Date:         Sat, 30 Apr 2022 03:47:04 +0000
Reply-To:     Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject:      Happy Friday! Some fule injection and idle tips.
Content-Type: text/plain; charset="us-ascii"

When it comes to diagnosing most any equipment fault, in order to get past guesses, making adjustments, and just tossing parts and money at a problem it is critical to have a full understanding of the process at hand and having the tools to measure everything that effects the process, especially what you can't see, feel or hear.

For the Waterboxer, getting a smooth, nice sounding idle has some challenges even when all is working well. The intake track is not well balanced at low speeds, ignition timing is retarded, and the lean mixture is further aggravated by cylinder, injector, and air flow imbalances that make a "lean misfire" a normal condition.

For the diagnostics many would like to get an easy fix. Remote diagnoses really gets back to just guesses and tossing parts. One my chuckles is the frequent suggestion of checking the throttle switch. While it is there for a number of purchases, it does little to effect steady state, closed throttle idle. If it fails closed, it will cause an off ldle stumble, surges, etc. At speed a closed switch will effect mixture causing full throttle enrichment when that is not needed. As for actual idle effect, at closed throttle, if the enigne is over run such as going down a hill or down shifting to slow the vehicle down at some RPM the fuel is cut off. As the engine slows down and fuel supply is restored, (injectors turned on) the O2 sensor is bypassed for a short time. This is where the engine basic settings need to be spot on to avoid idle surges or stall outs.

Next thing to check is engine condition, fuel and air delivery, and ignition. Fuel delivery includes the injectors having good spray patterns and being balanced. Air delivery includes not having any vacuum leaks, or un metered sir flow. As the Waterboxer does not use a PCV valve or other metered crank case ventilation metering vacuum leaks include bad valve cover gaskets, defective pistons, rings, and even valves and guides.   Bad intake valves and worn guides are fairly common.

As for mixture control the O2 sensor actually provides a some diagnostic capabilities. Using a good multimeter, the output can be measured and proper operation can be easily confirmed. A meter with a bar graph display will update much faster than just the number display. Going back to understanding the process, the O2 sensor is not there to maintain an ideal mixture. The goal is to switch from rich to lean and back quickly so the the 3 way catalyst and support HC and CO reduction (lean) and NOx reduction (rich) simultaneously. So with the voltmeter you want to see the sensor output contantly going above and below ~.5 volt.

Often disconnecting the O2 sensor wil help the idle leading one to believe that the sensor is defective. The next step here is determining if the sensor is bad and causing the mixture to go rich. For Digifant the design is to keep going rich until the signal is sensed and if not, going rich enough to make the vehicle undriveable, forcing a repair. For digijet this failure often goes unnoticed expect maybe for bad fuel economy or an emissions inspection failure.

Almost never does a bad sensor cause the system to go too lean. If with the sensor connected the idle goes bad and the sensor is showing a voltage reaction, you then need to look at the fuel and air delivery issues mentioned earlier. A single bad leaky injector will dump fuel in that one cylinder and the O2 sensor will drive tings lean and then the 3 other cylinders will fail to fire. There goes the idle. Excess oil blow by or suck through the valve guides can also cause the O2 sensor to overly lean out the mixture. The O2 sensor works by generating a voltage based on the difference of O2 in exhaust compared to the outside air. As such any contamination such as oil or coolant that doesn't belong is a problem.

Hopefully some of this is helpful.

Dennis