robbied31

iTrader: (1)

Hi,
I have spent the last few days trying to troubleshoot a problem and have held off posting as long as I can. I put a 2000 LQ4, PCM and 4L80E trans in a 67 chevelle. I did it with the guidance of all of you guys in the conversions and hybrids board. I have put about 5000 miles on it over the past year and a half. It is bone stock with hooker swap headers and it has a camaro intake and accessories. I copied the VE tables from a stock camaro tune to the LQ4 tune and that is how I have been running it for the past year and a half. Me and the kid have been working on it to make is somewhat bearable looking so it can be his daily driver. He said it stalled on him a couple times the other day but started right back up. Then later that evening it died in rush hour traffic. He pushed it to the side and called, I brought the laptop with HP Tuners and pulled a Crankshaft postition sensor code. after it cooled off a little, it started back up. we tried to get it home but it died again. So we towed it. after a little research it seemed logical that it was the CPS, so I replaced it and did a CASE Relearn, then I did an idle relearn because it was idling bad. I seemed to have solved the dying/not starting back up issue, but I am left with a bad idle issue. It surges bad while being stopped at a red light or stop sign. While driving it runs great, but idles high while driving.

Here is everything I did......
Changed CPS
Changed the 2 02 sensors
put a new maf on [took it back]
changed the TPS
changed the IAC
looked for vaccum leaks, found one at intake and fixed
changed MAP sensor

Can anyone give me some guidance?

Thanks

Rob

96lt4c4

iTrader: (5)

I have some experience tuning older ODB1 vehicles. Most of the time from what I have seen is that when everything is right as far as no mechanical problems and you have idle surge it is becasue of headers putting the 02 sensors in a different place. My truck had bad idle surge after my 383 build with long tubes and it ended up being my proportional gains table. Also could be too lean VE table. Do you have a wide band 02 sensor?

You could try lowering the values in the prop gains table and see what happens.

robbied31

iTrader: (1)

I apreciate your input, but it has run for a year and a half with 02's in the same place with the same tables. Are You thinking new 02's might require a new tune?

I do not have a wide band.

robbied31

iTrader: (1)

I was thinking I have a mechanical issue, not a tuning issue as it has run for 5000 miles on the tune I have. Do new sensors require new tuning?

96lt4c4

iTrader: (5)

What brand sensor do you have? The bosch sensors from Autozone are junk. They can cause either lean or rich conditions and are not as accurate as the original AC Delco 02 sensors. I only use AC Delco. Most of the time the bosch sensors will casue you to run a little richer. I have confirmed this my wide band.

DaveX

Do you have a wideband hooked up to it? It sounds like you are running a VE table from a 5.7 litre on a 6.0. Is your AFR correct? If you don't have a wideband hooked up, what are your LTFT's at idle?

Are all of your airflow tables from a 6.0 tune or a 5.7 tune?

ROCKETWS6

With the tuning soft ware what are the fuel trims at? It sounds like you might have a vacuum leak,take some carb cleaner around the intake gaskets and see if the idle changes

DrkPhx

iTrader: (15)

If you're still running the stock cam then it should purr like a kitten at idle with zero stalling or surging. I have more questions than answers.

- Why did you use the VE table from a Camaro? Just curious.
- What year Camaro is the table from and did you copy any other tables?
- Are you using the LQ4 MAF or F-body MAF? This has a big impact.
- Do you have any datalogs? You can never have enough information when it comes to tuning. The scan tool is your best friend.
- What injectors are you using? very important and key factor here.
- What about the fuel system? You need to measure fuel pressure with a mechanical gauge at the rail. At minimum it should read 55 psi.

Assuming there are no mechanical problems and you have the LQ4 injectors and MAF, I would start with the completely stock LQ4 tune as a reference. You also should datalog and look at the long term fuel trims as well key sensor outputs.

robbied31

iTrader: (1)

@ dave. I don't have a wideband. I changed 3 tables due to research on changing from vortec intake to f-body intake. Can't remember which ones, I will figure it out and post. I will get ltft's. I had to walk away from it for a day.

@ rocket. I found a small vaccum leak but fixed at intake.

Did I forget to mention that when I unplug the MAF, it purrs like a kitten? Idles a little high but smooth.

DaveX

Well if you have the factory airflow tables for that motor it probably isn't related to anything controlling the IAC, which can be a pain to get ironed out.

It could be lean, or rich.. the LTFT's should tell the tale there.

What MAF are you running? GM factory for that motor? Has it been de-screened or altered in any way?

robbied31

iTrader: (1)

DrkPhx, I had read that some tuning should be done due to the change from the Vortec intake to the F-Body intake. I changed 3 tables, I will have to go back to figure out exactly which ones.
2000 camaro.
I am using F-Body intake, injectors and throttle body. I am using the LQ4 MAF. I have a log from a drive around the block today..... I will attach.

I see my LTFT's are off the chart! attached are current tune and log. I am not sure what controls the LTFT's.

Thanks again!

Rob

robbied31

iTrader: (1)

everything is stock except for the headers. LTFT's seem to be 25 or above as it seems they don't log above 25. What does this point to?

DrkPhx

iTrader: (15)

I can't open the files because I use EFILive. Assuming your injectors are scaled correctly, it's either the VE table or MAF table, but probably the the MAF table.
Make sure the airflow arrow on the MAF is pointing in the correct direction; toward the engine.

First, make verify fuel pressure at the rail and make sure it's at least 55 psi. Positive LTFT's indicate a lean condition and if they are consistently above 25% a trouble code will be set, usually one for each bank.

- Verify fuel pressure
- Make sure the correct injector data specific to those injectors are loaded.
- If you're using the LQ4 MAF, then you need to use the corresponding MAF table to start with. You probably will still need some tweaking, but this a good starting point since the truck MAF tables have higher values.

robbied31

iTrader: (1)

I cannot thank you for your help enough! I do however feel the need to say again that this car was running for a year and a half for about 5000 miles before the breakdown. So things like the MAF being backwards and tables changing seem impossible, but I will double check.

I will find a guage to check fuel pressure tonight and find out exactly what changes I made way back when to the tune. I am starting to thnik I got a vaccum leak and just haven't found it yet.

thanks again.

Rob

DrkPhx

iTrader: (15)

You're welcome. If indeed the car was running perfect before, then it could very well be a mechanical issue like a vacuum leak. Start there before messing with the tune. If you have a catch can, check the hose connections on that as well.

Also check for exhaust leaks.

robbied31

iTrader: (1)

Fuel pressure is at 56 or so with key on motor not running. with motor running it is very steady at 58 or so. steady also when revving engine. I am not able to find a vaccum leak at the intake and I am not able to find an exhaust leak. No catch can either.

What am I missing?

garygnu

are you using the stock ls PCV system?if so check the PCV lines for leaks,they get brittle and rot.

robbied31

iTrader: (1)

As embarassed as I am to admit what was wrong, I am going to because it is too rare that the surging/bad idle threads ever get answered/closed.

the camaro intake has a port on the passenger side just behind the throttle body. It used to have a metal tube coming out of that port with a rubber cap on it. Well, somehow the metal tube is gone, I don't know if when the kid broke down it backfired through the intake or what, but it disappeared. I had a huge vaccum leak that was obviously making it run way lean while the computer was adding fuel trying to compensate.

Thanks for the help guys!!

Rob