My little sister's car that she got for a good deal a few years ago... It needs some attention in other areas, but it idles rough, but responds well enough when accelerating. Its behavior reminds me of when the fuel pump went out on my Cavalier a long time ago. Is there an easy enough way to verify it's the fuel pump outside of it ultimately dying and not firing up again? Could it be something else more obvious? Again, the codes it has right now are P0171 and P0300. Thanks!
2003 Malibu P0171 and P0300
- Thread starter Blang
- Start date
P0171 is a lean condition which could be caused by a fuel pressure problem or a vacuum leak. The P0300 is a random misfire code which could be caused by a fuel problem. A fuel pressure test will indicate if you have the correct fuel pressure at idle. I would see if you can find a scanner that can read live data misfire info to narrow down what cylinder is misfiring.
3.1 V6 has a handful of plastic/rubber vacuum hoses on top to the purge valve/PCV/fuel pressure regulator
Inspect those
Pull the hose off the FPR, make sure it doesn't dribble out fuel
Inspect those
Pull the hose off the FPR, make sure it doesn't dribble out fuel
SammyChevelleTypeS3
$50 site donor 2023
Checked the fuel filter already I imagine?
Thanks for the responses. Update... my little sister lives far enough away that I haven't had a chance to and spend time with her car yet. My parents and brother-in-law got anxious and took it in after my brother-in-law replaced the fuel filter. Not a waste of time to replace the filter, but it didn't solve the problem. They took it to a trusted mechanic who noticed some loose vacuum hoses. He also replaced the mass airflow sensor (not convinced that needed to happen) and replaced the plugs and wires.... I wonder if he went a little overboard, but he didn't charge an outrageous amount. So I'm not mad, but wish that I could have been a little more directly involved. At the moment it is running well, but I still have a disturbance in the force that something could still come up...
They wanted it fixed and took it somewhere, no big deal at least you are not married to the problem someone else is and that is a good thing IMO.
SammyChevelleTypeS3
$50 site donor 2023
I used to spray WD40 over the top of a running engine to help pin point vaccum leaks. Always worked great. When the spray hits close to the leak you can tell by the engine speed change. I am pretty sure vacuum leaks and those type of gremlins have pretty much been greatly reduced with today's better designed fuel injected engines.
Your P0300's can be many things, beyond the fuel system. But the lean codes also point in the direction of manifold/intake issues. Could also be a MAF issue. First things first in order of cheap to expensive fixes:
Replace your air filter. Check all air intake ducts and bands - tighten that puppy up and make dead sure your airbox seals tight after clipping it in place.
Use an unlit propane torch to just hose a spray of fuel all around the intake hoses and upper manifold gaskets. If the idle changes, you found a leak. A scan tool with real-time monitoring of fuel trims will help you *vastly* - this will help you chase the lean condition.
MAF sensor test with same realtime OBD-II Scanner. Set it to monitor grams/Sec. (Yes, evil metric) But your intake of air weight should match your engine displacement which makes it simple to diagnose. A 2.2L engine should flow 2/2.5 grams/Second. A 3.6, 3.6 or so grams/Sec. A 6.0L, 6 grams/sec. (See the pattern here) If it's off, remove the sensor carefully and wash it down with MAF sensor cleaner. CRC makes a great and cheap chemical you can find at Walmart, let alone anywhere else. Read bottle instructions. Ultimately, simply do not physically touch the fine platinum wires in the sensor. Just wash the wires and the plastic block, honeycomb...whatever, thoroughly. Set aside for 20 minutes to air dry and reinstall. Again, be sure the electrical connector is Guttentaught, along with your screws and bands that hold your intake together.
Fuel pressure test at the injector rail(s). GM vehicles are really sensitive at moment of key on, crank to start - and idle. If it's out of spec:
Replace any inline fuel filters you can find from tank socks to anything in the engine compartment or resting against a frame rail. (Usually by driver's door on the undercarriage - some in engine bay)
Check/replace fuel regulator. (Non-GDI)
If fuel pressure is out of spec (REALLY low), or drops quickly to nothing with engine off, key out..... and you got to all physical filters and regulator - you'll likely need a fuel sender replacement. This includes tank sending unit, socks, and possibly a wire harness chop and swap.
Be really ready for a possible swap of plug boots, plugs (If over 75~150k miles - again, model dependent) and possibly coil packs. A full plug, boots and coil job will possibly cost you as much or more as a fuel sender job.
IF it's a GDI, there can be issues with you FSM box. On many models it's passenger side trunk mounted behind the fabric and carpet right up by the taillight. On others on driver's side rear under the bed/body adjacent to the fuel tank. This is NOT an easy diagnosis. The same physical module is used against MANY makes and models of GM products, from Chevy, GMC, Cadillac, and Buick. It *absolutely* needs to be flashed to your specific vehicle application. At this point, it need to see dealer attention or a local shop with access to GM's bi-directional tools and flash programming.
IF it's a GDI engine: there is a very remote possibility of injector issues. Usually involving removal/cleaning/replacement. It's really hairy work to complete because the upper half of the engine and intake is built up around the injectors. Be it on your head and skills do you undertake that check and service. Again, at this point; seek Dealership or local garage tech to help you there.
Modern fuel injection is hands down - amazing. The physics alone is a life's study. But boy-howdy when it goes wrong? I'd sooner eat a bag of cinder blocks.
Replace your air filter. Check all air intake ducts and bands - tighten that puppy up and make dead sure your airbox seals tight after clipping it in place.
Use an unlit propane torch to just hose a spray of fuel all around the intake hoses and upper manifold gaskets. If the idle changes, you found a leak. A scan tool with real-time monitoring of fuel trims will help you *vastly* - this will help you chase the lean condition.
MAF sensor test with same realtime OBD-II Scanner. Set it to monitor grams/Sec. (Yes, evil metric) But your intake of air weight should match your engine displacement which makes it simple to diagnose. A 2.2L engine should flow 2/2.5 grams/Second. A 3.6, 3.6 or so grams/Sec. A 6.0L, 6 grams/sec. (See the pattern here) If it's off, remove the sensor carefully and wash it down with MAF sensor cleaner. CRC makes a great and cheap chemical you can find at Walmart, let alone anywhere else. Read bottle instructions. Ultimately, simply do not physically touch the fine platinum wires in the sensor. Just wash the wires and the plastic block, honeycomb...whatever, thoroughly. Set aside for 20 minutes to air dry and reinstall. Again, be sure the electrical connector is Guttentaught, along with your screws and bands that hold your intake together.
Fuel pressure test at the injector rail(s). GM vehicles are really sensitive at moment of key on, crank to start - and idle. If it's out of spec:
Replace any inline fuel filters you can find from tank socks to anything in the engine compartment or resting against a frame rail. (Usually by driver's door on the undercarriage - some in engine bay)
Check/replace fuel regulator. (Non-GDI)
If fuel pressure is out of spec (REALLY low), or drops quickly to nothing with engine off, key out..... and you got to all physical filters and regulator - you'll likely need a fuel sender replacement. This includes tank sending unit, socks, and possibly a wire harness chop and swap.
Be really ready for a possible swap of plug boots, plugs (If over 75~150k miles - again, model dependent) and possibly coil packs. A full plug, boots and coil job will possibly cost you as much or more as a fuel sender job.
IF it's a GDI, there can be issues with you FSM box. On many models it's passenger side trunk mounted behind the fabric and carpet right up by the taillight. On others on driver's side rear under the bed/body adjacent to the fuel tank. This is NOT an easy diagnosis. The same physical module is used against MANY makes and models of GM products, from Chevy, GMC, Cadillac, and Buick. It *absolutely* needs to be flashed to your specific vehicle application. At this point, it need to see dealer attention or a local shop with access to GM's bi-directional tools and flash programming.
IF it's a GDI engine: there is a very remote possibility of injector issues. Usually involving removal/cleaning/replacement. It's really hairy work to complete because the upper half of the engine and intake is built up around the injectors. Be it on your head and skills do you undertake that check and service. Again, at this point; seek Dealership or local garage tech to help you there.
Modern fuel injection is hands down - amazing. The physics alone is a life's study. But boy-howdy when it goes wrong? I'd sooner eat a bag of cinder blocks.
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