I recently got a new project car, a custom 2000 cavalier z24. When I got it, it was a no start no crank. Got it running after cleaning ignition contacts and putting in new battery, coils, and plugs.
She was running fine for the most part, but now from time to time she starts sputtering at lower rpms if you happen to give it just a bit too much gas. Figured this might be fuel related. Replaced fuel filter, and was going to replace injectors. Somehow I ended up with the wrong injectors, and the ones in the car seem to be hardwired instead being able to remove a clip for plug. So for the time being I cleaned off the old injectors because they were filthy. Also found that the coupling for the airbox to the throttle body was pretty worn and didn't appear ti be seating properly, so replaced that to hopefully keep it air tight in that area. Also cleaned map sensor while I was down there. Disconnecting it showed an obvious difference, so figured it was still operable.
At first she sputtered briefly, then she ran like a champ. For a little while, now the sputtering is creeping back up little by little. So right now I'm thinking one or more injectors might actually be failing, or perhaps I have an issue somewhere in the exhaust.
Was hoping to get some extra opinions so I have a few new ideas. If any extra info is needed is be happy to give it.
Do have a code P0171 for lean fuel mixture.
Does the sputtering continue as you give it more gas? Or does it smooth out at higher RPM? No issues at idle?
THE .ORG IS MY KITCHEN!
For the most part it does smooth out once I'm going. Highway on ramps are the worst right now. If I'm very gentle on the accelerator I can usually coax her up to speed, but when you try to give a bit more gas from time to time she'll start sputtering. As far as idling, this matter is very sporadic. Most of the time she's fine, but occasionally you can hear it in the exhaust, like a misfire (straight piped, easy to hear). Though a bit more rare, she has started up and idled very rough for a good 10 minutes with the P0171 code popping up. That hasn't happened too recently now though. After the recent work the sputtering is remaining at a minimum, but is still there. Just can't wait to get this car in peak running condition. Thank you so far for any help into this matter.
Check for any possible vacuum leaks, they may only present themselves when cold or when warm. Sometimes, when metals expand/contract in different temperatures, they can cause leaks to show up or disappear. Also, check your throttle position sensor for a possible dead spot that may be causing the ECM to not see the throttle being partially open. Might as well clean the throttle body while you're at it. I assume there are no exhaust leaks creating a false lean code? If you have a leak before the O2 sensor, it can throw a lean code because fresh air can enter the exhaust. You have no misfire codes? It could also be an issue of bad gas, low fuel pressure (bad pump or restriction in the line), faulty injector(s), crud in the rail, idle air control valve sticking open, etc. Basically, you want to check for anything that can either cause excess air to enter the system, or limit the amount of fuel. If you can, seeing some live data with a scan tool may be helpful.
Is your exhaust straight pipe after the cat, or has the cat been removed?
Important: After repairs use the scan tool Fuel Trim Reset function to reset long term fuel trim to 128 (0 percent).
•Fuel pressure —- System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle at various road speeds and/or loads to confirm. Refer to Fuel System Diagnosis.
•MAP sensor — An output that causes the PCM to sense a lower than normal manifold pressure (high vacuum) can cause the system to go lean. Disconnecting the MAP sensor will allow the PCM to substitute a fixed (default) value for the MAP sensor. If the lean condition is gone when the sensor is disconnected, substitute a known good sensor and recheck. Refer to Symptoms.
•Fuel contamination— Water, in even small amounts, near the in-tank fuel pump inlet, can be delivered to the injector. The water can cause the following conditions:
– Plugged fuel filter
– Lean exhaust
– DTC P0171
•Check for poor O2S 1 or MAP sensor connection at the PCM. Inspect the harness connectors for the following conditions:
– Backed out terminals
– Improper mating
– Broken locks
– Improperly formed
– Damaged terminals
– Poor terminal to wire connection
•Inspect wiring harness for damage. If the harness appears to be OK, observe the O2S 1 display on the scan tool while moving connectors and wiring harness related to the engine harness. A change in the display will indicate the location of the malfucntion
•Check brake power booster check valve for possible leaks.
THE .ORG IS MY KITCHEN!
I had this exact same issue a while ago on my 2.4. Tried the fuel filter, plugs l, coil packs, TPS. Eventually the solution was replacing the white coil pack housing and the boots that connect the housing to the plugs. Apperently over time small cracks in the boots or housing can cause a short to ground and interrupt the spark. Not sure of this is the same issue for you but my symptoms were identical to yours. You can go look at my old post for more details.
Hope this helps.