My buddy's truck has a problem, no power, no smoke, replaced VP44 with a known good pump, same problem (only took me a little over an hour), tested MAP sensor, it's outputting the correct values.. any ideas?
Anyhow, the long and the short of it is I'd like to make a OBD2 sniffer and code resetter.. anyone have any experience with this?
Did you check the tps? Very common fault, normally will have a dead band in pedal before totally going, or it usually sets a code. You can do the key on/off trick to display the current codes for now...
Scan tool shows the TPS position is correct, didn't see any jitter in it, and it went from 0 to 100% with no problem... There are some stored codes that don't display, and we dont' have a tool to retrieve them right now.. We have a MaxiDiag 802 (I think?) but my friend's friend has a Snap-On one that should be able to access the stored codes...
I just ordered up a Seeed Can bus shield and OBD2 cable, I'd like to be able to sniff what the scan tool is doing so I can do it myself later.. Truck won't be back here for a week though, so I'm just getting things ready
I have not tried to read codes and clear codes yet, but I can say 2nd gen dodges are the WORST car to try and figure things out on. Even though it is obdII much of the can bus data is A. not there on standard PID's and B. when they are there not in standard equation for OBD as you found out for map values.
Over on Mopar1973man's site we have been doing some can sniffing using a obdlink tool and tera term.
https://mopar1973man.com/topic/11544-obdlink/?page=1
supported PID's
Quote01 - MIL Status Light
04 - Engine Load
05 - Coolant Temperature
(11) 0B - Manifold Pressure
(12) 0C - RPM
(13) 0D - MPH
(15) 0F - Intake Temperature
(17) 11 - APPS Sensor
(20) 14 (Unknown yet)
(28) 1C - OBD Compliance should report 05 hex.
(29) 1D - (Unknown yet)
Quote14 - No Data either key on or running
1D - No Data either key on or running
81 - Return 0 no change if key on or running
84 - No Data either key on or running
8C - Returned 0 with key on but then returned 12. So I checked its returning 2 bytes of data. Varies with RPM of the engine. Using (256*A)+B I get a number ranging from about 3,500 to 11,000...
8D - Return 0 no change key on or running.
Big issue you will have is figuring out what pins to use on the obd. It seems that both the ecm and pcm report back but the ecm reports data faster.
ISO 9141-2 protocol is the only way we have gotten a response from the ecm, using the nonstanrdard header of 486
Does the scan tool have to request each item, or does the PCM send it out all the time..
Looks like I'll have another steep learning curve here... at least I have some experience in the area
I have not found any canbus data coming across the network to the tool that was not requested by the tool.
however this is only the iso 9141-2 protocol, I have not found a way to read the sci bus yet, as that requires you start commands at 7812.5 buad then jump to 64000 once you get the communications going. you cannot use a canbus shield to do that, rather you need a usb to serial cable with some fancy code.
I believe that is what the CCD network is for, but alias that is voodoo black magic on a %100 complete non-standard protocol at a VERY odd buadrate.....
Remember that joke about if Microsoft made cars? Well.. apparently they did design the electronic system, since who in their right mind would make up this weird funk... sure aggravating
Also don't use the standard OBD pin out for the plug under the dash. Again not standard.
Use
https://mopar1973man.com/cummins/articles.html/24-valve-2nd-generation_50/51_engine/electrical/ccd-chrysler-collision-detection-data-bus-r329/
Note the pins that are changed between gas and diesel trucks. I don't honestly know which pins the ISO protocol uses but I am guessing it is 6 & 7 on the obd.
I think I might just plug into the harness directly and to hell with the OBD2 plugin... I'm getting a standard DB9-OBD2 cable, which is evidently going to be useless for this application.. I think i have some old DB9 cables around I can hack up