Replaced Fuel Pump / TPS Etc.

[AstroManiac]

OK... my buddy & I replaced the fuel pump, fuel filter (though it was new & only had 25 miles on it) & TPS on his 98 Astro AWD 4.3 "W". (See TPS Symptoms post)
The new fuel pump, fuel filter & TPS were purchased at the local Chevy dealer.
After replacement, the fuel pressure is still 55 psi & when you pinch off the return line it only goes up to about 62-3 psi!
It still runs great, until it warms up, then the flat spot/hesitation starts in again even with the new TPS!
So... we changed the temp sender (by thermostat housing) & the temp sensor (in the left head) & it didn't help at all, as it starts the hesitation again when it warms up!
We also installed a new oil pressure sender, no change!
He bought a new "spider" & we installed it & no change!
He said "WTF" & bought a new coil & a ICM (ignition control module) NO CHANGE!
Another buddy had a brand new ECM (engine control module) from Chevy he let us try, NO CHANGE!
ANY IDEAS before it gets stolen & burned???

98 Chevy Astro AWD 4.3 "W" 200,000 miles
Ventura County, CA

[dunedog]

email Skippy, I remember he or his bro inlaw having a crazy problem like this.......

[LaGrasta]

You've ruled out so many items, whatever is left has to be small and identifiable. I can't offer what that is, but keep asking around, it can't be anything not worth repairing as the truck runs well overall. I t does sound like some sort of sensor that "clicks" once warm, thus telling the computer to react with different metering.

[sfeaver]

Do you have access to a scan tool? Sounds like you will need to watch the scan data to see what sensor is going out of range. You could also try unplugging a sensor and see if it improves. The PCM will use default values then. I'd try that with the MAF sensor, IAT sensor, and oxygen sensors.

A plugged cat might cause that too.

Scott

[dunedog]

Have you sent a PM to Skip yet!

[skippy]

dunedog is right , we chased the same thing down for over a month on a 92 that kept throwing a code 42 whick is a ESC electronic spark control . we spent over a month & 400 $ changeing parts & trying things , including a timing chain & gears . we finally just for shits & giggles changed out a coolant temp sensor i had lying on my desk .............& wouldn't you know , all the problems went away !!! we were friggin pissed .

good luck man !!!!!!

i'm leaning towards the same thing with yours , the motor runs fine when cold but acts up when warm . if the coolant sensor is telling the computer its still cold when its not, its going to run rich as hell till the computer knows the motor is warmed up .

does it smell like its running rich ? or smell like extra gas after it warms up a bit ?

[skippy]

A scan tool or a code reader will give you an idea where to start & whats going on . i just picked up a code reader on line for 32.00 $ & $8.00 shipping . it will help you figure a few things out rather than guessing .

[AstroManiac]

OK... we're using an INNOVA scan tool & some other expensive one that another neighbor loaned us. Both show the same info & ALL parameters etc., etc. show to be within specified limits.
Since he changed the O2 sensor that threw a code & said it wasn't working, there have not been anymore codes.
We changed both the temp sender next the the thermostat housing & the temp sensor that's in the left cylinder head.
The catalytic converter has less than 2000 miles on it.
The exhaust does not smell rich & it has never acted rich.
It's getting close to someone stealing it!

[kings-x59]

I'm usually off the mark on quirky problems like this for the newer year models, but you might look into the pulsator. My '89 doesn't have one, but as I understand it, it resides between the fuel pump and the fuel supply line. I've read very long threads about these causing problems that are difficult to find and resolve.

[AstroManiac]

98 Astro AWD 4.3 "W"

Even though we had already changed them, with the possibility that the new ones were bad, we we went ahead & swapped the temp sensor by the thermostat housing & the temp gauge sender in the left head.
NOTHING CHANGED... it still runs great when cold & even after it warms up... with the engine cover off, HOWEVER... about 6-8 minutes after putting the engine cover back on, it starts the hesitation & dying when you hit the throttle!
We drove it with the engine cover off & warmed up & it seemed to run fairly well!
We installed the engine cover with the engine running & about 6-8 minutes after the cover was back in place, the problem was there again!
We went back over everything & double & triple checked everything again!

What else is there that would be affected by the extra heat buildup with the engine cover in place???

[Water Boy]

Does your have the stove pipe?
Maybe the stove pipe valve is directing heated air from the manifold into the intake system.
And with the doghouse on, the heat is worse.
Just another thought........

[AstroManiac]

Nope... no stovepipe.

[LiftedAWDAstro]

You may want to pull the distributor. I have heard of a few cases of the gear stripping out in them and it runs bad or not at all. It's a long shot but a possibility especially with the mileage. How are the plugs and wires?

[lockdoc]

I had a hesitation in my 92 for the longest time. It turned out to be the EGR. Apparently it would stay open just a teensy, weensy bit. Just enough to cause problems

[AstroManiac]

We've checked the distributor gear, even though it was replaced about 20,000 miles ago & it looked great.
We've also checked the EGR & it is working properly & it is also fairly clean. It was replaced about 10,000 miles ago.
Still no codes!
After letting it cool down yesterday afternoon, my buddy fired it up & continueously drove around a couple blocks until it started its hesitation problem. From when he started until that happened was about 15 minutes.

In 45 years of mechanic-ing, I've never had a problem I couldn't figure out & this Astro is really giving me a headache!
My buddy that owns it, has spent quite a bit of money for parts & it feels like a full-time job working on this stupid thing.
Give me an engine with a distributor that uses a set of points & a good old carburetor any day!