Went to atco twice this season, once in july and then yesterday. In july it was about 70 degrees during my best run and yesterday was about 45 degress during my best run. I was stock during the run in july except for the hotcam. Run yesterday had all the mods in the sig and NGK tr55's gapped at .047, and I ran with the cut out open. Times yesterday were worse than in july with no mods!! In july 60 ft was 2.191, 1/8 9.067, 1/4 14.031, 99.31 mph. Yesterday 60 ft was 2.150, 1/8 9.133, 1/4 14.128, 98.81 mph. Anyone have any ideas as to why the times are going the wrong way. I am frustrated and stumped. Also, at the top end, after I crossed the line and let off of the gas, the car would back fire twice and then stop. An advice is appreciated.

 

60' = 2.191
60 - 1/8 = 6.875
1/8 - 1/4 = 4.964

60' = 2.150
60 - 1/8 = 6.983
1/8 - 1/4 = 4.995

Although you have a better 60 foot on the cold track, you're making less power all the way down the track based on the ET but MPH is only down slightly. In the colder air, it's more dense meaning there's more oxygen to burn which needs more fuel.

First guess is that the engine is running leaner in the lower altitude air. Perhaps the knock sensor is detecting knock and retarding the timing.

Try adjusting the timing.
Try more fuel pressure.
Try running without uncapping the exhaust.
Try a regular spark plug to the factory recommended gap
Perhaps the new cam needs more gear or converter.

 

I had the cam in during the run in july as well so I dont know if that would decrease my times now. I am getting a stall and gears next anyway thou. Also, I did make one pass with the cut out closed and I ran a 14.4xx, so it definitely got worse. I have a scanner so i can check timing and knock retard tomorrow and report back, did not have it at the track with me but similiar weather temp now anyway. I also have the LT4 KM btw. Thanks

 

IMO try running with the stock MAS and closed exhaust. The after market MAS make the car run lean plus the open exhaust does the same thing. I have a feeling you were running way too lean. You might want to get a LT4 knock sensor as well. Noise may be picked up as ping or maybe due to the lean condition the timing was knocked back due to real pinging.

 

I agree, dump the aftermarket MAF and try the stock one. MAFs are not the place to be looking for hp.

 

trapping under 100 with a cam?

something is very wrong, at this temp at Atco you should be trapping over 100 stock.

 

It could be any of a great number of potential problems from the simple to the complex. I would try and rule out all the simple stuff first... When was the last time your fuel filter was changed? Is the air filter clean? Either of those probems can create the scenario you describe.

A loose or burned plug wire could have it running on seven cylinders, the transmission could have slippage (sometimes synthetic fluids can make a perfectly fine tranny slip a bit). Perhaps you are getting some knock, perhaps the aftermarket MAF is a problem...

Have you had any other symptoms? Is it getting worse or better gas mileage on the street? Harder starting? Lights dimming at night?

Go back over all the basics first before spending money. Something obviously isn't right and adding more variables to the mix will make is more difficult to diagnose.

If the the valvetrain is too tight it will also result in low mph and poor ET. You have a cam so perhaps that could be something to look at before beating on it again and potentially making a minor problem into a major one.

 

Who did the tune for the LT4 HOT cam?

What gears does the rear have... not sure 2.73's, stock stall and the HOT cam would be a good combo.

In any case, you wouldn't want an LT4 knock sensor.... if you have false knock retard from the roller rockers, you would want the LT4 knock module.

 

Fuel filter was changed 2 months ago, air filter should be clean as well. Car has 3.23's in it stock. Hotcam was installed when the shortblock was rebuilt and No tune was ever performed. First run in july was with the car completely stock EXCEPT for the hotcam. I have 3.73's and 3200 stall in my garage waiting to be put on and then i was going to get the PCM tuned for everything. I just wanted to make some passes before I did the stall and gears. Trans was not slipping either. And I think the engine has the stock RR's and springs. I still have the OEM MAF, but want to try and figure out what is wrong first befoer just throwing that back on.

I had to work 10.5 hours yesterday so I didnt get to touch the car, will pick up a fuel pressure gauge and throw it on the car to see what is going on at idle and WOT by removing the vacuum line. Will report back details. ill also hook the scanner up and and report back the numbers for both cases as well.

 

If you used the stock RR's, you limited the gains from the HOT cam. It's lift numbers are 0.525 I&E with the 1.6RR's. With the 1.5 stockers (probably slightly less than 1.5 in actuality) you only have 0.492 I&E. Lack of tune isn't helping, and who knows whether that hurts more with or without the added mod's.

 

I thought that it was deemed best to change valve springs when using a Hot cam?

And what if the MAF is ''what's wrong''? You're ***-u-me ing that it can't be the problem.

 

Ok guru's, here is the data I pulled. All runs have the cut out open. Ist column is key on engine off with gran. maf connected, mid column is idleing with gran. maf connected, right is idleing while gran maf is disconnected.
Baro ("HG) 28.04 27.82 27.82
LT Fuel trim off on on
LT Fuel TR CL 0 16 16
LT Fuel TR L 128 120 108
LT Fuel TR R 128 141 120
Evap Duty % 0 0 0
EGR Duty % 0 0 0
IAC Position 156 45 42
Idle Req RPM 3188 713 650
Inj L PW(mv) 0 4 4
Inj R PW(mv) 0 4 4
ST Fuel TR L 128 126 119
ST Fuel TR R 128 130 125
Knock Retard 0 0 0
Knock Sensor 0 10 7
MAF (Gr/s) 0 9 471
MAP (v) 4.80 2.14 2.27
Spark Advance 0 16-20 17-21

I am not completely certain but I think it felt a little bit faster with the MAF disconnected. Also, with the MAF connected, when I would let go of the throttle the Injector pw would drop to 0 for left and right and it would feel like the car was hitting a wall. Felt similiar with the MAF disconnected but I didnt look at the pulse width then.

Hope someone can provide suggestions with the info I provided. Thanks guys!

 

As I explained to you in response to your PM, the Graqnatelli is a "hit or miss" mod. It may give you 10-15HP by intentionally under-reporting air flow at WOT (high MAF AFGS), and leaning out the stock overly-rich PE mode tune. But it may not. You aren't going to measure the impact of the Granatelli by pulling the MAF connector off at idle. Your problems are at WOT. Taking a couple simple frames of data at idle won't tell you if its reporting the correct air flow, whether its leaning it out too much or too little.

Idling with it connected, you have a case of "split" BLM's..... pulling out fuel on the left side and adding fuel on the right side. But, that's just at idle.... you need to know what its doing at peak air flow, when its affecting your HP on the track.

Also a little puzzled by the two "knock" readings.... knock retard is commonly reported by a scanner, but I've never seen a scanner report "knock sensor". What kind of scanner are you using? What is the EXACT label on that data field.

When you snap the throttle closed, its normal for the PCM to shut the fuel off (PW = 0) until you get well below 2000rpm. Then at about 1500rpm it wil turn the fuel back on... you can normally feel it do that.

 

The exact title is Knock Sensor. Maybe the value is the number of times it picks up knock? it is an Actron Super Scanner that can read OBD I and II because I have a 95 with the GM 1.5 setup.

What would cause split BLM's and is it ok to have this?

What sort of test can i set up to get reading at WOT so that i can give you guys more information to work with. Should I go to an empty parking lot and have someone watch the readings at WOT with the maf connected and then disconnected? How about pulling off the vacuum line to the fuel regulator and then doing the two runs? Any other ideas>?

Thanks for the replies!

 

While driving at WOT, check the readings for the left and right O2 sensors. While the narrow-band OEM sensors are not all that accurate at the WOT A/F ratios, they may show you whether you are running grossly rich or lean.

As far as I know, only the Corvettes got the "1.5" PCM. The 95 F-Body PCM is identical to the 94 PCM, and OBD-I. They just changed the ALDL connector on the 95's.

Split BLM's at low load can be caused by an aftermarket throttle body, reversion from a cam with high overlap. They can also be caused by having something affecting only one bank of the engine, like exhaust leaks before the O2 sensors, misfires, leaking injector, etc. You don't want to see a significant difference in the BLM's from left to right bank.