94 GMC Sierra down on power

[Orangepeel]

Can you hook up a meter to the O2? I'm wondering if it's running very rich. Like maybe the temp sensor went out.

I did test the coolant sensor and the ohms I got seemed to correctly correlate with the actual engine temperature pretty closely

 

[mattd]

Vacuum should drop to 0 at snap throttle.

 

[Orangepeel]

Vacuum should drop to 0 at snap throttle.

And if it doesn't? When I checked it at 2500 rpm it stayed steady I didn't check it on throttle snap

 

[mattd]

And if it doesn't? When I checked it at 2500 rpm it stayed steady I didn't check it on throttle snap

if it doesn’t you have a breathing restriction

 

[Orangepeel]

Well the air filter and housing is off because it's tbi so very easy to remove so as far as the intake side I can't imagine what else would be restricted.

 

[clinebarger]

Snap the throttle all the way quickly.

 

[D60]

Well the air filter and housing is off because it's tbi so very easy to remove so as far as the intake side I can't imagine what else would be restricted.

I think breathing is inhale and exhale. How hard is it to drop the collectors?

I know you pulled the O2 but that isn't much for exhaust gases to escape. You can put a gauge in there

 

[Orangepeel]

if it doesn’t you have a breathing restriction

Appears to be fine. Snap goes to zero and then comes back and stabilizes

 

[PontiacHO]

Is it starting in low gear? Transmission shifting as it should?

 

[Orangepeel]

if it doesn’t you have a breathing restriction

Operates flawlessly. Fuel pressure is 11 and stays that way even when you rev it up drive it down the road etc. fuel pressure holds steady

 

[Orangepeel]

Is it starting in low gear? Transmission shifting as it should?

Yes. I have noticed when you first fire it up it runs good it'll rev right up and Park and then after a couple minutes it'll start cutting out when you rev It up and then randomly it'll be okay and then I'll do it again but it always seems to run perfect for the first couple minutes it's fired up.

 

[D60]

Yes. I have noticed when you first fire it up it runs good it'll rev right up and Park and then after a couple minutes it'll start cutting out when you rev It up and then randomly it'll be okay and then I'll do it again but it always seems to run perfect for the first couple minutes it's fired up.

Cap and rotor or ignition module?

 

[meep]

Weird. Has a compression test been done? Still wondering if the exh is restricted?

 

[PontiacHO]

Could be several things, low fuel pump pressure. That era (electric in-tank) had short fuel pump life. I’ve seen ignition issues cause problems such as failing modules, internally shorted coils, frayed wiring at the coil pickups, failing coil pickups, and sticking mechanical advance weights. If it were mine to solve, I’d rent a proper fuel pressure gauge first. If that shows no problem, order a complete distributor from Rock Auto.

 

[Orangepeel]

Distributor replacement fixed it. Runs perfect now! My guess is the pickup coil was weak but you have to dismantle the distributor to replace it so it seemed more intelligent just to replace the entire thing. She runs like a scalded cat now!

 

[D60]

Distributor replacement fixed it. Runs perfect now! My guess is the pickup coil was weak but you have to dismantle the distributor to replace it so it seemed more intelligent just to replace the entire thing. She runs like a scalded cat now!

I was wondering about this. If fuel pressure is ruled out I've seen weird behavior due to temp changes with distributor/ignition stuff.