Hey I have a 383 LT1 236/242 cam. It was in my buddies car before and I swapped it into mine. The only differences between our cars is he had a 3600 Stall, and 1 7/8 long tubes. Where I have a 3000 Stall and 1 3/4 long tubes.

Now when im driving around town I get some cam surge it seems, I only get it from around 1000-2100RPM. It isnt much but it flucuates around 50-150RPM. To me its annoying bc i know its there lol.

Also my wideband jumps when this happens..driving along its around 15.5:1 but when it flucuates its goes up to 16.3 then 15.5 then 16.3 ETC.


Could this maybe have to do with Fuel Pressure? Its around 42PSI (with the vaccum on)

Where could I tune this in tunercats?

Jay

 

Its probably because of reversion due to the large cam. I would first just try to add a little more timing in the tables where you are seeing the problem a couple degrees will make the car more tolorent of the leaner mixtures. Another thing to try might be to go into speed density mode and see if its still there, sometimes the maf gets confused when stuff flows the wrong way or stagnates. Other than that, just live with it or go open loop. Theres really not alot of room for adjustment on the part throttle cruise area the way the stock pcm is set up.

 

you may beable to play with your o2 sensor constants if you have tables for that, i'm sure you do. i dont tune LT1 stuff but on L98 stuff, there are o2 sensor tables where you can adjust your o2 sensor swing point milivolts and that will allow a friendly low rpm idle and part throttle driving response on a big cammed car.

the surging i believe is a fuel and air issue, so tuning the o2 sensor values will help keep the fueling right at low rpms low engine load levels. too much overlap with the cam will allow too much fresh unburned o2 into the exhaust stream and the o2 sensor will be reading this oxygen and think your leaner than your actually are and it will add fuel when it really shouldnt. lowering the o2 sensor swing point is suppose to correct that problem, or so this is my understanding

 

The only problem with adjusting o2 swing points is that they are only valid within a short range of mv, after that a/f ratio begins to change very rapidly. The other trouble with o2 sensors is you have to take what they say with a grain of salt. The o2 sensor will show very lean for any misfire rich or lean. It can also show lean from not enough timing to get a complete burn on a lean mixture.

O2 sensor swing points are based on airflow in the lt1, they have closed loop modes listed from 1-64 iirc. You can adjust these tables, but I would do so very carefully. You do have a wideband to monitor whats going on here so you're ahead of the game there. The problem i think is that your maf or map sensors get confused by the cam in these areas. If you have the capability to log, take one and post the problem area on here.

 

OH I just remember would the plugs im running reflect this problem?

The car before ran Autolite 104 coppers for N/A

Im running TR7s gapped at .038 for when i wanna hit it with a 150 shot. (timing charts are set up for N/A right now tho)

Should I maybe step up to a TR6 and try that?


Jay

 

how does the plugs look? If they arent somewhat clean then maybe they are not hot enough to efficiently burn that mixture. If thats the case, try a hotter plug.
TR7's are 2 steps colder than stock right? i dont think you really need to go that low with a 150 shot. TR6 one step colder than stock with 5-6 degrees timing pulled should be safe.

then again with high compression and hot ignition you should run a step colder plug n/a anyway from what i hear and read. Then on the shot go one step colder than that so the TR7's shouldnt be that bad i guess.

You may start by playing with the timing as suggested above and give it more or less timing at lower rpms and lower loads to see if you can solve your part throttle problems. See if that helps

 

Actually the compression on my motor is 9.75:1.....I canot get the plugs to burn a nice brown either (but also my idle is leaned out) most of my plugs burn lean it shows. I think im gonna order a set of tr6s and try them out.

Jay

 

lean idle isnt really a concern as most cars will be idling alittle lean..but too lean will cause problems

i think there are some issues with the tune first before you play with the plugs but it wouldnt hurt to try

 

My Closed TPS spark advance is...(if that is for idle) My buddy had it leaned out in idle bc it was spitting fuel out of the exhaust.

0 -0
400 -32.0
800 -32.0
1200-32.0
1600-34.0
2000-34.0
2400-34.0
2800-35.0
3200-37.0
3600-37.0
4000-37.0
4400-37.0

Jay

 

Thats a boatload of closed throttle advance, most stuff runs fine with 27* or so. Try backing down the timing a little to 27 or 28 degrees in the 400 800 and 1200 range for closed tps advance.

You may need a hotter plug, the big cam and low compression isnt helping you at all.

Plugs burning a nice brown all over are almost always rich, the only brown you should see is with a plug reading tool and a light down inside of the threaded part of the plug. I have pulled many a propperly running new plug with a bone white porcelin on the dyno. You can also check the grounding strap for info on if the plugs are hot enough. There should be discoloration on the strap about halfway down it from the electrode. This is easiest to see with the galvanized or yellow coated plugs, after a hard run it will discolor and give you a good reading.

 

I had this problem with my Impala SS and ended up doing an open loop tune on it to get rid of the surging. It runs great now.