Exhaust leak / rough idle / no MIL? Show Senior User Thread Starter Join Date: Jan 2008 Location: Issaquah, WA Posts: 105 Likes: 0 Received 1 Like on 1 Post Exhaust leak / rough idle / no MIL? I have a '94 F250 7.5L with a rough idle that I've been poking at for a while. I decided to pay a professional mechanic to diagnosis the issue. I was informed that there is a broken bolt on the exhaust manifold which is causing a lean condition. I know about the leak, but haven't bothered with it because it quiets down once warmed up. A couple questions: The engine idles rough cold and warm. I'm not that familiar with OBD I, but I assume that the o2 sensors don't come in to play until the PCM goes in to close loop once warmed up. Could an exhaust leak really cause a rough idle when the engine is cold? If the engine is running leaning, wouldn't I see a MIL? Again, I'm not that well versed in OBD I but I'd be really surprised that something with an O2 sensor wouldn't trigger a MIL if it was running lean. The only relevant codes I have is 327 (EGR feedback signal is/was low – EVR or PFE) and 18 (SPOUT circuit grounded). That seems a more likely culprit of the rough idle than the exhaust leak. Any thoughts or advice? Join Date: Jul 2016 Location: Millcreek WA. Posts: 143 Likes: 0 Received 0 Likes on 0 Posts Exhaust Leak Yes a exhaust Leak can cause a rough idle your engine runs on a set amount of vacuume probily about 17 psi so with the exhaust Leak your vacuume is going to be lower making tho enginenew run rough.But I have a tool I made to locate even the smallest of leaks. Go to one of my post and check the tool out.Ultimate Automotive Leak Detector. Join Date: May 2011 Posts: 4,734 Likes: 0 You are correct, the o2 sensor isn't involved until it's warm. How bad is the leak? Work on the stuff you know isn't right, even if you don't think they're contributing to your drivability. Egr system is easy to test and exhaust leaks are pesky at the very least. Can also unplug the egr and see if idle cleans up. Senior User Thread Starter Join Date: Jan 2008 Location: Issaquah, WA Posts: 105 Likes: 0 Received 1 Like on 1 Post The leak isn't too bad. Plus it pretty much goes away once the engine warms up and everything expands a bit. I'll try the EGR idea. The only reason I'm reluctant to mess with the manifold is the bolts/nuts are very rusted and I really don't want to deal with snapping a bolt that I can't get out and having to pull the head for a machinist to fix. If the EGR doesn't have an effect, I'll just have to commit to the manifold. Thank you. Join Date: Oct 2005 Location: Kentucky Posts: 18,417 Quote: Originally Posted by cscott952 I have a '94 F250 7.5L with a rough idle that I've been poking at for a while. The only relevant codes I have is 327 (EGR feedback signal is/was low � EVR or PFE) and 18 (SPOUT circuit grounded). That seems a more likely culprit of the rough idle than the exhaust leak. Any thoughts or advice? You will never get a mix of two AND three digit codes. It's two OR three digits. Your 1994 truck should display three codes. Please re-run the KOEO tests and stored code (Continuous Memory aka CM) display. List them by number and when they were displayed. Join Date: Jul 2016 Location: Millcreek WA. Posts: 143 Likes: 0 Received 0 Likes on 0 Posts Exhaust Leak If you want to locate a exhaust Leak real easy go to my post on exhaust smoking on one side and check out the tool and the description this tool really works for everything. Senior User Thread Starter Join Date: Jan 2008 Location: Issaquah, WA Posts: 105 Likes: 0 Received 1 Like on 1 Post Quote: Originally Posted by Ultimate Automotive Leak Detector If you want to locate a exhaust Leak real easy go to my post on exhaust smoking on one side and check out the tool and the description this tool really works for everything. I know where the leak is. My question is if it could cause a rough idle Trending TopicsJoin Date: Jul 2016 Location: Millcreek WA. Posts: 143 Likes: 0 Received 0 Likes on 0 Posts Exhaust Leak Yes of course a leak depending how large will affect the Idle of the engine the hole system counts on so much back pressure and that in turn creates a set amount of vacuum and with one or the other not working correct then a rough Idle you will get most times like I said depends how big the leak is. Join Date: May 2011 Posts: 4,734 Likes: 0 No no....engine needs no back pressure, efi system reads no back pressure. Exhaust has nothing to do with vacuum on a stock truck application of this nature. Carry on. Join Date: Jul 2016 Location: Millcreek WA. Posts: 143 Likes: 0 Received 0 Likes on 0 Posts No back preasure Sorry my bad I knew that was thinking without back pressure no vacuum when in reality vacuum come from the pressure of the exhaust moving clearly with no back pressure again sorry and thank you for the correction. Senior User Thread Starter Join Date: Jan 2008 Location: Issaquah, WA Posts: 105 Likes: 0 Received 1 Like on 1 Post The idle is really lean. My WB O2 sensor showed ~20-22 AFR. I unplugged the O2 sensor which brought it to about 13.5. The idle remained rough, but obviously that lean condition needs to be fixed. I'm going to drive it a bit with and without the 02 sensor connected to see what the cruise and WOT AFRs are out of curiosity. I suspect the O2 sensor is bad, so I'll replace it. I'll also repair the exhaust just to rule that out as a cause and make the truck sound nicer when its cold. Thread Thread Starter Forum Last Post Jay72V10 Exhaust Systems 2 02-14-2013 10:18 PM Domestic_Nuwbee 1987 - 1996 F150 & Larger F-Series Trucks 20 12-23-2010 12:41 AM remmers 1987 - 1996 F150 & Larger F-Series Trucks 4 03-23-2007 03:21 PM FARM69 Small Block V8 (221, 260, 289, 5.0/302, 5.8/351W) 6 10-16-2005 12:39 PM venumb Bronco II 9 01-03-2001 12:05 AM What problems can an exhaust leak cause?When your vehicle has an exhaust leak, your air-to-fuel ratio balance could be disrupted. Improper air-to-fuel ratio can cause the engine to run less efficiently, causing it to reduce overall engine efficiency. Smelling gas fumes inside your vehicle can be a sign of an exhaust leak.
Can exhaust leak cause engine to shake?Bad Vibrations
If a car vibrates it can mean a lot of different things, but one of the most common causes is an exhaust leak. You will often feel a small constant vibration while driving that will get worse as you accelerate.
What are the signs of an exhaust leak?Here are 5 indicators you have an exhaust leak.. 1.) Loud Operation. If you have an exhaust leak, one of the most noticeable symptoms is noise. ... . 2.) Loss of Power. An engine runs optimally when exhaust flow is uninterrupted. ... . 3.) Poor Fuel Economy. ... . 4.) Exhaust Odor While Driving. ... . 5.) Vibration.. Can clogged exhaust cause rough idle?Yes, a clogged catalytic converter can cause rough idle.
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Can a exhaust leak cause rough idle
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