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FLY NAVY
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308 Posts
Discussion Starter · #1 · (Edited)
Go figure while I'm deployed, something goes wrong with the truck that has never left me stranded in the last 4 years.

Cliffnotes: Truck stalled at highway speed. No CEL. Cranks and fires, but only about every 4th attempt. Once running, it's idling lower than normal, with fluctuating RPM. It usually stalls within a minute, or will stall if you put it in gear. I've researched a bit on here and most everything points to IAC valve, but I wanted to see if anyone else has a different opinion before I start ordering parts for it.

My dad was driving my truck at highway speed and said it very suddenly lost power, and wouldn't maintain RPM regardless of throttle position. Luckily, he was able to pull over on a runaway truck ramp. He could restart the truck, but he said it wouldn't stay running and had a rough idle.

After being towed home, I had my wife take a video (posted below). I have had her and my dad check the intake and all vacuum lines for leaks, and they couldn't find anything. I've had my intake separate from the TB before, and it also ran roughly, but it was still drivable at low speed.

I had her tap on the IAC with a hammer, and no change.

Mods are: K&N intake, SCT MAF, SCT XCAL3, Accufab TB (.99v TPS), ported Eaton, 4# lower, LT headers, mid pipes, catback.

What does the collective genius of LR think?

 

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Old Guys Rule
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74 Posts
While certainly not the most knowledgable person on this forum to offer help...I believe the IAC can be ruled out as you indicated your Dad couldn't maintain RPM at any throttle position. It's my understanding that the IAC only really comes into play at idle with the throttle body in its resting position by metering bypass air to maintain idle control.

It really sounds to me like a fuel delivery problem or a bad load of fuel. May want to have the fuel filter changed and fuel pressure checked. Could also be a sensor problem...any check engine light occurrences?

Thinking out loud here...

Maybe we could enlist the help of another list member that is close by to help get the truck up and healthy again.

I thank you for your service to our country and hate these kind of things happen while you are away ensuring our freedom!

Cecil
Gulfport MS...:bigtu
 

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AYHIN
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3,004 Posts
I agree with both of the previous responders. The IAC would not cause a shut down at highway speed. The filter or bad gas would be two things I would look at along with maybe a broken "Y" bad hose/connection in the fuel tank. Pumps could be suspect too. The voltage dropping resister to the fuel pumps could also be suspect. Jump it out to test.

Do you have a fuel pressure gauge on the truck to see what the fuel pressure is doing?
 

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FLY NAVY
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308 Posts
Discussion Starter · #5 ·
I agree with both of the previous responders. The IAC would not cause a shut down at highway speed. The filter or bad gas would be two things I would look at along with maybe a broken "Y" bad hose/connection in the fuel tank. Pumps could be suspect too. The voltage dropping resister to the fuel pumps could also be suspect. Jump it out to test.

Do you have a fuel pressure gauge on the truck to see what the fuel pressure is doing?
Thank you everyone for the replies. No fuel pressure gauge unfortunately.

I don't think it's bad fuel. The only reason I think that is that I filled up my Jeep with the same 92 octane from the same station, same pump within a couple hours of the fueling the truck. No issues on the Jeep.

I actually haven't changed the fuel filter since I bought it. It's been 4 years, but only 9,000 miles. That looks like an easy fix, and a likely culprit, and even if it's not the culprit, it's a good chance to upgrade to a Navi filter.

If that doesn't cure it, jumping the resistor is the next thing I'll try.

This is something that will have to wait until I get home, but if anyone has any other ideas, I'm all ears.
 

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AYHIN
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3,004 Posts
How long had it been sitting with that fuel in it before this happened? Gas these days tends to gel after a while and can clog the filter as well as the injectors.
 

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FLY NAVY
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308 Posts
Discussion Starter · #8 ·
How long had it been sitting with that fuel in it before this happened? Gas these days tends to gel after a while and can clog the filter as well as the injectors.
It had been driven within the past week or two prior to the incident.

Fillup was 01AUG. It had been driven a couple times before the stall occurred yesterday.
 

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AYHIN
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3,004 Posts
It had been driven within the past week or two prior to the incident.
Understood. Not trying to be an ass here but did it sit awhile with that fuel in it before the first drive?

Like I mentioned the Ethanol in the gas can gel over time and it is a cumulative event. I have seen it gel quickly and have seen it sit all winter with virtually no issues.

A generous application of Techron in the tank (two bottle in a half tank) and drive that through the system followed by a single bottle in a full tank can clear it all out. It does not sound like the truck is drivable but if the fuel filter is changed due to clogging then it would be prudent to clean out the gel in this manner. This is of course assuming this is the issue but there are several potential problems it could be.
 

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FLY NAVY
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308 Posts
Discussion Starter · #10 ·
Understood. Not trying to be an ass here but did it sit awhile with that fuel in it before the first drive?

Like I mentioned the Ethanol in the gas can gel over time and it is a cumulative event. I have seen it gel quickly and have seen it sit all winter with virtually no issues.

A generous application of Techron in the tank (two bottle in a half tank) and drive that through the system followed by a single bottle in a full tank can clear it all out. It does not sound like the truck is drivable but if the fuel filter is changed due to clogging then it would be prudent to clean out the gel in this manner. This is of course assuming this is the issue but there are several potential problems it could be.
Since the last fill up on 01AUG, it had been driven at least 3 times that my wife told me of. I specifically told her I didn't want it to sit more than two weeks.

I'll add Techron to the list of fuel fixes. If gumming was the issue, would it hurt to go ahead and add the Techron even if the truck wasn't going to be driven until I get home in about a month?
 

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AYHIN
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3,004 Posts
Since the last fill up on 01AUG, it had been driven at least 3 times that my wife told me of. I specifically told her I didn't want it to sit more than two weeks.

I'll add Techron to the list of fuel fixes. If gumming was the issue, would it hurt to go ahead and add the Techron even if the truck wasn't going to be driven until I get home in about a month?
If it is NOT going to be driven until you arrive home I would opt for Stabil mixed into a couple of gallons of fuel then pored into the tank. Figure up about how much fuel is in the tank now and add the fuel that you are pouring in and mix the ratio accordingly. If possible once the Stabil is in, idle the truck long enough to get it to circulate into the fuel lines and injectors.
 

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Registered
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382 Posts
My truck JUST done the EXACT same thing. My mechanic just called me and told me its the fuel pump resistor. He also said this resistor is no where to be found locally, getting it from the dealership. Hope this helps
 

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FLY NAVY
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308 Posts
Discussion Starter · #13 ·
My truck JUST done the EXACT same thing. My mechanic just called me and told me its the fuel pump resistor. He also said this resistor is no where to be found locally, getting it from the dealership. Hope this helps
Sweet man, thanks. Checking the resistor is on my list of things to do when I get home next week.
 

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Driving it daily!!
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110 Posts
I am having the same issue. Fuel pressure is within range, fuel pumps (I had the entire hat assembly--figured why not), fuel pump relay, fuel pump resistor, and fuel filter all changed, did not fix it.
Drives my nuts! Does not do it while truck is cold (odd), but once it warms up it hits about 600 RPM and surges.
I am seriously thinking about going with new plugs, new COPS, and hand cleaning the injectors--NOT looking forward to that.
It will not throw a code, I have been told that injector problems won't cause a code.
 

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FLY NAVY
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308 Posts
Discussion Starter · #15 ·
Update:

Fuel filter replaced. No joy.

Also tried testing the fuel pump resistor. I tried hooking up my ohmmeter and I'm not sure I did it right, but I didn't get anything close to .620 ohms. I put the two leads in the "pinholes" on the resistor connector.

Plugged the resistor back in, and tried jumping the Hi/Lo relay, with no joy either. Truck still will fire, but idles rough and dies after a few seconds. Giving it a little throttle doesn't help to keep it from dying.

I've ordered a new resistor, so another week down.
 

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Old Guys Rule
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74 Posts
I'm told you can bypass the resistor with a piece of wire for a simple test to verify it being the problem.

Testing the resistor is pretty simple. Set the meter to ohms on the Rx1 scale. Short the leads together and you should get a reading near zero. If it's an auto ranging digital meter just select ohms and short the leads together and you should read near zero. Then place the leads on the resistor terminals and it should also read near zero...if not what does it read?

Cecil
 

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Registered
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697 Posts
I once had a similar prob.

Truck would start, idle, sometimes die. would die if throttle was even touched.

Pressed the fuel rail test port, had wife turn key on and got weak spray of fuel out of it. (The spray should have been hard enough to hit the hood)
It was VERY apparent, no gauge needed.

Removed bed, pulled fuel hat. One rubber hose to fuel pump 1 slipped off of the "Y" fitting. Replaced hose. clamped all three with screw clamps. Reassembled.

FIXED.
 

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Registered
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1,024 Posts
May wanna try looking into what mizlplix mentioned. Also, back when I had my cobra, I would get the same symptoms randomly. Car would shut down for a second or so while driving. One day it just wouldn't fire up. I checked all my connections and sure enough the crank sensor plug was loose. The locking tab on the sensor plug broke off so it was causing intermittent stalling, shutting off. Check all ur connections
 
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