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91 LS no start, no power to fuel pump relay!UPDATE TO MY 91 LS400 no start!

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Old 05-04-14, 02:04 PM   #1
ZGagnon
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Default 91 LS no start, no power to fuel pump relay!UPDATE TO MY 91 LS400 no start!

Have read several threads on no start, fuel pump issues but i am still stuck.

UPDATE TO MY 91 LS400 no start!

so quickly when the issue started i was just running to the store and on the way back i hit a stop sign, motor felt like it was missing so i got home and parked it and at idle it usually idles around 800rpm which is was but every few seconds the rpms would jump up to 950 or so.. turned it off, tough to start back up but it started and still have start sputter. turned it off again and now won't start, turns over but won't start, let the car sit a half hour and it started up fine, next day didnt want to start again..… so started to diagnosis starting with fuel or spark.

first thing we noticed is when turning the key over to "ON" we did not hear the fuel pump turn on… check connectors coming into the fuel pump, no power…. then into the Fuel Pump Relay on the left side of the engine bay there was no power going into the relay… read there could be blown capacitors in the ECU, so opened the ECU to see no issues in there…

SO if anyone has any ideas please throw em my way… Right now there is no power coming into the FUEL PUMP RELAY. where should i back track from there. EFI relay seemed fine. but fuel pump relay seems to be where I'm stuck.

ALSO.. did the little mod where in the diagnostic port in the engine bay you jump a wire from B+ to FP… fuel pump turned on and got gas flowing into engine. But still no start…. any help would be AWESOME!
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Old 05-04-14, 02:43 PM   #2
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did u spray a small amount of starting fluid into the fresh air intake hose..then try to start it
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Old 05-04-14, 03:53 PM   #3
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did u spray a small amount of starting fluid into the fresh air intake hose..then try to start it
what will that help me prove? just wondering.

i still don't have power going to my fuel pump relay.
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Old 05-04-14, 04:09 PM   #4
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can u communicate with the ecm?

Last edited by python; 05-04-14 at 04:15 PM..
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Old 05-04-14, 04:18 PM   #5
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btw this is what happens when people do not follow up on their threads..makes forums useless
http://www.clublexus.com/forums/ls40...ump-relay.html
not directed to u btw
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Old 05-04-14, 05:22 PM   #6
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This thread may be of help:
http://www.clublexus.com/forums/ls40...y-problem.html
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Old 05-04-14, 05:45 PM   #7
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Quote:
Originally Posted by python View Post
btw this is what happens when people do not follow up on their threads..makes forums useless
http://www.clublexus.com/forums/ls40...ump-relay.html
not directed to u btw
Quote:
Originally Posted by RA40 View Post

yup i have read both of those pages before posting my thread.
and no trunk wire issues and popped open my ECU and saw no visible damage to any capacitors.

so again i am just stuck at no power to my fuel pump relay.. is there anything in between my ecu and the fuel pump relay that can be checked?

I appreciate the replies guys.
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Old 05-04-14, 07:22 PM   #8
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fuel pump module..in the trunk by the gas cap fill neck..remove the tool kit thing and its behind there
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Old 05-04-14, 07:56 PM   #9
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fuel pump module..in the trunk by the gas cap fill neck..remove the tool kit thing and its behind there
so power would go to my truck module first, then go back to the engine bay to the fuel pump relay, then back to the trunk to the fuel pump?

cause again.. i have no power coming into the fuel pump relay.

and seems threads keep telling me only 93-94+ have the module in the trunk. but ill take a look tomorrow.
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Old 05-04-14, 08:30 PM   #10
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Circuit opening relay?

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Old 05-04-14, 10:04 PM   #11
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will check the opening circuits for sure, think i saw em located right next to the ECU thanks for the diagram that really helps
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Old 05-07-14, 04:21 PM   #12
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so update.. which is really no update i guess since I'm trying to figure this out by myself not really know what I'm looking for….

i was able to get the car started by jumping +B to the FP… smoked a bit.. did some light revving and removed the jumper wire and continued to run until i gave the motor a nice 3500-4000 rpm rev and it just died.

I have noticed when you do the +B to FP jump the pump does go on, i do hear fuel into the lines in the engine but also noticed that it wouldn't do it unless the fuel pump relay was in which is weird cause i thought jumping that bypassed everything.

Figured out which circuit opening relay wa which and they both seem to have tested out fine only thing i did notice when the plug was plugged into that relay, and testing the wires with my test light.. both middle wires lit up.. then one of the wires gave a faint light and as soon as i touched it i could hear the "click" from inside the relay and did hear the fuel pump turn on..

but since then trying the jumper wire hasn't started the car, i tried it yesterday and wouldn't work, but when going out today it started.. weird.

again I'm just so lost and it all confuses me.. I've read every thread of guys having the fuel issues and cannot seem to find similar ones

I have checked…
AM2 fusible link - its good
7.5 IGN fuse - its good.
EFI main relay is fine.
Power going in and out of the circuit opening relay - seems fine (this is where i start to get confused)

still no power to fuel pump relay or resistor…. and fuel pump of course

I just don't know exactly what I'm looking for and how to properly test for it.. i can do any other type of mechanical work to a car, but when it comes to wiring.. I'm clueless.
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Old 05-07-14, 05:07 PM   #13
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You need to find out the root cause why the circuit opening relay is enabled. Why don't you read the fault code first?
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Old 05-07-14, 05:45 PM   #14
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trying to track down an OBD1 reader. but the engine light wasn't there when the first problem occurred. only now one since starting it up with the +B/FP jumper mod
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Old 05-07-14, 06:01 PM   #15
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Old 05-07-14, 06:01 PM
 
 
 
 
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