Q's for Tuners or Ford Techs

Miles said:

the tuner wasn't there, so I was talking to the shop owner. Not sure of the ratio, but it must definitely be running lean as the voltage is close to zero (less than 0.4v indicates lean condition vs greater than 0.6v which indicates rich).

Click to expand...

The question is, are the readings true?

01Steeda said:

SVTTech, can u explain the vacuum leak theory a bit for me. I understand what your saying just not sure why that would effect the 02's.

Click to expand...

jstreet0204 said:

Not sure when he will log back in but I'll answer for him. The o2 sensors only have a range of a/f ratios of 14:1 to 15:1 any thing that would cause a lean condition (vacuum leak) leaner than 15:1 would show voltage very close to 0 volts.

Click to expand...

CORRECT!!!! I can tell Jstreet knows his EEC

Now I am going to give a lenthy drawn out boring explaination nobody will read

well the 02 sensors provide feedback to the pcm on the amount of oxygen in the exhaust.. thsi allows to computer to compensate by adding or subtracting fuel to the base mixture.

Now a vaccum leak allows unmetered air to enter the intake without being metered by the MAF sensor. This is cause the PCM to add to little fuel to the mixture becuase the maf readings are lower than the actual amount of air entering the engine.

to compensate for this the PCM adds fuel to the mixture and when it gets to +25 percent it sets the p0171,174 codes.

Now about the 02 readings.

Air will find the point of least resistance to enter the motor, at high vacumm closed throttle this is thru a vacumm leak like a bad intake gasket or vac line and at open throttle this is thru the throttle body. This is why vacuum leaks effect idle and not WOT operation.

The stock narrow band sensors can only read mixtures near 14.7.1 IF it is WAY lean or WAY rich it can read 0 or near zero voltage. One way to tell if this is vacumm leak realated is to watch live data and rev the motor up, if you start to get a reading from the o2 sensors at higher RPM's then it's most likely a vacumm leak simply because vacumm is low at higher RPM/LOAD and the throttle body is open so air will find the point of least resistance to enter the motor.

You can not tell if there is a vacumm leak by running the engine with a guage on it and reading if the vacuum is normal. For one the amount of vacumm produced by a eninge depends a lot on the cam specs.

Plus the engine continuously produces vacumm while it's running and the throttle blade is closed, so a small to medium sized leak will not effect vacumm readings. If you had a leak SO large that it overcame the capacity of the engine to produce vacumm then it would not run.

So using a guage to find a small vacumm leak is just not going to be very effective.

I am starting to wonder how accurate the info they are giving you is. because any tuner should know this stuff

he does.. and thats why he said thats not my problem.... just wanted to connect the dots myself.

thanks

Miles said:

Not true - read every word, and very helpful. Thanks again svttech!

Click to expand...

Well I am glad sombody read it. So how are you making out with your problem. They find it yet?

Miles said:

*EDIT*

Ok, I've got the car back, and have starting messing around with the XCal2. I've logged RPM's, Front O2 sensor voltage, MAF AD COUNTS, Short term and Long term fuel trims.

Note: I never saw a change in the open_loop_flag - it remained at 0 the whole time.

At idle:
Long term fuel trim: remains at 1.0
Short term fuel trim: hovers around 0.875
MAF (AD COUNTS): stable around 220-230
O2 Voltage: 0.001v

As car revs to 3K:
Long term fuel trim: remains at approx 1.0
Short term fuel trim: increases to 0.953
MAF (AD COUNTS): steadily increases to 377
O2 Voltage: increases to 0.05v

As car drops back to idle:
Long term fuel trim: remains at approx 1.0
Short term fuel trim: increases to 0.984
MAF (AD COUNTS): steadily decreases back to 200's
O2 Voltage: steadily increases to 0.4v as revs drops

Looking at the short-term fuel trims, I am running lean - between 12.8 and 13.8 as the car is reving up to 3K. As the car comes back down to idle, the A/F ratio enters 14.x range and peaks at 14.4. I can see that as the A/F ration enters the 14.1+, the O2 sensor voltage starts to rise to.

So from all of this, I think I am looking at a faulty MAF.

Thoughts from the experts?

Click to expand...

it's too rich for the sensors to read properly. Your long term and short term pid values and maf values are much differnt than I am used to reading..

Ford scan tools give us a long term fuel trim as a -25/ + 25 reading and I usually read the MAF in MAF V so maf voltage.

What are you using to read the live data? maybe I can look up how to translate it into the values we use on our scan tools. Hopefully Jstreet will chime in he has more experiance with aftermaret tunning software than me.

well one thing I think you need to look at is your fuel rail presure sensor. Hook a fuel presure guage to the schrader valve and get a presure reading. Then in live data get the readings for (FRP) thats what the PCM is seeing for fuel presure. If it's higher than the actual rail presure you will have this problem.

Miles said:

*EDIT*

Ok, I've got the car back, and have starting messing around with the XCal2. I've logged RPM's, Front O2 sensor voltage, MAF AD COUNTS, Short term and Long term fuel trims.

Note: I never saw a change in the open_loop_flag - it remained at 0 the whole time.

At idle:
Long term fuel trim: remains at 1.0
Short term fuel trim: hovers around 0.875
MAF (AD COUNTS): stable around 220-230
O2 Voltage: 0.001v

As car revs to 3K:
Long term fuel trim: remains at approx 1.0
Short term fuel trim: increases to 0.953
MAF (AD COUNTS): steadily increases to 377
O2 Voltage: increases to 0.05v

As car drops back to idle:
Long term fuel trim: remains at approx 1.0
Short term fuel trim: increases to 0.984
MAF (AD COUNTS): steadily decreases back to 200's
O2 Voltage: steadily increases to 0.4v as revs drops

Looking at the short-term fuel trims, I am running lean - between 12.8 and 13.8 as the car is reving up to 3K. As the car comes back down to idle, the A/F ratio enters 14.x range and peaks at 14.4. I can see that as the A/F ration enters the 14.1+, the O2 sensor voltage starts to rise to.

So from all of this, I think I am looking at a faulty MAF.

Thoughts from the experts?

Click to expand...

What kind of headers do you have? Also, what was the ECT? You need to get some closed loop logs to be able to diagnose this. Once in closed loop, o2 voltage should swing back and forth. So let the car warm up and try it again. I have a theory on this, but I'll wait to see the cl logs.

I don't know much about the SCT datalogging, so I don't know which one is better to use. I'd also log coolant temp, and maf voltage instead of ad counts. Fuel pressure if you have it. On the headers, are they coated?

ok those readings you posted are normal..

sorry for the long delay in getting back to you.. somtimes I miss updates on threads and forget about them

if 1.0 is stoch meaning 0 added or subtracted to the base fuel map then those readings are fine.. your maf voltage is fine too... So i would think the problem has to be in the 02 sensors not getting hot enough..

well My problm was found this morning. Something about a strand of wire in the computer harness connecting a 5v reference.. or something lol. I am not a mechanic nor a tuner, but he has been telling me it is a wiring problem and he found one. We'll know more tomorrow when he gets on it and can see how the computer reacts... but I am hopefull

Miles said:

Sorry for the long delay - Steeda had loaded a band-aid tune onto my car that had left it in permanent open loop

My coolant temp is fine (matches my autometer gauge). The MAF Voltage is fine too, right around 1v.

All fuel injectors are turned on, but I can't seem to get fuel pressure on the datalogger.

So now, Bank2 is getting a nice normal voltage between 0.2x and 0.3x, but Bank1 is showing up as basically 0

My headers are not coated

THANKS ANYONE WHO CAN HELP!!?!

Click to expand...

This is what I would do.
First swap the front o2's around, and see if Bank2 goes to zero. If it does, it's a lazy o2, and just replace it. If it doesn't look for exhaust leaks. You should probably do a smoke test, but if you don't have a shop that can do it, you can use a smoke bomb in the tail pipes, and stuff rags in the end. If no exhaust leak, then try wrapping the collectors of the headers with header wrap. This would help if the o2's aren't getting hot enough at idle, but I suspect if this was the problem, you'd see it on both sides.

Miles said:

Hey, that's good news. Next up on my to-do list is check the voltages at the HEGO harness.

I suspect this isn't the issue for me though, as Ford did a complete electrical analysis and all seemed aok.

Click to expand...

well all looked right on my harness as well when they ohm'd the lines. it wasnt until he passed current accross it that he saw the voltage drop.