sTz

While I’’ve never had the need with the C7, I’m curious as to whether the M7 could be started with a dead battery on a roll by popping the clutch, or is there a start/stop ignition feature to prevent this type of maneuver.

I imagine that there would have to be a degree of charge remaining to engage the start button, and know that there are obviously other means to starting a car with a drained battery, but was wondering if the “bump start” technique is still possible.

This might be addressed in the OM, but I briefly looked and didn’t see anything... Thanks

The HACK

I’ve been told since the early 2000s that roll starting a modern car is more trouble than it’s worth, as the spike in voltage from a roll start instead of using the starter plays HAVOC on all the car’s electrical systems.

In a pinch, where you don’t have access to roadside assistance? I suppose it’s worth trying to get it moving to a point where zombies and masked killers can’t get you. But the last car I tried that on was a 1991 BMW 3 series and it ended up needing a bunch of electrical work after.

JMII

Just guessing... but given all the computers in the C7 I doubt it. The car will not start without sensing the clutch being depressed and that switch requires voltage to function. Plus the push button ignition clearly requires voltage to work.

Zjoe6

Nope. This car needs power for all the electronics.

owc6

This from p.10-74 in the '14 OM under the section "JUMP STARTING":


"Trying to start the vehicle by pushing or pulling it will not work, and it could damage the vehicle."

orca1946

Good question as we all did this in our older cars when we were young!

Vette Ski

GEEEZE, I haven't pushed started a car since the '60's !
Rich

MikeERWNC

How would you get power to the injectors if the battery is dead? Fuel through the pumps?

The HACK

The wheel drives the transmission, the transmission drives the engine. As the engine turns, the alternator will supply power. That's always been the basics of push starting a car.

The clutch interlock merely prevents he starter from turning without the clutch being depressed, but the MECHANICAL means of supplying spark via alternator doesn't change. It does, however, as I mentioned before, plays havoc on all electronic systems because unlike using a starter to get the engine turning, the alternator supplies higher voltage and F**Ks up all electronics with the resulting spike. It SHOULD work, but the price you pay afterwords isn't worth is.

jimmbbo

Identical warning in the '17 OM page 293

Bill Dearborn

The problem is the BCM and the ECM need a minimum voltage to work. If the battery is truly dead there is insufficient voltage to power them. The BCM controls the overall charging system while the ECM provides the turn on signal to the alternator. On a car with a good battery and doing a normal start the ECM provides the turn on signal after the engine has started and stabilized at its idle rpm. The ECM then controls alternator output voltage by varying the pulse width of the turn on signal. The smaller the pulse width the less voltage generated. 10% pulse width is 11 Volts. 0 pulse width will be 0 volts.

There has to be sufficient voltage produced by the battery for the electronics to work. That voltage level is probably 9 Volts or higher. Without that level the ECM isn't alive and can't control the ignition or the fuel delivery to the engine and can't provide the alternator turn on signal.

A system voltage spike occurs happens after every start. In Start Mode the BCM sets a voltage level of 14.5 volts right after the engine starts and the ECM supplies the proper pulse width to get 14.5 V.

I haven't had a starter failure on my C7 but did have a failure with my C6Z which left the car stranded in the middle of the paddock at a track event. We tried push starting the car (the battery was fully charged) but the car would not start.

Bill

JMII

Good point. I was thinking of the start up routine for all the subsystems firing off in the proper order. Push starting rearranges that sequence in a way GM never accounted for.

Further proof this ain't going to work - just look at problems reported around here by people whose batteries are almost dead. The car might have enough power to start (IE: spin the engine) but all kinds of other stuff fails due to lack of voltage or current flow. Basically the car runs off the battery and the alternator recharges it. If the battery is dead or can't hold a charge the whole electronic system is compromised.

Widgeon5

Just out of curiousity I tried to start my M7 by rolling it down an incline (and this with a full battery.) It was a mistake. Engine did not start, and numerous electronic gremlins appeared. And then it would not go with the starter either. I thought I had really done some damage, but after turning everything off for a minute it started normally and everything has been fine since. I won't do it again.

Vette Ski

I know a lot of us carry ( or should ) carry a P.P.S. I have the Micro-Start X P-1, Personal Power Supply. It is an older model but it sure saved a few people I came in contact with that had dead batteries on the side of the road or in parking lots.
Rich

~Stingray

Never had the pleasure of trying. My oldest car is a 1980 and it hasn't died on me yet. Ya, float chargers!

4thC4at60

I can still do it in my '88 Ferrari....

Yes, I know that's old... couldn't resist... yes, I know... I should have....

Vette Ski

Graduated Dickenson high school in Jersey City in '64. Few of my friends drove $hit boxes back then didn't have the money to buy new batteries, ( so we had to push start many a time ) could barley afford the $0.26 per gallon of gas. But we did have a good time, and I made it out alive !!!
*** My first car was a '55 "black" 2 dr. hardtop ( 265 ci Powerglide 2 speed trans ) I bought from my Uncle in '65 for $35.00
My first New car was a 1965 green Impala 283ci 3 speed manual
***My first "Great" car was my '67 Granada Gold Chevelle 327ci.4 speed
*** And my Last "Great" new car is my '19 "black" GS
Rich

JScottH3

yep. The last time I did it was with my '59 Ford in 1967.

Walt White Coupe

I know this is going against the grain but my C6 was manual trans car. Occasionally if the car was on a hill, I'd put the car in what we use to call the run position but with the C6 and the C7 you just have to hold the start button for 10 seconds without the clutch and it goes into test mode or something like that. Now as long as the battery has enough juice to put the electronics into that test mode, if you roll the car and drop the clutch, and it will start. Didn't do anything abnormal to my C6 and my C7 is an auto so won't be trying it with that car.

sTz

‘60’s!?! I was bump starting a beater Mustang well into the ‘90’s. Made sure I always parked on a hill just in case


Thanks everybody for your responses. Good to know that it’s not possible...