Surging at boost onset.
 

Background:
1992 with Begi-Shanghai kit
Tan Tops with Begi FMU
Braineack-built MS
Begi Intercooler
AEM UEGO wideband
Full TunerStudio

When cruising on the highway earlier, I noticed that the A/F Ratio was bouncing very rapidly, switching from 15 - 17.xx. Boost gauge was at around 0 psi and approximately 3,400 RPM.

I went home, got the laptop and tried to repeat the scenario. With the virtual gauges in TS on my side, I saw that the pulse width gauge was also going nuts.

This is only seem to happen when very gentle on the throttle. Once past 0 psi or if I step on the gas more, the car doesn't surge.

If I remember correctly, the car did not have this behavior when I was on bandaids (last week). The reason why I said that is because I am using the same tan top injectors prior to MS going in.

Req fuel is at 8.8, based on the calculator.


1. Is this a symptom of a failing injector(s)?

2. I've played around with Open Loop Mode settings, and I currently have it going into Open Loop at 70kpa. Should this be lower?

3. Richen up AFR targets? Richen up (increase #) in VE table by hand?


I think the car has almost 1 hour of VE Analyze live, but the surging is still there.

I'm half tempted to put in 440cc injectors I have, but I am not 100% sure if they are clean or not (got them used).


On my 1st tank of gas with MS, my mileage also dropped from 24mpg to 19.4 mpg. At the moment, I'm not as concerned about this as I am with the surging.

The msq and log file are attached, including screen shots of the table and the log in megalogviewer right around where the surging is about to happen.

Thanks.

Ditch the FMU and tune

it's not even the FMU, it's just symptomatic of requiring tuning!

More ve anayze live tuning or changing the values in the cell manually?
Is it also not enough resolution on the table? Since the prob is due to spiking lean at light throttle, should the afr target be richened up in that area where it is occuring?
Load dyno would be ideal but not possible at the moment.
Thanks.

This reminded me of when I was running band aids, before the 02 clamp went it. The ecu was trying to pull fuel to bring AF Ratio back to stoich and at the same time, boost is starting to ramp up and fuel is needed.
This time, the oscillations are much faster though.

The way I understand it is it will try to hit the A/F Ratios in the AFR Table, and make adjustments in the VE table as a result.

But, as richyvr said above, this may very well be a tuning issue. I'd love to follow this, but need a point on which direction to go.
Not asking for hand-holding, just pointer in the right direction.
BTW, added also is the EGO screenshot.

disable ego correction if you need to tune the fuel ve table

Just turned ego a controller authority to 0.
Brb.

Sent from phone

It's still there, but not as harsh. Perhaps more VE Analyze Live will smoothen it out some more. I've also increased the numbers in the 3400RPM & 84kpa intersection by 4 points in the ve table. Then more VE live tuning and look at the numbers.

With the EGO controller authority set to 5 before, does this mean it was 'fighting' with VE analyze live?

He will get a much better tune without the fmu raising fuel pressure at boost onset (0psi) which is exactly where the trouble starts. How do I know? I have the exact same setup with blue top injectors and no fmu.

Ve live filters out ego correction and accel enrich if im not mistaken.

What is your overrun fuel cut value set to?

Try increasing the KPa value upto 35 or something and see what happens then

Paulj- kpa over run settings is 20. It was closer to 30 before and changed to 20 when the lean spike problem was noticed.

Well, I loosened the small needle valve on the FMU and the response was better with less spiking. Unfortunately, I won't be able to test until tomorrow morning. But on the short drive with a brief stint in the problem area, the AFR was solid and consistent.