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Old 02-12-2011, 04:15 PM   #1
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Running Lean

Okay so a few months ago my wife's '98 V6 started stumbling on start up and would idle WAY below 1000rpm and even stall. it would only last a moment or two and then we could drive normally. If we stopped somewhere and came back to the car it would start its rough idle crap again. We have a scanner and we got a P0717 and a P0174 code (banks 1&2 running lean). We've checked the vacuum lines for leaks (none) checked the IAC for proper operation, checked the TPS and its okay, the MAF sensor is clear, the fuel filter is only a year old with less than 8Kmiles on it. We've run injector cleaner through it and thsoe should be clean. We replaced the DPFE sensor (it was operating out of proper voltage specs) with a genuine Motorcraft unit ($100!!!) and that did not solve the idle problems. Today we got a P0401 code (EGR insufficient flow) which is wierd because that unit was operating fine a few weeks ago. We're also going to replace the intake manifold gasket in case theres a vacuum leak there. Is there anything else we should look at? My wife LOVES her car and will not part with it so its troubling to be having this constant issue with it and no solution in sight.

Thanks for your help.

PS: Does anyone think that this 10% ethanol in the motor has anything to do with the above issue?
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Old 02-12-2011, 04:19 PM   #2
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Ethanol isn't the issue... It actually burns well and has cleaning properties. I would lean more towards a fouled injector or injectors. Or a sensor malfunction which is causing the engine to lean the a/f
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Old 02-12-2011, 04:20 PM   #3
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Nope on the ethanol. Egr could do it. Vacuum leak could do it. Dpfe sensor possibly but don't remember what code it sets.
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Old 02-12-2011, 04:32 PM   #4
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Re: Running Lean

We're getting the egr now and it'll be replaced tonite. The car is still running the orignal part. Would a weak fuel pump cause this issue?

Also note that the problem is inconsistent. There are days the car runs "fine".
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Old 02-12-2011, 04:38 PM   #5
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Originally Posted by Her98StangV6
We're getting the egr now and it'll be replaced tonite. The car is still running the orignal part. Would a weak fuel pump cause this issue?

Also note that the problem is inconsistent. There are days the car runs "fine".
The pump may cause it however you would lose power and it would likely jerk
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Old 02-12-2011, 04:49 PM   #6
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Re: Running Lean

Yeah, we dont get that. Just the rough start up and restarts.

One other thing we did. We replaced the spark plugs with Motorcraft SP486's. Now the owners manual calls for a AWSF-42EG for one bank and the -42E for the other bank. But I cant find those particular plugs anywhere so I went with the SP486's. We replaced the coilpack with a Screamin' Demon performance unit (45Kvolts). Now I'm wondering if the stock ignition wires are up to the task of carrying that much voltage. Thoughts?
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Old 02-12-2011, 04:54 PM   #7
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Re: Running Lean

Okay, my father-in-law (retired USAF) says the EGR itself is fine but the gasket is shot. That could be the cause of the vacuum leak. We also passed on the IMG as the problem is not constant.
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Old 02-12-2011, 05:01 PM   #8
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Google dpfe sensor. I think you have more than 1 problem.
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Old 02-12-2011, 05:33 PM   #9
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Re: Running Lean

Hopefully its a vacuum leak with the egr gasket. *crossing our fingers*
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Old 02-13-2011, 10:33 AM   #10
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Re: Running Lean

Okay, not the EGR gasket. Still getting rough start ups.
Note that its NOT every time and after that the car runs "fine." I know its running lean bcuz its guzzling fuel and the exhaust smell is of raw fuel. MPGs suck. She's getting about 220mi/tank.
So I'm gonna replace the whole EGR now.
Any more thoughts/ideas? O2 sensors?
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Old 02-13-2011, 11:25 AM   #11
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Hey guy. Research dpfe sensor for the 3rd time. That's your egr problem. Check for vacuum leaks with a water hose.
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Old 02-13-2011, 11:41 AM   #12
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Re: Running Lean

Second time: Its a brand new DPFE straight from motorcraft. 1 month old. 1st post.
How do I check for vacuum leaks with a water hose?
Would that be same as spray carb cleaner while the motor (cold) is running?
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Old 02-13-2011, 11:44 AM   #13
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Water hose is easier. Not full pressure around the sealing surfaces.
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Old 02-13-2011, 11:45 AM   #14
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Engine will stumble or you will hear it.
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Old 02-13-2011, 12:21 PM   #15
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Re: Running Lean

Okay we'll give that a try. We'll keep you posted. This is so annoying...
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Old 02-13-2011, 04:39 PM   #16
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I'm having the same exact problem with my 99 v6. I have to put it in neutral so it doesn't stall. It only idles/stalls low when in gear. and getting about 200 miles per tank.
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Old 03-01-2011, 08:03 PM   #17
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Re: Running Lean

Hey, so the wife says that on a full tank the acts normal but around 1/2 a tank is when the trouble arises. Could the gas cap be the problem? Would a bad seal be related to a loss in fuel pressure? And hence, stumbling upon start up?
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Old 03-01-2011, 09:17 PM   #18
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Originally Posted by Howephillip
I'm having the same exact problem with my 99 v6. I have to put it in neutral so it doesn't stall. It only idles/stalls low when in gear. and getting about 200 miles per tank.
Is your engine light on? Bc I had a friend with this prob and he had to change o2 sensors.
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Old 03-01-2011, 10:20 PM   #19
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Re: Running Lean

My CEL's have come on but they've been for "banks 1n2 running lean" and "EGR insufficient flow". The EGR problem was a melted vacuum line. The "lean" code hasn't come back on in a while but we're still getting a rough idle at start up. Anyone think a bad gas cap could be to blame?
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Old 03-01-2011, 10:26 PM   #20
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Originally Posted by Her98StangV6
My CEL's have come on but they've been for "banks 1n2 running lean" and "EGR insufficient flow". The EGR problem was a melted vacuum line. The "lean" code hasn't come back on in a while but we're still getting a rough idle at start up. Anyone think a bad gas cap could be to blame?
Gas cap not the blame.
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Old 03-01-2011, 10:52 PM   #21
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Re: Running Lean

Okay.... What part does the gas cap play in emissions since that is one of the parts they test? What would they test it for?
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Old 03-01-2011, 11:00 PM   #22
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Okay.... What part does the gas cap play in emissions since that is one of the parts they test? What would they test it for?
Just to see if it seals. It has a check valve in it. I will allow air to go in so vacuum doesnt suck the tank in. It does not let vapors go out though. Evap system let's vapors at times go into the engine instead of the atmosphere.
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Old 03-01-2011, 11:13 PM   #23
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Im sorta havin the same problem but its not at start up. I come to a stop and in drive my car idles really bad then stalls out. Ive changed spark plugs and IAC. Im gonna change my crank sensor and fuel pump and MAF this weekend so hopefully it stops the bad idle.
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Old 03-01-2011, 11:18 PM   #24
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Im sorta havin the same problem but its not at start up. I come to a stop and in drive my car idles really bad then stalls out. Ive changed spark plugs and IAC. Im gonna change my crank sensor and fuel pump and MAF this weekend so hopefully it stops the bad idle.
You would probably come out cheaper just having a mechanic diagnose it for you.
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Old 03-01-2011, 11:19 PM   #25
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Re: Running Lean

I know I'm grasping at straws here, but what would happen if the check valve failed or the cap was not sealing properly? From the standpoint of fuel delivery. (Last question tonite. =)
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Old 03-01-2011, 11:19 PM   #26
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Do you have a tuner. It will bring up the trouble codes
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Old 03-01-2011, 11:20 PM   #27
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I know I'm grasping at straws here, but what would happen if the check valve failed or the cap was not sealing properly? From the standpoint of fuel delivery. (Last question tonite. =)
Not sealed is good cause it vents the tank. A little more than when built but I can't see that causing such a big problem
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Old 03-01-2011, 11:21 PM   #28
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I am a mechanic. My crank sensor is bad so is MAF sensor and my fuel pump went out. Ive already checked my CCRM module it aint that so its my pump. Im not gettin any pressure.
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Old 03-01-2011, 11:24 PM   #29
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I am a mechanic. My crank sensor is bad so is MAF sensor and my fuel pump went out. Ive already checked my CCRM module it aint that so its my pump. Im not gettin any pressure.
Great process of deduction. Where were ya when my last mechanic just kept replacing parts on my moms van and it turned out to be a loose ground
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Old 03-01-2011, 11:26 PM   #30
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I know I'm grasping at straws here, but what would happen if the check valve failed or the cap was not sealing properly? From the standpoint of fuel delivery. (Last question tonite. =)
Well if the check valve failed. The tank would try and suck in creating a vacuum. U can always leave the cap loose and try it. It's not gonna hurt anything. It will eventually set an evap code but no damage. The evap system will not cause your car to run bad. It is in place to keep gas fumes from escaping the fuel system without being burned. Thats why it's there. Its the evaporative emissions system evaporated fuel fumes.
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Old 03-01-2011, 11:26 PM   #31
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Well im not just replacing any old good working parts. There all bad.
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Old 03-01-2011, 11:33 PM   #32
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Well im not just replacing any old good working parts. There all bad.
So you have a bad iac, crank sensor, maf sensor, and fuel pump, all at the same time? Was it struck by lightning?
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Old 03-01-2011, 11:50 PM   #33
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So you have a bad iac, crank sensor, maf sensor, and fuel pump, all at the same time? Was it struck by lightning?
No not all at same time. MAF went out a while back just never changed it till now. I changed my iac a while back. Now ima do my fuel pump this weekend.
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Old 03-01-2011, 11:51 PM   #34
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No not all at same time. MAF went out a while back just never changed it till now. I changed my iac a while back. Now ima do my fuel pump this weekend.
Ok that's cool. And your car is an 08?
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Old 03-01-2011, 11:54 PM   #35
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No its not an 08. Its a 2000 gt
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