Pop-starting--can you do it?

[SamSnyder]

My wife killed the battery leading to a debate about whether you can bump-start a fuel-injected 5.0. A jump start saved her but can you do it? Don't you need power for the pump and injectors? Her crazy co-worker was trying to get her to try, but jumper cables saved her bacon first.

 

[86bluecobra]

i guess if your battery is stone dead it wouldnt work. but usally there is enough juice in it to run the electric fuel pump for the 5 sec it comes on for before the car fires. if the battery is stone dead then dont bother trying

 

[kslushy]

Yes. From experience, the minimum speed you need to have pushed the car is about 5 mph.

 

[HISSIN50]

The puter will even open the coil's dwell when it 'senses' it is being compression started, but I can see why Sam is asking - with everything completely dead, I am not sure how it would start. No juice for the FP (if pressure bled off), no spark and no injector pulsing......ergo no soap.

I wonder if anyone has compression started a completely dead (no static charge on the battery - nada) car? I dont see it happening.

BTW, there is some horrible flashing message to the right of the quick reply box - anyone else getting that? I gotta go find aspirin.

 

[Linz]

Yup, have had to do it several times.

 

[tjm73]

You can bump start EFI cars. I've done it. I had a Tempo (remember them things) that I left the lights on with once. Turn the key and nothing about 4 hours after I parked it. No one would jump the car even though I had jumper cables (a-holes ). Anyway my buddy and I push it out of the parking spot and get ready for the push. Get it up to about 5 mph and I jump in clutch the floor, shifter to 2nd, pop the clutch, it jerks a couple times and vrooom it's running.

The question about needing electricity to run the fuel pump is valid, but the logic is incorrect.

The fuel in the lines is under pressure even after it sits for a while. It may be low pressure, but it's pressure. The ignition system also saves stored energy inteh coil packs to run the spark in the event that this has to be done. Once the alternator starts turning it's making electricity for the system to run on and the injectors start firing.

I think I read someplace once that EFI systems are designed to allow this type of starting as a fail safe if it's ever needed. Most of the time when a battery is "completely dead" it still has a little bit of power too.

 

[Zero_chance]

Its even in most service manuals that "provisions are made to allow push starting."

 

[slo65]

my friend had a evo rs and didnt believe me, so i told him how to do it, he was all amazed

 

[megan_92]

my car pop-starts like a pro.

 

[wake]

ive had 2 do it, about a 2ft roll down hill and pop of the clutch.

 

[HISSIN50]

The question about needing electricity to run the fuel pump is valid, but the logic is incorrect.

The fuel in the lines is under pressure even after it sits for a while. It may be low pressure, but it's pressure.

So when the battery is completely discharged (part of the original scenario as I read it), how does the EEC power up? Ask a few stangers what their fuel pressure is after a few hours (esp ones with adjustable regulators) - the car will NOT start with very little fuel pressure - not w/o excessive priming.

Also, we dont have coil packs - there is no capacitive capability that I know of in one of our ignition coils to help with 'dead battery compression starts'. Opening the coils dwell is as good as it gets.
The EEC has capacitors but they are only to store learned strategies/settings. they are not there to help start the car.

And I thought we were going off the premise that the battery was completely dead (I prefaced what I said with there being no surface/static charge). In other words, if you could remove the battery and compression start the car (if one was able to w/o frying the puter and other electronics), would the car start from whatever tiny amount of alternator output there is from the initial bump.....That is the question as I interpreted it.

I thought Sam had a very interesting question. TJM is about the only one I see who posted about the completely dead battery scenario (Though I respectfully disagree with a point or two of his). If others are talking about having a completely dead battery, they did not say so in their posts. I have the feeling there was a surface charge.

 

[darthcual]

Wow i smell a test coming on! Someone this weekend will A) take their battery out of their stang and B) roll it down a hill and into the woods popping the clutch screaming, "Start BABY START!!!!!" LOL

 

[HISSIN50]

Wow i smell a test coming on! Someone this weekend will A) take their battery out of their stang and B) roll it down a hill and into the woods popping the clutch screaming, "Start BABY START!!!!!" LOL

I am hoping not - that is a good way to fry electronics.

And it is best not to roll into the woods while doing tests like this.

I really dont know myself - i do whatever I can not to compression start or even jump start dead batteries (very hard on the charging system). I have enough issues to deal with around the house and with the cars w/o creating more.

Tjm - sorry if I came off strong in the last post. Might just have to agree to mutually disagree on what might happen when the battery is dead.

 

[hllon4whls]

Just a note, the battery needs to be there to keep the alternator from spiking the voltage to god knows how high.

It will seriously fry some electronics.

 

[351LX]

A Toyota I used to own had a relay between the battery and the fuse box that would trip if the voltage got below a certain point.That way, if you left your lights on or whatever it was impossible to completely drain the battery.I didn't know this until one day when I left the lights on and had to push start it.It started right away, but nothing in the electrical system would work for about 10 seconds until the battery voltage got high enough to reset the relay.It is entirely possible other vehicles have the same type of system and unless you actually measure your battery voltage it would appear that the battery was completely dead.

 

[BaXTeR3221]

I heard that the battery didn't even need to be in the car. From what i heard, some cars need it in there just to complete the curcuit but mustangs aren't one of them

 

[HISSIN50]

I heard that the battery didn't even need to be in the car. From what i heard, some cars need it in there just to complete the curcuit but mustangs aren't one of them

Like Hllon and I above him mentioned, the battery needs to be in place on any computer controlled car to prevent an unwanted voltage spike. In the old days (non-puterized cars) people would check alternators by yanking a battery cable while the vehicle ran - most folks suffered no real issues from this. Not so with puterized cars.

 

[cjman15]

Would u even need the keys to do this?

 

[HISSIN50]

Would u even need the keys to do this?

to get it to compression start, yes. Otherwise the vehicle will load up and act like it will catch (as you let the clutch out), but since there is no ignition or injector pulsing, it wont start (it feels like a failed attempt to compression start).

 

[Ranchero5.0]

I've heard and read over the last few years that some of the early SD cars will not pop start. Ford changed the puter after people complained about not being able to pop start it to sense the motor turning over from the TFI and adjust the dwell to start easier. My '93 did after the starter crapped out at the emmisions place.

Jamie