Hi Guys!

After a bit of advice. I recently hooked off the standard air filter housing and replaced it with a 'dual snorkel' set up from a 70's corvette.

I have yet to run two CAI pipes to the snorkels, but I'm running it like it is at the moment.

The only thing I've noticed is what appears to be a notable flat spot in the RPM range from around 2.5/2.7k up to around 3.25k.

Now it never really pulled like a train before but now you can really feel it sort of struggle as though it's running out lean.

Does the TBI ECU counter for the A/F ratio or are the stock injectors not man enough to deal with the extra demand?

Any help or advice appreciated.

Andy

 

Andy,

You probably are feeling it running leaner than it was. The other possibility is it is getting a hotter intake charge which is either causing detonation or loss of power.

The TBI ECM can compensate at part-throttle in closed loop pretty well, but go WOT and it runs in open loop, ignores the 02 sensor and runs on programmed values. The one exception to this is if the car is running lean at part-throttle. If its lean at part-throttle and go WOT it will use the last long term fuel trim value aka BLM value as a multiplier to add more fuel.

That being said I have run open elements on stock TBI setups and even headers and not really had to touch the chip.

I would put a fuel pressure gauge on it. I have seen factory TBI regulators set anywhere between 9 and 13 psi. Obviously the higher the stock fuel pressure, the better the car takes to airflow enhancing modifications. Most STOCK engines enjoy somewhere between 11.5 and 13.5 psi.

If you have access to a laptop its not hard to build a WinALDL cable to datalog the ECM and see whats going on.

 

Thanks for the reply, I would love to Data log the ECM, I didn't think it was possible though. Could you please link me to a place to make the WinALDL cable? I'm a ham so I think I should be capable of making up a lead. Much appreciate the detailed and thorough reply!

 

cable schematic is at the winALDL web site. needs serial port or an adapter usb to serial.

 

Cheers guys!

Got all the parts, will be knocking one up later.

I took the car out for a quick spin after work, and driving it at wot you really feel the lack of power when it shifts to third from second, dropping it right on the start of the flat spot at around 2500rpm. If I then lay off the throttle and accelerate up again it seems to pick up much faster!

 

Put the original stuff back on, see if the flat spot goes away.

 

Hi,

Yep, shall be testing it out this weekend at the track hopefully. Will be refitting the original air cleaner with the single snorkel and CAI hose.