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Grumpi300,
I thought that fix was only for modifications with increased HP boost and/or turbo mods. My 300 has not changed from the stock engine. I thought alternator because I am at 197,760 miles and figured with the other problems it was due for an alternator replacement anyway. The last time I had a tune-up about 50K miles ago is because I had to replace my flywheel that cracked and since I was getting that done I had the belt, plugs, etc. done. I was having what I have determined to be VSS issues with my cluster and a check engine light that would not go off. I recently found that I had a connector plug leading to the check engine light. The mechanic who did the flywheel, tune-up, etc. could not figure out the check engine or cluster problem (he said it was a short somewhere and I paid to have my cluster repaired for nothing -- because I found it was VSS). So I figured if he could not properly diagnose VSS problem and overlooked unplugged connector he may not have done the tune-up he claimed as well as heater core he said he replaced but still my heater does not work. Are you saying that the fuel pump ECU mod will help with my engine not starting? At this point I am not sure it is a fuel problem that keeps the engine from starting because I got no response from the starter fluid sprayed into the intake. I agree that part of the problem I was having initially was poor idle from time to time but even with that I never had the car kill once it was started -- at least not until I was having the backfire problem that I initially suspected was all spark plugs not firing. Were you having similar problems as I described and this mod fixed it?
I am suspecting its actually a battery issue -- the heavy corrosion on the battery that led me to suspect alternator was failing now leads me to believe a dead cell or cells in the battery. If the battery is dead I do not believe the car will start with just the alternator -- I know I tried to jump it and that should have supplied enough battery power to start the car -- still my gut tells me it is not lack of fuel preventing the car from starting.
My Soarer cranks, but doesn't start. I have done the fuel pump ecu bypass, swapped relay under the fuse box and replaced water temp. sensor. When I switch the key to the ON position, I don't hear the fuel pump prime. Fuel filter was replaced one year ago; ALL fuses have been checked and are in good order.
I disconnected the intake tubing and soaked a rag with fuel and she started and ran until the fuel vapors had evaporated.
Is it fair to say the in-tank fuel pump may need replacing?
Jahrod,
I don't want to guess but my problem ultimately ended up being the battery. I went through the process of elimination with my possibilities. It could be your ECU that is causing the problem and it could be as simple as the battery because the cells go dead. My battery was just over 2 years old and the problem started about 6 months prior to that. I thought there was no way it could be the battery and that is why it was the last option I tried before I replaced it. Here are a few links for you to review all but 1 are lexus forum responses:
I'm in the same boat as you guys. I do remember a friend of mine/my mechanic was fixing my car back then and we thought it was the fuel pump so he jumped the FP and +B terminals on the diagnostic port to keep the fuel pump running all the time when the key is in the ignition but then later on it still had an idling problem so he figured it was a sensor and in the end it was a bad MAF Sensor but now having that MAF replaced about a year ago I'm back to this issue. here's some of the stuff I've been reading lately to see what could be the causes and some of them if you read enough will tell you how to check these.
First and foremost take your battery to autozone or any local auto parts store to have your battery checked
Itry doing the jumper on the diagnosis port in the engine bay and if it works then that means the fuel pump is fine and its something with the relays or the fuel pump ecu.. you can do that "mod" and leave it there but beware fuel pump will stay on when key is in ignition and can flood if your fuel pump is running fine
If fuel pump is fine, Check the relays under the hood fuse box its metal circular you can switch it with the other relay in there if it starts and runs fine it's just a busted relay.
check the spark plugs
check the distrbutors (something about unplugging some plug and putting it on the metal for the spark test) i'm sleepy im only saying this from the top of my head
check the igniter in the engine bay above driver footwell
we also have one ignition coil idk where
check the ground wires there's a ground wire attached to the positive clamp on the battery if you trail down you'll see a wire grounded to the car, see if thats tightly on or corroded
Check the one driver side under the dash in the footwell left side theres a relay i think it'll have the numbers 1 2 3 and 5 on it of some sort it might be brown i can't recall I have to read more. the prostreet URL will lead to how you can check its continuity. these are the stuff I've mainly read but yet to test so dont hold it against me GL hope to hear back from you guys, I HOPE I figure this out soon this is my daily and my girlfriend has been driving me around... I feel emasculated
***Update I just fixed my car this weekend, our mechanic stopped by and he said it could just be a grounding issue so I sanded the paint to the metal where the ground is for full contact and replaced my battery terminals while i was at it since it took a lot of effort to keep it snug on the previous one. Also replaced my spark plugs since i busted 4 & 6 power washing my engine bay ........ but it runs fine so far but we'll see in a couple days. Also our mechanic advised that if it runs perfect one day and then the next day after driving it a couple miles it starts acting up i.e. stalling and dying on you or not letting your engine turn over it after just driving it then chances are it could be the ignition control module igniter (located in engine bay above the driver wheel well). Check if its literally hot after just driving it and it could be that going bad.
i had extremely similar problems. ran fine some days, the next day would run for a mile then quit. Ended up being a bad ECU capacitor. if you have fuel and have spark the next time it wont crank up and just turns over connect a computer to see if its communicating.
My Lexus cranks over, getting fuel pressure, getting spark from plugs,yet it still wont start ?
I had the same issue....checked all the usual suspects, ecu etc, even checked spark...but in the end, it WAS the plugs! Changed them all out, and it worked.
Took me 4 days to get it figured out and I was hitting my head against the wall because I checked the plugs and all of them had spark, just not enough I suspect in the end.
I know for me it was actually the battery and it took me a while to get it started after installing the new battery probably because it was flooded from all of the attempts to start it when I thought it was the starter/ecu problem. I would make sure the battery is eliminated because these cars will not work if your battery is a problem -- it can even look like an idle problem. Just my 2 cents after replacing plugs, starter, alternator, etc. only to find they were not the problem.
My 98 SC300 was running fine but making a really bad sound from the alternator bearing going out. I had a spare generic alternator in my parts collection. The brand is unknown but it for sure is not a Toyota/Denso part. I disconnected the battery, swapped the new one in, and put the battery cable back on. I go to start and it will just crank. I spent some time here reading many threads about a crank and no start condition. The security light does go out when the key is in the ignition and the keyless entry works fine so I think the key is being recognized properly.
Before getting into the repair, my question is if you turn the key to run should you hear the fuel pump come on and stay on or is the system designed to have the pump come on in the start position then stay on after you release the key and let it go into the run position? If it is the latter, there is no way I can hear it over the starter noise.
My first step will be to check the EFI relay then pull the trunk liner to see if I have 12 volts at the fuel pump connector. If I do, I will check the resistance on the pump pins and hotwire it for a second to see if it comes on. Dpending on how this goes, it will be on to the fuel pump ECU which thankfully has the same part number for all SC3/4 so getting one is easy. If I do need to swap the pump, how low does the fuel in the tank need to be to avoid a spill?
I really doubt the control unit in this car did not like the generic alternator and decided to not allow the engine to start.
03-15-15, 10:00 AM
Tzxlyd
GL hope to hear back from you guys, I HOPE I figure this out soon this is my daily and my girlfriend has been driving me around... I feel emasculated 
