Auto Mechanic PLEASE

[Tinkerer]

2004 Astro AWD - 120,000 miles
about three weeks ago I lost about 3/4 of the HP. At anything more than 1/4 throttle the engine falls flat on it's face and starts to spark knock
It acted like the exhaust plugged up. I tested for plugged catalitic converters - less than 1 PSI at idle and never saw more than 2 PSI when reved up. Changed the cap and rotor. changed the inline fuel filter ( it was plugged compaired to the new one) Just checked the fuel pressure at the port on the back of the motor. It was 53 at idle and went up to 60 at higher RPM's. I plan to change the plugs and wires after the engine cools off. Air filter is clean. I did have it scaned and the only code was for MAF sensor. I have one off of a good running 2000 ASTRO. This was done before changing the fuel filter. ( couldn't get the old fuel filter out untill two days ago with WD 40) The good used MAF did nothing.
This is a work van and I can't do my job without it. If I take it to a dealership they will just change parts untill they find out what is wrong. The new parts that get installed won't get removed even if they don't help.
HELP

Steve

 

[Tinkerer]

It acts like it is running out of fuel ( running lean above 1/4 throttle ) What voltage should I get from the TPS at idle and full throttle?

 

[ROGUE]

The Tech Forum

Ive had real good luck getting help from sites like this.

 

[rschap1]

Guys at LS1.com have helped me with my GM questions too
My car does ALOT of wierd stuff (trans shift points, surging, idle speeds) with a bad MAF sensor.
I went through a couple remanufactured ones from Autozone, a cheap Ebay one, then a new one before finally getting a good one.
Both AZ remans were bad from get go.
The Ebay aftermarket cheapo ran for a couple days then acted up and threw codes/turned on SES light.
Last one is now about a year and a 1/2 old. Acting up now and then probably needs replacing again.
Runs FAR worse in this heat.
Fine in cooler temps.
Those seem to effect a lot of stuff.

 

[espritmike]

It's a fuel pump! Very little problems with these. I'm a 24 year veteran ASE master tech who owned an astro way back and actually have a 2005 AWD astro torn down in my shop right now (doing an engine on it= 27 hr job). Do all the other stuff first, in the end, it's always a fuel pump. Good luck, Mike

 

[Tinkerer]

Well the first test said the exhaust wasn't bad. Yesterday It got worse. Stoped into a service shop to have it scanned. still shows MAF codes. talked to one of the mech's and he said he wanted to retest the cats. turns out the back one was plugged. changed the cat and I got most of the HP back. compute had to relearn how to run the engine. runs great now , still have the vacuame controled A/C damper problem though. Will tackle that and the new plugs and wires this weekend.

 

[Tinkerer]

Thanks everyone. Hey the fuel filter was plugged.

 

[rschap1]

Congrats on the fix