90NA300ZX

I've already been trying to get help on a few local boards, but with no luck...so i'll try the Z boards out...

i already printed up the guide to finding and fixing hesitation problems from TT.net...but it doesnt seem to help me...


my problem HAS to be electrical...it's:

A) only when the car is at temp...not at all on startup does it do this
B) does it randomly...with no pattern...will do it for a day or two, stop for a day or two...or do it for a week, stop for a day, or run great for a month, and then one morning start acting up...


here's what's going on...

The car will lose spark...i put my foot on the gas, and the rev's dont go up...not steadily at least...it looks/feels as if i'm tapping on and off the gas, and this causes the car to buck violently while trying to drive...but i know it's getting fuel...i hear the pump going behind me, smell raw fuel, and every now and then get a nasty backfire (this only happened a couple times) due to the raw fuel not being lit, and just flowing into the exhaust...

at first we were POSITIVE it was my PTU sub-harness...because by playing with the wires on it, and bending them...we got the idle to smooth out while the problem was occuring...so i borrowed a friends, and it worked great. next night, i go to try it again to be sure the problem was fixed, and sure enough it started acting up again as soon as it was warmed up...i pulled over, and for the hell of it, left the friends subharness on, and switched his ptu over too to see if mine was bad...but the problem kept up...so much in fact that i could have my foot wide open throttle and NOTHING would happen...car bogged completely down...at full throttle i barely was able to keep it running...

a few friends suggested it being a ground somewhere...but, i dont understand why or how this could be the case. wouldnt a bad/loose ground cause total power loss? my lights dont dim, fuel pump doesnt quit...everything fine except the spark...(and just for the record, my EFI harness is brand new too)...i'll check the ground under the throttle cable cover just to be safe, and i'll run a few new ones from the neg terminal of the battery since more grounds is never bad...but i still dont think this will fix it...

the only two things i can think of are:

A) some other type of loose wire, that i can't identify because i'm know educated enough in this, that would be directly related to spark, and ONLY to spark...because with the habit of this problem being to random and intermittent, it sounds almost like it HAS to be a loose wire somewhere coming loose every now and then, and other times laying just right so that the car runs great...

or...

B) maybe my spark wires are just getting pinched between the plenum and the throttle cable cover? i have them all tucked under there to keep things clean...and once the car gets hot, they get hot, and they get angry...maybe...but this i think would be more of a problem that would be every time the car gets warm, and not just every now and then at random...



for those of you that have read this far, thank you so much for your patience...and i really hope you have something useful to contribute...or can point me in a direction i have neglected to check yet...



thanks to all the members of all the Z boards for the continued help with my hell project...it's always much appreciated guys


-Andy

snwbrderphat540

hmmm.... thats tuff, could very well be a ground. so many things on teh car get grounded and with one off it can run like crap, not run at all, or barely notice. jsut cause one of hte engine grounds or throttle body grounds w./e the ground is is off, doesnt mean it will be signified by an electrical outage somewhere. so dont rule that out.

js9krcr01040

When you put in the new EFI Harness did you make sure you grounded that d noe point on the PTU side of the harness? It is located on the drivers side underneath the main fuse box. Very hard to get to but can cause alot of damage if not grounded properly. I would pull that apart, make sure its grounded and cross your fingers. Its a very easy ground to forget betcause its so hard to see.

91zxtt

That sounds very similar to the problem I'm having. Let me know when you find it. I've checked and re-checked all of the grounds and they're all tight. I'm thinking I have a prboblem with the MAF, O2 sensors or the ecu was improperly mapped for the 555 injectors. I haven't had time to directly check each of these things though.

grevels

If it is not a loose ground I would try another ECU. I had a different problem that had to do with spark and I tried everything including a new harness. It ended up being my ECU.

silvrhand

I would almost say this is a serious grounding problem, also check the ground on the tranny mount as well. Remember there needs to be good connectivity to the body, I would suggest the grounding kit as well.

Remember no rust, and make sure your cables are in good shape on all grounds.

90NA300ZX

thanks for all the input guys, i plan on buying a new grounding kit and running more to the tranny, chassis, and block...

but could somebody please explain to me how a bad ground would cause spark issues? i'm very uneducated i guess in this field, and i know grounds are essential...but if the ground just goes from the battery neg terminal to the tranny, chassis, or engine, how would it being off affect spark and only spark? i'm not doubting any of you, and will definitely check the grounds, esp. the one that js9krcr01040 mentioned...but i still dont get why a ground, or how, could cause this...

CanyonCarver

I don't mean to be sarcastic in responding to your grounding questions...... but try this: Touch your tongue to a wire coming from the positive side of the battery. Note what you feel. Then touch your tongue to two wires, one from each, the positive side and the negative side of the battery. Note the difference. You may then realize the importance of good groundz.

EDIT: Don't actually do this. It would be safe to try it on a small 9v battery tho. Touch you tongue to one side only. Then do it to both sides.

90NA300ZX

i fully understand the importance/significance of grounds, i've done a good handful of stereo installs and know what happens when the two touch...


what i'm trying to understand is what ground could possibly cause spark cut, and only spark cut. if a ground just goes from the neg term of the battery to the tranny or chassis...why would it cause spark cut if it came loose? wouldn't it cause the entire car to lose power...lights to dim, or even for it to just die alltogether?

DonnyZ

My friends S13 had a similar problem, well, nearly identical actually, turns out his igniter was circling the drain so to speak, picked up a used one and viola, no more spark loss. Not sure if this is your problem, but if you have a friend w/ a Z32, you could try borrowing his/her igniter and see if it fixes the problem, if so, then you know exactly what you need to get. Although, I'm still learning a lot about Z's (they seem to be the red-headed stepchild of Nissan), so I could be completely wrong.

CanyonCarver

You can check the wires for continuity from the coil pack to the ptu and from the ptu to the ecu. You can also ohm check the ptu per the fsm --->>> HERE

We shall be assuming that all of your connections have been relieved of any green crud.

90NA300ZX

all the connectors are in great shape, the EFI harness is literally brand new, and i just got the new ptu harness in today, well, it's used...but in great shape...the ptu is slightly used, but also in great shape...

i already tried putting a friends ptu on while the problem was occuring, and the problem kept right on occuring...while it did get a BIT better...but i think that was just coincidence, if it was the ptu, putting a good one on would have fixed it, not just made it a little better...because it was still pretty bad...


tonight after putting on the new ptu harness, it ran great, so i beat the **** out of it a bit to see if i could induce the problem, and it ran great...so i turned it off, waited a little while, and took it out again...and then again, and again...and it was great..

what sucks about that though is that i've tried swapping over harnesses and ptus already, so i know my problem isn't fixed...this is why it's called an intermittent problem...it's not there now, but will be again soon i'm sure...

CanyonCarver

Maybe go back to grevel's statement and try another ecu. I've seen a few people now with problems that can't be tracked down and it eventually boils down to the ecu. ie: burnt circuit, moisture, loose connection. You can check all of the circuits with the fsm and a multimeter.

z-hag

i had the same problem when i bought me 50AE--was the ecu--replaced it, ran to sacto from sd--perfect.

snwbrderphat540

did you try disconnecting the ECU and cleaning the hell outta the connections. i did that when mine had spark problems fixed it right up. might not even be a broke ECU just bad connection.

90NA300ZX

as soon as the rain stops here, my to-do list is as follows:

-run fresh main grounds from the battery neg terminal
-check/look for all and/or any loose connections/grounds already existing
-check ecu connection/clean all connections
-check with volt meter power between battery neg term and ptu
-start looking online for a good used ECU if none of this works

i'll keep everybody updated, thanks for all the help thus far guys

Comorat2x2

I'm not sure how you are coming to the conclusion that it HAS to be an electrical problem. I'm no mechanic by any means but the symptoms you are describing are the exact same ones I had when one of my injectors was on it's way out. The hesitation, the bucking (VIOLENT BUCKING, scared the crap out of me when it happened at 85mph), the backfires once in a while and the raw smell of fuel. All were what I had for a little while and then just got worse when the injector finally died.

I would strongly suggest testing each injector if you have the resources. It sounds like you may have one fixing to die.

Riz Z Speed

I suggest having a glance at the fuel dampner and/or the fuel pressure regulator since you'll be into the fuel system anyway.

Comorat2x2

I'd really like to know the final outcome of this.....

snwbrderphat540

yeah me too....damn z32 mysteries...the one thing i dont miss about the car...everything else....i miss like crazy...

90NA300ZX

sorry it's been so long...ever since i replaced the ptu harness, it's been running fine...which sucks, because i know the problem isn't fixed. When i swapped over the friend's harness, the problem was fixed for a day, then acted up the next day...and his car runs fine with that harness, so i know my problem is elsewhere...it's just so hard to justify working on the car now though because

A) it's running fine... and
B) the season is coming to an end...pretty soon i'll have all winter to work on it...


i know it's a time bomb waiting to go on me again...not like it's gonna destroy the car, it'll just leave me stranded again if the problem starts acting up bad again, or i'll just have to limp it home with it bucking like crazy...but i refuse to work on it the last month i have it on the road, especially since it was off the road from april to late august last year...

i did pull the plugs and check the coil packs...the all checked out fine there...as expected...for those that doubt that it's electrical, please tell me what else it can be...if it was a going/gone injector, i wouldn't be losing all cylinders like i do...

and if it was a fuel related problem/part that is on its way out on me...why would it be such an irregular pattern? a part that's going on you gets progressively worse...this is all or nothing, and for a while now, it's been nothing...no problem at all...

Z Car Barbie

Have you checked the ECU for trouble codes?

z-hag

problem sounds just like the problem i fixed by replacing my ecu

CanyonCarver

I've seen a few instances like that where the ecu is the problem. Maybe try someone elses good ecu. Or when it acts up, you can start testing all of the ecu pins per --->>> THIS