FAQs—GMC W5500 Forward
The engine of my GMC W5500 Forward starts fine, but it stops running after a while. What's wrong with my truck?
It's possible that your truck's battery is not staying charged. When it stops running, jumpstart the engine, then remove the jumper cables as quickly as possible and wait. If your truck keeps running after 10 to 15 minutes, then the battery is likely the problem. You should also inspect the battery cables for corroded connections before considering to replace the battery. However, if the battery still won't hold after charging, then take a look at the alternator as it may not be recharging the battery. There are a couple of easy ways to confirm a bad alternator. First, crank over the engine, turn on your GMC 5500 Forward's lights, and observe. If they start bright then slowly fade, then the alternator might not be giving the proper charge that can operate your vehicle's accessories. Next, if you have a voltmeter or multi-meter, test your truck's battery if it has charge left in it. The voltmeter should read around 12.6 volts with the engine off and 14 to 15 volts when the engine is running. If the voltmeter reads below 13.5, then the alternator might not be keeping up with the battery's charging needs.
I noticed that my GMC W5500 Forward is not running smoothly while idling. How do I find what's causing this?
First, change your oil filter as it might be affecting your engine's performance. If your GMC 5500 Forward is still not idling smoothly, examine the end of one of the spark plugs. If it looks sooty, then it could be due to a bad fuel pressure regulator. You should also check the other spark plugs to see if they are in the same condition. If you replace the fuel pressure regulator, you should also change the spark plugs as they could be fouled out from the faulty component. You can also try cleaning them instead, but if your truck still runs poorly even after replacing the regulator, then the spark plugs need to be replaced.
When I step on the brake pedal of my GMC W5500 Forward, it feels spongy and doesn't respond until the pedal almost reaches the floor. Why is this happening?
There are several possibilities as to why your GMC W5500 Forward's brake pedal feels spongy or almost non-responsive. There could be air in the brake lines, which you need to bleed out. The brake fluid could also be aerated, and if this is the case, you need to completely flush out the brake fluid and replace it with a fresh, new, clean batch. You should also check for overheating conditions to make sure that there are no other components affected. Another possibility is that the parking brake is not well-adjusted, which you need to do whenever you upgrade the rear disc brakes. It is also possible that there is unequal pressure between the front and rear lines, and you need to test the proportioning valve and replace it if it's faulty.