a few weeks ago i noticed the car sort of hesitating or lightly backfiring at about 4000rpm or so - didnt worry me too much as the thing has never really run correctly since i bought it. then over time, it was starting to do the same thing but at lower revs, more 3500rpm ish - it came to my attention when a hilux chopped me off the line at some lights now it does it at anything near 3000rpm, some times more at 2500 and other times you can get a little above 3000rpm - if you go over the 3000prm and you are accelerating at all it will backfire/stutter quit badly - last sunday i tried to get off the lights fairly quick without asking too much of the car, and it went crazy... started missing/backfiring/lurching plus tacho was bouncing off 2500rpm to 500rpm and back like twice in a second - it did this about half a dozen times. this continued for 50metres, as when i went to back off the throttle it looked like it was going to stall, then i would accelerate a bit more and it would go crazy again... all this in a flash of about 10 seconds. i pulled over and did a u turn to go home and could only accelerate with just the weight of my foot resting on the throttle, and couldnt rev over 2000rpm without backfiring etc happening again (ie if there was a hill to go up then there was no way i couldve made it) - did an ecu check and it spat out the det sensor code, even though i thought i had it already by-passed. i had used the wrong strength resistor. went and replaced the resistor with the right one and wiped the ecu memory and 55 came up. car was out of safety mode but still backfiring/hesitating over 3000rpm. - been driving it off boost the last few days and it is ok if you are under the dreaded 3000prm limit, but today on the way home it started to hesitate a little (barely noticable) when lightly accelerating in 3rd/4th at 2000rpm. - swapped the ptu over tonight and tried to start the car... turns over but no ignition, check ecu and it now has 21 showing..... so i took the ptu out (obviously that one wasnt working) and put my one back in after cleaning it up with a nail file... car starts and runs but still backfires etc at 3000rpm so what else?????? im thinking it is something to do with timing as it seems to only happen when the timing should be advancing ie when accelerating or coming on boost. tis giving me the shits im getting awesome fuel economy but thats not what i bought a 300zx for
Sounds like a major vacuum leak to me. If the air going into the engine is not metered it will do this. Only other lead I could suggest is a spark plug. Does it get pressively worse when it warms up?
I suffered a lot of those symptoms on my zed. This is what i did to cure it. Have you cleaned all your elec. connectors for a start? are all cylinders firing? Check coil packs, spark plugs, and fuel injectors and connectors. Start there and pray its that simple! Good luck with it.
Sounds like MAF sensor issues If the mass air flow meter fails, the ecu will use the tps voltage as a substitute, but will only allow operation to around 2400rpm in fail-safe mode. Worth a look. Bob in Oz
I had a similar problem a few months back. No acceleration, backfiring, generally undrivable. I cheched the coil pack connectors and fitted a S2 PTU and new TPS. All has been good since. Also, I know it sounds stupid but check the 2 connectors next to the engine fusebox. Black and Brown out of memory. They supply power to all the engine sensors. No sensors = no engine function after idle. I only suggest it because ive been caught out by it.
Engine missfiring Does it also do it at idle?? If it does try removing the centre nose panel to access the AFM and cover most of the AFM withn your hand while revving and see if this rectifies the problem, what could be happening is that as BOB suggests the AFM is dying and the car is running lean. By placing your hand over the AFM you change the air/fuel mixture. Good luck
Hey Kirst I had the exact same issue and it was a split vacuum hoes. We should be able to have a look at it tomorrow between working on Dans car.
Does sound to me like a failing AFM, but not a failed one. Once failed you will completely cut out at 2500 rpm. When I changed my pod filter from a unichip to a K&N, they didn't have quite the right adapter, so I built up the clamping area with elec tape as a temp measure for 1 day. Well, 1 small piece of elec tape made it's way onto the mesh of the AFM and disrupted the airflow, so the ECU was getting incorrect readings. The O2 sensors were stuck on a value of "1", and I was backfiring spluttering, and it made the car virtually undrivable. Swap with another members AFM and see what happens. It might just be the connectors of the AFM need tightening (crimping)
guys has anyone thought of checking or changing the spark plugs and leads, and or ur getting shit fuel which intern is ****** the engin function of ur car, or your engin is on its way out, by the sounds of it you push/drive it hard. see its a 17yr oldish car depending on moddle its like and old lady you cant ride it hard with out breakin shit where as new or young girl u can ride her hard and she dont break. if that makes sence.... anyways ill shut up now. k bye good luck with ur car hope u fix the problem.
if all else fails check timing on dyno, had 2 zeds do this one was mine and one was a mates both had retarded timing
CAS Had a similar problem a while ago, i replaced the CAS and now is OK, if you can get a hold of a conzult you can test it, then again you could test the works.
ok the z is still running like shit.... but you can get the revs a bit higher but it starts to backfire/stutter at 3500 and all hell breaks loose at 4000rpm. the following have been checked AFM - swapped with another PTU - swapped with another Coil pack connectors changed O2 sensors - unplugged and it is running the same DET Sensor - not working but now bypassed and no change Fuel filter was changed 2 months ago Spark plugs were changed 4 months ago with NGK platinums Conzult run - CAS, timing, TPS, injectors, coil packs all ok No boost leaks (did have some but no change now they are fixed) Car idles fine, but has a very small miss randomly now and then. Car runs on all cylinders but when you get to mid rev range it starts backfiring will be getting a fuel pressure gauge this weekend to check it is getting fuel but can anyone think of anything else??
Could try another set of plugs, get a cheap set of coppers. Something may have happened in the last 4 months to ruin them.
Heres another test for you... Even tho conzult says somethings ok...dosn't mean it is. Run the motor at idle and wiggle the CAS plug...if the motor cuts or hesitates, then theres your problem. Even if it does nothing, pull it off and clean and tighten up the female terminals in the plug, with a nail file or tiny flathead screw driver. I had the same issue with the black zed...just needed the CAS plug terminals tightened up a little bit. Didn't throw a code.
two possible causes not on your list yet could be fuel pressure regulator or even the fuel damper.....no smell of fuel in the engine bat is there?
