Hey guys! I need your help. I am dealing with a stumble (miss?) that I cannot seem to cure. My setup is a BHW, with a stage2+ standalone Malone tune, GTC1549VZ, intake flap delete, MAF delete, and dynamic EGR. I'm on the original injectors and cam, both of which are somewhere around 100k miles old. The cam is not showing signs of wear and the lifters look fine.
Here’s a video of the ‘stumble’: https://photos.app.goo.gl/vvhnREc5uLijYxCX6
The stumble is most prevalent when the engine is cold, and prevents accelerating past 2.5-3k RPMs when it hits. As the engine warms up, the stumble becomes less dramatic, and eventually only happens at 3k RPMs. If I somehow push past, say, 3.5k RPMs, everything is normal all the way up to redline. If I have been driving for, say, 30 minutes or more (trip into town), there’t no stumble. I have an occasional 16705 show up in VCDS. I’ve checked the torsion value, injector opening times, and idle stabilization values, all of which seem within range.
Now, what have I done? First and foremost, I installed an OEM crank and cam position sensor. The stumble exists when the cam position sensor is not installed, so its not the cam crank trigger. The stumble is a more recent development, so I am assuming the crank trigger wheel is okay. The stumble became less intense when I replaced the crank sensor. I have checked the CTS, MAP, IAT, and O2 sensors, and the 5v bus seems to be a stable 5v when the engine stumbles, so I’m assuming at this point that this is not a sensor issue.
I had read that EGR issues can cause a similar stumble, so I unplugged the EGR and went for a cold drive, the issue persisted.
Malone recommended that I check and clean the injector harness, so I ohmed every inch of injector harness, and cleaned all contacts. I ensured that the contacts at the injectors were tight. They have solid connections at all points.
I peeled back the looming and checked all grounds, powers, and splices throughout the harness, cleaned and replaced a couple, and the issue persisted.
Most recently I have run a full can of liquid moly diesel purge and installed a new 2uc fuel filter element, which also seems to have softened the stumble ever so slightly, but it persists.
What do you guys think?
Here’s a video of the ‘stumble’: https://photos.app.goo.gl/vvhnREc5uLijYxCX6
The stumble is most prevalent when the engine is cold, and prevents accelerating past 2.5-3k RPMs when it hits. As the engine warms up, the stumble becomes less dramatic, and eventually only happens at 3k RPMs. If I somehow push past, say, 3.5k RPMs, everything is normal all the way up to redline. If I have been driving for, say, 30 minutes or more (trip into town), there’t no stumble. I have an occasional 16705 show up in VCDS. I’ve checked the torsion value, injector opening times, and idle stabilization values, all of which seem within range.
Now, what have I done? First and foremost, I installed an OEM crank and cam position sensor. The stumble exists when the cam position sensor is not installed, so its not the cam crank trigger. The stumble is a more recent development, so I am assuming the crank trigger wheel is okay. The stumble became less intense when I replaced the crank sensor. I have checked the CTS, MAP, IAT, and O2 sensors, and the 5v bus seems to be a stable 5v when the engine stumbles, so I’m assuming at this point that this is not a sensor issue.
I had read that EGR issues can cause a similar stumble, so I unplugged the EGR and went for a cold drive, the issue persisted.
Malone recommended that I check and clean the injector harness, so I ohmed every inch of injector harness, and cleaned all contacts. I ensured that the contacts at the injectors were tight. They have solid connections at all points.
I peeled back the looming and checked all grounds, powers, and splices throughout the harness, cleaned and replaced a couple, and the issue persisted.
Most recently I have run a full can of liquid moly diesel purge and installed a new 2uc fuel filter element, which also seems to have softened the stumble ever so slightly, but it persists.
What do you guys think?