Vacuum Warning Switch... mpg's

[Bluebird]

My vacuum warning light started coming on at idle, (idle speed is good). I read the shop manual for advice, seemed like it could be the switch. So bought one from the dealer, easy install, however the light is coming on sooner now, and goes away as soon as I drive away. Brakes working fine and the vacuum line to the heater/air conditioning controls working well. What do I check next? Thanks in advance to all who have experience with this problem.



Also on a 350 mile trip to Santa Barbara CA, one way freeway I got 28. 55mpg calculated, about 900 pounds, with a little bit of rain. Wow I love this truck!

Happy Holidays:-laf, Patrick

 

[JLEONARD]

I had that problem and found a very very small crack in one of the plastic hose fittings. Replaced that and the problem went away.

 

[Bluebird]

Old part better than new...

I found streched out vacuum hoses at the vacuum pump, and the brake booster. I replaced one hose, cut the other shorter for a snug fit. I put the old vacuum warning switch back in, all is well, light turns off in two-seconds after start up and stays off at idle :-laf. I believe the new one is not within specs per the shop manual. Manual states it will function properly between 8. 5 and 25 inches of vacuum. I believe the new one must be set up differently. Anyway, I called the dealer, of course they would not refund because it was special order and an electrical part. However, since it is under warranty they will replace it, hopefully the first one I got was defective



Patrick .

 

[RedRamAndy]

Pardon my ignorance, but does a truck built in 4/1989 have this warning light? The cluster of lights to the right are "water in fuel" "low fuel" "wait to start", and "anti-lock". These all light upon key-on along with the "low oil pressure" lamp in the cluster. I've never seen a vacuum lamp. Is it burnt out and hiding?
Thanks.

 

[Bluebird]

Warning lights...'89,'93

I do not know what an '89 warning lights looks like, (my truck is a '93). The one that lights when the vacuum switch is activated is amber, with a B in the middle of what looks like brake shoes, it is on the bottom row of message center. It is now coming on once in a while



Patrick.

 

[Bluebird]

Vacuum light on again???

How do I check if my vacuum pump is going bad? I've check all hoses and switch. Any experience is appreciated



Happy New Year, Patrick.

 

[PToombs]

Throw a guage in it and see what it pulls. Try stepping on the brakes and see if the vacuum drops drastically. If so, the booster is probably bad. You can also shut the truck off, and see how fast it drops. If it drops right off, the check valve is bad. You can also shut it off, watch the light, and see when it comes on vs vacuum to check that.

My FSM isn't nearby or I'd look and check the specs for you.

 

[Bluebird]

Where's the check valve...

Where is the check valve? Can I replace that component? The brakes perform well, the light will go off with a little throttle off idle, (idle is fine). Thank you for your input



Patrick.

 

[PToombs]

The check valve is in the plastic piece inserted in the booster, where the line connects. Should be able to get one off the "Help" rack at the auto parts.

From the 93 FSM, The switch monitors booster vacuum. If the vacuum falls below 8. 5 inches for a minimum of 8-10 seconds, the switch completes the circuit, causing the light to come on. Vacuum pump output ranges from 8. 5 to25 inches of vacuum.

Then there is some basic troubleshooting of the switch, Put a vacuum on the switch, if the light goes out at 8. 5 in. , there is a loose hose or fitting, if it goes out at 25 in. , the switch is bad, blah, blah, blah.



Sometimes I should reread posts. :{ I typed all this and then reread and saw that you have an FSM. (and I'm not gonna delete it either! )

 

[19Kgvw]

My light has also been coming on and staying on longer recently..... I guess it's time to start some trouble shooting also..... this is good to get me motivated.

 

[19Kgvw]

more info.....

Throw a guage in it and see what it pulls.

Just to clear up my ..... where and how do you attach the gauge into the system?

And the guage..... what do I buy ( standard vaccum guage from 0-50 psi??)

 

[PToombs]

Yes, standard guage should work fine. As to where, depends on what part you are testing and what you are looking for. After the plastic insert on the brake booster is after the check valve, before it is not. Meaning that there should be vacuum for a while after you shut it off after the check valve, before the valve will drop right off.

Hope this helps.

 

[19Kgvw]

Yes, standard guage should work fine. As to where, depends on what part you are testing and what you are looking for. After the plastic insert on the brake booster is after the check valve, before it is not. Meaning that there should be vacuum for a while after you shut it off after the check valve, before the valve will drop right off.

Hope this helps.

This helps a bunch Pete- thank you for the details. I wish that that type of intuitive thinking came easier for me... .



Rich

 

[PToombs]

No problem, I was trying to up my post count anyways. :-laf