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Hi Everyone. Little back story for you. My buddy had a 1995 Sc400 that he could not for the life of him get fixed. It was his daily and all of a sudden just would not crank over. Him being in need of a vehicle, and me having a spare decided to trade him and see what I can come up with. This Post will be more of a "Talking out loud" of my troubleshooting process. Any suggestions, ideas, concerns anyone may have would be greatly appreciated as i am getting to the point of being stuck with yard art haha
Here is my situation. 1995 Lexus SC400 120,xxx Mi (Cali Car)
The car cranks over strong (view the timing belt moving, but will not catch. Occasionally you will get a small fart or burp out of her but that is all.
No Check engine codes
No spark from Plugs nor off the coil packs Coil Packs
No spark from ether bank/side
Battery is good But swapped a known working for good measure
Coil packs were replaced with a junkyard cars for testing
Igniters were swapped out and working in a good running car
ECU was repaired and swapped out and working into good running car
Fuel Pressure (hear/feel fuel running in rails (12V mod as well)
Crankshaft Sensor is brand new
Right side Cam sensor is reading 1110ohms
Left side Cam sensor is reading 920ohms??
Thoughts:
If the fuel pressure isn’t enough, could that tell the ECU not to send spark?
Damaged Wires from the ECU to sensors as there is a ton of weird/soldered/cut wires
Does the ECU actually power up? No Check engine light comes up How do I test this
How does someone start testing for shorts in wires ?
Could the timing being off prevent spark all together
After work tonight Ill probably take a look at the timing, its notable that the belt is cracking really bad and will need to be replaced before driving. But I want it to start before going to all that work. Its very possible its jumped teeth.
Thanks for reading all my crap. Here is a pic of my two girls for all your trouble
1996 Sc400 Lexi (Blue)
1995 Sc400 Luci (Red trouble maker)
That's excellent, I will try that when I get home! So if I can successful complete this test (which from what I gathered already I will) Then I need to confirm the wiring from Sensors to the Ignitier/ECU, is that correct?
To my understanding yes, it will rule out the ignitor as the issue (common problem). After that I would open up the ECU and check for any leaking capacitors.
Timing being off didn't prevent spark on my 95 which had a similar issue, but certain plugs wouldn't get spark when the timing was off. So are you testing spark on all plugs or just one? I bet DEMONSC4 is right with this one, and if you don't want to waste money on parts just go to Autozone and have them order it for you. Test it, and if it doesn't fix the problem just return it.
Also here's a thread that I made a while back in which I got a ton of help in on a 95 SC400. Might be some good info for you in here.
Basically the car looked good, but the timing belt slipped a few teeth and wouldn't fire up. If your belt is cracked I would address that right away, and do an entire timing belt kit. Remember it has to be perfectly aligned, so if it's even 1 tooth off you'll have no start issues. Or extremely rough start and conk out. 95 has no worries with valves hitting pistons etc... but if you do have to replace the belt, do the entire kit while you're in there or you'll be kicking yourself in the *** later on when the tensioner or pump goes. Good luck.
To my understanding yes, it will rule out the igniter as the issue (common problem). After that I would open up the ECU and check for any leaking capacitors.
Happy Monday! I got a chance on Saturday to dig in. I did the igniter test with perfect results.Both sides would flow from the igniter, to the coil and out through the main cap wire. However without spinning the distributor rotor I could test it through to the plugs. I took the caps off and noticed the caps were all corroted and the rotors were both cracked in half ! I got the parts and replaced both pieces, both sides with no positive results. I did get a chance to verify that the roters were lined up correctly while in there.
A s for the ECU, I had already cracked it open and saw it was very damaged. Got it repaired locally, and placed it in a buddies 1995 Sc400 to test if it was actually fixed. It ran great!
Timing being off didn't prevent spark on my 95 which had a similar issue, but certain plugs wouldn't get spark when the timing was off. So are you testing spark on all plugs or just one? I bet DEMONSC4 is right with this one, and if you don't want to waste money on parts just go to Autozone and have them order it for you. Test it, and if it doesn't fix the problem just return it.
Also here's a thread that I made a while back in which I got a ton of help in on a 95 SC400. Might be some good info for you in here.
Basically the car looked good, but the timing belt slipped a few teeth and wouldn't fire up. If your belt is cracked I would address that right away, and do an entire timing belt kit. Remember it has to be perfectly aligned, so if it's even 1 tooth off you'll have no start issues. Or extremely rough start and conk out. 95 has no worries with valves hitting pistons etc... but if you do have to replace the belt, do the entire kit while you're in there or you'll be kicking yourself in the *** later on when the tensioner or pump goes. Good luck.
Ohh really? To be honest ive tested 1-2 plugs on both banks and came to the conclusion that non were sparking... I will go home today and test all 8 and see if any of them get spark! The timing belt and additional pieces are on on the top of the priority list (before even insuring the thing) however I thought that If I cant get it started I dont want to spend the money on it, but since the belt is so cracked maybe it has slipped a few teeth and are causing it!
My only other lead is the left cam position sensor that was reading 920 ohms, which is low and right at the allowable threshold , where the other CPS is sitting around ~1140 which is at the top of the threshold . Im wonderingif for the couple bucks I just swap this out
I had a couple buddies who are Lexus techs come on over and after a few hours of going through everything top to bottom they noticed something funny. When cranking/turning over the RPM gauge does not move. We double checked the Engine speed sensor (Crank sensor) and its all good! There for they deduced the issue is more then likely a broken wire from the ECU to the starter relay, or the starter relay to the Igniter since testing the signal at the igniter there was no power at the RPM side.
No signal, no spark
Tomorrow they come back with ecu pin outs and we will run a new line!
So we got the pin outs and tested Continuity for all PCM pin wires to the igniters. Every single one tested fine
Did the same for the Cam Shaft Sensors to PCM and Crank Sensor to PCM
Out of pure desperation we checked and found out that we have no pulse at the Injector. No power is being sent to there.
So now we have No Spark, No Injector Pulse, No CEL, No hope lol
I'm Kidding, I feel like the No Injector pulse could relate to Ether the PCM being broken, which wouldnt make sense since it started up the other 95 SC400 no problem
OR
There is a security Immobilizer Anti-Theft gremlin which is hiding its self. Does anyone know how to confirm that the Antitheft system is in fact disabled. Could cranking the car, and it turning over confirm that?
I can mention that after opening up the drivers side kick panel that wires had been previously cut and reconnected via solder and butt connectors. It almost looks like there was an aftermarket system at some point
Are you sure the CEL is working? I had an instance where my SC400 was obviously not running right, but there wasn't a CEL. Turns out the bulb had been swapped out by the P/O, code pulled, issue fixed.
One thing to check, it's a long shot, but what if your camshaft position sensor harness got caught up in the serpentine belt? It's a very prevalent mistake especially for the every day DIY'er. I know the vehicle will start with it partially connected, but how about completely torn off? Some vehicles won't turn on at all if it does not detect a signal from the cam position sensor.
Are you sure the CEL is working? I had an instance where my SC400 was obviously not running right, but there wasn't a CEL. Turns out the bulb had been swapped out by the P/O, code pulled, issue fixed.
One thing to check, it's a long shot, but what if your camshaft position sensor harness got caught up in the serpentine belt? It's a very prevalent mistake especially for the every day DIY'er. I know the vehicle will start with it partially connected, but how about completely torn off? Some vehicles won't turn on at all if it does not detect a signal from the cam position sensor.
Just a thought.
Yes im pretty sure its working. The CELlight comes on when I turn the car on, turns off when cranking but when I go pull codes from it, the cell light just flashes ever.2 seconds with no stops
Last night I was poking around and actually found a park of the harness that looked to be melted. It was on the drivers side of the car, running from the firewall along the engine head, past the fues box and splitting to the igniters, down below the engine (camsaft I think) and back around the battery
I peeld back all the plastic and tape to expose 2 damaged wires seen below( Black with red stripe and blue wire) as well as what I thought was the "Melting" that turned out to be some black gummy goop that was coming out of this weird repair also seen below.
Left harness has some weird shielding/goop
Has anyone seen this? This random black/red wire comes up from the harness and connects into the larger wire I guess?
Right hardness (from earlier picture) has the broken blue and black/red wires. Black/Red wire was re-soldered to no avail. Blue wire still i connected although should be rewired as well
Ive been grappling with all of these issues myself and was able to fix it(I think) with a different ignition switch. I install one from my parts car turn the key and the motors idling, then it dies from lack of fuel. Remove the battery add gas reinstall battery and Im back to page one with no spark. I believe that the second one I installed was faulty so its worth a try.
07-22-16, 12:38 PM
95 Sc400 No Spark Mystery Extraordinaire
