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I think I am chasing a vaccum leak. Any advice ? Login/Join 
7.62mm Crusader
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1998 Buick 3800 non super charged. Plugs are new AC. Shes been at rough idle about a week now. I am hoping its not intake and plenum, even though thats not too costly. Doing a carb cleaner check tomorrow. I found a vac line diagram to follow. I actually hope its IAC valve or EGR. Had it scanned tonight but check engine light was gone and no stored codes. Anyone have knowledge of the 3800 ?
 
Posts: 13728 | Registered: December 23, 2008Reply With QuoteReport This Post
7.62mm Crusader
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Originally posted by David Lee:
1998 Buick 3800 non super charged. Plugs are new AC. Shes been at rough idle about a week now. I am hoping its not intake and plenum, even though thats not too costly. Doing a carb cleaner check tomorrow. I found a vac line diagram to follow. I actually hope its IAC valve or EGR. Had it scanned tonight but check engine light was gone and no stored codes. Anyone have knowledge of the 3800 ?
She idles at 1000 to 1100 cold, 800 fully warm and 700 under load.
 
Posts: 13728 | Registered: December 23, 2008Reply With QuoteReport This Post
186,000 miles per second.
It's the law.




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Have you checked the fuel filter?
 
Posts: 1579 | Registered: August 19, 2001Reply With QuoteReport This Post
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Try cleaning the air intake throat.

98 still has the aluminum intake?




 
Posts: 6930 | Registered: October 15, 2008Reply With QuoteReport This Post
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Check coil packs, spark plug wires and spark plugs? I'm assuming you checked those first. Despite the fact that you just replaced them make sure you did not accidently crack one.

I'm assuming you checked for arcing wires and coils also? No codes leads me to believe that it's in a non SES indicator sensed part. I don't remember if that is an electronic EGR valve, if not it could be stuck slightly open by carbon buildup and not throw a code. I doubt the IAC is involved, that should throw a code as it is fed thru the PCM.
 
Posts: 4746 | Location: Livingston County Michigan USA | Registered: August 11, 2002Reply With QuoteReport This Post
7.62mm Crusader
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Originally posted by Excam_Man:
Try cleaning the air intake throat.

98 still has the aluminum intake, right?
I believe its aluminum and think the gaskets and plenum are only 2 years old.
 
Posts: 13728 | Registered: December 23, 2008Reply With QuoteReport This Post
Man Once
Child Twice
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Run any Tekron through it largely?
 
Posts: 9622 | Location: NE OHIO | Registered: October 22, 2004Reply With QuoteReport This Post
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A mechanic I worked with years ago diagnosed vacuum leaks with an unlit propane torch. He would set the flow rate very low and run the nozzle along vacuum lines. When the leak was located the idle would smooth out due to the mixture getting better. Don't know if this will work on later model vehicles but it sure made quick work of vac leaks back when.


A poor widows son.

 
Posts: 2060 | Location: See der Rabbits, Iowa | Registered: June 12, 2007Reply With QuoteReport This Post
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The black plastic intakes are known for cracking around the EGR tube. Then antifreeze goes in the intake valves.




 
Posts: 6930 | Registered: October 15, 2008Reply With QuoteReport This Post
7.62mm Crusader
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Originally posted by shovelhead:
Check coil packs, spark plug wires and spark plugs? I'm assuming you checked those first. Despite the fact that you just replaced them make sure you did not accidently crack one.

I'm assuming you checked for arcing wires and coils also? No codes leads me to believe that it's in a non SES indicator sensed part. I don't remember if that is an electronic EGR valve, if not it could be stuck slightly open by carbon buildup and not throw a code. I doubt the IAC is involved, that should throw a code as it is fed thru the PCM.
I can check the EGR tomorrow. I have new wires, Duralast. ACs on it now but they're ageing. I mentioned the IAC as its pintle gets carboned too. Oyyyy..fun.
 
Posts: 13728 | Registered: December 23, 2008Reply With QuoteReport This Post
7.62mm Crusader
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Originally posted by bettysnephew:
A mechanic I worked with years ago diagnosed vacuum leaks with an unlit propane torch. He would set the flow rate very low and run the nozzle along vacuum lines. When the leak was located the idle would smooth out due to the mixture getting better. Don't know if this will work on later model vehicles but it sure made quick work of vac leaks back when.
Ive heard smoke test too but will only have carb cleaner.
 
Posts: 13728 | Registered: December 23, 2008Reply With QuoteReport This Post
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BTW, a little FYI. We had a 92 Bonneville with a 3800 that had the unnerving fault of stalling out while driving. Just shut down for no reason, no SES codes. I worked in a Pontiac dealership at the time, our techs could find no reason for the shutdown. Really fired up the wife as it shut down on her in the fast lane at her customary 80-85 mph on I-96 one morning.

I found it one day after my wife got a new car and I took it over. Stall out, I pulled off the road. Car cranked normally, no fire. Cycled the ignition on and off. Second crank I am looking at the tachometer, no movement of the tach needle. Suddenly as I am watching the needle, it jumps up, car starts up. Got back to work, replaced the crank sensor, all good after that.

That failure would not trigger a SES light as the crank signal was lost to the PCM. Acted like the ignition switch was turned off, PCM read this as shut down.

This might save others some grief with diagnosis, I hope.
 
Posts: 4746 | Location: Livingston County Michigan USA | Registered: August 11, 2002Reply With QuoteReport This Post
7.62mm Crusader
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Originally posted by Excam_Man:
The black plastic intakes are known for cracking around the EGR tube. Then antifreeze goes in the intake valves.
Only coolant loss is up front at a fitting or hose. I keep after that.
 
Posts: 13728 | Registered: December 23, 2008Reply With QuoteReport This Post
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From memory I think that if the IAC is stuck open it increases the idle speed and sets a code as the pintile reading does not match the TPS.
 
Posts: 4746 | Location: Livingston County Michigan USA | Registered: August 11, 2002Reply With QuoteReport This Post
7.62mm Crusader
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quote:
Originally posted by shovelhead:
BTW, a little FYI. We had a 92 Bonneville with a 3800 that had the unnerving fault of stalling out while driving. Just shut down for no reason, no SES codes. I worked in a Pontiac dealership at the time, our techs could find no reason for the shutdown. Really fired up the wife as it shut down on her in the fast lane at her customary 80-85 mph on I-96 one morning.

I found it one day after my wife got a new car and I took it over. Stall out, I pulled off the road. Car cranked normally, no fire. Cycled the ignition on and off. Second crank I am looking at the tachometer, no movement of the tach needle. Suddenly as I am watching the needle, it jumps up, car starts up. Got back to work, replaced the crank sensor, all good after that.

That failure would not trigger a SES light as the crank signal was lost to the PCM. Acted like the ignition switch was turned off, PCM read this as shut down.

This might save others some grief with diagnosis, I hope.
Even the old cars are pretty smart. TPS sensor crossed my mind but I havnt a clue how it would act. Sort of sticking with vaccum or EGR for now. They sure got a load of sensors.
 
Posts: 13728 | Registered: December 23, 2008Reply With QuoteReport This Post
Page late and a dollar short
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quote:
Originally posted by David Lee:
quote:
Originally posted by Excam_Man:
The black plastic intakes are known for cracking around the EGR tube. Then antifreeze goes in the intake valves.
Only coolant loss is up front at a fitting or hose. I keep after that.


Also another FYI. If you have the plastic fittings at the front for coolant hoses, GM replaced those with metal ones. Get them. I don't know if the aftermarket has them available in metal too.
 
Posts: 4746 | Location: Livingston County Michigan USA | Registered: August 11, 2002Reply With QuoteReport This Post
7.62mm Crusader
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quote:
Originally posted by shovelhead:
From memory I think that if the IAC is stuck open it increases the idle speed and sets a code as the pintile reading does not match the TPS.
Thank you. I think I can rule out IAC then. I dont know how to test the coil pack.
 
Posts: 13728 | Registered: December 23, 2008Reply With QuoteReport This Post
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I retired from GM dealership parts departments the end of June, I figured 47 years in it was enough for any person..........
 
Posts: 4746 | Location: Livingston County Michigan USA | Registered: August 11, 2002Reply With QuoteReport This Post
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Coil pack, look for arcing to ground with the engine running in the dark. May not be real visible, take your time. Also, a small grayish white "witness mark" may show on the coils or the wires where they arc to ground.

Those coil packs were usually "go or no go".
 
Posts: 4746 | Location: Livingston County Michigan USA | Registered: August 11, 2002Reply With QuoteReport This Post
7.62mm Crusader
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Originally posted by shovelhead:
I retired from GM dealership parts departments the end of June, I figured 47 years in it was enough for any person..........
Man their prices are high. I priced sway bar bushings today at Buick in Burlington, KY, I politely told them I will buy elsewhere. $80.00 for 1 end. Bolts are $5.00 each, WTH ? Auto Zone ordered me a kit with everything for $30.00 tax included.
 
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