Rough Idle LS376 help

Got the engine started, Fuel is now up to 60psi. The LS won't idle unless I choke about 85% of the air intake. The i get a rough idle but it's the only way to get any idle.

When i give it some gas, i need to choke less, say around 50% and it runs smooth at 3K rpm. I put my MAF sensor exactly 10" off the intake.

Anyone have any ideas? Will i have to reflash my ECU to change up the air/fuel ratio?

Here is a link to how it runs unchoked....
YouTube - ‪P8030036‬‎
 

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Stupid question, but you said your cats were glowing red before - doesn't that usually mean a crapload of raw unburnt fuel is exiting out the exhaust ..... either really rich a/f, clogged injectors, valve/ring problems, etc.... - I'd imagine one of those would be responsible for your idle problem? Probably a/f and need to get on the dyno to get it tuned properly?
 

Craig Gillingham

Banned because I can't follow the forum rules.
basically the Ls376/480 is a screw up engine. The GM plug and play is a crock of shit and indeed isnt a plug and play and not compatible.

see this for other horror stories

LS Engine Problems Engine Problems

you have 2 options.

  1. swap cam back to standard Ls3 cam with plug and play Ls3 ecu
  2. swap Ls376 for drive by wire compatible ecu - motec - gems etc
do not bother trying to make this engine work and STOP running the car as is as can cause damage and ruin CATS-you would find that the AF ratio is hap hazard on a dyno . to verify look at some engine oil it will smell of gas....
 
basically the Ls376/480 is a screw up engine. The GM plug and play is a crock of shit and indeed isnt a plug and play and not compatible.

see this for other horror stories

LS Engine Problems Engine Problems

you have 2 options.

  1. swap cam back to standard Ls3 cam with plug and play Ls3 ecu
  2. swap Ls376 for drive by wire compatible ecu - motec - gems etc
do not bother trying to make this engine work and STOP running the car as is as can cause damage and ruin CATS-you would find that the AF ratio is hap hazard on a dyno . to verify look at some engine oil it will smell of gas....
wouldn't it be a lot easier to just put it on the dyno and have them tune the a/f, timing, etc... rather than start swapping stuff?
 

Craig Gillingham

Banned because I can't follow the forum rules.
wouldn't it be a lot easier to just put it on the dyno and have them tune the a/f, timing, etc... rather than start swapping stuff?
efilive or hptuner software for gm ecu is ok for small tuning of the ecu where say a LS3 plug and play runs ok but on a dyno just needs "tweaking" to make it even better.
each change takes a while to flash, with a reboot in between to take hold.

With the Ls376 ecu its so far off that a whole load of tuning/dyno mapping cant get this engine finalised to a degree where its street usable and you will be left with a big tuning bill and an engine on the dyno that is hap hazard on Af ratio and jerky at low idle.

i have spent hours and $$$$on this engine along with hennersey venomGT and if you read the PH thread so have many others

but everyman must pursue his own thought process but i gaurantee will end up with 1 of the 2 options above or living with a jerky low speed engine that has inconsistant AF ratio lean to rich..hap hazard...not good

Tuning guys will be willing to have a go at tuning this engine but then again they would..
 

Craig Gillingham

Banned because I can't follow the forum rules.
wouldn't it be a lot easier to just put it on the dyno and have them tune the a/f, timing, etc... rather than start swapping stuff?
a quote from the other thread to re-iterate the point to alex of not bothering trying to tune..

"Also, when using the e67 ECU with anything much over a stock cam, the software is so complex you end up turning off some of the tables and inputting bogus data just to get the motor to idle and warm up properly. Otherwise the Fly-by-wire throttle and ignition timing chase each other around so much that frequently the ECU throws its hand in and usually the throttle body stops responding. Im sure in very experienced hands all the E67/hot cam issues could be resolved but it seems a very time consuming and costly process as each time you make an adjustment you have to re-flash it over to the box.
Personally I think there are several alternative user-friendly ECU/software packages out there for non-stock LS builds.
Its a shame this combo continues to be sold if its not plug and play, which Im sure most customers assume ?"
 

Randy V

Moderator-Admin
Staff member
Admin
Lifetime Supporter
Cam - What Throttle body, wiring harness and ECU are you running.. Give me the numbers on them. I might know what your problem is.
 

Fran Hall RCR

Moderator
GT40s Sponsor
Cam,

if the red light in the fuse box is glowing you have set a fault code....clear this first by disconnecting the battery...if it comes back and is lit again you need to find the source of the problem first and foremost...

We used exactly the same ECU/376 set up on John Salmons car and had a pedal code that came back twice....once cleared the engine ran fine.

The idle stability has become better with use as the LTM has learned the idle protocol and now sits at 820 rpm no problem,.

Others having trouble with tuning may have created their own issues as I know GM did not "knock up" a Calibration in five minutes for this or any other engine.

This is a great plug and play system that works very well as supplied and there is plenty of room for tuning ..so long as the person doing the tuning is switched on....and truly capable....not just a forum or internet jockey ....

Many owners of FF GTM cars are also using the same GM crate package with little to no ill effects ....
 
uhh, ok i'm stupid. Mass air flow 180 degrees out. redrilled holes, stuck it back in runs like a FRICKIN CHAMP! Thanks craig for the hint on powerheads. i needed to make sure the maf air intake faced the input. big dif.
 
The blue flames coming out the back was kind's fun! Do you mean to say you had the MAF on backwards?

Regardless, it's a BIG DAY congrats on having a car that make car sounds without you making "vroom, vroom" sounds from the drivers seat.
 
Had a similar problem with my car. After market ECU (Autronic) and toyota V8. Problem was the ECU needed a manifold vaccum sense to it to map correctly and no-one told me. ECU had a small input spigot (which I thought was a static air pressure sense, but it wasn't. It wouldn't idle unless the throttle was held open and the CAT's glowed RED.
 
Cam,

Glad you resolved the issue so quickly! LG Motorsports has a chassis dyno and are certainly skilled at tuning an LS engine. They are in Garland (when the time comes).
 
The blue flames coming out the back was kind's fun! Do you mean to say you had the MAF on backwards?

Regardless, it's a BIG DAY congrats on having a car that make car sounds without you making "vroom, vroom" sounds from the drivers seat.

Mesa, yup, the tiny scoops were faced toward the engine, not the air filter. I could only get it to run if the air was swirling around in the intake. Didn't see a word about it being directional in the crate engine paperwork. It sounds like there are a few dozen people that had the same problem out on blogs so i don't feel that bad.

Although i really miss the flames. I had some 2 foot flames for a while.

Throttle response is quick off the DBW. Man it sounds SWEEET!:thumbsup:
 
Throttle response is quick off the DBW. Man it sounds SWEEET!:thumbsup:
Can we get a little of that aweet music coming our way brother?
Maybe a U-Toob or a mpeg?

It would be a nice pick me up for a guy who is a year away from this moment in time :(
 
By opening your big mouth, now YOU are on the video 'poop' list too J !
Come on guys, video or at least sound bite for us little motor city (RCR) crack heads.

Give us a hit :)
 

Craig Gillingham

Banned because I can't follow the forum rules.
vid would be good. please add dyno sheet and a/f results across the board. driveabilty vid also please to show just how "better" the idle stability becomes and how long this takes.you may have solved a big problem to a few that are currently swapping the cam or plug and play ecu.....
 
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