Another Vacuum Question

Galligher · 07-10-2001, 10:12 AM

I have a 91 LX with an AOD. I have not had it that long and it has a hesitation/backfire every once in a while when the engine is under load. I hooked a vacuum gauge up to it last night and got a steady 15 PSI (Vacuum) at 800 rpm idle. If I "goosed" it, vacuum dropped to nothing and then raised to 19 (~1000RPM). When idle came back down, it dropped back to 15.
I tried using propane, but it did not work. I opened the line that normally goes to the diverter valve and let propane in it and noticed no increase in RPM???? I then sprayed carb cleaner in it and again nothing??? I also noticed that when I disconnected the line vacuum did not change. This is what is really leading me to believe I have a leak, or is it that the line is small enough not to have a great effect.
Any help???
Thanks,
Brian

PKRWUD · 07-10-2001, 02:50 PM

15" is a little on the low side. Warm up your engine, with the vacuum gauge connected and while it's idling, disconnect the gauge, but don't plug the hose. let me know what happens to the idle when you do this.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

jimberg · 07-10-2001, 03:40 PM

Is everything stock? A more radical cam will give you lower vacuum at idle. I have an E303 and get 12" at idle.

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351W 89 Mustang GT Convertible

galligherb · 07-11-2001, 09:00 AM

Well, I did just as you said and here are the results: Idle increased very little (could hear but couldn't really see on the tach) and it ran a little rougher. The engine is stock. I forgot to mention this before, but I am pretty sure it has a head gasket leak (uses some water, no external water). But I don't think that is all of my problems, I think I have vacuum leaks as well. I will be changing head gaskets soon. I just don't understand why the propane or carb cleaner did not really work. I have thought about starting fluid, but ????

PKRWUD · 07-12-2001, 12:36 AM

If the idle increased when you disconnected the vacuum gauge, then it's slightly rich, and thus adding any fuel enrichment (ie: propane or carb cleaner) won't raise the idle.

What makes you think you have a blown head gasket, and if you do, why are you driving it or attempting any other tuning? A blown head gasket is a serious problem and needs to be taken care of before anything else. Any tuning can't be properly done with a bad head gasket either, and besides, you will be replacing all of the intake gaskets anyway when you replace the head gasket. You need to find out if you have a blown head gasket. Check your compression and use your vacuum gauge (your vacuum gauge should fluctuate as you increase the idle speed with a blown head gasket).

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

Galligher · 07-12-2001, 09:29 AM

Call it intuition about the gasket leak leak. Compression is OK, all cylinders are close to each other. I think it's a very small leak that only happens under certain conditions. It doesn't leak that much. I have not had the car very long and will be replacing them soon. Thanks for your help! I'll see what I can do about curing the rich condition (probably need to look at ignition!) and replace gaskets and then get back with you. I have replaced a couple of hoses that were cracked so I know there are more lurking somewhere in there!
Thanks Again!
Brian.

jimberg · 07-12-2001, 11:05 AM

Have you done a compression check?

------------------
351W 89 Mustang GT Convertible

Galligher · 07-12-2001, 11:53 AM

Yes, I forget the exact #'s but I think they were around high 130's low 140's (or maybe that was the 2.3T that I looked at for a freind??). There was one that was slightly lower (suspect). I may just pull it and replace bearings and rings if the bores are not too bad. If it is a small head gasket leak, the combustion chambers should be nice and clean!!!!

jimberg · 07-12-2001, 12:23 PM

Have you tried a cylinder balance test?

I guess if you're not opposed to pulling your engine, I guess it couldn't hurt to just rebuild everything.

------------------
351W 89 Mustang GT Convertible

Galligher · 07-12-2001, 02:47 PM

That was my thought along with with motor mounts. Then start saving for that Kenne-Bell supercharger...

07-10-2001, 10:12 AM	#1
Galligher Registered Member Join Date: Dec 1998 Location: Ft.Wayne, IN Posts: 12	Another Vacuum Question I have a 91 LX with an AOD. I have not had it that long and it has a hesitation/backfire every once in a while when the engine is under load. I hooked a vacuum gauge up to it last night and got a steady 15 PSI (Vacuum) at 800 rpm idle. If I "goosed" it, vacuum dropped to nothing and then raised to 19 (~1000RPM). When idle came back down, it dropped back to 15. I tried using propane, but it did not work. I opened the line that normally goes to the diverter valve and let propane in it and noticed no increase in RPM???? I then sprayed carb cleaner in it and again nothing??? I also noticed that when I disconnected the line vacuum did not change. This is what is really leading me to believe I have a leak, or is it that the line is small enough not to have a great effect. Any help??? Thanks, Brian

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07-10-2001, 02:50 PM	#2
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	15" is a little on the low side. Warm up your engine, with the vacuum gauge connected and while it's idling, disconnect the gauge, but don't plug the hose. let me know what happens to the idle when you do this. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

07-10-2001, 03:40 PM	#3
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Is everything stock? A more radical cam will give you lower vacuum at idle. I have an E303 and get 12" at idle. ------------------ 351W 89 Mustang GT Convertible

07-11-2001, 09:00 AM	#4
galligherb Registered Member Join Date: Jul 2001 Location: Ft. Wayne, IN Posts: 1	Well, I did just as you said and here are the results: Idle increased very little (could hear but couldn't really see on the tach) and it ran a little rougher. The engine is stock. I forgot to mention this before, but I am pretty sure it has a head gasket leak (uses some water, no external water). But I don't think that is all of my problems, I think I have vacuum leaks as well. I will be changing head gaskets soon. I just don't understand why the propane or carb cleaner did not really work. I have thought about starting fluid, but ????

07-12-2001, 12:36 AM	#5
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	If the idle increased when you disconnected the vacuum gauge, then it's slightly rich, and thus adding any fuel enrichment (ie: propane or carb cleaner) won't raise the idle. What makes you think you have a blown head gasket, and if you do, why are you driving it or attempting any other tuning? A blown head gasket is a serious problem and needs to be taken care of before anything else. Any tuning can't be properly done with a bad head gasket either, and besides, you will be replacing all of the intake gaskets anyway when you replace the head gasket. You need to find out if you have a blown head gasket. Check your compression and use your vacuum gauge (your vacuum gauge should fluctuate as you increase the idle speed with a blown head gasket). Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

07-12-2001, 09:29 AM	#6
Galligher Registered Member Join Date: Dec 1998 Location: Ft.Wayne, IN Posts: 12	Call it intuition about the gasket leak leak. Compression is OK, all cylinders are close to each other. I think it's a very small leak that only happens under certain conditions. It doesn't leak that much. I have not had the car very long and will be replacing them soon. Thanks for your help! I'll see what I can do about curing the rich condition (probably need to look at ignition!) and replace gaskets and then get back with you. I have replaced a couple of hoses that were cracked so I know there are more lurking somewhere in there! Thanks Again! Brian.

07-12-2001, 11:05 AM	#7
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Have you done a compression check? ------------------ 351W 89 Mustang GT Convertible

07-12-2001, 11:53 AM	#8
Galligher Registered Member Join Date: Dec 1998 Location: Ft.Wayne, IN Posts: 12	Yes, I forget the exact #'s but I think they were around high 130's low 140's (or maybe that was the 2.3T that I looked at for a freind??). There was one that was slightly lower (suspect). I may just pull it and replace bearings and rings if the bores are not too bad. If it is a small head gasket leak, the combustion chambers should be nice and clean!!!!

07-12-2001, 12:23 PM	#9
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Have you tried a cylinder balance test? I guess if you're not opposed to pulling your engine, I guess it couldn't hurt to just rebuild everything. ------------------ 351W 89 Mustang GT Convertible

07-12-2001, 02:47 PM	#10
Galligher Registered Member Join Date: Dec 1998 Location: Ft.Wayne, IN Posts: 12	That was my thought along with with motor mounts. Then start saving for that Kenne-Bell supercharger...