Dead cylinder #3! Ignition or Fuel?

[Jennys280Z]

Spark plugs have 60 miles

The #3 plug came out looking brand new.

I've pretty much ruled out some culprits below:

Ignition coil: Wouldn't effect only one cylinder 100% and other cylinders not at all.

Distributor: All tune-up parts almost new. Distributor cap metal contacts show the same pasty white surface wear indicating it's operating correctly

even for cylinder #3 i.e. they all look identical.

Spark plug wires: Almost brand new NGK set. Tested resistance on #3 wire as 5,980 Ohms which should be fine especially for a wire 2+ft long.

Spark plug: Looks like it never even fired...unless it's been firing in a cylinder with no-combustion (no fuel) in air only. The center electrode

does look dark and glossy. I thought it was wet with gas when I first pulled it out, but it was dry. I don't have a new plug to compare it to exactly.

No odor or substance on the plug besides a very weak gasoline smell, if that. No oil in the cylinder, no antifreeze or antifreeze smell, no gasoline in the oil, no signs of any strange shorts or arcing inside the distributor, cap, wires, engine or plug. Everything in the ignition circuit looks fine, and I never saw any sign of spark blowing out or grounding improperly (at night, etc). So the inspection of the ignition system suggests that it's not an ignition problem. I've verified spark at the wire with a timing light too. I'm too scared to pull the end cap off the plug with the motor running to know for sure, Ha!

Cylinder #3 compression is 140+PSI in a COLD motor which rules out any mechanical problem (rings, valves etc.)

A few years ago, I did clean the fuel injector connectors. Since then I've only put about a hundred or so miles on the car. If it's possible for a spark plug to remain looking 99.9% brand new when firing in cool-ish air with no combustion, is it possible to plug the injector in backwards and thus disable the injector completely and still have this phenomenon with a plug that was sparking the whole time? The #3 injector wire is a bit longer than some of the others, there's a bit more "slack" in the wire (a bigger curve) and it's not discernable whether the wire got twisted or that the plug was installed upside down. Is this connector keyed (does it prevent one from connecting it wrong)?

A webpage from AtlanticZ says that the +12V end is always closer to the front of the car. It doesn't say how to distinguish one from the other. The new pinch-style connectors look nice too

http://atlanticz.ca/zclub/techtips/injectors/connectors/index.html

I'm at a loss. The only other possibility I can think of is a defective spark plug (which seems like such a remote possibility it's not feasible) but is there anything else that could be causing this that I'm not thinking of?

The car seems to be running good and even smooth at idle although it idles too low until it fully warms up. Starts immediately, fuel pressure is steady in the mid 30s. A hot motor has a 1000 RPM idle. Presuming it's running on five cylinders (which I have to do looking at the plug) (6/5)x = 1000RPM; x = 1200RPM implied idle speed with all six cylinders. And this kinda implies that I've raised the idle speed adjust high enough to compensate for a dead cylinder at idle.

I don't want to run the motor again until I have a gameplan. I have a stethoscope and intend to listen to the injectors for the first time in a few days hopefully after some direction here? I understand I'll hear a clear buzzing sound when the injectors are opening. I'm skeptical a spark plug can come out looking this brand new firing for 60 miles without fuel. Or if someone here with more experience can verify that it's indeed possible that the ignition is fine (based on all evidence) and that it's simply a lack of fuel and combustion, I will pull off the injector connector and plug it in opposite of how I did before I start the motor again.

I hope I didn't fry the ECU or at least that circuit to the ECU by wiring it backwards by accident.

And if the problem is ignition, would all of the unburned gas really be going out my exhaust valve so perfectly like that, and not getting in my oil, without getting on the plug itself for that matter? I don't have the experience to know either way but I want to fix the problem without wasting too much money. Just collecting all my thoughts, I'm thinking this is a fuel problem more and more. My gut is telling me that a spark plug firing in relatively cool air with no fuel will look brand new for more miles than I put on it.

Previously to this problem, or to at least to knowing about the problem, I tested the injectors at the ECU pinout and they were all showing very close to battery voltage. My battery is usually under 12V (down in the 11s) even a day after I drive it. I've either abused the battery by not regularly starting the car or I've got a drain somewhere. And not to risk stating the obvious but the injector is not leaking any fuel. I'd need even more help if it was I use Chevron 93 Octane with Techron, have treated the gas with Seafoam and in other tanks other injector cleaners prior to that, if that would make any difference to a physically clogged injector. Plugs are NGK BPR6ES

Thanks!

Jenn/Sean

Edited August 11, 2014 by Jennys280Z
paragraphs and neatness

[bartsscooterservice]

You can put the spark plug in the lead hold ( or put ) it against some metal part of the engine and check for a clear blue spark when you turn the key. I think it's the injector that's clogged, or the injector is not getting voltage to open up and let fuel pass it into the combustion chamber. Maybe you need a set of new injectors ?

[EuroDat]

The RPM is always the same. You don't need to compensate for a dead cylinder. The tacho gets its signal from the coil negative. Its the same trigger the ecu gets to tell it what speed the engine is doing. The only way it would read 1/6 slower is if the coil was missing a pulse on number 3 spark plug. I would check the plug like Bart mentioned to be sure, but it sounds to me like an injector problem. It could be a number of things, blocked injector, injector coil open circuited, injector dropping resistor or wiring to injector open.

If you have a fuel gauge in the system reading the pressure you can do a simple test on the injector to see if its working or blocked. Disconnect the injector plug and use 9 volt battery to activate the injector. If the pressure drops, you know its opening and it is not blocked completly anyway. You can compare the rate of pressure drop with one of the other injectors to get an idea what is normal. You might need to run the car between tests to build up pressure reduce the chance of flooding. Dont use 12 volts to activate the injector. They normal see a lot less voltage (around 7 to 8 volts average) during pulsing.

You can also do a bunch of tests in the FSM to varify everything is working ok.

Chas

Edited August 11, 2014 by EuroDat

[madkaw]

Got to be an injector issue. Boy you will like your car when you have all 6 cylinders running- .

You need to correct hour charging/battery issue Asap. Low voltages can lead to ECU or other electronic problems

[240260280z]

Usually it is the wiring and the connectors rather than the injector.

Try swapping the injector connections between 2&3 or between 4&3 to see if the problem moves. (There is enough slack in the wiring harness to the fuel rail to do this). This trick is a quick way to determine if it is a problem in the harness/connector or the actual injector is dead.

A good cleaning of all electrical connections in a Bosch EFI system is a wonderful treat to your car.

[Jennys280Z]

Update: Sounds like the consensus is a fuel injection issue. I have to agree with this. No evidence of ignition issues, and after all, if the plug wasn't firing and the injector was functioning, I'd expect at least some gasoline on the plug, not a bone-dry-new one like that.

Looking at some old notes, when Jenn was cleaning the injector connectors she broke a small piece of plastic off of the rim of the #3 injector connector. It must have been just barely hanging there with a spot of glue or else it wasn't completely broken off yet. The instant I touched the metal retaining clip with a tiny screwdriver the piece of plastic went flying and landed on the heat shield. At least when things go flying in these old cars we have a reasonable chance of finding them. Plastic or rather the lack of it is another one of the benefits of these older cars, guess I can't escape it all the time unfortunately. But would something as simple as this cause a total malfunction of the injector? And I'm guessing from the replies it's impossible to plug these things in backwards?

Seriously doubt something like this really cause a total injector failure? The connector seemed to be plugged in normally and held tight by the clip; I would think this wouldn't make any difference. Just a strange coincidence... The contact surface of the connector itself is probably looking a lot greener than it should. The male connectors on the injector itself don't look too bad.

I was rigging up some wire on a 9V battery but maybe I'll swap two nearby harness connectors instead. If the problem moves to another cylinder it's the wiring/connector and if it doesn't it's the injector itself. I've never listened to injectors with a stethoscope before so I don't know exactly what to expect to hear...hope it's easy enough to be foolproof. Pulling a brand new looking spark plug out of cylinder #2 or 4 would be the backup way to tell if I'm stetho-challenged.

[S30Driver]

The broken plastic where the injector clip goes is not causing your problem.

Blue's injector connection swap is the way to go to isolate the problem.

If you don't have a stethoscope, just use any rigid handy device - a long screwdriver, snowbrush handle, and hold it to your ear.

You will hear the injector CLICK when it fires.

[Jennys280Z]

I'm going to swap connectors #2 and #3 which look like there's enough play in the wires to swap them. I wired up a 9V battery to test with that real quick but I'm going to run the motor with the swapped connectors first before I do anything else that may put gasoline on the spark plug and possibly muddy/confuse my results. So I assume either there will be a pristine dry spark plug coming out of #3 or #2. And hopefully neither because I just cleaned the connectors thoroughly with some sandpaper and some Caigs D5 on the male side and a wire brush and Caigs on the female and they're looking better now. #3 is pretty hard to reach, and even see with the fuel regulator and plumbing in the way but it's hard to think that just cleaning would make the difference between a completely dead injector and a normal one. So I doubt I'll luck out like that, and I'm not really gung-ho about actually fixing this problem ourselves whichever one it turns out to be. At the very least I'll diagnose it and we'll have a handle on what needs to be done.

I'll use the stethoscope too while the motor is running to try to hear who's not clicking between #2 and #3.

To answer one of my questions above, the connectors ARE keyed. It might be possible to plug them in backwards, but it'd be obvious because the top side doesn't look anything like the bottom (though the two shorter sides are visually the same) which is hard to tell until you actually take one off. The bottoms have most of the plastic cut off to fit along the curved surface of the injector.

I see new injectors are $380 at MSA, and it's recommended that all six get replaced together. New connectors are also similarly priced. Labor would probably make this easily a $1,000 job no matter what parts we need. So many pros here but I doubt you'd have the patience for a hundred bad questions if we attempted a DIY. Another problem is I don't know any pro mechanics I would trust implicitly with this job. There's a Z specialist across town but I told them what year my car was and what problems I was having and they didn't even want to touch it. Fuel injection and no scanners? Eww Yuck!! It seems too many real mechanics are spoiled with OBD2 now. A Toyota specialist nearby didn't even want to look at our third generation Camry with OBD1. He actually implied on the phone that I just get a new(er) car.

[EuroDat]

If you are thinking of buying a set of injectors there are cheaper suppliers on ebay. The Standard FJ3 it a common replacement. If you are not out for high performance they seem to work fine unmatched out of the box.*

75 76 77 78 79 80 81 82 83 Datsun 280z Fuel Injectors | eBay

Its worth buying the o-ring gasket set from MSA and replace them while you are doing the injectors.

My connectors were all badly worn and damaged. They were aftermarket and the cable was so short I couldn't swap injectors. I had problems with 3 and 4 were partially blocked and I found them using the 9 volt battery and the fuel gauge. I ended up reverse flushing them to get them back up to the other four.

I got a set of these connectors for mine. This seller was really quick, 5 days to Europe. The quick release makes it easy to do any testing and I made the cable a little longer so I could switch cables on injectors for testing if needed.

6 Injector Connectors Datsun Nissan 280z 280ZX Z31 300zx EV1 Quick Release | eBay

Chas

Edited August 12, 2014 by EuroDat

[240260280z]

The injectors are simply based on a solenoid design. A coil of wire that pulls on a slug of metal when energized. Since the slug is not magnetized/polarized, the polarity of the coil is not important thus the connectors pos/neg are not impt....but Nissan did wire these all the same.

[siteunseen]

Standard FJ707Ts are good and not too expensive, $30. They come with the O rings and a clamp.

https://www.google.com/search?q=standard+fj707t&rlz=1C1BOFA_enUS494US494&source=lnms&tbm=isch&sa=X&ei=h_TpU77GIcme8gHfoYG4DA&ved=0CAcQ_AUoAg&biw=1280&bih=620

[Jennys280Z]

Siteunseen I was reading through an older thread about you going with the FJ707ts and I wondered how you were getting along these days. Good to hear you're alright.

Thanks Blue, it was wishful thinking that something was just plugged in wrong.

Thanks all, I'll look into the more affordable EFI parts for sure.

Got the injectors swapped but haven't had time to run the motor yet. I'd be out there right now driving it around but I don't want to wake up the neighbors. Damn you, Flowmaster!

So instead I decided to replace my old battery with a brand new one tonight, until I learned that Autozone has nerfed their Duralast Gold batteries sometime earlier this year. My old equivalent size-24 "DLG" battery has 750 CCA, the new replacement DLG with an "S" added to the part number comes in at only 575. Then he had to switch stickers on the two batteries to make mine look like his, because he already ran the swap through the system before I decided to do it and it was somehow irreversible. So when I go back to Autozone in a few years to replace the battery again it'll look like I swapped it already tonight when I didn't. But at least it'll have that "S" on there so there's no chance of a problem. The last straw was his $2000 battery tester was outputting some crazy numbers on all of the 24's he had left and it was the only tester he had. Leaving with an inferior battery was bad enough already. Leaving with one that wasn't even known to be good was too much to ask for.

Interesting how a battery with 11.99V or 12.4V between the posts can be in a highly discharged state. I thought the relationship between battery voltage and its state of charge was pretty basic or linear, but I learned there's no accurate way I can tell what the charge percentage is from a volt/multimeter. I wonder if people just wing it, or keep charging their battery till they see 12.xx V, or if the car still starts with the old battery they don't even stress it? I read some articles online last night about discharged batteries and one said that they can cause phenomena like injectors not opening, hmmm. The same article also said that running voltage will be a few volts higher than battery voltage, implying that the battery voltage still provides a baseline voltage even after the car is running? It seems the more I read online and discuss with a sales clerk, the more conflicting info. I get. It would seem that if the alternator is okay and the motor is running, the battery voltage has nothing to do with it, but it seems even more that the battery still does, and so the alternator functioning correctly is more a matter of charging the battery effectively.

It also appears that I lose between 0.5-1.0V from the battery after installing it in the car, even still testing voltage between the posts. Normal or not, neither the sales guy nor me know for sure. On the bright side, my new tool set included a 10mm deep socket that makes taking the battery on and off a cinch now compared to the knuckles and cussing required with an open end wrench. When I know I'm not going to be driving the car for a while, I'm just going to leave the negative cable disconnected most of the time and see if that "solves" the discharge issue.

Thanks again for all the help! This site is the best Z clinic on the internet hands down. Yes, we owe it money, I acknowledge that.