Crank, no start, 5 months in, frustrated (1 Viewer)

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Northlake, Texas
the crank sensor has an ohm range for them to be good Mine 1999 would run die run die. found the ohm specs and it was out of range. be something to check easily. also check the wiring to the sensor it could have gotten nicked or rubbed by the serpetine belt, same with cam sensor wires. under the rear vehicle driver back door is a connector for the fuel pump as well.
 

Cosmo Kramer

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Louisville, ky
Not sure if you've tried this, but it's something, see below. good luck

Neutral safety switch??


 
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Dec 4, 2017
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Shade, Ohio
Thanks, Did you have a throttle body DTC/OBDII code?
I did, P1128 I think, so its not exact same condition as yours. But seeing as the ECU controls basically everything and is known to get goofy for no reason, I'm always suspicious of it making other similarly bad decisions if everything else checks out.
 
Joined
Oct 23, 2017
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Chicago
Not sure if you've tried this, but it's something, see below. good luck

Neutral safety switch??


the bypass kit from medtro/Jackson is the answer... I have a 1998 LX470... would start and run just fine... but then at times would only crank.... and not fire up... at random... it turns out there was/is some sort of short in the fuse box under the hood... that would not allow the security system to pump the fuel... I got the kit from medtro on this site, and have not had the problem since... when it was acting up, I took it to the dealer and they were clueless... here is pic of the thread regarding the kit from
1619818235084.png
 

Mauser

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If you were closer I could loan a used ecu to try. I bet shipping to Canada from New Mexico wouldn't be cheap though.
 
Joined
Oct 29, 2020
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Location
Calgary, AB
the bypass kit from medtro/Jackson is the answer... I have a 1998 LX470... would start and run just fine... but then at times would only crank.... and not fire up... at random... it turns out there was/is some sort of short in the fuse box under the hood... that would not allow the security system to pump the fuel... I got the kit from medtro on this site, and have not had the problem since... when it was acting up, I took it to the dealer and they were clueless... here is pic of the thread regarding the kit from View attachment 2661366
Yes, I saw this, but ruled it out with troubleshooting. It is not intermittent, fuse is fine, no deformation, good voltage and the LX does not start with the bypass. I ran a line from battery + to the appropriate relay connections and it still does not start. If the fuse box, relay or fuse was the problem I believe it should start. It does not.
 
Joined
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Calgary, AB
If you were closer I could loan a used ecu to try. I bet shipping to Canada from New Mexico wouldn't be cheap though.
Thanks. My check engine light is on with the key on, so I ruled out the ECU. I understand if the ECU is bad the check engine light is out.
 
Joined
Oct 29, 2020
Messages
35
Location
Calgary, AB
Not sure if you've tried this, but it's something, see below. good luck

Neutral safety switch??


I tried playing with the shifter, put in Nuetral, moved around. In and out of park. No difference. Would this cause the engine to die while driving? That is what happened, on snowy winter day on the way to the ski hill.
 
Joined
Oct 29, 2020
Messages
35
Location
Calgary, AB
the crank sensor has an ohm range for them to be good Mine 1999 would run die run die. found the ohm specs and it was out of range. be something to check easily. also check the wiring to the sensor it could have gotten nicked or rubbed by the serpetine belt, same with cam sensor wires. under the rear vehicle driver back door is a connector for the fuel pump as well.
So mine just won't start unless the fuel pump is directly wired. It starts and runs for a couple seconds and then dies, even though the pump is running. It won't start at all if the pump is not hot wired.

Any other ideas?

Next is the Fuel ECU and check for continuity between the fuel pump and fuel controller (ECU).
 
Joined
Oct 29, 2020
Messages
35
Location
Calgary, AB
It would seem so, have you chase the wiring from fuel pump to fuse block? A recent thread I saw showing pics of mice damaged wires was horrifying. Was there any work that was done prior to it's no run status?
There is no continuity between the fuse block and fuel pump and not enough power, was at 3 V.

Is the fuse wired to the fuse block or is the Fuel ECU between the fuse block and the fuel pump?
 

pawwright

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Dec 14, 2008
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1,272
Did you change the crank sensor? I didn't reply as someone replied earlier with that suggestion - Unlike @jpd motorsports my sensor was in spec when tested. For giggles I put in a new one as I had one - and it fired up right away and haven't had an issue since, 7+? months later.
 

ramangain

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So mine just won't start unless the fuel pump is directly wired. It starts and runs for a couple seconds and then dies, even though the pump is running.
This sounds suspiciously like a mechanical issue with a fuel pump trying to pinch out one last turd before death, not electrical. Does a known working fuel pump do the same thing? Trees from the forest and all of that jazz.
 
Joined
Sep 1, 2018
Messages
283
Location
Florida
Just to summarize my understanding:
  • Seem obvious that there's an issue with getting power to the fuel pump while cranking/running, but...
  • Two different fuel pumps wired directly to the battery will start the 100, but...
  • When it starts, it rapidly ends up sputtering and dying, even though the fuel pump is still humming along happily.
Based on these facts, it seems you may have two problems that may or may not be related. First is the issue with power to your fuel pump: as someone else has stated, you need to chase those wires as best you can and figure out where there's a break/corrosion/etc.

I think your second issue may be crank/cam sensor related, and may be tied into your fuel pump problem.

MOST ECUs run the fuel pump for a couple seconds to prime the system when you turn the key (I don't know if the 100 does this). Then, when they detect RPM sync (basically, when they see a signal on both the crank sensor and the cam sensor that makes sense), then the ECU turns on the fuel pump again. No rpm sync, no fuel pump.

However, you could be getting and losing RPM sync because of bad grounding or a bad sensor. When the fuel pump is connected to ECU controlled power, it's not enough signal to switch on the fuel pump. When you hardwire it, there's enough rpm sync to fire the plugs for a bit but then it loses sync again and the engine dies.

I think someone else said it, but I'd be ohming out all your crank and cam sensors, and check their wiring for continuity or damage, and seeing if there's an issue there.

Edit: I'll just add, codes can be incredibly useful for this sort of thing, but a lack of codes doesn't mean much either. Don't take it as truth either way. Good luck!
 
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Joined
Sep 1, 2018
Messages
283
Location
Florida
I've been informed in another thread that the LC will only supply voltage to the fuel pump while actively cranking. @mixtec did you check voltage while cranking, or only when turning the key to 'on'?
 

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