Dinosaurs In Space Posted May 17, 2020 Share Posted May 17, 2020 (edited) Hi All, I'm at my wit's end with this. Long read ahead I've been having a low load stumble at all RPMs with driving for a few months now. I can get it to replicate the stumble by sitting in neutral and revving to 2000 -3000 RPMs trying to hold constant throttle input. The AFR is reading 14.7 perfectly then the car 'burps' and the AFR jumps to 13.5ish, the RPMs jump then the car recovers. This happens about once every 1-2 seconds. This DOES NOT happen at idle. When I force the car into open loop using AP, it still happens in open loop. I'm not getting ANY codes.. and I am getting some roughness on all cylinders (but not much) Thing's I've tried: All new parts are OEM *New Air Filter *New MAF *New Front O2 *New Coil Packs *New NGK LFR7AIX plugs (same as it had) *New DW65C fuel pump (with new OEM in tank filter) *New Battery *New Crank Sensor *Cleaned all ground straps *Tore apart fuel system to look for debris, all new Orings + gaskets *Disabled AVCS (in tune) *Changed Tunes (have been running same tune for over a year with no problems) *Cleaned throttle body *Intake leak test @ 5psi - no leaks 05 LGT Wagon 5-spd Mods are as follows: ~30k on engine / parts since rebuild *IAG Stg1 block *EFR 6758 *ID1000 with top feed fuel rails + plumbing *Tomei FPR *Stock Airbox + Perrin Inlet pipe *Stock header + Custom UP pipe *3" TBE Log attached - You can even see the AFR change in the LM-1 data (installed in factory 2nd O2 location) Any help is greatly appreciated! I haven't driven this car in a few months!AFR Issues.csv Edited August 17, 2020 by Dinosaurs In Space Link to comment Share on other sites More sharing options...
rhino6303 Posted May 17, 2020 Share Posted May 17, 2020 (edited) Look through the stumble thread for more ideas like the sti fpr setup and longer fuel line but I think the best solution is to reroute the fpr vacuum line from the #4 intake runner to the bpv vacuum source line. Try that and get back. Edited May 17, 2020 by rhino6303 Link to comment Share on other sites More sharing options...
ttnio Posted May 17, 2020 Share Posted May 17, 2020 i had hesitations/stumbles on accelaration on most occasions till my crankshaft position sensor gave up the ghost>P0335 dtc. I did a r/r routine on the sensor (cheap & easy), been running fine, no more code no more symptoms. 89000 miles ago. Link to comment Share on other sites More sharing options...
Dinosaurs In Space Posted May 18, 2020 Author Share Posted May 18, 2020 Look through the stumble thread for more ideas like the sti fpr setup and longer fuel line but I think the best solution is to reroute the fpr vacuum line from the #4 intake runner to the bpv vacuum source line. Try that and get back. Sorry, this is not the typical fuel stumble issue. I've already dealt with that problem on this vehicle years ago and found a solution that works for me. Link to comment Share on other sites More sharing options...
Dinosaurs In Space Posted May 18, 2020 Author Share Posted May 18, 2020 i had hesitations/stumbles on accelaration on most occasions till my crankshaft position sensor gave up the ghost>P0335 dtc. I did a r/r routine on the sensor (cheap & easy), been running fine, no more code no more symptoms. 89000 miles ago. Sorry, that was one sensor I forgot to list in the original post that was also changed.. Edited original post. Link to comment Share on other sites More sharing options...
08SpecB_DE Posted May 19, 2020 Share Posted May 19, 2020 Have you talked with any tuners? Maybe one of them could help. Link to comment Share on other sites More sharing options...
Dinosaurs In Space Posted August 15, 2020 Author Share Posted August 15, 2020 (edited) Bump Car will run 100% fine in idle. Monitoring the 'idle mode sw' in cobb, as soon as it turns to OFF the car starts stumbing, no matter how much pedal is applied. -New Pedal -New Engine wiring Harness -Replaced (used) throttle body Next step is compression test I guess.. Edited August 15, 2020 by Dinosaurs In Space Link to comment Share on other sites More sharing options...
Dinosaurs In Space Posted August 17, 2020 Author Share Posted August 17, 2020 (edited) SOLVED: for anyone who cares... Noticed 0.05 VAC on the +5 VDC sensor line and slowly disconnected sensors trying to find the issue. Took it all the way to the ECU trying to find the 5 VDC regulator circuit.. No luck I installed an LM1 in the secondary O2 location in my 3" downpipe for tuning.. Apparently this guy had crept over to the heat shield and cut the wiring to where when the downpipe shook, it shorted out the +12v line which caused the ECU to stumble... Disconnected the sensor and it runs good as new. What a ******* nightmare. Hopefully this post helps some one in the future.. and hopefully it isnt me. Edited August 17, 2020 by Dinosaurs In Space Link to comment Share on other sites More sharing options...
awfulwaffle Posted August 17, 2020 Share Posted August 17, 2020 That there's a twist. Good find. Link to comment Share on other sites More sharing options...
Max Capacity Posted August 18, 2020 Share Posted August 18, 2020 Wow, that's a odd problem. 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
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