How much vacuum at idle?

gray87GT · 05-13-2001, 06:18 PM

I am still trying to figure out my engine so I decided to check the vacuum inches at idle. My idle is set around 750-800. I read the vacuum from the tree on driver side firewall, in an empty port. It read 12 inches....is that enough, or do I have a leak somewhere? Thanks (F303 cam)

joe4speed · 05-14-2001, 12:57 AM

I have about 15-18 inches at about 800 rpm's idle. with 167,000 miles on the engine

------------------
Joe!
1988 GT, 167,000 miles!!! 13.71@105mph Check out my listing! Click here! Or my website:
www.joe4speed.com
1999 Ninja ZX-6R 10.32@135mph!
1993 Olds Eighty Eight LSS

Jeff Chambers · 05-14-2001, 06:19 AM

I run 8 to 10 inches, warm at 1000RPM. Its only a .500 lift cam, but longer duration and my engine has quite a bit of compression. It doesn't affect me though since I don't have power brakes any more.

------------------
Jeff Chambers
Trophy Stock #3
11.611 Seconds / 116.7 MPH
Chambers Racing Team

jimberg · 05-14-2001, 10:20 AM

Every engine is different so it would be very difficult to tell you if that were right. Do you have any symptoms that would lead you to believe that you have a vacuum leak?

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

gray87GT · 05-14-2001, 11:06 AM

Let's say I am coasting in 2nd gear, if I apply a little pedal it will run really sh*ty. If I apply a little more pedal it runs good, I only have a problem if I barely give it gas. If I only give it a little gas it will run sh*ty until I back off or apply more gas. It has a eally wierd smell after I run it, at first I though it was my new MAC exhaust, but now I thibk it just smeels rich. Am I loading it up with I apply a little gas?

------------------
87 GT, BBK shorty's, MAC High-Flow H-pipe, ASP pullies, BBK 70mm T.B., Cobra intake, no smog pump, Windsor Jr irons, Comp cams 1.6 rollers, F303 cam, FMS HD water pump, Tri-Ax, FMS subframes, Battle boxes, SSM liftbars, FMS King Cobra clutch, mass-air conversion, 73mm C&L, 24lb injectors, BBK AFPR, 3/8" no EGR spacer,MAC pro-dumps, FMS 3.73's, and other piddly sh*t.

jimberg · 05-14-2001, 02:22 PM

What RPM range are you at when you're coasting in 2nd? Also, is your hi-flow h-pipe hooked up correctly to the air pump? Oh, I just saw, no smog pump. That's bad. Your cats won't work properly without one. That's likely your problem.

muskrat · 05-14-2001, 06:52 PM

I know your pain. Have the same problem. Been working on it for 3 months, has nothing to do with smog pump. Car runs excellent in open loop, as soon as closed loop problems start. Even with this annoyance for normal driving my car runs 12.01 consistantly with 1.90 60 foot times on drag radials. Wish I knew the answer. I have had several so called experts look at it, but no fix yet yet.

jimberg · 05-14-2001, 07:30 PM

The smelling rich is related to the lack of air pump. The HC isn't being catylized properly.

If he's at low RPMs with a cam that isn't designed for low RPMs and he applies slight throttle, it probably will run really crappy. We need more info for sure.

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

muskrat · 05-14-2001, 07:37 PM

Jimberg: sent you a private message. I don't think his problem is running rich, rather it is a lean rich hunt by the computer. If he disconnects his 02sensors he will find that the car will run fine, however it will through a check engin light, and may cause problems with the cats if the o2's are left disconnected.

smokedchevy · 05-16-2001, 12:27 AM

Mine car is running perfect and it idles at 17 inches of vacuum.

gray87GT · 05-16-2001, 07:43 AM

Thanks for the help guys. It really happens in all the gears if I am cruising slow, around 2,000-3,000 RPM's ussualy though. Do you think it could be my o2 sensors? I know I am not near my power potential with this set-up, but all I care about right now is that it's running good and not hurting anything. But it sure would be nice to lose that hesitation.

gentb · 05-16-2001, 08:19 AM

Don't want to stray away from the subject but I am interested in this. I just put in a new engine with the Crane version of the E303 with the help of a friend that is a certified Ford technician. I had before and after the swap extremly low vacuum. Brake boost being very eratic. Idle was OK before the swap. Now I am occasionaly hunting an idle but usually OK. We cleared the computer but did not reset after the swap. At low revs I get a real hard pedal most of the time. Anybody tried an auxilary vacuum can?

86GT · 05-16-2001, 09:55 AM

The only problems I've had with my Fcam is the low speed driving, at 1,700 or less rpm, then it runs bad. I've got the same thing with my cats, but I know its from no smog pump, which I will be hooking up shortly.

I'll post my vacuum numbers when I test it tomorrow.

jimberg · 05-16-2001, 11:38 AM

I'll guess I'll try to be clearer on this. I don't think the running rough problem is related to the smog pump. Just the rich smell. If you have cats in place, you SHOULD have a working smog pump otherwise the cats are not going to work properly and will eventually clog causing an exhaust restriction.

I have a CompuCam 2040 (E303) and have no problems with vacuum or brake boost. I also have a 351W which is why I may have more vacuum.

Gray87GT, the circumstances you're testing are so unusual so I guess we still need a little more information. When you're at 2000-3000 rpms with your foot off of the gas, is the clutch in or out? Since it's at 2000-3000 rpms I suppose I can assume that it's out and you are using the engine to slow you down. This is the point at which vacuum is highest. (That's just an FYI, but not necessarily a cause). If your TPS is off in the high range (Mine's set at .98 volts), your ECM may think that you're at normal cruise and opens the EGR which would make it run crappy. Magazines say that closest voltage you can get that is under 1 volt is best. If you're at .999 and you tap the throttle, that may cause the false reading by the ECM.

To test this theory, disconnect the EGR vacuum line so that the ECM can't open the EGR. See if it still does it.

Crap, just noticed that you have the EGR blocked, but I'll leave this for the other people to try. It is still possibly related to EGR, though. Do you still have the EGR spacer with the EGR valve hooked up to avoid EGR codes? If so, the ECM may be adjusting fuel values thinking that EGR is present. If you don't, then maybe your engine doesn't like the transition from engine braking to slight throttle. I'll check to see how my engine responds to this because I've never actually done this before.

Another thing you could try is to bump your TPS down a little if it is high or on the edge.

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

gray87GT · 05-16-2001, 05:10 PM

jimberg- Thanks for the info. Yeah, I have the BBK plenum spacer with no EGR port, and I also disconnected the one(i think one)vacuum line to the EGR valve. You are right, I cruise in gear with clutch out at low RPM's fine.......the only problem is when I BARELY touch the throttle. It seems like the problem is when there is VERY little or NO load on the engine, if I drive part throttle it runs great. It feels like it's carburated and the instant I apply a little throttle it loads up. I changed the fuel filter last week, I was hoping that would fix it. I have fuel pressure set at 39# w/o vacuum. Could it be the cam/head combo? I really don't know. I really appreciate all your help, along with everyone elses.

One more ? jimberg. If I wanted to put my air pump back on, would I have to install the metal tubing to the back of my heads? And if I have to do that do I have to drill the holes in the exhaust ports to activate the smog rail? Or can I just hook the pump another way? Thanks

jimberg · 05-16-2001, 06:12 PM

Well, I had a chance to do what you are having problems with and mine has no problem, so it's not just a hidden Mustang "characteristic".

It may just be a characteristic of your cam and head combo. I think you should check your TPS, though, just to be sure. To be honest, though, I would probably just not worry about it. As long as the engine runs well otherwise.

As far as the air pump goes, I think it would be less costly to just get an off-road h-pipe or x-pipe. You've already pretty much removed all of the emissions stuff anyway. Otherwise, the only thing I can say with certainty is that all the thermactor plumbing would have to go back. As to how to do that with your heads, I can't say since I don't know.

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

jseaton · 05-17-2001, 10:40 AM

The rule of thumb is to not have under 15 inches of vacuum at idle unless you have a bigger cam or the elevation where you live is higher. 12 inches sounds pretty good though. The best way to check it is to watch the vacuum as you are driving and have a load on the engine. It should drop to around 3 or 4.

------------------
82- 347, SVO A4, Scat Billet Crank, Crower Rods, Nowak Pistons, TFS Heads W/Crower Stainless Rockers, Victor Intake, Gold Claw, Paxton Fuel system, MSD ignition,

05-18-2001, 04:09 AM

The only thing that i can think of is your original idea of a vacuum leak. One thing you can do is get a small bottle of propane and hook a hose up to the valve and poke the hose around different parts of your engine. If nothing happens, then you don't have a leak, but if the car suddenly runs better then you know you have a leak in that area. It may just be the F-cam with your combo doesn't like idling or low rpm's at all like jimberg said. Good luck!

86GT · 05-18-2001, 02:37 PM

One thing I've found about the F-cam so far is that it hates being driven under 1,700 or so, then it feels like its bogging. That's just one characteristic of the cam.

My vacuum at 900 rpm idle (if I read the gauge correctly) is 14 inches.

05-13-2001, 06:18 PM	#1
gray87GT Registered Member Join Date: Jan 2001 Location: Minnesota Posts: 177	How much vacuum at idle? I am still trying to figure out my engine so I decided to check the vacuum inches at idle. My idle is set around 750-800. I read the vacuum from the tree on driver side firewall, in an empty port. It read 12 inches....is that enough, or do I have a leak somewhere? Thanks (F303 cam)

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05-14-2001, 12:57 AM	#2
joe4speed He said Member...heh, heh Join Date: Sep 1999 Location: Jupiter, Florida U.S.A. Posts: 3,718	I have about 15-18 inches at about 800 rpm's idle. with 167,000 miles on the engine ------------------ Joe! 1988 GT, 167,000 miles!!! 13.71@105mph Check out my listing! Click here! Or my website: www.joe4speed.com 1999 Ninja ZX-6R 10.32@135mph! 1993 Olds Eighty Eight LSS

05-14-2001, 06:19 AM	#3
Jeff Chambers Moderator Join Date: Aug 2000 Location: Milan, OH Posts: 2,699	I run 8 to 10 inches, warm at 1000RPM. Its only a .500 lift cam, but longer duration and my engine has quite a bit of compression. It doesn't affect me though since I don't have power brakes any more. ------------------ Jeff Chambers Trophy Stock #3 11.611 Seconds / 116.7 MPH Chambers Racing Team

05-14-2001, 10:20 AM	#4
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Every engine is different so it would be very difficult to tell you if that were right. Do you have any symptoms that would lead you to believe that you have a vacuum leak? ------------------ 351W 89 Mustang GT Convertible

05-14-2001, 11:06 AM	#5
gray87GT Registered Member Join Date: Jan 2001 Location: Minnesota Posts: 177	Let's say I am coasting in 2nd gear, if I apply a little pedal it will run really shty. If I apply a little more pedal it runs good, I only have a problem if I barely give it gas. If I only give it a little gas it will run shty until I back off or apply more gas. It has a eally wierd smell after I run it, at first I though it was my new MAC exhaust, but now I thibk it just smeels rich. Am I loading it up with I apply a little gas? ------------------ 87 GT, BBK shorty's, MAC High-Flow H-pipe, ASP pullies, BBK 70mm T.B., Cobra intake, no smog pump, Windsor Jr irons, Comp cams 1.6 rollers, F303 cam, FMS HD water pump, Tri-Ax, FMS subframes, Battle boxes, SSM liftbars, FMS King Cobra clutch, mass-air conversion, 73mm C&L, 24lb injectors, BBK AFPR, 3/8" no EGR spacer,MAC pro-dumps, FMS 3.73's, and other piddly sh*t.

05-14-2001, 02:22 PM	#6
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	What RPM range are you at when you're coasting in 2nd? Also, is your hi-flow h-pipe hooked up correctly to the air pump? Oh, I just saw, no smog pump. That's bad. Your cats won't work properly without one. That's likely your problem.

05-14-2001, 06:52 PM	#7
muskrat Registered Member Join Date: Mar 1999 Location: va Posts: 35	I know your pain. Have the same problem. Been working on it for 3 months, has nothing to do with smog pump. Car runs excellent in open loop, as soon as closed loop problems start. Even with this annoyance for normal driving my car runs 12.01 consistantly with 1.90 60 foot times on drag radials. Wish I knew the answer. I have had several so called experts look at it, but no fix yet yet.

05-14-2001, 07:30 PM	#8
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	The smelling rich is related to the lack of air pump. The HC isn't being catylized properly. If he's at low RPMs with a cam that isn't designed for low RPMs and he applies slight throttle, it probably will run really crappy. We need more info for sure. ------------------ 351W 89 Mustang GT Convertible

05-14-2001, 07:37 PM	#9
muskrat Registered Member Join Date: Mar 1999 Location: va Posts: 35	Jimberg: sent you a private message. I don't think his problem is running rich, rather it is a lean rich hunt by the computer. If he disconnects his 02sensors he will find that the car will run fine, however it will through a check engin light, and may cause problems with the cats if the o2's are left disconnected.

05-16-2001, 12:27 AM	#10
smokedchevy Registered Member Join Date: Jun 2000 Location: ventura,CA Posts: 438	Mine car is running perfect and it idles at 17 inches of vacuum.

05-16-2001, 07:43 AM	#11
gray87GT Registered Member Join Date: Jan 2001 Location: Minnesota Posts: 177	Thanks for the help guys. It really happens in all the gears if I am cruising slow, around 2,000-3,000 RPM's ussualy though. Do you think it could be my o2 sensors? I know I am not near my power potential with this set-up, but all I care about right now is that it's running good and not hurting anything. But it sure would be nice to lose that hesitation.

05-16-2001, 08:19 AM	#12
gentb Registered Member Join Date: Mar 2001 Location: Starr,SC Posts: 16	Don't want to stray away from the subject but I am interested in this. I just put in a new engine with the Crane version of the E303 with the help of a friend that is a certified Ford technician. I had before and after the swap extremly low vacuum. Brake boost being very eratic. Idle was OK before the swap. Now I am occasionaly hunting an idle but usually OK. We cleared the computer but did not reset after the swap. At low revs I get a real hard pedal most of the time. Anybody tried an auxilary vacuum can?

05-16-2001, 09:55 AM	#13
86GT Sniffed too much n20 Join Date: Oct 1998 Location: Ont, Canada Posts: 1,018	The only problems I've had with my Fcam is the low speed driving, at 1,700 or less rpm, then it runs bad. I've got the same thing with my cats, but I know its from no smog pump, which I will be hooking up shortly. I'll post my vacuum numbers when I test it tomorrow.

05-16-2001, 11:38 AM	#14
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	I'll guess I'll try to be clearer on this. I don't think the running rough problem is related to the smog pump. Just the rich smell. If you have cats in place, you SHOULD have a working smog pump otherwise the cats are not going to work properly and will eventually clog causing an exhaust restriction. I have a CompuCam 2040 (E303) and have no problems with vacuum or brake boost. I also have a 351W which is why I may have more vacuum. Gray87GT, the circumstances you're testing are so unusual so I guess we still need a little more information. When you're at 2000-3000 rpms with your foot off of the gas, is the clutch in or out? Since it's at 2000-3000 rpms I suppose I can assume that it's out and you are using the engine to slow you down. This is the point at which vacuum is highest. (That's just an FYI, but not necessarily a cause). If your TPS is off in the high range (Mine's set at .98 volts), your ECM may think that you're at normal cruise and opens the EGR which would make it run crappy. Magazines say that closest voltage you can get that is under 1 volt is best. If you're at .999 and you tap the throttle, that may cause the false reading by the ECM. To test this theory, disconnect the EGR vacuum line so that the ECM can't open the EGR. See if it still does it. Crap, just noticed that you have the EGR blocked, but I'll leave this for the other people to try. It is still possibly related to EGR, though. Do you still have the EGR spacer with the EGR valve hooked up to avoid EGR codes? If so, the ECM may be adjusting fuel values thinking that EGR is present. If you don't, then maybe your engine doesn't like the transition from engine braking to slight throttle. I'll check to see how my engine responds to this because I've never actually done this before. Another thing you could try is to bump your TPS down a little if it is high or on the edge. ------------------ 351W 89 Mustang GT Convertible

05-16-2001, 05:10 PM	#15
gray87GT Registered Member Join Date: Jan 2001 Location: Minnesota Posts: 177	jimberg- Thanks for the info. Yeah, I have the BBK plenum spacer with no EGR port, and I also disconnected the one(i think one)vacuum line to the EGR valve. You are right, I cruise in gear with clutch out at low RPM's fine.......the only problem is when I BARELY touch the throttle. It seems like the problem is when there is VERY little or NO load on the engine, if I drive part throttle it runs great. It feels like it's carburated and the instant I apply a little throttle it loads up. I changed the fuel filter last week, I was hoping that would fix it. I have fuel pressure set at 39# w/o vacuum. Could it be the cam/head combo? I really don't know. I really appreciate all your help, along with everyone elses. One more ? jimberg. If I wanted to put my air pump back on, would I have to install the metal tubing to the back of my heads? And if I have to do that do I have to drill the holes in the exhaust ports to activate the smog rail? Or can I just hook the pump another way? Thanks

05-16-2001, 06:12 PM	#16
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	Well, I had a chance to do what you are having problems with and mine has no problem, so it's not just a hidden Mustang "characteristic". It may just be a characteristic of your cam and head combo. I think you should check your TPS, though, just to be sure. To be honest, though, I would probably just not worry about it. As long as the engine runs well otherwise. As far as the air pump goes, I think it would be less costly to just get an off-road h-pipe or x-pipe. You've already pretty much removed all of the emissions stuff anyway. Otherwise, the only thing I can say with certainty is that all the thermactor plumbing would have to go back. As to how to do that with your heads, I can't say since I don't know. ------------------ 351W 89 Mustang GT Convertible

05-17-2001, 10:40 AM	#17
jseaton Registered Member Join Date: Sep 1998 Location: carrollton,texas,usa Posts: 59	The rule of thumb is to not have under 15 inches of vacuum at idle unless you have a bigger cam or the elevation where you live is higher. 12 inches sounds pretty good though. The best way to check it is to watch the vacuum as you are driving and have a load on the engine. It should drop to around 3 or 4. ------------------ 82- 347, SVO A4, Scat Billet Crank, Crower Rods, Nowak Pistons, TFS Heads W/Crower Stainless Rockers, Victor Intake, Gold Claw, Paxton Fuel system, MSD ignition,

05-18-2001, 04:09 AM	#18
84stangLX Guest Posts: n/a	The only thing that i can think of is your original idea of a vacuum leak. One thing you can do is get a small bottle of propane and hook a hose up to the valve and poke the hose around different parts of your engine. If nothing happens, then you don't have a leak, but if the car suddenly runs better then you know you have a leak in that area. It may just be the F-cam with your combo doesn't like idling or low rpm's at all like jimberg said. Good luck!

05-18-2001, 02:37 PM	#19
86GT Sniffed too much n20 Join Date: Oct 1998 Location: Ont, Canada Posts: 1,018	One thing I've found about the F-cam so far is that it hates being driven under 1,700 or so, then it feels like its bogging. That's just one characteristic of the cam. My vacuum at 900 rpm idle (if I read the gauge correctly) is 14 inches.