare cam sensor in the glove box because of their reputation for leaving you stranded, is there anything on the 4.0 that is commonly recommended to carry like the crank sensor?

 

[Jerry Bransford]

That's caused by a leaky check valve inside your fuel pump. Given enough time sitting, a leaky fuel pump check valve allows the fuel to drain down out of the fuel rail adjacent to the fuel injectors and back into the gas tank. The additional time it takes to start the engine is how long it takes the pump to get the fuel back up from the gas tank to the fuel rail.

If you're handy I'd replace just the fuel pump in the fuel pump assembly and go with a Bosch who is the OEM maker. They're available on places like Amazon. Bosch no longer makes the entire fuel pump assembly which includes the fuel pressure regulator and gas gauge sender so if don't want to dig into that to replace the pump itself you're stuck with aftermarket fuel pump assemblies. Store brands, Airtex, Spectre, and most other cheap replacements are not worth the effort to install. Especially store brands like Duralast from AutoZone even with their lifetime warranties... they don't last long enough to make them worth installing even if they will give you a replacement when it fails (prematurely).

So if you are up to a little extra work I'd replace just the fuel pump itself with a Bosch which will last a long time.

In the mean time you can cut down on how long it takes to start by cycling the ignition switch 3-6 time, pausing 2 seconds each time it's in the On position, to give the fuel pump more time to get fuel back up to the fuel rail before you try to start it.

 

[Jezza]

Could also be a leaking injector. That's what mine was. Proper way to test this is to use a fuel pressure gauge and watch for pressure loss over time. The spec is, pressure should not drop below 30psi in less than 5 minutes. If it does, you should isolate the system from the rail connection back to the pump and test again. If you still have pressure drop, then replace the pump. If the pressure does not drop, the issue is most likely an injector.

 

[B1Toad]

Thank you both, I will check it out. I checked out the fuel pump online and it looks easily doable. Jezza, if it is a leaking injector will a Blackstone sample show fuel dilution in the oil?

 

[Jerry Bransford]

Thank you both, I will check it out. I checked out the fuel pump online and it looks easily doable. Jezza, if it is a leaking injector will a Blackstone sample show fuel dilution in the oil?

It can indirectly show fuel contamination from a lower than usual flashpoint.

 

[Jezza]

Thank you both, I will check it out. I checked out the fuel pump online and it looks easily doable. Jezza, if it is a leaking injector will a Blackstone sample show fuel dilution in the oil?

Possibly, but you would probably not understand the data unless you had a baseline.

 

[DropTopDon]

I had the same issue on my old TJ a year or two ago. My crank was about 10 seconds and the colder it was the less it seemed like it wanted to start. I replaced the fuel pump with a bosch and still had the same symptoms. Not sure what year your jeep is, but for my 04 it ended up being the camshaft position sensor. I replaced it with a NAPA sensor and it fixed the problem immediately. Mopar would probably be better. Not saying it isn't a leaky check valve, but you could try getting a new camshaft sensor and seeing if it fixes it, and returning it if the problem remains.

 

[Jerry Bransford]

Possibly, but you would probably not understand the data unless you had a baseline.

Blackstone will indicate if it's above normal.

 

[801 Driver]

You might try turning your ignition to the on position a few seconds while the sensor lights cycle while the pump pressures up and then hit the start position which might give you a little more insite to where the problem is. Mine goes for a few days without starting sometimes and it works for me. I have an older Dakota Sport that is the same. I just wait for all the lights to clear off the dash then hit the start position and it fires right up. It is too old to spend a lot of $ on if I do not need to. Good luck at finding your problem.

 

[Jerry Bransford]

You might try turning your ignition to the on position a few seconds while the sensor lights cycle while the pump pressures up and then hit the start position which might give you a little more insite to where the problem is.

X2, though that often requires that the ignition switch be repeatedly cycled on-off on 3-5 times because the fuel pump only runs 1.8 seconds each time the ignition switch is turned on. It shuts off in 1.8 seconds if the engine doesn't start by then.

 

[Jerry Bransford]

You might try turning your ignition to the on position a few seconds while the sensor lights cycle while the pump pressures up and then hit the start position which might give you a little more insite to where the problem is. Mine goes for a few days without starting sometimes and it works for me. I have an older Dakota Sport that is the same. I just wait for all the lights to clear off the dash then hit the start position and it fires right up. It is too old to spend a lot of $ on if I do not need to. Good luck at finding your problem.

What's the 801 mean? Anything to do with a Zenith?

 

[801 Driver]

You are correct sir. I purchased one already built several years ago. It has a Superior 360ci and Dynon glass pannels. Kinda a "Sky Jeep"

 

[Jerry Bransford]

You are correct sir. I purchased one already built several years ago. It has a Superior 360ci and Dynon glass panels. Kinda a "Sky Jeep"

Oh NICE!! I started building an Avid Magnum many years ago but stopped when I discovered the final net cost of the Lycoming O-320 it ran on. That's when reality set in lol. How's she fly?

 

[801 Driver]

Love it. I had gone to the Zenith "Rudder School" where you build a rudder over a weekend and look over their facility. I had a friend who built one of the first 750s and saw how many hours he had devoted to it over a year and a half. No way would I have that much time in my life. I then found a Savanah VG with a 940 Rotax in Ohio and flew it a few years. 26mph stall, 88mph cruise, 60 ft grnd roll with two on board. Really a fun plane but it had no place to take anything along even a fold up chair or a small bag. Decided to sell it and go for the 801 with rear seat area. Found a nice one up in Michigan (I am in OK) for sale. Builder was a sheet metal man and watchmaker, so it was a good build with me redoing some of the wiring I did not like. It has a 38mph stall, about a 260 ft roll with two on board, and cruzes right at 100mph. (I do mph with my STOLs and Knots with my Cherokee 235, works for me) Again, I love that 801, first thing I did was remove the slats and installed little plastic vortex generators on the wings and the stabilizer. That change it tremendously, made it much much better handling at very low speed and landing, great improvement over the slats. As I am getting older and my life has changed I have toyed with selling one or both of them. Other hobbies are taking up more of my time and I no longer have long distances I need to travel frequently with the Cherokee as in the past. I may be "thinning the herd" in the near future. Ha Ha

 

[801 Driver]

Woops, we did not mean to HIJack your thread, just got carried away. Keep us updated on your trouble shooting ideas and results of your findings.

 

[mattc10]

Hey B1Toad,
I just swapped out a fuel pump on my coworker's Jeep that had simliar symptoms. I got the replacement from Quantum Fuel Systems.
https://www.highflowfuel.com/qfs-26...wrangler-yj-4-0l-also-hemi-ls-swap-1991-1995/

 

[B1Toad]

Had time to work on it today, it had sat for 2 days and this AM was near freezing, I cycled the key five times and it started right up. So now I need to get a FP test gauge and figure out if it's the pump or an injector or 2. Also sent oil sample in. Question: is there a regulator in the return to keep pressure up and could that be another possibility?
edit: Just started studying the FSM and I see the regulator is at the pump only, not at the rail.

 

[B1Toad]

Got my testing done today. The rail held pressure for a long time after shutdown when closed off from the supply, the supply side bled down pretty fast to 20 PSI in under a minute and then slowed but continued to drop. The FSM says it should hold a minimum of 30 PSI for 5 minutes so I am looking at a pump.
As long as I am in there I want to replace everything possible which looks like the pump and filter/regulator unit (I realize the complete assembly is NLA). Looking for advice on what brand to buy for all of it. I have seen a couple suggestions on this thread including Bosch, Quantum and Walbro. So if you wanted the best regardless of cost which would you get and from where?

 

[B1Toad]

Looking at the Bosch it flows 415 LPH vs the Walbro at 255 LPH but would I even need 415 LPH on a stock 4.0? I do want the best but I also want what fits best without too much modification. Could the Bosch be a problem with such a high volume?
The FSM says a good fuel pump will pump .25L in 7 seconds which comes to about 128 LPH.
Also the Walbro comes in 3 different inlet/outlet orientations, I guess I'd need to drop the tank first to see which one I need?