Engine vacuum
 

I need some help. About a month ago I changed the timing belt on my '88 Escort Pony. Before changing the timing belt the engine vacuum was steady at about 20-21 inches of vacuum at idle and would go to about 24 inches of vacuum during deceleration. Since I changed the timing belt engine vacuum at idle is steady at about 17-18 inches of vacuum at idle and also about 17-18 inches of vacuum during deceleration. I've checked for vacuum leaks and have none. I've also checked and rechecked to make sure I didn't get the timing off by a tooth, the timing marks line up perfectly. Fuel mileage is also down by about 2-4 MPG since changing the belt. This has me stumped, any suggestions would be appreciated. Engine runs smoothly with no stumble or hesitation and the vacuum gauge needle is perfectly steady at idle.

You may want to check your ignition timing. Retarded ignition timing can cause low vacuum and loss of economy.

Thanks for the reply. Don't know if the ignition timing is retarded or not, but I'm a little off in the head. (maybe not quite retarded, but close) I'll try to get the timing checked, I don't have a light so I'll have to get someone else to do it.

What I hear is they practically always end up half or quarter tooth off, if you go forward (advance) you get the good vacuum and low end, if you go backwards you get the 4000rpm nitro button effect.

My nitro button must be broken too then!!!

Hmmm anything else happen at the same time, change to thinner or different oil? Cheap oil could have stuck up your rings and got you more blowby, thinner oil might allow more blowby on high mileage rings.

Nothing else happened. Just a drop in vacuum and lower MPG. All I did was change the timing belt and water pump. Since the bearing was shot in the water pump I was looking forward to higher MPG, because it would make less strain on the engine to turn it. Looks like my plan back fired. I've gone over the vacuum lines several times just to make sure I didn't knock one off while working under the hood. They are all attached and in good shape. There was one in question so I replaced it, but it didn't do any good. I've also check electrical connections to sensors and can't find anything disconnected that I might have knocked loose. I'm not feeling very well today, but if I feel better tomorrow I think I'm going to pull it into the garage where I have A/C and start going over everything I can find to see if I can find any thing at all that isn't right.

I took the car for another drive a while ago and the vacuum is up some. Back to about 18-20 inches of vacuum at idle and 19-22 during deceleration. This is leading me to wonder if the timing belt just needed to stretch some before the timing is just right. I know when I was putting this belt on, even with the tensioner all the way back I had to fight with it for 30 minute to an hour before I was ever able to get it on the pulleys, I've never had that much problem before. Maybe this belt was just a little to short throwing the timing off??? I've decided to keep driving it for a couple more weeks to see what happens before taking everything apart and possibly finding nothing wrong. I don't feel like looking all day for something that isn't there.

An update on the vacuum situation. The vacuum continues to vary by large amounts. I have noticed that the engine vacuum increases when the weather is warmer and decreases when it's cooler. It never did this before I changed the timing belt. This still has me stumped. Still open for suggetions.

Hmmm that's opposite what you'd expect to happen, should get slightly more vacuum when it's cooler, slightly less when it's warmer...

However... hardened hoses and seals may leak vacuum when cool and soften up enough to seal when warm. Also vacuum lines may completely collapse when hot enough, so if there's a leak further down the hose and it collapses when hot it will seal off the leak.

A thing I'd look at is the PCV valve bung, they harden up and seal poorly.