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lexpert, Lexus Master tech
Category: Lexus
Satisfied Customers: 2100
Experience:  Master Certified with lexus, 8 years experience with Lexus
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I cant get it to start 91 ls400. I have no power to fuel

Customer Question

I cant get it to start 91 ls400. I have no power to fuel relay. Ive checked crank sensor, both cam sensors, ignitors, nee plugs, caps and rotors, new fuel pump, fuel filter, cleaned iacv, cleaned egr and modulator. I even jumped the fuel pump with a waire from battery and i get fuel in rail and i have spark just no pulse at my injectors
JA: Is the power loss consistent, or does it fluctuate?
Customer: It wont start but sometimes when it does it runs amazing oerfect idle, only thing ive noticed is when i let off the gas while driving my rpms drop down then come back up and sometimes it dies at a stop and wont restart again
JA: What is the model of your '91 Lexus?
Customer: Ls400
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Are you a robot
JA: I'm an assistant to the Lexus Mechanic. I work with them to help customers like you.
Customer: I said everything i have done in my first message
JA: Anything else you think the mechanic should know?
Customer: It just recently installed a new alternator, and thermostat. I have noticed a very small loss of coolant like going from max to min in about three weeks but no smoke from exhaust i havent found the leak
Submitted: 1 year ago.
Category: Lexus
Customer: replied 1 year ago.
Ive also swapped the ecu with three different ones, and checked every fuse and relay. I just grt no power to fuel relay and no injector pulse.
Customer: replied 1 year ago.
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Customer: replied 1 year ago.
Well tonight i swapped to my original computer again, i found i have a vacuums leak on my iacv but i will fix it tomorrow morning quick. The car is showing its idling at 300 in park. Its like its cammed and has a huge lope. Sounds cool but definitely not running as it should. Its has started for me about 7 times all the times i tried. I need to recheck my fuel relay because it is not clicking like it should so i have just left the Hard wire from the battery to the fuel pump. I feel like something is still wrong. Thats a huge drop in rpm, car will idle at 600ish with the air conditioning running. What coukd it be if its not vacuum leaks
Expert:  david craig replied 1 year ago.

Hi Im David, sounds like you have some issues going on here. Lets try to figure it all out. correct me if im wrong, you have no injector pulse. you have a coolant leak that isnt visible, and you engine is loping.

Expert:  david craig replied 1 year ago.

Here is a schematic of the engine control system. you might want to check the associated fuses and relays to the injectors. you might want to do a cooling system pressure test to verify where the leak is, and you might want to get a can of throttlebody cleaner and spray around all sources of the possible vacuum leak such as the intake base, throttlebody, air intake tube, all vacuum fittings/hoses.

Customer: replied 1 year ago.
Man tgats not for my car. Mines a 1981 and is obd1. The vac leak is atmy iacv itll be fixed. My big problem is no power to my fuel pump relay
Expert:  david craig replied 1 year ago.

it says a 1991

Expert:  david craig replied 1 year ago.

just going by what the original entry was

Expert:  david craig replied 1 year ago.

lexus wasnt around in 81 brother

Expert:  david craig replied 1 year ago.

91-95 were the same...all obd 1

Customer: replied 1 year ago.
Ok i meant 1991 lol typo there but i was going by the link said obd2, i apologize im just very frustrated with this. The car runs great but i hace to run a jump wire from my battery to my fuel pump. The loping idle i am assuming is because of the massive vac leak at iacv, ill have it fixed tonight. I am just stumpee on the fuek relay ive checked crank sensor and both cam sensors. What else can disavle the fuel power
Expert:  david craig replied 1 year ago.

if you look at the diagram the fuel pump relay is fed by the circuit open relay which is fed by the 10 amp ign fuse....look there

Expert:  david craig replied 1 year ago.

let me know if you find anything

Customer: replied 1 year ago.
Ok i knoe the 10amp fuse is good how can i test the circuit relay
Customer: replied 1 year ago.
Sorry for all the bad typing im in the car
Expert:  david craig replied 1 year ago.

pull it out. find where 12 volts is coming into it, then jump that voltage to the other side to feed the fuel pump relay..... dont text and

Customer: replied 1 year ago.
Ok so i checked relay and seems to be fine. I fixed the vacuums leak and it ran fine. I drove it and let it runs for more thsn 2 hours and it kept starting back up. Then just now i went to start it and it cranked snd began to turn over and then stopped and is just cranking again. I have spark and fuel to rail but no pulse. I noticed that it seems to do this when its really humid outside if that means anything
Expert:  david craig replied 1 year ago.

Ok thanks for getting back to me, let me do a little digging in my resourcres. Ill get back with you. we'll figure this out.

Customer: replied 1 year ago.
Its the craziest thing ive ever seen. I truly am dumbfounded
Expert:  david craig replied 1 year ago.

Ill probably join you in the dumbfounded category......its gotta be a loose connection or chaffed wire... Ill be back

Expert:  david craig replied 1 year ago.

sorry for the delay. you need to check the ground at the computer. make sure they are tight and not corroded

Expert:  david craig replied 1 year ago.

you ready to tackle this?