Does This Look Like a Vacuum Leak?

[cptinjak]

Procharged 1997 c5. SD tune by RPM in Maryland. Stock cam, headers and BBK intake.

Pretty sure what I'm seeing is an intake manifold leak. I have no faith in these BBKs.

The odd thing is that the scanner is not showing me STFTs. I'm not sure why this is. Can anyone help an amateur out?

Thank you,

Jack

[Pekka_Perkeles]

It won't go to Closed Loop, because the temp values have been maxed in the tune.

Go to: Engine/Fuel/Open Loop & Closed Loop/Closed Loop Enable. It is now 285 fahrenheit and engine will never reach that temperature.

Download a stock tune from the repository and use "compare" to see what has been changed.

Ah, one more thing. The MAF DTC's are not properly configured. It will still try to use MAF while there's no physical MAF at all (2 bar CoS). Change the P0101-P0103 to "MIL on first error". Or just do a search in this forum how properly set the DTC's for 2 bar MAP/CoS.

[cptinjak]

Thanks Pekka. This is the first non-maf car I've worked on so I am in unfamiliar territory!

Jack

[cptinjak]

Made the changes you suggested. Also replaced intake manifold gaskets to rule out a vacuum leak there. Any more ideas? I'm searching for 2bar info but not coming up with anything great.

Thanks,

Jack

[cptinjak]

Also, are we looking at a dead 02 sensor? is that what is causing the idle surge?

Jack

[DrLoch]

Are you using a WB as well to compare with what the NB are reporting? If not, that's what you should invest in especially if you are going to continue your tuning efforts.

[Pekka_Perkeles]

Also, are we looking at a dead 02 sensor? is that what is causing the idle surge?

Maybe not.

Now, with STFT's enabled, it wants 50% more fuel. With stock cam, it doesn't sound good. If it is properly tuned, there might be a mechanical issue like fuel pressure being low.

Please enable also LTFT's. In fact, compare everything under "Engine/Fuel/Open Loop & Closed Loop" and put back to stock settings. Then lets see what happens.

Since it has a stock cam, I would also put back stock values in "Idle/Airflow/Adaptive Idle Airflow/Max PN... Min PN... Filt PN...". Same thing with Throttle Cracker and Throttle Follower settings (stock values).

[blownbluez06]

Looks more like you have the wrong map sensor in there with that much vacuum, but I see it going to 100 when it died. You're way lean at idle because that's normally a decel area on the VE and possibly fuel pressure like Pekka mentioned.

[Pekka_Perkeles]

Looks more like you have the wrong map sensor in there with that much vacuum, but I see it going to 100 when it died. You're way lean at idle because that's normally a decel area on the VE and possibly fuel pressure like Pekka mentioned.

If this really is with stock camshaft, then having 40 kPa at idle is not uncommon, at least with colder engine. I've typically seen 40...45 kPa at idle when warm with stock cam LS1. Of course it's difficult to compare, since logs posted here do not seem to be at steady idle. MAP values in the first log might be ok, but can't be sure.

I'm just guessing, but perhaps the VE values aren't right because of not being properly set for 2 bar CoS (P0101....P0103) when originally tuned?

[cptinjak]

The car was brought to me in this condition. The owner bought it less than a month ago and it was running totally normal. After a couple weeks driving it, this idle issue began.

The fuel pressure issue is something I hadn't thought of. Despite the idle issue, the car still runs well at WOT. The owner even took it to the drag strip in its current state (against my advice) and was trapping in the mid 120s with it.

Because it WAS running well, and now isn't, I am assuming that we are probably looking for something mechanical, but dont have any idea where to start, considering the issue ONLY happens at idle.


Jack

[cptinjak]

If this really is with stock camshaft, then having 40 kPa at idle is not uncommon, at least with colder engine. I've typically seen 40...45 kPa at idle when warm with stock cam LS1. Of course it's difficult to compare, since logs posted here do not seem to be at steady idle. MAP values in the first log might be ok, but can't be sure.

I'm just guessing, but perhaps the VE values aren't right because of not being properly set for 2 bar CoS (P0101....P0103) when originally tuned?

This is an interesting thought. What could make it suddenly act this way compared to idling normally before?

Jack

[Pekka_Perkeles]

This is an interesting thought. What could make it suddenly act this way compared to idling normally before?

Jack

Well, the airflow calculations that the PCM does are one of the most important functionalities. It is the base for all subsequent fueling calculations. Any anomalities in airflow calculations - such as PCM trying to use MAF when it's not physically there - should be avoided.

Now, I've seen cars not having properly set into 2 bar CoS mode to have strange behavior. Plenty of power, runs well at highway when cruising, but permanent or random problems with idle (as an example).

I've always recommended to get the base first right and not trying to cope with a situation where CoS mode is not running right. I understand that it might be frustrating to start tuning VE again just because there seems to a be a slight problem at idle. By fixing the P0101...0103 you'll get rid at lest one of the possible problem sources.

In your case there might still be a mechanical issue.