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93 LS 400 not starting

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Old 12-02-13, 05:56 PM   #1
93whitels
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Default 93 LS 400 not starting

Hello everyone, this is my first post. My car seems to have trouble starting. It sounds like it wont turn over and run when you turn the key. Recently i replaced the engine wire that connects the cam and crank sensors as well as a few other things to the ecm i believe with a harness that had crimped connections. The car started and ran well for about a month. Then one day the check engine light came on and eventually had to limp home. I got a tps sensor code as well as a rear driver abs code because my trac and trac off light was on as well. Additionally I had a coolant level low warning light. I went to the junkyard and replaced the engine wire because the other one wasnt in good condition and this seemed to fix it last time. Also replaced the tps and coolant level sensor. Still no luck. I had an extra ecu that i swapped, still no start. If i turn the key to only the on position the throttle trac motor makes a clicking noise for about ten seconds, then turns off. I was thinking of replacing it but couldnt find it at the junkyard. Sorry for such a long post. Any help would be greatly appreciated. Thanks.
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Old 12-02-13, 08:33 PM   #2
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So when you turn the key to The "start" position, the engine cranks but fails to start, or do you just get nothing?
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Old 12-02-13, 09:32 PM   #3
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Yes it cranks but it wont turn over and run. It will just keep cranking until you let the key go. Thanks
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Old 12-02-13, 11:29 PM   #4
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I a situation like this you have to make sure you firing on all cylinders getting gas and air. Timing could've jump
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Old 12-03-13, 12:04 AM   #5
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How do i check for spark and fuel pressure? Also, i read about a capacitor issue on the ecu. If timing is off, how do i go about taking belt off and aligning the marks. Any idea about the throttle tractrac motor clicking. What about accelerator pedal position sensor? I couldnt seem to locate it. Does something have to be done with a scanner to sync these parts up? Thanks
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Old 12-03-13, 04:29 AM   #6
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Well you need to double check the codes using this method and post them here, for folks with a '95 or newer LS400 with OBD-II, just get an inexpensive scanner.


Just break it down to the basics, for an engine to start you need 7 things:


● Strong healthy battery

take a quality multimeter and verify the battery has at least 12.5V DC with car off


● Good fuel

Check for enough gas in the tank (don't laugh, happens all the time)
check fuel pressure on the rail with an inexpensive fuel pressure gauge


● Good spark

Get a couple of T-pins at Wal-Mart and run Paul "Scanner" Danner's famous igniter bypass test which is shown below - this will test the coils, the igniters themselves, and all of the associated primary and secondary side wiring. If you have firing at the coil wires as a result of this test, even with a broken plug wire somewhere, the car would still run (badly) on 7 cylinders, so you have spark! This test is genius because it takes one minute, and no tools or labor or disassembly, all you need is a multimeter, a test lamp, and 2 T-pins - you can actually skip the multimeter portion, as he has already figured out pull-up vs. pull-down for you on LS400.



Paul Danner's igniter bypass test




● Proper ECU inputs

the ECU must receive accurate information from both cam position sensors & the crank position sensor, otherwise it does not know when to fire the coils or when to trigger the injectors


● Proper ECU function

The ECU's in all years of LS400 can develop failing ECU capacitors, which causes the ECU to become confused and everything comes to a screeching halt, you can test this with Yamae's ECU ripple test


● Correct valve timing

For this check, I would invite over a friend who has replaced a timing belt before, you need to positively identify top dead center, using the position of the rotor on the driver's side coil - you turn the crank pulley until the rotor is almost there pointing at the distributor cap contact for cylinder 1 and then slowly turn the crank (always clockwise) until the no 1 cylinder is at the top of its stroke at the same time the rotor is in the position to send fire through the coil to cylinder 1 - at that point the crank pulley mark should be at 0 and cylinder 1 should hold air pressure because both intake and exhaust valves valve should be closed.

If the cylinder #1 does not hold pressure, you are on the exhaust stoke and need to turn the crank pulley 1 full revolution and check for pressure again. When you have the crank at the 0 degrees mark, the rotor pointing at cylinder #1 contact on the driver's side distributor cap, and cylinder #1 holds pressure, you are there! - This is top dead center. (TDC) If you go too far and go past top dead center, don't back up! - just rotate the crank two more times and then you will have another chance to bring it right in line again. Never turn the crank backwards (counter-clockwise when viewed from front of car). - always turn the crank in the direction the engine runs, clockwise!

At top dead center, the cam pulley marks and cam pulley backing plate marks on each cam should line up, while crank pulley is still at 0 (TDC) - if not, and you are sure you are at top dead center, then you have likely jumped time and need to follow the factory procedure for replacing the timing belt and tensioner.






● That spark at the right time

The ECU fine tunes the ignition timing, but you can do a rough check with a timing tight. As the distributors are turned with the timing belt on this car, the ignition timing is dependent on the timing belt being aligned correctly as explained in the previous paragraph, as well as the rotors being installed in the right direction.

Last edited by LScowboyLS; 12-03-13 at 06:44 AM.
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Old 12-03-13, 01:18 PM   #7
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When the engine was starting and running, I pulled engine code 41 throttle position sensor signal and abs code 34 rear left wheel speed sensor signal malfunction. Also had a low coolant level warning light. Now that the engine is not starting and running, the car will not give me any engine codes or abs codes. The check engine light doesnt even turn on when jumpered. My battery shows 12.6 volts so its good. My car had half a tank before this, but Ill buy some gas just to be sure and a fuel pressure gauge to check the fuel pressure on the rail. I will buy some t pins and a test lamp, already have a multimeter, and check for spark. How can i test ecu inputs? Can you tell me how to check that the camshaft and crankshaft position sensors are in range? Is there anyway to check the ecu function without the car running? For correct valve timing, when you say check pressure, are you talking about compression? Should i buy a compression gauge for that too? And finally do i check the ignition timing with a timing light once the engine is running? Thank you so much for all your help.
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Old 12-03-13, 01:35 PM   #8
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I really don't think you will need to worry about ignition timing, and yes, a compression gauge that works in a continuous "live" fashion (not peak & hold) would work, you are just trying to determine whether the valves are closed, to determine if you are on the compression stroke or the exhaust stroke.

the camshaft sensor and crank sensor tests can be found here

some of my friends who are poor or else pranksters get their friend to stick his finger in spark plug #1 hole to see if they are on the right stroke, but that might give your unsuspecting friend a sore finger - lol

kind of reminds me of my Dad, who told me when I was 5 years old that we were gonna find out if the lawnmower engine was firing properly and had me hold the spark plug wire while he pulled the cord! - that "shocking experience" was the beginning of my lifetime interest in working on cars!

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Old 12-03-13, 06:46 PM   #9
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Thats funny,lol. So i bought the fuel pressure gauge, compression gauge, test light, and some more gas. I will go through everything step by step as you have suggested over this week and let you know the results i get. Thanks again for organizing all this information in one place for me, i really appreciate it. Ill check back soon.
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Old 12-05-13, 01:49 AM   #10
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Update. The fuel pressure gauge I bought didn't seem to have the banjo bolt fitting I needed to test the fuel pressure. It seems that there is one online I can order that comes with that fitting. I decided to skip ahead to Paul Danners igniter bypass test. Success, I got spark from both wires! I then proceeded to test the ecu inputs. The Camshaft position sensors and the crankshaft position sensor were within good operating range. Anyways after reading around, I ended up buying some starting fluid. I read that if it dies 2-3 seconds after starting, the fuel pump is bad. If it keeps running, the fuel pump is good. Not sure how accurate this is, but I gave it a try. It started! Only after a couple of tries of course and giving it some gas on the third try was it running. However its running really rough though with the check engine light on and still not telling me the codes when I jumper it. So now I'm wondering since its running(badly), should I still check the fuel pressure or can I skip that now? Can I get the resistor to do yamae's ripple test locally(like at radioshack), or is it only available online? I must admit I've already ordered the capacitors for the ecu and I'm getting a computer friend to help me do it. Since I read that when its not giving codes, ac compressor turning on and off, and basically all the problems i'm having, its the ecu. I still have to check my timing belt, but I'm hoping its the ecu. I'm gonna check my tps as well to make sure its in range because I replaced it with a used one of ebay. Also my trac throttle motor still clicks for ten seconds when left in the on position, not sure if this is normal. Thanks again for all the help.
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Old 12-05-13, 10:34 AM   #11
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Fuel pressure is a likely suspect. Start with the easy stuff and replace your fuel filter:

http://www.lexls.com/tutorials/EFI/fuelfilter.html

I've not done a fuel pump, so I don't know how difficult that may be, but the filter is quite easy.
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Old 12-05-13, 12:00 PM   #12
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If you ordered the low cost fuel pressure gauge I linked to above, you would have the banjo bolt adapters!
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Old 12-07-13, 06:37 PM   #13
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So I was able to follow the repair manuals procedure for checking the fuel pressure and I got 48 psi with key turned to on position. Normal pressure is between 38-44 psi. So it was a little high. Then I started the engine with the vacuum hose going to the fuel pressure regulator plugged, and I got 38 psi, which was within the normal 38-44 psi range. I then reconnected the vacuum hose and it should've dropped to between 28-34 psi but stayed at 38 psi, but my vacuum hose is cracked at the connection. So I think my fuel pump is good, I might need a new fuel pressure regulator and vacuum hose since it was a little high. One other thing I realized was that I actually replaced the sub tps not the regular tps, which was why the check engine light came on in the first place. I plan to test the tps and replace it if not within normal range. I still have to check the timing as well with the compression gauge. I plan to do those tomorrow. If both of these end up being fine, I'll have to wait till the capacitors get here to repair the ecu to see if that's it. At least it starts up now, just running badly. Hope to update again soon. Thanks for all the replies.
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Old 12-08-13, 10:12 PM   #14
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So I was able to test the tps and I ended up replacing it because it wasn't the correct ohms. It's still doing the same thing though. I have to spray starting fluid and pump the gas to get it to start and run. Once its running the check engine light will stay on and it won't rev past 2000 rpm. Didn't get a chance to check the timing yet, so I'll get to that tomorrow. Any other ideas besides timing and the ecu? Thanks.
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Old 12-08-13, 10:24 PM   #15
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make sure that the caps you got are the ones from the links from post #1 of my ECU thread - other caps will not work, they are a very specialized type.
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