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DinkyDauBilly
Novice
Jan 15, 2013, 2:46 PM
Post #1 of 17
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This is on a 2002 Jeep Liberty, 3.7L, auto, 71K. I initially was getting an SES indicating a minor EVAP leak; changed and repaired (trimmed) cracked hoses and that error went away. However, I now receive a P0303 code. The engine runs well until I hit about 45 mph; then the light comes on, and flashes. If I stop, turn off the ignition, then restart, the light stays on, but the missing stops, and the engine seems to run normally ... until I get back up to about 45mph, and the light starts flashing and the engine misses. I can clear the code by turning the engine off, then putting the key in the ignition (not start) position, and then erasing the code with the scan tool. The engine will run fine (at least it seems so) until I get the Heep up to about 45 again. Very occasionally I can get it up to higher speed than that before the trigger, but never more than 65mph.
A Live Data capture shows most readings as seeming 'normal', but ... in the frame before the Trigger, Bank 1 Sensor 1 % drops to 0, and stays at 0, while Bank 1 Sensor 1 V reads (starting with that frame) .30; .08; .26; .06; .04; .02, and so on. Bank 2 Sensor 1 %, in the frame before the trigger, also drops to 0, and stays at 0, while Bank 2 Sensor 1 V reads (starting with that frame) .88; .82; .90;.88;.90; .84, and so on.
Short Term Fuel Trim, both banks, and Long Term Fuel Trim, both banks, drops to 0 at the Trigger frame, and remains there throughout the rest of the sequence.
Vehicle speed during this sequence is 47 mph; ignition timing is at 31.50 +/1 during this sequence. Coolant temp is 199.
The plugs were changed about 3 months before this started occurring. I swapped plugs (1 and 3) with no change in behavior; swapped coil packs, with no change in behavior. Also, the injectors have been cleaned - shop cleaned, not Walmart bottle cleaned.
This is the first trouble I've had with this vehicle; it's been a sweetheart prior to this. Got it new in 2002.
I'm thinking perhaps a wigged out PCM. Any assistance greatly appreciated.
Oh ... yeah ... I have all the Live Data info in PDF format, up on our website ... but of course, I can't include a link to it, not in this post.
(This post was edited by DinkyDauBilly on Jan 15, 2013, 3:45 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Jan 15, 2013, 6:35 PM
Post #2 of 17
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Re: SES Code P0303
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Very strange that your misfire seems to be speed related and then can be reset like that.
Honestly this is going to need a labscope put on it to monitor ignition coil primary and injector voltage for cylinder 3 while the misfire is happening to see if either one of those goes away or becomes wacky. That would at least give you some direction because right now you don't know if spark, injector, or mechanical is causing your issue.
They have to be careful also because on some vehicles the PCM disables the injector if the PCM detects a catalyst damaging misfire on a certain cylinder. This can lead you to believe there is an injector problem when the PCM is doing as it is designed. Just remember that even though a PCM can disable an injector for high count misfires it won't do that while the engine is cranking.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jan 15, 2013, 6:36 PM)
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DinkyDauBilly
Novice
Jan 15, 2013, 7:27 PM
Post #3 of 17
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Re: SES Code P0303
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Hi Discrete!
Yes, it's really weird. It's almost like the cause and effect are reversed. Is the misfire causing the code, as one would normally think, or is some twitch in the PCM causing the misfire and then the code?
So, I understand your point about the ignition coil primary and the injector voltage. A question, however. You'll note that I swapped coils (1 and 3) and the problem remained as before, no changes. Would that not rule out a coil problem? Also, though I mentioned the shop cleaning of the injectors, I did not mention that the injectors checked out electrically.
What do you think about the sensor readings flatlining one frame before the trigger frame, and the fuel trims flatlining at the trigger frame? It's like all those sensors are going dead at the same time.
Oh ... one other thing ... the speed related thing - I set the transmission in 2nd and tooled off down the road, to see if the trigger were related to RPM. Nope. It triggered at 45 mph, give or take a couple MPH.
(This post was edited by DinkyDauBilly on Jan 15, 2013, 7:32 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Jan 15, 2013, 7:40 PM
Post #4 of 17
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Re: SES Code P0303
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Swapping the coils may rule out a coil problem, but you want to check the operation of the PCM coil driver by monitoring the coil primary voltage or amperage to see what is happening when the misfire appears. The same goes for the injector voltage or amperage. You just want to see what happens to either one of those drivers when the problem occurs.
It could be that the O2 sensor went lean due to the misfire and the PCM went open loop on that bank. A misfire will cause a lean condition because the oxygen that isn't used during the combustion process gets pushed into the exhaust.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jan 15, 2013, 7:42 PM)
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DinkyDauBilly
Novice
Jan 16, 2013, 9:21 AM
Post #5 of 17
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Re: SES Code P0303
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OK ... I think I see. Sadly, however, there is no one down these parts that can do those kinds of tests The nearest such place would be some 60 or more miles up the pike. Well ... there is one GM dealer that probably has the equipment to do that, but that dealership is the original source of every sob story you've ever heard about getting screwed brainless by such outfits. I am seeing in my future a slow drive to The Big City ...
Thanks for your help with this.
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Sidom
Veteran
/ Moderator
Jan 16, 2013, 8:22 PM
Post #6 of 17
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Re: SES Code P0303
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Post the link but change the Ws to Xs that way it won't be live...
I'm sure you've already tried but I'll ask any.......Can you duplicate the miss while the vehilce is sitting still? Have you run a compression test on bank in question?
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DinkyDauBilly
Novice
Jan 16, 2013, 10:39 PM
Post #7 of 17
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Re: SES Code P0303
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There are two:
http://www.writingplaces.com/...tyLDScan12262012.pdf
and
http://www.writingplaces.com/...tyLDScan01122013.pdf
I cannot duplicate the miss while the vehicle is standing still. The error does not trigger until the vehicle hits that 45mph mark. I can then stop the vehicle, turn it off, and restart, and while the SES light remains on (not flashing), the engine runs without missing. I then accelerate back up to 45mph, the SES will start flashing, and the miss kicks in. I can drive this thing all day around town with no problems. And I can drive home from town on the highway without problems, so long as I keep it below 45.
No, I have not checked the compression.
I repaired your links. For some reason you used "xxx" instead of "www"
(This post was edited by Hammer Time on Jan 17, 2013, 4:15 AM)
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DinkyDauBilly
Novice
Jan 17, 2013, 5:18 PM
Post #8 of 17
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Re: SES Code P0303
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Sidom suggested I use the xxx's. I was under the impression that we could not post links to external sites?
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Hammer Time
Ultimate Carjunky
/ Moderator
Jan 17, 2013, 6:38 PM
Post #9 of 17
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Re: SES Code P0303
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Only to your own documents, pictures or youtube uploads. No other sites.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Sidom
Veteran
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Jan 17, 2013, 9:54 PM
Post #10 of 17
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Re: SES Code P0303
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Well it's not like Chry didn't have their problems with PCMs in that time frame but it's the speed that is a bit weird.
A compression test would probably not revel much since it runs fine at idle and lower speeds.....You would have to check it when the problem is happening....
If you take it out of overdrive does this do anything for the miss???
It might help if you could rig up a vacuum gauge and moniter the reading when the problem happens....I see the MAP readings but personally I would put a gauge or transducer on it while I was driving it.... If you get a shaky reading that could indicate a valve sticking.....
When the SES light is flashing, that means there is a misfire going on that is bad enough to do damage to the converter
(This post was edited by Sidom on Jan 17, 2013, 9:57 PM)
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DinkyDauBilly
Novice
Jan 18, 2013, 1:52 PM
Post #11 of 17
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Re: SES Code P0303
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Overdrive has no effect.
I didn't do a compression check mostly because it just doesn't act like a valve problem. But to cover all the bases I'll do one.
Thanks for the suggestions.
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DinkyDauBilly
Novice
Jan 18, 2013, 2:11 PM
Post #12 of 17
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Re: SES Code P0303
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Another question - I do most of the repairs and upkeep on our vehicles - mechanical stuff - but the electronics and diagnostics thereof are something for which I have been at the mercy of scoundrels. I am using an Innova 3130 scan tool. I would like to reduce, if not fully eliminate, that vulnerability. I've been looking at some of the PC-based tools. What would recommendations be for something capable of providing more, and more useful, diagnostic data?
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DinkyDauBilly
Novice
Jan 18, 2013, 3:11 PM
Post #14 of 17
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Re: SES Code P0303
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If you were scoundrels, would you be here answering questions from people like me?
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Hammer Time
Ultimate Carjunky
/ Moderator
Jan 18, 2013, 3:56 PM
Post #15 of 17
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Re: SES Code P0303
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No we wouldn't but we often get people coming in here and throwing out general accusations about the auto repair business and techs in general and that doesn't sit well with us. There are bad eggs in every business so don't lump them all together.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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DinkyDauBilly
Novice
Jan 18, 2013, 4:28 PM
Post #16 of 17
(2017 views)
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Re: SES Code P0303
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Well ... I fail to see where you're getting 'general accusations' and 'all' from my rather accurate observation about my local circumstances. I've asked reasonable questions, in a reasonable manner, and thanked those who have provided suggestions and otherwise tried to help me out with this problem. If that ain't sufficient, hey ... go ahead and dump my account.
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nickwarner
Veteran
/ Moderator
Jan 18, 2013, 7:17 PM
Post #17 of 17
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Re: SES Code P0303
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We get people who want to brand every single tech in the earth a thief here every day. To make matters worse, we also have to deal with them at work every day accusing us on ripping them off because some guy at a parts store, cousin's neighbor's friend's uncle Billy Bob who knows things about cars, and everything else you can come up with says we are a scam without having even seen the car, done a single test or even had the type of tooling capable to do the tests needed or the knowledge to understand the results. So the branding of every single shop in your area as ripoffs stands out to us because we've had it before from problem customers who themselves can't tell the difference between a good tech and a bad one due to their ignorance of how a complex modern vehicle functions in its most basic form.
So far you have been reasonable, but realize we all volunteer out time here and are all professional techs. No shadetree guys throwing out nonsense here. We all donate our time to give other the knowledge we have spent many years and many thousands of dollars to learn and master. We use information systems that cost hundreds per month and use toolsets that cost more than a new Escalade does to be able to do it right the first time.
I'm usually one to snap out when people accuse techs as a whole of being shady. In this case I'm trying to take a different approach. I want you to see things from our perspective. We will help you find the issue with your car and fix it. We will do it free of charge on our own time and at no charge to you. But we catch more crap than a colostomy bag on a daily basis and it adds up after a long day.
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