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Is this a decent combo? Any ideas how to make it run better

This is a discussion on Is this a decent combo? Any ideas how to make it run better within the Internal Engine forums, part of the LSx Technical Help Section category; A while back I bought a 99 z28 vert LS1 6spd car in amazing condition. Incredibly clean, 100% rust free ...

  1. #1
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    Red
    1999 Trans Am

    Is this a decent combo? Any ideas how to make it run better

    A while back I bought a 99 z28 vert LS1 6spd car in amazing condition. Incredibly clean, 100% rust free with a perfect body and paint aside from slight spidering of paint on the front bumper cover due to someone bumping it in a parking lot at some point (it also came with a new unpainted SS hood so I figured I'd get them both painted at the same time. The seats had been recovered in black leather with gray inlays with Z28 embroidered into the headrests and the rest of the interior was immaculate..
    So anyway now on to my actual question. The car had 65k on it and shortly before I bought it the previous owner had done some mods. The short block was left stock but he swapped the stock cam for a BTR Stage IV Cam (Gross Valve Lift .620 int .593 exh Duration @.050 int 235 exh 242 on a 111 lsa), he went with a new chev perf hd timing chain, chev perf HV oil pump, chev perf ls7 lifters, ls chromoly pushrods 7.4 long, new timing cover gasket, chev perf LS1 multi layer head gaskets, and replaced the stock heads with some 799 castings that were supposedly lightly ported and had the valves replaced along with the new springs from comp cams which came with the cam. He topped it off with a FAST 92 intake and FAST 92 TB and resized 36 lb injectors, factory MAF sensor and a racetronics fuel pump (Wire harness still in package, I'll install it at some point). EGR, AIR, and cruise control were all eliminated. It also has pacesetter ceramic long tubes, y-pipe, and slp loudmouth II catback, but does have dual flowmaster cats and downstream 02 sims in order to pass emissions/inspection in my state (New Jersey, all they check is that it has cats installed, o2 sensor readings, and a lack of trouble codes, no actual sniffer test.
    My main questions are as follows: Is this a decent combo? To me it seems like it would do better on a larger cube engine, but I don't know much about ls builds. I'm not sure how/where it was tuned but he did till me that one shop he took it to said that it was costing him at least 30 rwhp and had other issues. Since I've had it I've noticed it runs best in hot weather, good idle, good power, no issues. The colder it gets the worse the idle gets, sometimes stalling, I have to allow it to warm up to operating temperature before driving it or it will stall quite often, even after warm it seems to hunt for an idle and sometimes stall. The strange part is if I shut it off and allow it to sit for 5-10 mins after it's warm it will run perfectly. Also it occasionally throws an alternator DTC, I forget the actal code but I think it's terminal L or something along those lines, it will occasionally throw a knock sensor code and a TPS code, I tried replacing the throttle position sensor with no change as well as checked the wires for continuity and resistance and found no problems, I've checked the reading from the tps from closed to wide open and all appears normal. Also while looking at freeze frames for the code there is always a normal reading showing. I was told by the previous owner that he was told these codes are related to the tune.. Not really sure where to go from here, any advice would be appreciated, maybe it's time to buy some tuning software and try to learn?

  2. #2
    Spaz is My Mentor SMWS6TA's Avatar
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    98 T/A w/a little mods...

    Cam cars sometimes need to warm up a bit to idle, Sounds like you got a good deal with all of the mods. That cam is a little less then what I have in my 403ci so it's a healthy cam combo. Not know if and where it was tune could be a lot of your issues.

    If he was running sims makes me wonder if it was tuned. You can tune out the rear O2's, egr, & air pump codes. It may be a good idea to talk with Frost ( tunedbyfrost.com ) and see if his mail order tune could help you more. Trust me tuning can be a nightmare.

    The TPS needs to go through a relearn procedure.

    Insert key turn to on (do not start), hold for 3 seconds then turn off.
    Disconnect TPS plug form harness, turn key on (do not start) for about 10 seconds then turn off
    Connect harness plug, turn key on (do not start), now open the throttle blade all the way open and hold for 2 seconds then close, turn key off.
    Turn car on. The TPS should now be set.

    Having a knock code could be low octane gas, make sure you're running t least 91 or higher.



    Now having what I just went through with my FAST102 and the events of last year I have to tell you to make sure your intake is sealed. I thought mine was and went through Hell trying to get mine tuned since last April. I found a couple of weeks ago that the rear bolts that clamp the intake close the nuts had fallen off them, Had a 8" vacuum leak basically. Found it by freak accident. So after new seals, bolts and a good amount of loctite it's all back together. Now I have to wait till I can afford getting it tune.

    You can see the fun I had by clicking on the engine build thread in my signature.
    http://www.ls1.com/forums/f7/my-6-liter-build-174257/

    http://www.ls1.com/forums/f8/my-8-8-rear-build-165553/

    6.0L Block - Forged 403 built, breaking it in , Polluter Stg3 Cam, FAST 102mm Intake, NW102 TB, MSD wires, NGK TR6 plugs, Truck Coil Packs, LS3 Fuel Injectors, CC Pacesetter LT Headers, TS&P ORY, QTP e-Cutout, Magnaflow Muffler, 104mm Air Lid & Line Lock, Catch Can, Stage 2 T56 w/Viper shaft, PRO 5.0 Shifter, Tick MC, Monster Stg 4 Clutch, QT SFI BH, MWC DSL, UMI: SFC, PHB, LCA's, LCA Relocation Brackets & TA, Hotchkis Springs (1" Drop), YR1 Snowflake Wheels wrapped in NT555 tires & Custom Fab Ford 8.8 rear w/4.10 Yukon Gears, WSQ Hood, 3"CM Strange Eng Drive Shaft.

    Horsepower never lies, but is often lied about!

  3. #3
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    Is it running a MAF or speed density? Did the prior owner have it dyno tuned?

  4. #4
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    1999 Trans Am

    Jeff: It's running a factory maf sensor. Car was never dyno tuned, it was street tuned by some shop in PA. He did take it to a shop that does dyno tuning and dyno pulls and had the car dynoed (Made 420 RWHP and 370 FtLbs)and they reviewed the tune for free and pointed out several issues with it to him but he was unable to elaborate any further because he said that he didn't understand any of what the guy was telling him..
    Lately I've been letting it run until it reaches full operating temperature (like a good 15-20 min since its been around 15F in the morning lately) after which it seems to run fine. If I start driving before it reaches operating temp it will surge at idle like a car with a bad vaccum leak, driving along it's fine but whenever I stop the idle will bounce up and down between 200-900rpm for a bit and eventually smooth out and hold at 900 (which is what the idle is set to) but if you rev it a little it will start doing the same thing again. The part which is confusing me is how it only acts up if driven before fully warming up and even once it reaches operating temperature remains the same, but if you simply wait for it to warm up completely BEFORE driving it everything is fine..
    Been thinking about getting a mail order tune from Frost, just worried I'll end up with it running worse and not being able to switch back.. kinda wish I still had another pcm

  5. #5
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    Red
    1999 Trans Am

    Also about the rear 02 sims, I'm not 100% sure if there are in fact sims hidden somewhere or if it's programmed like that (is that even a possibility?). It has rear 02 sensor readings when viewing engine data (which allowed me to pass inspection) but there is nothing plugged into the connectors for the downstream sensors..

  6. #6
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    The rear O2's (after cat) do not affect how the engine runs at all. They simply set off the check engine light if they detect an emissions issue.

    Sounds like something is off in the tune absent a vacuum leak or fueling issue. Can you see the PCM switch over from open loop to closed loop?

  7. #7
    Moderator 35th-ANV-SS's Avatar
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    Sounds like the rear 02 sensors are tuned out if nothing is plugged in and you don't have an SES light on. That's preferred over using simulators.

    I would also guess a vacuum leak or tuning issue. Typically, you are better off with an actual DYNO tune as opposed to a mail order when dealing with an aftermarket camshaft installed.

    I'd suggest not to drive it too hard until you figure out the underlying issue. I would hate for the car to be running lean and you driving it leading to bigger issues.
    It's on jackstands.

  8. #8
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    1999 Trans Am

    Is its still possible to get rear 02 readings with the sensors tuned out? Embarassed to admit this, but I'm an ase certified maser tech, I just know litterly nothing about tuning.. Already eliminated the possibility of a vaccum leak, smoke tested it and couldn't find a single leak and smoke pressure held perfect.
    To answer the above questiong it does go into closed loop.
    Also after a month of testing it I've confirmed 100% that the car runs completely normal if I allow it to reach operating temperature before driving. If I drive it any sooner it will still hunt for an idle at stops and doesn't change even after it reaches operating temp, however if I park it for a few mins and restart it's good to go again 100%. Also it doesn't throw any codes what-so-ever as long as I allow it to warm all the way up..
    The car does seem to run fairly rich but until I get around to installing my wideband I am unable to confirm the AFR under various conditions.. I have a feeling I just need a good tune but don't know of any shops in my area who do tuning, don't suppose anyone know a place in eastern NJ (Hamilton, between Princeton and Trenton). Aside from that does anyone have any other input?

  9. #9
    Moderator 35th-ANV-SS's Avatar
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    Having the rear 02's tuned out means that within the tune itself there is a false voltage reading for the 02 sensors making the PCM think they are there and working properly even though they're not physically there.

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