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1996 LS400 died while driving, now starts for a second then dies: Update: Solved
So I've got a 1996 LS400 that died on me while driving. If you turned the key to start, it would run for half a second, then quit. It wouldn't even respond to pushing the gas pedal down while starting, so you can already rule out the IAC. It's as if someone turned the key on, then off. I ruled out wiring and fuel pump issues, and the I've narrowed the problem down to there being some sort of issue with the cam sensor or PCM
Basically, on a whim, I unplugged the driver's side cam position sensor, just to see what would happen (also since it's more accessible than the passenger side cam sensor plug). To my surprise it start right up and ran fine, like nothing even happened.
I shut it down, plugged the driver's side cam sensor back in, and it went right back to the way it was before. It'd start for half a second then die.
So at this point I was thinking awesome, it's just a bad driver's side cam sensor. So I unplugged the passenger side sensor, plugged the driver's side in and went to start it, expecting a no-start condition. Welp, it started right up and seemed to run fine (at first). So at this point I'm really confused.
However, after the engine warmed up, it started to run rather bad, and it'd have a hard "double" misfire (two consecutive misfires) every few seconds. I shut it down, plugged the passenger side cam sensor back in, unplugged the driver's side, and restarted it. It ran perfectly with no misfires.
I then plugged the driver's side cam sensor back in, with the engine running, and the engine immediately started to run worse. What's more, is the moment I touched the gas pedal, the engine instantly quit. No sputter, no nothing, just like someone turned the key off. I found that I could reproduce this readily by starting the engine with the driver's side cam sensor unplugged, plugging it in while running, then touching the gas pedal. Instant hard stall every time.
So at this point, I'm leaning towards the driver's side cam sensor being faulty, but I got a feeling the problem may lie deeper. There are no codes either, which further makes me think there might be an issue with the PCM. You'd think unplugging the cam sensors would throw a code, no?
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To sum up the post:
- Starts, dies with both cam sensors plugged in.
- Will start & run with one cam sensor unplugged, doesn't matter which
- Runs good on passenger side cam sensor, runs bad on driver's side
- If you plug in driver's side cam sensor with the engine running, it will die the instant you touch the throttle pedal.
Additionally, the past few weeks I've been having an intermittent "rough" starting issue. Sometimes it fires right off, other times it will take ~2 seconds of cranking before the engine catches fully. I think the issue may be related.
Anyone else got any insight before I go tearing the front of this motor apart to get the cam sensor out?
That's what I was thinking. I get a code if I unplug the MAF, but nothing at all from unplugging either cam sensor.
I have an ELM327 bluetooth adapter. There's a free software for Ford vehicles called ForScan that an access advanced "dealer service tool" functions of Ford vehicles through the cheap adapter. Is there an equivalent for Toyota vehicles?
I think the basic Torque app will get the codes. I did notice there's a Toyota specific app called ELMScan Toyota on Android that seems to have more Toyota specific capability. Haven't tried it though. https://play.google.com/store/apps/d...antoyota&hl=en
Well no need to speculate. I just pulled the ECU, noticed a "Re-manufactured by an independent re-builder" sticker on it, and cracked it open.
This "independent re-builder" did a lazy and sloppy job recapping the computer previously. They only changed half the caps, and used cheap 85*C rated Taiwanese caps. Well, as you can see, the capacitors they didn't replace started leaking, and have corroded and damaged some of the PCB. I'm hoping I'll be able to clean it up, but there is a lot of damage.
As you can see, a lot of the soldering they did is dodgy, and for whatever reason, they scraped a ton of the solder mask off the PCB in random areas. I've ordered up a complete set of capacitors, and I'm hoping I'll be able to clean the corrosion off and repair this PCM. Also, does anyone have any idea what's going on here? There was a random SMD capacitor just stuck to the PCB's conformal coating, not soldered to anything. It doesn't match any other SMD component in the computer, and I can't find any obvious spot for it to go. Did that re-builder accidentally drop it in here?
Since the board looked badly damaged, other than the replacements, check the damages of traces and through holes. Those were often eaten by the leaked liquid which is very strong alkali. You'd better check the continuity of those using a multimeter. Fix the damage using a thin copper wire and the solder. Don't forget to protect the board using a Cortec ElectriCorr VpCI-286 or an equivalent.
Sometimes other parts are damaged and it's too late to fix, I must add.
That does look bad, but you did find the problem. Excellent diagnostics effort on your part. Sad result, but better than throwing parts at it blindly and hoping for the best.
That does look bad, but you did find the problem. Excellent diagnostics effort on your part. Sad result, but better than throwing parts at it blindly and hoping for the best.
One of my favorite diagnostics techniques is just to try unplugging things I suspect might be the problem, and see what happens.
Generally what I've found is that most automakers have a "fail safe" pre-programmed for sensors. So having no sensor plugged in at all is better than having a bad one plugged in.
Since the board looked badly damaged, other than the replacements, check the damages of traces and through holes. Those were often eaten by the leaked liquid which is very strong alkali. You'd better check the continuity of those using a multimeter. Fix the damage using a thin copper wire and the solder. Don't forget to protect the board using a Cortec ElectriCorr VpCI-286 or an equivalent.
Sometimes other parts are damaged and it's too late to fix, I must add.
One of my favorite diagnostics techniques is just to try unplugging things I suspect might be the problem, and see what happens.
Generally what I've found is that most automakers have a "fail safe" pre-programmed for sensors. So having no sensor plugged in at all is better than having a bad one plugged in.
Without knowing the algorithm of the system, that method will often make you confusions.
Actually you were confused and had to ask others.
Without knowing the algorithm of the system, that method will often make you confusions.
Actually you were confused and had to ask others.
I was looking for input as to why what I was observing was happening, because it was unexpected given what I was doing.
I already knew the LS400 computers have fail-safe sensor replacement programmed in - for example many people on here report their cars running better with the AFM/MAF unplugged, when the MAF is faulty.
Recapped the computer, repaired damage traces - no change, still ran the same.
Turned the engine to 0* BTDC and noticed the driver's side camshaft was way off the mark, while the passenger side was still close. We took the whole front of the motor apart, and it appears that the brand new Dayco timing belt stretched and causing the driver's side cam to jump a tooth. The belt tensioner was at the outer limit of its travel, and the belt was hardly tight at all.
06-04-16, 09:05 PM
1996 LS400 died while driving, now starts for a second then dies: Update: Solved
