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Old 04-13-2013, 10:52 PM   #1
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Default 99 Grand AM misfiring

I've read through the archives and have seen others with the similar issues but have not seen much for solutions that corrected the problem.

I have a 99 grand am with the 2.4 4cyl motor. It was slightly hesitating when going up hill (under load) occasionally. Then yesterday driving flat and just cruising along on the freeway the engine lost all power and from then on misfire/stumbles like its on only 2/3 cylinders. It was hooked up to a monitor at the time and it immediatly threw a 0300 and 0200 codes with the blinking check engine light.

Limped it back home and even though the engine temp was fine the exhaust was scorching hot (I'm assuming from detonation of fuel.)

replaced both coils, plugs, boots and the plastic housing and had the ICM tested (OK) put together, cleared codes, and fired it up. Still runs like crap but now only throws the 0200 code (injector timing) I ohmed the injectors (all good) now I'm out of ideas.


The car does have a new timing chain and water pump (500 miles)

One interesting thing is when I try to rev it up the trac light will come on with the car not even in gear. Wondering if this is related I.E. ECM failure or just an anomoly.
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Old 04-14-2013, 12:47 AM   #2
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Start with getting the fuel pressure checked. A failing fuel pump is a common cause for random misfires.
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Old 04-15-2013, 01:46 PM   #3
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0200 is injector elecrical fault and likely the cause of 300. check for power at the connectors first.

Potential causes of an P0200 code include:

Open or shorted injector
Injector low internal resistance (basically an injector that works, but is out of specs)
Grounded driver circuit
Open driver circuit
Driver circuit shorted to voltage
Wiring harness intermittently shorting against underhood components


Possible Solutions 1. If you have multiple misfire/injector codes, a good first step is to unplug all the fuel injectors and then turn the ignition on, engine off (KOEO). Check for presence of battery voltage (12 Volts) at one wire of each injector connector. If all are missing, check for continuity to ground on the voltage circuit by using a test light connected to positive battery and probe each voltage feed. If it lights up, then there is a short to ground on the voltage feed causing a short. Get a wiring diagram and repair the short on the voltage feed and reestablish proper battery voltage. (Don't forget to check for a blown fuse and replace as necessary). NOTE: It'* possible for one injector to short out the whole battery voltage feed to all the injectors. So if you have lost voltage to all the injectors, replace the blown fuse and plug each injector in, one by one. If the fuse blows, the last injector you plugged in is shorted. Replace it and retest. If only one or two battery feeds are missing, then it'* more likely to be a shorted battery voltage feed in the individual injector wiring harness. Inspect and repair as necessary.

2. If you have battery voltage fed to each injector harness, then the next step is to get a noid light to check for injector driver operation. A noid light will insert into the injector harness in place of the fuel injector and flash rapidly when the injector driver operates. Check each fuel injector connector. If the noid light flashes rapidly then suspect the injector. Ohm each fuel injector if you have a resistance specification. If the injector is open or the resistance is higher or lower than the spec, replace the fuel injector. If the injector tests out, the problem is likely an intermittent wiring problem. (Remember that a fuel injector can work properly when cold but go open when hot, or vice versa. So it'* best to do these checks when the problem is occurring). Check the wiring harness for any chafing, or the injector connector for loose pins or a broken lock. Repair as necessary and retest. Now, if the noid light doesn't flash, then there'* a problem with the driver or the driver circuit. Unplug the PCM connector and ohm the fuel injector driver circuits. Any resistance means there'* a problem. Infinite resistance points to an open in the circuit. Find it and repair it, then retest. If you can find no problem with the harness and there is no fuel injector driver operation, then check the PCM powers and grounds. If they are okay, the PCM may be at fault.
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Old 04-18-2013, 02:23 PM   #4
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I've checked the injectors, and the connectors with a "noid" light. Everything seems fine. I did notice low voltage at the battery so I pulled the alternator to have it checked (checked out good at the local auto parts store) during reinstallation I noticed the 4 wire connector had a loose wire (just broke off when I barely touched it)

meanwhile had the battery on the charger for 24 hrs, installed new connector, rehooked battery, cleared all codes and fired it up. still runs like crap! Fuel is actually dumping out the exhaust pipes now and the only code I got this time was P0300 (ignition)

I'm going to pull the timing cover tonite just to make sure I have not jumped a tooth on a cam. Everything in there has less than 200 miles on it but I guess a tensioner can fail.........

On a side note... the connector for the alternator had 3 wires, the new one has 4...... I changed them wire for wire but now the battery indicator comes on. what is the fourth terminal on the alternator for?
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Old 04-18-2013, 03:27 PM   #5
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on some cars the voltage sensing is internal to the alt, some external. as long as the wires you canged end up the same it should be fine
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Old 04-23-2013, 05:29 PM   #6
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I pulled the timing cover just for piece of mind because the new chain only has 200 miles on it. Everything was good in there. no jumped teeth

Started from scratch:

1. each injector ohmed out at 2.4
2. the noid light was super bright on #4, barely on #3, engine would not run enough for 1&2 to check
3. KOEO NO voltage at any enjector connector (with or without PCM connected)
4. Checked all fuses, INJ fuse good (did find a bad fan#1 fuse tho lol)
5. with PCM disconnected, 5.0 ohm from one side of connector to gnd
OPEN from other side of connector to ground (same for all 4)

I'm trying to be as thorough as possible in the diagnosis and post results so other may not go through this
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Old 04-23-2013, 09:49 PM   #7
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How'* you catalytic converter?

You said the exhaust was excessively hot, that'* also a symptom of a clogged catalyst. Had the EXACT issues you're having on an 01 Camaro, and did all the same checks. Ended up being a clogged cat, swapped it for new and it was fixed.
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Old 04-24-2013, 07:40 AM   #8
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you need to find out why you dont have voltage at the injectors, could be wires open or chafed to the body
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Old 04-24-2013, 09:27 AM   #9
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Instead of using the noid light, use a volt meter on the wire side of the electrical connectors going to each injector to see what voltage you get when the car is idling.
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