Is It The Fuel Pump?

[larryp]

New to forum but was impressed with amount of knowledge being shared.

Have a serious problem with my 91 LS. Started with a very small leak in fuel tank. Rather than buy a new tank I removed it and had it welded. Engine used to run perfectly and start on first click. Now it takes 6-8 seconds to start when cold, runs rough until warm and even then it will start bucking under constant throttle. Runs good at full throttle. Think i might have damaged fuel pump during repair.

Here's the steps i went thru on the repair.

DIsconnected fuel pump and fuel guage connections at tank.

Removed tank (was almost empty).

Flushed tank with water (left fuel pump in tank for all repairs )

Had tank welded.

Replaced tank and reconnected fuel pump and fuel guage connections.

Added fuel from fuel can (may have been old)

Took forever to start and then ran rough immediately.

Filled tank with premium - no improvement after a couple of days

Replaced fuel filter (i was somewhat prepared after reading posts but it is an ugly job)

Only slight improvement after filter replacement.

Have used 3/4 of a tank of gas and still having same problems.

I suspect i damaged fuel pump somehow during repair. it's also possible there was water left in tank but i would think that would have worked itself out by now (also added a can of gas line water remover to tank).

As i said engine ran perfect prior to repair. Started immediately in all kinds of weather.

Sure could use some guidance before i spend the buck to replace the fuel pump.

Thanks

[silvermate]

well I don't have a definate answer, but i believe you are on the right track, i bet you got some debris sucked up in your fuel system. and could have damage and or clogged the following;

fuel pump

fuel filter

injectors

those are the Major things i would personally check or have checked out, it has almost certainly IMO got to be one of those.

[SKperformance]

a fuel perssure gauge is the only way to tell

but you may have clogged an injector or 2

do you get any black smoke at start up?

[JPI]

So there is still water in the tank? That could be one of the reason why the car run rough. Why would you weld the tank when there was fuel in there? A bomb was about to blow. I would remove the fuel pump, exam all your connection. Remove the old fuel and put in fresh one.

JPI

[larryp]

a fuel perssure gauge is the only way to tell

but you may have clogged an injector or 2

do you get any black smoke at start up?

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No black smoke at start up. Put in new fuel pump and no difference. I know it's got to be fuel related since that's the only thing that was messed with and it ran perfectly before. Have gone through about a full tank of gas. Getting pretty frustrated.

What's best way to check injectors or unclog?

[larryp]

So there is still water in the tank?  That could be one of the reason why the car run rough.  Why would you weld the tank when there was fuel in there? A bomb was about to blow.  I would remove the fuel pump, exam all your connection.  Remove the old fuel and put in fresh one. 

        JPI

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There may have been small amount of water in tank (< 1/4 cup).

Tank was removed and flushed with water so there was no fuel in tank when welding B) .

[ArmyofOne]

So there is still water in the tank?  That could be one of the reason why the car run rough.  Why would you weld the tank when there was fuel in there? A bomb was about to blow.   I would remove the fuel pump, exam all your connection.  Remove the old fuel and put in fresh one. 

         JPI

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There may have been small amount of water in tank (< 1/4 cup).

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thats what did it. you are going to have to run the gas all the way out. and then hope you didnt permanetly destroy any engine compnents. water inside your engine is a bad thing, and even 1/4 cup of water can do it. you cant mix gasoline and water. thast like oil and water, they wont mix. i have seen a teaspoon of water dumped into a 20 gallon gas tank (experiment in auto class) and it messed with the ECU on the car. made the ECU think it was running lean so it adjusted the fuel mixture., only it never adjusted back. adding more fuel, the next tnak of gas ran too rich and smoked something fierce, also blew the O2 sensors.

moisture in the fuel system is not a good thing.

[VBdenny]

I think the fuel pump is electric. If you arc welded it you might also have damaged it with electocal current. What brave soul welded it? That is so dangerous, a friend of mine tried to weld his jeep gastank and it blew him across the yard and made the tank look like a bubble. He was luckly not to have been hurt or killed.

[SKperformance]

Well if you changed the pump i woul look further up to the injectors

the motorvac would be the best bet first

[larryp]

Well if you changed the pump i woul look further up to the injectors

the motorvac would be the best bet first

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Well I gave up out of frustration and took the car to a local repair shop that specializes in Lexus repairs.

The mechanic called this morning and gave me good news. :D When i put the tank back in, i evidently failed to reinstall the washer on the high pressure fuel line. The result was that most of the fuel was being pumped back into the tank.

Now he is looking at why there is so much pressure in the tank. Recently (before removing the tank) i noticed that a lot of pressure was being released when the cap was removed which is probably the root cause for the leak in the tank. The tank appeared as though it had been hit from the inside and was pushed out which created a hairline crack that leaked very slowly. Something is not allowing excess pressure to be released.

And by the way, there was a post on the forum that said that the hissing sound when removing the cap was actually air rushing INTO the tank. I don't believe this is correct. While inspecting the gas cap i noticed a relief valve inside the cap that is spring loaded to allow air IN when the pressure gets too low inside the tank. So my question is what relieves excess pressure that builds up inside the tank?

I'll keep you posted. By the way, repair cost so far $112. I was having nightmares thinking i might have to replace the ECU.

[SKperformance]

the cap releives atmoshperic pressure

so yes it does rush in and out

that might be you need a new gas cap

[914lps]

the cap releives atmoshperic pressure

so yes it does rush in and out

that might be you need a new gas cap

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Glad to hear you got it fixed. By the way, the standard practice for wealding a gas tank is to fill it with water, and weld it with the water in it. That way there can be no gas or fumes. And yes, it can be wealded that way, but you need to be a good wealder. It may be easer for most folks to use a fiberglass patch, or on of those store bought patches.

On the gas cap. When my tank is down to about 4 gal., and I take the cap of, after a long 300 mile drive, I get a big rush of air out of the tank... Has me thinking about a new gas cap.

[larryp]

I got her back and she runs fine. The excess pressure is being caused by a clogged carbon cannister. The mechanic said he could replace it for about $300 or i could just leave the gas cap partially open to allow the excess gas vapor to escape.

The gas cap vent is a one-way vent. It will draw air into the tank when the pressure in the tank is lower than atmospheric pressure, but it doesn't vent out (which is why he suggested leaving the cap partially open). I asked about this triggering the check engine light and he said the older models don't monitor this (mine is a 91).

Well in the end i'm happy to have it back to normal, but it turned out to be a $220 washer. ($100 for a fuel pump i didn't need, and $120 to have it diagnosed and get the washer replaced. If i had paid more attention while lying on my back disconnecting fuel lines i might have seen the washer drop on the ground. :chairshot: Hopefully someone, somewhere will benefit from my trials and tribulations. Thanks to everyone that responded.

[SKperformance]

thanks for the update

i am sure it will help

[JPI]

thanks for the update

i am sure it will help

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I'm glad you have it fix. What washer? Have pictures?

JPI

[larryp]

thanks for the update

i am sure it will help

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I'm glad you have it fix. What washer? Have pictures?

JPI

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No pictures. It's a copper washer on the high pressure fitting on the bottom of the fuel tank.