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Old 08-29-2021, 06:37 PM   #1
boost86
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SR20DET dying @ idle -- injector problems w/ new 740cc DW injectors

S13 SR20DET w/ PowerFC & new DW 740cc injectors..

Problem:
Car will not idle for more than a few seconds before going lean and dying. Verified the lean condition on my wideband.

Installed new 740cc DW injectors, recalibrated PFC for the injectors & voltage. Injectors set up correctly on the table, latency set to 0.02

If I ramp up the latency to 0.48, the car will idle at around 12:1 af ratio. It misfires a bit and doesn't sound great, but it will maintain an idle. Has anyone else experienced this issue when going from stock (370cc) injectors to larger injectors?
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Old 08-30-2021, 07:24 AM   #2
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Just a few follow up questions..

Are you running a MAF or MAP?

What turbo are you running?

Have you double checked every other thing that you've touched since it was running well?

I've heard of 740's causing a rough idle, but usually it's under a rich condition.
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Old 08-30-2021, 07:50 AM   #3
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did you adjust your IACV?
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Old 08-30-2021, 09:17 AM   #4
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@burnsauto: It is a MAF car. I have an OEM Z32 MAF and a new ISR Z32 MAF I just tried. Both yield the same result. Turbo is an S15 turbo. I didn’t change anything other than the injectors, so I am not sure what else to check. Perhaps fuel pump?

@dorkidori_s13: I did play with IACV screw to try to fix the problem a while ago, didn’t seem to do me any good. In fact, I probably messed up the IACV’s proper screw location. This is worth investigating some more. Thanks for the suggestion.
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Old 08-30-2021, 10:24 AM   #5
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Quote:
Originally Posted by boost86 View Post
@dorkidori_s13: I did play with IACV screw to try to fix the problem a while ago, didn?t seem to do me any good. In fact, I probably messed up the IACV?s proper screw location. This is worth investigating some more. Thanks for the suggestion.
if you want to reset it. turn the screw all the way in... then youll need to back it out until you hear the motors RPMs start to rise. blip the throttle by hand in the engine bay to help the motor reset its idle to the adjusted height of the IACV screw while doing so.

mine is backed out roughly until the screw is flush with the top of the enclosure i believe. it takes a little tinkering, but youll know once you got it. if the IACV screw is set too far in, when you rev the car... it will die out on you due to lack of air coming into the intake manifold to idle. if adjusted out too far, the idle will be way too high. youre looking for roughly 700-900 at idle (factory idle is 750, but its kind of a bitch a the IACV is super touchy in that range). my SR tends to idle at 800-900 with my PowerFC DJetro. ive got my idle on the controller set to 780rpms. ive never really been able to get it to a perfect 750, but i just dont have the patience or care to perfectly set it.

after a friend of mine who tunes my car and i put my motor back together, he cranked the IACV screw all the way in. car wouldnt idle for shit once the throttle was blipped (even without touching the throttle, it was bitchy). after getting the car home and driving it around a bit, i got really annoyed by the car constantly dying and thought to check the IACV screw. low and behold, found out my buddy had tightened it all the way down. i backed it out to where it normally is supposed to be... car idled like a top again.

also another thing... make sure to check the voltage on your TPS. i think at idle its supposed to be .45-.49v. if you are still running your stock TPS that came with your motor, i suggest replacing it with a brand new OE unit. TPS's can cause all of sorts of annoying issues when they get old as they grooves worn into them from cruising and then slamming shut (or not properly adjusted voltage wise). i replaced my mine 2014, helped quite a bit as there was a groove in mine that was screwing with voltage at certain throttle positions. when I removed it, i turned the flapper arm thing and could feel 2-3 grooves as i moved the flapper arm. the brand new OE unti i installed DID NOT have these grooves. the brand new unit actuated smooth as butter.
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Last edited by dorkidori_s13; 08-30-2021 at 03:42 PM..
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Old 08-30-2021, 12:17 PM   #6
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Sounds like it needs tuning
you cant just install PFC some numbers and go

First
0. boost leak test or tuning is a waste of time
1. start engine, check for leaks, disable O2 sensor (ETC->O2 compensate "OFF")
2. Tune the engine idle cruise (cruise first)

-> Idle/cruise a/f ratio is 14.7 to 15.2:1 with O2 comp *OFF*
To do this adjust injector global % and lag time to reach 14.7 to 15.2:1 air fuel ratio while cruising at 20mph 40mph low speeds. Then, come back to idle and make minor adjustment for idle.

Once the global inj % adjustments are close, you will want to use
"MAF VOLTAGE %" adjustment table;
Scale the MAF voltages to A/F values (ex. 2.54v : 100% or 90% or 80% or 110% etc)
So the maf voltage matches a percentage that yield appropriate a/f ratio
..also make sure correct maf is selected


Just to get the car driving normal you may need go back and forth between maf voltage scalar and the global injector % and lag time delays depending how much adjustment is needed in the maf scalar. In other words if the maf scalar starts looking "jagged" 80% 110% 90% 105% etc... go back and mess with the delays and global inj

Finally you can use the base map to account for small idle region inconsistencies
And pay attention to the maf voltage when lifting from throttle to determine if the bypass is working correctly or interfereing
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Old 08-30-2021, 09:12 PM   #7
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@dorkidori_s13: Okay, tried changing the height of the IACV screw (luckily it's a new IACV with metal screw). It did change the idle RPM but it still dies. Good suggestion though.

I tried checking voltage on the TPS but it was hard to get a reading on it. I ran off the middle wire. Disconnected the TPS entirely, car ran like poop but idled, then died as usual. I ordered a new TPS for it today-- we'll see what happens when the new TPS arrives in the mail.

@Kingtal0n: Checked for boost leaks. All couplers are new ETS couplers torqued with t-bolts. Never had any boost leaking issues when it was on the dyno. Changed my bypass valve to my old one, still nothing. Runs the same, then dies.

Car was tuned by Jason from Link. Car ran great before, only changed the injectors to the 740's & rescaled everything in the ecu. I am tempted to believe you that something isn't setup properly. But I used DW's provided settings for the injectors. Dare I go against their provided voltage scaling?
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Old 08-31-2021, 06:50 AM   #8
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If you saved the old tune for the 370's, throw the original injectors back in and go back to the original tune. Just trying to pinpoint the exact issue. Then you can narrow it down to tune or a defect in one of the injectors. If it runs fine, then you may want to contact your tuner and go over things with him. He'll be able to steer you/take a look at everything. DW has gotten better with their quality control over the years, but it doesn't mean that something isn't physically/electrically wrong with one of them.
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Old 08-31-2021, 07:41 AM   #9
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oh... one thing for sure. replace the ECU water temp sensor (SR uses same sensor as KA). mine died while putting everything back together. car went from starting, to barely running, to wouldnt turn over within 24 hours because of that stupid sensor. can be had at autozone for like $20.
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Old 08-31-2021, 10:19 AM   #10
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Here is a video. Couldn’t keep it alive long enough for the wideband to show it go lean.

https://youtu.be/jFZTZgeaR0A
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Old 09-11-2021, 03:31 PM   #11
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Update: PROBLEM LOCATED.

The issue was lying in the Inj Lag (mS) vs BatV table in the PowerFC. Essentially, the values provided by Deatschwerks were very wrong. The car idles at 14.1-14.3v. At this setting in the table, the car most agrees with a setting of 1.1. Next, the injector latency is now set at 0.22. At this value, the car does not stumble when flicking the throttle.

Moral of the story: Don’t be an idiot like me— make sure your car is tuned correctly.

P.s. I installed a cheapo replacement TPS and it works as well as the OEM Hitachi unit does. I believe it was $15-20.
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