94 302 running lean
 

I have a 1994 Mustang GT that has a TFS Street intake 70mm TB, Pulleys, K&N FIPK,Bassani X-pipe and Flowmasters.

I just installed a Lunati cam, TFS twisted wedge heads, 1.6 roller rockers, 24lbs injectors, 190lph fuel pump and 75mm MAF calibrated to 24lbs. My car is running very lean. My mechanic says he thinks the O2 sensors aren't working properly. Could he be right or could I need a custom tuned chip? Someone else said that I might need a fuel pressure regulator. What could it be?

You don't need a fuel pressure regulator. You should have plenty of fuel with your injectors and fuel pump. How do you know you're running lean and how old are those o2 sensors? Considering the money and time you just spent, I would replace them if they are original.

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351W 89 Mustang GT Convertible

Hello jimberg,

Thanks for your reply. I brought my car to a different mechanic for a second opinion who said it was running lean. I guess he could hear it and smell it. In addition, when I'm driving it on the freeway, even at around 70mph, it feels like it's spuddering a little. The O2 sensors are original with about 94000 miles on them. I'm gonna have them replaced on Monday. Thanks for your help. T.Capitule

Get your cars CPU hooked up to a scantool before you buy anything. Find out what your injector pulse width is and find out you O2 sensor readings. This will tell you for sure whether or not you need new O2 sensors. It might me a faulty pump or incorrecly installed pump.

Which brand of pump did you buy? The Ford Racing pump is complete but the BBK is only partial. You have to use parts from your old pump leaving room for error. Sensors are expensive, find a scantool first and check your MAF readings as well. I damaged my sensor when installing the Vortec unit and it made me lean out. I had to buy a new one. Goodluck.

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95GT B303 cam, 1.7 rockers, 65mm TB, milled heads, 355's K&N, BBK Longtubes, Flowmaster cat back, pulleys, msd coil, 9mm wires, Tremec 3550, Pro5.0 shifter,10.5 Motorsport clutch, FMS aluminum driveshaft, weld in subframe connectors

O2 sensors with 94000 miles on them should be changed. Period. Your car will run its best when the feedback the computer gets is most accurate. They could have been damaged when you did the exhaust or when you did the heads. Who knows. Just consider it money well spent no matter what the outcome.

You should probably hook up a fuel pressure gauge to make sure that your FPR hasn't gone south on you. Make sure you have 37-40 psi and that it goes down if you apply vacuum to the vacuum port. You may also want to perform a leak down test.

You should never need a custom tuned chip to run normally (maybe to smooth out an idle with a radical cam or something). They come in handy when you want to run leaner or richer than stock, or with a different timing advance curve.

Did the mechanics get the codes from the computer or did they just put a dab of oil on their finger and taste for problems? http://www.mustangworks.com/msgboard/smile.gif

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351W 89 Mustang GT Convertible

The mechanics thought it was running lean just by hearing and smelling the engine. I replaced the O2 sensors on Friday and I can see a little difference but not much.

There's an article on the same problem I'm having in the newest MM and FF magazine called Idle Surge. The stone pony project car has basically the same mods as me except for different brands and it was having the same problem until they changed their 94-95 computer to a 93 computer. I'm thinking of doing that now but it's about $600.00 more than what I have now after spending all my money on the upgrades. I was going to try the custom chip next. I'm not sure how radical is considered radical for a cam but my specs are as follows:

lift at valve .500/.510
advertised duraton 284/292
duration at .050 tappet lift 218/226

I just read a post on another site where the guy put a 93 computer in a 94 with that harness from best products. Thats the first time i've ever heard of it. Is it really $600? That seems like a waste of money to me, when all you need is a custom chip. JMS knows exactly what to do with your computer and its half that price!! My 94 with all my bolt-ons ran like crap until I put the chip in. Also (if you get a chip) you will need an AFPR and a good gauge.

It's really $600.00 plus you still have to get a new ignition. I'll call JMS and see what they can do for me. AFPR, does that mean fuel pressure regulator???Check out MM and FFs the article about the Pro-M thing is in there. Thanks for the advice.

If you install an adjustable fuel regulator and psi gauge you can simulate having bigger injectors by increasing your pressure. stock pressure measured with the vacuum line disconnected is about 38-42 lbs. an adjustable reg will let you raise it to about 65lbs.