Diagnosing a No-Start
I’ve been seeing a lot of No-Start related threads popping up lately, and I figured a basic Tech Article for diagnosing a few of the most common No-Start problems might be in order.
Any images posted are courtesy of my 1990 GSX – your setup may differ slightly; refer to your Service Manual for year or make specifics.
This guide is obviously not meant to offer a complete list of things that could be keeping your car from starting. However, checking these things BEFORE posting your problem will help us better understand your situation, and give you a better chance of getting the right advice very quickly.
If you don’t have a Factory Service Manual, another very helpful DSM Tuner member has posted a Tech Article with links to download these. Refer to this article for these files:
And we begin…
So, you go out to your car one morning, and, lo and behold, it won’t start. The DSM Gods must be angry with you…Time to start the diagnostic process. For quick reference, I have sectioned this article off into the basic problem areas by symptom. Find the area (highlighted in Bold) that most closely matches your problem area(s)….or just read the whole thing, so you’ll know what to look for on that fateful day, whenever it may occur.
I – Does the car NOT crank, or crank slowly?
If the car doesn’t crank at all, or cranks very slowly, areas to investigate include the following, in order of likelihood:
1. Check your battery terminals and cables. Loose, corroded, or broken battery terminals or cables will drain your battery. If the car cranks very slowly, your battery may have some juice left. If not, it may be completely dead.
2. Using a DVOM (Digital Volt/Ohm Meter), check the voltage on your battery. Red probe goes to the positive post; black probe goes to the negative post. If battery voltage reads low (anything lower than 12 volts is low!), your battery has been drained. This could be due to any number of things. Did you leave an interior light on by mistake? Are your battery terminals loose or corroded? Did your battery ground out on an aftermarket strut bar? Is your alternator going bad? Take your battery to your local AutoZone, O’Reilly, Advance Auto, or similar parts house. Most of these chains offer free battery testing and free charging (especially if you bought your battery from them).
3. If you have an Automatic, is the car in Park or Neutral? If you are M/T, are you depressing the clutch all the way when starting the car? If yes, your Neutral Safety Switch or Clutch Safety Switch (respectively) may be faulty. Refer to FSM for proper testing procedure, or just unplug it.
4. When you turn the key, do you hear the starter click? If not, time to check it. Refer to FSM for complete testing procedure. Check the starter relay first. On a 1g, this is located under the dash, to the immediate left of the steering column. There are three relays down there – the starter relay is the one in the middle. With KOEO and clutch depressed, battery voltage should be present at the relay. On a 2g, the starter relay is located near the radio.
5. Check the Alternator fuse (80A in a 1g, 100A in a 2g). This is located in the main fuse box under the hood, and should be the largest fuse in there, making it easy to spot. Careful – it’s also the only fuse that is secured by a bolt, so keep this in mind when attempting to remove it. (See image below for location)
6. Pull the upper cover off of your timing belt and make sure you have not snapped or damaged the timing belt. If you are at all in doubt about the condition of the belt, pull it out and replace it. If there is any possibility that you could have jumped timing, run a compression test to verify if (or, more likely, how many) valves were bent.
II – The car cranks, but just won’t start.
There are four main things a car needs to run: Fuel, Fire (Spark) at the right time (Engine Timing), and Compression. Once the car has all of these things, it really has no choice but to start – remember, cars are just machines. With a car that cranks but doesn’t run, the first thing you need to do is diagnose which one(s) of these four basic necessities you’re lacking.
1. Checking for Fuel:
The DSM fuel system is fairly straightforward. Sparing you the painstaking details, there are a couple of things you will need to do to verify that you’re getting fuel. Try spraying some starter fluid into the cylinders and try to turn the car over. If the car will start, you are most likely not getting fuel.
Start by removing the fuel line from the filter (passenger) side of the rail (Careful! The fuel system is under pressure, and since you can’t start your car, you can’t relieve the pressure in the lines. Keep your face away from the fuel line, and wear protective eye gear. Imagine sticking your face in front of a bottle of champagne before uncorking it. Get the idea?)…Stick the end of the fuel line into a clear container and have a friend crank the car (or turn on the fuel pump via the check connector behind the battery). In a normally operating fuel system, plenty of clean gasoline should fill the bottle pretty quickly. If you don’t see a lot of fuel, or if it looks nasty, change your fuel filter (refer to VFAQ). If nothing comes out at all, you will need to make sure your fuel pump is turning on. Open the fuel filler door and remove the filler cap. Have a friend put his or her ear up to the filler hole and listen as you crank the car (in a 1g, you have to crank it! Putting the key in “ON” will accomplish a whole lot of nothing). You can also power the fuel pump via the check connector. Stock fuel pumps will emit a faint buzzing or whining noise when they turn on. Larger aftermarket pumps (especially Walbro) will usually be loud enough for you to clearly hear inside the car yourself. If you don’t hear the “whine”, that’s your problem – your fuel pump isn’t powering on. Possible reasons for this include a faulty fuel pump, disconnected or damaged wiring to the pump, or a faulty MPI relay, among a few other things. If you are getting fuel to the fuel rail and your fuel pump is operating, but the car still doesn’t start, it’s time to consider fuel pressure. Pull the return hose from the Fuel Pressure Regulator and see if it’s wet with fuel after cranking the engine. If it’s dry, your Fuel Pressure Regulator could be faulty. Buy or borrow a fuel pressure gauge (these are fairly inexpensive, and can be purchased from any AutoZone, O’Reilly, or Advance Auto, etc.). Follow the manufacturer’s directions and refer to FSM to check the fuel pressure. Remember to remove the vacuum line (small rubber vac line going to the Fuel Pressure Solenoid – the one your Boost Gauge should be T’d to) from the fuel pressure regulator and pinch it closed with your fingers (or an adequately sized bolt). The specs you’re looking for are as follows:
1g N/T: 47-50 psi
1g Turbo (A/T): 41-46 psi
1g Turbo (M/T): 36-38 psi
2g N/T 4G63: 47-50 psi
2g Turbo: 42-45 psi
Next, check to make sure your injectors are firing. Measure the resistance at the injector clips with your DVOM. Resistance should read 2-3 ohms at the injectors, and the clips should be receiving battery voltage while cranking. Take a long, rubber-topped screwdriver and place the metal end on top of each injector, and your ear on the other. Crank the car, and listen for a sharp metallic “clicking”. You’ll hear the clicking each time the injector fires. If your injector’s aren’t firing, try swapping out your Injector Resistor Pack with a known good unit. These don’t usually go bad, but when they do, they’ll keep the injectors from firing. The ECU may also be at fault here, or the wiring to the injectors may be damaged.
2. Checking for Spark:
Before checking for spark, first remove and inspect your spark plugs. Are they improperly gapped or have they been fouled by age, improper fuel mixture, etf? If so, replace them and try to start the car again.
To check for spark, disconnect one of the spark plug wires and attach a spare spark plug (it’s always good to have a spare handy – you can use a cheap-o one from Wal-Mart for testing purposes). Place the plug and plug wire onto the valve cover and have a friend crank the car. Do you see spark arcing onto the valve cover? Sometimes it’s best to do this test at night – this makes it easier to see the spark. Repeat this test on all 4 cylinders to verify that you’re getting spark all the way across. If you’re not getting spark on some or all of the cylinders, first check the condition of the spark plug wires – does the spark try to arc through the wire while you’re testing? If so, the wires are damaged and must be replaced. Next, check resistance at the coil. Specs differ by year, so refer to your FSM for the specs for your particular vehicle. If everything tests out okay and you’re still not getting spark, pull the ECU and check the board for damage due to capacitor leakage. DSMs are not getting any younger, and are notorious for leaking ECU capacitors. One final culprit could be the CAS. These differ by year as well, so again, refer to FSM for appropriate testing procedure and specifications. First, however, you might want to make sure the CAS is not turned 180* out (i.e. “on backwards!”).
3. Checking Engine Timing:
The procedure for checking and setting engine timing is fairly complex, so I will let you refer to the VFAQ for this one. Here’s the link:
4. Checking Compression:
Checking compression is another thing that is best covered in the VFAQ. Here you go: http://www.dsmgrrrl.com/FAQs/compression.htm
III – Fuel, Spark, Timing and Compression are good, but the car still won’t start!
We’ve narrowed it down this far, and we’re definitely making progress. There are a couple of things we can check now that will usually “seal the deal”.
1. Has your car been sitting for any length of time?
If you’ve stored your car, or it’s been down for a while, and now won’t start, you can bet that the gas in the tank has gone bad. Drain the gas tank via the drain plug on the bottom of the tank, and remove the tank (refer to FSM for exact removal instructions. Remember to remove the fuel pump and all related electrical connectors first. Dropping the fuel tank will take about an hour if you’ve never done it before). Clean the fuel tank with high pressure water and let it air dry IN A SAFE LOCATION (away from any possible danger of sparks or extreme temperatures) for at least 24 hours. Fill the tank with a few gallons of high octane gas, as well as a bottle of Fuel System Cleaner (like Seafoam) and/or Octane Booster.
2. Does the car eventually start, or act like it’s trying to start?
Is the problem especially bad after the car has sat overnight, or on a cold day? This is likely your ECT (Coolant Temperature Sensor). The ECT is the first sensor the ECU looks at when you start your car. The ECU asks it "How cold is it outside today?" and the Temp Sensor responds. The ECU takes that information and decides how much fuel to send to the injectors. If your ECT is faulty, the ECU will either get an incorrect reading back, or no reading at all, and will stay in open-loop, dumping fuel into your cylinders, making your car excessively hard (or impossible in some cases) to start.
The Coolant Temp Sensor is located on your thermostat housing, towards the bottom, on the left/front. It is a two-prong male connector (one prong on a 2g). Inspect the wires going to the sensor first – there is a lot of heat down there, and wires can become brittle and snap off of the connectors due to age and extreme temperatures. The following information demonstrates how to check the operation of the ECT on a 1g. For 2g, refer to FSM.
Testing the Coolant Temperature Sensor on a 1g:
Unplug the black plastic clip and turn the key ON (do not start the car). Connect the negative probe of your DVOM to a good ground on the car, and the positive to one of the plugs in the clip. With key ON you should see approx. 4.5-4.9 volts. You may have to try both of the plugs until you find the one that sees voltage – one sees voltage and the other does not.
Assuming this checks out okay (99% of the time it will), we will now move on to resistance. Basically speaking, as the temperature of the coolant INcreases, the resistance value will DEcrease.
With the engine cold and the sensor unplugged, turn your DVOM to resistance (ohms) and connect the probes to each of the two prongs on the sensor. The prongs on the ECT will form a sort of "T" shape: kind of like this: | \
With engine cold, resistance should read somewhere between 2,200 to 2,700 ohms (if it's a little higher, it is due to extremely cold ambient temperatures. Somewhere close to this range is okay though).
The next step in this test would normally involve starting the car and getting it up to operating temperature. However, if the car will not start at all (probably the case if you’re reading this), you can replicate this part of the test in a heated dish of water. See below for instructions and necessary water temperatures. If you can get the car to start, plug the sensor back in and start the car now. Get the engine up to operating temperature, and turn it back off. Unplug the sensor again, and repeat the resistance test. (BE CAREFUL, it is VERY HOT down there now). The resistance should now read approx 280 to 350 ohms.
If the car will not start at all, or if you can't quite reach the sensor, you can unbolt the sensor unit and reproduce the testing procedure with a dish of water. If you do this, have a rag or bolt handy to plug the hole you make by removing the sensor -- lots of coolant will come out. You can drain the coolant first if you want to avoid this.
Put the bottom of the sensor (round, gold metal part) into a dish of room temp water (50-80*) and measure resistance. Then, heat the water to approx. 180-200* (not quite boiling), and repeat, using the same resistance values stated above.
If resistance is not within specs, replace the sensor.
Related resistance specs for 2g Turbo engine:
Cold (68*F): 2.1 - 2.7 kOhms
Hot (176*F): 0.26 - 0.36 kOhms
Testing procedure is similar for 2gs. Refer to FSM for complete testing procedure.
Coolant Temp Sensor on a 1990 GSX Circled in Picture (Pay no attention to the letters. But if you’re interested, “A” is the Coolant Temp Fan Switch for the A/C, and “C” is the Temp Gauge Sending Unit).
There you have it. Chances are, if you’ve tried everything listed here and your car still won’t start, it’s time to post your problem in the forums for some detailed advice. Don’t hesitate to send me a PM if you’re unsure about any of the testing procedures listed here, or would like to see images of any additional parts.