Too much fuel, or timing retard?

[douglas vincent]

So now that I have the 370 cc injectors in, car pulls fine and hard....until 5250 rpm or so. Then it starts to cut out/ bog, but without any of the jerky feeling, just starts slowing down. It is not lack of fuel, I already tested this by giving it extra fuel at high rpm via the extra injector. This just caused the motor to seriously bog.

I am running 5 psi right now.

Before I installed the larger injectors, I just had the extra injector as the extra fuel. In the low gears 1st and 2nd I didnt have any problems pulling hard to 6k. But I would bog out in the high rpms in the next three because too much fuel would start to build up. I would have to let up for 1/2 a sec or so then then floor it again. Now I "bog" out in all gears but only at 5250 rpm and up.

Obviously I need a stand alone, but any ideas?

Thanks

[vrg3]

It could be too much fuel, right? I have two thoughts:

1) Maybe the fuel trims are going nuts and messing with high-load fueling. You might want to try running without the oxygen sensor (and with an ECU reset), to see if that helps at all.

2) Or... maybe you're hitting the MAF sensor's rail, causing the ECU to throw the injectors open at 100% duty cycle. Although.... The MAF sensor maxes out at around 200 grams per second. 100% duty cycle with four 370cc injectors is about 20 grams per second of fuel. So you'd be getting an air/fuel ratio of about 10:1, which isn't too too bad. In any case, you might want to put a voltmeter to the MAF signal and see if it's getting very close to 5 volts.

[douglas vincent]

How do you check the MAF signal with the voltmeter? ie, which wires and how do you hook up the voltmeter?

Thanks

[vrg3]

You can either measure the signal at the ECU (just measure across the "MAF sensor (signal)" and "MAF sensor (ground)" pins, or you can measure it at the sensor.

To measure at the ECU, just use my pinout chart:

http://www.graphics.cornell.edu/~v/ecupins/

If you'd rather measure it at the sensor, these are the pinouts. If you unplug the MAF sensor's harness connector and look at it head-on with the locking tab on top, the pins are numbered 1 through 5 left-to-right:

Code: Select all

 ----| |----
| 1 2 3 4 5 |
|___________|

These are the pin specifications:

Pin 1: Red wire, power supply (+12v)
Pin 2: White wire, signal ground
Pin 3: Black-with-red-stripe wire, ECU ground
Pin 4: Black wire, signal
Pin 5: Blue, something else

So you would measure the voltage between pins 4 and 3 (since the Hitachi sensor actually doesn't use pin 2 at all). If you connect your voltmeter to thin wires you can wedge the wire in between the connector and the sensor.

[douglas vincent]

I try to test it tommorrow.

[douglas vincent]

or tommorrow

[douglas vincent]

Ok, off boost it maxes out at 3.6-3.8

On boost, it starts at 3.6 and climbs up and up and up, as the rpms rise. Until it hits 4.6-4.8 at 5000 plus rpm.

[vrg3]

Okay, that's probably alright then.

What about the unplug-the-oxygen-sensor test?

[douglas vincent]

A $3 50K poteniamter (sp?) fixed it.

I hooked up a poteniometer inline with the signal line (#4). This allows me to modulate the signal by about 12%. Don't ask me why, but it does.

So I can "richen" or "lean" the signal.

I can cruise along and tune it by feel as the engine will either increase or decrease in power at just the right setting.

I cranked it up to 5k on boost on an on ramp and then cranked it "lean". Instantly all hesitation dissappeared and the reading dropped from 4.8 to 4.1. Wow, what a difference.

And no audible knock.

Now to see if my milage gets better.

[vrg3]

Basically the ghettoest AFC ever.

So it seems like the hesitation was due to too an overrich mixture then?

4.8 volts is about 175 grams per second, and 4.1 volts is about 110 grams per second. So you reduced the airflow signal by about 37%.

I don't know if this is a workable solution in the long term, though. First of all, you're relying on the finite input impedance of the ECU's ADC input, which might not stay steady. The sensor's output impedance might not behave well either. But more important is that the MAF sensor's transfer function is nonlinear, so you'll get different corrections at different airflows.

[douglas vincent]

Ghetto is my middle name. Douglas Ghetto Vincent

You can definately tell when it is running rich = less power and bogging.

The lean thing is going to be test run after test run of basically slowly turning the knob until it quits bogging at the high rpm. Hopefully at this stage I will Goldilocks, just right.