High vacuum at idle, drops like a rock when gassed.

[jmkissler]

1995 Ranger 2.3 manual trans.


At idle vacuum is sitting at 25 +/- a bit. When I step on the gas, moving or stationary, vacuum drops to between 8 and 10. I've seen low vacuum at idle, typically from some sort of leak. I have never seen high vacuum at idle and low under power.

I guess am asking what is the normal vacuum range? I was told by a buddy that the ranger should be sitting at about 18, drop a little but not 17.

Has anyone seen an issue like this? If so, can you point me down the right path? I have searched the forums but haven't found anything that fits.

Thanks guys.

 

[alwaysFlOoReD]

IMO That's normal...ish. I have not seen 25 for idle vacuum, that seems high. Dropping down on throttle is normal. The throttle plate forms the vacuum, when you open the plate the vacuum leaves.

 

[scotts90ranger]

I'm assuming you are looking at a normal vacuum gauge that ranges from 0 (atmosphere) down to 30" Hg not some fancy absolute pressure gauge where 0 is absolute 0...

Making that assumption, big numbers at idle is a good thing, means the engine is an efficient air pump. My turbo 2.3 and Geo Tracker are in the neighborhood of 22-25" Hg at idle. Assuming no engine load there is a chance the vacuum could increase at higher speed but that depends on a lot of variables, and that is steady state like if you open the throttle a little and hold it. If you are opening the throttle fully it should go to 0" Hg, and at full load (any speed) it should be 0" as well but 2" wouldn't surprise me with an air filter and smallish throttle in the way...

What is really bad is if the engine idles at 15" Hg or less, that generally means there is a major issue... at least it does in my experience (and believe me, I've ran a LOT of engines in dynos, recordings received from customers, etc...) My Tracker currently has a head gasket blown between #2 and 3 or 3 and 4 don't remember and it idles at like 10"... The idle vacuum will decrease with elevation as well, I think around 1" per 1000 to 1500 feet elevation.

 

[jmkissler]

Ok. That tracks. I live around 5000 to 5500 feet. On my other vehicles, vacuum was not that high... but I also didn't live here, so...

When i bought this truck, it had problems. So far I have replaced the cat, exhaust, dpfe, egr (still getting a P0401 error again after the cat/exhaust install), thermoresistor, purge flow sensor, and a myriad of other things. I need to throw a new valve cover gasket on there as well... maybe a new starter solenoid since she doesn't like to start when it's cold (she gets the occasional push start). So far I've been liking it, even when running like crap, she gets better mpg than my s15. Now... if I could only do highway speeds.

 

[tomw]

That's pretty high vacuum for idle rpm. The drop when the throttle opens is perfectly normal. Given you have trouble going highway speed, I'd check the timing belt to see that the marks are aligned. If they are off a tooth, you can have performance and power problems. I think one way gets you poor power at low rpm, and you have to really run up the rpms to get the thing to move from stopped. The other way kind of starves the engine at higher rpms. It may have been spark timing, but cam timing can do the same.
tom

 

[jmkissler]

That's pretty high vacuum for idle rpm. The drop when the throttle opens is perfectly normal. Given you have trouble going highway speed, I'd check the timing belt to see that the marks are aligned. If they are off a tooth, you can have performance and power problems. I think one way gets you poor power at low rpm, and you have to really run up the rpms to get the thing to move from stopped. The other way kind of starves the engine at higher rpms. It may have been spark timing, but cam timing can do the same.
tom

Tomw, That is something I had been thinking about. The current timing belt has been on for about 120K miles. I was trying to get the parts together to put in an electric fan. I was hoping to do them at the same time, given the amount of work. I was told by the previous owner that changing the timing belt was 18 hours worth of work, so I'd like to do them at the same time.

After throwing in a new cat and exhaust (picked up a gibson) the truck has been doing a lot better, but not quite there for highway.

 

[tomw]

Changing the timing belt is about a 2-3 hour job, tops. I chose to remove the radiator to prevent my clumsy from poking a hole, and to change the hoses at the same time, but it is not necessary. Someone has the wrong idea about required time. You can get an estimate for that service on the web if you don't want to do it yourself.
When they fail, they usually will fail at startup, with a few teeth removed, and the belt slipped out of place. Crank no start... They can fail while moving, but less often.
tom