Hey all, new bug hit the truck. I am dumbfounded by it...

Some history, nearly all wiring under the hood was replaced, new exhaust from block to rear bumper, new fuel injectors, fuel filter, fuel lines, etc. TPS was adjusted properly, kick down is adjusted properly. The engine is bone stock with the exception of a 'blaster coil'. The truck passed smog after all my work with no issues.

Recent changes include proper tire inflation, leaf spring helpers, and making 4 seperate 100 miles trips with a bed full of stuff (helping someone move).

Over the past 2 weeks, I have been having an issue that is getting worse and worse, and now is making it pretty much impossible to drive without manuelly shifting my automatic transmission.

The tranny shifts way too early, and harshly. I'll be going 25/30 mph, it will shift harsh, and the speed drops to 20mph then sloooooooowly climbs back up. And repeats for every shift. When it does this, if I floor the gas pedal, it won't down shift. If I force it to down shift, it will shift, but the engine seems like its putting out nearly no power.

Happens when it is cold and hot, but theres a small window when it seems to shift properly. (Starts off doing it... seems to be better for a few miles then starts doing it again, and stays bad untill the truck has been left to sit for hours)

I tried shutting off the truck, and then driving again, issue stays with it.


I checked my vacuum lines with a vacuum guage, no leaks.... but I think I may have found an issue, the VSV (i think thats what it is, 2 vacuum lines, a wire, and an air breather on a small 2 inch plastic thing over the valve cover). There is no vacuum coming out of it, but 15psi going in. When reving/idling, no difference on the outlet.

When reving the vacuum through out all the hoses instantly drops to 5psi, then climbs back up quickly to rest around 25 psi.

I also noticed my power steering pump is leaking fluid.

Other than that, everything seems normal....


Any ideas?

 

bypassing the VSV SIGNIFICANTLY improved the issue, but did not solve it... So I will be getting a new one eventually...

 

Uh....where is this VSV located?

Have you tried pulling any codes from the diagnostic box?

 

Also, you said you adjusted the TPS properly, but did you test it?

 

Don't go replacing that VSV just yet.

Here's the general troubleshooting guide for an A340H auto tranny....

http://personal.utulsa.edu/~nathan-b...30generalt.pdf

 

Ahhh......but, you have an '86.

http://personal.utulsa.edu/~nathan-b.../4generalt.pdf

That's better.

 

what vsv? there's a vsv for the trans too?

I've got 3 vsv's... one for the EGR, one for the pair and one for the charcoal canister purge.

Are you telling me my stock system is wrong?

How does it ever pass smog checks?

 

Whats that you say, Abe? One for the "PAIR"?


Question to the OP: So you just went and randomly checked the VSVs on the valve cover?
On my '88 there are three: A/C idle up, PAIR, and fuel pressure regulator. They are in that order from front to back.

 

to fix the problem u have to drop out that trans and pop in a 5spd...the A340H's are garbage. or u can pop in a new A340H and go through the same problems 70,000 miles later.
just my .02 cents

 

He doesn't have the A340H. But, I do and they are good transmissions......VERY good, for what they are......which is an automatic.....which sucks.....hehehe. Really, it's a strong, reliable transmission. Over 200k miles on it now with no problems even after a serious wreck and miles of hauling lots of trailer weight.

You sure you only have 3? You should atleast also have one for the FPR.......that would make 4....and the headlamp fluid reservoir and muffler bearings. So, 6 in total.

Seriously, though, there's no vacuum switching valve for the transmission. Whatever's been disabled had nothing to do with the functioning of the transmission. All that I figure that has occurred is that you've helped reduce the vacuum load placed on the engine by the tranny in some round about way. Hard to say how since I don't know what VSV you'd disabled. Now, where's that switching valve located?

Oh.....and that one for the purge, if it's the same as on my '86, it's a bimetal switching valve. Basically the same in function, it's not electrical design.