99 astro low power on takeoff.

[78 Chevyrado]

Hey guys, been a while, I been working so much I don't have much time for squat these days.  well trouble with the van and I guess I'm so tired i can't figure it out.

I don't want to just go throwing parts at it.

I've replaced some rotted vacuum lines and the intake pressur sensor.  pressure sensor had a bad seal one you can't buy without getting the whole sensor.

Problem is

If I stop at a redlight, and go to take off again, it has no power at all, on slight inclines I've gotten stuck a couple of times...

Once the van is up to about 10-15mph, all power returns and it acts normally, but eats gas.

I've done the upgrade for the 99 CSFI to MPFI for the 4.3L V6.  I can find no vacuum problems apparently, and nothing out of place, I did this upgrade bout a month and a half ago, or 5000k ago.  just last week it started showing the symptoms i described.

I need it fixed asap, but im obviously too tired (dumb) to get this done right now without throwing parts at which i never want to do.

Any ideas?  As far as I know, everything is ok on outside visual inspection.  i never had this before, be insanely powerless off the line but get power back at 10mph..  dunno the rpms.

Any help will be greatly appreciazted.

may not reply quick, as ill likely be sleeping but im hoping to get this fixed on the weekend.  i dont wanna have to use the truck anymore, trucks suck for my kind of work.  all of them.  love my van and need it back up to speed.

OH YEAH!  also....  one other thing.  if i stay on the throttle too long like getting up to freeway speeds, the ac selector changes from AC or MAX to the floor.  let off the gas and it goes back to wherever i set it in about 15 seconds.  pulled the dash apart this weekend, found no vacuum lines leaking...  and nothing under the hood.  really theres only one line to  the engine i can find and it runs the ac controls.  unless the vacuum resivoir ball has a leak...


Thanks fellas...
Kenny

[zieg85]

Take the air filter element out and take it for a ride

[jaredts]

Vacuum leak maybe?  I realize you have been all over the vacuum hoses but maybe one of your injectors isn't in all the way or an intake leak.  Can you put a vacuum gage on it?  The hvac going to the floor seems to signal extra low vacuum.

[bd]

First thought on the low power issue is a restricted fuel filter.  Test drive it with a pressure gauge installed downstream from the filter and it will be evident enough.  On the vacuum doors defaulting to floor - a vacuum leak or check valve for the reservoir.  Hope you're feeling up to par, soon.

[Irish_Alley]

could be a cat problem did i mention i hate cats of all types well maybe not all. but remove the upstream O2 sensors see if that helps. but also with when was your last tune up?

[78 Chevyrado]

thanks for the replies guys, ima try all this stuff.

I put a new tps on it today because the one i had was ragged feeling.  it did improve a little bit but did not fix it.  it also has a pretty new air intake temp sensor.

on these if it is the cat, its expensive because the cat is made into the y-pipe.  total bs.

I'm scared its a crack in the plastic intake manifold.  which is a big job to get out. and if it is ill have to take it off totally just to check for cracks, its so cramped in there.

I'll pull the 02 sensors and try that and see.  cat is hollow sounding when i rap it with a hammer.

will hook a fuel psi guage up to it this weekend.  would have done it today but i loaned and and didnt want to buy another not to have to waitr a few days...

[jaredts]

Could you check for a vacuum leak by spraying wd40, starting fluid, whatever around the intake without taking it off?