One of the most common themes of our website questions relate to running problems. There is version A - "I live somewhere where they have never seen a Vanagon and although I trust my mechanic, I don't think he knows what he is doing" or version B "I live somewhere where they have never seen a Vanagon and although I think the mechanic knows what he is doing, I don't trust him". Then we are usually asked if we think that the Diagnostic Tool that we rent/sell will help them. Surprisingly, we usually say no as the Diagnostic Tool is intended for specific intermittent symptoms that cannot be duplicated while the vehicle is stationary, but occur randomly while driving. Most running symptoms can be diagnosed by more conventional methods. You do not need to be a professional mechanic, you do not need to have a lot of tools, but you do need to be determined, methodical and armed with a Bentley manual. (Please note that although there are many similarities on the earlier model Vanagons, we are describing procedures for the 86 - 91 models) The 5 most common problems are:
- Poor tune-up condition
- Malfunctioning oxygen sensor
- Poor oxygen sensor ground
- Faulty values from coolant temp sensor
- Throttle switch and idle control components
Plan of attack
Inspect tune up parts
- pop the clips loose that hold the distributor cap on and inspect for carbon traces in the underside of the cap and how burnt the end of rotor looks.
- pull one spark plug out to inspect how old they are
- check the plug wires for corrosion or cracks - ohm test the wires, but keep in mind that they will sometimes test correctly but not conduct spark so sometimes just best to replace them if they are old
- make sure all of the parts are approved quality Bosch parts. Inspect air and fuel filter. Finally follow the correct procedure described in the Bentley manual for checking the timing to complete covering your bases in the tune-up area.
- It's best to eliminate all of these maintenance items as possible causes of the trouble before going after more intriguing culprits. Although we don't, as a rule, subscribe to the school of throwing parts at cars to try to fix them, in some cases a few inexpensive parts can eliminate a couple of other problem areas for minimal expense. With oxygen sensor and coolant temp sensors(see Fuel Injection Category) costing about $100 combined (with Bosch oxygen sensor), if neither have been replaced in recent history, this may be money well spent to eliminate these possibilities. Poor oxygen sensor ground is very common problem. The ground wire travels all the way from the oxygen sensor wire harness to the computer and then back to the engine where it grounds on the left cylinder head next to, or with, the main engine ground strap. This ground wire exits the wiring harness a few inches back from the halls unit plug at the distributor. Snip the end off the ground wire, solder on a new eyelet connector and clean the block where you are attaching it and tighten it well.
- Throttle switch and idle control components - The throttle switch must be both in working order and adjusted correctly. With the engine not running and key turned off, you manually operate the throttle arm back at the engine and see if you hear a click just as you move the throttle on and off the idle or relaxed position. If not, then you should attempt to adjust it. The throttle switch must be adjusted correctly so that the idle stabilizer computer (situated behind the passenger side tail light housing) and idle control valve kick into action when you are in idle mode. If the throttle switch is adjusted correctly and the idle either hangs up at high rpms or the vehicle is prone to stalling, then one of those two components is likely at fault. (Please review Bentley manual procedures on testing these two components). While you are here it's also wise to check the throttle body itself. When you grab the shaft you should be able to rotate it but should not witness significant movement if you try to rock it back and forth.
More elusive candidates
- Bad air flow meter
- Other flaws in wiring harness (other than grounds)
- Fuel pressure regulator
- Plugged catalytic converter
- Intake Leaks
- Faulty ECU
- Air flow meter - Bentley manual will describe method to test air flow meter. Use volt/ohm meter connected as described across two of the connectors and manually move the wiper under the plastic cap to see if you have a continuous, as opposed to erratic, progression of values on the ohmmeter. This will diagnose a bad air flow meter 90% of the time but keep in mind that on occasion we have had ones that test correctly but fail in a different manner. You can also check the air flow meter flap for free play, as slop or weak spring tension can also be an indication of a worn out unit.
- Wiring harness - Look for cracks in the insulation on wires - disconnect connections and inspect for damaged or corroded connectors. Careful with this next suggestion - while the vehicle is running massage and move wiring harnesses around to see if the running condition will improve or worsen. DO NOT do this with the spark plug wires or the coil wire but do it with the various branches of the engine wire harness. Pay particular attention to a wire that comes off the back of the alternator, goes back to the firewall and then turns left and goes over to a wire distribution box. Sometimes the wire starts to break at the connector that comes off of the alternator and while still attached it is not making a connection.
- Fuel pressure regulator - Very uncommon but we have run into this one a couple of times. A blown fuel pressure regulator will result in the fuel pressure jumping from in the 40 lbs of pressure range to 100+ lbs of pressure. Van will run extremely rich. Tested with a fuel pressure gauge connected off the fuel line T near the oil breather tower.
- Plugged catalytic converter - Engine sounds constipated - won't rev up correctly and has a whooshing sound as the exhaust is trying to escape through any means possible. Keep in mind that although catalytic converters can fail and plug up on their own, this often occurs because of another malfunction that causes the catalytic converter to overheat or break up. Always best to have emissions analyzed after a catalytic converter has broken up to confirm that various emission readings are in their correct range.
- Intake leaks - visual check of all vacuum lines in engine compartment, tighten intake manifold bolts, tighten clamps at intake boots and inspect and wiggle injectors to determine if the fuel injector seals have deteriorated. Again be careful, but cautiously spray limited amount of brake clean or chem tool at these connections while the vehicle is running to see if it changes dramatically indicating a leak. Have fire extinguisher nearby and again be very careful and be very conservative in your spraying. A loose spark can ignite it before it evaporates if you apply too much.
- Faulty ECU - fortunately when an ECU fails is usually fails all the way and the van does not start and run. There is too much going on in the ECU to be able to test all of the functions of the ECU so it almost becomes a process of elimination when everything else checks out correctly that the ECU is the next most likely prospect. We really don't have a suggestion other than plugging in a known good unit to test the theory, but we know that is challenging if you don't have access to spare test parts or other Vanagons.
Hopefully some of these hints will help you with your troubleshooting endeavors. Also you may find helpful both the system overview and the component orientation for the vehicle's fuel and ignition systems found with the description of our Diagnostic Tool. Whether you follow our suggestions or not, we would advise mapping out a strategy. It is less overwhelming if you list out the possibilities and devise an organized approach, and then, with a little luck, even a cunning non-mechanic can claim victory in the battle of man v. machine.