1977 280z - Pin 1: Test Ignition Coil Trigger Input Circuit returned 3.6v

[jkeese01]

My car cranks but chokes out if you press on the gas. It will only rev if you very slowly increase the acceration.

Performed several successful test from the Electronic Fuel Injection manual. When I tested the voltage on pin 1 from the harness, Test #2 - (1) Ignition Coil Trigger Input Circuit, it was supposed to read battery voltage, but read only 3.6 volts.

Anyone run into this problem? I'm only finding people that performed this test successfully with a reading of 12v.

Thanks.

[jkeese01]

I noticed the center bottom wire (top wire in this picture) disconnected on my Z and plugged it in. This is when all the trouble started. Just unplugged it, now the voltage on pin 1 is the battery voltage and the Z runs normal.

Does anyone know what the bottom (top wire in this picture) center wire is for?

Thanks.

Edited June 3, 2012 by jkeese01

[ZCurves]

This is good information. I saw that you had the EFI manual, Do you have a copy of the '77 FSM or Electrical Diagram? Perhaps that would help you find out what the wire is for...You can pick up a copy of the '77 Electrical Diagram Here.

[cbuczesk]

I looked at the diagram that ZCurves provided. One BL (Black w/bLue stripe) wire goes to the condensor and the other BL wire goes to the ignition switch "START".

Chuck

[Zed Head]

A shorted condenser seems to fit the symptoms. The OP could check continuity from the condenser body to the wire end. Or just disconnect the condenser at the other end of the wire (it should have a bullet connector) and see if it still drops voltage when connected.

[jkeese01]

Thanks for the diagram. Print as poster form over 14 pages it's very easy to trace. I was trying to use the one on the FSM pdf, a very low quality copy.

Checked the unplugged wire with a multi-meter and it goes to ground (alternator condenser).

Alternator Condenser wire plugged in - Pin 1 drops to 3.6v, car cranks and idles but chokes if you press on the gas.

Alternator Condenser wire unplugged - test normal at battery voltage, car cranks and revs.

but ...

Drove the car last night for the first time in 3 weeks (about the time I plugged in the condenser wire). The car ran a little rough, but did run. Three weeks ago it was running perfect. After driving about 2 miles, the car started choking again, but could still be driven.

<b> Could having the alternator condenser plugged in damaged the coil? </b>

Thanks.

Edited June 5, 2012 by jkeese01

[Zed Head]

In theory, your coil shouldn't work if the current isn't cut off but maybe the drop in current through the ignition system is enough to collapse the coil field. I'm no expert. But the condenser wire should not go to ground.

And the condenser in question should be the one by the coil, not the alternator condenser. Many people run without it, I think that it's there for voltage spike protection, or random radio noise.

You can test your coil by measuring resistance across the primary circuit (+ and - posts) and across the secondary circuit (one of the posts and the main wire). The specs are in the FSM, Electrical section, but I think that they are around 1 ohm and 10 ohms, respectively.

[jkeese01]

(Typo above: should be coil, not alternator)

Thanks for the diagram. Print as poster form over 14 pages it's very easy to trace. I was trying to use the one on the FSM pdf, a very low quality copy.

Checked the unplugged wire with a multi-meter and it goes to ground (coil condenser).

Coil Condenser wire plugged in - Pin 1 drops to 3.6v, car cranks and idles but chokes if you press on the gas.

Coil Condenser wire unplugged - test normal at battery voltage, car cranks and revs.

but ...

Drove the car last night for the first time in 3 weeks (about the time I plugged in the condenser wire). The car ran a little rough, but did run. Three weeks ago it was running perfect. After driving about 2 miles, the car started choking again, but could still be driven.

<b>Could having the coil condenser (which is broken and measures ground) plugged in damaged the coil? </b>

Thanks.

[jkeese01]

Tested the resistance across the two terminals below the coil per FSM page EE-30, good range is 1.6 - 2.0 ohm, tested at 2.0 ohms. Then tested the continuity from wires disconnected from the Ignition Unit ("R" and "G" colored wires), tested at 750 ohms, FSM says around 720 ohms is good. Some of the other test require an oscilloscope.

I'm going to assume the coil is good. Was hoping the coil would fail the test and be the cause of the car run rough when the engine warms up.

More testing.

Thanks.

[Zed Head]

It really sounds like you have a short from ignition circuit, causing the big voltage drop when that wire is connected.

Test resistance from ground to the wire at the ballast resistor that affects the way the car runs. One probe on the engine block, the other on the wire end, measuring resistance. It should be infinite. If you get a resistance reading, then the condenser is bad, or there is a short in the wire to the condenser, and it may be causing the poor spark. It would be taking current (shorting) that would normally be used to charge the coil. That might explain why the car runs good with it disconnected. It would behave similarly to a bad coil.

[stroccoli]

I had a similar problem on my 78' (no balast resistor in the engine compartment)

It would bog on rapid acceleration, but very slow increase in throttle would not cause it

When it failed the tachometer would die (zero), and ignition stop.

Also during regular driving conditions it would balk randomly between 2-3000 RMPs

After chasing through the entire ignition system, trying an AFM (another site recommended) and the tps (I thought maybe the 2-3k throttle position might be doing something), and coil I thought hmm... distributor vacuum ?

I dis-connected the vacuum advance and it's corrected (doesn't bog).  Ordered a new distributor.

Apparently in mine the vacuum advance is shorting out the ignition circuit in the distributor. 40 year old parts behave strangely