M4rk

Hey everyone,

I am a recent new owner of a well maintained ’97 LS400. Despite this being my secondary vehicle, I have really grown to enjoy it. Sadly, the car died on me last week, leaving me stranded and now has a mysterious no-start condition I cannot figure out. I feel like I've tried everything I can, and am almost ready to give up.

Apologies in advance for the long post..


Issue Description

• Engine no-start condition
• Engine cranks, feels like it wants to start – catches on a little, resultant smell of burned rich fuel mixture or oil
• It did in fact start once, ran at an estimated ~100 rpm for a short duration of mere seconds, albeit very roughly, and died off

Background Info

• Engine shut off with no warning or hesitation while driving at approx. 65km/h or 40mph, roughly 5 minutes following a cold start, as if the key was just turned off
• Was unable to restart it immediately following the incident, crank but no start – would not catch on
• Pushed the car to a safer spot (downhill road), pulled some fuses and it actually restarted, but only for about 20 seconds, died off in the same manner
• Unable to start since
• No stored CEL codes during this whole process
• Fuel level is approx. 40%

Vehicle Info/History

• Timing belt and pump done by Lexus about 30k km ago
• Recent wires, coils, plugs and rotors about 10k km ago
• I replaced the ECT sensor about 400km ago due to only yielding 21mpg
• No prior electrical or mechanical problems
• No CELs
• No issues starting, fuel gauge seems accurate
• No prior rough engine operation whatsoever during my ownership

Troubleshooting Performed
ECU

• Replaced ECU capacitors – one of six was touching a harness pin connector on the inside and had a tiny amount of leakage, no damage to PCB observed
• Battery pulled many times
• No immobilizer light flashes
• Tried with another key

Electrical

• Tested EFI, CIRC Open and Fuel Pump relays – all operational
• Tested fuel pump resistor – confirmed resistance to be perfect as per service manual
• Checked all fuses – no issues
• Bypassed both CIRC Open and Fuel Pump relays – no change

Fuel

• Tested fuel pressure on driver side rail at ~45psi
• Tested fuel pump for operation – audible confirmed
• Tested fuel flow visually – fuel flows
• Fuel damper raises, sound of fuel flowing in engine bay

Spark

• ECU bypass igniter test – both coils fired a spark
• While cranking - both coils fired off a spark at regular interval (maybe 1/1sec)
• Testing each plug will be next

Air

• No change with MAF unplugged
• Not much troubleshooting can be done here apparently, resistance measurements apply to 98+ MAF type unless I am mistaken

I am really stumped and ready to throw in the towel on this one, but I don’t like giving up. It almost feels like the car isn’t getting enough fuel, based on it catching on a little tiny bit, but my tank isn’t empty and the pressure reading also states otherwise. Any help is welcome and greatly appreciated, no matter how crazy!

Cheers,
Mark




Edit: fixed, see post #14

dicer

Pretty much leaves the ECU.
That is if there is no mechanical faults.

peterls

Can you get a hold of another ECU from the same car that is running well, just to test things out? If your car doesn't run with a different, good ECU, then at least you have eliminated that problem for good. If it does run with it - well then, it would be easy.

dicer

That's how to do it.

M4rk

Thanks guys, sadly no spare on hand. It would be the last resort to purchase another given the ~$300 USD price tag.

I will try a few more things - starter fluid, injector pulse and spark on all eight.

Here is a video of the behavior from yesterday. I had to lift off the key to prevent more awful noises.

dicer

ECU ! Been there done that.

Legender

hmmmm... sounds a lot like my situation. But any no start would sound the same. But mine is on a 2000 model and not historically prone to failing ECUs. Not that it can't happen. Just less likely.

mpmp

A long read but it might fix your problems:

https://www.clublexus.com/forums/ls-...capacitor.html

M4rk

The first thing I did was replace the capacitors to rule that out. I will report back tomorrow with more findings.

M4rk

Update:

• Verified timing to match up at TDC
• Car started on starting fluid stronger and longer than thus far (MAF was unplugged) - so we have a fuel problem
• Successfully connected to ECU via TechStream, detected CEL due to unplugged MAF, however was unable to run any tests - the error suggested low voltage
• Sure enough, I was reading 11.9V with the key in RUN despite having just charged the battery... not good... same on the charger!
• Thinking the current draw is too high while cranking to power the injectors, I tested one with a test light while cranking - both times I only saw one pulse
• In addition, while I was connected via OBDII I noted the ECT and air intake temps were correct, and the TPS value also responded to the right foot correctly

So, tomorrow I will put in a known good battery and attempt to start. Hopefully she comes alive and I can test the alternator. Since I do have the PS pump leaking, I think I know how this will end.

dicer

Where did you get Techstream?

M4rk

A friend.

Sadly no dice on above plan of attack. Same behavior even when the car gets a boost. Cranks strong, catches on but no cigar. I compared injector pulses on both banks - pass side is regular, whereas driver was sporadic. A little video to demonstrate:


Unplugged driver cam sensor - no CEL. Unplugged pass cam sensor - CEL. Wiring to ECU tested fine on both, no shorts there. Both test to have proper resistance as per service manual. I will try swapping the sensors and also start searching for a new ECU, unless there is something else that could cause this behavior?

Legender

I would suggest swapping the sensors just as you plan to do to see if the problem follows the sensor. Otherwise I think you are looking at possibly something in the ECU not receiving data from the sensor as it should.

M4rk

FIXED!

We ended up trying a few more things over the last day, so I cannot pinpoint the exact root cause of this problem, but I have a strong feeling towards it being a combination of two things, mainly the ECU.

First of all, we (my dad, I am incompetent when it comes to soldering) re-soldered all of the newly installed capacitors. I did some more extensive research of the ECU's input signals via my TIS subscription, on this board and via Google, and came across THIS excellent document, courtesy of Lextreme, which outlines the specific the signals needed during cranking. We verified all of them for shorts, except for the crank sensor, which was left for last due to the slightly more difficult access from underneath.

Lo and behold, a CEL P0335 triggered (crankshaft position sensor A circuit malfunction) on the first cranking try with the re-soldered caps, previously never seen during this whole ordeal. Crank sensor was checked for shorts, none of which were found, and to have the correct resistance, so the sensor was pulled and found to be a bit dusty and with a slight on the scuff where it faces the teeth. I sheared off the bolt holding in, which was a pain to fix, but the CEL was remediated once re-installed!

At the same time, while monitoring the engine RPM during cranking (supplied by the crank sensor), I observed a steady 160RPM, whereas prior to the above fixes, the value would fluctuate. We were obviously onto something here. In addition, based on another thread on here, all of the engine bay harness connectors were removed and re-installed for good measure.

She fired right up on the first try



A BIG thank you goes to this board for the wealth of information shared on here, as well as Lextreme for that PDF.

Cheers!



P.S., THIS is also how bank 1 injector pulse should look like:

Legender

Excellent work M4rk and thanks for taking the time to share your results. Most helpful for others.
Congrats on getting her back up and running....