Surging Idle Problems

askiles

askiles

Goblin Guru
So I am having continued issues with my 2.0L SS/SC engine surging (fluctuating in RPM) at idle. It surges from about 800-1200 RPM’s constantly. I have checked all vacuum ports. No leaks. I have checked all electrical connections. They are all connected. I am getting the P0650 engine code, but I don’t think that is related. I have taken apart the throttle body, made sure it was clean, and manually actuated the butterfly. All good there. I made sure the intake was all clamped and there were no leaks. All good. I am looking for more ideas. At this point I am thinking it is in the custom tune that I had done by Intense Racing, but we shall see. I am in talks with them about the issue.

 
ctuinstra

ctuinstra

Goblin Guru
So you had the tune done after you stripped the donor and before you built the car? Do you have any other mods such as larger injectors? Our car also surged but it did it as the donor as well. All the stupid mods did not help, in fact they caused all the issues. We have made progress but still have underlying issues.
 
askiles

askiles

Goblin Guru
The donor ran, and ran just fine. No surging. It did not have any mods. I bought a running, driving, fully registered and on the road car so I could avoid issues. Lol

I had the tune done while the car was apart. I sent me supercharger to Intense Racing and had them port and rebuild it, and I also bought a lot of mods to go with it, and sent them the PCM to which they put a tune on to accompany the mods. I think it’s their level 5 modifications. So smaller pulley, bigger injectors, colder plugs, etc... All of the mods to accompany the smaller pulley. According to them. I bought it all as a package, with them knowing what it was going into.
 
ctuinstra

ctuinstra

Goblin Guru
Yep. Welcome to the wonderful world of the mods. The larger injectors (assuming they are 60# or greater) do not idle well at all. Some people don't have a lot of issues with them, but we sure did. I could go on for some time about its but it's getting late. The primary issue is the larger injectors are very unstable at low duty cycles required at low RPM and no load. Also there is a min PWM in the ECM that won't allow the injectors to open and shorter than say 1.3ms. This is also causing our overly rich condition from idle to mid.

One thing I was able to do was to raise the idle speed by 50-100 RPM and that smoothed it out completely, but that is just a band aid. We are looking at going to a boost referenced fuel system to also help (hopefully substantially). But we have a fuel pump that is inconsistent in pressure and doesn't always want to turn on so we are changing it out this weekend and it will be interesting to see what effect it has on the fuel pressure, it's often way too high which is making it worse).

Another way to put it is the larger injectors are inconsistent in the spray and the ECM is having a difficult time trying to compensate for them.

What size pulley and injectors?
 
askiles

askiles

Goblin Guru
2.5” pulley. 60lbs injectors. Also the tune to go with it all. We will see what Intense says. I guess worst case, I go with smaller pulley and stock injectors. The headache is not worth it. Intense says it will all work with their tune, so I will put it in their court.
 

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Ross

Ross

Goblin Guru
Whhhaaattt? That is less modifications... boost reference fuel system is the next logical step. (Since I'm spending your money).
Maybe dual injector fuel rails with stock injectors in one rail. :)
 
askiles

askiles

Goblin Guru
Would you guys suggest I possibly bite the bullet, get an HP Tuner's MPVi2 and some credits and fix it myself?? Thoughts?
 
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JSATX

JSATX

Goblin Guru
askiles said:
Would you guys suggest I possibly bite the bullet, get an HP Tuner's MPVi1 and some credits and fix it myself?? Thoughts?
Click to expand...
Only if you have someone also using HPT to remote tune it for you like ZZP. HPT is infinitely more complicated than I originally realized, and it will require a ton of handholding by someone very familiar with it.

I’m probably 40 hours deep working with it and if I were to rate my skill 0-10 I’m a .5
 
Lonny

Lonny

Administrator
Staff member
How much driving time do you have on your new tune?
It's possible some of the surging will fix itself as the ECM makes adjustments.
 
askiles

askiles

Goblin Guru
Lonny said:
How much driving time do you have on your new tune?
It's possible some of the surging will fix itself as the ECM makes adjustments.
Click to expand...
Almost no time...it is hard to drive it with it surging like this. It wants to die sometimes when it dips down in the RPM range.
 
askiles

askiles

Goblin Guru
JSATX said:
Only if you have someone also using HPT to remote tune it for you like ZZP. HPT is infinitely more complicated than I originally realized, and it will require a ton of handholding by someone very familiar with it.

I’m probably 40 hours deep working with it and if I were to rate my skill 0-10 I’m a .5
Click to expand...
Understood. Hmmm...
 
ctuinstra

ctuinstra

Goblin Guru
askiles said:
Would you guys suggest I possibly bite the bullet, get an HP Tuner's MPVi1 and some credits and fix it myself?? Thoughts?
Click to expand...
They don't make the MPVi1 anymore. The MPVi2 is out. The credit system is different slightly now. There are things that I can help you with specifically with this issue, however, I am not a full-time tuner (and I'm beginning to think some of the full-time tuners aren't either).

If you hold the the RPM to say 900-1000, does it smooth out for you? Just a check is all. It wouldn't hurt to get a fuel pressure gauge just to check it also.

This is a very good article that talks about some of the issues with the larger injectors. I won't go into detail about it now. But the one thing they talk about that hit home with me is the min pulse width and it's exactly what I was seeing. Default the car is set to 1.3ms and the Siemen injectors are good down to 1.4ms. I'm thinking about trying the Bosch sometime but I've been able to work around our idle issue for now.


https://forum.hptuners.com/showthread.php?44040-LSJ-Injectors-101-Your-basic-how-to
 
askiles

askiles

Goblin Guru
ctuinstra said:
They don't make the MPVi1 anymore. The MPVi2 is out. The credit system is different slightly now. There are things that I can help you with specifically with this issue, however, I am not a full-time tuner (and I'm beginning to think some of the full-time tuners aren't either).

If you hold the the RPM to say 900-1000, does it smooth out for you? Just a check is all. It wouldn't hurt to get a fuel pressure gauge just to check it also.

This is a very good article that talks about some of the issues with the larger injectors. I won't go into detail about it now. But the one thing they talk about that hit home with me is the min pulse width and it's exactly what I was seeing. Default the car is set to 1.3ms and the Siemen injectors are good down to 1.4ms. I'm thinking about trying the Bosch sometime but I've been able to work around our idle issue for now.


https://forum.hptuners.com/showthread.php?44040-LSJ-Injectors-101-Your-basic-how-to
Click to expand...
Oops...I meant MPVi2...

That's interesting about the injectors. I will have to bring that up to Intense and see what they think about that. Apparently they have had many other Cobalts use this performance pack and run just fine. So we will see what they can iron out...
 
ctuinstra

ctuinstra

Goblin Guru
Keep in mind these aren’t 100% Cobalts anymore. The intakes are different as us the exhaust. Intakes can have an affect on the tune.
 
askiles

askiles

Goblin Guru
ctuinstra said:
Keep in mind these aren’t 100% Cobalts anymore. The intakes are different as us the exhaust. Intakes can have an affect on the tune.
Click to expand...
That's exactly what my tuner was saying. He said that the Cobalts are finicky at best when it comes to the intakes. So hopefully he just has to tweak something with that and we will be golden.

Lonny, what did you do tune wise on your SC Goblin? Or is your PCM completely stock?
 
ncgoblin

ncgoblin

Goblin Guru
Unplug the MAF sensor see if it changes. This sounds similar to the MAF not being plugged in for my SS/SC.
 
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