Wretched Fuel Economy City Driving

[toyman]

I'm lucky if I see 8 mpg around town. AFR is 14.7 at idle and runs between 14.3 - 15.1 at light throttle. The cells in the O2 target feedback map are all set at 14.7 for light throttle (load breakpoints -14.69 to -4.93 PSIg). I'm thinking that I should set the AFR to 14.7 to load breakpoint -2.39. Those cells are currently set at AFR 13.5 from -2.39 to -0.04 PSIg.  O2 target error and O2 feedback numbers are nominal. Should I just continue to cut fuel and raise the AFR?

The idle is good at 750 rpm in neutral but pulses a bit (700 - 800) while stopped and in drive. Is this due to the 270HR cam? Idle air learned value in neutral is -6% to -4%.

Or is there something else that I need to look at?

[toyman]

No one with additional insight as to how to improve fuel economy. My concern is that I might lean it out too much and not hear any pinging/detonation. There are no knock sensors on the block.

[Blue351]

Can you give more info on the combo?

13.5 : 1 at -2.39 to -0.04 PSIg (essentially WOT) is a decent A/F ratio and might be slightly lean for max power. 14.7 for idle and cruise is good. Are you pretty confident in your A/F readings? I don't know what kind of wideband set up you have but wiring can be very finicky because of grounding. Also, have you checked for exhaust leaks that could throw off readings? If you have catalytic converters, is the O2 sensor before or after them? Are you mashing the throttle around town?

[trbo2dr]

i think he's forced induction so 0 psig manifold pressure is more like cruise and not wot.  i thought i read somewhere that he was running a kenne bell blower and maybe that's part of the problem.  screw blowers are more efficient than a standard roots type blower but not as efficient as turbos.  this is just a guess but iat's are probably higher (comparatively) and require more fueling to cool and control combustion.  also, i don't know if kb's have bypass valves or not but if they don't that would mean more parasitic loss and more fuel consumption.  as for the iat's, maybe try water injection.  that would help cool things down which would allow you to run a little leaner on the afr's.  in the mean time pull some timing along with fuel and make small changes. 

[Kristopher]

AFR is only part of the equation. Don't neglect ignition advance. Also injector phasing will make a difference on your AFR if the fuel isn't optimally atomized. You should have some room for improvement.

 

[toyman]

Can you give more info on the combo?

13.5 : 1 at -2.39 to -0.04 PSIg (essentially WOT) is a decent A/F ratio and might be slightly lean for max power. 14.7 for idle and cruise is good. Are you pretty confident in your A/F readings? I don't know what kind of wideband set up you have but wiring can be very finicky because of grounding. Also, have you checked for exhaust leaks that could throw off readings? If you have catalytic converters, is the O2 sensor before or after them? Are you mashing the throttle around town?

The H/C/I combo is: Edelbrock performer heads/Comp 270HR mild blower cam/KB 2.1 L with max boost of 8 psi. So WOT is in boost territory. IIRC AFR in boost is ranges from 12.6 (0 psi) to 11.4 (8 psi)

WB is a Zeitronix Zt-2. I'm satisfied that the grounds are okay. EMS and WB share the same ground point and have a dedicated negative wire from the battery. Offsets should not be an issue.

O2 sensors are before the high flow cats

The WB readings are calibrated to read the same on the Zeirtonix software & gauge and the AEM at idle. O2 sensor volts are set to match the analog values.

There are no exhaust leaks.

Had a chance today to watch the pulse. Injectors are pulsing and the AFR is moving between 13.9 to 15.2. It's as if the IAC is opening and closing and yet as soon as I put the car in neutral the RPM become steady at the commanded setting. I don't have this issue when the RPM is set at 850.

[toyman]

i think he's forced induction so 0 psig manifold pressure is more like cruise and not wot.  i thought i read somewhere that he was running a kenne bell blower and maybe that's part of the problem.  screw blowers are more efficient than a standard roots type blower but not as efficient as turbos.  this is just a guess but iat's are probably higher (comparatively) and require more fueling to cool and control combustion.  also, i don't know if kb's have bypass valves or not but if they don't that would mean more parasitic loss and more fuel consumption.  as for the iat's, maybe try water injection.  that would help cool things down which would allow you to run a little leaner on the afr's.  in the mean time pull some timing along with fuel and make small changes. 

You are correct. This is a KB 2.1 L install with 8 psi boost. IAT's are high. Once warmed up they range from 220* - 240*. KB's do have a bypass on their S/C in the 8 psi and up configurations. Mine is the standard without the bypass. I've been added timing (ignition map) while pulling fuel in these low load cells. You're suggesting it's the other way around. Is that correct? I think AEM reads timing of 18* at idle.

[toyman]

AFR is only part of the equation. Don't neglect ignition advance. Also injector phasing will make a difference on your AFR if the fuel isn't optimally atomized. You should have some room for improvement.

 

I'm not at my computer tonight. Where do I look for changing injector phasing and which way would I go from the current setting. I'm guessing this is in part determined by the cam specs.

[Blacksaleen95]

No one with additional insight as to how to improve fuel economy. My concern is that I might lean it out too much and not hear any pinging/detonation. There are no knock sensors on the block.

You got something else going on... What's the timing in the pt/light cruise cells?  Don't be afraid to add some timing in the light throttle/cruise areas, using common sense of course... If the engine is not under load or is steady state/high vac you shouldn't have to worry about detonation too much...

[toyman]

No one with additional insight as to how to improve fuel economy. My concern is that I might lean it out too much and not hear any pinging/detonation. There are no knock sensors on the block.

You got something else going on... What's the timing in the pt/light cruise cells?  Don't be afraid to add some timing in the light throttle/cruise areas, using common sense of course... If the engine is not under load or is steady state/high vac you shouldn't have to worry about detonation too much...

Timing is 20* in the idle area up to 1350 rpm and -4.93 Psig cell and lower. 24* at 1700 and 30* at 2050. Changed my FB min and max to -20 and +20 with the dead band at 25 and - 25. Reset idle vs target values to to maintain a -4+/- reading. Pulsing now is less noticeable and less frequent.

Still getting lousy fuel economies around town.

Haven't driven the car lately and will be parking it shortly until next spring.

[Blacksaleen95]

Sounds like it's going in and out of decel fuel cut. Does it buck? What are the dfco options?

[beerfarm]

Timing is 20* in the idle area up to 1350 rpm and -4.93 Psig cell and lower. 24* at 1700 and 30* at 2050. Changed my FB min and max to -20 and +20 with the dead band at 25 and - 25. Reset idle vs target values to to maintain a -4+/- reading. Pulsing now is less noticeable and less frequent.

Still getting lousy fuel economies around town.

Haven't driven the car lately and will be parking it shortly until next spring.

Judging by the cal I have in my heavy truck, I think you can definitely add more timing down low. I run 25* around Idle cells.
I don't think you will fully get your idle to stop hunting @ 750 rpm with a KB without a little modifying  to the Ignition v.s. Rpm Table. Add a couple of degree when in goes under target and pull a couple above. I can get my cam idled stable at 800 (something I thought would never happen..  ) You may also try shutting O2 feedback off at idle to see if your fuelmap is off a bit. Might be trying to mask problems the O2 sensors can compensate for. That will beat the hell out of a steady idle as well.
As far as your mileage goes, I am averaging 9 around town with a 5000lb 4x4, so I would definitely keep working on your tune...

[toyman]

Sounds like it's going in and out of decel fuel cut. Does it buck? What are the dfco options?

DCFO are:

Fuel Off above 2500 rpm
Fuel Off below load -10.2 psig
Fuel Off below TPS 3.12%
Fuel Off coolant mi 32F

It does not buck. Gently swings back and forth, slightly now, less than 100 rpm. Without plugging in the laptop I'm thinking that the idle TPS is 1.25%. Is the 3.12 % TPS cut off the issue?

[beerfarm]

DCFO are:

Fuel Off above 2500 rpm
Fuel Off below load -10.2 psig
Fuel Off below TPS 3.12%
Fuel Off coolant mi 32F

It does not buck. Gently swings back and forth, slightly now, less than 100 rpm. Without plugging in the laptop I'm thinking that the idle TPS is 1.25%. Is the 3.12 % TPS cut off the issue?

Those setting should be fine.  All  those conditions must be met for Decel to enable , so Fuel Off above 2500 is keeping DCFO from interfering with idle.

[Blacksaleen95]

When you're cruising and you decel, what map reading do you get?   If you're close to 10 or below it may not be tripping the dfco which would be the reason for bad gas milage.

You should be able to actually hear the tone of the engine change once it's hitting dfco.  You can also monitor the dfco parameter to make sure it's activating...your wb should peg lean.

-10psi is quite a bit, that's approx -20 inHg... I'd be surprised if you're pulling that much vac on decel.  Take a log at idle and decel and post it. Your decel vac is always going to be higher than your idle vac so it's a fine line where the dfco setting needs to be for it to work correct.