Hard stumble at acceleration

[aaronb]

My 98 350 vortec, 4l60e with 115k miles,falls flat on its face on acceleration. it just started a couple days ago. Its really bad on the 1-2 shift.
I put a fuel pressure gauge on it. At idle I'm getting 52 psi, with the key on and not running the psI is at 58. I let the truck sit with gauge on it for 10 minutes and the pressure never dropped. With the truck in park I can Rev the hell out of it and it won't stumble.
It has a new cap, rotor, plugs and wires. All ac Delco.
I thought the fuel pump was the culprit, so I bought a new delphi and no change with the issue.
I also put in a new fuel filter aswell, even though the old wasn't bad.
I pulled the upper intake off last night and I'm not seeing any leaks with the spider or regulator.
The tps sensor tests good, I cleaned the maf sensor.
There are no engine codes.

 

[aaronb]

I replaced the spider with the new updated version and it still stumbles hard off the line, and will continue up through the gears.
I'm thinking now it's either ignition or I hate to say it transmission related. The tranny was rebuilt 6 years ago and has around 40k on it.
Still no engine codes.

 

[SAATR]

It sounds like an EGR issue, as flow problems in that system will cause hesitation and stumbling. I had a similar issue that was corrected just by replacing the valve, but sometimes it is necessary to clean the pipe and intake ports as well. I would pull the valve and inspect the pintle and seat, as well as the passages in the intake manifold.

Sent from my XT1254 using Tapatalk

 

[aaronb]

I pulled the egr off and it the pintle moves freely.
I'm going try and get a hold of a good scan tool to try and figure it out.
Would the map sensor cause a heavy miss under load only.
It just sucks that there is no check engine light on.
What makes it worse, I have a buyer out state that wants the truck and wants to drive it home.

 

[aaronb]

Little update. I rented a scan tool. Changed out the cap and rotor. I'm getting the p0300 code. Random misfire.
In park at idle the truck is backfiring out the exhaust.
I've been datalogging watching the different values and I noticed with the o2 sensors they will read from .245 and up to .895 within seconds.
Reading up on the code it doesn't say anything about the o2's causing this issue. It has a new complete fuel system from pump to the mpfi upgraded spider.

 

[aaronb]

Got it figured out.
It ended up being the cam position sensor. Pulled the plugs and 4 of the 8 were covered in fuel.
So it got a new set of ac Delco iridiums.