MarcR94v6

I'm just learning about software to see if it can help me, so I'm new to this. If a misfire is not detected by the PCM, is there any scan tool or monitoring software that can help me pinpoint the problem? This is for an 94 OBD-1 car, btw.

jay_lt4

obd1 cars do not have misfire detection, only obd2 cars have it

if you have a tech2 scan tool you can de-activate the fuel injectors by cylinder # and find your misfire, otherwise you back to basics, checking plugs and wires

MarcR94v6

So in other words, no? I can't find it through monitoring sensor values with Datamaster or a similar program? God damn obd-1.

shoebox

Nope. OBD-I does not detect misfires.

MarcR94v6

just to be clear, I can't even find it through Datamaster telling me my MAF is off calibration or 02 sensors are not to spec?

Injuneer

There is nothing in DataMaster that evaluates the various sensor values and parameter readings, then deteremines that there is a misfire, and which cylinder it is. It would be pretty hard to look at the raw data and pick out a specific misfire. You will see a blip in the MAP, a lean reading on the O2, etc. But picking that data out of a few thousand frames of data log would be close to impossible.

MarcR94v6

ok, thanks. Looks like I'm stuck with throwing parts at it.

bobdec

MarcR94v6, Datamaster will give you an overall picture of how your O2 sensors and MAS are functioning. But remember Datamaster takes 10 snapshots a second. At 2000 RPM thats about 33 crank revolutions, 16.5 spark plug fires (2 per cyl) so they all blend together when the engine sensors are scanned. However the PCM being much faster can actually track and report on each individual cylinder. OBD2 software takes advantage of this and the PCM can report cylinder misfires to the scan software. OBD1 PCM does not track or report misfires to Datamaster therefore no way to see them at the cylinder level. Is your rebuild new, when did this start after the rebuild or come on later. A shop with a high voltage probe on the coil wire can usually pick off a bad HV component.