anmar A

hi guys, i have a question, so I bought a pacesetter long tube headers for my 1993 z28, and the guy who installed it told me that i might need a higher flow injectors because i will be running lean after installing the long tube headers. I didn't believe the guy so i asked him to hook a A/F meter and see if the car runs lean, I got the car back from him with long tube headers installed and the A/F gauge installed too"sounds awesome, with the loud mouth catback". so here is the question, i noticed that the gauge reads rich when cold start, stays between rich and normal after a while when idling, but when start driving it will go lean and stays lean, it would not change on both banks, but when idling it will go to normal, so do i need a higher flow fuel injectors? the guy told me that he would install a higher pressure fuel pump and higher flow injectors with an adjustable fuel pressure regulator and that will help the car not to run lean anymore? any ideas?

lt1-xjs

Install a 160* thermostat and contact "pcm of nc" and talk to Alvin. Inquire about their bolt on tune, they'll send you a new chip. You don't need a pump or injectors.

Injuneer

If your only mod is long tube headers, you do not need larger injectors or larger fuel pump. The headers may improve the engine's volumetric efficiency (VE), so since your 93 runs speed-density A/F control the VE tables might benefit from reprogramming. But the change should be so minimal that the O2 sensor feedback in closed loop will keep the engine from running lean. You don't ever tune a car with an adjustable fuel pressure gauge, because the closed loop feedback will eventually defeat the changes.

What kind of "A/F meter" do you have? Is this a simple gauge that piggybacks off the stock narrow-band O2 sensors? The stock O2 sensors are not intended to be accurate anywhere besides at stoichiometric 14.7:1. What kind of "lean" reading are you seeing? When the ECM enters closed loop, the O2 readings should be cycling rapidly back and forth between rich and lean.

Do you still have a functioning AIR pump? If so, on startup, the O2 sensors generally read lean because of the extra air being added to the exhaust.

anmar A

i dont really know the brand of the A/F meter but it has two banks and it has LED indicators for Rich, Normal and lean. i dont have AIR pump, and the gauge shows that i am running rich on startup (cold engine) and when warmed up it fluctuate between rich and normal, but when start driving under load (like 2,000 rpm or above) it would go to lean, it will not fluctuate at all just stays lean all the time. i think lt1-xjs suggestion is valid, because i freed up the exhaust so my VE changed and probably the look up table that it is flashed into the pcm dont have the new value so it cant compensate.

Injuneer

Your 93 has an ECM, and it's not "flashed".... it's a removable PROM.

The "A/F Meter" you are describing is basically running in parallel off the stock narrow-band O2 sensors..... really not accurate at all, and may be causing the O2 sensors to be inaccurate.

Rich on cold start is normal WITHOUT an AIR pump... ECM richens the mixture for cold start, just like the choke on a carb. At about 206 seconds from startup, assuming the coolant is approaching normal temp and the O2 sensors are hot, the ECM should go into closed loop. In closed loop, you should see the LED's appearing as a psychedelic light show, flashing rapidly back and forth between rich and lean. That's the way the ECM controls the A/F ratio. And that's why using the stock O2 sensors and some LED's just doesn't work.

The feedback from the O2 sensors allows the ECM to add up to 25% extra fuel in closed loop to compensate for a lean condition. Headers will not improve VE by 25%.

anmar A

ok then do you suggest to reflash the eprom from pcm of nc?? it is way cheaper than getting the fuel system upgraded?

bw_hunter

It's cheaper, yes, but that's not the point. Upgrading your fuel system will not fix the issue you describe. In fact, it doesn't seem that you have a problem other than a AFR gauge that is feeding you meaningless information. What I believe Injuneer is saying is that the changes to the exhaust system are well within the computer's ability to compensate.

I have some advice that you will probably not like. 1) find a new mechanic...his advice is incorrect 2) remove and toss the AFR gauge. 3) listen to Injuneer and the other knowledge folks on here...they'll guide you much better than most other sources.

anmar A

thank you guys for your help, I think the mechanic is trying to mislead me, i think i will go ahead and contact pcm of nc and have them program and send a chip for my car. is there any risk involved? i removed the cat, air pump and EGR, i do agree that the A/F gauge will not give a very accurate info, but it give a rough idea.
any thoughts?

bw_hunter

Because of the way the narrow band lambda sensors work, their accuracy away from the stochiometric idea fuel air mixture is not good at all and pretty close to useless. For any air/fuel gauge to work properly, you'll need a wide band sensor. You car is not so equipped, making the data you get from the gauge, again, worthless.

You might see an improvement in performance with a reprogrammed chip but it won't be from the data you see on your gauge. The tuner will take everything you've done into account and will adjust the tune to fit it. He/she will advance the timing, among other things, to take advantage of a more efficient engine.

Sorry to be so blunt, but I think you should take off the A/F gauge and sell it some kid in a Honda...they'll buy anything. It's not doing you any favors at all...

Injuneer

You are assuming you have a problem based on a crude instrument of questionable value. Find out if you have a problem before assuming you need a tune. Best thing you could do would be a free download the 1993 F-Body LT1 version of TTS DataMaster, get a cable, run a data log with the engine operating under the conditions which you believe produce a problem, and let us look at the data log to determine if there is any evidence of a problem.

TTS Power Systems

lt1-xjs

If you want real results just throw it on the dyno with wide band. For best results, order the chip, change it on the dyno and then send it back to be tweaked. Bottom line, short of a dyno tune which would not be required for a bolton car.

anmar A

ok, that sounds good, i will order the chip from pcm of nc, i checked the aldl usb cable and it is about $60 idk why would a cable cost this much, any ways how would you know if the car has aftermarket cam, i bought the car from a guy on craig list and i dont really know if the engine is still stock or been modified, he didnt say anything and i didnt ask. is there an easy way to tell?

lt1-xjs

You don't need a cable and I wouldn't order the chip until you know what your mods are. Especially if you have a cam. I assumed it was stock since you just installed headers.

Injuneer

He needs a cable to run a data log using Datamaster.

I think you confused him when you said "order the chip, change it on the dyno and then send it back to be tweaked." Basically you told him to buy a chip and somehow change it on the dyno. Not sure how that is done unless someone has the Moates chip burning hardware.

Seems odd that he wants to buy a series of parts and a chip that may not be needed, but doesn't want to spend money on a cable.

lt1-xjs

A stock car will benefit from a Bolton tune 8-10 hp plus improve driveability. He could dyno the car, swap in the piggyback chip, see the gains and get the A/F ratio all at one time. If the A/F is off, pull the piggyback and send it back with the A/F chart to be corrected. Most are spot on and require the 160* stat and he wouldn't need a data log. In order to get the correct chip he needs to know the mods.