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Tool Talk Discussion Forum

Major Vacuum Leak '93 Bonnieville

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Glenn F.

02-26-2008 15:20:41




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My '93 Bonnieville recently developed what I assume is a major vacuum leak. It is hard starting, will not idle, and has almost no brakes. The only way I have any brakes is by applying them sharply, let off, apply sharply, etc. The car is undrivable.

I blocked off the vacuum supply to the brake assist, and it's no better. I do not see any problems.

Are there any "typical" places I should be looking? It seems it should be easy to find...?


Thank you,
Glenn F.

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Leland

02-27-2008 22:58:31




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 15:20:41  
at lot of those gm's had bad intake gaskets try spraying wd 40 around intake where it bolts to heads if it smooths out you found the leak



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Glenn F.

02-27-2008 05:41:28




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 15:20:41  
Update:

I listened as I pressed brake peddle and was able to hear a hiss. Checked and found a broken line at passenger's rear, (garage floor is wet from melting snow, so fluid of floor was not readily visable). So, brake problem is not vacuum related.

I am thinking teh idle/dying problem is the EGR valve. I took it off and tried to clean/free it up a couple days ago. It worked good for a few starts and then started dying again. Last night I took it off and fiddled with it again, put it back on, and the car runs fine. It looks like I'll be replacing it.

Thank you to each of your for your speedy/knowledgable responses. I can't believe how much I appreciate you guys/this site.

I'll post back when I get the car back in service.


Glenn F.

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dave guest

02-26-2008 19:18:34




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 15:20:41  
You better find it or I would have to buy it. Curiosity killed the cat. No. I think it livened it up. Are you sure all cylinders are firing?



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RusselAZ

02-26-2008 19:16:39




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 15:20:41  
The EGR valve is stuck open. Any other vacuum leak you could hear.



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Bob Huntress

02-26-2008 18:38:37




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 15:20:41  
Take a can of starter fluid, and start near the brake booster. Spray a small amount in areas along the firewall, and then the top of the engine. When you hear the engine start to race very slightly, it is where the vacum leak is. You will need to spray in close as you pin point where the general area of the leak is. The vacum leak will pull whatever it draws into the intake, and subsequently the cylinder, so when the ether is drawn into the cylinder of a running engine, it will cause a momentary racing. Using this method, you can check each line and component where a leak could be present. The closer you are to the leak, the more racing sound you will hear.

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shannon from ohio

02-26-2008 17:41:25




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 15:20:41  
"O ring or pcv valve failure in the pcv cap?" (This is located on the end of the plastic plenum (Right side) turn cap about a quarter turn and it will come off,you should see top of pcv valve.This is assuming you have the 3800 Series II Engine..... ....



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[email protected]

02-26-2008 17:22:09




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 15:20:41  
If you are losing that amount of vacuum, it should be really easy to hear and locate. It will sound like someone blowing through a straw. You can also take a small propane torch, open the valve and don't ignite it. Once the engine picks up RPM, while moving it around the top of the block, you are close to the leak.



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Goose

02-26-2008 16:57:59




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 15:20:41  
Does it have a plastic or metal upper plenum? In the mid '90's some rocket scientist at GM designed a polymer plastic upper intake plenum that was prone to deteriorating and leaking, but I'm not sure of the year they started using them. The replacement plenums were metal. Leave it to GM to find a way to screw up an otherwise bullet-proof engine.

I have a '92 Olds 88 with the same 3.8 engine, but it has a metal upper plenum.

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Glenn F.

02-26-2008 17:49:51




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Goose, 02-26-2008 16:57:59  
Yup....Plastic. No visable cracks. Possibly a bad seal where it bolts on...?

Glenn



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Glenn F.

02-26-2008 17:10:19




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Goose, 02-26-2008 16:57:59  
You're smarter than me. Is the plenum the six combined "tunnels" which make up the mixing chamber? They are right on top of the engine.

I'm gonna check with a magnet, but when snooping around I tapped and squeezed them, as they have a rather "plastic" look which made me curious. If they are plastic, it is rigid plastic.

Thanks,
Glenn



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bradk

02-26-2008 16:26:04




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 15:20:41  
Sounds like EGR valve is stuck open. ~brad



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Glenn F.

02-26-2008 17:18:01




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 Re: Major Vacuum Leak '93 Bonnieville in reply to bradk, 02-26-2008 16:26:04  
I had questioned the EGR valve. I removed it and (not knowing how a new one would react) depressed each of the three spring loaded "valves," while soaking them in carb cleaner. They appear to be functioning properly.

The only difference between me and the shade tree mechanic is the garage roof over my head....

Thanks,
Glenn



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bradk

02-26-2008 17:36:56




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 17:18:01  
OK -Thought of another common thing on the older 3800.Check the PCV grommet located at RF corner of the engine(not vehicle),firewall side, at intake.A rubber elbow goes from an intake runner to the underside of intake (crankcase). The elbow goes over the PCV valve which sits in the grommet.The grommet or elbow may be shot from the years of heat. Clear as mud right? ~brad



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Mulligan

02-26-2008 16:20:06




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Glenn F., 02-26-2008 15:20:41  
Take a regulated air hose and blow air up the power booster vac line into the motor and listen.

Perhaps take a 4' chunk of garden hose and put one end to your ear and use the other as a probe.

perhaps if you get the flow right you will find the leaking air.



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504-2

02-26-2008 18:44:48




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 Re: Major Vacuum Leak '93 Bonnieville in reply to Mulligan, 02-26-2008 16:20:06  
Glen, I have found 5 or 6 plastic nipples that cracked and then broke off when I moved the hose around. All were older 3800(I keep forgetting it has been 5 yr since I worked at the shop)it is the vacuum main line at the engine that goes to the brake booster on the passenger side. They were a real bear to get out, I would grind down a hack saw blade and cut it in three pieces and then use a screw driver to chisel it out. The hose has a 90 where it goes on the barb.

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504-2

02-27-2008 16:33:33




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 Re: Major Vacuum Leak '93 Bonnieville in reply to 504-2, 02-26-2008 18:44:48  
Well I said it had been awhile, the line I was thinking about is a bypass hose for anti freeze not vacuum.



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