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3800 Mystery vacuum leak by Threedog
Started on: 06-21-2015 07:03 PM
Replies: 4 (247 views)
Last post by: Threedog on 06-22-2015 06:21 PM
Threedog
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Report this Post06-21-2015 07:03 PM Click Here to See the Profile for ThreedogClick Here to Email ThreedogSend a Private Message to ThreedogEdit/Delete MessageReply w/QuoteDirect Link to This Post
Engine is a 3800 Series II(NA) in a 1986 Pontiac Fiero.

It SOUNDS like a vacuum leak,LOUD VIDEO here is a video of it being shut down and the massive "slurping" sound after it does(pardon the loud engine, there currently no exhaust after the headers).
The vacuum leak sounds like it is coming from the throttle body, there is a large hissing sound when the engine runs.

-I have gotten a few codes, two for random misfires and one for "bank 1 running too lean". The car idles alright, but if you give it gas it will idle too low, boost RPMS trying to live, and repeat until it stalls.
-I have checked fuel pressure, it holds steady at 48-50PSI(OE recommended 45-55)
-The MAF sensor looks like this, and has been cleaned. It also gave constant Hz readings followed by steady increases and decreases with engine RPM(suggesting it was working). The MAP sensor was also removed and cleaned.

Here are the Vac lines:
Throttle body has two ports, the upper is stock, leads to the fuel pressure regulator(on the right) and purge solenoid valve(on the left). The fuel pressure regulator is new, working, and receiving vacuum. The bottom throttle port is plugged.


this is the purge solenoid valve. The line feeding into the back of it leads to the upper port on the throttle body(the line on the left in the previous picture) and the other line goes strait to the purge canister, pictured here.

Finally, here is the last vac hookup, the large hose runs to the brake booster(like stock), and the small one is labeled as "accessory", which I have plugged as I have no use for it.

Things I have tried/ideas:
-Plugging each individual vac line, the problem remained each time.
-I just replaced the thermostat/housing/gasket, could I have ****ed that up? Could it cause the sound?
-Bank one headers to crossover pipe bolts are loose, which is causing a pretty large exhaust leak. Could that have thrown the "bank 1 too lean" code?

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Threedog
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Report this Post06-22-2015 10:54 AM Click Here to See the Profile for ThreedogClick Here to Email ThreedogSend a Private Message to ThreedogEdit/Delete MessageReply w/QuoteDirect Link to This Post
Bump

Anyone?
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2002z28ssconv
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Report this Post06-22-2015 04:32 PM Click Here to See the Profile for 2002z28ssconvClick Here to visit 2002z28ssconv's HomePageSend a Private Message to 2002z28ssconvEdit/Delete MessageReply w/QuoteDirect Link to This Post
Get you a can of ether (starting fluid) and gently spray it around where you hear the sucking sound. If you spray near a vacuum leak you will hear an immediate change in RPM. Examine that area closely. Be sure to look for cracks in the black plastic intake manifold too.

[This message has been edited by 2002z28ssconv (edited 06-22-2015).]

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84fiero123
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Report this Post06-22-2015 06:12 PM Click Here to See the Profile for 84fiero123Click Here to Email 84fiero123Send a Private Message to 84fiero123Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by 2002z28ssconv:

Get you a can of ether (starting fluid) and gently spray it around where you hear the sucking sound. If you spray near a vacuum leak you will hear an immediate change in RPM. Examine that area closely. Be sure to look for cracks in the black plastic intake manifold too.



I like using the starting fluid trick but have heard others use a propane torch, not lit of course and it will do the same thing, engine revs.

Then there is the smoke method as well as just connecting a vacuum pump to one of the line to see if it hold vacume.

Steve

------------------
Technology is great when it works,
and one big pain in the ass when it doesn't



Detroit iron rules all the rest are just toys.

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Threedog
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Report this Post06-22-2015 06:21 PM Click Here to See the Profile for ThreedogClick Here to Email ThreedogSend a Private Message to ThreedogEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thats the odd thing. I have tried almost everything. Theoretically the engine should hold a good idle with everything plugged short of the fuel pressure reg(right?), but it doesnt.
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