Engine "hiccups" while cruising

  • #1

    Engine "hiccups" while cruising

    I'm sure some of you saw me mention that I was having issues with my old ECU (an 84T with Nistune). I replaced it this past weekend with an 87T ECU with a new Nistune board. After replacing it we more or less had to retune the car as almost nothing was able to port over from my old tune, I guess due to address file differences. We got that handled without much trouble, my tune isn't terribly far off a stock tune. It runs great for the most part, good AFRs in boost, pulls smoothly, etc. The issue I'm having is the car will "hiccup" from time to time. We were watching AFRs and apparently it is randomly spiking really rich, which makes the car lose a bunch of power for a second. Can't find any obvious reason why. Any ideas on where to start looking? My first suspect would be something in the ECU or tune, as that is the only big thing that changed.
    Prius… because Pretentious wouldn't fit across the back of the car…

    Cheap, Fast, Reliable - pick any two

    My 1986 Turbo Build
  • #2
    Are you running an O2? Maybe that is acting up since it is only occurring during cruise.
    2007 Nissan 350Z Base: 13.476 @ 103.870 MPH

    1988 Nissan 300ZX Shiro Special New Setup [email protected] MPH
  • #3
    No o2 operation or one installed. it's been nulled in Nistune as well, setting the activation out of normal range.
    Damn dirty angels....these cars!

    Current Daily Driver - 86 Turbo.
    Under the cover - THE BANANA… that needs to be re-energized.
    sigpic
  • #4
    I also can't find any reason for when it does it. Will be cruising along and it kinda bumps once, then will do it again a few minutes later. RPM doesn't matter, will do it when cruising along in 4th rather than 5th, though it isn't as noticeable at higher rpm. Kinda makes me wonder if it's isn't losing spark momentarily or something.
    Prius… because Pretentious wouldn't fit across the back of the car…

    Cheap, Fast, Reliable - pick any two

    My 1986 Turbo Build
  • #5
    Mine used to do that. It was really noticeable in lower gears trying to hold a constant speed. As much as I'd like to blame Nistune, it also did it with my JWT prom, just not quite as severe. It might be an ecu issue.
    2007 Nissan 350Z Base: 13.476 @ 103.870 MPH

    1988 Nissan 300ZX Shiro Special New Setup [email protected] MPH
  • #6
    That would suck, as I just bought this ECU and got Nistune installed on it.
    Prius… because Pretentious wouldn't fit across the back of the car…

    Cheap, Fast, Reliable - pick any two

    My 1986 Turbo Build
  • #7
    Confirm it isn't something mechanical. … leaking injector or something.
    http://z31performance.com/showthread…2-2-(-now-NA2T
    My build thread (:
  • #8
    Momentary spikes to rich indicate ignition misfire. I would suspenct coil, transistor, or CAS/distributor assembly. Does the dizzy have good bearings in it with no wobble or up/down shaft movement?

    1986 300ZX Turbo…sold
    1990 Skyline GT-R…new money pit
    2014 Juke Nismo RS 6-speed…daily
  • #9
    It is running a PRW-2, and RSB-07 CAS.
    Damn dirty angels....these cars!

    Current Daily Driver - 86 Turbo.
    Under the cover - THE BANANA… that needs to be re-energized.
    sigpic
  • #10
    I'll have to check the distributor. As far as I know it's the factory original coil. A new one is like $20 on Rock, so I may go ahead and order one. Anyone have a preferred brand? I did swap the dizzy to a backup I had prior to replacing the ECU, and it didn't get driven all that much after. Since I didn't have these issues before I could also look at swapping that back.
    Prius… because Pretentious wouldn't fit across the back of the car…

    Cheap, Fast, Reliable - pick any two

    My 1986 Turbo Build
  • #11
    Swapped the dizzy and the coil, no change at all. It's also hesitating and stuttering now as it gets into boost. I'm suspecting something tune related as if you watch the logs, as soon as it starts having issues you can see the injector timing start flopping back and forth from 5ms to 10ms. There is also a spike in injector timing every time the car hiccups while cruising. I've posted about this on the Nistune forums but haven't gotten any feedback yet.

    You can see what I'm talking about in the attached image. This is a 3rd gear pull.

    Capture2.jpg
    Prius… because Pretentious wouldn't fit across the back of the car…

    Cheap, Fast, Reliable - pick any two

    My 1986 Turbo Build
  • #12
    Checked the spark plugs recently?

    1986 300ZX Turbo…sold
    1990 Skyline GT-R…new money pit
    2014 Juke Nismo RS 6-speed…daily
  • #13
    Originally posted by NissanEgg View Post
    Checked the spark plugs recently?
    In terms of time, no, but miles yes. They were fine when we installed them when I put on the OWO heads. That wasn't more than a couple thousand miles ago, if that.

    It runs great outside of these issues. Comes off the line fine. If you give it half throttle so the boost doesn't get too high it will rev all the way through to redline. Under normal driving it accelerates smoothly. It just randomly "hiccups" while crusing, and does this stupid stutter/hesitation when boost gets much past stock levels.
    Prius… because Pretentious wouldn't fit across the back of the car…

    Cheap, Fast, Reliable - pick any two

    My 1986 Turbo Build
  • #14
    My hesitation in boost was a slightly damaged spark plug. One of the electrode tips was partially missing.

    1986 300ZX Turbo…sold
    1990 Skyline GT-R…new money pit
    2014 Juke Nismo RS 6-speed…daily
  • #15
    Ok, I'll take a look at them.
    Prius… because Pretentious wouldn't fit across the back of the car…

    Cheap, Fast, Reliable - pick any two

    My 1986 Turbo Build