'90 LS400 fuel pump system problem
10-01-13, 11:58 AM
#31
Pole Position
Further, this entire fuel system from inline fuel filter, fuel pump have been changed, not to mention the gas tank has been cleaned and flushed.
10-02-13, 12:03 PM
#32
I hope you didn't spend all that time and money just replacing stuff, without doing this one simple test.
Wouldn't you really be mad at yourself if the pressure is low, and it turns out the "new" FP is defective, or it is getting low voltage? It's really a simple test, and is the first thing a mechanic should check.
Wouldn't you really be mad at yourself if the pressure is low, and it turns out the "new" FP is defective, or it is getting low voltage? It's really a simple test, and is the first thing a mechanic should check.
10-02-13, 12:23 PM
#33
Pole Position
I hope you didn't spend all that time and money just replacing stuff, without doing this one simple test.
Wouldn't you really be mad at yourself if the pressure is low, and it turns out the "new" FP is defective, or it is getting low voltage? It's really a simple test, and is the first thing a mechanic should check.
Wouldn't you really be mad at yourself if the pressure is low, and it turns out the "new" FP is defective, or it is getting low voltage? It's really a simple test, and is the first thing a mechanic should check.
Even when the engine is cold and warm?
Well thats my dilemma you see, I only experience intermittent rough idling once the engine is warm. Otherwise my 1UZ is a beast..
10-03-13, 01:15 PM
#34
Fuel, air, and spark. Yep, in theory ICEs are pretty simple--But-- the devil's in the details. And one of the really important details is adequate fuel delivery. Since a cold engine is in open loop, and it goes closed when it reaches normal temp, the fuel pressure could be just low enough to really affect the performance after that transition.
10-03-13, 02:01 PM
#35
Lexus Champion
well since the 96 model has huge issues with failing ECU capacitors, fix that first, because without a known good ECU, the poor car is just confused as hell.
and speaking of open loop vs. closed loop, in open loop (cold) the ECU is working off of its map in ROM, and not having to make decisions, which is more evidence to suspect the ECU.
if you are going to fix or replace things all over the place in an effort to solve this problem, at least start with the common things that fail in a '96 and could cause these symptoms - and in a high humidity hot place, like Miami or the Caribbean, the ECU has a bulls-eye on it as the likely culprit!
and speaking of open loop vs. closed loop, in open loop (cold) the ECU is working off of its map in ROM, and not having to make decisions, which is more evidence to suspect the ECU.
if you are going to fix or replace things all over the place in an effort to solve this problem, at least start with the common things that fail in a '96 and could cause these symptoms - and in a high humidity hot place, like Miami or the Caribbean, the ECU has a bulls-eye on it as the likely culprit!
03-11-14, 07:57 AM
#36
Understandable. But question, If the problem were to be of fuel pressure in nature, wouldn't my rough idling occur all the time?
Even when the engine is cold and warm?
Well thats my dilemma you see, I only experience intermittent rough idling once the engine is warm. Otherwise my 1UZ is a beast..
Even when the engine is cold and warm?
Well thats my dilemma you see, I only experience intermittent rough idling once the engine is warm. Otherwise my 1UZ is a beast..
After reading the thread, I saw that a couple of your questions were not answered:
1.) why doesn't the fuel pump run when the ignition is on with the jumper in place?
Jumper at the diagnostic check connector FP to B+ so you will be upstream of the circuit opening relay.
2. why is there a resistor in the fuel pump circuit?
Normal operation is with the resistor in the circuit, this for longevity of the pump. The resistor is only bypassed when signalled by the ECU for hot starts to help overcome fuel percolation. It is not a "full-throttle" switch as erroneously stated earlier. The manifold vacuum controlled pressure regulator is used for full throttle.
3. If you are getting lurching and dying WITH your jumper in place, fuel pump windings are suspect. They open when electrically hot, then recover as the windings cool. Your diagnosis is affirmed if you find that the symptoms occur with a lower fuel level, and do not occur with a full tank.
Colin
03-21-14, 04:28 PM
#37
If you are getting lurching and dying WITH your jumper in place, fuel pump windings are suspect. They open when electrically hot, then recover as the windings cool. Your diagnosis is affirmed if you find that the symptoms occur with a lower fuel level, and do not occur with a full tank.
Colin
Colin
Colin
03-22-14, 09:52 AM
#38
Driver School Candidate
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What's a MAF?
I rencently had a problem like yours THE CAR WAS BUCKING AND QUITING I found it to be the MAF was shot I cleaned it and it made no difference I got one at a a used lexus parts shop in Santa Ana Ca phone 714-569-999 it's called 999 used lexus parts I paid $140.00 for a used one and the dealer wanted $1,000 for the same thing. and it is now working perfectly
12-16-14, 01:28 PM
#41
Driver School Candidate
Where is the location of the "FP & +B" connector on a '94 Celsior'? I cant locate it!
Thanks in advance.
12-16-14, 04:37 PM
#42
Driver School Candidate
Matt, did you ever resolve this?
After reading the thread, I saw that a couple of your questions were not answered:
1.) why doesn't the fuel pump run when the ignition is on with the jumper in place?
Jumper at the diagnostic check connector FP to B+ so you will be upstream of the circuit opening relay.
2. why is there a resistor in the fuel pump circuit?
Normal operation is with the resistor in the circuit, this for longevity of the pump. The resistor is only bypassed when signalled by the ECU for hot starts to help overcome fuel percolation. It is not a "full-throttle" switch as erroneously stated earlier. The manifold vacuum controlled pressure regulator is used for full throttle.
3. If you are getting lurching and dying WITH your jumper in place, fuel pump windings are suspect. They open when electrically hot, then recover as the windings cool. Your diagnosis is affirmed if you find that the symptoms occur with a lower fuel level, and do not occur with a full tank.
Colin
After reading the thread, I saw that a couple of your questions were not answered:
1.) why doesn't the fuel pump run when the ignition is on with the jumper in place?
Jumper at the diagnostic check connector FP to B+ so you will be upstream of the circuit opening relay.
2. why is there a resistor in the fuel pump circuit?
Normal operation is with the resistor in the circuit, this for longevity of the pump. The resistor is only bypassed when signalled by the ECU for hot starts to help overcome fuel percolation. It is not a "full-throttle" switch as erroneously stated earlier. The manifold vacuum controlled pressure regulator is used for full throttle.
3. If you are getting lurching and dying WITH your jumper in place, fuel pump windings are suspect. They open when electrically hot, then recover as the windings cool. Your diagnosis is affirmed if you find that the symptoms occur with a lower fuel level, and do not occur with a full tank.
Colin
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