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Discussion Starter · #1 ·
Alright people I have a couple of issues with this car. I recently picked up a 00 Gt. It was modified, terribly, by one of its previous owners. Long story short, the guy I bought it from knew nothing about it. If you need to know what mods it has I’ll list them but none I think contribute to these issues.

It has 30 lb injectors. It wasn’t tuned for them so I got an x4 with a canned tune to start me off. It runs better than before but not perfect. There are codes for the egr system, which was deleted, and P1152-c. I cant find much info on this code but it seems to be somewhat ambiguous. My long term fuel trims are -25 so I know it’s dumping fuel and the ecu is trying to compensate for the over rich condition. The datalog shows fuel pressure at 39-40 psi at all times. Maf and tps seem consistent. There have been a few instances where I’ll hold the gas steady at a certain rpm and it’ll surge a little. There is a surge at idle, it’ll bounce around from low 700s to 850 or so. I’ve checked the iat and ect and even tried wiggling every harness under the hood and nothing does anything. No vacuum leaks either. Also sometimes it will rev up to like 2k on its own then fall back to idle. I’ve also unplugged the maf and it still reads .39 lbs/hr for whatever reason. It doesn’t change anything except I noticed the short term fuel trims almost matching the long terms except they are positive so the net fuel trims are around 0. It still doesn’t idle well though. What else can I check before I pull out all my hair?


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you have to address the long terms at -25

that is NOT correct running conditions

you better verify the 02s are NOT lying

if you cause a air leak, open up something after maf, you should be able to drive the 02s lean
simple test
 

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Discussion Starter · #3 ·
I’ll do that when it stops raining. Also I have longtubes and I know the tune needs to be adjusted but that wouldn’t have any effect right?


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if they never heat up, yes that is an issue
 

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Discussion Starter · #5 ·
Ok I’ll see what I can do. What about all the other issues like surging and all that? Could they be caused by the o2 sensors too?


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hard to say, without the data stream in front of me

regardless, i wouldn’t concern yourself with that

diagnosis is ONE step at a time

you must first verify 02 signal, if pcm cannot control fueling, anything else is moot
 

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Discussion Starter · #7 ·
I reinstalled the tune (I needed to change tire revs per mile anyway) and it seems to run better above 1k rpms. But I noticed a few things; the fuel trims aren’t as bad, bank 1 is around -8 and bank 2 is -14, Theres a noticable bog when taking off like Im new at driving a stick and it’s now revving high when coming to a stop. It’s not my first new edge so I know that’s normal but it wasn’t like that before. Also the iac percentage will creep up randomly, I think my iac is going bad.

Also, I pulled the vacuum line off the frps to create a vacuum leak and it had no effect on my fuel trims. Who is a good tuner for these cars? I’ll try to talk to a local tuner but I don’t know if anyone tunes mustangs anymore, let alone a 2v.


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what fuel trims?

long OR short?

why are you talking tune?

if your 02s are lying, why would a tuner even touch your car?

you either diagnose, or take it to a diagnostic shop and pay for it

your choice........

do you know what short and long term fuel trims mean?
 

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Discussion Starter · #9 ·
what fuel trims?

long OR short?

why are you talking tune?

if your 02s are lying, why would a tuner even touch your car?

you either diagnose, or take it to a diagnostic shop and pay for it

your choice........

do you know what short and long term fuel trims mean?
I was talking about the long term fuel trims. Short term fuel trims were around 0.

I’m talking about a tuner because it has 30# injectors and longtubes, both require at least a base tune to compensate. Once I have at least a tune for both then I can diagnose further.

And yes I’m quite aware of what long and short term fuel trims are.


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I was talking about the long term fuel trims. Short term fuel trims were around 0.

I’m talking about a tuner because it has 30# injectors and longtubes, both require at least a base tune to compensate. Once I have at least a tune for both then I can diagnose further.

And yes I’m quite aware of what long and short term fuel trims are.


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that is good.

you introduced unmetered air into the system, and you got NO response from 02s.

once you verify the tune is correct

what will you do next?
 

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Discussion Starter · #11 ·
that is good.

you introduced unmetered air into the system, and you got NO response from 02s.

once you verify the tune is correct

what will you do next?
That’s what I need help with as I don’t want to throw parts at it. I can replace the o2 sensors to see if I get a response out of those.

The only way I know how to verify the tune is correct is by datalogging. Any help there?

When looking at other threads with the same code it seems that it’s because of the long tubes and it throws everything else off. Does that sound about right?


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I am going to ask you what you think you should do given the info i give you


02 sensors create voltage..........

What should we measure, to see if the 02s are lying?

STOP with the tune crap!!

we will get to that in time
 

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Discussion Starter · #13 ·
I guess back probe the o2 sensors to see what the actual voltage is?


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at the sensor and at the PCM

excellent, i await your results
 

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Discussion Starter · #15 ·
I couldn’t get to the sensors under the car because it’s too low for my ramps and I don’t have a safe place to set up jackstands. Though I did try to create another vacuum leak today by unhooking both the frps vacuum hose and the vacuum hose going from the drivers side valve cover to the intake. Not only did it still not have any effect on short term fuel trims but there was no vacuum coming from the intake tube side. It seems someone plugged that port. I swear if I saw the person who did all this to the car I’d kick him in the nuts as hard as I could…

Jumping the gun a little, the other day I ordered another maf for dirt cheap to try out. It’s not here yet but in the next few days. It’s at least one of my problems I think. Unplugging it while running doesn’t have much of any effect and the short term fuel trims add fuel so it’s net zero in terms of fuel. The throttle response sucks and there is a hanging rpm issue between shifts, otherwise I’d run it like that.

I have new front sensors coming in too. Now here’s the kicker, I’ve felt around under the car as best I can and don’t see or feel where rear o2 sensors are so that leads me to believe there are none. It’s not throwing codes for them though and they aren’t turned off in the tune so I’m a little confused.


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backprobe at the ecm if you cannot reach at the sensor

you need to look at 02 voltage

0volt is lean
1 volt is rich

02s are driven by the ecm, rich and lean, that is how they control fuel

if you are fixed rich, the ecm will pull fuel

that is why we need 02 voltage
 

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Discussion Starter · #17 ·
I get that but what I meant in my last post is that it seems the maf is reporting the wrong airflow causing the o2’s to compensate for the incorrect amount of air. I will pull the ecu down from the bracket tomorrow when I have more time.


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what is the maf voltage at idle?
 

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Discussion Starter · #19 ·
So the o2 sensor at idle was about 1v at the ecu. I couldn’t get to the maf wires without wire piercing probes. So instead, I pulled the harness off the tps and noticed the fuel trims were better and it idled lower, smoother and the tps % was almost solid unlike before. It seems there are a few gremlins at work here. I’m also going through all the wires and I’m swapping the accel coils in it to old ones that were on my old 00 Gt. Hopefully they are still ok.


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use stock coils

why are you disconnecting the tps?

maf has to be probed while connected, or look at processed data through scan tool

02 sensor fixed at 1volt, this is where to concentrate

add air to system, and watch voltage, if you cannot drive the sensor to 0volts, there is a circuit problem
 
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