Truck dies under load

[SilveradoDude]

My truck (85 Silverado, 305, 4bbl Q-Jet) will not even hold idle under load. I adjusted the curb idle over the weekend and that helped a little but it was really a stop gap.

I checked the selected items:
1. The choke works fine, in fact the choke works great. No problems. The truck started on the first turn.
2. The distributor is bolted down fine.
3. The truck idles rough in Park and completely dies when put under load

The carb is a rebuild, around 6 years and 20K miles old.
Any help is appreciated.

[BLE 'BURBAN]

Check for vacuum leaks.
Also when did you last change your fuel filter?

[f.monroe]

Check the EGR Valve . Frank

[James McClure]

Dude, sounds like a vac leak. Check brake booster and PCV lines. Also check the booster itself. With engine off you should have at least 1 good power assist brake apply. Try pluging vac line to the booster also. Check ALL vac lines. Next spray some carb cleaner along intake to head junction to check ouiter part of intake gasket. Next pull the PCV valve and install a vac\fuel pressure guage in the PCV hole. If lower part of intake gasket is OK guage will show pressure, if it's bad you'll get a vac reading. Replace carb after you have ruled out any vac or ignition problem. jim

[SilveradoDude]

I will check for vacuum leaks and let you guys know. Thanks.

[89 crew]

How is the electrical? plugs, wires, coil? unless I misread your problem I'm gonna guess electrical. possible bad rotor, coil, or the button under it, or wires. I would start it up after dark, have someone put it in gear and load it while looking. If you don't see fire flying, open the cap and remove the rotor. See if it is arcing through to the shaft. then check the button in the cap see if it is making good contact.

[gchemist]

Hey dude,
Welcome to the site.

[SilveradoDude]

OK, I popped on a reman carb and it does run better and it doesn't exactly die under load BUT:
1. I need to give it a little gas before putting it in gear or it does die
2. Double checked all the vacuum hoses (still might be the EGR)
3. How do I check the EGR without replacing the EGR?
4. The carb starts out idling very high as if utilizing the choke (even though the truck is warmed up), I tap the gas and it idles near normal, I tap on it again it appears to engage the choke again as it begins to idle high.
5. It still idles rough under load but it does idle. I checked around the engine and two plug wires fell and were sitting on top of the hot exhaust manifold (they could be toast I will check).

And ideas appreciated.

[SilveradoDude]

Anyone?

[f.monroe]

Take the EGR off and check for carbon buildup that would hold it open . If clean , reinstall and unplug the vac source to it . Plug wires could also be breaking down and causing the problem . I have also heard of plugged up cat converters causing this prob . There are many things that can cause it .

Let me ask this , when did this prob start ? How long has it been like this ? Was it a sudden prob or did it just get worse over time?

If it hasnt had plugs and wires in a long time , they wouldnt hurt .

Frank

[SilveradoDude]

Originally Posted by f.monroe

Take the EGR off and check for carbon buildup that would hold it open . If clean , reinstall and unplug the vac source to it . Plug wires could also be breaking down and causing the problem . I have also heard of plugged up cat converters causing this prob . There are many things that can cause it .

Let me ask this , when did this prob start ? How long has it been like this ? Was it a sudden prob or did it just get worse over time?

If it hasnt had plugs and wires in a long time , they wouldnt hurt .

Frank

Taking of the EGR vacuum does what exactly? I will replace all plug wires.
It is kind of hard to say but it was a slow progressing problem and then it got instantly worse. do I need to make any adjustment on this new carb?

[SilveradoDude]

have you guys seen the price of a new EGR valve these days? $142!!! You gotta be kidding.

[89 crew]

Most of the time all that is wrong with an egr valve is carbon build up. you can usually clean them.

[SilveradoDude]

Originally Posted by 89 crew

Most of the time all that is wrong with an egr valve is carbon build up. you can usually clean them.

That's what I intend to do. I'm not dropping $142. I thought $20-30 max.

[89 crew]

If you want to test to see if it is an egr problem just unhook the vac hose and put a bolt in it. if it runs the same it most likely isn't bad.

[SilveradoDude]

OK, I think the truck dying under load was definitely the EGR valve. Thanks for the help. But the new carb is idling kinda high. What is the best adjustment procedure for a 4bbl Q-Jet?

[SilveradoDude]

I still have a few outstanding issues from that reman carb.

1. The carb kicks into high idle on cold start and doesn't kick down (even when you hit the accelerator a second time) until the truck warms up.
2. The truck is idling a little high even when the truck warms up.
3. The carb is using too much gas.
4. If it is really hot outside a get just a little dieseling when I turn the truck off.