04 M6 GTO, 110,000 Miles. Just like the title says, its been having weird ilding issues ocasionally, and will misfire if you try to drive it right away while the problem is occuring. When it doesnt idle weird, it runs fine. Anyone have any ideas? The motor's stock, all it has is longtubes, and a full exhaust. is there a bad ground? is an injector bad? Anyone have any ideas? I am stumped.
I did the following so far:
Noid light on all the injectors.
Checked fuel pressure.
Checked the injector voltage as well.
Changed the MAF, TPS, and the IAC as well, problem still occured.
Noid light test was fine, but I didn't catch it when it was acting funny, so I'll have to try it again, same with the voltage, fuel prsssure was during rough idle, and it was fine.
Any help is appreciated, like I said, I'm, stumped =(
Sounds like youve gotten a good start with the noid light, but what is the voltage?
Injectors are groundside controlled by the ECM. They should have battery voltage when the key is on.
Injectors share power with coils, so a bad coil could pull the system down. Injector resistance should be around 14ohms, and a bad one could pull them all down.
you may also have a bad ECM, or bad wires to the ecm. I dont know if GM watches the driver wires for the feedback voltage of injector coil field collapse or not. that really helps convert a p0200 into a 201-208.
Get supply voltage to each injector and Resistance next.
I already thumbed through that thread, thanks though!
Quote:
Originally Posted by Konnie the Goat...
Sounds like youve gotten a good start with the noid light, but what is the voltage?
Injectors are groundside controlled by the ECM. They should have battery voltage when the key is on.
Injectors share power with coils, so a bad coil could pull the system down. Injector resistance should be around 14ohms, and a bad one could pull them all down.
you may also have a bad ECM, or bad wires to the ecm. I dont know if GM watches the driver wires for the feedback voltage of injector coil field collapse or not. that really helps convert a p0200 into a 201-208.
Get supply voltage to each injector and Resistance next.
The voltage from all the injector wires were all 12v, but now that i think about it, one injector was about .3-.5 low. I'll have to recheck them. To do the ohm resistances. you just check from the injector wires coming off the harness correct?
I appreciate all the helpful information, I'll go pop the hood.
and all testing is done with the key in the on position but with the engine off.
Now with it i'm seeing 5.93v on each injector if i connect both DVOM probes to the injector wire, but if i run the ground wire to the battery it reads 12.23. every single injector is the same. would the injector voltages meet the 7-10 volt range if i turned the car on? Now what I really need to know is how I test resistance. which ohm setting I pick, which probe to use on the non 12 inj. wire, and where to put the other one. Thanks!
Per my previous post, I have tested all 8 injectors, and they all read the same: an 11 ohm resistance on the 2000 setting of my multimeter.
So to recap:
-Each injector wire has 5.93 volts across the injector wire with the key on, engine off.
-Each injector wire grounded to the battery has 12.23 volts.
-Each injector shows an identical ohm resistance.
So I'm lost on what to do next.
Edit: Re-read Konnies post(s) and saw that a bad coil could pull all injector ohms down. But I measured injector resistance by unplugging the injector and checking the actual injector. All 8 of mine were 11 ohms, and they were all supposed to be around 14?
1. Disconnect the ignition coil output wire at the distributor cap.
2. Connect a spark plug to the end of the ignition coil output wire which you just disconnected.
3. Connect a ground wire to the threaded portion of the spark plug.
4. Disconnect the ignition coil ground wire from the negative terminal on the coil (Green Wire).
5. Connect one end of a ground wire to the ignition coil negative terminal.
6. Turn the ignition switch to the ON position.
7. Tap the other end of the ignition coil ground wire jumper on an good grounding point (for example the battery negative terminal) and look for sparks at the spark plug that correspond to the frequency of your tapping of the ground wire.
8. If you have a good spark at the spark plug, the ignition coil is good.
9. If you don't get a good spark, check for approximately 12 VDC from the coil positive terminal (black wire) to ground with the ignition switch in the ON position. You should also get approximately 12 VDC from the coil negative terminal (Green wire) to ground
Ignition Coil Resistance Check
In addition to the test above, you may elect to perform an ignition coil resistance check as confirmation of the coil's condition.
1. Check the ignition coil primary coil resistance by connecting an ohmmeter between the positive (Black wire) and negative (Green wire) terminals on the coil. The resistance should be 0.4 to 0.6 ohms.
2. Check the ignition coil secondary coil resistance by connecting an ohmmeter between the coil output terminal and the ignition coil negative terminal. The resistance should be 5000 to 7200 ohms.
Per my previous post, I have tested all 8 injectors, and they all read the same: an 11 ohm resistance on the 2000 setting of my multimeter.
So to recap:
-Each injector wire has 5.93 volts across the injector wire with the key on, engine off.
-Each injector wire grounded to the battery has 12.23 volts.
-Each injector shows an identical ohm resistance.
So I'm lost on what to do next.
Edit: Re-read Konnies post(s) and saw that a bad coil could pull all injector ohms down. But I measured injector resistance by unplugging the injector and checking the actual injector. All 8 of mine were 11 ohms, and they were all supposed to be around 14?
11 ohms is fine. that 14 figure is a ball park. I aint worried about that 11.
I am worried about that 5.93v. that seems real low for KOEO. Youve got battery voltage on the hot side, which is good. the ground side is a possible problem. Disregard the coils, thats a hotside only problem.
We need to focus on the control wires from injector to ECM, and the ECM grounds. Since all 8 are like that, look at the ECM grounds real good. The ECM may also be dead.
11 ohms is fine. that 14 figure is a ball park. I aint worried about that 11.
I am worried about that 5.93v. that seems real low for KOEO. Youve got battery voltage on the hot side, which is good. the ground side is a possible problem. Disregard the coils, thats a hotside only problem.
We need to focus on the control wires from injector to ECM, and the ECM grounds. Since all 8 are like that, look at the ECM grounds real good. The ECM may also be dead.
You are seriously the most helpful person ever Konnie, Thanks for checking in again. When you say ECM grounds, what exactly do you mean? The harness for each side of the motor is split for the injectors correct? they go into the fuse box and then to the ECM?
EDIT: looked at the image you linked in the other thread.
So One wire from each injector goes into the ECM, then they are grounded out from there? or do they ground into the ECM? I'm going to check each wire going into to the ECM from the Injectors and report back.
Another thing I should note:
I went and drove the car. And I was able to replicate the issue. I'll list the parameters below:
-Car was warm-ish
-Turned it on, all was fine
-got onto the main road (about 20 feet from starting point)
-gave it about 15-20 percent throttle, and all power faded away, and the RPM slowly dropped
-If I let my foot completely off the gas, it just continues coasting back down to 0 MPH
-if you try to get back into the thorttle, it'll start misfiring up till about 3500rpm, then the CEL will flash for multiple misfire, then all the power comes back and the light stays off.
When it does that I think it's a bad coil bringing everything down, Then again, I just don't know.
All modules (ECM, TCM, BCE, etc) have their own power and ground connections. The 'grounds' for the injectors run to the ECM, and the ECM has transistors that act as switched to ground each injector, turning it on. those switches will connect to the main ground bar in the ECM, and then to the body of the car via wires coming from the ECM.
Since we have 12v using battery ground and barely 6v using ECM ground (via the transistors), we need to find WHY we lost 6v. Now it is unlikely that ALL 8 injectors have bad wires. Possible, but rare. So we look at the ECM ground that all 8 share. Because the injectors have 3 things in common: Power (which we know is 12v for all), ECM (for control, and which is saying there is an issue), and Grounds (at the ECM).
The wiring diagram is here somewhere. If you cant find it let me know. but if you follow the wires out the ECM, you'll see them branch off and bolt to the body. Make sure they are corrosion-free and tight.
All modules (ECM, TCM, BCE, etc) have their own power and ground connections. The 'grounds' for the injectors run to the ECM, and the ECM has transistors that act as switched to ground each injector, turning it on. those switches will connect to the main ground bar in the ECM, and then to the body of the car via wires coming from the ECM.
Since we have 12v using battery ground and barely 6v using ECM ground (via the transistors), we need to find WHY we lost 6v. Now it is unlikely that ALL 8 injectors have bad wires. Possible, but rare. So we look at the ECM ground that all 8 share. Because the injectors have 3 things in common: Power (which we know is 12v for all), ECM (for control, and which is saying there is an issue), and Grounds (at the ECM).
The wiring diagram is here somewhere. If you cant find it let me know. but if you follow the wires out the ECM, you'll see them branch off and bolt to the body. Make sure they are corrosion-free and tight.
has all of the pinout info. So of the info I've found I'm going to check those three grounds off the Harness, and If all of those are fine then I guess I'll look more into the pinout diagram and see if I can decipher that
Ok So now with the key on, engine off, I get between 6.04-6.10 volts on each injector (probe touching each pin of the injector harness) Battery voltage is 12.40 Volts as well. :Bomb:
Just an update on this. voltage across the injectors with the engine on is around 8 volts on every injector, Which is where I think it's supposed to be. This to me know sounds like a coil problem, since hotside voltage is fine in the injectors, as well as the grounds going into, and out of the ecm. I will start testing coils this week.
Is is possible for you to look at the misfire counters in the ECU while this occuring to determine if the problem is attributed to one bank or both banks?
Is is possible for you to look at the misfire counters in the ECU while this occuring to determine if the problem is attributed to one bank or both banks?
Unfortunately, I have no way of checking misifres. What I am going to end up doing is buying a new coil and moving it around to see if the problem goes away after a specific coil has been replaced. The reason I've come to this is as follows
-Ohm resistance on all injectors is fine.
-Voltage is fine everywhere.
-All PCM grounds are fine.
My last theory is once the coils start getting a little heat in them one or more of them start acting all funky, pulling the voltage down on the rest of the injectors and coils on that side.
Just an update on this: Grabbed a new coil the other day, and switched coil pack #2, which did nothing. But I switched coil pack #4, and i'm 75% sure the issue has been resolved, I just haven't driven it under the parameters of the issue enough to be positive. I will report back if it occurs again!
Last edited by ForzaFTW; 12-10-2012 at 06:36 PM.
Reason: Grammar.
So just to kind of update this if anyone was curious. I tried a million different things and nothing was working. Then one day while I was at work, a GTO buddy of mine came in and I explained the problem to him, and he suggested checking the o2 sensors. The cars rear o2 sensors are turned off, and he explained that one or both of the front o2 sensors must be reading really really rich, bogging the engine down; but then when you floor it, the car stops reading off the o2 sensors and uses the tables in the tune, and that's why everything goes back normal when you're full throttle.
So sure enough, I replaced both front o2 sensors with brand new densos, and it seems that the problem is gone! the car also gets slightly better mileage, doesn't smell like gas as bad on startups, and is a bit smoother around 2,000rpm (there was a dip in power around 2k, I thought it was low end loss from not retuning the car after my headers)
So overall, I think the problem is solved.
I'd like to thank everyone who helpedand gave me ideas/input, especially Konnie, You're seriously one of the most helpful people on the forum, and I GREATLY appreciate your help.
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2004 GTO Owner
Intermittent P0200. Any help is appreciated.
