I have a 87t2 which I purchased about 4 months ago the car ran fine exept that when cruising at 4th or 5th gear 2500-2800rpm my fuel mixture would lean out for 1 second and go back to stoch several times. It would do this only when cruising. I did a full tune up change plugs, wires etc. but the problem didnt go away. changed boost sensor(Note: the boost sensors id was not ledgible) put a n327 in. The car kept doing the same thing but worse now and at the same time it started the fuel cut(Note: the fuel cut happend sporadic and sometimes at less than 4 psi). I noticed the stock boost gauge would not work when the cars leaning out and when it did work I got fuel cut at about 2-4 psi. I decided to change the boost sensor again, this time I put in a n350 and the car keeps leaning out while cruising when the stock boost gauge doesn't work. Now when the stock boost gauge works the car runs fine but sometimes it will give me fuel cut. I think its a bad fcd or a broken wire because the car runs perfect when the stock boost guage is reading and will give me fuel cut when it feels like it. Need input from you guys, I have been dealing with this problem for about two months and I'm running out of ideas.

Note: The car is running at 10psi, stock ports, rb exaust, walbro fp HKS blow off.

I will realy appreciate any input Thanks

 

The broken wire theory sounds valid. Maybe use the factory diagrams, and run your own wires in parallel with the Mazda ones between the sensor and the ECU. The MAP should have +5, gnd and signal.

Justin

 

Pull off the FCD and see what happens.

 

In someone's spare time, explain to me how you can use a S5 boost sensor on a S4 car?

The 87 has four wires in the plug. A 12vdc B/W, a Br/W ref voltage wire, a Br/B wire for ground and a Br/R wire for the signal to the gauge and the ECU pin 2B.

Now your using a S5 sensor that has but three wires, none of which is 12vdc, and your connecting it to a S4 FCD. Now, how does that work out????????? Everyone is going along with the use of the N350 so there must be an explanation.

Also they can stop making a seperate FCD for S4 and S5 if that is the case. Signed: Disillusioned In Tejas.

 

Technically there's no reason why a S5 MAP sensor can't be used on an S4. All the ECU needs to see is a 0-5V signal that varies with manifold pressure. Most MAP sensors (including the S5's) are 3-wire (5V in, 0-5V signal out and ground) but for whatever reason the S4 MAP sensor also needs 12V to work properly. This was discussed ages ago and IIRC it was to power some signal conditioning circuitry (but don't quote me). The S5's MAP sensor obviously doesn't need this.

The S4 FCD will work because it's getting the 12V it needs from the S4 harness.

 

thanks for all the inputguys. I will check your sugestions out and update you on my progress

 

wait, my stock boost gauge died a few days ago also. does that mean i am running lean? but so did my engine tmp. gauge.! guage cluster?

 

It was a faulty fcd thanks for all your help