LQ4 lean on start up.

[pormgb]

I have an LQ4 in a 65 Corvette, that is running super lean.

I'm in the very early stages of getting the motor tuned, but this has me stomped.

I'm using the tune from my LS6, with changes to IFR, B0104, VE and MAF tables to reflect a 6.0, in preparation for final tuning. I've tried adding to VE and MAF tables with no luck. I also did a misfire log, and there were no misfires. I have a wideband for AFR viewing, and I grabbed the injector data from another thread

Any idea?

Specifications

- 2002 LQ4, Sloppy Mechanics Stage 2 cam
- Bosch 42lb Fuel Injectors
- FPR, vacuum referenced


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[nonnieselman]

Have you gotten the VE/MAF tuned for when its at operating temps?

[pormgb]

Have you gotten the VE/MAF tuned for when it is at operating temps?

No, I have been unable to run the car long enough to get to the operating temperature and tune the VE/ MAF. The car idles between 21 and 22 AFR, sometimes higher,

[statesman]

Reduce all values in your IFR table by 5%. Do another log and see if the AFR is better or not.

[pormgb]

I reduced IFR by 5% but still no change. I also did a test by increasing the VE and MAF tables by 30%, and the IFRs came down, but seems like a lot of increase.

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[statesman]

I reduced IFR by 5% but still no change.

That's telling me that the problem is with your wideband sensor.

If you have narrowbands installed, then use them as a sanity check for the wideband.

[pormgb]

That's telling me that the problem is with your wideband sensor.

If you have narrowbands installed, then use them as a sanity check for the wideband.


The WB crossed my mind, and I think I have spare time to test it. I forgot to mention that the motor won't increase speed when I see the 20s IFRs. The engine revs up once I add the 30% to the VE+MAF.

[nonnieselman]

Where did you get the bosch injectors?

[pormgb]

Where did you get the bosch injectors?

I got them on EBay, and they were listed as genuine Bosch.

[pormgb]

I'm getting close to figuring out what's wrong. I discovered that B4205 was set to 122 degrees C, so the motor would not go into closed loop. I fixed B4205, and the motor goes into closed loop, and I see around 14.7 to 15 AFR at idle, and the motor revs up as expected. So the problem is related to open loop, because the motor runs between 18 and 22 AFR, until getting into closed loop. I have attached a log that shows the warmup process with B4205 fixed. I need to figure out how to set the correct open loop fueling, or do I need to enable fuel trims in open loop?



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[statesman]

Okay, I guess your wideband is working.

I don't know why your fueling would be so far out. If you have the equipment, you could check your fuel pressure at the rail. The only other thing I could suggest is for you to tune your idle using your fuel trims and then see if the next cold start goes lean.

[pormgb]

Okay, I guess your wideband is working.

I don't know why your fueling would be so far out. You could check your fuel pressure at the rail if you have the equipment. The only other thing I could suggest is for you to tune your idle using your fuel trims and then see if the next cold start goes lean.

I checked the fuel rail pressure without a vacuum and got 58PSI. I ran the car yesterday, and warm starts worked flawlessly, idling at 15 AFR. So, once the vehicle warms, the problem goes. The problem is in the open loop until the closed loop kicks in. LTFTs add up to 25% to sustain around 15 AFR when idling. I used a stock VE+MAF table and added 20%. Could my VE and MAF be that far out?

I do have a CALC Vet log taken at idle. I will see what that table is trying to add.

[statesman]

I used a stock VE+MAF table and added 20%. Could my VE and MAF be that far out?

That's highly unlikely. If you have a stock MAF sensor, then the stock MAF curve should be fairly close. I would adjust the IFR table until you get reasonably good fueling with the stock MAF curve.

[pormgb]

That's highly unlikely. If you have a stock MAF sensor, the stock MAF curve should be close. I would adjust the IFR table until you get reasonably good fueling with the stock MAF curve.

I removed 5% from the IFR table, and the startup AFRs improved. When the motor starts, it's around 13AFR, then creeps up to around 17 (with IFR changes). The first cold start idles very low, around 500rpm, until the motor begins to warm up, and restarts are perfect. Even with the IFR changes, the LTFTs are around +25%. I also removed the vacuum reference from the FPR, so there is a constant 58 PSI.

[statesman]

I removed 5% from the IFR table, and the startup AFRs improved. When the motor starts, it's around 13AFR, then creeps up to around 17 (with IFR changes).

Take another 4% or 5% out of the IFR table. You're still a bit too lean now.



I also removed the vacuum reference from the FPR, so there is a constant 58 PSI.

If you do that, you'll have to slope your IFR table. Don't drive the car until you do that.... or if you like the flat IFR table, then reconnect the vacuum reference.

[pormgb]

Take another 4% or 5% out of the IFR table. You're still a bit too lean now.




If you do that, you'll have to slope your IFR table. Don't drive the car until you do that.... or if you like the flat IFR table, then reconnect the vacuum reference.

The IFR is sloped, and here is what I have prior to removing another 5%.