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Thread: LM7 5.3 with xr259hr cam. rough idle, stall stumble.

  1. #1
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    LM7 5.3 with xr259hr cam. rough idle, stall stumble.

    I recently installed a comp cam xr259 hr cam on a 112 lobe sep with 206/212 duration & 515/522 valve lift.
    vehicle runs okay on stock factory gm tune. ildes okay but does lobe up and start to stumble for a bit then clears up and is okay. worse under load like parking lots a/c on and so on. driving down the road is okay.
    felt like a loss in power. currently do not have the hp tuners. a co worker has it for his turbo avalanche. he played with it for a bit and bumped the hot idle up to 700 from gm settings of 580 and seemed okay with the odd short stumble 90% better. I went to my appt to get the tune done on the dyno by a local shop. was able to gain 25hp and 30 tq across the board with a smooth strong torque curve. now up to 270 hp and 298 tq at the wheels. he set the idle to 650. it really seems to stumble now and has stalled once while switch from drive to reverse to back into the driveway. my airfuel ratio seems strange to me under wot the ratio drops to 12.3:1 wich to me would seem to lack in power.
    I used to before the cam install be able to break the wheels loose on demand from a stop, now they wont even chirp. sure the dyno results show I made gains on paper but the truck does not better then it was.
    not the truck does have the intake tube from airrade with the deck plate mod to the front of the air box. and has a cat back exhaust.
    looking for anyone with the same cam or someone else with a suggestion or help.
    I have read a lot of posts and searched the internet but no real info.

    now I just use the truck for a daily driver and towing are 6300 lb travel trailer every second weekend, wich is the reason for the cam. looking for possibly saving a bit of fuel and more power up the hills.

    I can get the file for the tune it is store on the laptop at work, can post in a few days if it would help.

  2. #2
    Definitely post up the tune and log of AFR would be handy or at very least O2s to give some indication of fuelling. Without the tune, assuming mechanical is all good, then one can only generalise and say airmass/airflow modelling is not optimised and nor is the timing - generalising, but that's about the long and short of it. As for the dipping and idle characteristics, once the fueling is sorted and timing, you can ensure the IAC modelling is complete and then the idle will be mostly spot on; fuelling inaccuracy accounts for most of the common idle issues

  3. #3
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    Quote Originally Posted by SSUte01 View Post
    Definitely post up the tune and log of AFR would be handy or at very least O2s to give some indication of fuelling. Without the tune, assuming mechanical is all good, then one can only generalise and say airmass/airflow modelling is not optimised and nor is the timing - generalising, but that's about the long and short of it. As for the dipping and idle characteristics, once the fueling is sorted and timing, you can ensure the IAC modelling is complete and then the idle will be mostly spot on; fuelling inaccuracy accounts for most of the common idle issues
    here is the tune the shop did if that shows any info. wont be able to get a data log untill tomorrow night.
    final.hpt

  4. #4
    Stock tune would also be handy for a comparison. It is difficult to see from eyeballing it, a log in either full MAF or full SD showing AFR error would confirm, include timing obviously, but to me it looks a bit like the respective airflow/airmass models could use optimising, it just looks "too neat" for my liking. Also, timing is quite low in the areas where you would see when trying to "break the tyres loose" although the burst knock and the AFR adders, whilst I understand their use, seem a little odd to me. Honestly, I feel you'd be better served by tuning it yourself. I think there is more to be gained. Out of interest, how long did it take to 'tune' the vehicle and was any of it completed on road or all dyno?

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    The tune was done on the dyno only then followed by a road test then parked.
    it took 2.5 hrs and charged 450$ and the idle sucks and stalls. this was my main concern.
    I will be doing a log tonight and I will post my stock tune aswell.
    I found some helpful info on you tube with the hp tuners idle setup. I will be trying that tonight aswell.
    I have been constantly reading for idle setups but most are to do with non electronically controlled tbs. they all talk about iac counts and drilling the throttle body. just seems hard to find the right places for a drive by wire info.

  6. #6
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    Here is the data log before i tuned any changes with idle surge. data log while driving and a data log idleing after tune.
    aswell as the tune changes i made.

    i set the idle to 675 advanced the idleing timing in gear and in p/n by 17 degrees. added 10% to the base idle airflow.
    seems to idle without surging. when driving and throttle released seems to hold speed rather than decrease speed. when the a/c kicks on in gear there it is noticable and idle drops about 100 rpm for a moment then recovers.

    any input would be great. i have never played with tuning before. just looking for any ideas or advice.

    tune before changes, 5252 tune read only no change.hpt
    tune after cahnges, idle tune after changes.hpt
    idle surge before tune data log, warm start idle surge.hpl
    after tune driving log, after idle tune changes.hpl
    after tune idling, after idle tune idleing.hpl