Tech tips: Diagnosing the no-start.

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I've noticed a lot of you are decent enough handling mechanical issues that crop up, but many of you are scratching your heads over driveability diagnosis, so here's a quick cheat-sheet if you ever have starting issues, and some shadetree-friendly ways to fix em:

No start, engine will crank:

Check spark first. Easiest way to do this is pull off a plug boot, stick it over the end of a screwdriver, and hold it so any exposed metal part of the screwdriver is about half an inch from a good ground source, like the radiator support, or a metal bracket that's bolted to the block, but DRY. Don't do this on the valve cover as it tends to be oily, and we're not trying to have a barbecue. The spark should be evenly timed and bright white or bluish. If its a dull orange like a lighter flame, it may not be enough to start the car, try again with the coil wire instead to see how strong the spark is. If it's still orange, check voltage at the coil when not cranking the engine. It should be close to battery volts.

If you've got no spark at all, check the coil's voltage. If you've got voltage there, and no wiring seems to be out of order, it many times is the hall-effect sensor in the distributor, or the crank sensor that's gone south. Methods of testing these vary based on engine, so I recommend having it taken to a tech, let them know you've got no spark, that'll help speed things along usually. If you have spare distributors and crank sensors, you can always try swapping them out, but be careful to install the distributor properly. Mark the rotor's point position on the base of the distributor cap mount before you pull it out, and insert the new one in the same position. Unplug the fuel pump fuse before trying to start it again, as your timing may be *WAY* off, and you'll need to adjust it accordingly.

Next on the list, checking fuel, and this one is a lot harder usually.

Carbs are easy as hell, just shine a light down the throat of the carb, and kick the throttle fully open. You should see a small squirt of fuel. That's the accelerator pump, and that means you've got fuel in the bowls, so you're fine there. The jets don't generally clog, but it never hurts to spray a bit of carb cleaner on the boosters to take off the varnish. If you get no squirt, get a 20oz or 2L bottle, and disconnect the fuel line to the carb, then block off the fuel inlet on the carb, and feed the line into the bottle, and turn on the ignition. You'll most likely fill up that 20oz fast, but if you get a steady stream of fuel, that's all you need. Note that mechanical fuel pump cars (240's use an electric pump and fuel injection, but I figured i'd add this in anyway) need to be cranked over, not just turned to "on", and their fuel flow will sometimes seem a bit erratic.

For fuel injection, firstly find the test port on the fuel rail. (If it doesn't have one, you can remove the fuel pressure regulator and put some rubber hose on the end of the rail, and run it to a 2L bottle). Lay down some newspaper or paper towel around the port and press in the schraeder valve with a ...well, anything relatively small. You should be half covered in fuel spritz now. If not, cycle the ignition on and off a few times, and try again. If you get nothing, or fuel just drips out, check your fuel pump fuse. If that's good, and the wiring on the way to the fuel pump itself is good, chances are you need a fuel pump, or relay. If you get spritzed, you've got good pressure on the rail, so on to the injectors, which much more annoying to test.

Firstly, there's 2 types of injectors, the ones the normally power the car, and usually also a "cold start" injector, or two, that only run while the engine is in open loop, as a fuel supplement, since fuel injected cars don't have a choke.

FYI, this is also why late 80s/early 90s cars with a lot of miles tend to smell badly of fuel while warming up. It's pretty normal.

Anyway, to test the harness, you'll need a noid light. This is because the injectors are ground-side controlled by the computer, so you can't just hook up any old meter to them. The resistance has to be correct, or you run the risk of damaging your ECU. Most auto parts stores carry noid lights, I think they come in 3 sizes. When you go to buy it, just have em pull an injector for your car and match up the plug size with the plug on the noid light. Once you have that, just pop off an injector plug and put the noid light on, one at a time, until you've been thru all of them. The noid light simply lights up when the circuit is complete. Crank it over and watch it blink. If it doesn't blink, its usually a crank/cam sensor issue, or distributor sensor (cam sensor as well, they'll have one or the other). If you've got spares and the wiring looks good, swap em out and see if it works, but only do one at a time, and test.

Next in line is timing. The third and final thing you need for ignition. This one's a bear usually, as it specifically concerns the mechanical end of things, and usually involves taking apart the front of the engine. Thankfully, this only tends to happen with no-start issues right after fresh rebuilds, or on engines with timing chain failures, in which case the timing is usually the least of their problems. But anyway....

Firstly, pop off your timing cover. I just made that sound super easy, didn't I?

You don't always have to completely remove it, all you really need to see is if the timing belt is still attached, first. Got belt?

If you do, this is right about where you have the choice whether or not to dig into a HUGE project just to diagnose, or to take it to someone else. Pop off the timing cover *fully*, and bring the engine to TDC with a wrench. Make sure to turn the same direction the engine rotates, or you may loosen your balancer/pulley bolt, and that only ends badly when the fan belts are still attached. Moving on, there should be no obvious signs of damage to both the cam and crank gears. Now, for DOHC, the dots/markings on the cam gears generally face each other, or both face straight up, and directly at a similar marking on the cylinder head. SOHC tends to face straight down towards the crank, or again at a similar marking on the cylinder head. Pushrod engines almost always have markings that face each other.

To be honest, if you get to this point, and your engine is even remotely close, or over, 80k miles, just replace the timing belt/chain and make note of it in your car log.

If your marks line up, pop off the valve cover and watch the valvetrain to make sure its moving smooth and solid as you turn the crank by wrench. Look for signs of galling or other mechanical failure, and largish metal shavings in the top of the head. Also check to see that none of the valve springs are broken, and that the tops of the valves' narrow ends are properly contacting the rockers, or the active sides of the lobes if it doesn't use rockers. If you've got any of this, you're usually better off replacing the head. Machining damage out of the head is a pain, and oversized bearings, being a surface thats *designed* to wear instead of the cam itself, tends to make larger clearances in time. Better off working with a fresh, undamaged head.

A few notes here, never use the starter to crank the engine with the timing cover off. Some cars have guides built into the cover, or parts of the guides anyway. Do it slowly, and by wrench. Also, if you need to use a DVOM to check voltages and whatnot, you're better off with a model with a digital screen. These models tend to have the proper level of resistance to check computer circuits *without* the possibility of damaging or destroying them, save for fuel injector harnesses. They'll either be digital or say something about being computer friendly on the box.

This may be edited as needed, since I sort of just skimmed off the top of my head here. Also not that this is not a have-all, be-all thread for no-start diagnosis. The only one of those I know of is about a thousand pages long, and exists on the ALLDATA CD or per-car at your local dealership. Most mom and pop shops don't have access to that kind of data. That said, it's not like the techs there are bad at what they do, it's just that they don't have all the available tools for a proper diagnosis at their fingertips. If you've got questions, feel free to ask em.