Contour Enthusiasts Group Archives Forums Modifications 3.0L Duratec ?Help tracking down the stuttering problem....Long...

Ed, I just want to remind you that when I pulled my backplate off I did not have the high rpm 'leaning out' problem. That only happened when I pulled the whole centerpost out. The Centerpost in does something to the amount of air flowing through the tube even though the backing plate is off. You should be ok if you leave the centerpost in. Then get the Greddy or APEX SAFC and tune the B*itch in so that you can see some real torque increases.

warmonger

BlackPantherSVT & warmonger...

Thanks for the info. I am always hesitant to "alter" stuff, especially expensive stuff. I have studied the backing plate carefully and believe I could reproduce one if necessary, including the little gap at the top (so many details). I believe I might try (when I do) a different avenue...I think a hole at the end of the venturi tube (in the backing plate) and possibly a short extension tube fitted and butting the venturi would produce the same effect and would be easier to reverse if necessary. While I had it out the last time I removed some heavy casting flashing in the airstream, I think that was good for 5-10 HP for sure...I thought I actually felt a difference! O/T...I have sent money for a DMD to Terry. I think the jury has returned a favorable verdict for the DMD! I hope that will extend the life of "my little darling" as my wife is fond of calling her.
I wish there were some way of attaching some vib pickups to the side of the block to quantify any improvement. I'm sure, however, if, as reported, you can actually hear and feel a reduction in NHV in the seat of your pants...it must be better.
Anyone thought of a way to move the knock sensor or attach another one to the bottom end and re/wire it to give us vib data? It is nothing more than a vib p/u anyway. Wish I were smarter instead of just wiser (read older)

Thanks again...Ed

Don't worry, I was already calculating 'older' from the cautious attitude! I must be somewhere toward the older side because I've been cautious about the choice of a fuel management computer.
I'm crossing over right now, going from Youths land to Mens land...that's 31 yrs. I've been so wild its taken me a long time to get responsible.

As far a the knock sensor, it could be done, but all the electronics would have to be designed separately and then you would need to figure out how you wanted it to indicate vibrations. I think it only picks up vibrations that are characteristic of knock, tuned in a way. So all you would get is a knock indicator light I'm guessing.

warmonger

I took the plunge and ordered a Pro-M Bullit 75mm MAF from SP motorsports today (emailed them). Along with it being "tuned" for my exact application, I asked them to make it run just a little rich below 3300 rpm. I'll see what they say and go through with the actuall order when SP calls me. Hopefully this will be "one" of the possible ways to cure these lean-misfires below IRMC opening when warm, one that will work 100%. Anyone with thoughts on the Pro-M? TtEl.

My only thought on buying the pro-m is that IF they can't tune it in for you, then you will end up buying an optimizer, an APEX SAFC, or a GReddy in the long run. If it works, no sweat, but these other options do offer custom tuning which you may end up doing later on anyway.

warmonger

No luck here with the S-AFC. Although it is a must have device I love it I have run the car rich and lean and the stuttering is still there. I am checking out my pressure in my fuel line to see if my pump is bad. Hopefully thats it.

BlackCoog,

Let me know on what you find out on that one. I know I am not the only one who would be interested in that bit O knowledge. TtYl.

I tested it but nothing huge to tell about. The pressure on my cougar was at 49psi and when up as I began to rev it. When I excessively reved it the pressure started to go down. I really don't know what that means. Keep watching the post I will let you know when I rig this pressure tester up so I can see it in the car. I need to get a longer hose and some other misc stuff. Hopefully it will work so I can see the guage when the stuttering actually happens.

I look forward to something, but wouldn't you think that you would have issues at High RPM, like pinging if your fuel pressure was off?

I check mine a lot, but my stuttering issue is definitely got a mind of its own. I decided to go back and try the 19# injectors with the GReddy, and the problem persists either way. The only problem with the 19# injectors is that my modified stock MAF doesn't work at all. The only headway I have made so far was with the 24# injectors and the modified stock MAF. With the stock unmodified MAF and 24# injectors the problem was the same, just fuel trimmed like a biitch. With the cut out center post I got the best driveability. The stuttering was mostly gone. I had to increase the signal with the Greddy like 15% above 3K rpm though.

Here is an interesting thought: The only time the car didn't stutter is when the engine was cold and the car was first started. This meant that the air was at its most dense. If the engine was cold it wouldn't warm the air much as it goes through the air intake. IF??? the AF ratio were actually too rich, then at cold startup it would have the most dense air and therefore the fuel would have enough oxygen to combust correctly. NOw lets say that 5 minutes later the engine is warm and it is warming up the incoming air. The air gets less dense and would theoretically require less fuel to keep a good AF ratio. If the fuel being dumped in hasn't been reduced, then perhaps the mixture is too rich?
When I cut the centerpost out of my MAF, I got a lower voltage reading throughout the RPM range. THis would signify less airflow and would require less fuel. Evidently it is reading a lot less airflow because I have to richen it up so much with the GReddy above 3000 rpm.
Maybe you could also look into this possibility when you are playing with your APEXi. I know you wrote that you tried leaning it out, but you must make sure that the car is getting an unmodified signal at idle and light cruise loads. You must also reset the pcm everytime you do any major adjustments like leaning out the AF.

Anyway, I will be going back to the 24# injectors in the morning with the modified MAF and my new airflow map in the GReddy. We'll see what that does.

warmonger

Still out of my league and I'm sure you have already thought of it...but, what would happen if you installed a fixed ohm resistor in place of the water temp sensor to simulate a cold engine all the time? Why would this be a bad thing? Would it run rich so much that the cats would foul eventually? Mine seems to run really good when cold too.

EDIT...And what about this thread??
IAT Mod

...Ed