Running out of money

I have a 99 GA 2.4l. Misfire code p0303. I've changed:
All 4 plugs
All 4 wires
swapped coils from side to side
New ICM
New Coil housing
Checked both coils primary and secondary resistance
Checked voltage to ICM and out of ICM to trigger coil (test light flashed)
Checked voltage to all injectors
Checked resistance to all injectors

EVERYTHING checks within limits

It will run but it runs crappy. Everytime a code comes up its P0303 so its not random. I erase and code pops again within 2 minutes. I know its a misfire because I can hear it.

Looking at changing the injector but I am running low on funds and was wondering if you guys have another free check idea.

Also where would be the best place to get the injector for cheap. Most places I look have 2 different types. Not sure what the difference is..EGR?

Anyways you input is appreciated.

If the DTC P0303, focus on cylinder 3.
1) Compression check.
2) Roll Spark plug, spark plug wire, or COP to another cylinder.
3) Roll Injector 3 to another pos.

Just because your injector 3 got a signal, and clicking sound, doesn't mean that it's working.

A diesel shop can micro bath, trigger, and test the flow rate.

Yup sorry should've stated I swapped the plugs during this process. Also the plug wires were swapped I don't know how many times....

Swapping the injectors......you say that like it's an easy thing. Don't you have to have a special tool to disconnect the injector from the rail?

If I buy a new injector or get it cleaned would it be a good thing to buy/clean all 4? Or can I go with just 1?

thx for the quick reply.

Call a local diesel shop for a price, it's probably $20 per injector for cleaning.

I have taken a known bad injector for a good cleaning and it works great.

If money an issue, you might also consider one from a salvage yard.

http://www.autopartswarehouse.com

Remanufactured (cleaned) - $50
New - $150

Installation = plug + play

might want to try to do a resistance test on the injectors coils.

I do not know the right value, but compare it with the others.

There is a chance that you will see a way different resistance there. That would confirm a bad injector coil, so replace the injector if it happend.

Else try to swap the injector.

The resistance test might not show anything, however it's easy to do so might want to try before doing harder stuff.

Fuel injection update....OK so I did some more research and followed the diagram in the repair manual. Fairly simple. Power should come straight from the fuel pump relay to the injectors, 12 volts. Fuel pump is getting power. It comes off the same line. I believe the ground is given from the PCM for the injectors to open and close.

Scenario 1: Labeled cyl 1234 in that order:
Resistance on the wires reading across the 2 wires in the harness; power off:

361.2k ohms 360.8k ohms 369.5k ohms 183.2 ohms

Power on:
348.8k ohms 348.5k ohms 1.566M ohms 172.2 ohms

Voltage check from wire to wire in the harness (grey-other)
0 volts 0 volts 2.54 volts .01 volts

Also checked (grey-ground) same results as above.

I also disconnected the PCM and checked resistance of the wires of the injectors (grey-other)

open open open open
All like they should be.

SOOOOO:runaround:
Should there be 12 volts sitting at the injectors in the "on" position straight from the fuel pump relay?
Leading to the PCM? If so did you buy it at autozone or similar?

you need to disconnect the wires going to the injector before making mesurements.

so disconnect the harness and then mesure the injectors.

As for the 12V, most of the thing get a constant 12V once the ignition is on, with whatever path. However the ground part is controlled by the PCM (because it's easier and more efficient that way electronics wise)

Need to roll injector 3, if there's no flow rate it's not going to work.

All my voltage and resistance checks are with all of the injector connectors disconnected. That is what is so weird to me. Why would I not have power to those connectors but yet have power to the fuel pump. They are all off the same leg of the fuel pump relay.

As for power checks the ignition was in the on position when checking for voltage..

Resistance checks were done also with connectors off and power off and on to see the difference.

Not getting 12 volts on any of the injectors and 2.54 volts only on the 3rd one is really stumping me. According to the manual the power wire is a straight shot from the Fuel pump relay to ALL of the injectors. So how the heck is the car even running??????? Yet I can start it up and drive around the block skipping the #3 cyclinder.....

Anyways I'm not going to jump on the #3 injector just yet until I can figure out what is going on with the power.

Keep the suggestions coming please!!!

There may be a problem with the PCM, if there is on voltage on the other injectors then cyclinder 3 also should have 0 volts just like the other 3 do. If you can if possible try to get a different PCM, just for testing purposes then see what the voltage is on cyclinder 3 injector is. Hopefully it is 0, if it is then the PCM is bad, but if it is not there is still another problem.

Try to mesure the voltage with the engine running. The relay for the fuel pump might get disengaged after priming until you start the car.

12V come really straight the relay via the grey wires.
ground is provided by the PCM, but it control it, so your multimeter can give weird results.
#1: black
#2: light green with black stripe
#3: pink with black stripe
#4: light blue with black stripe

Check the voltage of the 4, it should be close when the engine is running. however... don't trust it blindly.

Why the multimeter can go weird? because there is 2 ways to control the flow: give a partial ground (the PCM will vary it's ground resistance, called linear) or use pulse width modulation (PWM). PWM can cause the meter to misread, the cheapest the meter the worse it can get.

Are you sure that you really mesured the resistance with the harness disconnected? your poweroff/on make it confusing...

Try to mesure the voltage with the engine running. The relay for the fuel pump might get disengaged after priming until you start the car.

12V come really straight the relay via the grey wires.
ground is provided by the PCM, but it control it, so your multimeter can give weird results.
#1: black
#2: light green with black stripe
#3: pink with black stripe
#4: light blue with black stripe

Check the voltage of the 4, it should be close when the engine is running. however... don't trust it blindly.

Why the multimeter can go weird? because there is 2 ways to control the flow: give a partial ground (the PCM will vary it's ground resistance, called linear) or use pulse width modulation (PWM). PWM can cause the meter to misread, the cheapest the meter the worse it can get.

Are you sure that you really mesured the resistance with the harness disconnected? your poweroff/on make it confusing...

Connectors still disconnected:

Now we are getting somewhere. The power to the fuel pump relay is controlled by the PCM :banghead: As soon as I turn the key on, the pump runs and I have power to the injector connectors. The pump stops and no power.:runaround: Like it should.....

However:
#1 gets 11 volts .....0 volts after pump stops
#2 gets 11 volts .....0 volts after pump stops
#3 gets 9 volts AND once the pump shuts off it gets -2.54 volts
#4 gets 11 volts .....0 volts after pump stops.

SOOO it seems that there is (-)power coming from the PCM through the pink/black wire which means PCM is screwing this up right?

the -2.54 seems wrong.
How do you mesure the voltage? which probe to what wire?

OK, connectors off of the injectors. Red lead to grey wire, black lead to colored wire.
Wife turning key inside. As soon as she turns it to "on" I hear the fuel pump; and read the meter 11 volts.
Key still on, pump stops and I leave the leads there never move I read -2.54 volts. (only on cyl 3)

With all other positions the same way I get voltage until the pump stops then 0.

Crazy huh?

All DC Voltage btw.

What about: another grey wire with the #3 colored wire? Do you get the same negative voltage? If so, you might have to follow the wire to the PCM and see if the wire is fine there... as it seems to be the PCM... OR that the grey wire is broken, hence why you get a weird reading... Since all grey wires are the same, using another would confirm that the prob come from the coloured wire

Checked the Pink/black wire from #3 to all of the grey wires and same thing 9 volts then to -2.54 everytime. I will try and check the pink/black wire to PCM later tonight and check for resistance.

Does the resistance of #4 grey/blueblack mean anything to you? 180 ohms when the rest are 360 K ohms? Could have a dual failure here.

Thx for your quick responses.....1 step at a time.:thumbsup:

could be a dual failure, or a normal thing... check for oxydation at the PCM...

Checked resistance from #3 pink/black lead at Fuel injector to PCM.

.01 ohms resistance. So thats good.

Also no oxydation or discoloring on that pin at the PCM.

I can not say without doubts that it's the pcm, but it seems to be it... somehow... Personally, I'ld see if the injector are easy to swap. if they are, I'ld swap the #3 with a known to be good one. Reset the code then see if you still get a misfire on #3 or it go on the other. Personally I think it will stay on #3, but might be worth checking. a swap is free, a pcm is not

Phantom, thank you for your time. I will see in the next few days how much time I have to swap them however, I will get a new PCM as it will take a few days to get it.

I will keep everyone updated when/If I get it fixed or we will visit this again:smokin:

As promised an update is here:

Bought a remanufactured PCM from A-zone for 122$. Picked it up today and installed when I got home. Easy enough.

Checked resistance again of the wires for the injectors and they all matched. Turned the ignition on and checked for power. All at 12 volts then 0 when the pump cuts off. ALL Normal

Went to start it and it cranked over but did not start.

Looked up the relearn process. Did that and on the 4th time it started right up. NO CODES and running smooth as silk. I ran it for 15 minutes in my garage and will put it back together tonight.

Phantom I want to thank you once again. I hope what we both learned here we can pass on to others in the future.

THAK YOU VERY MUCH :)

now... if only it was "that easy" to find my lost usb key... white one lost in the white snow... with 4-5 snow falls since then....

now... if only it was "that easy" to find my lost usb key... white one lost in the white snow... with 4-5 snow falls since then....

Lol................yeah, good luck with that :rofl:

How about a magnet, or metal detector.

magnet catched nothing...

As for metal detector... I don't own one, but I plan on making one this week end :D

Measure the resistance from the grey wire of number 3 to the grey wire of a different injector. Should be no resistance.

Any other DTC's besides P0303? On some cars, if the PCM senses an injector circuit problem, it disables the ground triggering to that injector to keep from burning out an injector driver circuit in the PCM. Meaning if the injector is shorted and the PCM detects it, it will disable the bad injector. When this happens, there is an additional DTC stored on the PCM. I forget exactly the code, P1XXX, so you may need a scan tool capable of reading GM extended service codes.

tblake: you're late, he fixed it already. Might want to read the whole thread next time :D