MotaBike Mike

Hey guys and gals. So here's to scoop on a strange problem I have been trying to track down.

Car 2007 350z HR
Stock Engine aside from a Greddy Cat back
Light weight fly wheel and aftermarket clutch
Everything else stock other than suspension mods.

The problem: So we changed the spark plugs on this car without unplugging the throttle bodies, we simply removed the from the intake and set them aside. We did clean the butterfly valve surfaces without opening them. Car ran fine for one and a half drift days with no issues. Then about half way through the second day we noticed a little hesitation in second gear while full throttle andn this has since progressively gotten worse. Now the car surges/bucks violently under wide open throttle or 3/4 throttle, all the way from idle to redline. It bucks so violently that it feels like you are engaging the clutch and disengaging it rapidly as you accelerate. Think of someone learning the drive a manual only at full throttle, and we're obviously not pumping the clutch while we're accelerating.Car only does this in 1st and 2nd gear. However you can run all the way to redline with no issues at all at 1/2 throttle, driving it around normally you wouldn't notice the problem until you accelerated hard.

Steps Taken so Far: Checked for any pending codes on the ecu and came up with nothing. No MIL light on either. It felt like a fueling issue and with no codes present we changed the fuel pump out with a factory Nissan unit. No change. We swapped cam position sensors, crank position sensor, and MAF's from a running car with no change. Also decided to give changing the fuel pressure dampers a try since they were cheap and available, so those were replaced with new units. No Change. We also cleaned the grounds associated with the accelerator position system and throttle bodies as per the FSM. We also re-leared the accelerator position sensor, and the the throttle bodies, making sure that all the parameters set in the FSM were met before relearning the throttle bodies.

I did some searching around here and only saw a few issues about idling and surging, but nothing quite like this. If anyone has had any experiences with something similar and fixed it I'll take all the help I can get.

Thanks for Looking,
Mike

bealljk

iTrader: (13)

10,000% sure you connected the ignition coils back correctly? not sure how misleading the HR ignition coil connectors are (compared to the DE). Have you investigated coil packs? Any way to get a few 'known good' coil packs and swap them in?

although unlikely, any thoughts on swapping in a new set of spark plugs in and/or swapping your old set back into the car?

Why did you do a spark plug change in the first place?

Can you trouble shoot your injectors? possibly swap a known good set in - probably not the cause but do check every box?

what are you tuning with?

MotaBike Mike

I'm fairly certain the coils are back in the right positions, as the car runs perfectly other than WOT in first and second gear. The coil packs on the HR pretty much are only long enough to go back where you pulled them from. We could pull the injectors from my running car to swap onto to this one, (my friends), though that means pulling the plenum at least I believe. I'll have to look to be certain, either way that means replacing intake gaskets on both cars just for a test that may or may not give any clues. Also I it feels like its dropping all power not just on one or two cylinders, so that leads me away from injectors as well, as it would be very odd to lose all the injectors at once. That's the only reason we haven't swapped those yet. Not opposed to looking at the coils, although I would think the ECM would be picking up at misfire and throw a code. I have no idea why they changed the plugs. I guess for preventative maintenance? Car has roughly 130k on the clock. Definitely replaced with the factory Nissan Denso iridium plugs. Also no tuning on the car, just simply scanning the factory ECU with an Autel scan tool. We've looked at the timing while WOT which seems to be normal, also O2 sensors are switching as they should be, accelerator position sensor voltage is within the specified range. It almost feels like you're literally lifting off throttle and then going back full throttle every second or so, makes me think throttle bodies or something.

bealljk

iTrader: (13)

I'm far from an expert on either the HR or DE ... but may people mix-up cylinder #4 and cylinder #6 and the car runs, rough albeit, even with them mixed up. Most people dont run the car past 2k to 3k rpm ... If it was me, I'd check your FSM and check continuity between your coils ... it's essentially free.

At this point (IMO) you have to check everything - long and short. Coils / misfiring would probably flip a CE, yes.

You have to replace the intake gasket every time you take the plenum/intake off? I dont know if I've ever replaced the intake / plenum gaskets?

I ask about tuning bc some standalones will test-fire your coils and injectors...

Anyway you can swap TBs?

MotaBike Mike

Yeah I'll look into the coils and ohm them just to rule them out. Swapping TBs is doable, but from what I hear these HR's are very finicky about their throttles, so I'm a tad hesitant about removing my working ones! I'll exhaust all other options and then I guess we'll cross that bridge when we get there. Yeah I've run this car all the way up to 7000 rpm at half throttle and it revs all the way with no issues. So weird.

MotaBike Mike

Ok guys, we figured it out. So still boggles my mind that the car never threw a SEL or any pending codes at all. We reset everything with the scan tool, Idle air volume, throttle body position, exhaust valve time actuators, everything with no change. However, while we had the scan tool hooked up we decided to increase the injector open time by 25% and that solved the problem, but obviously the car ran pig rich everywhere except on WOT. So we made sure we hadn't hit any fuel lines with a cone and pinched them just to rule out a low fuel volume issue, since we had good pressure at the lines. Found nothing in the way of a pinched fuel line. We decided that we needed to go back and recheck all the stuff that had been done previously just to make sure that the coils were all plugged in properly and we didn't have any broken plugs or anything from the install. As we were taking the intake boots off we noticed the driver side had a tear on the underside. Probably from forcing it back in or out when doing the spark plugs earlier. Then as the engine would torque over under heavy load it would pry the boot apart and lean out bank 2. Which is why adding 25% duty cycle to the injectors was masking the problem it was basically preloading the fuel mixture so the problem when away when adding fuel. So we taped up the driver intake boot as a temporary fix and went for a rip. Car ran perfectly. So if you changed something on a car and then it starts running badly, 9 times out of 10 it's your fault, so always just go back and check it, you'll save yourself from pulling your hair out! Thanks for the input @bealljk !

bealljk

iTrader: (13)

what do you mean the intake boot? like the coupler between the TB and the charge pipe?

not true … 10 out of 10 times it's my fault!! But the flip side, when everything goes right, 10 out of 10 times its bc of me!

Happy it all worked out!

MotaBike Mike

Correct the rubber coupler between the TB and the MAF. It tore in the flex section of that coupler on the bottom side I even wiggled them and then ran my hands around the bottom but never took them off. What ya gonna do? At least it's fixed!

iideadeyeii

iTrader: (6)

I know your pain. I spend an hour and a half trying to diagnose a blinker problem on my Audi this weekend. . . ended up being a fuse..there's 3 fuses associated with the blinkers and I only checked 2 of them.