motor runs lean after 3000rpm

Predator · Oct 18, 2012

Ok I've tried just about everything i can think of and can't find any posts about it on here...
I have a 1993 GT with an E303 cam, stock heads..

Every time i shift hard and run the rpm up my fuel runs lean!!
But only after the car warms up it runs fine before..
I've replaced all these parts it did it before i replaced the part
Fuel filter
Stock fuel pressure regulator to BBK regulator 30psi at idle
Stock throttle body to BBK 75mm
Stock mass air meter to Pro-M 75mm
Checked the TPS sensor for idle and wot Voltage

The old setup ran 15/1 cruising and 12/1 wot

The new runs 14.5/1 cruising and 10/1 wot

But when it warms up it runs 17/1 or 18/1 and wot after 3000 rpm

Any idea?? I think is could me the fuel pump

ryanw · Oct 18, 2012

Pull the vac line off the fuel reg and make sure the pressure is around 39-42 psi. Then put the vac line back on. Also make sure your fuel pressure gauge is reading correct..

We had another guy on here that had a bbk or maybe it was a summit fuel pressure gage on his fuel rail. When the gauge read 50 psi, it turned out he was runnng 30 psi. So if this is the type of gauge you have, go to the parts store buy a test fuel pressure, just to make sure yours isnt off

Predator · Oct 18, 2012

I had the stock regulator on and it did the same thing..
The BBK goes from 30psi to 35 when cold and revved up..
When its warmed up it goes from 30 psi to 25

Predator · Oct 18, 2012

Ok i pulled the vacuum line off and it went to 40psi? Now what??

Grawg72 · Oct 19, 2012

I had a similar issue on my stock 86 GT, turned out to be a detached fuel pump sock, and debris in the tank.

Predator · Oct 19, 2012

Ok thanks!!!

R.M.B · Nov 1, 2012

sounds like a clear cut fuel volume issue. id make sure my fuel lines look good, and since they probably do id continue right to the pump.

Predator · Nov 20, 2012

Ok I Still need alittle help...
i changed the Fuel pump to a BBK 255 90psi and that fixed the issue of the mustang running out of fuel past 3000 RPM but now my Wide Band Air/Fuel reads extremely Rich and constently moves around.. ill be crusing at 2300rpm and highway speeds and it will go from 14:1, to 10:1 and went its idling it seems to be loading up on fuel...

Any idea's thought about buying the Bama chip to see if the MAF sensor is off?
no check engine light..

flattusmaximus78 · Nov 20, 2012

What maf and injectors?

If you have the stock 19lb injectors and maf put them in and set fuel pressure to 38psi vac off. Make sure your fuel pressure guage works to. I would adjust mine and then a minute later the guage would jump up a little.

If that doesn't work your car may need a a tune, some cars can run a cam untuned.

Predator · Nov 21, 2012

I believe they are the stock 19 injectors.. i have a Pro M 75mm MAF cal. for 19
And a BBK 70mm throttle body.. BBK regulator.. set at 34 with vacuum off

And E303 cam.. im just at a loss i dont want to buy a tuner if its just the O2 sensors..
But i dont want to replace them if all i need is the tuner lol im at a loss..

ryanw · Nov 21, 2012

Set it at 39-42 with the vac line off.

Predator · Nov 21, 2012

The car is dumping to much fuel into the motor now as it is.. bumping the fuel pressure up wont help the issue...

Dont get me wrong the car runs extremely well... never ran better but its fuel mixture is way off and alway going crazy

ryanw · Nov 21, 2012

Are you sure you fuel pressure gauge isnt reading way off ?

flattusmaximus78 · Nov 21, 2012

Throw a stock fpr on there if you have one as well. I have some brand new 02's I had in my car for like 50 miles before I sold it if you want em for a couple bucks.

Predator · Nov 21, 2012

FPR??? I believe the gauge is reading correctly but that's way i set it at 34 psi
Im running rich way to rich now.... since i replaced the fuel pump the motor doesn't starve for fuel it has way to much...

How much for the O2 sensors? What brand?

ryanw · Nov 22, 2012

Just go buy a mechanical fuel pressure test gauge. You need to be 100% sure that its readings are correct and that your gauge is not reading wrong. This test is cheaper then buying some mail order chip

Predator · Nov 22, 2012

Is the SCT 4-Bank Eliminator Chip w/ 3 Free Custom Tunes (87-93 5.0L) not worth the money?
Dont think the problem is the fuel pressure but ill check it anyways..
The fuel mixture ran good today headed to work for some stupid reason will see how
She runs in the morning on the way home..

ryanw · Nov 22, 2012

Im not sure some generic mail order tune is the right way of doing it. One size does not fit all. Seems like a lot of guess work to me. I understand you dont have any tuners near you so im not sure what to tell you.

You said you THINK you have 19 lb injectors. What color are they ? Orange tops ? And post picture of your set up. And please for the love of god, dont post little blurry pics. Full size please

Predator · Nov 22, 2012

Lol ok.. yea it sucks i dont know of any places around here that could dyno tune my car
And yes they are orange top.. i have to stock intakes one for a 87 gt and mine from my old motor witch is a 93
The injectors are the same color but mine off the 93 are shorter than the other ones..

Hope these aren't to blurry for you??
What pictures are you wanting??

Swapping part from my other GT

BBK 70mm throttle body

Pro M Racing 75mm MAF 19c

Injectors

FastStang91Lx · Nov 22, 2012

Set your fuel pressure with the vac line off the regulator. Set it to 39. You keep saying you set it to 34 with it on and running, or am I reading it wrong?

motor runs lean after 3000rpm

Predator

ryanw

Predator

Predator

Grawg72

Predator

R.M.B

Predator

flattusmaximus78

Predator

ryanw

Predator

ryanw

flattusmaximus78

Predator

ryanw

Predator

ryanw

Predator

FastStang91Lx

Top Contributors this Month

Recommended Communities