Speed Density Modders Please Help!

[arbailey]

I finally got my combo together and running. I know the computer needs time to relearn, but I don't want to damage anything in the process. I started off with the fuel pressure set to 44 psi (vacuum line off & plugged), and timing set at 13*. At around 3500 rpm under load / acceleration the car would "hit a wall" and hesitate. When backing off the throttle it would backfire. Thinking I had too much timing, I backed the timing down to 10*, and it seemed okay for a while but it did it again. Thinking it was loading up on fuel, I lowered the fuel pressure to 39 psi (vacuum line off & plugged) and it acted up again. Should I be adding fuel pressure? I don't think there are any vacuum leaks. It's acting like it has too much timing or it's running lean isn't it? All mods are listed below:

Fresh 306 currently has about 100 miles (Thanks Rick at RNH Performance)
FMS 65mm TB
FMS 67mm EGR Spacer
Explorer intake
Thumper E7's with GT-40 valves
Comp Cams XE264HR cam
Kirban AFPR
21lb injectors (from '03 GT)
Walbro 190 LPH Fuel Pump
FMS 1.6 Roller Rockers
FMS Shorty Headers
Summit Off Road H-Pipe
Magnaflow Cat Back
New Distributor, Cap, Rotor, Plugs
Newer (under 1,000 miles) "Firepower" Ignition Kit (Coil, Module, Wires)
Newer (under 1,000 miles) O2 sensors

 

[Daggar]

I can think of a couple of possibilities but you might start by either slowly reducing the FP or swapping back to a set of 19 lbers (if you have them lying around).

 

[arbailey]

You think it's getting too much fuel? I still have my 19 lb'ers. Any tricks on swapping them in without removing the intake? If not, is the upper to lower intake gasket reusable?

 

[lang williams]

i'd swap the injectors an let the computer "learn" for a while, then maybe try the 21's later.

 

[Daggar]

The upper to lower intake gasket is reusable if it's not damaged. Swapping in the 19s should help tell you a few things.

Let us know what the outcome is. I hesitate to just start leaning out the FPR without a wideband to back you up. If you have the injectors lying around, swapping them in and checking operation won't cost you anything but a couple of hours and might reduce your tail-chasing time.

 

[arbailey]

I thought with the increased air flow of the H/C/I the 21lb'ers would be a neat way to get more fuel without bumping up the fp, but maybe it wasn't a good idea.

 

[vristang]

I thought with the increased air flow of the H/C/I the 21lb'ers would be a neat way to get more fuel without bumping up the fp, but maybe it wasn't a good idea.

The airflow potential is there, but the computer doesn't know about it, not completely anyway...
Add into that the fact that the computer doesn't know the fuel injector size...
There are 2 sources of error in the tune.

Fuel pressure is kind of a sketchy way to tune sometimes, and it is difficult to compensate for the wrong injectors using fuel pressure.

If you put the 19's back in, things should improve
Let us know

jason

 

[v8only]

I agree, try the 29 pounders again. I'm running a similar combo, but a 97 explorer motor with a ported explorer intake, 19 # explorer injectors, ho mustang cam, aned 1.7 rr's, and it runs pretty damn well. while I think the speed density is killing my high end, it was still good for mid 14's in a heavy ass untuned vert with street tires that are years old, in other words, an upcoming speed density 13 second car.

what is your vacuum reading??

 

[v8only]

I agree, try the 19 pounders again. I'm running a similar combo, but a 97 explorer motor with a ported explorer intake, 19 # explorer injectors, ho mustang cam, aned 1.7 rr's, and it runs pretty damn well. while I think the speed density is killing my high end, it was still good for mid 14's in a heavy ass untuned vert with street tires that are years old, in other words, an upcoming speed density 13 second car.

what is your vacuum reading??

 

[arbailey]

I haven't taken a vacuum reading yet (I'd have to borrow a gauge). I know one thing though, my old combo of the original 140K shortblock with the stock cam, home ported E7's, and a Tmoss ported stock lower ran 13.49 @ 101.xx with 3.55 gears so I am expecting more out of what I have now (especially if I throw 3.73, 3.90, or 4.10's in the back!).

 

[Daggar]

You can achieve some outstanding results with even the stock Ford SD computer and tune if you become accustomed to tuning mechanically. In order to do that though, you're going to need to know what's going on with the car. You might start by getting the essential gauges going. Fuel pressure, Vacuum, and until you can afford a wide-band, get an AFR indicator of some sort to wire into your narrow bad 02 sensors.

Wiring a gauge to your narrow band sensors is little more than a light show as you're going down the road but it should at least show you whether you're running at stoich while at idle and low cruise. This will at least tell you whether you're in the ballpark. Beyond that, the gauge will be worthless. Some will tell you that it's able to show whether you're rich or lean when you get on it but you only get a 50/50 chance of the gauge pointer going into the correct direction for lean/rich because of the way the narrow band 02 sensor works. Consider it more of a "switch" than an actual sensor. You can be lean as hell but the gauge might indicate a rich condition because of how quickly the sensor changed signal voltage (and vice versa).

The moral of that last paragraph... Get a wide-band.

One other piece of equipment that I found critical is a vacuum line shut-off valve. You may not need this if your 19s clear up the above issue. I obtained a nice brass one from a pet supply store where they keep the fish tank stuff. What I found was that swapping heads, intake, cam, throttle body, etc... was pulling vac from the MAP sensor quicker than with the stock parts. As a result, the fuel was ramping up quicker than the motor (go figure). I was using 24# injectors at the time and everything ran pretty well but I was pretty rich during "tip-in" (beginning part of acceleration". To fix this, I slowly closed off the valve until tip-in was as close as I could possibly make it. All it does (basically) is increase the time it takes for the air pressure to equalize between MAP sensor and the manifold.

When you get a Vac gauge, I would suggest trying to run the vac source to the gauge as far away form the MAP sensor as you possibly can. I had an issue with this that drove me nuts for a few days while I tried tracking down the gremlin. The final fix was to install an orifice that I made out of a small piece of round metal that I drilled a .050 hole into. I installed this orifice in-line with the vac gauge and could not BELIEVE the difference that it made. My throttle was breaking up when the skinny pedal was to the floor and I would have sworn that it was an ignition problem until I finally nailed it down.

Moral of this paragraph... even minor modification to the Vacuum setup can have a large impact.

Finally... If you run into a situation where your AFR is good down low but lean up top... consider getting an electronic boost-a-pump (BAP) and wiring it in-line of your fuel pump with an RPM or TPS dependant window switch. At WOT, your computer reverts to a predetermined fuel table and stop taking inputs from pretty much all sensors except for the TPS. Your fuel regulator (of course) is being run by Vac but your EEC could care less at WOT. Ford Fox EEC's are pretty stupid... in this case it's a plus. You can use the BAP to increase fuel volume at WOT and get a bit of extra gas through the injectors at WOT. This works pretty well too. Since the computer doesn't care what AFR is WOT it doesn't even know that additional fuel is being delivered and won't even attempt to compensate for it. This works even better with your AFPR because you can slowly adjust your fuel pressure richer and richer (vac on) until the EEC is no longer able to maintain stoich at idle and back it off until it can. You get a fudge factor about 10% above or below stoich (idle and cruise). That's about as much as the EEC is able to compensate for.

Good luck and let us know how it goes!

 

[arbailey]

Thank you so much for all the info. I'm going to try and swap the 19's tonight. I'm also going to verify the TPS voltage throughout it's range, and double check ignition timing. I'll let you guys know how I make out. PS, as soon as I can I'm buying a wideband (maybe an LM-1?).

 

[Daggar]

The LM-1 is a very nice unit (albeit bulky). That's what I'm running. Let me know if you end up needing some permanent mounting ideas. My solution for my 86 turned out pretty nice (IMO).

 

[vristang]

To elaborate on the difference between 21's and 19's...


The 21's are 10.5% larger than the stock 19's.

The adaptive range is only +/- 12.5%

You now only have 2% of fuel adjustment available for other errors in the system.
That could be eaten up pretty easily by the intake and cam...

jason

 

[arbailey]

Thanks for all the info guys (and your offer Daggar - I'll let you know when I get one). The 19lb injectors are back in, I'll fire it up tomorrow and see how she does.

 

[tmoss]

Two things, one is to always use a dedicated line for the MAP (and F/P) to the intake as Daggar has pointed out. Second - reset your KAM by pulling the battery neg off for 20 minutes after installing the 19s so you fuel curve reverts back to stock paramaters rather than starting from where you are now.

 

[arbailey]

Well I threw the 19's in, set the timing to 13*, and the fuel pressure to 42 psi (off & plugged). Seemed alot better. When I got home I disconnected the battery for an hour and hooked it back up. Now I'm just gonna drive it and let it "learn". I'm still thinking of replacing the 19 year old MAP sensor too.

 

[Daggar]

Nice! Keep us updated.

 

[arbailey]

Hey Daggar, this is probably a dumb question but since my cam has 4* of advance ground into it and I advanced the base timing to 13*, have I essentially advanced my timing 17*?

 

[vristang]

Hey Daggar, this is probably a dumb question but since my cam has 4* of advance ground into it and I advanced the base timing to 13*, have I essentially advanced my timing 17*?

Cam timing is different from Ignition timing