Time for OBD1 connector.

The forum for all of your technical questions on your classic FIAT autos
Post Reply
User avatar
Posts: 200
Joined: Thu Aug 25, 2016 3:55 pm
Last Name: Conlon
First Name: Ronald

Time for OBD1 connector.

Post by rconlon@ou.edu » Fri Jul 13, 2018 10:38 am

While trying to diagnose a FI Spider with A/C, I thought about some sort of wiring addition that would mirror the connectors on the ECU and make them available to a multi-meter. This would allow for fairly easy diagnosing of the system.

Ronald Conlon
Ottawa, ON
2016 Fiat 500 Sport
1979 Fiat Spider 1999 to 2017
Member of Mira since 1999
User avatar
cinquemila club
Posts: 5767
Joined: Sat Jan 23, 2016 11:49 pm
Last Name: Artigue
First Name: Bradley

Re: Time for OBD1 connector.

Post by bartigue » Mon Jul 16, 2018 1:29 pm

You can diagnose at the ECU plug. Bosch made a tester that connected between the ECU and vehicle FI harness...they aren't easy to find. The issue with diagnosing at the ECU plug is you have to stand on your head. I've seen some extensions made with intermediate connectors to test the system but I'm not sure the effort is worth the trouble, I tend to measure everything at the sensor itself, not at the ECU, which works fine.

OBD1 and 2 are serial connections to computer(s) in the car; the Bosch ECU isn't very intelligent, it is a solid state box with two modes (lambda and not lambda [if the O2 sensor is busted]). All of the feedback from the system is measured in OHMs of resistance and ranges. Relative to a new car it isn't highly accurate, it won't "tell" you what it is doing, though most resistances given correspond to a value in something else. For example, the measured range of the temp sensor corresponds to an actual engine temperature, the measured range of the AFM correspond to things like amount of air, temperature of air, etc.

All of this can be found in the Bosch workshop manuals online - not the FIAT versions, but the Bosch ones. Even those are a big vague on translate the resistances given.
Brad Artigue
1982 Spider 2000
I've restored, worked on, sold, bartered, and bled for:
1970, 1979, 1980, 1981, 1982 124 Spiders -- 1969, 1970 850 Spiders -- 77 X1/9
User avatar
tremila club
Posts: 3358
Joined: Sun Jan 24, 2016 9:18 pm
Last Name: ridge
First Name: richard

Re: Time for OBD1 connector.

Post by rridge » Mon Jul 16, 2018 4:37 pm

I used to bid on the Bosch L-jet testers when they came up on eBay. Unfortunately L-Jet was used on some Porsches and the prices got too high for me. Haven't seen one in quite a while.
'81 Turbo Spider
Rockville, MD
Post Reply

Who is online

Users browsing this forum: kryger and 5 guests