6.2 surging on off throttle deceleration

[boneheaddoctor]

Here's my question, been searching for days without finding anything similar.

Truck starts and runs well, fairly decent idle occasional hiccup, no smoke. this started after sorting out an air infiltration issue with rubber hoses and old fuel filter. At least I started noticing it then. Runs better now than it has in the 15 years I've owned it.

1987 GMC V2500 TH400 tans, 4.10 gears 33inch tires, 3/4 ton 4X4 runs well but taking foot off of the go pedal at higher speeds (say 50 to 70 is where you notice it most through engine braking) the first few seconds there is a notable surging before it tapers off and stops.

While I was replacing the rubber hoses and fuel filter I also installed a low pressure electric fuel pump on the engine side of the 6 port valve as getting the engine running after a fuel filter replacement was an exercise in futility and always needed a second vehicle and jumper cables and about 20 minutes of trying before it ever ran again. So it would self prime. That resolved the hard starting and rough idle I'd suffered with for years.

Tuck only has 74,*** actual original miles on it. Any ideas...I'm completely stumped.

 

[boneheaddoctor]

I found the source of my problem above. The fuel pump I put on apparently had 14 PSI which is too high. I discovered through the help of others...that 9psi is the limit a Standyne DB2 can take before it screws with timing, advance and other stuff....and the sudden deceleration spiked that pressure and caused the surging. At least that's the theory until my even lower pressure pump shows up later this week and I can install it.