In the '60s and early '70s, vehicles were very basic: carburetor, coil, points, cap, rotor, plugs, etc. Intermittent problems were pretty much non-existent. It either ran, or it did not. When it did, all was cool and groovy. When it did not, you checked the basics: fuel, spark, compression. Whatever was missing... well, that was your problem—and there were typically only one or two components it could possibly be.
In the 1970s, things got a little more complicated. Something called "smog" became a new reality, and fuel started to get pretty pricey. So, engines needed to be a lot cleaner and a lot more efficient. The result was that vehicles got a lot more complicated. Electronic fuel injection replaced the carburetor. Electronic ignition replaced the points. High-tech devices were added to the exhaust, like catalytic converters and oxygen sensors. Vehicles were getting more and more complicated, and different manufacturers were going in different directions to solve the various problems. Consumers were getting hammered at the repair shop with HUGE bills to fix their complicated vehicle that their mechanic was ill prepared to fix, let alone diagnose. By the late '80s, passenger vehicles had full blown engine "management" systems—but nobody was in charge.
Around 1990, a consumer protection law was passed requiring an "on board diagnostic" (OBD) system on all passenger vehicles sold in the USA. Part of the system was the introduction of the infamous "check engine light" (CEL). That is, in fact, how you can tell if your vehicle has an OBD system: it will have a CEL, too. Now anytime the engine hiccuped, even intermittently, the CEL would come on and stay on until the problem was fixed. At first this requirement was perceived as an insult to good mechanics everywhere: just another form of "Big Brother" intrusion into our lives. Many thought it was just another "smog device," an additional hurdle to jump through when getting your vehicle through the bi-annual emissions test. Over time, though, the system has improved to the point where it is relied upon by mechanics everywhere. The other very important thing that happened was standardization. All in all, the advent of true engine management systems, along with an OBD acting as "upper management," has turned out to be a very good thing. Okay, enough with the history lesson: Now, what the hell is wrong with my VW?
No Bus or Vanagon, not even the 1990 and 1991 models, have any form of OBD. Late fuel injected Buses and all Vanagons are part of the aforementioned generation of vehicles that have much of the high-tech stuff, but none of the super-high-tech stuff. That is, a management system with no "upper management." This generation of vehicles are the trickiest to diagnose and fix. This is one reason VW dropped the Vanagon altogether, as it would have been too expensive to redesign it with an OBD. When a component fails or a connection is faulty on a Bus or Vanagon, it can be difficult to pinpoint. It takes an experienced mechanic with lots of spare parts: a dying breed, a dwindling supply.
Our best advice for anyone trying to correct a running issue is to proceed as follows:
Step #1: Replace all maintenance items. Make sure everything is up to date, including filters, fluids, all ignition components (plugs, cap, rotor, wires). And, use only OEM-quality parts. It is easy to waste a lot of time and money chasing a problem by replacing expensive fuel injection components, just to find it is a regular maintenance item that was causing the problem. Every Vanagon we ever sold at GoWesty got all the maintenance items replaced; every one was back to zero miles maintenance-wise, no exceptions. Click here to read our recommended maintenance schedule for Vanagons. This is all stuff that has to be done periodically anyway, and even if it does not solve the problem, it is by no means wasted time and money.
Step #2: Once all that stuff is covered, the next step is to visually check every single fuel injection and ignition electrical connection and all ground connections to the engine. That is, actually unplug every Bosch connector and look at the pins for signs of corrosion or dirt. Critical connections, like the plug at the electronic control unit (ECU or "computer") and blue fuel injection temperature sensor (water-cooled models), are especially important. We always replaced the two electrical connectors and plug going to the fuel injection temperature sensor, always. This same plug kit fits all sorts of places all over the EFI system. If in doubt: Replace it!
Fun fact, and a common mistake to be sure not to make: The green wire going to the oxygen sensor is shielded. The signal wire is the inner most wire which is insulated from the surrounding wire, which is just a noise shielding wire that is grounded. A common mistake when replacing this electrical connector is inadvertently attaching it to the shield instead, or in addition to the signal wire, voiding or actually grounding the oxygen sensor signal completely. This mistake has caused some mechanics (looking in the mirror now) a lot of time and frustration!
Step #3: Check and measure all the stuff you can. For example, with a timing light, verify the timing is correct and advancing/retarding like it should. Do an ohm test on all components for which the repair manual provides such test data. Do a pressure test on the fuel delivery system. Test, test, test all you can.
Step #4: Start replacing parts. Which part to replace first is somewhat a matter of experience; knowing what item causes what sort of symptom, and what items are most likely to fail. Based on our experience and knowledge, every Vanagon we ever sold got a full page of reliability enhancing items, preemptively. These are items that we know from experience are likely to be involved in a vacation cut short. Beyond the maintenance items in Step #1, if you were to ask us to list the items in the order we would grab and try, here it is:
• Temperature sensor-if plug is for sure good, replace sensor. If in doubt: replace both
• Air flow meter: If you have one from another vehicle that works well – try that first before buying a rebuilt one
• Digital Idle Stabilizer(pre-'86) - bypass it by unplugging the two plugs, and joining them, see if that fixes your problem
• Idle Control Unit ('86-on) - disconnect it, and see if that fixes you problem
• Distributor-especially if it is pre-1986 models with vacuum and mechanical advance/retard are far more likely to cause a running issue
• Oxygen sensor
• Electronic Control Unit (ECU)
• Fuel injector(s)
Step #5: If the problem persists, break for a cold beverage, take your dog for a walk, then sleep on it. Wake up fresh and double check your work tomorrow!
Thanks for reading, and best of luck!