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Thread: need help with cold start issue since new cam

  1. #1
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    need help with cold start issue since new cam

    i have a gen3 lq4 bored .030 with flat top pistons, 243 heads that are ported and bowl blended, pac 660 dual springs, fast 92mm ported intake, 92mm warr tb, fast 36lb injectors, 1 3/4" mid length headers into a true dual 3" exhaust with an xpipe and magnaflow mufflers. transmission is a t56 manual. car is an bmw e39 touring. i am running speed density with no maf.

    when I originally built the engine I was running a tsp 228/232 .600 112lsa cam. I got a mail-order tune from frost and everything was fine. great cold starts, driveability, and hot starts. cam pulled great down low but flattened out up top. so I decided to swap it out in favor of a more linear power band.

    I installed a tick sns stage 3 237/242 .633/.608 111+3lsa. cam was degreed, as well as ptv clearance was confirmed good. I changed a few things and got the car to run well enough to get to the dyno, figuring they would button up starting and driveability. they got driveability pretty good but couldn't get the cold start up either. we both agreed that instead of me paying them their hourly rate to try and diagnose it that I would bring it home and get it figured out and then bring it back to further dyno and street tune. the car did 430rwhp/390ftlbs conservatively on their mustang dyno.

    i brought it home and swapped out the walbro 255 fuel pump for a racetronix 255 and redid all the fuel lines in 6an with a hyperfuel adjustable pressure regulator(true return style) as i always hated the c5 fpr and walbro would bleed down fuel pressure right after prime cycle. cold starts will catch, fire, and die 3 or 4 times before it will start. hot starts fire right off 1st key everytime. I've tried playing with airflow, adding and taking away timing and fuel during cranking, kind of at a loss.

    sorry for the book, i just tried to put as much info as possible. ive attached a somewhat long log to show the cold start, drive, and then i shut it off and restart at the end while its hot. also attached the current tune. thanks in advance for any suggestions/ help.
    Attached Files Attached Files
    Last edited by Mentaleeill; 06-26-2020 at 09:58 PM.

  2. #2
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    Reduce your idle spark. Every time you try to start it, the transition from crank spark to idle spark kills the engine. The only time you're able to keep it running is when it flares enough for start flare retard to come in and yank a bunch of spark out. That should get you going...

  3. #3
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    I tried reducing idle spark, increasing cranking spark, played with fueling to compensate for more/less spark. Seems to stay the same, takes quite a few key cycles to get it to catch and stay, then when warm starts instantly.

  4. #4
    Senior Tuner Frost's Avatar
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    I told you in email that that TB was kinda junk (for THIS reason) and it has a lack of IAC airflow needed to get good cold starting. You can see that's the case in the logs too; even after the car is HOT-HOT, at the end when you re-start the car, it's idling at over 180 counts (hot). Sometimes you have to accept that the Chinese part doesn't do everything the OEM unit did.


    -EDIT- another glance shows it return to idle at 1100 RPMs/ > 90 counts... then it has to trim all of that down to like 3 counts (almost fully closed) just to reach commanded idle. That's it... that's all you got. It has almost no airflow through the IAC for it to move nearly 100 counts and not even drop 200 RPMs. And you can't open it any more at all to help cold start or you will end up with 0 counts warm. That's it. You are out of IAC. You cannot tune around this faulty part any further than has been done.
    Last edited by Frost; 06-30-2020 at 11:23 AM.
    Steve Williams
    TunedbyFrost.com


  5. #5
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    I have had a couple differnet 4 inch chinese throttle bodies and they are set up pretty stupid out of the box. If you have a dremel tool you can port the inside and the outside of the opening for the iac. I have done that and I bet it flows more then the factory one after I'm done. One other thing I don't like with them though is when I do a boost leak test they leak a bit out of the throttle blade pivot point. I haven't ever done a boost leak test on a engine with a oem throttle body, so not sure if they are better but I would imagine they would be.

  6. #6
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    I did mess with the warr tb with a dremel, opened it up a good bit. It seemed to idle a bit better, but had one he'll of an annoying whistle. I bought and installed a nick williams 92mm tb and the iac ports are way bigger than the warr was even after I opened it up. Trying to find time to play with this cold start issue.

  7. #7
    I've been fighting that same annoying whistle on the 92mm Warr unit on my 5.3/80E setup with Holley midrise,tick cam .613/.590 on a 113 LSA. Cold starts great, revs up then idles back down. Once at op temp it friggin howls when not under a load, takes a few seconds for IAC counts to drop to zero. I drilled a hole in the blade same size as stock TB, helped a tad but I guess I'm gonna need to open up the passage as well. Driving me nuts and sounds like a horrible vacuum leak.