myster

1990 4WD V6 SR5 Pickup.

I had a "slightly" cracked cylinder head replaced with a reman. head, along with head gasket and valve job. The quality of the work was questionable (part of a "recall" with a crumby dealership). The truck runs great now except for the fuel economy which immediately dropped from ~19mpg before the work down to around ~14mpg. The dealership says it could be the "vacuum switching valve" (PN 90925-05047). Does this sound reasonable? Is this valve easy to replace with standard tools, or does it require tearing apart the engine?

I found that part for ~$40 online, but I don't even know where it's located on the engine!

Any help would be greatly appreciated!

Thanks.

'BoatRunner

by 'vsv' your talking the bvsv? if so it's a little blue/green valve with two ends sticking out sideways...don't have a picture but i just replaced it in my own hg/valve job! Its located at the back of the engine under the intake manifold...and you do have to tear the top end of the engine apart to get to it unfortunately...as for fuel economy, i haven't checked mine since i did the job, but it will come soon

abecedarian

you had head work done...
have you had the cam timing checked?
have you had the valve clearances checked?

alltracman78

^Those, and dist/ignition timing.

There are a whole bunch of VSVs on your engine. I don't know from the P# which one it is, and I don't have ready acess to an EPC to check.
None require any real tearing apart.
It may effect your mileage, it depends which one it is.
However, if the tip got broken off and you have a small vacuum leak, that would definitely be a problem.
The VSVs are electronically controlled solenoids [think of them as on/off valves] that control when vacuum is applied to certain parts.


If it's this one it will be more of a hassle, just like he said.
It threads into a coolant passage, so there will be a bit of a mess too.
It controls when your engine burns fumes from the charcoal canister, and is turned on/off by temp [your coolant] instead of electronically.

*You could take that P# to the parts dept and see if they will show you on a diagram where that VSV is on your engine, it will be listed in the Electronic Parts Catalog [EPC]. *

TNRabbit

With a drop that big & that immediate, I'd guess a rather large vacuum leak somewhere for sure.

Also, if you've never replaced the O2 sensor, they can be damaged by water/coolant flowing into the exhaust (common with head/gasket issues). Bad O2 sensor may never throw a code, but will put your fuel economy in the crapper. They're pretty much crap after 100,000 miles, anyway.

thook

Words of wisdom, here.....