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 Post subject: Lean Spike on Tip-In- How to track down?
PostPosted: Thu Feb 02, 2017 12:14 pm 
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Newbie

Joined: Thu Feb 02, 2017 11:31 am
Posts: 7
Hi guys,

I have a 2002 WRX EJ205 engine that has a lean spike issue I am trying to understand. I'm fairly new to tuning, so please bear with me if I say something on the not-so-smart side of the scale.

Problem description:
Any sort of sharp throttle transition, be it from idle or from holding at midrange RPM, whether under cruise load or free revving, will show a lean spike before fueling returns to proper ratio. For example, blipping the throttle while at idle will produce a split second spike from 14.5 to ~17 AFR before it corrects and richens up. Both the stock O2 sensor, and a wideband sensor I have added, match up with readings, and the engine audibly bogs and hesitates on transitions even when free-revving. Steady cruising, as well as AFR at WOT or anywhere else in open-loop with a steady pedal, show perfectly normal AFR's. Idle is steady, vacuum gauge shows rock solid 20 inches vacuum.

Engine description-
-Non-AVCS JDM EJ205 using all US sensors, cam/crank gears, TGV's, intake, etc...
-Stock airbox
-Using stock WRX 420cc blue injectors.
-Using Perrin parallel fuel rails and stock FPR
-Fuel pump is a brand new walbro 255
-Engine compartment fuel filter is new
-No fuel flow issues when free flowing into a bucket
-Aftermarket downpipe and catless exhaust


Engine Diagnostic steps taken-
-Checked for vacuum leaks using carb cleaner and propane, none detected.
-Put a block-off plate in place of IACV- no change to lean spike
-Changed out all injectors for a second set- no change to lean spike or behavior
-Verified fuel pressure in the lines to be 42PSI directly before the FPR with an inline gauge.


Tuning steps taken- Starting with a 100% stock map
-Have CL to OL delay set to zero.
-IAT and Coolant temps look accurate- no funny #'s
-MAF voltage and TPS graphs look accurate- no flat spots or skips
-Enrichened tip-in values in 10% increments up to 50% and also tried lowering tip in activation requirements. This resulted in the same lean spike, but then a rich spike that leveled out to where AFR should be with the new throttle position.
-Scaled injectors to force 10% more fuel. Same lean spike, AF compensation values were consequently ~10%
-Scaled entire MAF graph by 10% and 20%. Same lean spike, AF compensation values changed by approx the scaled MAF values.
-Unplugged MAF sensor while engine was idling and tried several free revs. Stumble off idle/lean spike were almost totally unchanged from when MAF was plugged in.

I very much doubt there is a physical leak or any issue with the fueling system or injectors. That leaves, in my mind, a bad sensor that I cannot recognize or do not understand, or a tuning adjustment that I also do not understand. I'm open to any input you guys have.

Thanks much.


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 Post subject: Re: Lean Spike on Tip-In- How to track down?
PostPosted: Fri Feb 03, 2017 3:02 pm 
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Experienced

Joined: Thu Dec 18, 2014 6:31 pm
Posts: 745
Location: oregon
exhaust leak between the manifold to head, manifold to up-pipe, or manifold to cross pipe could show funny afr trends

seafoam treatment is fantastic for finding exhaust leaks, do it on a warm car, into the manifold to bypass valve line. if you live in a dense neighborhood your neighbors may not like you for the clouds you make but be assured that any place with a leak between the heads and tailpipe will spew smoke.

you didn't mention if you have a blow off valve, and sometimes pull style valves can be open during the right vacuum conditions - letting unmetered air in the intake tract - which pressure testing the intake would not show this

posting your rom and a log would help if it isn't any of those things

one thing I'm thinking about is per injector compensation, which stock is a value of +/- 0.030 (which I believe means +/- 3% fueling) depending on cylinder, which is intended for stock fuel rails/lines in series. This should be zero'd out for all cylinders if running parallel fuel flow.

_________________
'03 USDM WRX - EJ205/TD04/FMIC/SD - 2.72 g/rev @ 3950 rpm and 237 g/s @ 6100 rpm


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 Post subject: Re: Lean Spike on Tip-In- How to track down?
PostPosted: Fri Feb 03, 2017 3:55 pm 
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Newbie

Joined: Thu Feb 02, 2017 11:31 am
Posts: 7
Since I have an actual bog/hesitation and it occasionally pulls timing, I unfortunately don't think it is just an exhaust leak. I have the stock bypass valve, which I have verified operation of with a vacuum pump.

Thanks to you, I now understand what those ABCD injector values are for, and why they are +0.030/-0.030ms. User level has to be Debug to change!

I just did a compression test and came up with 160-165 on all cylinders- will try to change those injector values and balance the sides out!


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 Post subject: Re: Lean Spike on Tip-In- How to track down?
PostPosted: Fri Feb 03, 2017 5:21 pm 
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Newbie

Joined: Thu Feb 02, 2017 11:31 am
Posts: 7
attached is a log- revs from idle- no load


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 Post subject: Re: Lean Spike on Tip-In- How to track down?
PostPosted: Fri Feb 03, 2017 6:43 pm 
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Newbie

Joined: Thu Feb 02, 2017 11:31 am
Posts: 7
I enabled the second tier tip in enrichment, spent a long time playing around with where that comes in and the enrichment values, and maxed out the tip in disable applied counter threshold to 255. Tip in response feels very close to 'right' now. Large throttle blips in rapid succession can still cause it to choke, but nothing like before.

So I have read that the JDM heads flow better, but....175% increase in tip in values? Have I just band-aided over a real sensor problem?


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 Post subject: Re: Lean Spike on Tip-In- How to track down?
PostPosted: Sat Feb 04, 2017 3:40 pm 
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Newbie

Joined: Mon Dec 29, 2014 12:03 pm
Posts: 91
Hey Chally I remember this from face book lol.

Its way easier to see whats happening in the logs. If you take a look at time stamp 2065 the tip in enrichment causes a rich condition and then as soon as that happens the AF Correction goes to -10 -3 +8 +20.

At this same time you hold a constant throttle position just as the af correction starts to go to -10.

By the time stamp it can be seen that the stock tip in enrichment will time out. Stock enrichment time out is i think 29ms. If it were me what I would try is actually reducing the tip in enrichment: 0 it out test to see how lean it goes on tip in using a log, then adjust tip in enrichment accordingly. then retest with the new tip in enrichment setting to see if the original lean spike persists.


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 Post subject: Re: Lean Spike on Tip-In- How to track down?
PostPosted: Mon Feb 13, 2017 4:31 pm 
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Newbie

Joined: Thu Feb 02, 2017 11:31 am
Posts: 7
Thanks! I completely misunderstood how the tip-in timeout works.

I went back and zeroed tip in and worked with bumping the throttle and adjusting values until it smoothed out. I ended up with smaller enrichment values, but still a very high (as compared to stock values) 100ms timeout value.

I really appreciate the help. My usual solution would be to change to a different accelerator pump lever arm hole, if that gives you any idea of what I usually work on!

Attachment:
16142341_10154324579810835_1360978301938697816_n.jpg


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 Post subject: Re: Lean Spike on Tip-In- How to track down?
PostPosted: Tue Feb 14, 2017 3:40 pm 
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Joined: Thu Feb 02, 2017 11:31 am
Posts: 7
Another question, unrelated- I have a hard time setting up or changing parameters logged while in the car. A car with no heat an an intrusive rollcage makes it a pain. Romraider pares down the giant parameters list to what is actually available from the ECU when you connect to the car. Can I change it to show just those accessible parameters when I'm sitting nice and warm at my kitchen table and researching what to log/adjust next?


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 Post subject: Re: Lean Spike on Tip-In- How to track down?
PostPosted: Wed Mar 01, 2017 11:21 am 
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Newbie

Joined: Thu Feb 02, 2017 11:31 am
Posts: 7
This lean spike has now reappeared, despite no change in the tune file since I thought I nailed it down, and no changes under the hood. I've gone over every single harness wire from ECU checking resistance, multiple times. May try swapping ECU next to see what happens.


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 Post subject: Re: Lean Spike on Tip-In- How to track down?
PostPosted: Fri Mar 03, 2017 9:27 pm 
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RomRaider Donator

Joined: Sun Nov 08, 2015 3:11 pm
Posts: 61
I'm trying to track down the same issue. I used (old injector size/ new injector size) which was 0.42 and I multiplied that value to my TIP - IN table (ms) and it was damn close. I did a little bit of work with the closed loop maf scaling and it improved even more but it's still there. I'm getting there slowly but I rode the short bus to school so it takes me some time to figure out.


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