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  1. #1
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    Sep 2016
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    Pause in rpm when cruising

    When driving at low steady rpm, I feel like a flat spot for a split second where the rpm drops like I took my foot off of the gas pedal and then comes back. I have noticed this for the last week. I do have a check engine light on, the code is P0450 small evaporate leak. I have had this code before but never had these symptoms. Anyone else experience this before. What can be causing this slight delay? Since then I have cleaned my K&N air filter. My plugs were changed last year, throttlebody was also changed last year along with the egr,
    2006 Chrysler 300C (heritage edition)

  2. #2
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    Aug 2020
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    Southfield, MI
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    Potential causes
    Loss of synch (cam or crank sensor) - but should have a fault code after happening.
    Loss of spark - with new plugs and no faults, doesn't seem likely
    Loss of fuel - I don't think this would trip a fault unless it were happening long enough to cause fuel adaptives to walk out, which wouldn't happen with an occasional blip. Could be a loss of power to the pump.
    Loss of air - throttle closing briefly. Like all the others, it could happen if a bad ground or connection or pcm issue causing a momentary glitch, but most of those have obd1 circuit checks so I don't think this is the issue.
    Torque converter lock up issue - clutches may be having issue and at a low speed/low torque condition it's more noticeable.

    All the above are possible, but I think you would get other symptoms or have fault codes or see it more often. With the evap system leak you could have some problems with learning the purge (how much of the purge flow is air vs fuel) and when it tries to turn on or off you get a bigger fuel swing than expected that causes a rich or lean spike. I don't think it would cause a fueling based fault since it doesn't last long enough to corrupt the adaptives. Having said all that, it still feels like I'm stretching to match up the fault to your condition. What to do? Start with the simple stuff, check your easy to reach grounds and open the major wiring harness connectors and hit them with some electrical contact cleaner, along with the cam and crank sensor connectors (just be gentle with a 15 year old car those connectors can be sticky and fragile) to clean up any corrosion. Keep an eye on the tach to see if it happens in other conditions (but you don't feel them). Good Luck!

  3. #3
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    Sep 2016
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    I'm going to give a good look at things this weekend and report back. The check engine light came off now and I have no codes, but the slight blip in rpm still exists. I'm almost leaning towards a small vacuum leak. It's not a miss or a stumble caused by something ignition related.

  4. #4
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    Mar 2016
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    Is this a new issue?



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  5. #5
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    Sep 2016
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    It has started in the last 2 weeks intermittently.

  6. #6
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    Sep 2016
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    Had a chance to play with the car a bit last weekend. Checked for vacuum leaks using brake cleaner around the intake. All is good. Pulled down the Passenger side plastic inner wheel well, replaced the Evap canister purge valve, cleared the codes and drove the car. Problem still persists. But it's intermittent and doesn't always happen. I turned on my AC because it was really hot this weekend and realized it wasn't working. Found out my condenser had been hit by road debris and had a sizeable hole on the center of it. So I pulled for the front clip, replaced the condenser and fired up the car to see if all was installed properly. And of course it wasn't, I didn't clip in the tranny cooler line to it properly and was leaking out fluid. So it fixed that and all was good, but I did notice that the oil has never been changed in this transmission before and the fluid I saw coming out was a dark browny red and smelt bad. So I have an appointment booked to do a fluid and filter replacement so they can also flush the old fluid out of the converter. I have a strong feeling it's the old fluid.

  7. #7
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    Sep 2016
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    Markham, Ontario
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    Got the transmission fluid and filter changed, and that didn't do it either. Changed the oil thinking it might be something MDS related.... it wasn't. I bought a hand held Diablosport Predator tuner about a year ago off of Kijiji, but it didn't have any software in it, so just pitched it in the corner of the garage. This weekend I dug it out and went online and downloaded the updates to it, went to the car and put in the 93 octane CAI Performance tune into it. Throttle response and WOT is much better. I firmed up the shift into gears and extended the rev limit to 6k. The car starts and drives flawlessly and accelerates seamlessly, but when at a steady low rpm on the street while cruising it feels as though i took my foot off of the gas pedal for a second or 2 then you can feel it come back. It's weird, because when that happens, if i give it more gas, it accelerates with no issues.

    To summarize:
    Champion OEM spark plugs were done last year
    Mopar CAI K&N filter was cleaned
    Throttlebody was replaced last year
    Mobil1 Synthetic oil was done a few days ago
    Transmission fluid and filter was changed on Friday
    EGR was replaced last year
    EVAP canister purge valve was replaced last weekend
    OEM thermostat and rad cap replaced last year
    New OEM radiator replaced last year as well as a coolant flush
    Diablosport Predator 93 Octane Performance tune was put in this weekend

    This car is well maintained and in meticulus condition, no electrical issues, no trouble codes and has never been a problem child since new (original owner)
    Last edited by ttype; 05-31-2021 at 09:27 AM.

  8. #8
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    No good answers, if you want to try to continue the on-line diagnosis please put in some very specific details on when the issue occurs - mph, rpm, temps, pressures, gear, etc. Hopefully between the dash display and the tuner you can get those #s. Good luck!

  9. #9
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    Feb 2018
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    Could the converter unlocking then locking cause this?
    13 Chrysler 300S, 4XX stroker, cam motion 232/246 619/619 118 +4
    E-Force TVS2300, DW 65lb inj. 84 +4 TB
    FORE dual return fuel system, AIT 18% OD pulley, 1 7/8 kooks w/hi-flow cats, 3" Magnaflow Cat-back, FTI 2800 stall, Getrag 3.73 Brembo upgrade. Stage one MOPAR springs, XIX X39 22x9 +15 - 22x10.5 +22 with NITTO NT420V 265/35R22 - 295/30R22

    (Whipple Gen 5 3.0 (ordered 4/21/21)) Meth injection, ID 1050X inj. MMX 95mm TB

  10. #10
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    Sep 2016
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    It looks as though this issue happens in any gear under 1500rpm. Above that, it drives normal. I did get a check engine light come on yesterday and it was P3497. I cleared it with my hand held and it hasn't come back on a day later, and yes the problem of pusing is still there.

    A stored code P3497 means that the powertrain control module (PCM) has detected an abnormality in the cylinder deactivation system for engine bank 2. Bank two denotes the bank of the engine which doesn't contain the #1 cylinder.

    Moil1 Synthetic oil was done 5 days ago, and the car doesn't burn or drip any fluids.
    Last edited by ttype; 06-03-2021 at 11:30 AM.

  11. #11
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    So most likely it's torque converter unlocking (as mentioned by coanan) or kicking out of MDS, which seems more likely with the recent fault. Do you have the fuel saver indicator on the dash so you can watch and see if the MDS exit matches the bump (knowing the dash display has some hysteresis on it, might be good to tune in to the exhaust tone change too)?

    What grade oil did you put in? MDS is sensitive to the grade, but there is a specific fault for that. If grade is good and the bump seems to line up with MDS transition, then it could be oil sludging hurting the pressure/flow to mds lifters, or solenoids flaking out, etc.. I don't know any good way to narrow it don't without opening it up, so spend some time getting in tune with when it happens (mds dash message, going in or out of throttle, etc.) and maybe we can get a more precise diagnosis.

  12. #12
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    Quote Originally Posted by jdm7 View Post
    So most likely it's torque converter unlocking (as mentioned by coanan) or kicking out of MDS, which seems more likely with the recent fault. Do you have the fuel saver indicator on the dash so you can watch and see if the MDS exit matches the bump (knowing the dash display has some hysteresis on it, might be good to tune in to the exhaust tone change too)?

    What grade oil did you put in? MDS is sensitive to the grade, but there is a specific fault for that. If grade is good and the bump seems to line up with MDS transition, then it could be oil sludging hurting the pressure/flow to mds lifters, or solenoids flaking out, etc.. I don't know any good way to narrow it don't without opening it up, so spend some time getting in tune with when it happens (mds dash message, going in or out of throttle, etc.) and maybe we can get a more precise diagnosis.

    Sorry I haven't had a chance to respond, been busy with work to put any sort of effort into diagnosing this. I don't believe I have the fuel indicator light on the dash to monitor. I run Mobil 1 5/20 Synthetic oil. The motor is as quiet as a church mouse. No ticking lifters or anything of that sort. The motor is in perfect working order. looks like I'm going to look into the stall converter and buy the FTI 3200rpm. I was hoping I wouldn't have to drop this tranny and change anything due to my temperament. This just opens pandora's box for me which isn't a good thing. I will no doubt end up dicking around with it and start modding it as I have with every other car I have ever owned....



  13. #13
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    Funny, in the last 4 days of driving this issue has not happened and everything is driving as it's supposed to..... Very weird, although I did get another check engine light P0456 again which has me scratching my head because I already pulled down the passenger side inner wheel well and replaced the EVAP canister purge valve. That lasted about a week til it reappeared a couple days ago. I cleared it and it has come back yet, been 2 days since cleared.

  14. #14
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    Heh, your doing great, just like some dealerships. They try something, take your cash, it still does it, you take it back and try again for more cash, and so on. Rather they fixed it or not you pay and pay again.
    2013 Dodge Charger R/T Plus, Edelbrock E-Force 2300TVS 6.8 PSI, 450hp/459tq, Corsa CatBack, 3.06 Wavetrac 215mm Diff, Severe Duty Radiator, Dual Fans, OE Oil Cooler, Pursuit BR9 Brakes. DSS Two Piece Aluminum Tracking Number Received.



  15. #15
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    Jun 2013
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    Green Bay Wisconsin
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    Last time I dealt with evap leaks I had a bad hose.
    Mopar11 Charger, MMX Cam, BBK Shorty Headers, Hemifever tune, Getrag 3.91 LSD

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