Voltage drop when cranking starter

I'm trying sort out a couple of problems I've had since swapping my 350 to a 455 last fall. One is a starting problem and the other is that the engine sometimes dies after giving just a little throttle to go up an incline or just because I felt like punching the accelerator.
While looking at the starting problem I checked the voltage to the 12+ lead to the HEI ingnition and found that when the starter is cranking the voltage drops down to between 1.8v to 3.8 v. at the distributor and then returns to 12v when I let up on the starter. Is this normal? If it's not normal is it the starter drawing to much or the battery possibly getting weak?
The second problem is probably due to the carburetor that was selected for the rebuild was a poor choice for a cruiser and needs to be swapped which I plan to do this week. But a weak ignition could be playing into the problem as well. The spark plugs are carbon fouled and damp after drivng for just 20 or 30 minutes a low speed in the city. I've checked the fuel levels in both bowls and adjusted the idle mixture for the best vacuum and rpm but the problem remains. My plan is swap the carb to something a little more street friendly but I'm concerned about the voltage to the distributor. Any thoughts

 

Larry,
The 12+ distributor lead is off the fuse block. It's the same one I'd been using with a DUI distributor on the 350 for 3 years. I've checked connections at the block and the distributor and they seem stable.
The battery is almost 5 years old. It was fine until after the engine swap in late November. The engine has been started a dozen times since then but it never starts easy. I didn't suspect the battery at first because it always cranked the engine over fine but while looking for answers I noticed the voltage drop during cranking. Dropping from 12v to 3 v seemed excessive but I wasn't sure.
I replaced the old battery cables with new 2 gauge cables during the engine swap so I don't think that they are a problem. Connections at the battery and starter are good.
The starter came off of a 1975 455 engine block that I had in storage. It seemed to be fine so I used it.
I think that I'll replace the battery anyway if for no other reason than it is 5 years old.

 

Does it crank ok, and just not start?

I suspect that what your seeing on the dist + feed is that it is going open circuit, when the ignition switch is rotated to the start position.

A quick test is to wire a jumper lead to the battery from the + input to the Hei, and try that.

Most feeds in the fusebox go dead when the key is in the start position. It may have worked before with a points type distrib, if you still had the relay bypass hooked up to the coil..

 

Jim,
The old 350 had an HEI as well hooked to the same lead and did not have problems starting. The voltage at the lead now goes to between 1.8v and 3.0v when cranking the 455 but it does not go to zero. It does go to zero when the engine is turned off as you would expect. The 455 got new or rebuilt everything except the starter which I had laying around in the garage. Took the battery up to the parts store this afternoon and it tested OK. A print out of the test said that it had about 12.5 v and 772 cold cranking amps which suprised me. I expected to hear that it was near death. So now I'm thinking that the starter is drawing far more than it should but still cranking. It that possible? Anyone heard of this this happening?

 

check your amp draw on the starter anything over 250 amps then your starter is done but ya pretty common when a starter starts to go also check your ground wire is it hooked to the block or engine somewhere if its hooked to the frame it wont work the starter very well

 

A 5 year lifespan on the battery is the best you can expect to get. Replace the battery and get one with the proper CCA rating, the higherthe better.

 

Replaced the battery tonight but the voltage still droped below 4 volts at the 12+ lead to the distributor while cranking. Measured the voltage at the positive lead to the choke while cranking the engine and it only dropped to 10 volts.

 

if you have a resistor wire on the coil this may be correct
does it crank slow or what

 

When chasing a voltage drop, it is best to start at the source. Something to consider is the ignition system. Are you using the HEI on the 455? Where are you checking the voltage? If you are on the + side, that should have battery voltage when the key is on. Let's be methodical here, not jump from one poin to another. If the battery can crank the engine with the ignition dosconnected, we are looking for another problem. Let's address one thing at a time.

 

I'll try to answer everyone's questions
First, I'm not using a resister wire because it is an HEI so I'm going right from the fuse block to the distributor with 12+. I have 12+ at the distributor when the key is in the on position. So far so good.
Second, because of the starting problems I've had, I became concerned that I was not getting the spark I need from the distributor when the engine is cranking. So I measured the voltage at the distributor and I found that it drops to below 3 volts while cranking so I thought maybe I was on to something. Next I went to the 12+ lead to the choke just to see what voltage was there while cranking and found that it was around 10 volts. I thought this was odd because I expected to see the same drop that I saw at the distributor.
It took a long time but eventually the engine started today and it ran fine but I'm concerned that something odd is going on with the electrical system that I don't understand.

 

If the HEI voltage is that low, it is possible for the ignition to be affecting it directly. It is possible, for example the module to pull the voltage down that far if the transistor is partially shorted. Other shorts in that circuit include the ignition coil, and a possibly defective connection between the battery to the module, including the ignition switch, or the wiring. The reason that the questions were posed here was to help you solve the problem. Knowing, for example, the battery voltage at this point tells us where the problem may be. Troubleshooting voltage drops is easy, but you must be methodical in the troubleshooting, or the results will not be conclusive. I suggest, at this point, that you test the connections from the ignition switch to the ignition, including the one runnning from the battery to the switch, and from the switch to the coil. This will narrow the search, and provide the answers we all want you to have.

 

Yep:TU:

 

Ron, when I put my HEI in my car years ago I used 12 ga. wire from the 10 ga. purple wire that becomes hot when you turn your ign. switch to the on position. under the dash. Check with a test light turning the ign. switch on & off, not starting the car!! This gives you direct 12 Volts constant when starting.

My car has been set up like this for 20 years now, I found out about this in a car mag. article years ago. I now use a MSD 6al with my HEI and never changed any of the wiring.

When looking for this Purple. wire its in the large cluster of wires wrapped in the factory electrical tape about a inch round cluster by the steering column. You;ll have to slowly unwrap it and dig in to it to find it. Once found & tested, cut off a 3/4 section of sleeve off and split in the middle of the copper wire with a small screw driver to leave a hole. Slide the 12 ga. stripped wire in the hole and wrap around it and solder it or just wrap it real tight with plenty of elec. tape. ( should solder it and wrap it with tape) after testing for start up.

Now run your 12 ga. wire safely through the fire wall long enough to reach the HEI battery wire at the dist. and connect it. Should be good for 12 volts everytime. Doing it this way bypasses the fuse box, no delay with connections anywhere.

good luck!! jerrold :3gears:

 

Thanks everyone. Early on it was a bit confusing sorting things out because I also had a fuel issue that surfaced at the same time. I thought maybe a weak ignition could be contributing to the hard starting and the carboned plugs. Turns out the plugs were the fault of the carburetor. With that problem solved it was possible to focus on the electrical. The electrical is present most of the time then when you are about to give up the engine starts. I'll take your suggestions and move the 12+ to a better location. I'm certain that the starter switch is still causing intermitent problems and I'll deal with that on Tuesday.
On the positive side the car starts easier after the carburetor change. Took it out for a drive tonight and it ran well. The 455 has more power than I hoped for and will be a lot of fun this summer. It likes gas...a lot.

Hey Jerrold. Good to hear from you, thanks for the ideas.

 

Hey Ron, no problem, make sure you move that 12 volt wire, eliminate the headaches.

Enjoy that buick power,

good luck, jerrold