Modded Mustang Forums banner
1 - 9 of 9 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter · #1 ·
Greetings, I have a 92 LK with a TFS Stage 1 Cam, Holly Systemax Intake, FAC 170 Heads, 24 LB injectors and a Prom M MAF.

When checking my vacuum at the brake boost hose I have 13-14 in of vacuum at 1100 RPM's. When cold starting the car it's more like 8-10 in. of vacuum and increases after it's warmed up for several minutes but doesn't go higher the 13-14 and it takes 1100-1200 RPM's to get that.

I called trick flow and they said with their stage 1 cam I should be getting 19 in of vacuum at 900 RPM's

If this is a vacuum leak how big of a leak does it take to lose 7-8 in of vacuum or is this a rather small leak.

On a side note that may be related the car began trying to stall during the first minute of the first start of the day. RPM's will go from 1K-4K in a rythmic fashion and then become stable after about a minute. Once the car is warmed up all subsequent starts through out the day (even after 3-4 hours of sitting) don't have this issue
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #3 ·
you check for leaks? can of carb cleaner
I have and didn't find anything. I mainly checked the upper intake and vacuum lines. That's why I'm curious based on this loss of vacuum how big of a leak I'm looking for. Also, if it's not a leak what would the next obvious problem be?
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #6 ·
Do you think the car's rpm's surging and wanting to die till it's been running for a minute is related?

Also, it's not normal for vacuum to increase from 10-12 to 13-14 as it warms is normal; is it? I would think vacuum would pretty much remain the same.
 

·
Banned
Joined
·
11,614 Posts
ehh metal expands so could be closing a small leak
 

·
Powered by LSx tears
Joined
·
21,466 Posts
How many miles are on it? 19" is quite a bit, and it will only make that on a fresh engine. As the rings and cylinders get miles on them, they won't seal as well, causing less vacuum. That also explains the vacuum increasing as it warms up. Everything expands, and seals up better. Run a leakdown check if you can, and it will tell you a lot more.
 

·
Registered
Joined
·
14 Posts
Discussion Starter · #9 ·
How many miles are on it? 19" is quite a bit, and it will only make that on a fresh engine. As the rings and cylinders get miles on them, they won't seal as well, causing less vacuum. That also explains the vacuum increasing as it warms up. Everything expands, and seals up better. Run a leakdown check if you can, and it will tell you a lot more.
Thanks, I've had a compression test done before doing the heads and it was within specs of a new car. Never had a leakdown done. The car has 83K miles
 
1 - 9 of 9 Posts
Top