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Pls help! 93 ls400 fuel issues!

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Old 03-15-14, 09:52 AM   #1
mk2supra
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Default Pls help! 93 ls400 fuel issues!

Hi, I recently purchased an 93 with expectations if just being bad fuel pump. I though I confirmed it as it started and purr like a kitten when I used a spray bottle of gas(instead of either or starting fluid). Keep in mind I am on a budget so most part replacement is from u pull it ir wherever I can locate at other yards.after siphoning out the bad gas from sitting 3+ yrs I replaced the pump with a seemingly working one(passed general working test) but it wasnt until I bought a fuel pump control(as pump didnt seem to get power at plug) I saw some progress. When I first put the new fp control it started and ran for about 10 min. Goood but I test drove and it would sputter upon acceleration. It then stalled after running a bit and acted as it did before where it wouldnt start on its own. I took the plugs out cleaned them, and turnt it over once or twice(with fp relay out) and blew cylinders out(crud city) then put plugs back and it started, it ran rough and idled about 3-400. However in process it was getting dark I didnt hook up maf. So I turned it off, installed maf then it wouldnt start at all. Since I have pulled the fuel filter and drained the lines and.pulled and cleaned the plugs again and it started the same rough idle for a couple mins. Stalled then heres where I am. It seems it likes to start after I blow out the cylinders with a crank or 2 and clean plugs but only for a bit. Is there a way to test the fuel pump control? And any insight would be helpful I just feel like im getting closer but I hope its not fuel gremlins leading me on lol.
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Old 03-15-14, 12:47 PM   #2
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2 common issues on 1993 LS400 that would have these symptoms:


● failing Idle Air Control Valve aka IACV (there are tests in the factory service manual you can do to determine whether it is bad (normally bad bearings, and I know where to get a good deal on the replacement Japanese bearings) - the part itself would need to be rebuilt with these new bearings (easy job) because a new IACV is about $850, whereas the bearings are only ~$50

failing ECU capacitors
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Old 03-18-14, 09:46 AM   #3
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Well kinda progress. It seems like its flooding. I blow the cylinders out then clean plugs or at the start of the day when i haven't tried it yet and it will run...idle rough and rev a little but will bog down as if it doesnt get enough gas but th plugs are still wet. Are the injectors supposed to get constant power?
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Old 03-18-14, 09:51 AM   #4
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The plugs fire in sequence and wet plugs are really bad. It means all the fuel is not burning. Your check engine light should be on , what are the codes. Prolonged use could potentially damage your catalytic converters.
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Old 03-18-14, 12:35 PM   #5
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please use this procedure to download the trouble codes and then post them here

if you get no codes then that is even more evidence of failing ECU capacitors, which is very common on a 1993 model
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Old 03-18-14, 04:10 PM   #6
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I did that earlier and got code 47 for sub throttle position sensor. Keep in mind i did this a week ago experiencing same issue of flooding now i think about it, and got no codes. Ive been suspecting ecu like you said the whole time but didn't want to for fact Im broke at the time lol but ecu was 9/10 top search result Solution so i read about it from get. But that one time it started and ran good for 10 mins made me think there was a
chance it was something i could do with wrenches and time. How difficult are repairs to ecu if you have time or anyway to garuntee?
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Old 03-18-14, 04:12 PM   #7
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Garuntee Its the prob?*
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Old 03-18-14, 05:44 PM   #8
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You can sometimes see the bad capacitors in the ECM if you take it apart.

Injectors are not supposed to get constant power, should be pulsed voltage, usually the ground side is pulsed.
I'd say it could be a bad coolant temp sensor, would richer it up if it thought it was super cold........could also be a bad maf.
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Old 03-18-14, 07:35 PM   #9
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most sensors that go bad on LS400 will generate a code, but not always, having said that though, the fact that you problem is intermittent, is even more evidence for being the ECU, with AFM (MAF) being next most likely (they fail because someone attempted cleaning them with a solvent, such as "MAF cleaner" - a MAF cleaner solvent is fine for most cars, but not for 94 and older LS400) - generally speaking though, a ruined MAF would cause it to run bad all of the time.

with LS400, as with any mass produced car or manufactured item, the important thing to is to remember pattern failure, i.e. all of the cars of your year and model will have very similar issues, so if a lot of people are experiencing ECU issues or transmission mounts breaking or premature strut bar cushion failure, then you likely will too!
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Old 03-25-14, 02:51 PM   #10
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Quote:
Originally Posted by LScowboyLS View Post
most sensors that go bad on LS400 will generate a code, but not always, having said that though, the fact that you problem is intermittent, is even more evidence for being the ECU, with AFM (MAF) being next most likely (they fail because someone attempted cleaning them with a solvent, such as "MAF cleaner" - a MAF cleaner solvent is fine for most cars, but not for 94 and older LS400) - generally speaking though, a ruined MAF would cause it to run bad all of the time.

with LS400, as with any mass produced car or manufactured item, the important thing to is to remember pattern failure, i.e. all of the cars of your year and model will have very similar issues, so if a lot of people are experiencing ECU issues or transmission mounts breaking or premature strut bar cushion failure, then you likely will too!


Well i found an ecu from a 93 same yr and all. Same issue present. So unless the issues would be same in all malfunctioned ecu i doubt it is comp. It flooding leads me to think injectors may be stuck or could it be maf? Tho the time i replaced fuel pump control is when it ran best on own but bolt to bracket wasn't tightened all the way due to rushing so does that bracket provide ground to fp control and maybe it f'd up due to bad ground? Idk Im just trying to think Of any possibility

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Old 03-25-14, 03:29 PM   #11
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Quote:
Originally Posted by mk2supra View Post
Well i found an ecu from a 93 same yr and all. Same issue present. So unless the issues would be same in all malfunctioned ecu i doubt it is comp. It flooding leads me to think injectors may be stuck or could it be maf? Tho the time i replaced fuel pump control is when it ran best on own but bolt to bracket wasn't tightened all the way due to rushing so does that bracket provide ground to fp control and maybe it f'd up due to bad ground? Idk Im just trying to think Of any possibility
Based on your history here, you might have jumped the gun on the Flavor Of The Week - Bad Capacitors diagnosis.

What is this fuel pump control you speak of, and how is it related to bolt-to-bracket "ground for fp"??

If you have done your due diligence as far as ruling out the electrical (no codes) then play Classic Old School Mechanic.

You had crap gas in there, you flushed the fuel lines, and then you speak of flooding.
That is a perfect Classic Old School mechanic's diagnosis of a sticking injector pintle. Doesn't matter how nicely you rinsed out the lines, if there is bad gas or contaminants in the injectors, it has to either be run out with at least several minutes of running, or the injectors need to be removed and checked for drip, and cleaned.

If you have an individual cylinder's injector that refuses to close, that would make for bad running but you'd have a reliable start. A bad start is usually a cold start injector flooding everybody all at once.
A QuikTest is to clamp the return line down stream of the pressure regulator near the booster, put a pressure gauge on the tap, run up your pressure to 50 psi with a bridge between B+ and FP at the diagnostic connector (very quickly please, do not over-pressurize with the return blocked!) and see if you lose pressure too rapidly (back to "0" psi in a minute, for example.
Colin
(MAF sensor is not likely to give you a too rich condition at start, but the ECU does pay attention to water temperature sensor and cold start "thermo-time switch" any failures here should throw a code))
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Old 03-25-14, 04:38 PM   #12
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The fuel pump control is the little comp In trunk behind panel on passenger side above cd player. It says fuel pump control. I've read it controls the speed of pump etc and wasn't positive if bracket it connects to acts as ground and if so if improper install would fudge it up and maybe tell fuel pump to pump at max, like i said just trying to think of anything and electrical are my worst nightmare lol Im used to a mk2 supra, the caveman generation of efi...needless to say not much to electrically go wrong on those so all these computer controlled things worry me haha. Ill check for any new codes again tomorrow. It starts right up into the rough idle first try of day or after blowing cylinders out. The gas i drained was terrible but i did empty tank and put gas and a little treatment in.

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Old 03-25-14, 08:02 PM   #13
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that little fuel pump controller, likely needs new capacitors! (I am seriously not joking)
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Old 05-13-14, 08:39 PM   #14
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well current state is:

dash cluster illumantion/functioning not all there or hit and miss. just started out of no where after i tried the other ecu. idk if thats related. but the fp comp doesnt get juice like it used to needless to say doesnt like to start at all now but thats due to the lack of power from harness. i opened up my ecu and upon inspection saw atleast 2 caps that were bad to my untrained eye. im doing a rebuild service for my ecu, as worst case scenario if this lexus doesnt get going the 1uz is going to my mk2 supra. but i really want to get the lexus up!!! its such a nice car. im really hoping the main ecu solves it, and should i replace the fuel pump control(computer) at the same time? or wait try the reman'd main ecu first then proceed from there?

this is the fp computer just for clarification from my earlier posts
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Old 05-21-14, 01:57 PM   #15
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Well ecu cm back. Had 4 bad caps, 2which were empty. Plugged it in. Still nothing. I didn't see any power going to fp
control But found blown efi fuse. No dice. Jumped fp to b+ and nothing still other that i could hear fp. Spark seems there On the couple i checked before dark but there's no start now just turning over and no trouble codes.

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Old 05-21-14, 01:57 PM
 
 
 
 
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