Wrenching Tips: How to bring a non-starting car back to life

how to get old car started The face of a modern day Dr Frankenstein

Medically or magically, few feats impress more than reviving the dead. If we issued Hoon Merit Badges, starting a “No Start” car would be a major one. In today’s Wrenching Tips we’ll walk through the basic principles and steps to getting a mystery non-running car to at least fire. Getting it running and driving well are topics for another day. Think of this as a guide for what to do on the first weekend with your recently-acquired “free” LeMons car. Think of this as the 201 or 301 to the “my battery’s dead” Car Starting 101

bmw project carThe Uberbird in “as received”, non-running condition. The passenger side tire points straight ahead.

Mise en Place

First off, information is your friend. Find out from the friend/relative/seller/yourself whatever you can about when it last ran and the circumstances since then. “Ran fine last week” is a lot different than “sitting in a barn for 35 years”.

  • Finding a basic Haynes/Chilton/Bentley manual, factory service manual or even just a wiring diagram will speed up the debugging process.

  • Tool-wise, plan on bringing a multimeter, remote starter switch and an assortment of wires with quick-connects in addition to basic hand tools.

  • A spare battery, jumper cables or one of those portable jumper things might be necessary.

  • A fire extinguisher is always a good idea, doubly so in this case.

things heat upThis is what happens when you don’t expect the car to actually start – various things start smoldering

Initial Check Up

Just like the warnings in Cialis and Viagra ads, we need to check that this vehicle’s actually fit enough to fire up.

  • Check the oil and add/change if necessary.

  • Pull the gas tank cap and take a small whiff.  If it smells like gas and the car’s been sitting for a year or less, you might want to top it off with some fresh stuff. If it smells like anything else, consider draining the tank or (if it’s a vehicle with a puller pump) re-route the fuel line into a gas can.

  • Take a look at as many fuel lines as you can. They don’t need to be perfect, but if they’re obviously cracked and crumbling replace them.

  • Check the water in the radiator, make sure there’s at least enough that the water pump won’t spin dry and shred its seals.

  • Look for things like leaves or engine-bay insulation that have accumulated on the exhaust.

  • Verify there’s at least some fluid in the transmission, as spinning a dry input shaft is as unpleasant as it sounds.

Let’s Get Cranking

This isn’t just about jump starting, but if a turn of the key gets you nothing, the battery’s the first place to look.

  • Check for roughly 12V resting and more than 10V cranking; if less hook up a new/external power source.

  • If there’s voltage at the battery but no noise from the starter, then we need to check the starter solenoid. Its terminal is usually the smaller one on the starter, i.e. the one that’s not the giant cable coming directly from the battery/alternator.

    • If you’ve got no voltage here when the key’s turned to “start”, your problem is somewhere between the ignition switch and the starter. Typically there’s a relay that’s triggered by the ignition key switch that fails. Try to find that (this is where the wiring diagrams come in handy) and test it or wire around it.

    • Alternatively, you can connect the remote starter switch between the starter solenoid terminal and the battery as a bypass. Hitting this switch should make the solenoid engage (big click) and crank the starter motor. Doing so with the ignition key switch in the “ON” position may well start the car, depending on whether your problem is the key switch or the wiring downstream from it.

  • If you do have voltage here but no action, it’s the starter or solenoid itself.

Fuel, Compression, Spark

These are the core principles of getting a car to start and run. Whenever I’m stumped, I chant “fuel, compression, spark” and walk through what could be wrong. We’ll run through them in order from most likely to least likely: is actually fuel, spark, compression.


Whether carbed or injected, we need to make sure the right amount of fuel’s getting where it’s supposed to.

  • Check the fuel filter(s), which are usually near the fuel pump(s). In the short term, you can just bypass a clogged filter or replace it with a cheap clear-bodied one.

  • If the car has one or more electric fuel pumps, you can usually hear a “whirr” when the ignition is turned on. If not, check for electrical power at the pump and/or pressure in the line going to the carb or injectors.

  • On a mechanical pump, pull the line at the carb and route it into a bottle.

  • For carbureted cars:

    • On a car that’s been sitting for more than a few months, expect a carburetor to be full of gummed up old gas. Pull it apart and clean the innards as best you can, then maybe double-check that the float still floats. You’ll probably need to rebuild it, but cleaning it up should be enough to at least get the engine started.

    • Check that the idle screws are adjusted to where they should be (usually something like all the way in, then back 1-2 turns).

    • Beyond these tips you get into the black magic of carb tuning, which we’ll skip for today.

  • For cars with EFI:

    • We need to verify that injectors are working. Older injectors have an audible “tick” when they pulse. If this isn’t the case, the simplest (and most dangerous) way to check them is to unbolt and have it squirt into a bottle.

    • No squirt could mean a bad injector or bad electrical signal. To debug, mix and match injectors and wires to see where the culprit is.

    • Various EFI systems have different ways or regulating idle speed. Some have a stopper on the throttle butterfly, some have a bypass valve. If a car is firing but not idling, look into these systems.

    • If not injectors or idle control, then it’s time to check sensors: MAF, MAP, TPS and O2.

    • Most EFI systems are self-diagnostic and have a way of alerting you to what’s wrong. Post-1996 cars are all OBD-II and use a standard code scanner that can be bought or rented from a local auto parts store. OBD-I era cars usually have a brand-specific means of reading codes that involves something like shorting a hidden connector and deciphering a code of blinks of the check engine light.

fuel injector testing


There are only two things that can be wrong about with spark: you’ve got no spark, or you’ve got spark and the timing’s off.

  • To check for spark, pull one (or more) plug(s), re-attach the wire and crank the motor with the business end of the plug close to the block. Look for a spark.

  • Note the condition of the plugs. If they’re covered in soot, get new ones or at least sand them until they’re shiny. Gap to spec for your motor (if unknown, about .025-.030” usually works).

  • Provided you’ve got spark on all cylinders, find the timing mark on the crank pulley, hook up a timing light and make sure you’re remotely close to spec (or somewhere between 7-12 degrees advanced with no vacuum advance).


Most fuel and spark issues can be addressed with relatively simple and cheap parts, but when it comes to compress things get serious and expensive quickly.

  • Make sure the spark plugs are all in tight.

  • A compression test is pretty simple to do: get a compression tester, remove the plugs, drop a little oil in the cylinders if it’s been sitting and crank over the motor. Depending on the motor, you should see anything from 120-200psi (manual or the internet helps here), but most importantly the numbers should be pretty close to each other. 150, 155, 148, 110 = you have a problem.

  • But don’t despair yet! There could be a valve issue. If the cam timing or rocker/lifter adjustments are off, valves could be open or closed when they should be closed or open. Every once and awhile a timing chain/belt will jump a tooth. Keep in mind serious valve timing issues usually don’t happen just due to wear, so beware of valve Vs piston events.

  • All this said, usually a motor’s got enough compression to fire. Chances are it’s something else…or at least keep telling yourself that.

That wraps up this installment of Wrenching Tips. Hopefully it’ll provide a guide to make that “ran when parked” special a little less terrible of an idea. I know I’ve left out a bunch of things, so be sure to weigh in in the comments with more tips.

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19 responses to “Wrenching Tips: How to bring a non-starting car back to life”

  1. scoudude Avatar

    Using a grounded spark plug to check for spark can often lead to false diagnosis. The best method to check for spark is to create a ~3/8" free air gap. This rules out thinking you have no spark when you really do and just have a bad plug. It also tells you if the ignition system is strong enough to start the engine. The pressure and presence of fuel in the cylinder means that a greater voltage is required to jump the plug gap in the cylinder than it is in free air.

    1. Alan Avatar

      Or hold spark plug with hands and crank, If profanities start spewing from your mouth you have spark~experience
      Normally I look for bad grounds.

  2. fodder650 Avatar

    Any chance you could add to this article or create a second one if you have a seized engine? I have an MG Midget with a seized engine. So far we tried to break the engine free by popping it into gear. This felt very odd to this non-mechanic but I have learned that this is a normal way to free it up. Now the engine is sitting there with penetrating fluid working its magic.

    1. Tim Odell Avatar
      Tim Odell

      Soak those cylinders, and make sure you use good, real penetrating oil, not just WD40. JB-Quick, PB Blaster or Marvel Mystery Oil really do work much better.
      That said…reviving a frozen or seized engine on anything other than an old tractor or truck is a dubious value proposition. It'll probably need a replacement or rebuild even if you get it running. Just for the challenge (and chance to drive the car around the block once or twice) it's probably worth a shot (not much to lose).
      After that, I'd say try to turn it on the crank pulley with a big-ass wrench and/or impact (assuming it's accessible).
      Also make sure your starter's up to snuff: pull it and flush it with the electric motor flush stuff from an auto parts store. Then get a good battery and/or hook it to a running, modern car for maximum cranking juice.

    2. C³-Cool Cadillac Cat Avatar
      C³-Cool Cadillac Cat

      Um…large socket and breaker bar?
      Wait…I'm having déjà vu.

    3. dculberson Avatar

      Mechimike, of Lemons Tunachucker fame, revived a nasty ass Continental 460 by filling the cylinders to the brim with ATF. Do it through the spark plug holes. It'll free up the rings and pistons. Let it soak and give it a wrench now and then to see if it's freed up. Once it's free, get the ATF out of there and turn it over a bunch of times to clear the cylinders.
      The motor lasted a few races after that, and that's saying a lot.

  3. muthalovin Avatar

    My favorite CL ads usual read: "Runs when gas is poured into motor."

  4. OA5599 Avatar

    I've seen more than one car no-crank because the neutral safety switch connector got knocked loose.
    Also, an unfamiliar car may have theft-prevention circuitry built in. I used to work with someone whose car would not crank unless you pressed the driver's power door lock button while cranking. I borrowed a car once that wouldn't crank unless you used the remote keyless entry within 90 seconds of turning the key.

    1. Mad_Hungarian Avatar

      And if the car is a 1974 model, consider that the seat belt interlock could still be functional. I've seen 'em. Most '74 cars have an override switch under the hood somewhere. On GM cars it is usually up near the firewall on one side, and it kinda looks a little like a relay, except it has a black button on it.

  5. TurboBrick Avatar

    Grounds and relays! That's what kills EFI cars, loose grounds and bad relays.

    1. joshuman Avatar

      Any grounding wire that jumps to the engine from the body is under a lot of stress from heat and vibration. I give 'em a wiggle whenever I see them just to check how they are holding up.

    2. Tim Odell Avatar
      Tim Odell

      True, the starter solenoid relay was bad on the BMW.
      As was the of the fuel pump relay(s).

  6. MVEilenstein Avatar

    This is really good information. I always enjoy reading Wrenching Tips, even if I don't need to do any repairs. I often come back to these articles when I do.

  7. CJinSD Avatar

    Great tips! Thanks for articles like this one.

  8. BMW Avatar

    Of course it's an E24. I know just how he felt!

  9. Fritzo Avatar

    If you know what half of these terms mean, you don't need this guide to figure out why your car won't start 😛

  10. W140 Avatar

    Just fired a 1 year abandoned merc diesel. There's nothing like bringing one back!

    1. C³-Cool Cadillac Cat Avatar
      C³-Cool Cadillac Cat

      The beauty of diesels is, the fuel never goes bad or turns to varnish.
      I've parked out Cummins ISB motorcoach for 14 months, with it just plugged into 110V for the battery charger.
      Started like I'd turned it off five minutes earlier.
      It's kinda spooky.

  11. ˏ♂ˊ mzs zsm msz esq Avatar
    ˏ♂ˊ mzs zsm msz esq

    Three bullet points for carb, five for EFI 😉 Great article Tim, again I have learned a lot from you!