Help with lightly modified L31-R

[davkenrem]

I believe my issue is going to be a vacuum leak. When I was putting the new MFPI Spider in I didn't like the way the main plug fit and that my be my issue.

 

[toomanyhobbies]

I have not put a cam in a L31 yet aside from a stock cam that did not trigger P0300 codes. LT1 F-car cam, LT4 Corvette cam, Marine 395' aka Ramjet/HT383 cam have all triggered misfire codes around idle for me.

I have a ZZ4 cam (which I don't like) in my new L31-R with a blackbear tune and I threw a P0300 on Thanksgiving, while at idle, after a few months of no codes. I am also having cold start issues, where it runs rough and occasionally dies in the first minute. I changed from Delco to NGK O2 sensors in front and it runs better cold than it did, and I also had the same MAP code you mentioned and I put a 2 BAR MAP sensor in and that solved that problem. They are like $7 on ebay.

I am thinking of changing to the Comp 12-420-8 as I think the exhaust duration of the ZZ4 is too much for a modern EFI motor to run effectively (but I am far from an expert that's just the conclusion I have reached on my own). Lots of unburnt fuel at idle.

 

[L31MaxExpress]

I have a ZZ4 cam (which I don't like) in my new L31-R with a blackbear tune and I threw a P0300 on Thanksgiving, while at idle, after a few months of no codes. I am also having cold start issues, where it runs rough and occasionally dies in the first minute. I changed from Delco to NGK O2 sensors in front and it runs better cold than it did, and I also had the same MAP code you mentioned and I put a 2 BAR MAP sensor in and that solved that problem. They are like $7 on ebay.

I am thinking of changing to the Comp 12-420-8 as I think the exhaust duration of the ZZ4 is too much for a modern EFI motor to run effectively (but I am far from an expert that's just the conclusion I have reached on my own). Lots of unburnt fuel at idle.

Honestly I am surprised it runs at all with the 2-bar MAP sensor. If you are considering swapping cams and trying to run mail order tuning, might as well throw a stock cam back into it. Your ZZ4 is a very mild cam. Your cold startup issue is from a lack of tuning on the VE table, the MAF table, the Spark Advance table, and probably most importantly the airflow tables that control the IAC. If you have a scanner, you should open the throttle body up by turning the torx screw on the side several turns in. Then with the scan tool connected, the key on, and the engine not running, close the set screw until the TPS just Zero's itself. You want most of the idle airflow to enter through the throttle body with the additional volume of the IAC system able to compensate for this like cold start, accessory loading, etc.

 

[toomanyhobbies]

I had it tuned in person initially not mail order. I know you run the 0411 from reading your posts. Is the tuning I am lacking because they didn't take the time to do it or because of the older computer?

I will try the adjustment you describe above to address cold start.

Thanks



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[davkenrem]

After hooking up 02 sensors and fixing 2 wires not fully seated on spark plugs, I'm down to one code P0101 Mass Air Performance. I started looking for vacuum leaks but got rained out. Will tray again tomorrow. Will also look into testing MAP Sensor.

Thanks for the help so far, will report back.

 

[L31MaxExpress]

I had it tuned in person initially not mail order. I know you run the 0411 from reading your posts. Is the tuning I am lacking because they didn't take the time to do it or because of the older computer?

I will try the adjustment you describe above to address cold start.

Thanks



Sent from my iPhone using Tapatalk

Depemds on which vehicle we are talking about. My brothers LT1 cammed suburban and my cammed 305 Tahoe had black boxs. My Express van had an 0411 but I now run a Green/Blue connector 1 meg PCM from a 2006. The newer PCM is faster than the 0411 and supports psuedo flex fuel.

 

[L31MaxExpress]

After hooking up 02 sensors and fixing 2 wires not fully seated on spark plugs, I'm down to one code P0101 Mass Air Performance. I started looking for vacuum leaks but got rained out. Will tray again tomorrow. Will also look into testing MAP Sensor.

Thanks for the help so far, will report back.

Is it running any better having fixed those other issues?

 

[Steve A]

Depemds on which vehicle we are talking about. My brothers LT1 cammed suburban and my cammed 305 Tahoe had black boxs. My Express van had an 0411 but I now run a Green/Blue connector 1 meg PCM from a 2006. The newer PCM is faster than the 0411 and supports psuedo flex fuel.

Just out of curiosity, how much repinning was required from 0411 to the newer PCM?

 

[davkenrem]

Ok, finally getting a chance to report back. I did not find any vacuum leaks but the P0101 code is cleared. Took the truck for a short drive today started right up but will not idle well. It drops below 1000rpm. Slight backfire when accelerating and not much power. Cam Retard was at 1.7 at 1100rpm. The PCM Stored P0108 and P1106 both dealing with Manifold Absolute Pressure, but I replaced the MAP sensor a few weeks ago. I guessing the Cam and headers could be confusing the PCM at this point. I also looked at the PIDs for misfire and it was show as misfires on at least 3 cylinders, I can only hear them at idle. they seem to disappear above 1800 rpm. The only other thing I can think of is the Valves are adjusted too tight.

Anyone have any thoughts?

 

[L31MaxExpress]

Ok, finally getting a chance to report back. I did not find any vacuum leaks but the P0101 code is cleared. Took the truck for a short drive today started right up but will not idle well. It drops below 1000rpm. Slight backfire when accelerating and not much power. Cam Retard was at 1.7 at 1100rpm. The PCM Stored P0108 and P1106 both dealing with Manifold Absolute Pressure, but I replaced the MAP sensor a few weeks ago. I guessing the Cam and headers could be confusing the PCM at this point. I also looked at the PIDs for misfire and it was show as misfires on at least 3 cylinders, I can only hear them at idle. they seem to disappear above 1800 rpm. The only other thing I can think of is the Valves are adjusted too tight.

Anyone have any thoughts?

Not sure how I missed your post. In my experience the most accurate and easiest way to adjust the valves is on a running engine. Loosen them one at a time until they click then add 1/4 turn preload. I start with the driverside first. Then shut it off and button up that side. Then move to the passenger side.