yet another car won't start thread (long and confusing)

[mtcookson]

Cliffs notes at bottom

 

1975 280z stock engine. Fuel is being supplied, there is air, and there is spark. I'm pretty sure the injectors are firing but I'm not 100% sure. I know that when I pressurize the fuel system and supply a ground signal to the injectors all of them spray fuel correctly and with a nice pattern.

 

One thing I'm not sure of is how the injectors are supposed to be wired. I thought I had them wired correctly (had to reqire the injectors for cylinders 4-6 and wired them according to the stock injetor wires) but when comparing them to the manual and injectors 1-3 they seem to be reverse. Voltage is going to right/bottom terminal (see my nifty drawing thingy below) when the key is in the on position and when I supply a ground to the opposite side they pop open correctly.

 

injectors 4-6 (the ones i replaced the harness and wires on)

left terminal = ground/no 12 volt signal

right terminal = 12 volt signal when key is in on position

 

/ Retainer clip side

________

| __ __ |

|___/___|

 

/ Injector side

According to the thing above, does this seem correct or did I put the wires on backwards?

 

I smell fuel on the plugs but I've held the throttle wide open and I would think they would be soaked in fuel but they aren't. Sometimes when I hold the throttle open all of the way I'll get some blackish smoke coming out the tail pipe as if it wants to fire but doesn't do anything more than that.

 

I guess my basic question is, could it possibly be valve timing or maybe ignition timing?

 

If its valve timing, according to my Chilton's book, the engine must be at operating temperature to space them correctly. As you can tell quite easily that's impossible for me to do. Is there a different measurement I should use when cold compared to the .025 for intake and .030 for exhaust or whatever when hot?

 

Cliffs notes: 75 280z, stock everything. Getting fuel, spark, and air but will not start. Plugs smell like fuel but are pretty dry even after hold the tb at wot. All injectors spray fuel correctly, spark plugs are gapped correctly, and everything just plain seems correct.

 

Could valve timing be an issue and if so, how would I space them with the engine cold?

 

Thanks in advance!!

[datsunlover]

I dont think it would be valve related... posibly ignition timing though... Did this car run once upon a time? Or was it non running when you got it? You could try playing with the dizzy.. advance or retard it and see if she fires up.. sounds likt the same prob I had with and old 81 zx.. turned out (apparently... the guy I sold it to said he fixed it) to be a bad injector.. but you say yours all spray good... I know this sounds odd, but you could try pulling the two plugs out (on the cyl's that you're not sure of the wiring for the injectors) and see if it tries to run. Mine did! I pulled No 5 plug out, and cranked it over (by mistake actually...) and it actually ran! Not well, but it ran! (which was better than not running at all) I supose it could be an AFM issue as well.. check the conections to all the sensors too....

[mtcookson]

It ran all the time up until two years ago. THe previous owner had a bit of a run in with a deer and it banged up the hood and passenger fender pretty well. The antlers went through the windshield and the dash on the passenger side as well . After that he just let it set because he didn't really have the money nor the knowledge to replace everything which kind bites but was good for me.

 

Back on topic. Like I said, it did run up until two years ago when it just sat since then. Since that time a dang pack rat got in there and chewed up some hoses and wires. I have all of them fixed that I know of so hopefully there's not a hidden one somewhere.

 

I'm thinking the problem is ignition related myself now. Last night I shot some starter fluid in there and didn't get any response which would definitely seem to mean there is timing issues. I'll mess with the distributor a little bit and see what I can come up with.

 

Thanks for the help!

[mtcookson]

Went out and screwed with the timing and got nothing new... except for a broken bolt that holds the dist. in place. I didn't even put excessive torque on the thing and the bastard broke. Guess I'll have to drill and tap or something.

 

In the process of that happening I decided I was going to pull the dist. out so I could have easier access to the bolt to remove. So what I did was remove plugs 2-6 so that I could feel the compression stroke of 1 to get it at TDC. In the process of getting there I heard what I thought were some pretty scary sounding "leaks". After hearing that I decided to do a compression test. The results...

 

6 - ~150

5 - 100-110... uh oh

4 - above 150

3 - ~150

2 - 120-125... not again

1 - ~150

 

So... could it be that the valves just need adjusted on cylinders 2 and 5 or is my VH45DE swap starting a bit sooner than expected?

[A. G. Olphart]

Once you get it running, your compression may come back. Some of the valves had to be hung open all the time it sat, and rust will hopefully wear away.

 

Where did you have spark? At the coil, or at the plugs? (Bad cap/rotor)?

 

I know nothing of injection, but basic electricity says that if neither post of the injector is internally grounded, it shouldn't matter which way the juice runs through the coil. All the change in polarity would do is reverse the poles of the electromagnetic field.

 

Timing should not have changed; if it ran after he hit the deer (nothing broken by impact) it should run now. Is your gas OK?

 

Luck.

[mtcookson]

I had spark at both the coil and right at the plugs. Now that I think about it, since the electric system is DC the injectors would only be able to have the 12 volts on the proper terminal. Wrong terminal and it would try to pop the pintle into the injector, at least I'm pretty sure that's how it would go. I drained all of the old gas and put in some brand new gas.

[Guest 2slo4u]

Actually I believe that the injectors get 12v on one side from ignition 12v only when the car is on. The other side of the injector gets negative pulses from the engine computer under the dash to the left of your left leg. And it DOES NOT matter which polarity the injectors are connected. 12 dc does not care which way it flows through the injector coil. The injectors will open either way you connect them.

Try disconnecting the injector plugs and checking the terminals with a voltmeter. Put the negative voltmeter lead on the manifold to ground and test both injector pins after they are all DISCONNECTED. With the key off, neither of the pins will have 12v, but with the key on, only one will have 12v. You cant tell which is 12vpositive when the injector plugs are connected because the 12v makes a loop through the injector coil and it will seem to have 12v on both sides.

 

 

81zxturborustybutrunning

[mtcookson]

Well I know with the current setup they open correctly but I was almost sure that with a direct current you couldn't reverse the polarity. Kind of like running say, your fuel pump with a the polarity reversed. On a direct current it would run backwards but if it were an alternating current it would still run in the direction it was made to run. I'm not too keen on electricity so I could be totally wrong. That was just my take on everything.

[Guest 2slo4u]

Most 12dc motors will actually spin the opposite way because they have permanent magnets in them and the permanent magnet respond to the armature depending on the way the electricity is flowing through it. The injectors do not have a permanent magnet and rely on the current flowing through the injector coil to magnetize the pintle making it move only one way, open. The spring and fuel pressure then push it closed when the power is switched off. Don't worry man. The polarity doesn't matter. I've dealt with electronics for many years. (Not to say I'm the best) Someone will most likely chime in to confirm how they work and maybe you'll not be as worried about it.

Don't make it too complicated. They operate a lot more simply than you think. Time to get some winks, layta...

 

 

 

81zxturbo rusty but runs /all injector wires have been cut and soldered and I assure you: none of the wires are in their original polarities or positions, my friend. 8)

[mtcookson]

ahh, i get it now! thanks for clearing that up for me.

[Guest mtbrider586]

I have been reading alot of these post on no starts and I would like to share what I have found, on a customers car I have been working on.

I have been working on a 76 280z that would start and would die right away. what I found is a voltaage drop across the injector relay. the relay switchs on but only supplys 8.5 volts to the injector resistor. the injector resistors job it the drop the voltage down from 12 volt. measured resistance across the resistors is 13.5 ohms. I found if I jump a lead to the blue wire coming out of the injector relay that goes to the injector resistor with 12 volts the car starts up and runs fine. I am going to replace the relay tomarrow. voltage going into the relay is 11.75, so about more then 3 volt drop through the relay. wiring diagrams avalible at autozone.com

Fred

ASE MASTER TECH

[technicalninja]

You need three things for combustion; compression, ignition, and fuel supply. Test them seperately!

Your compression is fine for a motor that has sat long term. The low cylinders will probably come back up after a couple of warm up/cool down cycles.

Disconnect your dropping resistor pack (below clutch slave cylinder) this kills power to injectors to eliminate fuel system to test ignition.

Start with clean- non fouled plugs. Spray Berryman's B12 into intake (don't need much just a couple of seconds spray I usually spray it into FPR vac hose at center of plenum). Crank engine. If your ignition is functioning and is reasonably close to correct timing it with run fine. I can slowly feed B12 into intake to allow continuos running. I have moved cars across parking lots(with a helper driving car) this way. If it runs you have proven your ignition.

Always diag ignition first before FI problems. The B12 becomes your fuel supply system. If it runs on B12 then look to fuel system

It takes very little bad gas to poison new gas; the old stuff left in system after draining (in bottom of tank,F pump,filter,feed + return line, injectors and fuel rails) is enough to poison 5+ gallons of new. How well did you drain system?. When fuel goes bad in injectors it "gums" up the tips and the pattern can be a straight stream into intake. Liquid fuel doesn't burn very well- especially if it is poisoned also. Correct injector pattern is a cone shaped spray of such fine particals that the spray atomizes (disappears into vapors) 4-5" from tip.

You can listen for injector operation by placing the handle end of a screw driver against your ear and the tip on the metal body of the injector. You can hear the injector click when operating.

You can test patterns by unbolting complete rail system from intake (leaving injectors attached to rails), jumpering FP relay, and applting a 9V battery across inject terminals one injector at a time. You can sometimes clean gummed injectors by removing them, applying voltage to open and spraying B12 both ways through injector. Blowing backwards with air can help too.

In most of the cases of poisoned fuel cases that I have seen the fuel was hard to light with a match. Dip 2" of srewdriver in gas, shake off excess and try to light it with match. You might be suprised at results.

 

Hope this give you some testing ideas

Rick