427/425 Engine Problem

[Richard M.]

Re: 427/425 Engine Problem

As everyone can see this issue has been difficult to diagnose. We thought we had problem solved several times only to discover it wasn't. Adding to my issue whenever my engine would stall my battery was weak even though battery checked out OK. Found faulty voltage regulator was culprit and replaced. We determined my coil was getting hot after running for a period and replaced. After driving car for a few miles and returning to shop we thought the problem was solved. While car sat idling the problem surfaced and we were back to the same issue. We were convinced that the coil heating up was our problem. My mechanic put a volt meter at the pink ignition wire where it attaches to the white resistor wire in the TI harness with a reading of 12V with ignition on. We tested the other end of the resistor wire that attaches to the coil and got the same reading. This did not make sense as we should have a voltage drop at the coil side. I bought a resistor from NAPA and attached the pink ignition wire to one side of the resistor and the white resistor wire to the other side. We got a reading of 6V at the coil with ignition on. I drove the car for several miles returned to the shop and let the car idle. The engine continued to run great and the coil remained warm but not hot. Does anyone have any ideas what is occurring. Can you have a faulty resistor wire?

Walter, With a high accuracy Ohmmeter you can measure the resistor wire end to end. IIRC Dave told me it's about .6-.8 ohms or so.(I have notes somewhere) It's the Black wire in the 3 terminal plug at the TI Module which becomes the White braided wire to the Coil+
Wiring Diagram HERE

Also....

12V with IGN on indicates these possible faults....HERE

1- Open in Primary Circuit (I believe this means the Black wire from TI Module, through resistor wire, to Coil+)

2- Bad Ign Coil

3- Open Ground to Coil-

Attach a jumper between known good Ground Directly to Coil-

If now normal 2.5 to 4.5 volts, fault is Bad ground to TI Module/Coil- (Make sure the Ground Wire at the TI Module case has a good clean connection, as this is Coil-)

If still 12V... Bad Ign Coil.

[Walter R.]

Re: 427/425 Engine Problem

Richard, I have 12V with the ignition on at the pink wire where it attaches to the white resistor wire. I would think this should be 12V as it is coming from ignition. The 12V at the other end of the resistor wire that attaches to the coil is the reading we don't understand.

[Richard M.]

Re: 427/425 Engine Problem

Richard, I have 12V with the ignition on at the pink wire where it attaches to the white resistor wire. I would think this should be 12V as it is coming from ignition. The 12V at the other end of the resistor wire that attaches to the coil is the reading we don't understand.

Walter, There are 2 White wires, and both are resistor wires. This may be the cause of some confusion.

Yes your 12V at the Pink is correct, as it's from the IGN switch. That goes through a White resistor wire to power the Pickup Coil in the distributor as well as the TI Module. Also, during Crank, the small gauge Pink from Solenoid R terminal then supplies Battery Voltage for increased TI Module and PU Coil voltage.

Edit... The IGN pink goes to White, then back to Pink to TI Module. This is shown in TI Wiring diagram link.

The other White wire going to Coil+ is from the TI Module. This is a different White wire. Your 12V there with IGN on should be 2.5 to 4.5V.

Rich

[Richard M.]

Re: 427/425 Engine Problem

Walter, One more thing about Grounds. I may have mentioned before but here it is again. THis has to do with the mounting of the TI Circuit Board inside the Module Case.

You may want to remove the Module case from the car and open it up. There are 3 machine screws that hold the Circuit Boardf to the case. Thes create a ground for the Circuit Board.

If the Board is not grounded properly this can cause intermittent faults. You may want to open it and check these screws. THe original screws will bottom out when using the K&B Circuit Board(Green). I always use shorter screws and toothed lock washers there.

Rich
PS More info HERE
PPS Heading out for the day but I'll try to check in later.

[Walter R.]

Re: 427/425 Engine Problem

The white wire going to the coil from module shows 12V with the ignition switch on. This is why we installed a resistor at the pink ignition wire as we were getting this reading. After we installed the resistor the reading at the white wire that attaches to the coil was 6V.

[Richard M.]

Re: 427/425 Engine Problem

Walter also check rubber plug to TI Module. If Black wire is open that may cause problem also.

[Joe T.]

Re: 427/425 Engine Problem

I had 3 defective GM Restoration coils in my 1966 427/425HP (Two 1115231's and a 1115261). Finally found an original used 1115207 and problem went away. The defective made in China coils were so hot you could not hold them. Also when checking ohms when hot the reading was 0. Don't overlook the coils.

[Walter R.]

Re: 427/425 Engine Problem

I still have a pretty nice 66 but you can't drive it because there is no chance that it will run correctly. I did a complete rear end freshen up over the winter so things have been going on but I am back trying to fix my issue. The problem is consistent which is a big help. I drive the car out about 3 miles and return to garage. On start up and during the route car runs great. Temp on engine very normal. When I get back to garage if you let it idle within a minute or so engine starts to labor with RPM's dropping and eventually shuts off often backfiring before shutting off. You might be able to re-start or might not. When running I have 4.6 volts at positive side of coil. I have experimented with another coil the last few days and this experiment has worked consistently. When engine shuts down I quickly replace coil on engine with another coil that is at ambient temp. The engine starts up and runs great. I can replace the fresh coil after a short time with the hot coil and start engine. It might run for 60 seconds labors and shuts down. Something in my ignition is causing the coil to heat up creating my issue. Any ideas would be appreciated.

[Walter R.]

Re: 427/425 Engine Problem

Today I connected a ground wire directly from the battery to the TI module. I also ran a ground wire from battery to coil. Car started and ran great. I went on my 3 mile trip after returning to my garage the engine ran for about 7-8 minuets just idling before laboring and shutting down. For a short while I thought I was on to something but problem was still there. I don't know if ground wires helped or was a result of something else. I installed my other fresh coil, started the engine and it ran great with fresh coil at idle. Not sure what I'm going to do next, maybe an exorcism.

[Timothy B.]

Re: 427/425 Engine Problem

Have you thought about bypassing the ignition switch and going from battery + to a ballast resistor then to coil +.

If you find it helps go look backwards in the car wiring.

[Walter R.]

Re: 427/425 Engine Problem

I'm not quite sure where this would help. I have 12 volts coming from ignition to TI harness that connects to resistor wire. My readings at the coil + are within range. Given everything I have done it appears now I am at possible problem with distributor, TI module or I have two bad coils.

[Gene M.]

Re: 427/425 Engine Problem

Poster stated ”All new harnesses on car with complete TI ignition parts from TIS with the exception of distributor which he rebuilt.” Being this is in direct interface with the coil and temperature get extreme, I suggest you have these pieces examined. Being deficient in electrical issues myself maybe someone that is electrical circuit intelligent could “ring it out” I’m not implying by any means that persons here are deficient but merrily saying something out of the normal trail of diagonistics is required.

[Timothy B.]

Re: 427/425 Engine Problem

Walter,
I can only share a few thoughts, in one of your posts above you state 12v at the white wire and then you installed an additional resistor which yielded 6v at coil + with key in run position, correct?

Is the white wire you are speaking of a resistance wire? Have you tried to idle the engine without the added resistor, you may not have enough voltage because of this.

Are these coils reproduction coils?

[Walter R.]

Re: 427/425 Engine Problem

I don't have the resistor on anymore. This was one of my many attempts to fix issue which there have been many over two years. My ignition is set up correctly with everything correct and the volt readings are all in the range that you would look for. One coil is a NAPA over the counter and the other was sent to me from TI when he sent rebuilt distributor, harness and module. Both operate the same running fine on start up, during my three mile test run and the engine shuts down the same way with either coil. The coil from TI will be the one I will use when this becomes a driver car if that ever happens. I bought the other from NAPA as a cheap substitution to rule out a defective coil.

[Timothy B.]

Re: 427/425 Engine Problem

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

Is there any chance there could be a carburetor issue and not an electrical issue, have you given any thought to that?

I did not know NAPA made a coil for transistor ignition, what's the part number.