SR20DET going into limp mode / erratic timing

[sil80alive]

Hello, I'm wondering if anyone here can tell whats going on with my car based on this 2nd gear pull I logged:

http://www.resonatedesign.ca/2nd_gear_pull.xls

The car is a '91 180sx, stock SR20DET, 3" turbo back, hard intake pipe, walbro 190, running 12 psi. It ran great with this setup for 3 years until recently.

As you can see from the log, right around 2500rpm the timing starts getting pulled erratically, then at 3000rpm it retards to a solid 8 degrees, and feels slow. I've also noticed I smell gas / unburnt fuel in my exhaust after doing a WOT pull. Once in a while i will also get ignition break up / miss during full throttle, but i don't think that is related to the limp mode / timing pull.

It also feels better under half throttle, or progressive throttle. When I go WOT before 4000 rpm it just bogs. Very frustrating, I've already checked/replaced the following:

- new plugs, NGK BKR7E-11, gapped to .8mm
- new(ish) coilpacks, new coilpack harness
- new 300zx TT fuel filter
- checked TPS voltage, appears to be good (reflected in the log too)
- MAF voltage appears to be alright, i haven't tried cleaning it yet
- no boost leaks
- vacuum is at 19 in/Hg at idle, idles great
- checked for codes, 55, no codes.

Any suggestions? Thanks in advance!


----------
Aaron
91 sil80

[slider2828]

What is .8mm? Supposed to be .030 or soemthing that... Is that Close?

Sounds like a faulty knock sensor though... change and try it...

[sil80alive]

thats what a guy suggested on freshalloy, his symptoms were identical to mine. and yes .8mm = 0.031 inches

i'll give it a shot and post the results, thx for the input.

[tt99ol]

go with a slightly smaller plug gap, like .028
clean your maf
to check the knock sensor just disconnect the plug, the ecu only pulls timing if theres input from it but it wont affect driveability if disconnected

[sil80alive]

^ are you sure about that? the ecu does throw a code if its disconnected.. i have a few spare ones i'll try them and report back.

[flip3d]

+1 on knock sensor.

the ecu pulls timing and dumps more fuel when it senses knock.

i'm with tt9ol. go with the smaller plug gap.

and uh.. use 93?

[tt99ol]

yeah im sure
it throws a code to let you know it cant pull timing

[sil80alive]

+1 on knock sensor.

the ecu pulls timing and dumps more fuel when it senses knock.

i'm with tt9ol. go with the smaller plug gap.

and uh.. use 93?

I live in Canada, the highest octane Shell offers is 91. Husky offers 94 with methanol, but I did some research and the Husky 94 isn't all its cracked up to be.

[sil80alive]

UPDATE: took off the maf sensor, one sensor was clean, but one was completely covered in filth. cleaned with contact cleaner. the car already drives much better than it did since doing that, 1500 to 2500 feels normal again spool and rev wise. no hesitation on partial throttle anymore. still not 100%, going to log more, i'll post the results.

[Om1kron]

so yeah knock sensor you check it yet?

[sil80alive]

Not yet, I will as soon as I can. I don't want to just pull it incase I actually am knocking.. I want that timing pull for my piston rings sakes (just incase).

I need to find a used one and swap it in. I'll post results

so yeah knock sensor you check it yet?

[Om1kron]

Not yet, I will as soon as I can. I don't want to just pull it incase I actually am knocking.. I want that timing pull for my piston rings sakes (just incase).

I need to find a used one and swap it in. I'll post results

don't waste your time with that shit, grab a resistor unplug the sub harness and slap the resistor in there, see if it clears the ecu code and if the engine stops running like shit. I just did this, and now i'm no longer running a knock sensor.

1w 1m resistor trick
Simone Video Blog : Knock Sensor Magic on Vimeo (http://www.vimeo.com/5194327)

the verdict.
Simone Video Blog : Knock Sensor Resistor Trick Verdict on Vimeo (http://www.vimeo.com/5195325)

I run poly motor mounts, makes everything erratic and the knock sensors HATE that shit. Causes more vibration, thus timing goes stupid. All my wiring checks out and it throws the code with a knock sensor properly tq'ed down and threw it on a brand new knock sensor.

so nissan, your knock sensor can ead.

[sil80alive]

Ok, I know it's been a while since my last post, I've been unable to work on the car for a while. But I've started again.. so I am starting to suspect that I've just been running stupid lean and knocking (nothing audible though) causing timing to be pulled and fuel dumping. So I put a tiny video camera in my engine bay and recorded my fuel pressure gauge while doing some WOT pulls... the results:

Boost: spikes to 14psi, settles at 12psi
Fuel Pressure: spiked to 50psi, settles to 48psi

So you can see why I'm running lean now - Base fuel pressure is set to 36psi with vacuum connected, so I should be getting more like 57psi peak fuel pressure, and settling to 55psi.

Anyone got an idea why I'm getting good fuel pressure at idle but not at high boost?

[clark]

you have a walbro 190, that's why. swap in a walbro 255.

[slider2828]

What turbo are you running to get 14psi.... wouldnt' run that on any T25 or T28... Bring down to 12PSI and also your injector, unless upgraded at 12PSI its near 100% duty cycle and over 100% at 14PSI.... Measure Fuel pressure at idle without the vacuum in....

[sil80alive]

Well, I swapped in a Nismo fuel pump, and threw another set of injectors on too just incase. Still no dice.

Then I swapped ignitor and and coilpacks. Better now, but the issue hasn't disappeared. Sometimes it will pull hard with no breakup/backfire, and other times it does it alot.

I'm pretty frustrated at this point.. I'm ready to give up on this car..


P.S. I did some logging, the injectors are only seeing 80% duty at 13psi.

[sil80alive]

BTW - I do have a brand new OEM knock sensor, but it's so hard to get at, I don't even want to put it in... anyone know the memory address of the knock sensor on the ecu?

I could log it if I knew!

[tt99ol]

pin 27
that is all