TunerMax

iTrader: (2)

2003.5 G35 Sedan 6MT
120,000 miles

I've had an intermittent Misfire for while, since I bought the car. Because it was near impossible to track down the culprit, I never really bothered with it.
It was only notable as a minute little hicup in the exhaust at idle for the longest time, and not all the time.

One day recently it just started getting rough, missing hard on the highway, sounded like knocking so i pulled over and inspected what I could, then started it back up, no more issue. Strange? Yes.
After this I finally got the first code, the Random misfire (0300 I think?). Kind of a useless code, I already knew that !!!

It does this off and on randomly, but has been doing it more frequently, it's been cold lately, if that matters, dunno.
I also have very recently developed what MAY be an unrelated issue since installing my Walbro 255 and IsoThermal Spacer kit this weekend, where the engine seems to cut out completely (seems like a fuel cut) intermittently. this issue is also fixing it self, as in, it did it HORRIBLE yesterday and I limped it home, and today I'm stuck driving it, and it didn't do it once on the 15 mile drive in to work, but did misfire/hiccup frequently.

Here's what I've done/Eliminated:

- Coil packs are ON THE WAY, not yet replaced. All have been visually inspected
-Spark plugs are mint, I though this odd, figured I'd have one at least a bit fouled, but nope. They're less than 10,000 miles old, OEM, and are gapped perfectly
-Added/cleaned all grounds, including Injector grounds.
-Reprogrammed TPS close position manually
-Checked for vacuum leaks - Good

Also, my Fuel trims are all over the map, but are definately wacked. STFT has been from 20-25% + and 20% -
LTFT has been from 0% to 25% +

I'm running short on ideas... No codes... The only thing I can think of is a possible Manifold leak/crack but I have no idea how to check that without simply pulling the motor...?

Sorry for the long post, trying to be specific, any ideas where to go here boys? TIA

TunerMax

iTrader: (2)

Also mods are fairly slim right now:

FI Resonated Test Pipes
Custom temporary SRI with Z tube (Waiting for Supercharger)
Oil pressure & temp sensors installed, haven't hooked up gauges, will if needed to diagnose
AFR and Boost gauges - same story, installed but gauges not hooked up
ISOTHERMAL 5/16" Spacer kit (Throttle body, LIM, UIM)

I'm also questioning the TPS, but doubt it would cause a misfire, it would be more likely to cause the Fuel cut/bucking issue that has just come up though, if it's at fault at all.

pro_350z

iTrader: (3)

I had the same problem minus the fuel cut. It was a coil pack i might have f*cked up upon install.

TunerMax

iTrader: (2)

Well Hopefully the Misfire is coil(s), the OEM replacements are coming soon, so that will eliminate the possibility.

I need to get this running proper so I can hook the haltech up and tune the bish. I can't tune it running like this, obviously. That said, I HAVE hooked the Haltech up and get lean AFR's and sporatic readings because of these issues, so I'm half-way thinking the ECU is probably OK. BUT the Haltech runs as a Piggyback, so I don't know for sure.

TunerMax

iTrader: (2)

Update 09/11/2012:

Brand new OEM coils installed - no change
Brand new MAFS Connector replaced (Properly done) due to exposed wire found right at connector - no change
Clean MAFS - no change

The car right now will stall no a cold start unless I rev it up for a bit, once it's warmed a bit I can leave it alone and it will idle very rough, but stay running.

Fuel Trims on the past few tests have been strange:
LTFT is at 0%, it will not change.
STFT is pegged at +25% pretty much constantly

ALSO my Primary O2 sensors are now reading .020-.030 Volts, they don't change like they should be.

The Scantool I'm using is reading that the car IS IN CLOSED LOOP during this time, and I'm not getting ANY codes other than a P0300 (random miss) that is pending after initial start up before it warms a bit and the engine calms down.

Does any of the above throw up any flags for anyone? It's almost like LTFT is in OPEN loop but the STFT is in CLOSED loop...

I don't have an AFR Gauge handy as I sent mine off for repair, but I hope to get my Fuel pressure adapter in shortly so I can see what on earth it's doing! That's my next step, may as well hold off on taking it to the dealer until I get FP checked...

0jiggy0

iTrader: (13)

Sounds like a intake leak. Correct me if I'm wrong but your st and lt fuel trims are hitting +25? Maybe a mess up on the isothermal install, maybe a cracked vaccuum line. I'm leaning to the gasket because once the engine is warm it squezes down on the gasket a bit and closes the hole more.

Neimad

How did you check for vacuum leaks?

TunerMax

iTrader: (2)

I used carb cleaner, I've used Propane, I've also blown into the intake and it's sealed up until the throttle is overpowered from pressure and pops open. I even had my old man blow cigar smoke in there and nothing.

The carb cleaner and propane yielded no results that were notable, as the engine is running rough, but I monitored Trims during that time and nothing really notable changed.

And "0jiggy0" My LTFT are 'frozen' at 0%, they seem to be cut off, not locking in any LTFT. The only trims that are working right now is the STFT and they're pegged at 25%

Neimad

Did the O2's go full rich when you introduced the propane?

Might need to backprobe the O2's and see if the voltage is same as what ECM is seeing.

TunerMax

iTrader: (2)

Thanks for the great responses and ideas guys. I'm not fully satisfied with the vacuum tests to be honest, but that may be because this is the first car I've done it on and don't really know what to expect as a result, other than stalling from a bad leak when spraying.

I did monitor the trims during the check and didn't note anything specific, though I admit it was hard to tell because the STFT's were fairly sporadic due to the misfire.

As things sit now the test would be pointless because the STFT's are already pegged at +25%, right?

bender

iTrader: (3)

Did you try replacing the Mass Air Flow Sensor completely instead of just cleaning it?

I had a similar situation as yourself. Random misfire code which was hard to get the in the first place. Car would occasionally misfire on start up while idling, but got worse. Cleaned the MAF, the throttle body, replaced plugs, and checked for vacuum leaks. In the end I ended up replacing the sensor altogether and the problem disappeared.

NA&CH

iTrader: (74)

I am having a momentum kit installed and whent the guys went to start it up it had a misfire. They checked everything and it went to the injector harness. There was nothing going to the 4th and 5th injector.

Just a thought.

Chris

TunerMax

iTrader: (2)

Thanks very much dude! i haven't replaced it, no. I thought is try running the haltech first as it doesn't use the mafs, and once ready this car will be running without the mafs.... Would be sweet if that's what it is!.


I've questioned this also, dyou have any more info on location or parts replaced? Maybe just injector pigtails? Sick info thanks guys, good ideas/experiences, helps a ton!

bender

iTrader: (3)

If you're looking for a sensor, there's a guy on ebay out of Montreal who sells them for $175. They are new genuine OEM Hitachi in a Nissan box. Took me three days to receive it within the Toronto area. By far the cheapest I could find.

TunerMax

iTrader: (2)

That's sick! Thanks dude pm me the contact info if you can. I may find another local who will swap with me for testing too, that would be a great diagnostic test, popping a known good one in

NA&CH

iTrader: (74)

Ill ask SOHO for you.

Chris

TunerMax

iTrader: (2)

Thanks dude, look forward to the result. I'm going to call Nissan tomorrow and see if they can get the injector harness separate from the main harness, but I suspect it's all one unit.

I have no qualms soldering in a new string of wires, but without knowing where the issue is in the wiring it would be pointless/expensive.

TunerMax

iTrader: (2)

A couple updates, car has been parked for winter and is on blocks, it's been cold, but I have tried just a couple things:

1. Replaced the MAF plug completely due to one wire that had the sheilding off it. No difference.

2. Finally installed a Fuel Pressure gauge adapter. Fuel pressure is steady at 58 PSI.
Spec is 51 PSI, I consulted Charles at CJM and he said as long as it's steady, and doesn't change at higher RPM, I should be fine. Either way, fuel pressure is NOT the cause of this, it's solid with no fluctuations.

3. After running it to check the fuel pressure for a minute or two, the car started running fine.
This is a TOTAL guess, but I wiggled the wiring at the back where the injector harness goes in trying to get it to mess up again and I couldn't.

I think, given the tests, I'd like to replace the Injector plugs, and possibly the wiring while I'm in there, I'll be stripping and checking it either way.
I could only find them online, which sucks, I'd like to get them locally.

I'll also be hooking the haltech up to see what happens. And I might swap in the GTR injectors in case I simply have one or more crappy injectors causing this problem. But at that point I am stuck with the Haltech running things, which is why I haven't put them in yet.

boostintt

iTrader: (65)

having a very similar problem with my z.

so far:

replaced o2 sensors bank 2
cleaned MAF
checked for leaks (sprayed carb cleaner around plenum. no change in RPM)

the misfire is intermittent. mostly during WOT and when it idles it goes from misfire (around 900rpms) to working fine (1000rpms)

i thought changing the o2 sensors would do it.. i even reset the ecu and cleared all codes.

any help would be appreciated it..

boostintt

iTrader: (65)

i took out all 6 injectors in search of the "black" one which would indicate a faulty leaky injector.. they all look very similar to me.. and the tips all look white. can anyone confirm this? or is anyone able to see the faulty one?