fuel trim???

**94svtcobra** · 07-29-2008, 03:12 PM

the garage I had my car into said my fuel trim is jumping from up to around 1500 as soon as the car starts to accelerate then it corrects itself and drops back down, any ideas on how to fix this????

**Killercanary** · 07-29-2008, 05:32 PM

What do you mean by fuel trim?

**94svtcobra** · 07-29-2008, 05:48 PM

i'll have more info for ya in a little, I'm goin to pick it up. they just said that it was dumping too much fuel as soon as the car starts to accelerate the the computer adjusts it back down to a normal level of fuel

**Killercanary** · 07-29-2008, 11:40 PM

Mark, our cars are ODB-I and therefore difficult to log.

**u1arunit** · 07-30-2008, 12:34 AM

Originally Posted by Killercanary

Mark, our cars are ODB-I and therefore difficult to log.

Augh.. That's right. I forgot, 96+ is OBDII. I removed my post since it does not apply.

**94svtcobra** · 07-30-2008, 12:27 PM

I spoke with a few different shops today, one told me that they could try, but didnt promise nething and the other told me I need a new mass air flow sensor??

**Killercanary** · 07-30-2008, 12:39 PM

I'm sorry but I still don't understand the problem and how they determined that it was one. I know these cars fairly well and can probably help you with it, but I need a lot more information. What shop did you have it at? Does it have a chip tuned on a dyno? What is the reason they are telling you that it needs a new MAF? Why was it in the shop to begin with, are you experiencing a problem with it?

**94svtcobra** · 07-30-2008, 01:25 PM

I had it into the shop to have the header bolts tightened up, and to have them check this issue with the engine. the first shop told me to to have the computer retuned, then I called a few dyno shops the one told me that that they could try but werent promising anything, then lasota racing told me that my c and L mass air flow meter is junk and was probably the cause of it, I dont believe it has a chip or anything, the timing is advanced, but thats it. The issue is the computer starts the car with an "open" loop system until the sensors warm up and start reading correctly, then it's supposed to swich over to a closed loop system, but when the car begins to accelerate for some reason it swiches back over to a open loop system which is causing the car to dump more gas into the engine then needed and it chokes a bit. then it realizes it has to much fuel and switches back over to a closed loop system and accelerates fine

**Killercanary** · 07-30-2008, 02:23 PM

My question is how do they/you know that it is switching between closed and open loop? Your in good hands with Don LaSota, so I'd go with whatever he says. The C&L's are complete junk on the 94-95's especially due to the way our EEC's work. Are you sure that the pulse width doesn't just need adjusted in the high load/low RPM areas of the fuel map? That is what it sounds like to me. What does the car do? Our cars also pull a lot of timing in between shifts and it will feel sluggish when you first get on the gas until the EEC feeds in timing a second or so after you get back on the throttle. This can feel like the car is laying over and then taking off in some instances. This can be changed in the EEC with a chip in the timing retard and tip-in settings. I'm a firm believer that this is where a lot of people saw gains by switching to the older fox computers as they didn't pull anywhere near as much timing as the 94-95's do. Suppoosedly ford did this to cut back on the amount of transmission warrenty repairs they had to do as this produces less of a shock on the driveline. This was one of the first and most noticable things I had changed in my car when I first started to self tune it. Its been a long time but I feel like the stock EEC pulled something like 15-20*'s of timing between shifts which is a TON!

**Killercanary** · 07-30-2008, 02:31 PM

Also, the car should ALWAYS be in open loop under WOT. In a nut shell what this means is that the EEC ignores the O2 sensors and provides fuel and timing straight from the tables without "correcting" them based on the O2 and a few other sensors. The car usually starts in open loop until the sensors come up to temp and then it switches to closed loop and uses them as feedback to make subtle changes to the tune to keep the timing and fuel commands in check. In open loop, it shouldn't matter if the O2's are reading high or low as the EEC doesn't look at them in while in this condition. This is where dyno tuning comes into play. The basics of a tune are to tune the car under open loop conditions so that when the EEC isn't using sensors for feedback that its still providing the correct timing and fuel for optimum power production. Bumping the timing and fuel pressure can only do so much. Talk with Don more about this and go with his recommendations. Hopefully this will help give you a little better understanding of what is going on and why you may/may not need to change things.

Also, beware that the MAF for your car is the same as the Gt and that the cobra EEC has its internal setting changed to reflect the 24lb injectors that you came with stock. If you have a C&L now with a 24lb tube that could also be your problem as it should have the 19lb injector tube in it. I'm 99% sure I'm right on this, but double check this before you swap the tube.
Your MAF and the one from the GT send the same voltage per amount of air into the EEC, its inside the EEC that the fuel value for a specific MAF voltage differs. On a GT if you wanted to run 24lb injectors and got a "calibrated" MAF the MAF voltage for a specific amount of air would change before the EEC would see it. The EEC in turns thinks that a smaller amount of air is entering the engine and therefore commands a smaller pulse width (this is the amount of time that injector is open and its in milliseconds). Since the injector is larger though, this smaller pulse width will provide more fuel. This is not the correct way to tune for new injectors in the 94-95's though as it messes with the load values which also help the EEC determine how much timing and fuel is needed for the engine. I hope I haven't confused you, but the more you understand about this MAF and EEC in general the better off you'll be and it may save you from wasting money on parts you may not need.