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View Full Version : SR20DET rpm dips when applying throttle


Shirohige
04-27-2020, 07:07 AM
EDIT: Problem was the tune that was on it. My new tuner showed me how bad the car was tuned. Very low torque, low hp, running way too rich like max gas when its not needed, no stable boost. He lost braincells looking at that tune. He tuned it again and fixed it all, got 378 nm torque and 279whp from a s15 spec r turbo. He also fixed the hesitation for like 90%. He couldnt get rid of it completely but it feels like its not there anymore. Couldnt be happier

So uh:
https://www.youtube.com/watch?v=p4RqMP75rew&feature=youtu.be

That happens. Seems like throttle tip in hesitation. Only happens when i punch the pedal, if i press it in lightly it gives no issues. Once a bit higher in rpm (2-3k) you can hear/feel misfires.

Things ive done:
- new iacv (had to be replaced, old one was bad)
- tps set at .43v, was at 0.5v first
- spark plugs gapped at .28
- checked CAS. My PFC was showing 17-18 degrees when warm. Thought it might've been my CAS so i took it out, put the engine at TDC (frsport guide) and stabbed the CAS back in. The CAS is maxed out with bolts and is not in the middle. I'll have to check it again with a timing gun. PFC shows 15 now, but during misfires on idle it shoots to 16 and goes back to 15 really quick

- double checked all vacuum hoses for leaks (Found a leak on the oil/air seperator)
- new gas
- new fuel filter
- checked injectors to see how they spray, its all good. Injectors were cleaned and got new o-rings too (3000kms ago)
- New coil packs
- BKR7IEX plugs gapped at .28 (not even 3000km on them)


The car isnt even doing anything weird. It idles fine, no hunting or extremely high/low idling. When warm its 850-875. I let the car sit for 1.5 years. Note: Before it was sitting in my garage for 1.5 years it would drive fine with no hesitation (after it would reach 70 degrees celsius). I always thought it was a bad IACV. But now I get hesitation during both cold AND warm engine.

What can i even do at this point?

TheRealSy90
04-27-2020, 11:35 AM
It's normal for pumping the brakes to affect the engine idle since you are using the engine vacuum to actuate the booster.

Shirohige
04-27-2020, 01:47 PM
ive never seen it gain 600-700 rpms extra like that. Gonna do some tests tomorrow and see if the brakebooster is fine

Shirohige
05-01-2020, 07:52 AM
Alright its not bad gas either. Changed the gas, flushed the fuel lines, new gas filter. Still the same

mechanicalmoron
05-01-2020, 08:48 AM
ive never seen it gain 600-700 rpms extra like that. Gonna do some tests tomorrow and see if the brakebooster is fine

If it's dramatic, that's somewhere to check.

Did you just look at the hoses? Spraying carb cleaner around stuff can find huge vacuum leaks, but a smoke test is almost always way better, the only (very rare) exception I've found is some intake manifolds, where there is a long gasket that can suck in under vacuum, but not enough restriction to push the smoke out.

So it didn't do that, then it sat, then it did that, with no work or damage in the meantime? If that's the case, put some happy juice in the gas and drive it.

Throttle body clean and happy with no shaft leak, and stopping in the right place when you set the TPS? MAF clean and happy?

I've never used one of those cool-kid computers, do you have livedata? Is it a real adaptive closed loop system with fuel trims that you can watch?

Shirohige
05-01-2020, 09:01 AM
If it's dramatic, that's somewhere to check.

Did you just look at the hoses? Spraying carb cleaner around stuff can find huge vacuum leaks, but a smoke test is almost always way better, the only (very rare) exception I've found is some intake manifolds, where there is a long gasket that can suck in under vacuum, but not enough restriction to push the smoke out.

So it didn't do that, then it sat, then it did that, with no work or damage in the meantime? If that's the case, put some happy juice in the gas and drive it.

Throttle body clean and happy with no shaft leak, and stopping in the right place when you set the TPS? MAF clean and happy?

I've never used one of those cool-kid computers, do you have livedata? Is it a real adaptive closed loop system with fuel trims that you can watch?
Ye i sprayed carb cleaner around all of the hoses to find leaks. No leaks. Might do a boost leak test if i can. TPS is correct and the ecu doesnt use a MAF.

Also no, i always had the rpm drops but that would disappear once the water was at operating temp. So i figured it would be my IACV so i replaced it for a new one. After that it started doing this, but when the car reachs operating temps on water it still does it.

I can read some data on the handconsole that came with the ecu

mechanicalmoron
05-01-2020, 09:16 AM
Ye i sprayed carb cleaner around all of the hoses to find leaks. No leaks. Might do a boost leak test if i can. TPS is correct and the ecu doesnt use a MAF.

Also no, i always had the rpm drops but that would disappear once the water was at operating temp. So i figured it would be my IACV so i replaced it for a new one. After that it started doing this, but when the car reachs operating temps on water it still does it.

I can read some data on the handconsole that came with the ecu

So the tune is stock and it adapts right, even though it's running that ecu?

Can you read water temp from the computer? Make sure that's working right, it can be dead and have the gauge sender working fine.

What does fuel do? Is it adding or subtracting at idle, during tip-in, and at sustained higher speed?

As far as boost goes, obviously it needs to not leak, but it's under vacuum during throttle tip-in - but while you're thinking on those lines, you might make sure you have no intake restriction (turbo spins freely and doesn't have a giant piece of filter stuck on it, or something).

Shirohige
05-01-2020, 09:20 AM
So the tune is stock and it adapts right, even though it's running that ecu?

Can you read water temp from the computer? Make sure that's working right, it can be dead and have the gauge sender working fine.

What does fuel do? Is it adding or subtracting at idle, during tip-in, and at sustained higher speed?
Yes it will adapt, but i had it tuned 2 years ago.

It does show the water temp and you can see it rising towards 80 degrees or so. I can take a look for the fuel later and see if its visible for me. Thanks for that

mechanicalmoron
05-01-2020, 09:27 AM
Yes it will adapt, but i had it tuned 2 years ago.

It does show the water temp and you can see it rising towards 80 degrees or so. I can take a look for the fuel later and see if its visible for me. Thanks for that

I'm a chronic post editor - you got me before I was done.

But yeah, fuel trims are king, you can infer a huge amount from them.

Shirohige
05-04-2020, 08:06 AM
https://cdn.discordapp.com/attachments/543080258438692867/708700230291423272/ss.png

Alright took out the coilpacks today and saw that 3 of them have cracks all over them. I dont know if this is the issue, but i ordered new coil packs. These things are probably 25+ years old anyway.

Also the fuel stuff is fine, i checked it.

Shirohige
05-18-2020, 12:51 PM
Alright new coil packs in, same issue.

The last thing i can do is check the timing with a timing gun and adjust the cas if needed. After that im out of ideas.

Edit; somewhere this week ill be putting a new fuelpump cuz why tf not. This one is old, i dont think its the issue but ill just change it out for a new one. Getting a friend over with a timing gun too to read that shit aswell

Edit2: AFR while idle is good. Set the tps a bit lower today at 0.44v. Im gonna guess on a dying fuel pump or fucked up ignition timing. Either way ill find out soon

Shirohige
05-20-2020, 12:18 PM
Alright fucked around today and decided to read my AFRs.

At idle its perfect, nothing wrong. The moment i apply throttle it skyrockets so high that it cant even read it anymore lmao. I just get "- - -" on my gauge. i think around 17 is the highest it can show

https://cdn.discordapp.com/attachments/546947505594826767/712716599597072465/unknown.png

So that means too much air and too little fuel right? Ill be changing out my fuel pump this weekend probably. I remember when i took out my fuelpump the "sock/strainer" was grey-ish/black. I cant find any info on that being a culprit for hesitation tho? Anyway ill be changing that too. Im just gonna assume that my pump cant deliver the right amount of fuel after i give throttle from a dead stop.

My injectors were cleaned and got new o-rings and are not even 3000kms old so i doubt thats gonna be the culprit. Everything else fuel related is cleaned/new except the fuelpump. Ill keep this topic up to date

Shirohige
05-24-2020, 06:43 AM
Alright a fresh fuel pump didnt do anything. At this point im out of options.
Somewhere this week is where ill get my timing checked and after that ill just go to a tuner and let hem take a look at it

Shirohige
05-29-2020, 01:41 PM
Couldnt get my timing checked or get my car to a tuner.

Found out that i have a boostleak in my oil catch can. Does anyone know if that would cause the issues i have right now?

zombiewolf513
05-29-2020, 08:04 PM
Im having the same issue with my power fc sr20. Idles okay, afr a little rich (12) at idle, slight hunt, rpms dip and afrs spike lean just like your video. Is it possible its tuned to not use the iacv or use it disconnected from coolant?


Found out that i have a boostleak in my oil catch can. Does anyone know if that would cause the issues i have right now?
Your catch catch shouldnt be seeing boost, only vacuum.

Shirohige
05-30-2020, 04:38 AM
Im having the same issue with my power fc sr20. Idles okay, afr a little rich (12) at idle, slight hunt, rpms dip and afrs spike lean just like your video. Is it possible its tuned to not use the iacv or use it disconnected from coolant?


Your catch catch shouldnt be seeing boost, only vacuum.

Found out that its an air/oil seperator. Basically its leaking from there so ill just put a catch can on it somewhere next week. Even with only less than 10psi air running from my compressor through my turbo intake you can hear it leak air very loud.

Also, i doubt that my tuner tuned my car to run without the IACV. Because before i let it sit for 1.5 years my car would act normal once the iacv would open up more (70+ degrees celsius). Now after 1.5 years it has throttle dip in.

zombiewolf513
05-30-2020, 09:52 AM
Maybe the pfc is getting a bad coolant temp signal?

Shirohige
05-30-2020, 09:57 AM
Maybe the pfc is getting a bad coolant temp signal?
The readings on my commander are pretty normal. Dont have an aftermarket watertemp gauge connect so i cant confirm that. Dont have any weird symptoms too that a cts would cause.

zombiewolf513
05-31-2020, 12:07 PM
I went into the fuel/ignition timing correction settings on the power fc commander and turned the injectors all the way up, and that made the hesitation problem go away but the idle got rough and very rich (10.5 afr). Still trying to figure out what that means, but maybe itll help you too

Shirohige
05-31-2020, 12:42 PM
I went into the fuel/ignition timing correction settings on the power fc commander and turned the injectors all the way up, and that made the hesitation problem go away but the idle got rough and very rich (10.5 afr). Still trying to figure out what that means, but maybe itll help you too

Sounds like a tuner should correct your fuel settings then. Ill try that too very soon. Found out today that my spark plugs had a layer of oil on them and the spark plug wells had oil too. Looks like the valve cover isnt seated properly so ill get that shit done tomorrow

Edit: i also read a bit of the FSM today and they covered hesitation part. Said to disconnect your FPR vacuum hose and see if it still hesitates. And to pinch the hose that goes to the pcv and see if that fixes the problem

S14rebuild
05-31-2020, 02:16 PM
Did you do a full resistance sweep of the tps? Could have a dead spot.

Shirohige
05-31-2020, 02:30 PM
Did you do a full resistance sweep of the tps? Could have a dead spot.

Ye i did. It goes smoothly from 0.45v to 4.2 or something. No dead spots

Kingtal0n
05-31-2020, 02:45 PM
icant follow wtf is happening here but it sounds like somebody needs to perform a pressure test

fill the intake/turbo/plumbing to 20psi of pressure with the dead silence in a room and you must secure and stop all leaking air before anything you do tuning wise has any merit

zombiewolf513
05-31-2020, 08:01 PM
Sounds like a tuner should correct your fuel settings then. Ill try that too very soon. Found out today that my spark plugs had a layer of oil on them and the spark plug wells had oil too. Looks like the valve cover isnt seated properly so ill get that shit done tomorrow

Edit: i also read a bit of the FSM today and they covered hesitation part. Said to disconnect your FPR vacuum hose and see if it still hesitates. And to pinch the hose that goes to the pcv and see if that fixes the problem

Are you sure its oil on the plugs and not a layer of wet fuel on a carbon fouled plug? I found the same things, but i think the plugs might have fuel on em. Found this too:
https://youtube.com/zzMagT5rVMA

I tried the fpr hose and pcv hose things, no change there for me though. Interested to see what you find.

Did you do a full resistance sweep of the tps? Could have a dead spot.

Ye i did. It goes smoothly from 0.45v to 4.2 or something. No dead spots

s14rebuild is talking about testing the resistance, not necessarily the voltage sweep. Mine was sweeping voltage eh alright but was really f'd on a resistance test. Vid of the testing:
https://youtu.be/6SR0oIuC0z4

Changing the tps didnt resolve the issue on my end. Coil packs tested to spec @ 1ohm

OP: is your o2 feedback idle control turned on in your commander? When was the last time you replaced manifold injector oring seat things?

Shirohige
06-01-2020, 12:59 PM
icant follow wtf is happening here but it sounds like somebody needs to perform a pressure test

fill the intake/turbo/plumbing to 20psi of pressure with the dead silence in a room and you must secure and stop all leaking air before anything you do tuning wise has any merit

Yes this topic is a shithole, apologies. Did another pressure test today and found no leaks from the turbo all the way to the intake manifold.

Are you sure its oil on the plugs and not a layer of wet fuel on a carbon fouled plug? I found the same things, but i think the plugs might have fuel on em. Found this too:
https://youtube.com/zzMagT5rVMA

I tried the fpr hose and pcv hose things, no change there for me though. Interested to see what you find.


s14rebuild is talking about testing the resistance, not necessarily the voltage sweep. Mine was sweeping voltage eh alright but was really f'd on a resistance test. Vid of the testing:
https://youtu.be/6SR0oIuC0z4

Changing the tps didnt resolve the issue on my end. Coil packs tested to spec @ 1ohm

OP: is your o2 feedback idle control turned on in your commander? When was the last time you replaced manifold injector oring seat things?

Ye it was oil on the plugs (white tips on the plugs). Found out that i didnt torqued down my valve cover (im so ashamed to tell this lmao). Thats all fixed now. Doing the FPR thing and pinching the blow-by hose didnt do anything for me either.

My tps is quite new (not even 3000kms old) i did check everything on my tps and im 100% sure its fine. My tuner did disable 02 feedback when my car was getting mapped. Also the orings on my injectors arent even 3000kms old too.

I did found a leak between my exhaust manifold/turbo. Found out today that my car isnt building any boost and my turbo will only spool at like 5k rpms. All those gaskets are like 3000km old like the other gaskets. This car is cursed. This wasnt happening 2 weeks ago

zombiewolf513
06-01-2020, 01:23 PM
I did the test kingtal0n suggested but used soapy water and found a leaking throttle body gasket, a very leaky rubber injector seat, and valve cover gasket in cylinder 3. Im going to replace all the intake gaskets and injector orings. My valve cover gasket is new and i torqued to spec so i might need to just retorque the center bolt.

Kingtal0n
06-03-2020, 12:14 PM
If you touch the throttle (while O2 sensor is unplugged) and get a lean condition its either

the maf (a boost leak, pressure leak, poor maf placement, insensitive/dirty maf, etc... maf related)

or

the injectors (wrong size, leaking, not leaking, not opening properly (low voltage or w/e), dirty filthy rail or injectors, fuel pressure drop, etc...)

or

It needs tuning (wrong ecu, wrong tune, poor wiring connections, poor grounding, Bad O2 sensor BLM (Long term memory), etc...)

Because it goes like this:

maf -> ecu -> injectors

Shirohige
06-03-2020, 01:44 PM
I did the test kingtal0n suggested but used soapy water and found a leaking throttle body gasket, a very leaky rubber injector seat, and valve cover gasket in cylinder 3. Im going to replace all the intake gaskets and injector orings. My valve cover gasket is new and i torqued to spec so i might need to just retorque the center bolt.
Hope you get it fixed!

If you touch the throttle (while O2 sensor is unplugged) and get a lean condition its either

the maf (a boost leak, pressure leak, poor maf placement, insensitive/dirty maf, etc... maf related)

or

the injectors (wrong size, leaking, not leaking, not opening properly (low voltage or w/e), dirty filthy rail or injectors, fuel pressure drop, etc...)

or

It needs tuning (wrong ecu, wrong tune, poor wiring connections, poor grounding, Bad O2 sensor BLM (Long term memory), etc...)

Because it goes like this:

maf -> ecu -> injectors
Dont tuners usually turn off the 02 sensor?

Got the d-jetro power fc so i run a map sensor. Both my PFC and AVCR map sensors give the same value when idle so i doubt they are dirty.


Got the car tuned with these injectors and made around 300whp (2 years ago) so probably not the wrong size. I did take the fuel rail off and let someone watch the injectors as i was cranking the car a couple of times. Injectors did not leak. Also shouldnt a fuel pressure drop be across the whole powerband? I can rev it easily with no major issues (except a couple of misfires when i hold the rpms).

Im getting a timing gun tomorrow (i did take out the cas after all) and ill set it on 15 degrees. If that does not fix anything ill get it to another tuner and let him handle it.

Shirohige
06-04-2020, 01:59 PM
In the end it was the CAS which wasnt set correctly. Idle at operating temp was around 20 degrees. Turned the CAS and set it on 15 degrees and now i can apply throttle without hesitation. Couldnt try with a cold engine but ill try that tomorrow!

So if you have hesitation and misfiring and you messed with your CAS make sure its at 15 degrees. I did use the spark plug wire between the coil and sparkplug.

zombiewolf513
06-05-2020, 11:41 AM
Was your APFC reading at 15 degrees when it was out of timing?

Shirohige
06-05-2020, 11:49 AM
Was your APFC reading at 15 degrees when it was out of timing?

Yes it was reading 15 degrees. At cold start it still hesitates but ill let a tuner take a look

Edit: Well its actually not fixed lmao. Im actually done. Made an appointment with a tuner nearby and ill let him sort it out