My venture into LS world has been a complete nightmare. After failing two emissions tests, the car has now decided it doesnt want to be driven.

backstory: failed emissions by .03 NOx. suddenly has been slightly hard to start (cranks longer than usual) but runs okay.

Last saturday, I moved the car from the garage to the front yard (was going to wash it, got sidetracked). started fine, didnt really "drive" it, just moved it. Sat out in the sun all morning (temps were MILD that day, mid 80s, not too hot). That night, get ready to go out: Car cranks for a while... kinda sputters, and starts... but WILL NOT REV. giving it gas makes it pop/backfire/bog down, but it returns almost immediately to a stable (but high) idle.

... skip a week, and its still doing the same thing, and im running out of ideas. It doesnt throw and codes. I dont think its fuel related.

Cold start: hard to start, sputters, really low revs (bounces right around 300rpm). giving gas when cold makes it pop and surge, never goes above 1200rpm. The car cycles from the really low to really high idle. wont rev past 1200rpm MAX.

Once Warm: starts much faster, idles smooth! idles HIGH, near 1100rpm. pressing the gas makes it go crazy. easing into the pedal makes it rev til it gets close to 2kRPM. once it gets near there, any more throttle pressure makes it backfire and run like crap. occasionally it will get above 2k, and once it climbs to 3k, it will rev freely to redline. so from 3k-6k is completely smooth, i can hold it at 6k, no problem. Making me think its NOT a fuel issue. jumpering the pump (which makes the pump notably louder) does nothing to change running conditions.

I tried unplugging random things to see if they make any change.
EGR: no difference, no CEL.
TPS: no *real* difference, no CEL
AFM: throws code, runs really rich, but still doesnt rev right (thou revs slightly easier)

The car will idle and can be coaxed to higher RPM WITHOUT the TPS being plugged in and without displaying any codes.... I have tried swapping a different TPS in, no change.

Trying to pull codes from the ECU results in a steady repetitive flash,.. that means all good/no codes, right?

Im leaning towards the ECU being bad... but I pulled it not even two weeks ago and there were no leaking caps that I could see. I thought the TPS was bad so I swapped in a junkyard one, and it makes no difference. its almost as if the car is ignoring any input from that sensor.


Im really running out of ideas (and patience) for this car. if anyone can help, id appreciate it. Ive searched but nothing seems to describe exactly what the car is doing. Mainly because, every time I start it, it seems to do something different.


Sorry for the long rambling post. trying to be informative usually ends up meaning wordy. :X

 

You need to check the basics. It sounds like fuel to me, but without having diagnosed it, I can't say for sure. You need to be able to prove something, rather than just guessing and saying it might be this. You should check fuel pressure to see if you have the right pressure. If it were a plug, injector, wire, etc., you would have a miss on 1 cylinder, but not limit all 8 from revving.

 

From what you are describing I would suspect the ECU. Unhooking those things should have thrown some codes and it did not. Does your CEL cycle on then off when you start the car? It is supposed to. The capacitors in the ECU have fluid in them and after time they leak onto the board and cause all sorts of problems.

 

Check your catalytic converters to see if they glowing. You can be running on four cylinders. I had a problem similar to yours but I had a cel but couldn't pull any codes change the ecu now rev with no problem. All the ecu replacement change was the idle problem. I still have lack of power like I'm on 4 cylinders. I know this because only one of my cats glow red. Un-burn fuel on one side.

 

This might sound wierd. Coolent temp sensor?

 

Nothing weird about that. The ECT handles alot of info with the fuel. But if it feels like 4 cylinders maybe you should check the coils, especially the drivers side, its known to go bad because of the heat.

 

I replace both coils and the cts . Could it be a cam sensor?

 

i had a similar problem with a previous car anytime you are having problem reving and the carseems like its choking its usuallu your cat

 

I took my cats off. Mines was glowing red on the passenger side. That's what me say it running on 4 cylinders.

 

Check for damaged sparkplug wires. Its real easy to pinch them when installin the covers. Double check your firing order as well.

 

Hey I emailed you about buying this car, I hope you get it fixed I am still interested

-Jade

 

How to check the firing order and if it's off how to fix it?

 

Lexls.com has the tutorial for changing wires and it has the firing order listed.

 

RXG300,

Did you ever get your LS fixed or working? I'm having the same problem. No codes change the ECM with rebuilt one same problem. Let me know. Its hard to troubleshooting this problem with no codes!!!!!!!!!!!!!!!!

Chuck

 

So you have spark and fuel just seems to not run correctly. One or the other is off i assume. Check fuel pressure, borrow someone's AFM and try it on your car. Check sparkplugs and wires? Assuming you haven't done anything to the car recently then changed of order of wires is not going to be the problem but check for any disconnected plugs?