Ask Away! with Jeff Smith: Troubleshooting Hot Starting Problems in a Chevy 454

(Image/Detroit Demigod)

I have a ’69 Camaro with a 454.

I went to fill it with gas on its first run for the spring and drove it perhaps 20 miles. After stopping briefly, it would not restart. The engine sounded like it wanted to crank but turned over slowly.

The battery tested 12.8 volts and its only six months old, so I don’t think that’s the problem. I changed starter motors last year to try to cure this problem and it seemed like it was fixed. The fuel line runs along the frame and is close to the headers at one point. Could this be causing vapor lock after I shut it off? It starts fine when it’s cold. — D.G.

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Jeff Smith: While it’s possible that you might be suffering from vapor lock—especially if the fuel in the tank was still a winter blend, I don’t think the problem is fuel-related.

Your comment that the car experienced hot-start issues the previous year, leading to both a new battery and starter motor leads me to a completely different conclusion.

This is a growing problem as of late given the increase of low quality store-bought battery cables being in service.

I’m confident that your problem can be quickly repaired by replacing both battery cables.

It’s likely that the problem stems from either a poor ground circuit between the engine and the battery or a voltage drop in the positive battery cable.

You can perform a quick test to establish the actual culprit. But before we get into that, the answer is that your starter circuit is experiencing excessive resistance either in the positive battery cable down to the starter, through the ground circuit, or likely both.

To illustrate this, a good friend had a similar problem on his ’68 small-block Camaro.

I was at his house one day when the car cranked very slowly. He complained that he had replaced the battery, the starter motor and cables, and the car still cranked slowly. His battery was fully charged and he was about to remove the starter motor and return it as defective.

I suggested that instead we perform a voltage drop test on the battery cables. This test uses a common multi-meter set on DC voltage.

We hooked one lead to the negative battery terminal and the other to where the ground cable bolted to the engine. Next, we disabled the ignition and cranked the starter motor.

The digital voltmeter read 1.2 volts.

That might not sound like much, but a good connection and a high quality cable would actually reveal closer to 0.40 volt.

The test of his negative cable revealed that it had roughly three times more resistance as evidenced by the high voltage reading. In essence, we are using a voltage reading to indicate resistance in the circuit. We tested his positive battery cable and it read an even higher 1.4 volts!

My friend was highly skeptical that this was his problem.

I offered to make high quality battery cables for his car out of 1\0 copper, multi-strand welding cable with good copper lugs but he still thought that was a waste of time.

I insisted, reminding him that it would cost him nothing if the new cables didn’t work.

Only then did he relent.

We spent time building nice cables with copper lugs on each end, and installed them on the car.

We then reconnected the ignition lead and he cranked the engine over and it spun like it had 24 volts feeding the starter motor. We then disabled the ignition again and checked the new cables and found a voltage drop of 0.35 volts for both cables.

Once we were finished, I grabbed his old cables and used a hacksaw to cut them in half and threw them away (much to his displeasure).

I knew that he would be tempted to re-use them on some other project if I didn’t destroy them. They were cheap, pre-packaged cables, and obviously not up the task of cranking over his 10:1 compression small-block!

My evaluation is that your hard-starting problem is not at all related to vapor lock, but is related to heat soaking of the starter motor.

The heat increases the resistance which is why it starts when its cold but not when it’s hot. The issue is excessive resistance in the battery cables.

My suggestion is to replace them with high quality, multi-strand copper cables.

Ideally, build your own out of 1\0 copper welding cable using the copper lugs. You can find this cable at any good welding store or at Summit Racing which sells bulk lengths of cable if you will be building cables for more than one car.

The best way to know for sure if the cables are bad is to perform the voltage drop test.

The voltage indicated on the meter is directly related to the amount of resistance in the circuit. A voltage drop test must be performed dynamically. That means connecting the leads from the voltmeter to the opposite ends of the battery cable while the starter is cranking.

The higher the voltage reading, the more resistance there is in the circuit.  You can even test the amount of resistance between the battery post and the cable end if you like.

Most guys won’t do the testing, but if you make the effort, it will point to the exact problem area in the starter circuit.

Remember, heat creates resistance. When all the parts in the circuit get hot, the resistance in the circuit increases, making the job of moving current from the battery to the starter motor more difficult.