Just documenting my experiences with what started out as a P0301 (Cylinder 1 Misfire), which then morphed into a P0171 (System Too Lean (Bank 1)).
Stock 2002 MP5 with 112k currently. original owner. (thumb)
I had been noticing a gradual decrease in fuel economy over the past couple of years and was never really sure how to begin troubleshooting, so I left it alone. About 6 months ago, I noticed some rough idling, and again left it alone because it wasn't bad enough to annoy me. Then the idle got worse, not to the point of stalling, and I eventually got a P0301. I swapped injectors on cylinders 1 & 2, and after a few days the car popped the P0171 without any other codes. (To date, P0301 has never returned). I ended up deciding the injectors were dirty and sent them to DW for cleaning and servicing. DW also provided a new set of injector seals (lower O-rings). I installed them, and idling issues appeared to have been resolved. Over time, idle issues came back and my fuel economy took a horrible turn for the worse. I have been barely getting 300mi to a tank these last couple of weeks, and I know that in the past I could squeeze out 360-380 mi. P0171 came back a couple days ago, and after lurking on this site some more, I did the ol' starter fluid spray test because I could hear a faint hiss coming from the intake side. Sure enough, when I sprayed anywhere around the injectors or intake manifold, the engine idle changed dramatically. I assumed that the injector seals must have been okay b/c why would DW provide improper seals, so I changed the intake manifold gasket. That seemed to help a little, but when spraying directly on the injector seals, it still created dramatic idle changes on all 4 injectors. So, I ordered 4 new stock injector seals and installed them. Now, spraying the starter fluid has no affect on the idle.
Looking back, I suspect my problem was likely bad/old injector seals from the beginning, and while I can't really be sure if changing the intake manifold gasket or injector cleaning was necessary, they weren't a waste of time or $. I also can't explain why DW's seals seemed to disagree with my IM/block. Physically, they are a different shape and did feel much looser when the fuel rail was torqued down, compared to the stock seals. YMMV. This was also a lesson in "always start with the simple stuff" --> Changing the injector seals should have my first step, not my last.
For now, I've got no more vacuum leaks that I know of, and the idle seems rock solid (except when the AC in on, but that's a problem for another day). We'll see if any error codes come back.
fyi, changing the IM gasket only took about 3 hours, going exceptionally slow. And, it was pretty easy to remove just the top half (leaving the dynamic chamber in place). If nothing else, it's another skill added to my toolkit.
Stock 2002 MP5 with 112k currently. original owner. (thumb)
I had been noticing a gradual decrease in fuel economy over the past couple of years and was never really sure how to begin troubleshooting, so I left it alone. About 6 months ago, I noticed some rough idling, and again left it alone because it wasn't bad enough to annoy me. Then the idle got worse, not to the point of stalling, and I eventually got a P0301. I swapped injectors on cylinders 1 & 2, and after a few days the car popped the P0171 without any other codes. (To date, P0301 has never returned). I ended up deciding the injectors were dirty and sent them to DW for cleaning and servicing. DW also provided a new set of injector seals (lower O-rings). I installed them, and idling issues appeared to have been resolved. Over time, idle issues came back and my fuel economy took a horrible turn for the worse. I have been barely getting 300mi to a tank these last couple of weeks, and I know that in the past I could squeeze out 360-380 mi. P0171 came back a couple days ago, and after lurking on this site some more, I did the ol' starter fluid spray test because I could hear a faint hiss coming from the intake side. Sure enough, when I sprayed anywhere around the injectors or intake manifold, the engine idle changed dramatically. I assumed that the injector seals must have been okay b/c why would DW provide improper seals, so I changed the intake manifold gasket. That seemed to help a little, but when spraying directly on the injector seals, it still created dramatic idle changes on all 4 injectors. So, I ordered 4 new stock injector seals and installed them. Now, spraying the starter fluid has no affect on the idle.
Looking back, I suspect my problem was likely bad/old injector seals from the beginning, and while I can't really be sure if changing the intake manifold gasket or injector cleaning was necessary, they weren't a waste of time or $. I also can't explain why DW's seals seemed to disagree with my IM/block. Physically, they are a different shape and did feel much looser when the fuel rail was torqued down, compared to the stock seals. YMMV. This was also a lesson in "always start with the simple stuff" --> Changing the injector seals should have my first step, not my last.
For now, I've got no more vacuum leaks that I know of, and the idle seems rock solid (except when the AC in on, but that's a problem for another day). We'll see if any error codes come back.
fyi, changing the IM gasket only took about 3 hours, going exceptionally slow. And, it was pretty easy to remove just the top half (leaving the dynamic chamber in place). If nothing else, it's another skill added to my toolkit.
