View Full Version : High Vacumm at IDLE

03-04-2001, 08:44 PM
okay here it is 1979 K-5 Blazer 2WD has 1990 ZZ3 crate engine from chevy, performer intake and carb, MSD Digital 6 ignition on HEI, RV-3 cam. everyday for the last 10 years the truck has had 17 pounds of vacumm at idle 700RPM. one day i started it like normal and the engine has 26 pounds at idle. the engine does run the same as before, except it has less performance...like the feeling of having 25 horsepower less !! it starts okay, idles okay, and runs down the road okay......i have 2 ideas of what it could be timing chain jumped a degree or so advanced, or the cam went flat on a lope or two....keep in mind this happened instantly with no funny sounds at all....it has no smog on it....and a vacumm leak would cause less vacumm at idle...any GOOD ideas here would really be helpfull....buy the way 3 NEW vacumm gauges all read 26 pounds

03-05-2001, 10:45 AM
inhail, By pounds I asume you mean inches(vacume is measured in inches of meurcury ). Most likely you have a restriction in the air intake before the carb:plugged filter, collapsed hose , pluged air inlet ETC. Confirm this by testing with air filter cover off. If vacume is normal then find and repair restriction.
Good luck,Brad

mike reeh
03-05-2001, 11:34 PM
i agree.. take the air cleaner off and look again, if its the same, there is no problem.. the higher the vacuum reading, the better.


03-06-2001, 10:15 PM
okay guys i agree more vacumm is better. the problem i have is when it comes after 65,000 miles of use and one day jumps by 9 inches of vacumm....the air cleaner is fine, all the PCV lines are new, so is the brake booster hose...i just think something internally could be going on here. i took a plug wire off each cylinder and ran it and got the same vacumm reading on each one, meaning the valves and springs are okay. i did a compression check and found out I DO HAVE 65,000 on the engine :) it was almost the same to the tee on every cylinder.....i dont know what to think, so keep thinking here, ask a friend for me !!!!

mike reeh
03-07-2001, 09:02 PM
im not exactly sure how you figure that valves & springs are okay by removing a plug wire but anyways, do a COMPLETE and thorough tuneup, and thats that...make sure you check timing, etc.

my best guess is that timing changed, to make the engine run smoother at idle, but gave it less top end.. ******ed timing? check mechanical and vacuum advance systems, etc... if all that stuff checks out, then the motor is a-ok