1995 gmc rally van g30 5.7l 4l80e

[Evilthing13]

So I have this gmc van,I know it’s not a truck but the people on this forum seem to be the most knowledgeable community for these tbi gm engines and I figured the powertrain on this vehicle is basically the same setup as the trucks. Anyways I have a 95 g30 5.7l 4l80e rally van and I have an issue where when I accelerate the van seems a bit sluggish even for a 1 ton van, if I blip the throttle while accelerating it seems a little more power is returned.
To date I’ve installed a few new things I’ll list
Coolant temp sensor, TPS sensor, fuel filter, spark plugs, plug wires, cap, rotor, air filter, egr, 02 sensor, flushed the coolant, changed tranny fluid, rebuilt tbi and fuel pressure regulator, made sure timing was set to zero with the wire disconnected before reconnecting it and I have no check engine codes. Any ideas on why it’s still running a bit sluggish and picks up a bit more power if I blip the throttle. Also has a very subtle stumble off idle if I give it a good blip. If I floor the pedal the van doesn’t seem to come to life and pick up speed like I think it should just kind of slowly gets up to speed. 140k on the odometer. it is drivable and will get up to highway speeds around 75 mph it’s like driving a ship through the atmosphere so I don’t really go past that just seems like something is off.

 

[RawbDidIt]

So I have this gmc van,I know it’s not a truck but the people on this forum seem to be the most knowledgeable community for these tbi gm engines and I figured the powertrain on this vehicle is basically the same setup as the trucks. Anyways I have a 95 g30 5.7l 4l80e rally van and I have an issue where when I accelerate the van seems a bit sluggish even for a 1 ton van, if I blip the throttle while accelerating it seems a little more power is returned.
To date I’ve installed a few new things I’ll list
Coolant temp sensor, TPS sensor, fuel filter, spark plugs, plug wires, cap, rotor, air filter, egr, 02 sensor, flushed the coolant, changed tranny fluid, rebuilt tbi and fuel pressure regulator, made sure timing was set to zero with the wire disconnected before reconnecting it and I have no check engine codes. Any ideas on why it’s still running a bit sluggish and picks up a bit more power if I blip the throttle. Also has a very subtle stumble off idle if I give it a good blip. If I floor the pedal the van doesn’t seem to come to life and pick up speed like I think it should just kind of slowly gets up to speed. 140k on the odometer. it is drivable and will get up to highway speeds around 75 mph it’s like driving a ship through the atmosphere so I don’t really go past that just seems like something is off.

Have you checked vacuum and fuel pressure? I've seen these symptoms from small vacuum leaks, or from inadequate fuel pressure as well. Either way, it'll run slightly lean that way under sustained acceleration, but short bursts are fine (computer may compensate and dump fuel creating a rich condition as well, not sure how the ECM in the TBI compensates for O2 sensor readings, but this is common). 140k seems about right for a fuel filter change if you haven't already, or it could be regulator as well. Both parts are cheap, so if you're not at spec with fuel pressure I'd replace both and then check before going any further.

Edit: check vacuum first, the regulator uses the vacuum system for reference, so a problem there will affect fuel pressure.

Sent from my SM-N976V using Tapatalk

 

[Evilthing13]

Found multiple exhaust leaks at the manifold and the flange after I shoved a shop vac up the tail pipe and turned it to blow. Sealed em up and power is definitely restored and hesitation is gone!

 

[L31MaxExpress]

Now that you have the stumble gone. Try a little more timing. Advance it 2° at a time. Most TBIs like another 4-6° of base timing and will make alot more torque. Fuel pressure should be about 13 psi on a stock engine. If the fuel pressure is in the low-end of spec (9-10 psi) it will wake it up noticeably.

 

[AuroraGirl]

I used my tech 2 to help my uncle with his 95 GMC van. After pcv, vacuum leak fixed, and a slight advance on the timing we noticed it had a lot more pep too. My tech 2 said it would idle or cruise with no accelerator change from 10 to 18 degreess advance. That's according to the tech 2. I'm not an expert on timing but just sharing experience