to go flat as stated, would be all injectors, not just one. Could also be low fuel pressure. Could also be a bad MAP sensor.

 

Yes, but he's only stated a P0301, which is why I don't think it's a fueling issue unless it's injector #1. A general fueling issue would set more misfire codes, and most likely a P0300 as well.

 

not necessarily. JTEC nor NGC are smart enough for that (well, NGC *might* be). If all 8 injectors are only getting 34 (or 20 or 10) psi instead of 49psi only momentarily, that won't throw a code because the upstream O2's will still see fuel present and all pulses will be similarly lean, but then it will come back before it can verify the code.

For a code to be set, it has to meet several conditions. A code starts as pending, when a condition has occurred once. If that condition exists "x" more times in "t" time period, it will set a code. Otherwise, it will stay pending then clear out.

This is a situation where it may set a "fuel trim lean" code as pending, but since it comes back, that code stays pending then clears out.

 

If you say so, you're more up on the Dodge stuff than I am, but I'd think that if this were the case it would hit more than the #1 cylinder with a misfire code. If it's hitting the same cylinder every time, that points more towards it being specific to that cylinder, unless #1 is the furthest injector out which means it would see the lowest pressure when it drops off.

 

re-read what I said. it probably is hitting every cylinder. Btu the PCM won't see it unless he trims go out of whack for over a minute sustained. I forget what the actual criteria is, but I know for some codes (particularly EVAP) it has to exist for 3 start-run cycles before it will throw a code. If it's there for 2 start-run cycles then not the third, it clears out and counter starts over. Misfires are a little more specific.

 

OXYGEN SENSOR (O2S) MONITOR

Effective control of exhaust emissions is achieved by an oxygen feedback system. The most important element of the feedback system is the O2S. The O2S is located in the exhaust path. Once it reaches oper- ating temperature 300° to 350°C (572° to 662°F), the sensor generates a voltage that is inversely propor- tional to the amount of oxygen in the exhaust. The information obtained by the sensor is used to calcu- late the fuel injector pulse width. This maintains a 14.7 to 1 Air Fuel (A/F) ratio. At this mixture ratio, the catalyst works best to remove hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide (NOx) from the exhaust.

The O2S is also the main sensing element for the Catalyst and Fuel Monitors.

The O2S can fail in any or all of the following manners:

• slow response rate
• reduced output voltage
• dynamic shift
• shorted or open circuits
Response rate is the time required for the sensor to

switch from lean to rich once it is exposed to a richer than optimum A/F mixture or vice versa. As the sen- sor starts malfunctioning, it could take longer to detect the changes in the oxygen content of the exhaust gas.

The output voltage of the O2S ranges from 0 to 1 volt. A good sensor can easily generate any output voltage in this range as it is exposed to different con- centrations of oxygen. To detect a shift in the A/F mixture (lean or rich), the output voltage has to change beyond a threshold value. A malfunctioning sensor could have difficulty changing beyond the threshold value.



MISFIRE MONITOR
Excessive engine misfire results in increased cata-

lyst temperature and causes an increase in HC emis- sions. Severe misfires could cause catalyst damage. To prevent catalytic convertor damage, the PCM monitors engine misfire.

The Powertrain Control Module (PCM) monitors for misfire during most engine operating conditions (positive torque) by looking at changes in the crank- shaft speed. If a misfire occurs the speed of the crankshaft will vary more than normal.




FUEL SYSTEM MONITOR
To comply with clean air regulations, vehicles are

equipped with catalytic converters. These converters reduce the emission of hydrocarbons, oxides of nitro- gen and carbon monoxide. The catalyst works best

when the Air Fuel (A/F) ratio is at or near the opti- mum of 14.7 to 1.

The PCM is programmed to maintain the optimum air/fuel ratio of 14.7 to 1. This is done by making short term corrections in the fuel injector pulse width based on the O2S sensor output. The programmed memory acts as a self calibration tool that the engine controller uses to compensate for variations in engine specifications, sensor tolerances and engine fatigue over the life span of the engine. By monitoring the actual fuel-air ratio with the O2S sensor (short term) and multiplying that with the program long-term (adaptive) memory and comparing that to the limit, it can be determined whether it will pass an emis- sions test. If a malfunction occurs such that the PCM cannot maintain the optimum A/F ratio, then the MIL will be illuminated.


CATALYST MONITOR
To comply with clean air regulations, vehicles are

equipped with catalytic converters. These converters reduce the emission of hydrocarbons, oxides of nitro- gen and carbon monoxide.

Normal vehicle miles or engine misfire can cause a catalyst to decay. A meltdown of the ceramic core can cause a reduction of the exhaust passage. This can increase vehicle emissions and deteriorate engine performance, driveability and fuel economy.

The catalyst monitor uses dual oxygen sensors (O2S’s) to monitor the efficiency of the converter. The dual O2S’s sensor strategy is based on the fact that as a catalyst deteriorates, its oxygen storage capacity and its efficiency are both reduced. By monitoring the oxygen storage capacity of a catalyst, its effi- ciency can be indirectly calculated. The upstream O2S is used to detect the amount of oxygen in the exhaust gas before the gas enters the catalytic con- verter. The PCM calculates the A/F mixture from the output of the O2S. A low voltage indicates high oxy- gen content (lean mixture). A high voltage indicates a low content of oxygen (rich mixture).

When the upstream O2S detects a lean condition, there is an abundance of oxygen in the exhaust gas. A functioning converter would store this oxygen so it can use it for the oxidation of HC and CO. As the converter absorbs the oxygen, there will be a lack of oxygen downstream of the converter. The output of the downstream O2S will indicate limited activity in this condition.

As the converter loses the ability to store oxygen, the condition can be detected from the behavior of the downstream O2S. When the efficiency drops, no chemical reaction takes place. This means the con- centration of oxygen will be the same downstream as upstream. The output voltage of the downstream O2S copies the voltage of the upstream sensor. The

only difference is a time lag (seen by the PCM) between the switching of the O2S’s.

To monitor the system, the number of lean-to-rich switches of upstream and downstream O2S’s is counted. The ratio of downstream switches to upstream switches is used to determine whether the catalyst is operating properly. An effective catalyst will have fewer downstream switches than it has upstream switches i.e., a ratio closer to zero. For a totally ineffective catalyst, this ratio will be one-to- one, indicating that no oxidation occurs in the device.

The system must be monitored so that when cata- lyst efficiency deteriorates and exhaust emissions increase to over the legal limit, the MIL will be illu- minated.




DESCRIPTION - TRIP DEFINITION
The term “Trip” has different meanings depending

on what the circumstances are. If the MIL (Malfunc- tion Indicator Lamp) is OFF, a Trip is defined as when the Oxygen Sensor Monitor and the Catalyst Monitor have been completed in the same drive cycle.

When any Emission DTC is set, the MIL on the dash is turned ON. When the MIL is ON, it takes 3 good trips to turn the MIL OFF. In this case, it depends on what type of DTC is set to know what a “Trip” is.

For the Fuel Monitor or Mis-Fire Monitor (contin- uous monitor), the vehicle must be operated in the “Similar Condition Window” for a specified amount of time to be considered a Good Trip.

If a Non-Contiuous OBDII Monitor fails twice in a row and turns ON the MIL, re-running that monitor which previously failed, on the next start-up and passing the monitor, is considered to be a Good Trip. These will include the following:

• Oxygen Sensor
• Catalyst Monitor
• Purge Flow Monitor
• Leak Detection Pump Monitor (if equipped)
• EGR Monitor (if equipped)
• Oxygen Sensor Heater Monitor
If any other Emission DTC is set (not an OBDII

Monitor), a Good Trip is considered to be when the Oxygen Sensor Monitor and Catalyst Monitor have been completed; or 2 Minutes of engine run time if the Oxygen Sensor Monitor or Catalyst Monitor have been stopped from running.

It can take up to 2 Failures in a row to turn on the MIL. After the MIL is ON, it takes 3 Good Trips to turn the MIL OFF. After the MIL is OFF, the PCM will self-erase the DTC after 40 Warm-up cycles. A Warm-up cycle is counted when the ECT (Engine Coolant Temperature Sensor) has crossed 160°F and has risen by at least 40°F since the engine has been started.




DESCRIPTION - COMPONENT MONITORS
There are several components that will affect vehi- cle emissions if they malfunction. If one of these com- ponents malfunctions the Malfunction Indicator

Lamp (MIL) will illuminate.
Some of the component monitors are checking for

proper operation of the part. Electrically operated components now have input (rationality) and output (functionality) checks. Previously, a component like the Throttle Position sensor (TPS) was checked by the PCM for an open or shorted circuit. If one of these conditions occurred, a DTC was set. Now there is a check to ensure that the component is working. This is done by watching for a TPS indication of a greater or lesser throttle opening than MAP and engine rpm indicate. In the case of the TPS, if engine vacuum is high and engine rpm is 1600 or greater and the TPS indicates a large throttle opening, a DTC will be set. The same applies to low vacuum if the TPS indicates a small throttle opening.

All open/short circuit checks or any component that has an associated limp in will set a fault after 1 trip with the malfunction present. Components without an associated limp in will take two trips to illumi- nate the MIL.

Refer to the Diagnostic Trouble Codes Description Charts in this section and the appropriate Power- train Diagnostic Procedure Manual for diagnostic procedures.

 

Reread your post, but I still have to stand by what I said. If it's a fueling issue causing the misfire code, I would think it would generate a random misfire, or 301 through 306. It wouldn't always hit the same cylinder. The only fueling problem that would, or at least should, hit the same cylinder every time would be an injector problem, most likely a partially plugged injector. I wouldn't think it would be a stuck injector, because that would also give hard starting, a strong fuel smell and fuel trims out of whack. Outside of that, the fueling system is a common system, ie one pump and one line feeds the fuel rails that feed the injectors. If the pump is losing pressure, then all injectors should see that pressure loss and all cylinders should be reporting misfire codes.

It may just be that I'm stuck on the 0301 code here, but then I'm a firm believer in fixing the problems you know are there before tackling the ones you think are there. He may have two problems. A fuel pressure gauge would be needed to see if fuel pressure is dropping off under operation.

 

My point is that you can DEFINITELY have a misfire, but if it only happens for a moment, it will never trigger a CEL. It would have to have a misfire for over a minute nonstop for the CEL to set, based on the FSM declaration. Because this is an intermittent issue, it will likely never set a CEL for the true fault. It could be misfiring all 8 cylinders and never set a CEL since the situation self-restores.

The post-NGC controllers have knock sensors and faster O2 sensors that will set a misfire code immediately.

 

Gotcha. Thanks for the clarification.

 

Ok guys so maybe this will she'd a little light on the situation???
my check engine light is back on. Came on yesterday. So the first time the light came on it was the down stream O2 sensor. Stayed on for a day then came off. Second time it came on it was missfire in cylinder 1 and the fuel pressure sensor. Then after two days it came off. Now this third time I haven't scanned it yet. Gotta get to AutoZone. I'm interested to see if it's cylinder one again.
HERES THE KICKER... I put half a tank of 89 Insted of 87 went up one grade in gas. And 80 percent of my problem went away. It doesn't happen all the time now. And when it does if I lightly feather the gas the issue will go away within 30 seconds.

P.s if it is cylinder one again is it acceptable to change just one injector? Or should I just change them all....