VW Baywindow Bus - Bosch L-Jetronic Tester
by Richard Atwell
I've been looking for an L-Jetronic tester ever since I discovered Paul Anders's excellent webpage documenting all the various testers he's located and collected. There's also Jeff Bowlsby, who built a neat breakout box to test his wiring harnesses. Wow! I really respect the thoroughness of the 914 community: Pelican Parts used to rent out a D-Jetronic tester to it's customers.
Bus folk are lucky to be able to benefit from their documentation but unfortunately the 914 community eschews L-Jetronic, understandably in favor of D-Jetronic because it was far less common and on the surface it seems to have robbed the engine of precious horsepower. Little information exists about the testers that were compatible with the Bosch AFC fuel injection used in 75-79 VW busses.
I really just wanted one more as a curiosity because the basics of the L-Jetronic system can easily be tested with a VOM and FI fuel pressure gauge but if it was practical enough to build, mechanics at the VW dealer must have had a good use for them. I bet they were the only ones who could afford them.
I recently came across a Bosch L-Jetronic tester. At the time the owner could only describe it as possibly a tester for german ECUs but I recognized the wiring harness connector and did some research into the Motronic connector to see if I wasn't bidding on the wrong tester. Fortunately he gave me the part number and I contacted Bosch and eventually located someone familiar with the unit.
That company is absolutely fabulous: not only did they tell me that they stopped producing that tester in 1989 but they mailed me an operating manual and some sales literature. I was pretty hyped that it was a vintage Bosch ECU tester and eagerly awaited the documentation to verify it was intended to test L-Jetronic and got lucky.
I purchased the tester for $44. Since publishing this information the prices have skyrocketed because buyers and sellers know what this item looks like now. Don't pay more than $100 more this unit. They come up for sale all the time on eBay and have limited usefulness simply because the L-Jet system is so easy to diagnose and the ECU is so robust.
This documentation is for PERSONAL VIEWING ONLY. I have expended a great deal of time and expense researching and collecting it. YOU DO NOT HAVE PERMISSION TO DOWNLOAD THESE IMAGES TO OFFER AS DOCUMENTATION WITH YOUR AUCTION AND/OR SALE OF AN L-JET TESTER TO INCREASE ITS VALUE OR AUCTION AND/OR SELL THESE IMAGES IN PRINTED FORM SEPARATELY. BY READING THIS YOUR ARE AGREEING TO THESE TERMS AND YOUR AUCTION/SALE WILL BE SUBJECT TO A COMMISSION OF 50% FINAL SELLING PRICE IF YOU DISHONOR THIS AGREEMENT.
I've kept these images large so they are easier to read online. The sales sheet gives you a basic idea of what the unit does but it's not very descriptive.
The Bosch manual is pretty bad but it gives you an idea of what accessories are available.
It seems there are several versions of the Bosch Manual. A friend in Germany had a manual with WA-UBF 910/1 DBFSp (7.78) 1.5 CD printed on the back and it contained several extra pages with operating values in German, English, French and Spanish. Here's the English version which is much more complete than the sales literature.
An Alfa Romeo mechanic sent me a portion of a test manual that covers testing an L-Jet Alfa using our Bosch tester. Very useful. We are left to wonder, did Bosch ever published their own manual? Probably...
Recently I was contacted by man who wanted a photocopy of my manual. He was selling the same tester on eBay and wanted to provide a copy of the manual to the winning bidder. I gladly duplicated it and sent it along to him and for a lark wondering if he'd seen the supplementary cable that tests the fuel injector firing frequency. Bosch told me that the supplementary cable was still available but since it was $442.70 and my tester cost 1/10th of that I passed. As luck would have it, he forgot to list the cable with the auction and sold it to me. No good deed goes unpaid!
If you have a tester and want to build a cable you'll need to butcher an L-Jetronic wiring harness for the parts. You can locate the battery clamps easily I bet. The male FI connector was hard to find until I finally located Eagle Day as a vendor so it's now possible to build a cable. It's a little more complicated that it seems and I'm not 100% sure about the components on the circuit board. I've yet to identify the exact diodes used and the black object. Any help would be appreciated.
All wires are the same length - approx 7 1/2 ft. long from harness connector to each end.
Martin Peitz sent me some photos of the adapter box mentioned in the manual. Very hard to find in the USA.
My life long dream of running a mobile FI bus repair business is finally coming true! :-)
I don't know much about these others devices I've come across:
03/25/03 - Created
11/06/03 - Updated cable
12/06/03 - Added Alfa manual
12/14/03 - Added cable detail
12/22/03 - Added Program selector switch matrix
03/24/04 - Added other testers
03/26/04 - Added adapter box photos (thanks to Martin Peitz)
09/06/11 - Fixed broken photos, added translate button, updated footer
07/15/19 - Google update: new adsense code, removed defunt translate button
10/15/20 - Updated Eagle Day link