SR20 loses power in boost, but not all the time - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

rpierce · 04-06-2014, 04:59 PM

I'm having a weird problem with my redtop SR. It seems like it loses power under boost every once in a while, usually after i drive it for a long time and it gets warm. It still builds to full boost but it feels like it's going nowhere. It doesn't cut out violently or anything but if I let off the pedal and go out of boost I can feel it get it's power back.

Sometimes it'll go away for a few days entirely and the car runs great then it'll come back, which is making me think i keep fixing it, just to be sorely disappointed the next day.

As a reference I'm on stock redtop everything with an FMIC, Isis fuel pump, Z32 fuel filter.
-I borrowed good coilpacks from a friend and switched those around but it didn't fix my problem.
-Boost leak tested from hotpipe to intake manifold and didn't find any leaks
-Tried spark plugs at both .028 and .032 gap
ECU is throwing no codes (AKA code 55)
I've done other things I can't remember at the moment too.

I'm starting to run out of ideas. I'm thinking at this point borrow an ignitor from my friend and change temp sensor and maybe knock sensor.

Has anyone here had a similar experience or have any advice? Thanks in advance.

coupesallday! · 04-06-2014, 05:14 PM

Mine is doing the same damn thing. It also stalls when I'm in neutral after I drive for awhile. Can't figure it out it's really annoying.

Kingtal0n · 04-06-2014, 07:25 PM

its normal behavior for the old engines. the turbine/compressor on the T-25 is too small. either upgrade your turbocharger (even just a T-28 will help) or live with it.

Those engines are not intended for our climate or gasoline.

On the other hand, water/methanol injection would probably help. A real intercooler might also help (but no guarantee).
A literally COLD air intake (an intake pipe that pulls air from outside the engine bay) might help.

Annnd last, sometimes you can blame the ancient knock sensor. You COULD try changing the knock sensor.
What I used to do is, disconnect the turbine for long distance driving. It will help keep it cool, prevent from heat soaking everything under the hood, and causing you to go nowhere.

rpierce · 04-06-2014, 08:52 PM

Well that's what confuses me. It HAS happened a time or two when the car was pretty cold but usually happens when it's warm. (it's also been between 30-50 degrees for as long as I've been driving it so it's cold as shit outside). The knock sensor that's on it is practically new but isn't the OEM one, it's aftermarket. I don't think it's just a problem of blowing hot air. I also forgot to mention I run 93 octane.

Even when this problem arises it still idles great and runs fine out of boost. It's like boost is just a switch to fuck my shit up. As soon as I put my foot down it takes a dump.

sterlinge · 04-06-2014, 09:05 PM

Have you checked your fuel pressure when this happens? iacv working properly? How old is the fuel filter? Could even be sediment in the gas tank.

Kingtal0n · 04-06-2014, 09:26 PM

you are saying the problem occurs when it is COLD outside? 50*F?

SO just to be clear, it builds boost but it feels like you are applying the brake at the same time right?

I've only had that happen when the air intake temperature goes over about 140*F and always atrributed it to the ECU pulling timing because the hot air, combined with our shitty 10% ethanol 93 octane, was tipping off the knock sensor.

Usually I let the car cool off a bit and the problem goes away.

You can verify if it in fact the knock sensor by installing a resistor in place of the sensor temporarily. I will warn you, however, if indeed the knock sensor is pulling timing and causing this... problem... it is in fact doing you a favor!

I'd be interested to find out if the problem is NOT related to the knock sensor of course. That might point towards... yeah the fuel pump. Or other related aspects.
I never tried the resistor because I was more concerned with longevity of the engine than "where did my power go 6% of the time"

rpierce · 04-06-2014, 11:16 PM

Yes, that's exactly what it feels like. It makes a bunch of noise and builds boost but feels like the brake is on. The problem occurs pretty randomly, it just hasn't gotten much over the 50's yet in Ohio. It happened friday when it was about 40 degrees outside and when the car didn't even really have time to warm up. When I was pulling over to swap the coilpacks the coldpipe wasn't really warm so I can't see the intake temperature being super high like that.

I've counted out coilpacks unless I have more than 2 of them that are bad, but my coilpack harness does look like hell.

I wouldn't be surprised if the chinese isis walbro copy was the problem, I just want to eliminate the cheap parts before I spend around $100 on another fuel pump.

I have a bung for a wideband so I'm going to try to borrow one from a friend and see what it says when the problem pops up if that'll make diagnosing the problem any easier.

rpierce · 08-15-2014, 09:59 AM

Woops, forgot to post when I fixed it a few days after this post.

Turns out it was the knock sensor. I had 2 but I decided to install the brand new looking chinese replacement knock sensor instead of my used nissan oem knock sensor. Neither had any cracks or damage but some of the replacement ones are absolute garbage I guess.

04-06-2014, 04:59 PM	#1
rpierce Zilvia Member Join Date: May 2011 Location: Beavercreek, Ohio Posts: 241 Trader Rating: (14) Feedback Score: 14 reviews	SR20 loses power in boost, but not all the time I'm having a weird problem with my redtop SR. It seems like it loses power under boost every once in a while, usually after i drive it for a long time and it gets warm. It still builds to full boost but it feels like it's going nowhere. It doesn't cut out violently or anything but if I let off the pedal and go out of boost I can feel it get it's power back. Sometimes it'll go away for a few days entirely and the car runs great then it'll come back, which is making me think i keep fixing it, just to be sorely disappointed the next day. As a reference I'm on stock redtop everything with an FMIC, Isis fuel pump, Z32 fuel filter. -I borrowed good coilpacks from a friend and switched those around but it didn't fix my problem. -Boost leak tested from hotpipe to intake manifold and didn't find any leaks -Tried spark plugs at both .028 and .032 gap ECU is throwing no codes (AKA code 55) I've done other things I can't remember at the moment too. I'm starting to run out of ideas. I'm thinking at this point borrow an ignitor from my friend and change temp sensor and maybe knock sensor. Has anyone here had a similar experience or have any advice? Thanks in advance.

04-06-2014, 07:25 PM	#3
Kingtal0n Post Whore! Join Date: Jul 2005 Location: South Florida Age: 42 Posts: 4,829 Trader Rating: (17) Feedback Score: 17 reviews	its normal behavior for the old engines. the turbine/compressor on the T-25 is too small. either upgrade your turbocharger (even just a T-28 will help) or live with it. Those engines are not intended for our climate or gasoline. On the other hand, water/methanol injection would probably help. A real intercooler might also help (but no guarantee). A literally COLD air intake (an intake pipe that pulls air from outside the engine bay) might help. Annnd last, sometimes you can blame the ancient knock sensor. You COULD try changing the knock sensor. What I used to do is, disconnect the turbine for long distance driving. It will help keep it cool, prevent from heat soaking everything under the hood, and causing you to go nowhere. __________________ 5.3/4l80e/turbo 240sx playthrough: tinyurl.com/4l80er

04-06-2014, 09:26 PM	#6
Kingtal0n Post Whore! Join Date: Jul 2005 Location: South Florida Age: 42 Posts: 4,829 Trader Rating: (17) Feedback Score: 17 reviews	you are saying the problem occurs when it is COLD outside? 50F? SO just to be clear, it builds boost but it feels like you are applying the brake at the same time right? I've only had that happen when the air intake temperature goes over about 140F and always atrributed it to the ECU pulling timing because the hot air, combined with our shitty 10% ethanol 93 octane, was tipping off the knock sensor. Usually I let the car cool off a bit and the problem goes away. You can verify if it in fact the knock sensor by installing a resistor in place of the sensor temporarily. I will warn you, however, if indeed the knock sensor is pulling timing and causing this... problem... it is in fact doing you a favor! I'd be interested to find out if the problem is NOT related to the knock sensor of course. That might point towards... yeah the fuel pump. Or other related aspects. I never tried the resistor because I was more concerned with longevity of the engine than "where did my power go 6% of the time" __________________ 5.3/4l80e/turbo 240sx playthrough: tinyurl.com/4l80er

04-06-2014, 08:52 PM	#4
rpierce Zilvia Member Join Date: May 2011 Location: Beavercreek, Ohio Posts: 241 Trader Rating: (14) Feedback Score: 14 reviews	Well that's what confuses me. It HAS happened a time or two when the car was pretty cold but usually happens when it's warm. (it's also been between 30-50 degrees for as long as I've been driving it so it's cold as shit outside). The knock sensor that's on it is practically new but isn't the OEM one, it's aftermarket. I don't think it's just a problem of blowing hot air. I also forgot to mention I run 93 octane. Even when this problem arises it still idles great and runs fine out of boost. It's like boost is just a switch to fuck my shit up. As soon as I put my foot down it takes a dump.

04-06-2014, 09:05 PM	#5
sterlinge Zilvia Addict Join Date: Apr 2008 Location: Austin, TX Age: 35 Posts: 857 Trader Rating: (15) Feedback Score: 15 reviews	Have you checked your fuel pressure when this happens? iacv working properly? How old is the fuel filter? Could even be sediment in the gas tank.

04-06-2014, 11:16 PM	#7
rpierce Zilvia Member Join Date: May 2011 Location: Beavercreek, Ohio Posts: 241 Trader Rating: (14) Feedback Score: 14 reviews	Yes, that's exactly what it feels like. It makes a bunch of noise and builds boost but feels like the brake is on. The problem occurs pretty randomly, it just hasn't gotten much over the 50's yet in Ohio. It happened friday when it was about 40 degrees outside and when the car didn't even really have time to warm up. When I was pulling over to swap the coilpacks the coldpipe wasn't really warm so I can't see the intake temperature being super high like that. I've counted out coilpacks unless I have more than 2 of them that are bad, but my coilpack harness does look like hell. I wouldn't be surprised if the chinese isis walbro copy was the problem, I just want to eliminate the cheap parts before I spend around $100 on another fuel pump. I have a bung for a wideband so I'm going to try to borrow one from a friend and see what it says when the problem pops up if that'll make diagnosing the problem any easier.

08-15-2014, 09:59 AM	#8
rpierce Zilvia Member Join Date: May 2011 Location: Beavercreek, Ohio Posts: 241 Trader Rating: (14) Feedback Score: 14 reviews	Woops, forgot to post when I fixed it a few days after this post. Turns out it was the knock sensor. I had 2 but I decided to install the brand new looking chinese replacement knock sensor instead of my used nissan oem knock sensor. Neither had any cracks or damage but some of the replacement ones are absolute garbage I guess.