First off: this forum rocks! I've looked around and this by far is the best one for Blazers, let alone for any technical issues for vehicles.
Ok here goes. I'm new here and have spent well over 5 hours reading up on some of the threads here and elsehwhere. I've done some testing, and cleaning, and multiple other suggestions and I' still having issues.

If I've got this in the wrong thread/subsection, feel free to move it.

I've been having hesitation issues for about 3 weeks. But here's the strange part. when you start the car, it works fine, throttle response is great. power is great, no issues.

After about 8-10 minutes (sometimes as much as 20) if any demand is placed on the engine (going up a hill) it starts to act really sluggish. engine wont rev up like normal. sometimes I barely get up the hill. Once this happens, it stays that way until I shut it off. After I start it again, it has good throttle response and power again.

On a side note. We had the fuel pump replaced last year. ever since then it has made a slightly different sound but nothing too out of normal for a fuel pump. Just in the last few weeks its started to make another 'higher pitch' sound after running for about 5-10 minutes. It sounds to me like its straining. But I've checked the pressure (see below) and it seems ok.

A little background might help.(couldn't hurt right?)

2000 Chevy Blazer LS 4 door, 4 wheel drive 4.3L V-6 112K miles.
new fuel pump about 10 months ago.(aftermarket, unsure which brand)
new fuel filter.
cleaned MAF.
cleaned EGR valve.
plugs and wires are about 1 year old.
cleaned Throttle body on upper intake manifold.(while off I noticed even carbon buildup over the inside of the manifold- I checked the forums about fuel pressure regulators!)

Fuel pressure diagnostic test downloaded, printed, and completed:
1. fuel pressure ignition on -engine off. 59-60 psi
2. while running at idle its about 60-65
3. engine off, ignition off, it only goes down about 3psi and stays steady.
4. while running, and quickly using the throttle, it goes up to about 70ish and back down. seems very responsive to throttle input.

I don't know how to test to see if the Catylitic converter is plugged. its welded on and I would have to remove the entire exhaust system to replace it. Is there a way to test the fuel return lines? maybe they are clogged?

I have a digital multimeter. but I don't quite know how to test for bad ground or high resistance for the fuel pump.

Just a bit of background. I know quite a bit about how engines work, I've done an engine substitution for my 77 VW bus. I put a watercooled Subaru engine in it including A/C and Heat! I'm pretty confident that its a fuel starvation issue, but I may be wrong.(I'm not afraid to admit it!)

Any help would be greatly appreciated. thank you in advance for your time.

Cheers.

Jason

 

It does not sound like you have a fuel related issue. I would suspect an ignition (spark) related problem. You say that the wires and plugs were changed a year ago. Did this include changing the cap and rotor? If not, that would be my first step.

 

would that make a difference if the car has normal throttle response and power when cold?
I think I did replace the cap and rotor when I did the wires. Its worked fine up until about 3 weeks ago.

my big concern is the sound the fuel pump makes after a few minutes (before the car starts to lose power)

thanks for the response swartlkk

 

Ignition components like the ICM and coil will show degradation type problems when they heat up. So that is a good possibility for your symptoms.

 

I'll remove the cap and rotor to check them out. thanks again for the help.

I'll report back to let you know if it helped.

 

i just had this problem one of the problems is that the coil was arching to ground to check just wait until dark and start then watch the coil
2nd had to replace the iat sensor controls the air flow it is on the throttle body
3rd i had to change the map sensor this took care of all my sluggish issues i hoped this helps i just joined so hi to all

 

thanks for the response Chris95blazer.

I'll check the dist tonite, its getting dark in a few.

the thing that keeps coming back to haunt my thinking is this:

once the car craps out, turned off, and then restarted. the problem goes away for a while. the engine is still just as hot, and any parts affected by heat are still warm. It just doesn't make any sense. could a building up of pressure somewhere in the fuel system be causing the fuel pump to quit?

Is there a diagram for the fuel system somewhere?

thanks again folks.

EDIT: update on the distributor. tested at night and no sparking or arcing visible.

any other ideas?

 

Components being warm is different than components being hot due to operation. The coil and ICM can cool quite rapidly.

 

5 seconds? because in that time I can restart it and it has all its power back, and no hesitation issues.

 

The ICM has a heat sink. Depending on the actual operating temperature of the ICM and the temperature of the air under the hood, 5 seconds could bring a measurable decrease in the temperature of the ICM.

Bottom line, test the components.