The pain of it all.

Discussion in 'Technical' started by beaver, May 3, 2019.

  1. beaver

    beaver southern zeds

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    Here’s the problem.. My car has a slight missfire at idle. When the engine is first started from cold, it runs smoothly, no missfire, as it warms up it develops a missfire that practically disappears when fully warmed up @79c, although it is still there, it’s just a pop every now and then. I’ve heard other zeds doing the same at warm idle.. I asked questions, but the reply’s are the same.. cant find it, not sure.

    When my engine is free revved say to 2500rpm or held at a constant rpm, a slight missfire returns. The rpm drop to idle is also slow, when the car comes to a stop, any stop, foot of the throttle clutch in, the engine will high idle @ 900-950rpm before gradually returning normal idle 750-800 takes about 4-5 seconds, really annoying.

    When I accelerate the car in gear under hard or normal throttle, there is no missfire that I can here or feel, or see, on a logged graph.. consult datascan nistune. My first thoughts were Vacuum leak, so I started checking the normal things, did a BLT, found a tiny leak at one off the recirculation valves fixed that, started the engine same thing. Checked all the injectors the coil packs the spark plugs NGK PFR6B-11B which are new and gapped to 0.035" and firing. Moved onto the IACV, and air reg, no problems there either.. I should say that the air reg and the IACV have been internally (everything was dismantled including the air reg) cleaned to within an inch of there lives, and reinstalled with no change to idle.

    I new the Iacv and the air reg were good in the first place, because I could see both operating normally with consult, aac sits on 30% when up to temp, and can be manipulated up or down and make a difference using the program. I have twin maf’s selin setup, both mafs are Nissan ome and good, the tps is set at .46v and is also good. The engine is 3000 odd ks old from a top and bottom rebuild by joe imbesi, and is strong. So I pulled the plenum checked for any leaks round the gasket, nothing. Pulled the rails took them to asnew injector cleaning all good, checked all the vacuum lines while I was in there again, when it was back together I propaned tested the lot, nothing I could find sucked or leaked.

    Interestingly the stock boost gauge needle, at idle, sits pegged hard left, and the greedy controller shows vacuum at -99 which is as good as it gets.. So in reality I could possibly have saved myself the time of pulling most of the top of the engine apart and taken notice of the readings, but I had to be sure. So next I decided to do a compression test, and have as look at the bores with a endoscope.Warm Comp test showed even compression among the 6 pots varying by only a 4 psi peak was 180, the bores looked normal, piston tops were clean no burns, the battery was a little flat, so only one comp test was done.

    Did a vacuum test on the engine from the balance tube to get both sides, 20.5-21hg at idle, there was a tiny fast movement of .5hg @ idle smoothed out with any amount of throttle, I put this down to slight wear of the valve guides.

    The last thing I tried was the throttle bodies, they are pretty much set in perfect synchronization, and dialed in as per the manual. The tune I have is from czp by jim wolf for 16-18psi.

    So there you have it, another frustrated zedder.
     
  2. Blue300

    Blue300 New Member

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    Hi.

    I can understand your frustration. Maybe check over all your earth lines, make sure they are clean free of corrosion and have a good connection.

    Im doing a similar build and have had problem after problem tearing my hair out but alot of the time it was due to a poor earth connection causing extra resistance so that all the efi switches and sensors weren't getting their required voltage to work properly making them disfunction
     
  3. Martin Williams

    Martin Williams Well-Known Member

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    Have you got a spare PTU, try that. Any good tuning shop should be able to pinpoint whats causing this slight misfire.
     
  4. beaver

    beaver southern zeds

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    Thanks Blue, I look into that, although I've tried to make sure that all the earths to the engine are in place and cleaned I'll look again cant hurt.
    I added an extra heavy earth cable from the fire wall to the engine years ago, when those earthing kits were around. As far as I no,the earths from the main engine harness plugs/connectors.. such as injectors cas coil packs tps ect all seem to verify the earths are good.
     
  5. beaver

    beaver southern zeds

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    Yes Martin I swapped out a s2 ptu for another new s2 ptu, and it made no difference.
     
  6. beaver

    beaver southern zeds

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    I also brought another second hand air reg and IACV complete unit, cleaned that up internally made sure it was ohming correctly, put that on, and it made no difference also. The engine from cold start ran without missing until the air reg started to close, as I watched the aac % rise from 15% say to 20% the engine would miss slightly until warm idle 79c and then you could hear only a small pop or really slight stumble, with the aac @30%.
     
  7. East Coast Z

    East Coast Z Well-Known Member

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    A misfire will show on a scope whether it be ignition, fuel or mechanically related.
    Generally, Datascan, ConZult etc. aren't fast enough to "catch" them.
     
  8. beaver

    beaver southern zeds

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    Agree, but I dont have a scope, all I have is nistune data scan consult, and really when you compare logged graphs between these programs,
    generally they vary, sometimes substantially. Handy tools but limited.
     
  9. East Coast Z

    East Coast Z Well-Known Member

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    Not everyone has access to a scope.
    However, if you want to save time & rectify the problem, find someone who does.
     
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  10. THZX

    THZX Member

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    Engine is not fully warmed up at 79 degrees. There is still a couple of advancements/enrichments that don't reduce until 80 degrees eg After Start Timing Adv is 5 degrees at 79 zero at 80.

    A low temp thermostat can contribute to issues with ECU settings.

    K Constant will be an estimate with a JWT chip if you have larger injectors. A wideband or dyno will be necessary to achieve accurate AFR's.
     
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  11. beaver

    beaver southern zeds

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    At 2000 rpm, there are 10ms between ignition/fueling events, It took a long time to catch on that this was there. Its extremely fast... the cars electrical system goes from the normal 12V to as high as 300V in about 20 nanoseconds.

    Jim selin talking about Chinese hid ballasts causing radiated EMI/RFI idle issues or stalling . Not my problem although I have one the first of the translators, and yes it caused my engine to missfire when I first turned the hids on.. since that first event, turning the hids on dose nothing, no misfiring at all. The point is events happening nanoseconds or ms are extremely slippery, and even with a scope he had a hard time finding the connection between the crap ballasts radiating EMI/RFI waves causing the translator to stop momentarily then reset, causing the idle issues.
     
  12. zx299

    zx299 Well-Known Member

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    I agree with THZX, the JWT chip is a 'one size fits all' type of tune ........ really 'old school' and only provides 'ballpark' numbers for your K values & latency.

    If you're throwing too much fuel in, it will show up at idle and not at WOT

    I would suggest using a WB to check out your AFR's, because EVERY tuned chip I have ever come across has dumped way more fuel in than was necessary
     
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  13. beaver

    beaver southern zeds

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    Thanks THZX zx299, well Tony you did say the missfire could be the tune itself.
     
  14. THZX

    THZX Member

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  15. THZX

    THZX Member

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    You mentioned that there is occasional pop after warming up which suggests unburnt fuel. If issues have been evident after installation of JWT chip it's definitely worth focusing on the tune. Assume O2's are functioning correctly ,as mentioned by zx299 latency also needs to be adjusted to injector size.
     
  16. beaver

    beaver southern zeds

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    The o2's are working properly, I pointed out the issue(missfire) at your place when I came to pickup the steering wheel, I'm not sure if you could hear it all that well, because the exhaust was two feet away from a retaining wall, listing at the front of the car, like we were then.. its hard to here. I going to give you a call at some stage soon, if you dont mind..
     
  17. zx299

    zx299 Well-Known Member

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    Idle is open loop, so O2's are being ignored anyway. If you are running rich at idle, it will be either your K value or latency (or both). Running rich at higher revs is not noticeable because you just throw any excess fuel out the exhaust
     
  18. beaver

    beaver southern zeds

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    k-value is $c3 (dec-195) injector flow is 598cc estimated... injectors are nismo 615...
     
  19. THZX

    THZX Member

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    Incorrect. Idle/cruising is in closed loop
     
  20. THZX

    THZX Member

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    Aha .
    K value should be approx 178 if injectors have been flow tested at 598cc. 195 would contribute to rich AFR.
     

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