We get his question often. Especially regarding “special” internal air flow meter adjustments some believe are necessary. Adjustments such as these are not typical/normal adjustments per the workshop manual. These sorts of out of the ordinary changes are usually blamed on the fact that all GoWesty engines are larger displacement than the original 1.9 liter (1983-85 with Digijet EFI) or the 2.1 liter (1986-91 with Digifant EFI) engine. The reason we can get away with increasing the displacement without requiring changes to the EFI system is because the systems used on all 1983-91 Vanagons were air-flow-control (AFC) systems, often referred to as “air mass” based, or Bosch “L-Jetronic” type systems.
These types of systems calculate and deliver fuel based on the amount of air entering the engine, which measured by the air flow meter, in the case of the Vanagon systems. The meter and the rest of the system is not affected by engine displacement. This is in contrast to the earlier, first generation Bosch D-Jetronic used on the 1968-74 VW Type 3, and 1970-76 Porsche 914 with the VW Type 4 1.7 and 2.0 engines. That system was a purely manifold absolute pressure (MAP) bases system, that had no air flow measuring device whatsoever. MAP systems are extremely sensitive to any changes to the engine, displacement or otherwise—whereas the AFC type systems are not.
Here is how our engines differ from the original engines in terms of increase in displacement as a percentage:
• 2200/1.9 (+16%) Works with Bosch Digijet
• 2300/1.9 (+21%) Works with Bosch Digijet
• 2200/2.1 (+5%) Works with Bosch Digifant
• 2300/2.1 (+10%) Works with Bosch Digifant
• 2450/2.1 (+17%) Works with Bosch Digifant
• 2700/2.1 (+29%) GW-EFI system required due to 10:1 compression ratio
The worse-case as far as change in displacement compared to the original engine is swapping out a 1.9 liter with a 2.3 liter and using the original Digijet EFI: 21% increase in displacement. But here is the thing - from 0 RPM to about (100%-21%=79%x5600=) 4400 RPM, as far as the air flow meter is concerned: it makes no difference whatsoever. Air flow is identical as compared to a 1900 from 0 RPM to 5600 RPM (the point at which the system limits the RPM, or “rev limit”). The only difference in terms of air flow between the 1.9 and 2.3 starts above 4400RPM, at which point the 2300 demands more air than a 1900 ever could (because of the larger displacement). We have determined from testing that the system has plenty capacity to provide enough fuel, and then some above and beyond what the 1.9 ever needed. In fact, the same, exact injector part number was used on all water boxer engines, and it is even enough to feed our 2700—and then some.
So, while it is common to have to make adjustments to the air flow meter (even without an engine displacement change), those adjustments are necessary due to other factors, like worn out injection and/or ignition parts.
In the case of the Digijet system (1983-85) the usual culprit is the distributor (vacuum advance/retard and mechanical advance)—this has been a real headache for many shops, for a very long time. It is a throwback to ‘60’s technology (or more precisely, lack of technology!) and, unfortunately, there are no new replacements for these distributors currently available. In the case of both the Digijet and Digifant (all 1983-91), the air flow meter is usually the part that needs to be messed with. Here again, if you could buy a brand new Bosch unit—it would probably work fine. But, here again, no new ones exist….
The good news is that our GoWesty GW-EFI system is CARB approval for use in all 1983-91 Vanagon models originally fitted with either Digijet or Digifant. Two key, very important improvements of the GW-EFI system over both of the original, Bosch system is NO distributor and NO air flow meter, at all. The GW-EFI kit replaces the distributor with a modern coil-on-plug system that not only has zero moving parts, but it eliminates the super-high voltage ignition wires running all over the engine compartment—which are the #1 source of ignition source of engine compartment fires. This kit also replaces with air flow meter with an air mass sensor (AMS) which, here again, has zero moving parts. These two key improvements, along with the replacement of several other aging and no-longer-available items (not the least of which is the harness and all the plugs) not only make any out of the ordinary “adjustments” necessary, it improves overall reliability greatly.