say I drive my car about 20 miles to a garage and the car is completely stock besides and catback exhaust. Then I do a heads/cam swap and rebuild the shortblock, etc and put on headers and disconnect the o2s and plug the o2 bungs on the new headers, what happens with A/F ratios? Is the ECU just locked in to how it was running before i diconnected the the O2s? I ran the car a bit after breaking in the cam, and it seems to run fine.. would I be straight to drive the car a back to my garage (about 20 miles) before tuning it and setting up the ECU to run on open loop mode?

 

It would run with the same BLM's as stock and learn the new A/F slowly. You should be OK.

If it was me however, I'd reset the PCM after you do the heads/cam and have the computer learn from a fresh start with no stored values, I'd think it would dial in the right A/F faster.

Brian

 

I thought the PCM resets when you disconnect the battery? Also, how will the PCM learn the A/F ratios now without any exhaust oxygen sensors? Would it just try and run through the one on the intake?

 

If you unplug both sensors it will take approximately 50 miles before the car catches it and takes action for it. In the meantime you fuel trims will go crazy.

It seems like your skirting around instead of just getting a base tune to break the car in. Why? I know Ion is doing it.. just have him build you a base tune so you don't ruin a fresh motor...

Just me... sometimes the cheapest/easiest way out isn't always the brightest. Do it right and get a base file

 

I really need to drive the car from this garage to my house for now.

 

Do you really need the o2's?

 

nope

 

How will the car get the a/f without them?

 

I noticed a lot of people tend to do mail order tunes. Just out of curiosity, how close do these mail order tunes get to dyno tunes in terms of RWHP on say... heads/cam/nitrous cars?

 

Real close.

 

Pretty close.. Bryans stuff is unbelieveably accurate. Mine is less so being speeddensity. In speeddensity you can put a set of headers on a car and it will lean out a 1/2 point.

That being said, its still pretty dang close..I've done dyno days for a group of 93's speeddensity.org and the highest gain of the day over one of my mail orders would be somewhere around 10rwhp.. most being around 6rwhp.

 

You need them or you need to turn them off..that doesn't mean unplugging them. I don't know about the 94+'s but I put probally 250 miles on my car before it tripped the SES light and gave a o2 low code.

 

Do speed density cars use o2 sensors? Are they in open loop all the time?

 

yeah speed density car use o2s. They are not open loop.. I don't have a programmer but was planning on having it switched over to open loop when the car gets tuned.

 

For what reason?

You where gifted with a sensor that dynamically adjust your cars fueling to keep up with atomspheric changes. What part of that is a problem that you'd like to get rid of?