Factory Five Racing Forum banner
1 - 20 of 22 Posts

·
Charter Member
Joined
·
183 Posts
Discussion Starter · #1 ·
I have a blown EFI 302 (42# injectors, 255lph pump and custom chip) and just installed autometer's AF ratio meter to make sure that I don't run into any lean conditions on my setup.

I did notice the following that prompted me to seek the advice of more knowledgeable people...

When I start the car from cold, the meter indicates very lean which gradually changes to the stoich point as the sensors heats up. This is normal.

Now after the sensors are at working temperature, the meter starts jumping erratically between the stoich point (just off the rich indication) to way lean and back. This will keep on happening even when driving or under acceleration. I have no way of telling if the engine goes lean under boost but it does seem to be mostly in the stoich area...

I don't think this is normal. I swapped the sensors out and the meter reads the same.

Any ideas from the EFI Gurus??
 

·
Moderator
Joined
·
8,272 Posts
Stock type O2 sensors are designed to pretty much 'toggle' around the 14.7:1 stoichometric point and you should notice that on the meter under cruise conditions. The meter should bounce from rich to lean and back. However under WOT it should peg rich and stay there until you get off the gas. I have a J&S on mine with an LED readout and it pegs rich under WOT. I would investigate further. Maybe try to get to a dyno where they have a wide band O2 set-up. You definitely don't want to be running lean under boost.

Just as a side note when I installed 42lb injectors and a calibrated Pro-M 80mm MAF on mine it was leaner than 14.7 over 4000rpm. Very dangerous. Some time on a dyno with a wideband allowed a chip to be burned that corrected the problem.

Be careful until you know for sure that you aren't lean.
 

·
Charter Member
Joined
·
183 Posts
Discussion Starter · #3 ·
Mike

I do have an adjustable fuel pressure regulator that is set for 39psi with the vacuum disconnected. Do you recommend that I increase the fuel pressure to push the AF ratio rich under WOT? At the moment it is still just off the rich indication on my meter (presumably just over the 14.7:1) at WOT.
 

·
Moderator
Joined
·
8,272 Posts
You could mess with the fuel pressure but be aware that the Ford EECIV computer will learn that the mixture is rich when driving under part throttle closed loop conditions and will adjust the fuel table scalars accordingly. The EECIV can adjust up to +/-20%. So a change in fuel pressure will give you a temporary A/F ratio affect but it will likely eventually get 'tuned out'.

I would very seriously consider getting access to a wide band meter so that you can tell for sure what your A/F ratio is. Tuning a supercharged motor by trial and error is asking for a very expensive education.

You want somewhere between 11.0:1 and 11.5:1 at WOT for a good street tune on a Kenne Bell motor. A little leaner will get a few more HP but will be more sensitive to detonation. Kenne Bells seem to like to run a little more on the rich side than other superchargers.

BTW due to the fact that my A/F ratio was initally so far off after I had a chip burned I picked up a ton of power. More than 60 HP and 80 lbft at the wheels. By far one of the best investments I made on the car.
 

·
Premium Member
Joined
·
428 Posts
Firstly, I'm a rookie here, but I spotted this item and I think it would be the kind of thing that would help with more precise AF readings.

http://www.wmsracing.com/wmsweb/wideband.htm

What do you guys think? Is it worth the $ ?

These are the same guys that produce the SDS computer systems that Wayne has been selling for his stack intake systems.

Andrew
 

·
Moderator
Joined
·
8,272 Posts
Andrew.

That's just the type of O2 sensor set up that you need for accurately tuning A/F ratio. Most of those units cost more than $500 which is about the same price as a typical dyno tune and chip will cost you at a good shop. I did consider getting a wideband and also a twEECer to recalibrate my A/F ratio but decided that I would rather spend $600 for dyno time and a chip rather than $1000+ for a wide band and a twEECer and then still have to spend time learning the twEECer and tuning the car. It's up to you how you spend your money. There's no doubt I would love to have a wide band and a twEECer but finances dictate otherwise. However as these toys continue to come down in price they become a far more attractive option.
 

·
Moderator
Joined
·
8,272 Posts
Rickster.

Very good point. I knocked the engine harness ground off while changing my clutch a while back and it wreaked havoc with the O2 sensors. It's the orange or tan wire that normally goes to the back of the drivers side cylinder head. If you have a ground problem you will probably find that the computer will have all kinds of codes set. Mine did.
 

·
Premium Member
Joined
·
428 Posts
Mike,

Thanks for the explanation. I have looked at this item for my build and have questioned the need for it as opposed to the other items you mentioned. I now feel much better informed as to the options. I'm also going without the supercharger...

Cheers!

Andrew
 

·
Moderator
Joined
·
8,272 Posts
Andrew

You can always add the supercharger later. You know you want to :D

The dark side is calling young Skywalker.
 

·
Charter Member
Joined
·
183 Posts
Discussion Starter · #11 ·
Maybe I was chasing a ghost here... :eek: I took the car out today and made a few runs looking at the AF ratio and boost levels of the car. :D I could clearly see that when I go into boost (0-8psi) the AF ratio is on the high side of the stoich point (the last yellow and first green LEDs are on) and stays there while I play with the throttle going into boost and back to 0psi.

When I cruise again (typically between 15-20"hg of vacuum) the AF ratio would 'toggle' again.

BTW I did look for codes from the computer and got code 15 (PCM ROM failed), the other codes I expected. Could this be due to the fact that I have a custom chip installed?
 

·
Moderator
Joined
·
8,272 Posts
Sounds like you're still lean. With the kind of meter that hooks up to the stock O2 sensor you should peg dead rich and stay there until you get off the gas. And even then you may still be too lean. As far as the stock O2 sensor is concerned rich is anything less than about 14.1:1. That is still way too lean.

I have a piggy back chip (Autologic) that plugs into the port on the back of the computer and I don't get any codes. Maybe the chip you are using functions differently.
 

·
Vendor
Joined
·
8,399 Posts
THe SDS wide band is a good unit for the buck and those not needing a high sampling rate. Most of the $300-$400 widebands on the market use the Bosch LSU1 sensor and perform comparably. The higher $ units(MoTEC, Hirobo, etc) use the NTK L1H1 which the sensor alone costs $329 from NAPA. The SDS gives you 90% of performance of the big buck ones and 1000% better information than the narrow band O2.
 

·
Premium Member
Joined
·
7,237 Posts
CPA - my A/F gauge sits about 1 or 2 green LED's into the rich side under WOT, full boost. On the dyno, I'm at about 11.9 A/F ratio. It's SUPPOSED to toggle back and forth at anything part throttle. That tells you the computer is doing it's job by maintaining the A/F ratio close to stoich.
 

·
Moderator
Joined
·
8,272 Posts
CPA.

Don't rely on a narrow band O2 gauge to try and accurately measure A/F ratio. They are not accurate enough. Wade is quoting his A/F ratio from a dyno with a wide band set up, not from his gauge.

Wayne has very good info on the wide band set ups that you need to get access to. Either buy one, borrow one or rent one, but I suggest being easy on the right foot until you know for sure what your A/F ratio is. If you are running lean your repair bill will far exceed the price of a wide band O2 set up. Been there, done that!
 

·
Charter Member
Joined
·
842 Posts
CPA,

4402 is also blown, but with stock injectors, 190 lph pump and the same Autometer AF gauge as you have. What I see is identical to you except for:
1 – first green under cold start for about 45 seconds then leans out
2 – first green under WOT

I remember that the instructions wanted you to put the O2 sensor very close to the header. I located mine before the O2 sensor for the EECIV system…

Hope that helps…

Chris
 

·
Registered
Joined
·
324 Posts
CPA - What you describe is normal. Your Air/Fuel gauge will bounce around until you go into Wide Open Throttle. When the computer senses WOT, you should see it go rich. Your computer is in open loop at this point and your mixture will be more steady. If your using an A9L computer, your computer is looking for a certain Throttle Position voltage to trip the WOT. Just make sure when you go WOT that the A/F gauge pegs to the rich side. It is better to have a wide band, but yours is capable of alerting you to a dangerous condition (not full rich).

Good Luck,

Rich
 

·
Charter Member
Joined
·
183 Posts
Discussion Starter · #19 ·
I thought about it a bit and wondered whether my adjustable fuel regulator should be connected on the "pressure" side of the supercharger. I have a KB blower so it is easy to connect on either side of the manifold.
 

·
Moderator
Joined
·
8,272 Posts
Pressure side. The idea of the regulator is to maintain a constant pressure difference across the injector so the flow rate stays consistent. So if you are at 6 psi boost pressure in the intake the regulator should bump the fuel pressure by 6psi so that the pressure drop across the injector remains at 39psi (or whatever you have it set to).

BTW, an FMU modifies this pressure rise so that the injector actually flows more fuel due to the higher pressure. You can get different rate FMU's that add differring amounts of pressure per lb of boost.
 
1 - 20 of 22 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top