The first thing that most people think about when the car quits or won’t start is the carburetor (if the car has one) or the fuel pump. It might be a fuel problem, but it’s much more likely to be an ignition problem of some kind. (Check our ELECTRICAL STUFF for some of the possibilities.) And it might even be a compression problem, the least common (but often the most serious).
The first thing to note when the car “won’t start” is whether it is a crank-over problem or a run problem. Does the starter go “r-r-r-r-r-r-r” or not?
It needs to crank (make the “r-r-r-r” noise) and “turn the engine over”(actually the crankshaft) before anything else can happen.
If nothing whatsoever happens when the key is turned to the “start” position, it is easy to think first of the starter. However, there are a whole lot of things that have to happen for the starter to do its job.
- Ignition switch or starter button
- Starter relay (if fitted)
- All the wires and connections
- Starter solenoid (may be on the starter or remote)
- Starter motor (both internally and externally — I’ve had two cars who tended to have problems with the starter mounting bolts working loose)
- Ring gear on flywheel
- Ground cable from engine and body to each other and back to battery
- Battery condition
There are three things that a gasoline engine needs to run: fuel, spark and compression. This means that when your engine doesn’t run, you check these.
The easiest thing to check is fuel — spray some starting fluid (WD40 even works sometimes) or other flammable material (carefully!) into the intake (where the air cleaner is) and see if it sputs. If it runs, or tries to, until the fuel you’ve given it runs out, then you need to chase down fuel problems.
If it doesn’t, check for spark. You can take out a plug, hold the metal threaded part against the engine, and watch it while somebody cranks the engine. If you don’t see a nice fat blue spark, or only a weak yellow one, find out why.
If you can’t take the plug out easily, carefully remove the connector and wire from the plug, put a small insulated screwdriver up into it and contact the conductor, and hold the shank of the screwdriver near (but not touching) a ground and watch for spark. We have found that often the spark will build when you do this, and after a few spits, the engine will catch and run. (No, we don’t know why it works. Explanation, anybody?)
If the spark and fuel are OK, you need to look at compression. Sometimes it’s as simple as valve adjustment; could also be something like a timing chain or belt malfunction; and sometimes, it’s burned valves or rings or pistons. The initial compression that starts it all off is from the crankshaft being turned by the starter.
There is also the rare possibility that the engine has jammed completely and can’t be turned. Depending on the starter design, it might jam and not turn, or the starter drive might declutch and freewheel.
One of the weirdest running problems to find is a plugged exhaust. We see it a lot more with catalyst-equipped cars, because the cats are more likely to plug than a muffler, but ordinary mufflers can have their internal baffles come loose and block the flow, too. The car can act like it has some strange electrical or fuel problem, but all the components will probably check OK.
The first one we ever saw was a Renault that shut down seconds after it started. The most recent one we found was a Jaguar that would idle perfectly, but sput and die when the throttle was opened. I’ve seen some cars that would run for a few blocks and then die out, and restart after about 20 minutes. (This is characteristic behavior of a sick ignition module, as well.)
The Jag (an 1986 XJ6), bless the engineers’ hearts, has a plug in the exhaust manifold that you can take out for diagnostics, which makes it a very easy test. The Renault we found by accident, having taken out the plugs to run a compression check and somebody inadvertently bumped the starter with the plug hole open, and voila! The car stayed running.
This makes a possible way to check — if it stays running with one plug hole open — any plug hole open — that indicates that exhaust blockage is a likely problem. Obviously you don’t run for any length of time like this, but it is a quick step toward a possible solution.
Occasionally a no-spark condition is not actually from an electrical problem. Distributors either run off of the camshaft or a distributor drive usually connected to whatever drives the oil pump. Aircooled VW distributors drive off of the crankshaft with a reduction gear (distributors run at half engine speed.).
Occasionally there will be a mechanical problem with whatever drives the distributor — a bad timing belt, a broken drive gear; or something inside the distributor. Once we saw a Volvo that had had the shaft inside the distributor saw itself in half.
Electronic distributors or distributorless systems often run off of a sensor on either the front or back of the engine, connected by a long wire that can get damaged. These sensors read a pointer on either the front pulley or flywheel.
We had a BMW in once whose pointer had fallen off of the flywheel, and it is not available separately. The customer was very lucky — we found the pointer lodged on a crossmember under the car, and we were able to rivet it back on.
If the engine has just been reassembled or the timing train retimed and the thing just sputs and spits, check that the crank/cam timing is not 180º out of synch. It is easy to forget that the crank goes around twice each time the cam goes around once, so you might have it on the “wrong” top dead center. (If the distributor times off of the cam rather than the crank, this isn’t a problem.)
What you have to remember is that on the compression stroke, both valves on your reference cylinder (usually #1) are closed and the distributor rotor (if it has a distributor) is pointing at the wire for that cylinder.
All information here is offered as suggestions only; the final decision as to any car repair is that of the installer and/or the owner of the vehicle. This information is the result of our own best research and experience, but we make no guarantees or warranties of any kind as to its applicability to any specific situation.