I have a newly acquired '98 Cavalier with a 2.4L. Yesterday it started running rough and would not stay running. It felt like as I was driving that it was running out of fuel. I removed the the air tube at the throttle body and noticed that the intake had raw fuel sitting in the bottom of it. So I sponged it out, but the car still doesn't run well.
Any help is greatly appreciated!
Tony P.
Full Version: G.M. tech Question
my first guess was air meter, but the fuel sitting may indicate a stuck injector or a bad fuel pressure regulator. I had a buddy that had a bed regulator in one of those and it did the same thing. had fuel running out of the airbox.
you'll want to change the oil too, or at least smell the dipstick.
you'll want to change the oil too, or at least smell the dipstick.
we're going to check the injectors tonight. the only problem i have with that is, there is'nt any gas in the oil. hmmm. we have to start somewhere. thanks. any other suggestions would be helpful. but we are thinking injector
steve "pops" pastorino
steve "pops" pastorino
Hey Pops,
I was thinking a FPR makes perfect sense since there wasn't a noticeable amount of fuel in the oil. I didn't smell it either, just noticed that it wasn't overfull. I'm trying to chase down a Fuel Pressure gauge as well. I'm imagining that there will be a lot of FRP if the regulator is bad. Although the injectors in this motor spray onto the back of the valve not in the combustion chamber to the best of my knowledge (keeping in mind I'm a Ford guy). Which would explain the extreme amount of fuel present in the intake.
Thanks for the response I knew I'd run into someone here that has experienced this before.
Tony P.
I was thinking a FPR makes perfect sense since there wasn't a noticeable amount of fuel in the oil. I didn't smell it either, just noticed that it wasn't overfull. I'm trying to chase down a Fuel Pressure gauge as well. I'm imagining that there will be a lot of FRP if the regulator is bad. Although the injectors in this motor spray onto the back of the valve not in the combustion chamber to the best of my knowledge (keeping in mind I'm a Ford guy). Which would explain the extreme amount of fuel present in the intake.
Thanks for the response I knew I'd run into someone here that has experienced this before.
Tony P.
QUOTE (HRT187 @ May 13 2008, 11:51 AM) 
my first guess was air meter,
No air meter then, speed density.
Rough, Unstable, or Incorrect Idle and Stalling
Definition: Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.
Preliminary Checks
• Refer to the Powertrain On Board Diagnostic (OBD) System Check .
• Refer to Symptoms .
• Search for service bulletins.
Fuel System
• Check system fuel pressure. Refer to Fuel System Diagnosis .
• Check the fuel injectors. Refer to Sequential Multiport Fuel Injector Balance Test .
• Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis Testing.
• Check the fuel filter for being plugged or restricted.
• Check items which can cause an engine to run rich (long term fuel trim significantly in the negative range). Refer to Diagnostic Aids for DTC P0172 Fuel Trim System Rich .
• Check items that can cause an engine to run lean (long term fuel trim significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 Fuel Trim System Lean .
• Check for proper operation of the Evaporative Emission (EVAP) control system. Refer to Evaporative Emission Control System Diagnosis .
• Check for fuel in the Fuel Pressure Regulator vacuum hose.
Sensor/System
• Check the EGR valve for a stuck open pintle.
• Check for proper operation of the MAP Sensor. Refer to Manifold Absolute Pressure Sensor Output Diagnosis .
• Check for proper operation of the TP sensor.
• Check for proper operation of the ECT sensor.
• Check the Oxygen sensor (O2S 1). The O2S 1 should respond quickly to different throttle positions. If not, check the O2S 1 for silicon or other contaminants from fuel or the use of improper RTV sealant. The sensor may have a white powdery coating. Silicon contamination causes a high but false O2S 1 signal voltage (rich exhaust indication). The PCM will reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Refer to Oxygen sensor in Information Sensors/Switches Description .
Ignition System
• Check for proper ignition voltage output with the J 36012-A spark plug jumper wires and J 26792 spark tester or equivalent.
• Check the spark plugs for the following conditions:
- Check for wet or fuel fouled spark plugs.
- Check for cracks on the spark plugs.
- Check for wear.
- Check for improper spark plug gap.
- Check for burned electrodes or heavy deposits.
• If the spark plugs are fuel or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
• Check the Ignition Control Module (ICM) for proper ground connection.
• Check the ignition coils for cracks or carbon tracking.
Engine Mechanical
• Check the following:
- Compression.
- Sticking or leaking valves.
- Worn camshaft(s) lobe(s).
- Valve timing.
- Broken or weak valve springs.
- Balance shaft broken, damaged or incorrectly installed.
- Excessive oil in combustion chamber-Leaking valve seals.
• For incorrect basic engine parts. Inspect the following:
- Camshafts
- Cylinder head
- Pistons, etc.
• Refer to Engine Mechanical.
Additional Checks
• Check exhaust system for possible restrictions. Check for the following:
- Inspect exhaust system for damaged or collapsed pipes.
- Inspect mufflers for heat distress or possible internal failure.
- For possible plugged Three-Way catalytic converter. Refer to Restricted Exhaust System Check .
• Check for proper operation of the crankcase ventilation system.
• Check for malfunctioning engine mounts. Refer to Engine Mount Inspection in Engine Mechanical.
• An engine miss condition can be caused by Electromagnetic Interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase in RPM with little change in actual engine RPM change, indicates EMI is present. If a problem exists, check routing of secondary ignition wires, high voltage components (Near Ignition Control circuits).
• Check for intake and exhaust manifold passages for casting flash. Refer to Engine Mechanical .
Definition: Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.
Preliminary Checks
• Refer to the Powertrain On Board Diagnostic (OBD) System Check .
• Refer to Symptoms .
• Search for service bulletins.
Fuel System
• Check system fuel pressure. Refer to Fuel System Diagnosis .
• Check the fuel injectors. Refer to Sequential Multiport Fuel Injector Balance Test .
• Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis Testing.
• Check the fuel filter for being plugged or restricted.
• Check items which can cause an engine to run rich (long term fuel trim significantly in the negative range). Refer to Diagnostic Aids for DTC P0172 Fuel Trim System Rich .
• Check items that can cause an engine to run lean (long term fuel trim significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 Fuel Trim System Lean .
• Check for proper operation of the Evaporative Emission (EVAP) control system. Refer to Evaporative Emission Control System Diagnosis .
• Check for fuel in the Fuel Pressure Regulator vacuum hose.
Sensor/System
• Check the EGR valve for a stuck open pintle.
• Check for proper operation of the MAP Sensor. Refer to Manifold Absolute Pressure Sensor Output Diagnosis .
• Check for proper operation of the TP sensor.
• Check for proper operation of the ECT sensor.
• Check the Oxygen sensor (O2S 1). The O2S 1 should respond quickly to different throttle positions. If not, check the O2S 1 for silicon or other contaminants from fuel or the use of improper RTV sealant. The sensor may have a white powdery coating. Silicon contamination causes a high but false O2S 1 signal voltage (rich exhaust indication). The PCM will reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Refer to Oxygen sensor in Information Sensors/Switches Description .
Ignition System
• Check for proper ignition voltage output with the J 36012-A spark plug jumper wires and J 26792 spark tester or equivalent.
• Check the spark plugs for the following conditions:
- Check for wet or fuel fouled spark plugs.
- Check for cracks on the spark plugs.
- Check for wear.
- Check for improper spark plug gap.
- Check for burned electrodes or heavy deposits.
• If the spark plugs are fuel or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
• Check the Ignition Control Module (ICM) for proper ground connection.
• Check the ignition coils for cracks or carbon tracking.
Engine Mechanical
• Check the following:
- Compression.
- Sticking or leaking valves.
- Worn camshaft(s) lobe(s).
- Valve timing.
- Broken or weak valve springs.
- Balance shaft broken, damaged or incorrectly installed.
- Excessive oil in combustion chamber-Leaking valve seals.
• For incorrect basic engine parts. Inspect the following:
- Camshafts
- Cylinder head
- Pistons, etc.
• Refer to Engine Mechanical.
Additional Checks
• Check exhaust system for possible restrictions. Check for the following:
- Inspect exhaust system for damaged or collapsed pipes.
- Inspect mufflers for heat distress or possible internal failure.
- For possible plugged Three-Way catalytic converter. Refer to Restricted Exhaust System Check .
• Check for proper operation of the crankcase ventilation system.
• Check for malfunctioning engine mounts. Refer to Engine Mount Inspection in Engine Mechanical.
• An engine miss condition can be caused by Electromagnetic Interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase in RPM with little change in actual engine RPM change, indicates EMI is present. If a problem exists, check routing of secondary ignition wires, high voltage components (Near Ignition Control circuits).
• Check for intake and exhaust manifold passages for casting flash. Refer to Engine Mechanical .
If you have a code, I can send you the diagnostics for it if you give me your email.
QUOTE (Bishop @ May 13 2008, 02:23 PM)
No air meter then, speed density.
heh, good point, MAP then. MAF/MAP whats the difference?
I'm a buick guy, we use air meters. 
(even though I converted the GN over to speed density)
QUOTE (HRT187 @ May 14 2008, 09:48 AM)
heh, good point, MAP then. MAF/MAP whats the difference? I'm a buick guy, we use air meters. (even though I converted the GN over to speed density)
I'm a buick guy, we use air meters. (even though I converted the GN over to speed density)Speed density is a calculated airflow which uses the Ideal Gas Law to calculate cylinder air mass whereas MAF is real.
4 cylinders have difficulty with MAF due to reversion so the 'real' reading is not real.
Some manufacturers used the vane type MAF years ago but they broke a lot.
The current GM 4 cylinder models are now using MAF, but still use speed density in some cases and as a check.
Thank you guys for the info. I removed the vacuum hose from the regulator and primed the fuel system. Fuel shot out of the vacuum port like a geyser! LOL I've got one on order and I'll update the status on Friday.
Thanks again for the information!
Tony P
Thanks again for the information!
Tony P
just talked to tony. the car run good to work this a.m. he changed the fuel pressure reg last night. thanks for all your help
steve "pops" pastorino
steve "pops" pastorino
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