High RPM After reaching lambda Wideband 2k Idle

[OneSick99GT]

Hi Guys,
I've been working with @a91what on tuning my mustang. We dialed in my maf tables at a little above 1 volt for the very first column at lambda according to my wideband. At lambda it idles steady 2000 rpm with no deviation @ 14.6 to 14.7 lambda. No searching idle just dead on steady. I'm a bit confused as to why this may be. Things I have yet to rule out but doing so tomorrow.

I'm replacing my fuel filter with a brand new one.
I'm checking my fuel pressure before and after fuel filter replacement to verify any changes.
I bought a stethoscope to listen in on the injectors puslewidths and check my spark plugs for firing.

PS. My throttle screw is as low as it goes for air. My duty cycle for my IAC is around 15%. It starts out around 50% and lowers as the vehicle warms up. I'm also in open loop and have closed loop disabled.

I have 30lb injectors
255 walbro fuel pump
stage 3 comp cams
78 plenum and throttle body
Cold Air intake
Trickflow twisted heads 44cc
Aluminum Intake Manifold
90 Maf

I'm thinking the fuel pressure is off. Higher fuel pressure would seem to bring my maf tables down which results in my idle also coming down as well. What do you guys think?

 

[wmburns]

So what is the fuel pressure? Is the fuel rail pressure sensor (FRPS) intake vacuum reference line connected and leak free?

But remember it's not fuel that primarily controls RPM's. It's air. For the most part, fuel follows air.

I'm not sure it's reasonable to expect the idle to be low while closed loop has been disabled. But If the IAC duty percent drops from 50% to 15% would indicate:

• There's too much air entering the intake even after the IAC % is low. IE, a vacuum leak after the throttle body.
• The PCM is not really controlling the IAC. IE, the PCM is lowering the IAC duty % in an attempt to lower the idle but the IAC isn't actually doing anything.

Or use the ForScan ODB2 scanner to "command" a different IAC duty percent while monitoring the test light. For example if you were to command a 100 percent duty cycle the test light should go full bright and the idle should increase.

Bottom line we need to positively confirm that the PCM is able to control the IAC and that the IAC is responding. A test light with the pig tail on battery positive with the probe on the IAC signal return line should show the test light relative "brightness" changing as the IAC duty percent changes.

At 50% the test light should be half bright. As the IAC duty percent decreases, the brightness of the test light should also decrease.

If the brightness of the test light doesn't change with the IAC duty percentage then it likely means that the PCM isn't really in control of the IAC.

IF the PCM is in control of the IAC and the IAC duty percent is low (15 percent), then there HAS to be un-metered air entering from somewhere.

 

[OneSick99GT]

@wmburns I picked up an OEM pressure guage test kit from autozone a couple days ago to test my fuel pressure. However I was unable to use the OEM kit because my fuel rails are aftermarket and don't have the Schrader valve. Still learning which is good but I won't be able to test my fuel pressure until I receive my 9/16 to 1/8 female adapter. I actually have these at work so I'll be picking one up along with a fuel pressure gauge that will stay on my driver side fuel rail to monitor pressure.

The IAC- I have ran forscan and checked that the IAC does in fact control the idle when in closed loop. My duty percentage is low since I have my throttle screw mostly turned in atm. When I didn't it was around 45 to 50%. Higher when first starting. So IAC is working correctly.

I tried replacing my fuel filter today. I bought the disconnect tool but the 4 sizes were not for my mustang even though it said it fits most fords. I returned and got the one I needed. Tuesday I'll be replacing the stock fuel filter that has 98 k miles on it. I'm not sure this would cause the issue but possible.

What should my fuel pressure be with the changes that I've made? I have the ford manual and can reference that but should it be higher since I have larger fuel I jectors and performance parts or should it read the same still even after the mods I've made.

If the pressure is in fact good then I'm assuming the venom injectors, which has no tables for high/low or impedence available online will be replaced with ford performance 47 lb injectors.

Both my dad and I did the carburetor cleaner trick by spraying around the intake and listening for it to change the idle and found no leaks.

I haven't used the stethoscope yet, but plan to after verifying fuel pressure before and after replacing the fuel filter.

I did identify something that was amiss on my intake. I had a ground wire running to a bolt on my aluminum intake. Obviously this wire wasn't grounded. I re-ran the wire to my firewall clutch cable to give it a ground. I have no idea what this went to. Anyone have an idea? See picture below. The wire runs into the harness that also has wires going to each injector. I can't tell which way it goes though.

 

[wmburns]

What should my fuel pressure be with the changes that I've made? I have the ford manual and can reference that but should it be higher since I have larger fuel I jectors and performance parts or should it read the same still even after the mods I've made.

The fuel pressure should be the SAME regardless the size of the fuel injectors used. The intake vacuum referenced fuel pressure at the PCM should be 40 PSI. At the minimum cross against the fuel pressure (FRPS) as reported by the PCM.

I did identify something that was amiss on my intake. I had a ground wire running to a bolt on my aluminum intake. Obviously this wire wasn't grounded. I re-ran the wire to my firewall clutch cable to give it a ground. I have no idea what this went to. Anyone have an idea? See picture below. The wire runs into the harness that also has wires going to each injector. I can't tell which way it goes though.

Note, the fuel rail is supposed to be grounded to reduce the chances of static electricity building up in the fuel rail from the internal flow of fuel. That's why there's that tiny ground wire attached to the fuel rail.

 

[OneSick99GT]

I'm not sure what the wire goes too. It comes from the wiring harness that also supplys the injectors. So your saying that black ground wire coming out of that harness is for the injectors?

I'll report back my psi. Hopefully all is good.