427/425 Engine Problem

[Walter R.]

Re: 427/425 Engine Problem

Yes I checked Voltage at coil when engine starting to shut down and it is in correct range. Fuel system checked and double checked. Not the problem. Coil from NAPA not TI coil.

[Joe T.]

Re: 427/425 Engine Problem

The last thing I can think of is timing.. Had a problem with over heating causing the coil to break down when hot. The change in timing resolved my issue.

[Joe T.]

Re: 427/425 Engine Problem

Check out "1966 L72 running hot". You will see problems like yours..

[Walter R.]

Re: 427/425 Engine Problem

thanks. I will

[Walter R.]

Re: 427/425 Engine Problem

I check out post "1966 L72 running hot" but my engine is not running hot. Engine not overheating at all. The ignition coil is heating up evidently.

[Timothy B.]

Re: 427/425 Engine Problem

Yes I checked Voltage at coil when engine starting to shut down and it is in correct range. Fuel system checked and double checked. Not the problem. Coil from NAPA not TI coil.

Then could the problem be a junk reproduction coil (not uncommon) plus the NAPA coil is the wrong part for the TI.

Have you tried a known good original TI coil?

[Walter R.]

Re: 427/425 Engine Problem

The TI coil that I have is a Delco Reme that was sent to me by TIS with the module, harness and rebuilt distributor. I any willing to buy a proper TI coil as I have not ruled anything out with regards to ignition. I have definitely ruled out fuel as source of problem. Any recommendations on source for good TI coil? One other occurrence is this AM I started engine with Delco coil installed. Volt readings at + coil terminal was jumping all over the place from 0.6 - 2.6. Prior readings thken recently settled at 2.6 and did not move around by more than 0.2 during idle. I have no idea why the readings would all of sudden start jumping around like this.

[Richard M.]

Re: 427/425 Engine Problem

Walter, You can't get a stable DC voltage reading at coil+ with engine running. It is a pulsed signal from the TI Module output Solid State amplifier. It can only be accurately measured using a oscilloscope. With IGN ON, you should get 2.5 to 4.5 V DC with a meter. Follow the TI troubleshooting flowchart(in my earlier posts) to help diagnose.

For the record, a non-TI ignition coil will work but as stated earlier it just will not allow maximum spark voltage. I used a NAPA IC12 (points) coil for months on a L71 with no noticeable issues. I had 2 bad TI coils that failed hot. I went with a DR 207 NOS coil and the car has been fine for over a year now.

Back to the fault....

It certainly seems like vapor lock to me. When it stalls do you get fuel at the carb accelerator squirters immediately after the stall condition?

Yes it may be a bad coil when hot too. But the NAPA non-TI coil should work for fault isolation testing.

The only other thing I'd verify is the distributor Pickup Coil when it stalls. Immediately after stall, IGN OFF, then separate 2 terminal plug at distributor. Connect a Ohmmeter to distributor plug lead terminals. Measure 500-700 ohms. If not, there may be a intermittent internal connection that opens when hot.

Rich

[Richard G.]

Re: 427/425 Engine Problem

When the engine stalls did you check voltage at the coil + again to eliminate that as a possible cause?

Although confirming 12V at the coil is a great first step it doesn't confirm there is enough amp carrying capacity in the circuit.
This can only be confirmed when the circuit is under a load. Been bit by this before.

[Walter R.]

Re: 427/425 Engine Problem

Yes I have checked. One thing I am going to try next is to run a 12 gauge wire direct from battery to the TI harness bypassing ignition wire. At his point I feel my issue is in wiring or I have a amplifier issue. I checked resistance at distributor lead yesterday and reading was spot on. I am at a point now where I have to remove and replace parts until issue solved. If I don't find solution soon I will be forced to purchase $450.00 amplifier or $160.00 TI harness.

[Joe T.]

Re: 427/425 Engine Problem

I found my 3 bad "made in china GM restoration coils" by; when hot and engine shuts down, disconnect the negative and positive wires, read the ohms between the + and -. If "0" you have a coil that is breaking down when hot.. All readings will be fine when cold.

[Richard M.]

Re: 427/425 Engine Problem

Yes I have checked. One thing I am going to try next is to run a 12 gauge wire direct from battery to the TI harness bypassing ignition wire. At his point I feel my issue is in wiring or I have a amplifier issue. I checked resistance at distributor lead yesterday and reading was spot on. I am at a point now where I have to remove and replace parts until issue solved. If I don't find solution soon I will be forced to purchase $450.00 amplifier or $160.00 TI harness.

Walter, I recommend NOT to connect battery power directly to the TI Module by bypassing the Resistor wire. The original design required the resistor wire(IIRC apx 0.6 to 0.8 ohms) as a voltage reducer to ensure a stable but nominal voltage to the AMP and Pickup Coil. During RUN, the battery charging voltage could exceed 13.8 Volts and could possibly damage the AMP. I do not know what the K&B or M&H amplifier specs are but you might cause harm as this has never been published as a method to diagnose the TI system.

The only way battery voltage is supplied to the AMP and Pickup Coil is during START, via the Starter Solenoid "R" terminal connection back to the TI Harness. During Crank, the battery voltage will typically be 12.6 volts or less. When engine starts and key released to RUN, this is then disconnected.

To verify the harness when the failure occurs, I would use a ohmmeter to check the resistor wires end to end. If there is a heat related failure it would show then, but moving the wire could make it make/break so it may be difficult to verify.

Do you know which type of AMP Dave at TI Specialty included when he sent the rebuild system back to you? K&B or M&H? You may want to ask him to check his records. Either way it may be wise to open the AMP case to check ground from the circuit boards to the AMP case. The 3 internal mount screws create this ground path. If the screws are too long and bottom out this could create a intermittent ground.

Also, do NOT connect 12 volts directly to the Coil+. This would force a higher voltage directly to the AMP final transistor output and could damage the device, even though there is also a resistor in the path back to the AMP from Coil+.

Rich

[John M.]

[Joe T.]

Re: 427/425 Engine Problem

John, It was Chicago Corvette. I had purchased 3 GM restoration (made in China) coils. The all failed when hot. The coil from positive to negative should read .41 to .51 ohms. They would read 0 ohms hot then back to .46 when cold. They located an original 1115207 made in USA coil, refurbished it and problem solved. You can read the NCRS forum 1966 427 425HP coil. Other articles on the internet relevant to this problem also.

[John M.]

Re: 427/425 Engine Problem

Thanks Joe.
I now have a K and B circuit board and a K and B coil. All seems fine but only have a few miles on this setup. Prior to this I had the Kand B board and a 0.7 ohm generic coil and the car died at the entrance to a car show 30 miles from home. Got towed home 1st time in 20 years. Car started next morning.
Time will tell re this setup.