FredUSA

A week ago, my LX470 wouldn't start even though it cranked strong. I used a different car for one day, and the next day the LX470 started normally. The SUV ran perfectly for the next 5 days. Today it started normally in the morning, but after a one hour trip I stopped at an appointment for a half hour and when I went to start the SUV to return home, it cranked strong but would not start. I hooked up one plug wire to a spare plug and found that there was no spark at all. What is the possible cause of this intermittent problem???? If I can't diagnose the problem myself, I will have to spend big bucks to have a Lexus dealer find the problem. I think I have at least $200 with which to buy diagnostic equipment compared to having the dealer diagnose the problem. What should I do???

Z07

And you grounded the end of the spark plug while someone was turning the engine over and got no spark right?
If not, test for spark again grounding the tip of the plug to the engine block.

Check stored codes and follow their diagnostic maps if any. Suspect cam and crank position sensors. Tests on youtube show how to backprobe and see them output as the engine turns. If the computer doesn't know where the rotating assemblies are it won't supply ground to the coils.

Listen to the fuel tank as someone turns the key from off to run (not start) Do you hear the fuel pump run for at least two seconds? Was the plug you removed wet with gas?

Attempt starting with 1/4 throttle open.

Verify battery remains above 10.5 volts while cranking (and is 13+ with key off.)

Check ground straps.

Cross post on ih8mud in the 100 series section.

FredUSA

I posted a reply a minute ago, and it simply disappeared. What happened? Did I do something wrong in how I replied? FredUSA

FredUSA

Man, I hate retyping posts. Here is the condensed version. I used a new plug that I held down onto the intake manifold. The battery is new, and cranks like crazy. I am 99.9% sure the problem is in the ignition. The weird thing is that the problem "fixed itself" a week ago, and then came back. Maybe the SUV will start today, but now it is 50 miles away so I have to get there to try it. I will probably tow it to the dealer. A bad ground strap connection is a possible cause, but not likely in this case since everything looks to be in excellent condition. I wish I knew how to use OBD, but I don't have time to learn just now. I bought a "code reader" years ago, but never took the time to learn how to use it. What an idiot! Thanks for your help, and any further comments.

silverbul

I was going say what Z07 said, check cam & crank sensors. Both will kill spark from going to the motor. Safety feature to prevent damage. Also, the brain (CPU) can cause the truck not to start. Have that checked.

kwatt1

I'd lean towards a cam or crank position sensor. It's common for them to fail when they get hot and start working again when they get cool.

Once the engine starts, the vehicle will run if the cam/crank sensor fails to function correctly. however, I thought that it would throw a code in that event

FredUSA

Thank you all for your helpful comments. I just got my LX470 back from the dealer. I am incredulous about what they found, but I have no information at this point which would disprove it. I had installed a manual disconnect switch right after the battery on the positive side. This is the one you can buy cheap at Harbor Freight and has a removable red "key". As you may know, the LX470 has two tabs that bolt onto the clamp that attaches to the battery post. One tab is attached to the cable going to the starter, and the other goes to the vehicle electrics/electronics. The symptom the car had was that the electrics appeared to be working fine, the starter would strongly crank the engine, but there was no spark. I assumed the problem was somewhere in the electronics. The dealer said that when they connected the "scan tool", there was no electrical connection, so they "jumped" to the tab that goes to the electrical/electronics and the car started fine. They said that there were no codes stored except "low voltage". They removed the disconnect switch and all was fine after that. I have found that if there is no voltage on the e/e tab, nothing at all works -- not even the starter. So, my assessment is that the two tabs had at least 12V on them when the ignition key was "off", but as soon as the starter was engaged, the voltage to the e/e tab must have dropped below the required voltage to create spark. The only explanation would be that there was a poor connection due to looseness of the nut on the disconnect switch. The LX470 has not caused any problems since I picked it up from the dealer, so if the problem does not show up again, I will have to believe that the above explanation is correct. It really makes no sense to me, because I had checked the connections at the battery and disconnect switch and I thought they were OK. But, e/e problems can be strange, and this is certainly an odd case.

andrewko

I have a 2002 LX with 193K. About 10 days ago, I parked the car to get some takeout breakfast. When I returned, the car won't start. It cranked strong but wont catch. had it towed to my mechanic. They found no fuel was coming out from the hose at the fuel filter when the car is turned on. Replaced fuel pump and filter. Car drove fine the next week. On Friday afternoon we drove up to the local SoCal mountains for Labor Day weekend. Drove 2 hours there, drove back down Sunday afternoon. Stopped at Costco and when I got back in the car, same thing happened. Cranks strongly but won't start.

On Tues had it towed to my mechanic again. He removed the ECU/EFI module or relay next to fuse #11 in the big box in the engine compartment. His probe made different tones on 3 of the male connectors and one had no tone. He "jumped" it and asked me to start the car. Car started. The next day they did more diagnosis and when they applied power to the relay, he heard a click on the passenger side. He removed the kickpanel and found some wires and relays. He said it was a power relay. Took it out, shook it a bit and put it back in. Car started.

So now what? Nothing in the owners manual shows relays on the passenger side; only drivers side kick panel has a fuse box. Should I replace the ECU/EFI in the engine compartment and the relay in the passenger side kick panel? I feel like I am waiting for it to happen again. Thanks.