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Exhaust backpressure: How much is too much?

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Old 12-17-2010, 06:18 PM
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Exhaust backpressure: How much is too much?

2000 F-250 (stock 7.3L 4x4 auto 129,000 miles)

Backpressure at idle is 40ish psi (way too high I think? my sig. truck is 16 psi at idle)


Codes: p0470, p0478

What do you guys think?
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Old 12-17-2010, 06:26 PM
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I think you have a bad sensor....
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Old 12-17-2010, 06:30 PM
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I agree with Clay. You shouldn't have any back pressure at idle.
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Old 12-17-2010, 06:32 PM
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BTW, the truck is quite doggy, and won't build more thyan about 10 psi of boost. I'm thinking stuck EBPV????
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Old 12-17-2010, 06:40 PM
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I know when you unplug it your computer defaults to 40 psi so like clay said it's probly bad or a bad connection. Wet plug, loose wires, something. It should be around 12 to 15 at idle. I belive it's real close to barometric pressure.
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Old 12-17-2010, 06:48 PM
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It was like 42.30 at idle and got up to almost 45. when I got in it...

(as I said earlier, my truck is 16 at idle) (cold)
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Old 12-17-2010, 07:11 PM
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Quote:
Originally Posted by Kwikkordead View Post
I agree with Clay. You shouldn't have any back pressure at idle.
Dan is correct, except it will show ~14psi because of normal atmospheric pressure, 29.92 hg is standard.
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Old 12-17-2010, 07:19 PM
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Quote:
Originally Posted by Riffraff Performance View Post
Dan is correct, except it will show ~14psi because of normal atmospheric pressure, 29.92 hg is standard.
See I don't even know the difference in atmosphreic and barometric pressure but I was close.
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Old 12-17-2010, 07:25 PM
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Just thinking outloud here but could he remove the sensor and start the truck and see how much air is coming out, if it's 40# you would be able to feel it against the hood with it open. I've checked mine just to see how much pressure was coming out and I had to reach pretty close to the tube to feel the air. Also a word of caution, the air will be VERY HOTTT!!!
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Old 12-17-2010, 07:30 PM
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The two possibilities to this if it's not the sensor itself would be a plugged exaust (Cat or muffler) or a closing EBPV. You can unplug the EBPV to rule this out. Did this problem happen to start on a cold day where your EBPV was just opening and giving you these readings?
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Old 12-17-2010, 08:08 PM
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Thanks guys for the help! I just unhooked the EBPV, drove it, no difference. Still shows 40 ish psi (from 40.5-46.00)


I can check the EBP sensor tommorow.

A little more info: The owner said he got a superchips tuner a while back, and it made zero difference in performance (he then returned the tuner)

It feels pretty flat through the rpm band, none of that turbo feel from 2000 on up....
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Old 12-17-2010, 08:52 PM
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Anybody have more ideas?
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Old 12-18-2010, 12:12 AM
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Look at your EBPV linkage. If the rod is extended out all the time, the butterfly is in the closed position. If the rod is retracted, the butterfly should be open. This is accurate only if the butterfly and operating arm are firmly attached to the shaft. It is highly unlikely that they have come loose.
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Old 12-18-2010, 06:07 AM
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I'm on my phone so I can't see your sig but what kinda exaust do you have? Seems like a long shot but if you still are running factory maybe something is plugged. Did this high pressure arise all of a sudden or did you notice you were having power issues and started diagnosing?
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Old 12-18-2010, 08:43 AM
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This isn't my truck, it is a customers, and yes it has stock exhaust.

Story: I had the truck towed in because it started running very rough and then would not restart. (passenger side wiring harness unplugged under the VC)

He said for me to drive the truck after I got it running to see what I thought about the power, because he said it seemed doggy and won't hold its own up hills without downshifting (HE ALSO INSTALLED A SUPERCHIPS TUNER AND IT MADE NO DIFFERENCE IN POWER) the tuner is not on the truck now.

I have found that I can easily outperform it with my 95 5speed, and I mean easily! (this one has to go to 3k to get done what my truck can do at 2200rpm) And this truck is an automatic!!!!! Soi there is deffinately something wrong. It is also getting bad fuel economy (6.4 regen like fuel economy)

I am going to swapthe EBP sensor and see if I get the same reading, also ceck the up-pipes to the turbo.

I will post back after some more diagnoses this morning.

Thanks everyone for the ideas! Please keep them coming!
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