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

Then the next strategy would be to do a voltage drop test on the MAF wiring.
Youll need to identify the wires at the ECU end, disconnect the ECU plug, hook up some power down at the maf end and load the wiring with a dummy load, say, a couple of amps, and then do some voltage drop measurements up at the ECU end and get someone to tug on the wiring looms and see if you can make the voltage drop appreciably.
Over a wiring run that long, Id expect almost zero voltage drop.
You could just probe the wiring with a digital multimeter but this may not necessarily show up enough of a drama. Loading the wiring with a bit of horsepower should definitely show issues.

After that, id be looking long and hard at the actual ECU plug pins and specifically for the MAF sensor. They can be extracted quite easily from the connector block and be tightened up and refitted.

More later.
E

 

Once again, thank you. I will definitely do this. I know someone who will likely be able to help me with this (if I can steal some of his time). I'll report back after I've had a go at it.

 

Break through.....of sorts!

I spent a few hours today upside down with my feet sticking out the targa. Peeled back all the tape on my loom at the ECU. There was quiet a few joins and splices and about 3 separate crimp bundles. Thank you MickW for you post of this thread:
http://www.aus300zx.com/forum/showthread.php?p=908028
Normally I would have looked straight passed these as they all looked pretty neat and clean. However after reading this thread by Rollin I re-pressed each crimp and soldered where ever I could get it in. I did this with all of the wires that had a join of some type. When I hooked up the ECU again and started the car the misfire seemed to have gone. Now previously it would run for about 20seconds before the misfire would start, but this time I let it idle for about 5min with no problem. Woohoo, so I turn her off put everything back together and start her up to go for a drive and I have a proper misfire (not intermittant like before), constant and un-yeilding. So I put some coil packs and one cylinder has completely dropped (rear passenger side). I get a long screw driver and there is no tapping from the injector. At this point I've run out of daylight, but at least I know now what I'm dealing with. I've never been so happy to find a cylinder that's not firing :rofl:. Either I have another wiring problem or the injector has failed. Maybe I was dealing with two issues the whole time? Maybe the injector was faulty and finally failed? Not sure yet but I'll post up when I find out.

 

make sure the plug is fitted to the ECU correctly, they tend to bend and hold the end pins away from making contact.
A few years ago I had a Z that would drop one cylinder when warm, it was the ECU plug causing the issue.

 

We checked this exact thing at the tech day in Wyong, and also tried multiple ECUs

 

Yeah, the connector plug seats nicely and all wires look to be sitting properly. I really think now that the problem has been cornered and I know which cylinder isn't firing I should be able to work out what wrong fairly quickly. It's my guess that the injector has failed since I had a quick look at the injector connector and the wires leading to it and they look ok.

 

Thanks MickW.
I have been following this thread, incase the replacement injectors doesn't fix my intermittent mis fire.

 

Checking injector signal

If you feel that the injector signal is not present there is a very easy way to check this. Make yourself a test lamp. Grab a 12V globe (say a typical globe from a 12V torch, NOT a brake lamp, they can pull too much current). Grab a pair of wires strip the insulation and solder them to the lamp. Strip back the other ends of the wires and push them into the injector connectors. (careful not to short them together) Now crank the car over if the ECU injector driver is working you will see the lamp pulse on and off. Walah you have just made yourself a test lamp. Regards Ivan. PS told you it was most likely an injector.

 

your plugs may be fouled check them out specially if there crappy irridiums ,

id be looking for a leaky injector o-ring

 

Thanks for that. I have some spare injectors here and was thinking about just plugging in one of those. Would this do any damage to an uninstalled injector? Otherwise I will use your light trick.

 

I think the plugs will be ok (coppers) as I listened to the injector with a long screw driver and it wasn't operating. So I suspect that cylinder isn't getting any fuel.

 

I was under the impression that a incandescent globe has too much of a warm up time to work with the rapid ON/OFF signal of the injector. I know you can test injectors with 'noid lights' which are LED's with a suitable resistor in line- this causes a rapid flashing of the LED with the injector pulse.

 

Hey Mitch
Déj? vu



Wish you were here........looks like I might have another plenum pull ahead of me

 

Correct.

L8r
E

 

Na just make a new hole in the firewall, turn a complex job into a simple one. May swell use that extra foot of harness

 

To me it looks like you found the problem here with the harness. In repairing this, you either upset another wire or 3 or did not repair it adequately. without the proper tools it is a bit hard to correctly diagnose, but here you just need a noid light, a quick trip to jaycar and they would most likely have something you can use.

The most important thing you can do at this stage, troubleshoot the issue in a systematic manner.

Spark, fuel, compression, timing. Which one is that cylinder missing. Do not assume because it is a new engine that compression is good in that cylinder. it has been running long enough now for a lean burn to have an effect on things. Also check that spark plug, lean burn can also fry the plug.

I would do these steps in this order.

1. check spark plug condition and gap
2. compression test
3. spark output
4. injector output, both electronic and fuel
5. Take a manifold vacuum reading at idle

My feeling is you have either not repaired the wiring at the ecu well enough or have unsettled other wiring in that area.

 

Thank you for your thoughts on this Eric. I know everything points to an issue with that ECU loom area, but I have to say that I went over every join very carefully and I would be very surprised if there is an issue in that area now. I'll have another look anyway.

The nature of the problem has changed completely. Before we couldn't even pin the misfire to a particular cylinder. It almost seemed to roam around effecting different cylinders at each misfire. It would come and go but never seemed to be in one place. This time it is always present and the cylinder easily identifiable. Pulling the coil pack connector makes zero difference to the revs on that cylinder.

What is the easiest way to test that the injector is getting signal/current? I have some injectors here, can I just plug one in.....would that damage it in any way?

 

Shouldn't damage the injector from a quick test. However they do not like being run dry for very long.

 

Great, it wont take long to check. At least I'll be able to tell straight away whether it's the injector, or other electrical issue.

 

Wow - You've spent a lot of time and patience hunting this one down.

Assuming that it is the rear passenger side injector, which is injector 6, the first thing to do is to check the injector itself. If you have a multimeter, set it to a low ohms range, unplug the injector and check the resistance of the injector at its contacts - it should be around 10 to 15 ohms. You won't hear it click or anything, as the multimeter doesn't give it enough power to energise. If you see anything much greater than 20 ohms, or infinite resistance, the injector is dead. If you're not sure of the readings, check a known good injector reading against this one.

Next, check if it actuates by (very) briefly putting 12 volts across it. It doesn't matter which way around you put the 12 volts while it's unplugged - just put an earth on one side, and tap a 12 volt wire onto the other contact. You should hear the injector 'fire' each time you make contact with the wire. If you can hear it fire OK (maybe check another one the same way so you know what it should sound like), next thing to check is the wiring. Don't leave the wires connected too long though, or the injector will overheat.

The Z32 injectors actually have 12 volts running to them at all times, even when the ignition is off. To fire them, the ECU grounds the other connector. With the injector unplugged, check the white with black wire connector on the injector plug - it should have basically battery voltage on it, ie around 12 to 13 volts. If you can't figure out which connector the white with black one is, just check both - one should be battery voltage, and one won't, if everything is OK.

If you can't find battery voltage at the injector connection, then your loom is suspect somewhere between the previous injector wires and the number 6 injector. To check, you can hook the white with black wire on number 6 injector straight up to the battery positive, and see if the car idles and runs OK. If it does, then you have an injector positive wire problem. Check the wire continuity back through the loom to ECU pin 58 or battery positive.

If all looks OK, check for continuity between the other injector connection (ie not the 12 volt one), and pin 114 of the ECU. This is the 'firing' wire for the No 6 injector. With the ECU plug disconnected, if you earth this wire, you should hear the injector fire, even with the ignition off.

Another couple of things. Zeds run CRAP if they have old and weak batteries, even if the alternator is OK. I've experienced this myself. Unless you are 100% sure your battery is A OK, swap it with a known good or new one.

The second point is that a voltage output check on an alternator with a digital multimeter will not necessarily pick up a problem. Alternators make AC electricity, then convert it to DC by a series of diodes. If one or more of these diodes has blown, the alternator will still output a voltage, but it will be a very messy one, which the digital multimeters will not pick up. Another problem with similar signs is if the alternator brushes are worn, and are not making good contact inside the alternator. The best way to pick it up is by listening to the car radio on a weak channel (preferrably an AM band), and see if you can hear a lot of noise on the audio signal when the engine is running, but not when it's turned off. That noise will be the alternator output voltage jumping all over the place too rapidly for the digital meter to pick up. Another way is to use an old fashioned analog (dial) multimeter, and you can actually see the dial moving around as the alternator ouput varies. Best but least available is a CRO (Cathode Ray Oscilloscope), to look at the alternator output waveform. If it's not fairly smooth, the alternator is on the way out.

Hopefully this will help with your diagnosis, and get you back on the road.

Cheers,

Dangerous