General Maintenance & Repairs - LS1 Engine Problem - Runs fine cool but runs terrible in operating temp

The car is a series 2 VY Maloo. With the LS1.

On the way to work today after about 1 hours driving on the highway I dropped a gear to pass a truck merging onto the next lane. When I got past the truck I noticed the engine making a funny noise and having a lack of power. Sounded like really lumpy engine. When I got to the traffic lights it almost stalled and idol really badly, when taking off again it sounded worse, lacked power, jerky and spluttery.

I drove it to work and parked it for the day. This afternoon I came back to it. Started it, seamed ok... then it started again. Spluttering and shaking. I do sometimes get an engine warning light in the dash every few days/weeks but for some reason it never registers in the computer and when I put it in diagnostics mode, no codes show up.

First thing I thought was plugs and/or leads. Which it needed regardless, so I bought a new set of decent leads and top of the range NGK plugs. Installed them ok, started it back up ran fine then it started doing it again.

Only other thing I can think of is O2 sensor, even though it's not telling me that in the diagnostics...


The ute is back at work and I'm going there tomorrow to spend some more time working on it. I'll be buying a couple of O2 sensors anyway and putting them in as well as a new fuel filter. But if they don't fix it I'm at a dead end of my knowledge.

I'm definitively no mechanic but If I know what a problem is I'm more than capable of fixing it myself if it's not too complicated. Though if it's fairly serious I take it to a mechanic. Usually only internal stuff.

It would be good to go there tomorrow with a bit more knowledge especially from people who may have come across the same issue before. So I can do an elimination process to scout out the issue. But I think because it runs perfect when cold and sh!t when it reaches operating temperature narrows it down quite a bit.

If someone could dot point a few problems that might cause it and a way to check if it is that problem and even better how to fix it that'd be great.

To help out I've taken a couple of videos.

Thanks, Toby.

http://youtu.be/gLeA5bOafxw
http://www.youtube.com/watch?v=4PiPUi70lF8

Check your fuses. I had a similar issue a long time ago with my 98 formula (showed ses light, but wouldn't register codes on scanner) It was my main fuse which caused the maf not to function right along with other things.

There was a bare wire that occasional hit the frame causing a short and the fuse to blow.

Oh yeah I checked all the fuses. None are blown.

Could be a fueling issue when the system is hot; have you checked fuel pressure when the condition is occuring?

It could very well be a bad/failing 02 sensor. I've been telling people on here for years, all PCM's are not the same and do not operate the same. Failing 02 sensors do not always show up on everyones PCM for a code. Mine never did with bad 02 sensors. I only get the code when they are completely failed.....and the engine is running HORRIBLE.

Get a scan to see how they are switching while the engine is running and up to operating temp. You probably have a failing one.

Dirty MAF's also treat people differently. My car, having a MAF or totally unplugging it, my PCM handles things the SAME, engine runs the SAME, no codes. Other people report totally different affects and codes. Recently, a couple people reported what you are reporting....after warm up, engine runs terrible at partial throttle accelerations. They cleaned their MAF and fixed the problem.

I would start with a scan......

.

Replaced fuel filter, replaced spark leads, replaced spark plugs, replaced O2 sensors, cleaned MAP sensor. All injectors firing, all plugs firing, no error codes on self diagnostics mode. Engine still missing a cylinder or two. Taking to a mechanic Monday to get a Diagnostics and pressure test. Lets hope it's not the valves.

Replaced fuel filter, replaced spark leads, replaced spark plugs, replaced O2 sensors, cleaned MAP sensor. All injectors firing, all plugs firing, no error codes on self diagnostics mode. Engine still missing a cylinder or two. Taking to a mechanic Monday to get a Diagnostics and pressure test. Lets hope it's not the valves.

Did you check the ground wires on the back of the passengers side head.....see if they are tight. 2 or 3 bolts.....can't remember.

.

I'd recommend checking fuel pressure and doing a leakdown test as the next steps, based on what you've already tried and the absence of DTCs.

check the engine temp sensor.

Valve springs was the issue. Stuffed one.