OBD2 Readings

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itsbrokeagain

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Evening all,

After a fun day chasing down a new misfire it occurred to me whilst staring at the OBD readings on my laptop that I have absolutely no idea what what a fully working P38 4.6 looks like from a diagnostic point of view.

So does anybody have a set of readings for reference? I realise that a perfectly running V8 may be a bit of a long shot here...

Dave
 
It didn't. Just that running on 7 1/2 Cylinders feeling. Probably something to do with one of the LPG injectors deciding that permanently on was a good thing. As it happens, running it in the dark, I can see arcing on plugs 3 and 5. Nothing too serious but all contributing to the general "not right" feeling. Just wondering if long term trims of -90 were normal - I remember reading in another thread somewhere that GEMS long term trim readings were a little suspect.
 
itsbrokeagain said:
It didn't. Just that running on 7 1/2 Cylinders feeling. Probably something to do with one of the LPG injectors deciding that permanently on was a good thing. As it happens, running it in the dark, I can see arcing on plugs 3 and 5. Nothing too serious but all contributing to the general "not right" feeling. Just wondering if long term trims of -90 were normal - I remember reading in another thread somewhere that GEMS long term trim readings were a little suspect.
Click to expand...

If you can see arcing that is your problem. Change the leads. Too many people rely on electronic crap when the problem is staring them in the face.
 
Last edited:
wammers said:
If you can see arcing that is your problem. Change the leads. Too many people rely on electronic crap when the problem is staring them in the face.
Click to expand...


Of course. But I'd still like to know what the OBD readings for a nominally working P38 are.

Cheers

Dave
 
Quick update. Just got a chance to move the car somewhere really dark. Just looks like St Elmo's Fire now - ghostly blue glow from the base of all the plug leads. I guess the leads on 3 and 5 are just easier to see. Even managed to make my hand glow at one point!
 
itsbrokeagain said:
Quick update. Just got a chance to move the car somewhere really dark. Just looks like St Elmo's Fire now - ghostly blue glow from the base of all the plug leads. I guess the leads on 3 and 5 are just easier to see. Even managed to make my hand glow at one point!
Click to expand...

There you go then, job sorted, good old fashioned diagnostics and not one OBDII plug in sight. :)
 
Irishrover said:
Best way to check any ignition system out is to start the car in the dark..any problems will soon be highlighted as you have discovered, especialy with distributor driven motors.
Click to expand...

Built in resistance carbon cored leads deteriorate over time. This coupled to built in resistance plugs actually prevents current flow. The electricery will find it's shortest path to earth, hence the miss fires. Dark is good for miss fires on any engine with plug leads.
 
wammers said:
If you can see arcing that is your problem. Change the leads. Too many people rely on electronic crap when the problem is staring them in the face.
Click to expand...


yep, you dont always need the leccy stuff!!

itsbrokeagain said:
Of course. But I'd still like to know what the OBD readings for a nominally working P38 are.

Cheers

Dave
Click to expand...

you didnt have a normal running engine and the fix is straight forward, the engine ecu can't do anything about poor spark due to plugs or leads!

wammers said:
There you go then, job sorted, good old fashioned diagnostics and not one OBDII plug in sight. :)
Click to expand...

ive managed to sort alot of my issues out not having any software near the thing!!!
 
Hi

itsbrokeagain said:
Evening all,
After a fun day chasing down a new misfire it occurred to me whilst staring at the OBD readings on my laptop that I have absolutely no idea what what a fully working P38 4.6 looks like from a diagnostic point of view.

So does anybody have a set of readings for reference? I realise that a perfectly running V8 may be a bit of a long shot here...

Dave
Click to expand...

So, after all the banter about the pro's and con's of the use/none use of software and the "leccy" stuff, DOES anyone have a suitable "reference" reading for the 4.6 engine?

I could also do with a sample reference e.g.Rovacom Lite, with which I could possibly use to find a solution to my problem.

I'll post the problem in another message titled "No power and misfire/backfire"
 
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