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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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  #1  
Old 03-03-2008, 11:04 AM
Big_Man_Brad Big_Man_Brad is offline
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How to check for a vacuum leak?

Ok so i'm pretty sure the more people i talk to and the more i really think about it that i have a vacuum leak somewhere..I hear that poor mileage can come form a vacuum leak..When i first but in my vacuum gauge i had 21.5 vacum..And on my way home yesterday idling in my driveway i had 18..I sprayed starting fluid all under my hood and found no idle pick up...How do i go about finding a vacuum leak???Also as soon as i start my truck should i have maxium vacuum or will it take 5 or 10 minutes..Any help would be greatly appreciated..

Thanks
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1996 ford F-250 ext cab black 460 v8 e40d trans 4X4 Doug Thorley headers with true duels no cats and 2 40 series flow masters add a leaf springs in the front euro taillights bbk twin 61 mm throttle body K&N filter billet grille and bushwacker fender flares sitting in the garage to go on and herculiner..
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Old 03-03-2008, 02:04 PM
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Originally Posted by Big_Man_Brad
Also as soon as i start my truck should i have maxium vacuum or will it take 5 or 10 minutes..Any help would be greatly appreciated..
Vacuum should be generated instantly I would think. Did you check the brake booster and the vacuum resovoirs for leaks? You can isolate there items by disconnecting the vacuum lines that feed them and plugging them temporarilly while you monitor the vacuum signal on a gauge. You might want to try using an unlit propane torch to find a potential leak, a gas will get pulled in easier than a liquid.
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Paul (Conan) O'Brien

1990 5.0HO AOD XLT X-Cab F150 3.55LS, 1994 3.0L 5-sp x-cab Ranger 3.45, 2004 3.0L 5-sp X-cab Ranger Edge 4.10, 2004 2.5L 5-spd Subaru Legacy
1996 Kawasaki ZX11D, 2004 Honda 599, 2008 Kawasaki KLR650
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Old 03-03-2008, 02:47 PM
Big_Man_Brad Big_Man_Brad is offline
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Ok i'm going to go do the brake booster thing right now!!!
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Brad R

1996 ford F-250 ext cab black 460 v8 e40d trans 4X4 Doug Thorley headers with true duels no cats and 2 40 series flow masters add a leaf springs in the front euro taillights bbk twin 61 mm throttle body K&N filter billet grille and bushwacker fender flares sitting in the garage to go on and herculiner..
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Old 03-03-2008, 04:07 PM
Big_Man_Brad Big_Man_Brad is offline
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Ok i did that and i had no success..But i got a code reader and pickup a code..It was number 33..I read on fordfuelinjection.com that it has something to do with the egr..Could this have something to do with my vacuum problem and poor fuel economy.
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Brad R

1996 ford F-250 ext cab black 460 v8 e40d trans 4X4 Doug Thorley headers with true duels no cats and 2 40 series flow masters add a leaf springs in the front euro taillights bbk twin 61 mm throttle body K&N filter billet grille and bushwacker fender flares sitting in the garage to go on and herculiner..
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  #5  
Old 03-03-2008, 04:13 PM
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Yes it could. I would start troubleshooting that code. Test the EGR valve, the EVP, etc.

As far as detecting a leak, it should hold vacuum after you shut the engine off. If the vacuum disappears, then you have a leak somewhere.
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Old 03-03-2008, 04:43 PM
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It won't hold manifold vacuum after shutdown, but it should hold in the reservoir(s). The best way to find a vacuum leak is with a smoke test where smoke is pumped into the manifold (engine off of course) and then it's just a matter of finding where the smoke is coming out to find the leak. However, that's not something an average do-it-yourself driveway mechanic would be able to do. Have you checked ignition timing? Ignition timing can influence both manifold vacuum readings and fuel economy (power too, of course), so if it isn't correct that could be another possibility.
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  #7  
Old 03-03-2008, 07:45 PM
Big_Man_Brad Big_Man_Brad is offline
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The only recent thing i have done to it lately is the performance throttle body and i got the tps set at the right volts..This one might be over my head i might have to take it in..
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Brad R

1996 ford F-250 ext cab black 460 v8 e40d trans 4X4 Doug Thorley headers with true duels no cats and 2 40 series flow masters add a leaf springs in the front euro taillights bbk twin 61 mm throttle body K&N filter billet grille and bushwacker fender flares sitting in the garage to go on and herculiner..
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Old 03-04-2008, 07:53 AM
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Do you have metal juice can vacuum resovoirs on this truck, or the plastic versions? If metal I'll bet $$ they are rusted out on the bottom.
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Paul (Conan) O'Brien

1990 5.0HO AOD XLT X-Cab F150 3.55LS, 1994 3.0L 5-sp x-cab Ranger 3.45, 2004 3.0L 5-sp X-cab Ranger Edge 4.10, 2004 2.5L 5-spd Subaru Legacy
1996 Kawasaki ZX11D, 2004 Honda 599, 2008 Kawasaki KLR650
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  #9  
Old 03-04-2008, 08:08 AM
Big_Man_Brad Big_Man_Brad is offline
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I'm pretty sure there plastic but i'll check...
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Brad R

1996 ford F-250 ext cab black 460 v8 e40d trans 4X4 Doug Thorley headers with true duels no cats and 2 40 series flow masters add a leaf springs in the front euro taillights bbk twin 61 mm throttle body K&N filter billet grille and bushwacker fender flares sitting in the garage to go on and herculiner..
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  #10  
Old 03-04-2008, 03:10 PM
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i think i have a vacuum leak but do not know how to test the pressure. some help please.
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  #11  
Old 03-04-2008, 06:19 PM
Big_Man_Brad Big_Man_Brad is offline
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Yep they are plastic...Since my dad was home today he said he would help me..So my dad said that maybe my timing should be increased and first we did it by ear and he said it sounded the best then we did it with the light so now it's set at 17 degrees..He also told me that i got a miss..So we checked all the wires and they were good..I think its the passenger back cylinder..After work he said that were going to do a compression test..I hope everything goes ok...
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Brad R

1996 ford F-250 ext cab black 460 v8 e40d trans 4X4 Doug Thorley headers with true duels no cats and 2 40 series flow masters add a leaf springs in the front euro taillights bbk twin 61 mm throttle body K&N filter billet grille and bushwacker fender flares sitting in the garage to go on and herculiner..
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Old 03-04-2008, 06:23 PM
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On the 460, does the PCV valve dump into number 8 like on the 302?

If that is the case, it's pretty common to run into issues with the number 8 cylinder (rear passenger side) in high mileage motors.

Let us know the compression numbers.
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  #13  
Old 03-04-2008, 06:40 PM
Big_Man_Brad Big_Man_Brad is offline
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Hmm i'm not sure on that one...I'll let you know though...
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Brad R

1996 ford F-250 ext cab black 460 v8 e40d trans 4X4 Doug Thorley headers with true duels no cats and 2 40 series flow masters add a leaf springs in the front euro taillights bbk twin 61 mm throttle body K&N filter billet grille and bushwacker fender flares sitting in the garage to go on and herculiner..
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  #14  
Old 03-06-2008, 11:06 AM
Big_Man_Brad Big_Man_Brad is offline
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The compression is super the guy said..I don't remember the numbers right now..Than we hooked it up to his computer...Got not one single code..I was bumbed...He said my problem could be that the intake manifold where it hooks up to the throttle body its stightly bigger the throttle body for the mileage loss...And for the vacuum its where its suppose to be..He had no idea how i was getting 21.5 vacuum before...
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Brad R

1996 ford F-250 ext cab black 460 v8 e40d trans 4X4 Doug Thorley headers with true duels no cats and 2 40 series flow masters add a leaf springs in the front euro taillights bbk twin 61 mm throttle body K&N filter billet grille and bushwacker fender flares sitting in the garage to go on and herculiner..
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  #15  
Old 01-03-2010, 06:44 PM
rick_76 rick_76 is offline
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83 f100 4.9 6 cyl

I recently changed the intake manifold because it was leaking. I rebuild the carborator and it seems like I have a vacuum leak somewhere. I checked the compression on number 6 and I'm getting 95 psi and the rest are between 130-150 psi.
Does anyone know how I can fix this leak...?
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Old 01-03-2010, 06:44 PM
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