Contour Enthusiasts Group Archives Forums Modifications 3.0L Duratec Wiring Diagrams: 2.5L PCM vs 3L PCM

Our PCM is based on the amount of air coming into the engine (MAF) and not base on absolute manifold pressure. If you had a MAP and increased the engine size you would have a big problem since the MAP wouldn't change but the amount of air being sucked in would. The ECU simply wouldn't know there is more air coming in and run lean.

In the MAF situation the air coming in is directly related to the engine size (all else equal), increase the engine size and your increasing the amount of air coming in. The ECU takes this into account and adds more fuel accordingly. Now the SVT ECU is special since its ALLREADY programmed for a higher compression and has the timing for it, take a look at the dyno's and you will see that the SVTs are running rich.

Now take a ECU thats NOT designed for high compression and that doesn't run rich and you will have problems. Look at the NON-SVT guys that did 3L swap and they are running lean because they don't have the fuel flow. I wouldn't take a chance with the 3L ECU thats made for a hauling the kids to soccer practice.

I'm running a stock fuel and ECU system, I'm at the limits of the stock system with all the mods that I have done. But I'm not running lean nor do I ping (as long as a I keep a good 91 octane in it), I know Roger had a stock SVT ECU in his 3L and that swap was done by the first person that did a 3L, the owner of sho shop. He himself is also running a SVT ECU.

If you want to change the amount of fuel going in at WOT then you have to chance the fuel regulator. I picked up 5 ft lbs of torque when I barrowed one from Vadim for a dyno.

Okay, now I am confused. I knew you were putting out some good numbers but you were the only one. Several other folks who were running the stock SVT PCM were putting out about stock 3L numbers and some complained of pinging. Also, I thought that the SVT PCM went to a default fuel and timing map at WOT and that's what lead to lean and pinging conditions.

If I were running a 3L short block w/ SVT heads, and I wanted to use a stock PCM, I would most certainly use a 3L PCM. My main reason would be for timing. The SVT calibration is more agressive than the regular 3L, and the agressive timing of the SVT calibration and the higher compression, (and the fact that the combination of the 2.5L head chamber and the 3L bore is more prone to detonation anyway) makes avoiding detonation a real concern with that combo. While there is a stock knock sensor, do you really want to rely on it? on a constant basis? even if the knock sensor is working, it requires actual detonation to take place to trigger, so you are still dealing w/ detonation even if its working right.

I'm not saying using the SVT PCM will never work or anything, as at least David Z has shown that it can work, and work well. But you must remember that neither PCM is tuned for the combo being discussed here, so its a matter of choosing the lesser of 2 evils.

Despite all this discusison, neither way is ideal. Each combination should be tuned on its own (preferably on a dyno) for fuel and ignition timing.

To all those running an SVT PCM on a 3L engine w/ the 2.5L heads, I would really be interested to see a data log of your total timing vs. rpm on a dyno pull or a WOT accel run. I would almost be willing to bet that the majority will see the PCM pulling a lot of timing at high rpm especially due to the knock sensor. And fwiw, depending on a knock sensor like that is a bad idea, kinda like a safety net being used as a hammock.

Same here!

Come on now. Break out those laptops and run it on the highway for us...

Thanks rara, good to hear from you on this, as you (a calibration eng) know the 'baseline' engine dyno curves & data on the 3.0 conversion is a must have rather than run it and hope the knock senor will save it !

You know, all the arguments here hold water. However, I think that I have to give the most weight to David Z because he has the data to back it up. I will be more than happy to provide all the data I can from this project, including a baseline dyno with a list of current mods. I hope to be back together in under 2 weeks.

warmonger

No datalogs here, but I can tell you that my 3.0 with SVT heads and SVT PCM runs at ~.71 - .73 O2 volts during acceleration. About mid-13:1 A/F without correction (measure with low precision O2's - both through APEXi and OBD-II datalogger).

What's wrong with going with the 3L PCM and using a chip of some kind to increase performance???

Also, does anyone know what the redline is/was for the 98 Ford Taurus with 3L Duratec???

If you are going to be using a chip/piggy back device to alter the fuel delivery, then I guess the best ECU would be then one with the best timing for high compression. If you have some way of altering the timing, it wouldn't matter either way because at that point, you would have semi-full control of the A/F, so which ECU wouldn't matter.

1. Timing and A/F are two completely different animals

2. The SVT 2.5L PCM calibrations are written for a 2.5L 10:1 or 10.25:1 CR (depending on year, yadda yadda) high output engine (read as aggressive timing and A/F ratio, ie as far as you can safely go for that CR)

3. The Taurus 3L PCM calibrations are written for a 3.0L 10:1 CR normal output engine (read as less agressive timing and maybe A/F ratio)

Now, if you combine #2 w/ a 3L w/ a 11:1 or higher CR, you have a recipe for detonation. Sometimes it doesn't happen, sometimes the knock sensor makes the ill effects less apparent. But detonation is still going to be a major concern in this situation. Let's see, an 11+:1 CR, an overly small combustion chamber for the engine bore (ie leaves overhangs into the bore w/ much more likely hood of hot spots which can propogate detonation regardless of timing advance) AND a timing map that is aggresive even for a 10:1 CR engine is asking for serious trouble w/ regards to detonation issues. I'm glad to hear David Z hasn't had any problems (especially considering the crap that California is pushing as premium fuel ) though I am sort of surprised that he hasn't.
The reasons I would suggest the 3L PCM over the stock SVT PCM is a less agressive timing map, more suited to an even higher compression engine, and the algorithms in the 3L PCM are written to take into account the larger displacement of the 3L.

Personally, I would use whatever PCM I had, and have a chip custom-burned for my application, on a dyno if at all possible. This will aleviate any issues w/ either PCM, and provide the optimum safe tune (provided you have a good tuner) for your combination.

Another couple of points I want to bring up, because some may not be completely clear on them.

1. The Apexi can only alter the A/F ratio, and has no control over ignition timing.

2. Ignition timing, if set too agressive for a particular application WILL cause detonation.

3. An overly rich A/F can kinda almost compensate for a borderline detonation situation, hence the stock richness at WOT on the SVT PCM (ie, the timing is set about as far as it can go w/ out problems)

4. Aside from pouring a can full of metal shavings into your engine, detonation is THE fastest way to destroy an otherwise very nice motor. The forces that come with detonation are such that they can destroy even the strongest of engine components (I have seen plenty of holed pistons and broken con rods and even cracked heads and blocks to attest to this fact)