Long crank time and runs rough sometimes...

[Brasscatz]

On occasion I'll start up my Jeep and it'll run extremely rough for 30 seconds or so, and I have to give it gas to get past it. Usually when I give it gas, it'll kind of backfire, then straighten itself out. I can't figure out if there's an actual connection to this, but I seem to notice it happening more if I left my a/c on when I shut the Jeep off, meaning it's still on when I'm starting it again.

Now, starting yesterday it has cranked a LOT before firing up. I haven't noticed the running rough when this happens, though. It used to turn over maybe 2 times before firing, now it will crank and crank and crank before firing.

Any ideas?

[4.3LXJ]

You might check your fuel pressure. It sounds like it is bleeding off when the pump is not running. Try turning the key on for 2 seconds, then off, then on again and see if that helps. If it is, the check valve is leaking

[Brasscatz]

I tried letting the pump prime before starting (one key turn and wait till pump stops) and it still did it. Next time I started it (maybe sitting for 30 minutes after inspecting a roof) and I turned the key 5 times like that and it fired right up.

Not sure if it sat long enough (length of time sitting seems to have a lot to do with it). It's tucked in for the night, so I will be trying that in the morning. Where is the check valve?

[4.3LXJ]

Check valve is in the tank on the sending unit/pump assembly. Spendy to get a new valve since it comes with the new complete unit. Checking the fuel pressure will tell for sure

[Brasscatz]

Thanks, Steve. Do you think this also causes the intermittent running rough? I was leaning towards possible MAP sensor on that and it's been randomly doing that for over a month now.

[4.3LXJ]

If your rpms drop when that happens, check the IAC first and clean it. Then go from there

[Brasscatz]

No rpm drop, just runs like it's got really dirty gas or something for about 30 seconds

[4.3LXJ]

How long since the CPS was changed?

[Brasscatz]

to my knowledge.... never

[4.3LXJ]

If your fuel pressure checks out, then I think it is the CPS

[Brasscatz]

Thanks, I'll let you know. I don't have a fuel pressure tester, so I should just try the pump priming?

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[4.3LXJ]

Yes, start there

[Mudderoy]

Mine would take several attempts to start. Turning the key on and off three times would usually get it to start.

It would run rough.

Checked the fuel pressure, it was dropping to like 5 psi within 2 minutes of turning the engine off, it was fine while it was running.

Replace the unit in the fuel tank. Problem solved.

[Brasscatz]

Mine would take several attempts to start. Turning the key on and off three times would usually get it to start.

It would run rough.

Checked the fuel pressure, it was dropping to like 5 psi within 2 minutes of turning the engine off, it was fine while it was running.

Replace the unit in the fuel tank. Problem solved.

Maybe I need to take a trip to your house to use your fuel pressure tester and drop off a new sign :D

[Brasscatz]

Tried priming the pump with 2 key turns and it still took some cranking to start. Not as much, but definitely more than normal

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[4.3LXJ]

Get that fuel gauge on there so you can see what is going on

[Mudderoy]

Maybe I need to take a trip to your house to use your fuel pressure tester and drop off a new sign :D

Fuel pressure check, sure, another sign, no thanks. :smiley-scared003:

[Pookapotamus]

When you are shutting it off, is it very warm, I have had an issue when I was stock and after a long drive shut it down, did not want to start at all and ran like garbage in till it cleared. I was told that it was most likely heating the fuel rail so much that it caused vapor to form in the rail. Lots of fuel pressure but basically vapor locked an injector or two. I have since put a shield on the fuel rail, and heat taped it as well. Never had another issue, even when shutting down after a long hard hill climb.


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[Brasscatz]

When you are shutting it off, is it very warm, I have had an issue when I was stock and after a long drive shut it down, did not want to start at all and ran like garbage in till it cleared. I was told that it was most likely heating the fuel rail so much that it caused vapor to form in the rail. Lots of fuel pressure but basically vapor locked an injector or two. I have since put a shield on the fuel rail, and heat taped it as well. Never had another issue, even when shutting down after a long hard hill climb.


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I would say it's between 210-220 when I shut it off.

[xj-jake]

When you are shutting it off, is it very warm, I have had an issue when I was stock and after a long drive shut it down, did not want to start at all and ran like garbage in till it cleared. I was told that it was most likely heating the fuel rail so much that it caused vapor to form in the rail. Lots of fuel pressure but basically vapor locked an injector or two. I have since put a shield on the fuel rail, and heat taped it as well. Never had another issue, even when shutting down after a long hard hill climb.


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Do you have some details of how you did this Dana? I have this issue as well in the summer time.

[Pookapotamus]

I can't seem to find any pics, firstly I bought a stick on heat wrap and just wrapped the rail and injectors. For the shield all I did was get a piece of thin gauge steel and bend it in a U shape, then notched the steel so that the rail fit inside and the top of the U is on the top, thus shielding the rail from the heat coming up past the intake manifold. I think I also wrapped the Bottom of the U with heat wrap for extra protection. Just shields the rail from raidiant heat and lets it dissapate heat to atmosphere from the top.

Nothing really special, although I think I used stainless.


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[denverd1]

wouldn't a vapor lock injector or 2 just make those cylinders misfire? mine has done it with hot motor on a hot day once or twice.

sounds like fuel pressure to me too