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.

It's possible, although unlikely, that the cam was deliberately installed a tooth off from the factory. If the cam indexed very poorly, they may have moved it a tooth to compensate. However that's gonna be virtually impossible to tell now, unless you disassemble the whole freakin engine and start again.

Does high RPM power (4000+RPM) seem to be increased? That would indicate that your cam is retarded, and that you would need to advance it a tooth (if my theory is true).

It is not uncommon for cams to be ground 10 degrees off or more, especially if it is a custom cam, which is why they all need to be indexed. However in a very-high production situation, I'd be surprised if your cam was ground that far off (but it is still not impossible).

-Bob C.

bobc455, I've replaced the timing belt several times before, but at the time I didn't have the vacuum gauge hooked up so I don't know what effects it has had in the past. I've always put the timing belts on myself so I know they are are installed with the timing marks. I even tried taking the belt off and tried setting it 1 tooth off each way of correct and didn't see any significant change in vacuum, maybe 1 inch of vacuum difference. I've also tried adjusting the timing both ways at the distributor to the point it stalls and once again only about 1 inch variation. With the 1.9L engine and all of it's 88 HP it's hard to tell much difference in power either way. Really it seems like if anything it's got less power, but who knows one of the horses may have died. After all this is the Escort that has nearly 1/2 million miles on it.

RoadWarrior, this is one of the Escorts they made that didn't have a PCV valve, just the two vacuum orfices and I've been from one end to the other of those vacuum lines several times and found one that was in question so I replaced it, but didn't help anything.

I have question to ask. Suppose the MAP sensor went bad at the same time I changed the timing belt, what effect would that have on vacuum? Any? The only thing is, I would expect the fuel efficiency to have dropped more than 2-4MPG if that was the case. Any input? If it had just happened sometime when I hadn't just changed the timing belt, I wouldn't think that had something to do with it, but I've been over it several times checking for anything that I might have done wrong, unplugged or knocked off and everything seems to be right.

I think maybe I have found my vacuum problem. I pulled the codes from the ECU and found that I had a defective ignition module. I replaced it today and took the car for about a 2 mile drive. The engine vacuum was up, but the temperature was in the mid 90's too and the vacuum had been increasing with warmer temperatures. I'll be driving the car tomorrow morning early so I should find out for sure then whether that was the problem or not. Guess I should have checked the codes sooner, but I kept thinking it had something to do with the timing belt change since that is when the problem started. I sure hope this was the problem, I'm tired of only getting 40-43 MPG. I want to see those 44-48 MPG numbers again. This has pulled my average way down.

The ignition module didn't do the trick. I also tried changing the MAP sensor with an extra one I had, that also had no effect. I'm still open to suggestions.