Exhaust leak- surging - Defender Source
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  #1  
Old July 9th, 2013, 11:22 PM
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Tim Riccardi
1995 d90
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Exhaust leak- surging

I know this might have been asked many times, but I did not see anything in my searches. .

I have a stock 95 3.9 that has a exhaust leak between the pass side exhaust manifold and the down pipe.

I need to know if this would cause surging and a hesitation? I know it will make the truck run rich, but surge, I don't know.

I have a 4.6 that I am rebuilding and I just want to make sure the truck is running as good as possible before the swap.


Thanks Tim
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  #2  
Old July 10th, 2013, 02:59 AM
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Chris Davis
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Plenty of things cause it, not typically an exhaust leak, however. Usually dirty/MAL idle air control valve or vacuum leak. Usually not O2 sensors unless only occurring after warm up. I'd look for vacuum or IACV.
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Old August 1st, 2013, 12:56 AM
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Tim Riccardi
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Thank you for the response.

I just installed the cats back on the vehicle (it was a trail vehicle only) and removed the 470 ohm resistor. That is the one with no cats. So it is back to "normal".

The problem is the same as it was before I added the cats/tune resistor back to NAS. So I dont think its the O2's, since they were off when the non cat tune resistor was installed.

I checked the mech and vacuum advance and they seem to be working correctly. But, when I was checking the timing, it jumped around a good amount. I dont know if this is normal for a 3.9 or not. I would say it was jumping from 6-10 advance and the RPM's were 675-775. This was measured from the number one spark plug wire via timing light rpm meter.

The truck does have 120,000 miles on the original timing chain, but I have a 4.6 going in soon.
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  #4  
Old August 1st, 2013, 11:20 AM
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Jason England
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Spray liberal amounts of carb cleaner on the air hoses and other 'air' parts connected to the plenum ... after the MAF ... The revs will drop where cleaner is sucked in helping you locate a leak.


Consistent running is a function of having a balanced air fuel mix ... if you have an air leak then the truck will compensate by regulating the air via the AICV or increasing the fueling by opening the injectors longer. This is the map in the ECU. There are other inputs like fuel temp and engine temp ... but you get the idea.

If the timing is varying like Jeff suggests then the ECU compensates with air and fuel ... you can see how the engine could struggle to be consistent.
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Old August 1st, 2013, 12:13 PM
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Tim Riccardi
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I will try the carb cleaner later tonight.

I did break the dizzy down today and the weights/springs were ok. I just don't know how much a worn timing chain will effect the timing. Is it all metal or does it have nylon like some GM's?

What do you guys think about the truck running worse when cold? It almost runs perfect when warm, but that might take 2 hours of driving on some days.
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Old August 2nd, 2013, 05:48 PM
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Tim Riccardi
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Update:

The Vacuum advance is dead, it works 25% of the time, so I have just disconnected. I capped off the vacuum advance port on the Throttle Body, so no leaks.

I have been playing with the initial advance and have settled on 12* (30 total w/mech @ 1800). I know this is higher than most, but I have no vacuum advance and the car seems to be running better. Now the stumble is still there.

If I have in third gear and start coming up my drive (1200 RPM.s) there is a hesitation. Now I have been checking the mech advance and that is where it starts to come in. How smooth should it run?

I have a hard time believing it could be the coil, so my thoughts are on the ignition module, because it is a fast stumble.

I have no vacuum leaks that I can tell.
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  #7  
Old August 2nd, 2013, 06:07 PM
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Jason England
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Quote:
Originally Posted by boxerhips View Post
I will try the carb cleaner later tonight.

I did break the dizzy down today and the weights/springs were ok. I just don't know how much a worn timing chain will effect the timing. Is it all metal or does it have nylon like some GM's?

What do you guys think about the truck running worse when cold? It almost runs perfect when warm, but that might take 2 hours of driving on some days.
So you have thermostat failed open? Or

Faulty engine temp sensor. Not the one for the gauge the one for the ECU.
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Old August 2nd, 2013, 06:08 PM
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Jason England
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Trucks with Mallory's run like a sewing machine. Mine runs like a land rover.
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Soapy water / KY jelly, etc. is is basically a must. Yes, good idea to remove trim panels - only takes 5 more minutes to do so.
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  #9  
Old August 2nd, 2013, 09:13 PM
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Tim Riccardi
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How would a faulty temp sensor cause the stumble? Running rich I understand, the stumble seems like a spark issue.

I was wondering if a faulty ignition module can get worse when cold? Today was about 85 for me. I'll drive it home later and it should be about 65, I'll post results when I get home.
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