Troubleshooting Help

[Jseverin]

My Gn has a consistent miss at idle and low speeds such as driving in my neighborhood or parking lots. The car burbles, pops, and lurches until it shifts into 2nd gear and then it runs fine. The exhaust smells terrible and I even noticed a twinge of fuel smell in my oil when changing it. The car runs super smooth at highway speeds and has no problem making 21 lbs of boost, the problem only seems to be at idle and low speeds. Below are my scanmaster readings (which all looked normal to me) and the steps I have taken to troubleshoot thus far. I plan on bringing it to the performance shop I have had work done at tomorrow to take a look but I was hoping some of you guys could give me some ideas and possibly save me the 2 hour trip and maybe some $.

Scanmaster readings:
.O2 MV-bounces between 066-800 MV
.AF- 7
.L8 44-48
.Bat 13.9
.INT 126-133
.BL 126 +/- 10
.TPS .40 at Idle
.IAC 36-40 (drops as the car warms up)
.CC @10 cc every 2 seconds

Troubleshooting I completed:
1.Removed/checked PCV valve=operating normally
2.Checked plugs/wires=operating normally
3.Checked for vacuum leaks/replaced vacuum lines with silicone kit=no leaks found
4. leakdown test on all cylynders=no issues found
5.replaced fuel filter at last oil change=no difference in performance
6.had fuel pressure checked while it was at the shop being tuned= no issues noted (car is equipped with 50lb injectors and Walbro 307 fuel pump)

I honestly cant think of any thing else that could cause this issue, hopefully one of you guys with more GN experience can think of something I may have missed.

Thanks in advance,
Joe

 

[EVIL]

The pros will ask what's done to the car.

Is the maf stock?

D

 

[Jseverin]

The pros will ask what's done to the car.

Is the maf stock?

D

no, Has a MAF translator

 

[TurboBuRick]

A worn cam sensor can cause this. Start the car, unplug the cam sensor and go for a ride.

 

[Jseverin]

Cam sensor was good. Did some more tinkering and noticed several of the terminals on the ignition coil are pretty corroded. I am going to replace the coil pack. Not sure if I should replace the module as well. How can I tell if the module is bad?

 

[Chuck Leeper]

Cam sensor was good. Did some more tinkering and noticed several of the terminals on the ignition coil are pretty corroded. I am going to replace the coil pack. Not sure if I should replace the module as well. How can I tell if the module is bad?

Replace both. Look real close at the plug wire towers for carbon tracking down the sides. Check the condition of the CCI plug when you take the coil/module off.
Remove the coil, and see what the underside looks like. Look like melted bubble gum? Check the connectors/tabs on the coil connector wires.
All grounds on, clean, tight?
Injectors leaking? Could have a leak that over fuels a cyl, and is noticeable at low speed/idle rpm. Not something you'd likely notice at higher rpms.
Run the engine, shut it off, watch the fuel psi. drop quickly?
Let it sit for a time... Pull the plugs. Any of them wet?
If you want, you can pull them up, sit them on a folded paper towel, being SURE they are all clipped in place. hit the key for prime. Leaking?

 

[Jseverin]

Replace both. Look real close at the plug wire towers for carbon tracking down the sides. Check the condition of the CCI plug when you take the coil/module off.
Remove the coil, and see what the underside looks like. Look like melted bubble gum? Check the connectors/tabs on the coil connector wires.
All grounds on, clean, tight?
Injectors leaking? Could have a leak that over fuels a cyl, and is noticeable at low speed/idle rpm. Not something you'd likely notice at higher rpms.
Run the engine, shut it off, watch the fuel psi. drop quickly?
Let it sit for a time... Pull the plugs. Any of them wet?
If you want, you can pull them up, sit them on a folded paper towel, being SURE they are all clipped in place. hit the key for prime. Leaking?

Replace both. Look real close at the plug wire towers for carbon tracking down the sides. Check the condition of the CCI plug when you take the coil/module off.
Remove the coil, and see what the underside looks like. Look like melted bubble gum? Check the connectors/tabs on the coil connector wires.
All grounds on, clean, tight?
Injectors leaking? Could have a leak that over fuels a cyl, and is noticeable at low speed/idle rpm. Not something you'd likely notice at higher rpms.
Run the engine, shut it off, watch the fuel psi. drop quickly?
Let it sit for a time... Pull the plugs. Any of them wet?
If you want, you can pull them up, sit them on a folded paper towel, being SURE they are all clipped in place. hit the key for prime. Leaking?

hey Chuck, I think the injectors are my next check. Dug up my spark tester and the coil was fine. Just a little dirty, cleaned the terminals. The bad injector might explain why my oil smelled a bit like gas when I changed it.

 

[John Larkin]

Two questions: What chip do you have and how old is it? When is the last time or have you ever replaced the O2 sensor?

 

[turbo89]

Replace both. Look real close at the plug wire towers for carbon tracking down the sides. Check the condition of the CCI plug when you take the coil/module off.
Remove the coil, and see what the underside looks like. Look like melted bubble gum? Check the connectors/tabs on the coil connector wires.
All grounds on, clean, tight?
Injectors leaking? Could have a leak that over fuels a cyl, and is noticeable at low speed/idle rpm. Not something you'd likely notice at higher rpms.
Run the engine, shut it off, watch the fuel psi. drop quickly?
Let it sit for a time... Pull the plugs. Any of them wet?
If you want, you can pull them up, sit them on a folded paper towel, being SURE they are all clipped in place. hit the key for prime. Leaking?

THIS X 2 !!! SPOT ON !

 

[Jseverin]

Two questions: What chip do you have and how old is it? When is the last time or have you ever replaced the O2 sensor?

Two questions: What chip do you have and how old is it? When is the last time or have you ever replaced the O2 sensor?

i honestly don't know what type of chip is installed. Can't find anything in the records he gave me with the car. I found a turbo tweak street 93 in a box of spare parts that came with the car. If I'm not mistaken that is for stock injectors and turbo. Please correct me if I'm wrong. I haven't changed the O2 sensor in the two years I've had it. Scanmaster readings seem ok for the O2 sensor, and no trouble codes.

 

[John Larkin]

Third question: What injectors do you have? Any other mods you can share will be helpful.

The turbotweak chip will likely have a 4-digit number on it. If you find that, you should be able to email eric @ turbotweak and he can tell you what it is for. Confirm the numbers on your injectors - you say you have 50 lb injectors but it would be good to be sure unless you are completely sure already. And check the chip in the computer - look for a label on it too. You may have to remove it to see. Just unplug the orange wire by the battery under the hood first.

 

[Jseverin]

Third question: What injectors do you have? Any other mods you can share will be helpful.

The turbotweak chip will likely have a 4-digit number on it. If you find that, you should be able to email eric @ turbotweak and he can tell you what it is for. Confirm the numbers on your injectors - you say you have 50 lb injectors but it would be good to be sure unless you are completely sure already. And check the chip in the computer - look for a label on it too. You may have to remove it to see. Just unplug the orange wire by the battery under the hood first.

Not sure what brand but I'm pretty sure they are 50 lb injectors.

 

[Jseverin]

Hey dudes,
Thanks for the suggestions. I'm in the middle of moving so I haven't had time to dig deeper. When I get settled in the new place I'll dive in again. I suspect it's something with the fuel, but I don't have a pressure tester. Thinking the injectors or even the pressure regulator might be the culprit. I also have to pull the chip to see what is in it. Again, I appreciate the help fellas.

 

[Jseverin]

Ended up being a bad TPS causing a large portion of my problems. Replaced it and the car runs/smells better. Now I have to figure out while my blm is sitting at 150 at idle. While going down the road it's fine at about 128 but as soon as I stop it goes right to 150. Just moved to Florida (sea level) from New Mexico(4500 ft) could this throw off my blm?

 

[69RSCLONE]

Most likely a vacuum leak. You can unplug the orange ecm connector and reset the system. Then let it relearn the idle for the change in altitude. See if it helps. But I'd look for leaks, possibly the plenum gasket.

Sent from my SM-G935V using Tapatalk

 

[Jseverin]

Most likely a vacuum leak. You can unplug the orange ecm connector and reset the system. Then let it relearn the idle for the change in altitude. See if it helps. But I'd look for leaks, possibly the plenum gasket.

Sent from my SM-G935V using Tapatalk

Gonna hit up autozone or napa this weekend for a vacuum tester. The car still burbles a bit and stumbles when I let off the gas so I suspect vacuum as well. All of my other Scanmaster readings are perfectly fine just higher blm since I got here.

 

[69RSCLONE]

Grab a can of throttle body cleaner and spray around the intake. Listen for the idle to increase. If it does you have found the leak.

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[Jseverin]

Grab a can of throttle body cleaner and spray around the intake. Listen for the idle to increase. If it does you have found the leak.

Sent from my SM-G935V using Tapatalk

Did the propane test and found no leaks, if I reset the ecm will it wipe out the tune I had done back in New Mexico?

 

[69RSCLONE]

Yes. Write down all your settings first, then start with the base tune and work from there. Will probably be different than at higher altitude. Most likely needs more fuel.

Sent from my SM-G935V using Tapatalk

 

[TurboBuRick]

Gonna hit up autozone or napa this weekend for a vacuum tester. The car still burbles a bit and stumbles when I let off the gas so I suspect vacuum as well. All of my other Scanmaster readings are perfectly fine just higher blm since I got here.

The stumble when you let off is very common when using upgraded maf like lt1, ls1 it 85mm. They read air moving in and out so when you let off the gas, the air built up in the intercooler comes back through the maf triggering fuel and causing the stumble.

The best way I've found to check for vacuum leaks is using a shop vac. Put the hose on the exhaust (blow) side of the vacuum and the other end to the intake pipe or throttle body. Switch on the vacuum then use a spray bottle with some soapy water and spray suspected areas. I see a lot of leaks around the EGR block off and vacuum block.