FC idle mixture screw.. missing?
06-30-23, 05:49 PM
#1
Junior Member
Thread Starter
FC idle mixture screw.. missing?
Hey everyone, I’ve recently got my big street port fc on the road. Unfortunately the car is running dog rich at idle. On my AFR it’s ready 10:1 at idle. I went to adjust the mixture screw and it’s not even there!! The black circle connector is just hanging down by the map sensor. Is this my issue?? Or could this be the result of someone’s wiring “mod”. In my head it doesn’t even make sense the car is running without this, unless the ecu just defaults to crazy rich. Thanks everyone!!
06-30-23, 08:06 PM
#2
Rotary Freak
The ECU has a bunch of "failsafe" modes for failed or missing sensors. For example, unplugging the coolant temp sensor defaults to an assumed 176 degrees fahrenheit. I'm guessing that the ECU probably defaults to some middle-of-the-road value for idle mixture when the variable resistor is missing.
10:1 is really really rich though. I don't think the idle screw gets it that rich even when all the way at the extreme. I'd definitely pick up a variable resistor and try that first, but there might be something else up there.
EDIT: Looking at the Training Manual, I don't see any failsafe modes listed for the variable resistor. So maybe it is the cause of the issue after all
10:1 is really really rich though. I don't think the idle screw gets it that rich even when all the way at the extreme. I'd definitely pick up a variable resistor and try that first, but there might be something else up there.
EDIT: Looking at the Training Manual, I don't see any failsafe modes listed for the variable resistor. So maybe it is the cause of the issue after all
Last edited by WondrousBread; 06-30-23 at 08:16 PM.
06-30-23, 08:34 PM
#3
Junior Member
Thread Starter
It does have an AEM high output pump and I’ve wired batt voltage directly to it, so I’d expect rich afr at idle and low load, but I’ll start with a resistor and see if I can’t lean it out any.
on another note, I had a question about setting the tps. Since my car is heavily modded I’d like it to idle around 1k to 1200 RPM, do I set the tps at 750rpm and then adjust idle? Or do I set the idle to 1000 and then set the tps??? Thanks
on another note, I had a question about setting the tps. Since my car is heavily modded I’d like it to idle around 1k to 1200 RPM, do I set the tps at 750rpm and then adjust idle? Or do I set the idle to 1000 and then set the tps??? Thanks
06-30-23, 08:50 PM
#4
Rotary Freak
It does have an AEM high output pump and I’ve wired batt voltage directly to it, so I’d expect rich afr at idle and low load, but I’ll start with a resistor and see if I can’t lean it out any.
on another note, I had a question about setting the tps. Since my car is heavily modded I’d like it to idle around 1k to 1200 RPM, do I set the tps at 750rpm and then adjust idle? Or do I set the idle to 1000 and then set the tps??? Thanks
on another note, I had a question about setting the tps. Since my car is heavily modded I’d like it to idle around 1k to 1200 RPM, do I set the tps at 750rpm and then adjust idle? Or do I set the idle to 1000 and then set the tps??? Thanks
If your car is turbocharged, it might be a good idea to look into something for engine management. Even a simple SAFC + wideband will let you pull all that extra fuel out of the idle area and add it in as necessary at higher RPM. A standalone makes everything much more complicated and expensive, but also lets you tweak everything to your liking.
I would set the TPS first (along with ignition timing if required) with idle at 750rpm, then adjust it up. IIRC the TPS is adjusted with the car off anyways, so it won't make a difference, but the timing starts to advance above 1000rpm so you definitely need to check / set that at 750rpm.
06-30-23, 09:10 PM
#5
Junior Member
Thread Starter
Is your car turbocharged? If not, you won't outflow the stock NA pump, so there is really no advantage to a larger pump. It won't hurt anything except for the idle AFRs (as you've observed) and possible make the acceleration just off idle a bit lumpy, but there's really no gain to be had.
If your car is turbocharged, it might be a good idea to look into something for engine management. Even a simple SAFC + wideband will let you pull all that extra fuel out of the idle area and add it in as necessary at higher RPM. A standalone makes everything much more complicated and expensive, but also lets you tweak everything to your liking.
I would set the TPS first (along with ignition timing if required) with idle at 750rpm, then adjust it up. IIRC the TPS is adjusted with the car off anyways, so it won't make a difference, but the timing starts to advance above 1000rpm so you definitely need to check / set that at 750rpm.
If your car is turbocharged, it might be a good idea to look into something for engine management. Even a simple SAFC + wideband will let you pull all that extra fuel out of the idle area and add it in as necessary at higher RPM. A standalone makes everything much more complicated and expensive, but also lets you tweak everything to your liking.
I would set the TPS first (along with ignition timing if required) with idle at 750rpm, then adjust it up. IIRC the TPS is adjusted with the car off anyways, so it won't make a difference, but the timing starts to advance above 1000rpm so you definitely need to check / set that at 750rpm.
06-30-23, 09:16 PM
#6
Rotary Freak
Yes my car is turbo charged. To be honest this car has been a bit of a basket case, it’s a RHD that came to Canada with existing mods and then changed hands a bunch of times. As of right now it’s a massive street port running 10 psi with a FCD and whatever ecu mod was done in Japan. I ask about the tps because the BAC has been removed so to adjust the idle I have to open the throttle with the set screw. A Haltech is 100% on the list but you’re probably right, a fuel controller will help me a lot until I can cough up the 3k for a standalone.
In all honesty, it will probably never work very smoothly. The stock ECU has no tuning ability. You're already flowing air differently due to the street port. Add in a chipped ECU, a fuel pump that is overwhelming the stock reg, no BAC, and an idle set about 500rpm higher than normal. I'm going to assume you probably don't have the stock air-pump and ACV either, so the air-injection system is also missing.
I'd say the stock ECU is going to be confused by all of that, but the stock ECU isn't even smart enough to notice something is amiss.
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j9fd3s (07-01-23)
06-30-23, 09:39 PM
#7
Junior Member
Thread Starter
I forgot about that. Turbo cars have the bypass screw on the BAC, not on the throttle body. NA cars have the bypass screw in a different place. I would definitely adjust the idle speed where you want it first, THEN adjust TPS in your case.
In all honesty, it will probably never work very smoothly. The stock ECU has no tuning ability. You're already flowing air differently due to the street port. Add in a chipped ECU, a fuel pump that is overwhelming the stock reg, no BAC, and an idle set about 500rpm higher than normal. I'm going to assume you probably don't have the stock air-pump and ACV either, so the air-injection system is also missing.
I'd say the stock ECU is going to be confused by all of that, but the stock ECU isn't even smart enough to notice something is amiss.
In all honesty, it will probably never work very smoothly. The stock ECU has no tuning ability. You're already flowing air differently due to the street port. Add in a chipped ECU, a fuel pump that is overwhelming the stock reg, no BAC, and an idle set about 500rpm higher than normal. I'm going to assume you probably don't have the stock air-pump and ACV either, so the air-injection system is also missing.
I'd say the stock ECU is going to be confused by all of that, but the stock ECU isn't even smart enough to notice something is amiss.
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WondrousBread (06-30-23)
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06-30-23, 09:41 PM
#8
Rotary Freak
If it's not at risk of engine damage, drive and enjoy. Worry about the rich idle later
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