Ive had this motor for a couple years now. The engine has been having some rough idle on cold starts when it is less tha 50 outside. Seems like it misses. Once it runs for a few minutes it seems to run fine. I took a datalog with datamaster, and went from a cold start and drove around for about 15 minutes, i tried to get some WOT in there but it was kind of hard, as it was during rush hour.

I dont really know how to read these things, but there seems to be an excessive amount of retard during driving.

Can someone help me out here?

The engine is a stock 355 LT1
Hotcam, mildly ported heads, #30 injectors, shorty headers, 1.6rr
T56 Transmission

Zippyshare.com - 12.uni

Also, the EGR was tuned out supposedly, with a mail order tune, and the LT4 knock module is installed.

 

Get an error message "your system does not support this video file. click here to get the plugin". Even without clicking, it attempts to download some sort of plugin, which my security system blocks. Not sure why it indicates its a video file, and I doubt anyone is going to download some unknown plugin. The other "download" link tries to download a pirate game.

Seems like you might want to find a better site.

 

Never mind.... got it to download without the plugin issue. Let me look at it this morning. Did appear to be a large amount of knock retard.

Are you aware you can eliminate the DTC 84 that is showing up simply by placing a 2,000 ohm resistor across the pins in the skip shift solenoid harness connector?

 

I do now! I dont have a working SEL so i wasnt aware i had any codes being thrown.

 

DTC 84 doesn't turn on the SES light. It just sets the code, which shows up in a scan. Doesn't hurt anything, but getting rid of the code gets rid of the red "DCT Err" window at the upper right, and would make other codes more obvious if that window turned red.

Most of the data log looks fairly normal. The closed throttle TPS voltage is toward the high side (0.82V). Is it possible the throttle stop screw is out a bit, preventing the blades from closing all the way? The idle air counts do not indicate a problem, but if the TPS volts get too close to 4.90V at WOT it will set a code.

Things that look normal - IAC 39 counts; system voltage no less than 12.8V; barometer of 99.7kPa; MAP of about 50kPa at idle (maybe a shade high for the LT4 HOT cam), but not a problem; runs 185-190*F coolant temps with no sign of the fans running at all (add the fan relays to the 0/1 flag table in the upper right corner of DataMaster screen); air flow grams/sec at idle is 10.40gps; spark adv at idle is 20*; it is programmed for an 850RPM idle when fully warmed up.

What shows up as a problem:

-split long term fuel corrections (BLM's) at idle (Cell 16). Its pulling out 6% of the fuel on the drivers side, and adding 12.5% on the passenger side. The "split" disappears in the load cells (01-15), at least the ones you actually drove in (6, 7, 9, 10, 11, 14, 15) and it actually goes the other way, with the drivers side very close to normal (which is 128) and the passenger side SUBTRACTING fuel with BLM's below 128. Do you have an aftermarket throttle body?

-seems like a long time to closed loop, but maybe it's due to the cold weather. Took 296 seconds, vs a typical warm weather number of 205 seconds. It switches into closed loop when the coolant temp reaches 139.6*, so that would appear to be the controlling factor. Since the fans never come on, I'm wondering if the t'stat is stuck open, or maybe it doesn't have one.

-up to 8* knock retard. Seems to be responding to the knock sensor, not the knock count, although the knock count does increment in a couple places. Odd - seems to correlate to EGR operation.

-EGR is commanded to a 12.5% duty cycle in numerous places. The knock retard seems to pop up about the same time.

I would ask the tuner about the EGR.

 

Thanks for the reply Injuneer.

Since the mail order tune, there has also been a dyno tune done to it.
Since the dyno tune, i have added a stock TB that has been ported to 52mm. The tuner that did the dyno tune didnt really tell me much about how the car was running, all i know is that he picked up 30whp for me.

I will check my Tstat to make sure it is working properly. I know there is one in there.
As for the EGR, the fact that there is a duty cycle im assuming means that it is in fact, not tuned out?

Another thing that i think i should bring up is my passenger side O2 sensor is probably 24" approx if not a little more downstream from the bottom of the shorty flange. The dirvers side is actually on the header right before the flange. I dont know if this could somehow affect the closed/open loop. Or even the fuel corrections. Im going to try to relocate it closer to the engine when it warms up.

 

Is the TB the reason the fuel trims could be off? Its the only thing different since the tune.

 

Aftermarket throttle bodies often do not correctly utilize the idle air passages provided with the stock throttle bodies. That could lead to the split BLM's at idle. Don't know how they may have bored a stock TB. The bottom plate on the throttle body contains the IAC valve. You had to transfer your bottom plate from the old TB to the bored TB. Maybe the IAC got damaged. Maybe yhe throttle stop screw was not set correctly.

When you changed the TB, did you correctly adjust the IAC counts, idle RPM and TPS voltage? Appears you might not have. Are you sure all the gaskets are installed correctly and not leaking?

 

Everything was transfered over from my stock TB to bored one as is. The throttle screw has not been touched since I recieved the unit. I went and looked at the tb blades and they appear to be fully closed.

When I put the bottom plate on the TB I used RTV instead of a traditional gasket. Could this cause a problem? The pieces are powedercoated and I thought they may not seal properly with a traditional gasket.

If by this you mean messing with the tune, then no, I do not have the ability to do that myself.

You mentioned the EGR was commanding 12.5% duty earlier. What exactly does this mean, and does it mean it is still active in my tune? How could this be causing knock retard?

Thanks for your time and patience.

 

Is it possible when you tightened the bolts for the bottom plate, the RTV squeezed into the passages? That gasket seals both the IAC passage and the coolant passages. Is it possible you have coolant leaking into the IAC (I suspect you have already done the coolant bypass)?

You need to check the throttle body setup. Typically, you back off the throttle stop screw until you get the specified idle speed (this gets the IAC to the point where it just starts to open, then you continue to back off on the stop screw until you get the IAC counts in the range of 20-40. At that point you check the TPS sensor to make sure it is within the required range. Typical reading for the TPS in a factory setup is 0.67V. Some people seem to feel 0.50V is better, but I can't think of a reason this would be true. Since the LT1 TPS is not adjustable, the screw holes would have to be slotted to allow it to be adjusted. All this is done with a scanner, which tells you the true idle RPM, the IAC counts and the TPS voltage. None of it requires playing with the PCM program.

I don't know how your tuner "tuned out" the EGR. All I can tell you is that the PCM is trying to control the EGR vacuum solenoid to a pulse width modulated 12.5% open. It would seem to me that the way to tune out the EGR would be to raise the control parameters to values that you would not see in normal driving. But I gave up my stock PCM 14 years ago, so I really don't keep current on what the tuners are doing.

 

Well, I guess it is possible that the RTV occluded some passages. I will have to remove and reinstall with a conventional gasket.

You have definatley given me some useful info to work with. I will have to verify everthing you said is true for my engine and fix it if it isnt.


As for the egr,

I did some searching and found this thread:
https://www.camaroz28.com/forums/lt1...estion-624453/

And i found this post:
So I think its fair to assume that this is what I may be experiencing.
Since I am no longer in touch with the tuner who tuned my car, I don't have a copy of my tune. Is it possible to fix this without erasing my current tune through a mail order or something of the like?

 

I've finally hooked this up to my scanner again.
My idle speed is set at 850 and it stays right around there
My IAC counts were around 84
My TPS voltage was 0.76 volts.

Problem is my idle screw is back out all the way. What should I do?

 

Did you make some changes or something and is the iac count you reported when engine was still cold? Was you ac on? I ask that as Fred had stated above your iac counts were 39. My counts are about 30 and with ac they are I think in the 50 range. Optimum is 32 as thats what pcm starts with when reset.


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The only thing I've done since then was re seal the top TB plate and the IAC housing with actual gaskets instead of RTV. The engine was warmed up. A/C was not on.

The block marked IAC Pos are the counts right? If so, then they were right in the 80's at idle.

 

The top plate will not cause a "vacuum" leak... it just lets air in front of the blades that hasn't been through the MAF sensor. Should not affect IAC counts. Would affect BLM's.

Yes IAC Pos = "counts". Was the engine fully warmed up when you are getting counts in the range of 80? I looked at your data log from February and they are 38-40 with the engine fully warmed up. They are higher when you first start the engine though.