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Unread 11-20-2012, 06:35 PM   #1
seanom
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ScanXL readings, no o2 sensor, poor mileage

Sort of a continuation of another thread that started going off topic...
(seen here: http://www.jeepforum.com/forum/f13/s.../#post14469608)

I have developed very poor fuel economy. Keep getting p1294 code after changing TPS, cleaning MAP, cleaning throttle, seafoaming engine, throwing in fuel pump cleaner and checking for vac leaks.

There is a good chance I need to change my spark plugs but here are some diagnostics I ran with ScanXL which are kind of neat.

(silver words are relevant to old graphs only) One thing to note is that the computer reads the o2 sensors are present but I am not getting an actual reading from them in the computer.

Here is the link to some screenshots of Graphs from the computer: **Edit: the original link was of wrong data, the correct graphs can be found here: http://imgur.com/a/j18Mi

Additional note for the pictures is despite the spikes in rpm it generally stays put at around 1200 at idle in park. Goes up and down smoothly while driving.

Any info, comments, or questions are welcome. This is my first time really trying to read some of the extra info I can get from the program.

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Unread 11-20-2012, 06:41 PM   #2
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also if you right click and open the picture in a new tab it's quite a bit larger... or just drag it up to the bar if you run chrome.
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Unread 11-20-2012, 08:12 PM   #3
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Update: I just found out that you need to specifically select the o2 sensors to have their data displayed.. will do that tomorrow.
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Unread 11-20-2012, 08:34 PM   #4
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Judging by the charts, your intake air temp sensor or wiring is bad. -39 to 146C?
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Unread 11-20-2012, 08:45 PM   #5
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Quote:
Originally Posted by ZeeJay1997 View Post
Judging by the charts, your intake air temp sensor or wiring is bad. -39 to 146C?
Ya, I point that out in the comments for the graph.. also there are spikes in the Rpms, coolant temp and speed..

Not sure if that's an ECM error or a program glitch..

Edit: just did a quick search; spikes are likely from a cheap elm327 cord.. so I guess just read inbetween them
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Unread 11-20-2012, 08:49 PM   #6
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And the ECT reading is jumping around abnormally.
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Unread 11-20-2012, 09:00 PM   #7
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if you have a meter check this out
iacect.jpg  
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Unread 11-21-2012, 06:24 AM   #8
seanom
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Quote:
Originally Posted by ZeeJay1997 View Post
if you have a meter check this out
I can check that but apparantly this is why -

"ELM327 cables work with the speed of 38400, adjusts the speed of communication in the COM port"

Edit: what do you want me to check exactly? The voltage to see if its spiking between any of these?
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Unread 11-21-2012, 11:50 AM   #9
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your MAP is VERY low for idle about 1/3 what it should be
your ECT is never up to proper operating temp
your IAT is reading way wrong
spark advance is going crazy
long and short term fuel trims are all over the place
throttle position is wrong
rpm reading is crazy

i think you have a bad pcm. but verify with mechanical gauges the manifold pressure and get a thermometer on the intake and a coolant passage.
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Unread 11-21-2012, 05:44 PM   #10
seanom
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Hey, sorry ignore those readings - all that input data was bad due to some technical difficulties..

I sorted it out today.. Here is reliable data - http://imgur.com/a/j18Mi

To me everything looks pretty good - the o2 sensors are staying within the voltages they are supposed to (as far as I know).

Any input on these numbers would be great - or even a point into the right direction as to where to look for comparison.

This program is cool and I'd like to be able to use it to the full extent. And fix my fuel economy without trial and error replacement strategy.

Thanks in advance for any feed back at all.
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Unread 11-22-2012, 11:17 AM   #11
ratmonkey
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what were ambient temps?

your engine isn't up to operating temperature. it's 20*c low fix your thermostat
intake temps are lower than i'd expect as well
your engine vacuum is still VERY VERY low at all times. there's your high idle. you either have a vac leak or the iac is bad. your map could be bad as well though.
your o2 sensor switching appears to be pretty lazy for both sensors.
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Unread 11-22-2012, 03:16 PM   #12
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Quote:
Originally Posted by ratmonkey View Post
what were ambient temps?

your engine isn't up to operating temperature. it's 20*c low fix your thermostat
intake temps are lower than i'd expect as well
your engine vacuum is still VERY VERY low at all times. there's your high idle. you either have a vac leak or the iac is bad. your map could be bad as well though.
your o2 sensor switching appears to be pretty lazy for both sensors.
Thanks for the reply.. I'm going to check for a vac leak again and change the spark plugs.. I noticed the yellow seemed to be a bit slower than the blue but I think that might be the after the cat which might explain it.

Do you know what the MAP should be reading? I can't find what a proper kpa reading should be.
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Unread 11-22-2012, 04:09 PM   #13
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it should be drawing around 18-22psi vac at idle your's is drawing around 8 psi i think(conversion memory is rusty)
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Unread 11-22-2012, 07:00 PM   #14
seanom
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Quote:
Originally Posted by ratmonkey View Post
it should be drawing around 18-22psi vac at idle your's is drawing around 8 psi i think(conversion memory is rusty)
After way too long of looking around I finally found this explanation:

"To calculate manifold vacuum, subtract MAP sensor reading (in kPa) from 100. With a MAP of high 30s, the vacuum is in low 60s at idle. That vacuum would be about 18.5 inches which is about what it should be at idle."

This is for a WJ but I just looked through some other forums and this seems to be about where I want it. And according to the graph it is behaving pretty inline with the RPMs. Minus when I was parked; which might be because the engine wasn't really doing anything?
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Unread 11-22-2012, 07:19 PM   #15
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With switch on engine not running the kpa value should be somewhere near atmospheric pressure. At sea level and 32*C, the kpa should be 101.3. Mine usually reads 93-96, depending on the weather.

The 100 number in the formula you found is an assumed atmospheric.

A vacuum gauge is the best method to measure the intake vacuum.
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