Harrisonpa

Hey guys,

My LS has a funny problem. It has no power when I floor it from a stop. If I ease into the throttle it is faster. Somtimes also really struggles getting up some hills.

Mainly just at low rpm my car feels like it has no torque whatsoever and it drinks soooo much petrol.

Problem barely happens when car is cold. And gets progressivley worse until the car is warmed up fully and has no guts.

Ive checked/replaces:

• ECU rebuilt
• O2 sensors
• Everything spark related except igniters and dissy
• AFM
• TPS
• PCV valve
• Fuel Filter
• Thermostat
• Coolant temp sensor

Car runs good with the AFM unplugged except stalls when I try to rev it. Could easily spin wheels with AFM unplugged but not even close when plugged in. Checked AFM with osiliscope and seems to be reading properly.

The only thing I suspect now is:

• Injector seals
• Fuel pump ecu
• Knock sensors knocking at low rpm, causing timing to be pulled
• ECU still broken after rebuilt.

Im honestly just stumped. Ive seen others with this problem and seems no one has found a fix. Any help at all would be appreciated. Thanks.

400fanboy

Coolant temp sensor.

https://www.clublexus.com/forums/ls-...ange-pics.html

Harrisonpa

Forgot to mention I changed that too. one of the first things I did. Changed it for an aftermarket one.

400fanboy

Oh okay then.

You mention the car runs fine with the AFM unplugged. You say the engine won't rev out, but it can easily spin the tires. So is this the... opposite of how it behaves with the sensor plugged in? Where with the sensor unplugged, it has bottom end power but nothing up top?

Does the car run better without the sensor? Does it have any other conditions? High idle, check engine light, is the throttle valve actuation smooth, are the idle air valves ontop of the throttle body clean.

If you're getting bad fuel economy and have drivability issues, it should be getting enough fuel so it's probably? on the intake side. But I'm not sure. To me it's highly unlikely the ECU rebuild failed, but didn't break anything else at the same time.

I'm honestly not too sure. Only commented because coolant temp sensor - but you already thought of that and had already checked it . Best of luck figuring it out.

cj98ls

A few questions.
How many miles? How long have you had the car? Is this a problem you inherited with the car or was it running OK before you got it? If it was running fine before you got it, what did you change before it started running crappy? What condition are the vacuum hoses in? Cracked, broken and leaking? Stock airbox? Again, broken and leaking? Have connectors been replaced, and if so, were the wires/terminals swapped in correctly? Are you hearing knocking? Running premium fuel?

Harrisonpa

350000km had it for about a year

Has ran like this since i got it. After every part I changed it got slightly more responsive and feels better to drive. But after everything ive done still has the same problem of no low end power.

vacuum hoses look decent, no cracks just a bit old. airbox is stock but missing the part which brings air from under the hood so its a hot air intake. Air temps could be a cause but not 100% convinced since it drove the exact same with and without it. Broke in an accident and havent gotten a replacement.

All connectors are factory and wiring looks to be in good shape.

The car does have lifter tick but it feels like the computer is cutting the power.

Thanks for the help

Harrisonpa

No engine light or codes and plenum looks clean when looking from the throttle body. Cant say I know what the runners look like but probally clean.

With AFM plugged in:

• misfires while warming up and sometimes tries to stall when i rev it warming up. (thinking ECT sensor i got is a crap aftermarket one)
• When cold: more power low end, same top end power
• When warm: no low end power at WOT. if I slowly press the pedal it accellerates quicker and doesnt bog down.
• High end power feels good. When using kickdown button the car goes quick, mainly just dont have a good low end power.

With AFM unplugged:

• No matter the temperature of engine i can not rev it in neutral. revs drop and car stalls
• also stalls sometimes when coming to a stop
• loads of low end power, could definitely spin wheels
• top end power feels very similar to with it plugged in.

Thanks for the help

400fanboy

Your car driving more normal when the car is cold is because the ECU is in closed-loop mode, so something related to the programming of stuff it ignores in that "safe mode" seems related to me. What it could be - I haven't the slightest idea.

Yamae

I think you just did the typo. When it is cold, the ECU is not in closed-loop mode because the feed-back is disabled due to the lack of feedback signals.

Regarding the problem of no power and the bad fuel consumption, I'd check the ECU carefully forcing to stop the IGF signal and primary O2 sensor signals. Id' also check the ripple voltage.

Harrisonpa

any chance you know if theres a guide for testing what you said. Im not sure how I would test that

400fanboy

https://www.clublexus.com/forums/ls-...-by-yamae.html

Harrisonpa

Sorry for late reply, just had a read of that post and looks interesting. Seems like a good way to rule out the ECU. Thank you.

Harrisonpa

Also, Any chance anyone knows a scan tool which works on OBD1. Need to check the live data.

I feel as if the car is retarding the timing rather than cutting all the fuel. This is because when I floor it the O2 sensors read a constant 1v, meaning that they are reading rich. But since the car is barely accelerating, I feel as that the car is cutting timing and fuel is being dumped into the exhaust, making the sensors read rich. Trying to find the cause to why it would be cutting timing.

• Air intake temps are pretty high. On a hot day will be around 0.4 kohm resistance (about 60 degrees C) but at night reads 1.4 kohm (about 30 degrees). As expected the car is more responsive at night when it is getting colder air, but the problem still persists. I feel like having a colder intake will make the car faster, but will not solve the root problem.
• Knock sensors were tested with an osiloscope. They look to be responsive to engine revving and do not have any erratic spikes. Both knock sensors have very similar readings so doubt they are bad.
• Air flow meter also tested with oscoloscope, very responsive and the signal is very clear. Dont have any reference values but it looks to be good. frequency increased with revs in a very responsive way.

Is there anything else that im missing that could possibly retard timing. Makes me think the ecu is still bad (((. Once i get that capacitor ill be able to check that though

paulo57509

For the scan tool, you're probably going to have to search the used tool market. I have two scan tools that will data stream both OBDI and OBDII systems; an OTC4000E and a Vertronix.