Air/fuel gauge

[tuffenuff1222]

i already know someone is going to say throw it away and get a wide band but it came in my car and i dont have the money to buy a wide band at this time. but i rewired my gauges and i forgot witch wire the purple wire was tied into on my o2. ive tryed the black wire like they said on some places ive looked, but it seems not to be workin still. the gauge worked befor i unhooked it. can some one help me out. its the auto meter air/fuel btw narrow

 

[Paul]

If I remember correctly, Autometer's website has some car-specific instructions on which wire the signal lead needs to go to on the ECM. If you dig around there, you can find it.

Paul.

 

[tuffenuff1222]

i tryed finding it on autometer, any chance you know the link?

 

[tuffenuff1222]

never mind, thanks pual! you are alot of help!

 

[Paul]

I remember it being tricky to find. Glad you got it.

 

[Addermk2]

If you want the gauge to be slightly more accurate, run a ground wire to the body of it. I used worm gear clamps on each of mine.

it makes a huge difference in the feedback reporting speed of the O2's!

 

[tuffenuff1222]

i hooked it up today! thanks alot for the help!, i have it grounded to the plate holding the fuse panel. it seems to be reading pretty good. at wot it read pretty rich so i backed my fuel pressure down, it was up to 60? i backed it down to 52 it seemed more responsive. any tips?

 

[Addermk2]

put it at 39psi and stop dicking with things you dont know about.

 

[tuffenuff1222]

whoa, i hadnt messed with it. the car was set on 60psi when i bought it.

 

[Addermk2]

so put it back to 39PSI with the vac line disconnected (then reconnect it) and reset your computer

 

[tuffenuff1222]

alright so, i backed it down to 39 with the vac line off then, put the line back on and it red almost 20. it didnt seem to run well like that. so i bumped it up untill it read 39 with the vac on? but i didnt know i needed to reset my computer.

 

[Addermk2]

you arent listening.... 39 PSI with the vac line disconnected... end of story.

If the pressure drops below ~31 psi with the vac line connected, you need a new regulator

 

[tuffenuff1222]

im running 75mm maf, 70mm tb, 24lb injectors, im sure that has nothing to do with anything were talking about. i just figured id throw that in there. if its on 39 with the vac hooked up whats the difference than it being set to 39 with it off then hooking it back and it droping? it changes when you set it and then hook the line back regardless? im not trying for you to get short im just asking to learn this stuff.

 

[Paul]

you arent listening.... 39 PSI with the vac line disconnected... end of story.

If the pressure drops below ~31 psi with the vac line connected, you need a new regulator

Yep.

With the car idling and full vacuum introduced to the regulator, that's pretty much what should happen.

Paul.

 

[Addermk2]

im running 75mm maf, 70mm tb, 24lb injectors, im sure that has nothing to do with anything were talking about.

if its on 39 with the vac hooked up whats the difference than it being set to 39 with it off then hooking it back and it droping? it changes when you set it and then hook the line back regardless? im not trying for you to get short im just asking to learn this stuff.

*deep breath*
Fuel pressure is measured in PSI. PSI refers to positive pressure.
Engine vacuum is measured in in/Hg (inches of mercury). in/Hg refers to negative pressure.
-1PSI is ~2in/Hg

A fuel pressure regulator with a vacuum source (like yours) will change the fuel pressure of the vehicle based on the amount of vacuum being pulled inside the manifold (Vacuum reference fuel pressure regulator)

Assuming a stock car:
Your car should run at ~19in/hg at idle.
Your car should run ~39PSI fuel pressure with no vacuum source on it. This allows it to be working at the internal spring rated value.
When your car is idling, your fuel pressure should be showing ~ 39PSi - ~19in/Hg

Your car is set to run a specific fuel pressure based on certain flow requirements of your fuel injectors.
Your 24# injectors are rated to flow 24lb/hr of fuel @ 39.15PSI (i have the flow charts if you want them)


So long story short, You fuel pressure should NEVER be changed from ~39PSI w/no vac reference!
If your car runs like crap, its because of something else, and someone jacked your fuel pressure in an attempt to cover up the problem.

Things to check:
Verify that you are using the correct MAF.
Make sure all your sensors are in good working order... i.e. ECT, ACT/IAT, O2, EVP
Check for vac leaks (a vac/boost gauge is great for this)
Timing (nobody ever thinks about his one) Timing can affect the vac your car pulls based on flame front speed, completeness of the fuel burn, and mixture.

 

[tuffenuff1222]

alright thanks, well when setting the reg. i unhooked the vac line set it at 39 hooked the line back and at idle it brought it down to 19-20. now when i crack the throttle it brings it back to 39. thats what i was trying to say. so i tryed it again i unhooked the vac bumped it up untill when having the vac line on it read 39 at idle. and the car ran strong.

 

[Addermk2]

the fact that its dropping down to 19-20 means:

Your gauge is crap
your FPR is bad

one of those two is your problem

 

[BigTang]

Like Adder is saying you need to take a systematic approach to it and do it the right way. What regulator do you have?
Some like the kirban and the holley used to have a rebuild kit available for about $10 that came w/ a new diaphram.

What gauge are you using? the harbor freight kit I bought for the adapters reads no where near my autometer mechanical one and it matched my autometer electric one # for #.

What vac. are you pulling at idle?
You really can't test it by reving it w/o a load on it as the engine will make different amounts of vac depending on the load. and most importantly, do not try to tune w/ a narrow band.