I'm tuning my 91 SD,ECM _8D using Tuner Cat.I'm running a M.R. intake.All other mods are in sig.So here's the question I was getting a backfire in the intake when ever I'd give the accelerator a quick push.So I increased the pumshot.It seemed to clear it up a bit.What I'm wondering is how much can you increase it, is there a limit or just keep going till I get rid of the backfire.Here's where I'm right now,looking at the chart starting at the top the first 3 are at a 100 the next 5 are at 50.8 then the last 9 are at 32.9.From everything I've read the MR requires a lot of pumpshot.So how much is alot.Incase it matters I don't have my VE tables tuned yet.I've been working on them but I still have a ways to go.I 'm running rich just about every where. The lower BLM are mostly between 108 &116 the lower INT aren't so bad most of them are between 121 & 130.That's all below 2K RPM as if you guys didn't already know.The upper BLM are 120 &126 the INT are are pretty much 128.The upper one were taken on the interstate cruising about 60 mph over 2K but mostly under 3K rpm.I'm trying not to bounce around on the tuning I'd like to get the VE nailed down but the backfire has to go before I backfire.So that's why I skipped back to the pumpshot.so any help would be great

 

Don't get obsessed with that as your only answer.
Timing plays a huge role in backfires.
Might hunt around within the last couple weeks I included a timing table for an engine kinda sorta like yours