Missing NISSAN Twice a Year
Q:My 1998 4WD Nissan truck with the 2.4-liter four-cylinder engine has 118,000 miles on it. On a hot day, over 90 degrees F, after driving for at least two hours, the truck will start to misfire badly. The computer doesn't show any codes and after it cools down it runs great. This has only happened twice in the last year.
A:Twice a year isn't bad. With high mileage comes a longer list of potential causes of an intermittent misfire. That it occurs at high temperatures might be a clue, but a lot of failed components can be affected by expansion and contraction from changes in powertrain and ambient temperatures. Begin with the basics--starting with the ignition system. With six digits on the clock you shouldn't hesitate to replace the distributor cap, rotor, and ignition wires, if you haven't already. Also carefully inspect the ignition coil for burn marks where voltage may be leaking through. The ignition coil is an integral part of the distributor, and some of the distributors installed on Nissans like yours have had issues with moisture drainage. Look for moisture and/or signs of corrosion. If you see any, call Nissan parts and mention TSB #NTB00-086. They should be able to tell you if the TSB applies to your truck and give you the part number for a modified distributor to correct the drainage problem. Again, this so-called misfire could be a lot of things, but this is the best place to start.
Water On Passenger Floor
Q:Whenever I run the A/C in my 2004 Chevy TrailBlazer a pool of water collects on the floor at the front passenger seat. I assume a line is clogged somewhere. Is there an easy fix or should I have a professional look at this?
A:Give it a shot first. Condensation is formed on--and drips off--the air-conditioning system's evaporator (cooling component within the dash) and collects in the bottom of the evaporator/heater core case. The water is then routed through the firewall, into the engine compartment, and down to the street through a rubber drain tube. When this drain gets plugged up with debris, the water level will rise and eventually overflow onto the passenger-side floor. Carefully jack up and support the right front of the vehicle, crawl underneath and look for the evaporator drain tube pointing downward at the street. It's usually made of rubber, removable, and pulls off easily. But don't forget to duck. If the tube itself is obstructed and holding back the water, it's going to be a gusher. If you're lucky, and that's all there was to it, you can clear the tube of debris, reinstall it, and be on your way. But there may be more debris inside the evaporator case still plugging up the drain path, and that's going to require compressed air to blow it out. Worst-case scenario is that the drain path is clear, and condensation is entering the passenger compartment through a cracked evaporator case, or a bad seal against the firewall. Second-to-worst, there's so much debris collected in the case that it continually plugs up the drain over short periods of time. This requires removal of the evaporator case for a thorough cleaning. Either way, it's always a good idea to carefully inspect the plastic screening at the cowl, right at the bottom of the windshield beneath the wipers. This is where outside air enters the A/C system, and any missing, damaged, or misaligned protective screens will allow leaves and other debris to enter the evaporator case, consequently stopping up the evaporator drain.
Rough-running Jeep
Q:My 4.0-liter 1997 Jeep Cherokee hesitates and idles rough for a brief period, not long after starting it, then runs okay. It does this every time I start it. I had the computer, MAP sensor, cam sensor, and crank sensor replaced. No lights come on, and when it was put on the machine no codes came up. What could be the problem?
A:It could be a lot of things. Running rough shortly after starting the engine can go two ways. The problem occurring after a cold engine startup may indicate a lean condition (not enough fuel) caused by a vacuum leak, exhaust-gas recirculation occurring when it shouldn't, and so on. If the "shakes" are taking place following a hot restart of the engine, it can be the opposite scenario, maybe a leaking injector or fuel regulator sending too much fuel into the engine and causing an excessively rich condition. And depending on the mileage, some Jeep 4.0-liter engines have been victim to excessive carbon buildup on the back of the exhaust valves, causing miscellaneous misfire conditions. A temporary fix for the carbon buildup is the application of a top engine cleaner treatment; Jeep also came out with updated (stiffer) exhaust-valve springs to prevent it from happening again. Either way, it sounds like you've already invested time and money and have come up empty. You may want to get it to a Jeep service department (assuming you haven't already) before you take another guess. They're the most familiar with the 4.0-liter and have all the tools needed to perform an accurate diagnosis.
Sierra Fuel Delivery
Q:I have a 2002 GMC Sierra, 5.3-liter V 8, that starts rough, but runs fine once started. The engine catches after about 2-3 seconds. The idle isn't rough. I just changed the fuel filter and have run two tanks of gas through the system. The problem is getting progressively worse. I think it might have dirty fuel injectors. There are now 102,000 miles on this truck.
A:Dirty fuel injectors is a good guess, but it's still a guess. You have to be sure all the other ingredients are there, including good engine compression and spark from the ignition. But an extended crank is a fuel-related issue the majority of the time, and obstructed fuel injectors have been a common problem with this vintage GM system. Proper operation of the entire fuel delivery system must be confirmed first. That's all part of the correct testing procedure. Enough pressure and volume from the fuel pump to the fuel injectors is just part of what's needed for a quick start. Residual pressure is also important. When the ignition is initially turned on, the pump is activated for a few seconds to prime the system with fuel pressure. The unneeded high pressure is bled back to the fuel tank by the fuel-pressure regulator, while the correct amount of pressure is held steady at the injectors. The fuel pump has a check valve which prevents the pressure from bleeding back to the tank through the pump itself. This way there's constant pressure at the injectors when you start cranking the engine over. If a fuel regulator or fuel pump is defective and allows that crucial residual pressure to bleed back to the tank, you get an extending crank while waiting for the pressure to build up and fire the engine. Have the system tested by a professional. If the problem is with the injectors, you can choose between replacement or a specific cleaning procedure utilizing special tools and a top engine cleaner approved by General Motors. Anyone can replace the injectors. I'd be wary about a cleaning procedure being done effectively outside of a GM service department. The injector cleaner in a can which you pour into the fuel tank isn't going to fix the problem.