Seriously doing my head in....Can alternator cause misfire?

Great info Dangerous, thanks very much. I'm sure I wont be the last Z32 owner to spend many hours tracking down a misfire , and these types of hands on diagnostic tip can really help save time. I'm sure many other members will find this thread useful over time. I had previously tested all injector with a multimeter, but that was before this latest change of events so it's time to do it again.

 

Briz I feel for you mate and this thread has some good info for all of us .

I will be buying a new harness now .

 

Thanks Dangerous, for this, I have wondered how to test injectors.
Just need to know the correct proceedure for coil packs.

 

gmbrezzo, coil packs are easy to test too. It's a fairly good description in the service manual, but in general terms, any ignition coil pack is just a transformer with two windings on it. One winding is the primary, and this is what has 12 volts across it when the ignition is ON. The secondary winding is connected to the spark plug lead. When the primary winding has current flowing through it, it sets up a magnetic field - an electromagnet. This magnetic field is a form of stored energy. When the ECU (or the distributor in an old carby style engine) wants to fire a particular spark plug, it stops power going to the coil primary. The stored energy in the magnetic field inside the coilpack has to go somewhere, and the magnetic field 'collapses' and causes a very large voltage (thousands of volts) in the coil secondary. This large voltage is sent to the spark plug via the plug lead (the bottom bit of the coilpack in a Z32), and the voltage is high enough that the energy sparks across the plug gap. Once that's done, the ECU sends more power to the coil primary to build up enough energy for the next spark.

Because of the high secondary voltage, every part of the coilpack and plug must be kept well insulated and clean. Any dirt, grease, oil or cracks or scratches on the coilpack or spark plug can result in the spark voltage finding another way to get out of the coilpack by 'tracking' across dirt or out through a crack, which results in a misfire.

For the Z32 coilpacks, to check them, first of all check the resistance of the primary circuit with a good multimeter. That's the centre and left connector as you look down on the connector. It should be a very low resistance - around an ohm or less. Because that's a very low resistance, check your meter first by touching the probes together and making sure that the meter reading is zero. If it's not, some meters have a zeroing knob on them that you can adjust the reading to zero with the probes shorted. If yours doesn't, take note of the reading with the probes shorted and subtract that from the indicated coil pack primary resistance. For example, if the reading is 0.8 ohms with the probes shorted and 1.5 ohms across the coilpack, then the actual coilpack resistance is 1.5-0.8 = 0.7 ohms, which is fine. The primary coilpack resistance will probably be either around 1 ohm, or infinite (or very high) ohms, which indicates an open circuit in the primary - the coil is stuffed.

Assuming this measurement is good, take the coil pack out and immediately inspect it closely for any signs of cracks, carbon or dirt buildup. Any thin cracks or lines that look like cracks but are just dirt may be a cause of tracking/misfire. The most effective if not necessarily the easiest way to check the coil secondary is to disconnect or disable the fuel pump and purge the system of fuel and (carefully) set up the coil pack with the connector plugged back in and a known good spark plug plugged in, with the bottom electrode of the spark plug firmly touching a part of the engine to provide a good earth. Turn the engine over, and look for a spark. No spark at all either means that the earth isn't good enough on the plug electrode or that the coil is stuffed. Any spark at all means that the ignition system is still working, but look for a good, thick and bright "ZAP" of a spark. If unsure, compare against another coilpack known to be working OK (eg if testing just one coilpack because you suspect it is not providing a good spark, check the coilpack next to it as well). A weak spark isn't necessarily going to be able to ignite a lean or a rich mixture - Series one PTU's sometimes partially fail and cause a weak spark in one cylinder before failing completely.

If you're not careful, you may cop a shock from the coil, lead or plug. It will hurt, but it won't injure or kill you - think of it as a gentle reminder to be careful

There is also a carbon contact inside the coilpack assembly which can degrade or fail. You need to pull the lead off the bottom of the coilpack assembly to check it though, and if they're never been off, they can be hard to get off, and then back on. The carbon contact should be smooth and round, without any cracks or bits missing off it.

One last thing with spark plugs and coil packs - make sure the engine is well earthed! A bad engine earth will cause weak sparks, and will also decrease the efficiency of the alternator, and make engine mounted sensor readings innacurate. You don't need a 'grounding kit' or anything fancy. The standard Z32 engine earth is quite sufficient if it is in place and the connection and bolt is tight. If you suspect a bad engine earth is causing any problems, temporarily grab a single jumper lead and attach it from the battery negative to a metal part of the engine while the engine is running. If the problem goes away, start suspecting your engine earth is not all that it should be.

Cheers,

Dangerous

 

the wires get brittle and dry. and crack very easy, strip all the conduit back and check the wire physically.

the injectors should be around 12ohms resistance on the multimeter

 

Good advice in both of your posts mate This bit has got me thinking -

The following not be relevant in the OP's case, but you've inspired me

Seen a lot of posts about running rough / no go / failed S1 PTU straight after a rebuild or plenum pull. Have sometimes wondered if the plenum had
been powdercoated in those cases. We all know about the grounding points at the rear of the plenum, but they're just one part of the ground loop.
Those 8 bolts which hold the plenum to the block are another part. If the flanges on the undersides of those bolt heads are not in good contact with the metal
of the plenum then you might not get a good ground.
Same for the 2 pairs of bolts on either side of the plenum which anchor it to the block via the 2 brackets.
That just leaves you the EGR pipe flanges but sometimes they get deleted anyway.

Short version of a potential ramble -

Anyone who powdercoats their plenum then has possible electrical issues afterwards, try running a jumper cable from the ground points at the rear
of the plenum straight across to the battery negative terminal to help diagnose this.

Even if you haven't powdercoated the plenum, something else to be aware of - anything to do with grounding needs to be squeaky clean.
This might include random bolts. Remove all grease and grime from them, maybe even tickle them with clean emery paper or scouring pads.
And all those brass eyelet connectors need to be as clean as the day they were installed at the factory. Even the sweat from your fingers can tarnish them.
Try to avoid getting your blood or tears on them too

 

Epic thread - Come here if your having a missfire problem!

Might take a while to read - but every angle is covered in what is a vast complex problem sometimes - Well done all in helping build up a good informative thread base.

 

Update....

Well I managed to find sometime this weekend to have another shot at this problem. Thanks again Dangerous I followed your instruction and quickly found the source of the problem. Here's how it went:

1. Checked the white / black wire on the loom (injector 6).....12V present.
2. Put connector back on injector and earth out the other wire (from back of connector) and injector gave me the click I was looking for.
3. Pulled out ECU and tried earthing the same wire from near the ECU and.....nothing. (Well done Eric you were right again ).
4. Traced back along the wire until I found a join. It seem pretty good, was soldered and I'd already looked at this one previously and re-taped it up. This time I get the wires a good pull and what do you know the wire slipped straight out of the solder. Clearly whoever had done this join wasn't and expert and the join just wasn't good enough. So I stripped it all back and re-soldered the join and what do you know.....I have 6 cylinders firing again :thumbup:.
5. So I let her idle for a while and.........would you believe my random misfire is back [TIS]:bash:. Clearly I hadn't fixed that issue before at all, just aggrevated the other wire when I was playing under there .

So I took her out for a drive and all the old symptoms were there. I don't think this is a single cylinder issue because when you drive the car it's not just a drop in power like you would see with a single cylinder dropping out. What you get is an massive drop in power, like you have just run out of fuel. As I start to press the accelerator down it bogs right down like its starving for fuel and if I really push the pedal down a long way it starts to pull again and then your away. No shortage of power at this point. At I guess about 5000rpm it is doing what you'd expect... throws you back in the seat. It was starting to break traction in 2nd gear today when I took it out, so there is no shortage of power (stock motor, stock boost).

Question: My TPS is at 0.44 which is fine and it does move with the accelerator, but is it possible that it's not responding properly? Could my PTU be causing this?

 

That was happening to me in my pulsar turbo . It ended up being an injector where the end of the jet (or whatever its called) was bent .

Im assuming it was still clicking but fuel wasnt getting thru properly .

 

lordy ,,, if your head was not sufficiently done in before, it surely must be now ... !!!!

what a bummer ... keep at it and hopefully a complete solution is nigh.

 

Damn dude, I thought you were nearly sorted.

If you've already tried using temporary jumper leads directly from some grounding points to the negative battery terminal,
here's another straw for you to clutch at ( you did ask for lateral thinking / crazy suggestions ) -

Go to the relay box behind the LHS headlight. Remove the IGN COIL relay.
Remove the AIR CON relay and put it wher the IGN COIL relay belongs. Go for a drive.

Might sound strange but I recently worked on a Zed which had intermittent weak spark then died altogether.
Did the above and it came to life again. Dissected the relay and found the contacts scarred to buggery. Carbon and dags everywhere.

Goes without saying, but GOOD LUCK

 

What type of PTU are you using, OEM or Aftermarket? Reason I ask is I have had 2 s2 aftermarket ptu's fail due to not being mounted to a sufficient heatsink. They progressively get worse until you have a no start situation.

However, I do not think this is your problem, your issue appears harness related to me. I would be checking each wire individually with a meter and then checking each for shorts pin to pin and shorts to ground. Do these checks with the entire harness disconnected from everything to save confusion with incorrect readings.

 

You deserve a medal from Nissan!

Really feel for you A-Bris-Z- your a good member and have done everything and more 100 times over that you should have had a heartattack by now from the stress let alone a head full of grey hairs.

You are dedicated to the max and I hope you get some goodluck somewhere soon, I think it is loom related based on everything stated so far as well, but am at my wits end just reading the post alone and everything you have checked, let alone going through it like you are.

When you summarise everything that you have tested already, it really stands out that it could only be loom related - there is nothing else it could be, otherwise you would have picked up it by now with everything you have tested.

I agree with A2ZED in narrowing the loom down to keep it as simple as possible, I assume that somewhere in the loom it is breaking and making from the vibration and is giving the symptoms you describe.



You will be the foremost expert on missfiring in the world by the time your finished and so specialised in missfires that you will be able to charge people $1,000 PER HOUR - LOL



Seriously I really feel for you, but your dedication and persistance inspires me so much - If there was a ZED Medal out there - you would be a winner for sure.
Anyone from nissan ? Take note!

Wish I could help more than - "somewhere in the loom" - so all I can do is support you, pray that you get a break soon and wish you the best of luck in finding this little tiny insignificant microscopic problem that is causing you so much hell.



:zlove:

 

I feel for you Marcus.
You have completed the circle of life on the zed.
Intermittent mis - found problem - fixed problem - intermittent mis returns.
I am so hoping mine is still there so i can rule out the injectors, and plugs.

 

wow dude that really does suck. hope you figure out what the problem is.

 

It still has the same S2 PTU that you put in it Eric. I did switch it out for another one but there was no change. The dreaded harness peel , it is starting to look like this will need to be done. Do you think the Air Idle control could cause these symptoms if it wasn't functioning properly?

 

No, it won't be the IACV. Also you do not have to open up the harness until you have actually found a problem. Grab the multimeter and start probing, stop randomly replacing things here and there, you need to take a methodical approach as it is not a simple "replace part x" type issue. Intermittant electrical issues are the hardest to trace.

Start at pin #1 on the ecu and measure resistance to it's corresponding sensor/actuator connector in the engine bay. While holding the probes on each end, have someone wiggle and shake the harness about. If that check is ok, measure resistance from that same pin to earth and to all other pins in the ecu connector while shaking the harness. Do this with every pin. Do not use the multimeter on continuity check, make sure it is set to ohms.

Repeat this process for every pin in the ecu connector. You will, on some pins, have a circuit to others or ground. Keep the wiring diagram handy to ensure you should or should not have a circuit. If you are confident, start with just checking the ptu/coil wiring and injector wiring.

You need to have everything disconnected from the harness to not get a false reading. It is a slow process, but is the correct way to troubleshoot an issue like this.

By randomly checking and replacing things, you are most likely going straight over the cause, in the case of a damaged harness, sometimes the slightest movement is enough to give contact and make you think it is fixed.

 

Thread is to full of clutter but O2 sensors, I would fit brand new OEM sensors if you haven't already.

I wouldn't give a damn if they look OK on Consult or what ever, the symptoms you are describing are exactly the same as typical O2 sensor issues.

 

Thanks Eric. Here's my "to do" list now. A few quick tests first as per members suggestions with similar problem in past...
1. DET sensor by-pass
2. Disconnect O2 sensors
3. Test loom as per your instructions
The other thing I'm going to do that was suggested was to install a O2 wide band sensor. This might help tell me what is happening with mixture and will be a useful indicator long term to spot future issues.

 

Update...break through!!

You nailed it mungyz, chilledpain, NAzx. I disconnected the o2 sensors and she's virtually fixed. No pulling and lurching in the low revs range at any temperature. I'd like to make a few notes here to others that have followed this thread.

1. I replaced these O2 sensors last year with O2's that I purchased from Autobarn and were Fuelmiser's. The message here is be careful with generic brands, there is a reason why all the old members swear by the big brands. Here is a link to a thread I started when I was first looking for new O2's (http://www.aus300zx.com/forum/showthread.php?p=1086255#post1086255). In this thread I state that I would be a "guinea pig" and try these sensors ....turns out I wasn't lying.
2. So if like me you are trying to diagnose an difficult issue, don't rule out something you have already recently replaced.
3. Note that these O2 were seen to be operating correctly when we looked at them with ConZult. So just because they may look ok, it doesn't mean they are!! I think this was something that has sent me in the wrong direction early on.
4. This also explains why the car would start well and run great for a short time before developing problems. The O2's take a while to heat up and start working, and it wasn't until they started "working" that my issues would start.
5. I have some new Bosch sensors here that I'll install next chance I get. Hopefully it wont go back to it's old habits when I do that. I'll report back once this has been done.

In reflection I could have done this simple test a lot earlier and saved a whole lot of time and anguish, but just didn't believe that my new sensors that were shown to be operating properly on Conzult could be the problem, nor did I think that o2 sensors could cause such a severe problem. Afterall the ones I removed were completely dead and she was still running fine. I was wrong. On the bright side, I did find a dodgey connection on my loom I probably would never have known about otherwise, and all my the other ignition and fuel system parts have had a very thorough check over .