Got a problem with my 300zx. It misses on the driver side cylinder closest to the firewall (cylinder number #5?). Here the funny thing, it only misses when it gets up to operating temperature. Plugs have been changed and coil packs swapped to check, all checking out fine which leads me to believe its an injector problem. I'm going to ohm test the injector on that cylinder when I get a chance away from work. Has anyone seen this problem with the same symptoms before? Any help would be greatly appreciated
Did you set the gap on the plug yourself? They can often be out a fair bit. Also might be worth canging the heat range. What plugs are you running out of curiosity?
Plugs are NGK PFR6G-11. Same as old ones. They say they come pre gapped at 1.1mm. I checked the gap on the old plugs and it all matched up. I checked the gaps as I put the new plugs in.
Forgive me I'm not up on all the tech lingo, whats a PTU? The car is completely stock minus the stereo head unit if that answers your question. Car is a '93 NA
The ptu is the little square box bolted to the drivers side timing cover. Series 1 is silver and looks like a heatsink. Series 2 is a black plastic box.
Sorry. Ptu is the power transistor unit. Which is located (when looking into the engine bay) on the left hand timing belt cover. Is square/rectangular in shape. It will either (most probably) be alloy with cooling ribs on it. Or a black plastic casing. If its the alloy sort. This is a series 1 ptu. With age they can fail or begin to play up. Resulting in misses or poor idle, etc. the series 2 black units are an update. And much better by design. Your problem could be a result of either slightly faulty wiring or dirty terminals at the ptu. Or a failing ptu. Electrical breakdown due to heat and vibrations. The ptu is the trigger in essence for the coil packs. Might be worth inspecting if all else looks fine.
Just went and had a look and its got the alloy heat sink so its a series one. Is there any way of testing it to determine it is the culprit, and does a failing PTU match my symptoms? (only missing at operating temperature)
Unfortunately there isn't a real "sure thing" way to test them out. Usually sourcing a known working unit and testing it, is the best method. But most here would recommend spending the $65 it costs to get a series 2 unit and upgrading it. Ptus have been known to cause odd misfires when warmed up.
You're not supposed to gap platinum plugs as it can damage the coating on the electrode. Is it possible this happened when you were checking? Perhaps swap plugs with another cylinder and see if the problem follows...
Most cases when the PTU drops a cylinder, you get an ECU error code 21. You can run an ECU diagnostic using the instructions from the Tech Section.
Rob, don't worry i didn't gap them, i just checked them with a gauge by eye, not actually touching the electrode. Close enough is good enough for me. It has a normal idle (no missing on startup) so plugs aren't the issue. to IB, i've done ecu diags before but i totally skipped over code 21 (ignition circuit) looking for the word PTU when reading my old printed guide to it, thanks for the heads up! Also i looked up installing a series 2 PTU and from what i can tell you get a kit that includes a wiring harness aswell. Is it hard to install or is it just plug and play? and what price am i looking at. Sanouske says $65 but everything i see is a few hundred more
Is there anywhere in Australia I can get it for the same price? Only one i can find on ebay but it is grossly overpriced at $385
$65 is for a 2nd hand ptu a few of the members import from Japan with the connectors with pigtails. Many many many people have hard wired these units in and not had a drama. Myself included. Alternatively, yes you can purchase brand new for much more. But that's your call. Some info regarding hard wiring one in. http://www.aus300zx.com/forum/showthread.php?t=305719 Vader does also sell them. So perhaps pm him if you're interested.
Czp's price is actually allot better then I recalled. Shipping is pretty cheap and fast from czp. So you'll be winning with this option if you want new. If you want for testing purposes, to have a known working series 1 unit to test in your car prior to buying a series 2 unit. I could post you my spare. I will need it back though. Not unless a local to you has one.
Can you remove and replace/upgrade the PTU without removing surrounding parts or if that is not possible, what has to be removed?
Alrighty sweet. Theres a bloke that lives not far from me that has a few wrecked zeds that ill get onto to see if he has a working s1 ptu i can use for testing. If not ill get onto you Sanouske. Thanks everyone for your help, will let you know how i go
