Rich Decel problem

Vehicle specific forum for tuning the Foxbody Chassis Mustangs utilizing the LUX0, GUFA, GUFB, and GUF1 Strategy

Rich Decel problem

Unread postby ben90lx » Mon Jun 12, 2017 1:35 pm

Vehicle Details:
90 Mustang LX 5.0
Manual Swap (from SN95 so no gear switch) - TRLOAD = 0
Stock shortblock
GT40p heads
Cobra Intake
Paxton 1220SL with stock pulley
8" renegade crank pulley
UPR power pipe
Deka 80lb injectors
90MM LMAF in the fender well, cone filter on the end
Running Moates Quarterhorse with X3Z base tune modified for the above fuel system. I have tried with the A9L2 and have the same problem.

I'm experiencing a rich decel issue when not in DSFO. Car is in-gear engine braking. LAMBSE ramps way lean (clips to 1.3) to pull fuel out compensating for the rich condition and then I get a nasty lean tip in and horrible bucking until the HEGOs pull it back. I was running M39 Cobra injectors and thought maybe it was fuel puddling due to the spray pattern, so swapped in the 80lb dekas. I made a run without the supercharger belt to dial in FN035 (which in my case was pretty much identical to the factory X3Z numbers), and I didn't notice the rich decel.
Put the belt back on and went out for a run, and the problem is back.

My theory is that under engine braking at elevated RPM, closed throttle, the supercharger is dumping boost back through the diverter valve and I'm getting a bunch of MAF turbulence. Attached is a graph from a quick log, and the whole file zipped up. Am I dealing with a tune issue or a hardware problem? Anybody else ever experience this? My KAMS otherwise are within 2% at all MAFV. Any help would be appreciated, this is like the last piece in my puzzle and I'm lost.

Log.jpg


log2.zip
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ben90lx
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Vehicle Information: 1990 Mustang LX 5.0, Manual T5 swap, A9P ECU with Moates Quarterhorse, TunerPro RT.

Re: Rich Decel problem

Unread postby decipha » Mon Jun 12, 2017 3:47 pm

I didn't bother to look at the logs but yea if your getting compressor surge on decal the maf will be reading the air and causing it to go rich

I take it shes in a draw through and not a blow through?
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Re: Rich Decel problem

Unread postby ben90lx » Mon Jun 12, 2017 4:25 pm

Yeah, draw through.

Its probably not compressor surge as much as bypass valve dumping just upstream. I can't believe I'm the only one running draw through on a powerpipe.

What's the easy way to do blow thru with the Paxton discharge setup? Non intercooled currently.
ben90lx
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Posts: 4
Joined: Wed Jun 08, 2016 11:01 am
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Vehicle Information: 1990 Mustang LX 5.0, Manual T5 swap, A9P ECU with Moates Quarterhorse, TunerPro RT.

Re: Rich Decel problem

Unread postby ben90lx » Mon Jun 12, 2017 4:28 pm

Or, do i just tune my DSFO to kick in immediately? I have no issues coining back into part throttle after fuel shutoff
ben90lx
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Posts: 4
Joined: Wed Jun 08, 2016 11:01 am
Name: Ben
Vehicle Information: 1990 Mustang LX 5.0, Manual T5 swap, A9P ECU with Moates Quarterhorse, TunerPro RT.

Re: Rich Decel problem

Unread postby decipha » Mon Jun 12, 2017 5:20 pm

non-intercooled that's about the only way to run it, otherwise you have to sandwich the maf in a large pipe in the middle of a bend and it doesn't work that well

if its an auto car you don't want to go into dfso immediately as that can cause loss of control at high speeds when you go closed throttle, set the delay to 1.5 seconds
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decipha
Tooner
 
Posts: 13363
Joined: Mon Jul 15, 2013 5:29 pm
Location: New Orleans, LA
Name: Michael Ponthieux
Vehicle Information: Supercoupin' x10
90 (4x 5spds) - Dante, Ruby, Daja, Ava
91 4r70w - Skarlett
92 (2x) 5spd & auto - Bianqa, Andrea
93 auto - Danika
94 5spd Rionda
95 auto Aisha
Vehicle 2 Information: Others:
00 Lincoln LS - Luanda
98 Camaro SS - Bounquisha
02 Harley F-150 - Sasasha
03 Marauder - DyShyKy
00 Explorer 5L - Bernyce

Re: Rich Decel problem

Unread postby Paulie » Tue Jun 13, 2017 10:40 am

You may want to try putting a screen before and after the maf to help with turbulence. Also the slot style mafs are less sensitive to turbulence.
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Vehicle Information: 1990 Mustang LX 5.0, GUFB/A9L, BE/EA, Quarterhorse, HCI, Vortech S-trim 8#, Stock shortblock, FRPP 42# injectors, PMAS MH95, T-5.

Re: Rich Decel problem

Unread postby ben90lx » Tue Jun 13, 2017 6:23 pm

I will try the screen/honeycomb trick. I've seen it in factory turbo car setups.

Did anybody look at the log or the graph? It's hard to tell if the injectors are causing the maf voltage to jump around or vice versa.
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