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Car randomally runs like a** on >1/2 tank

9

99gtxws6

New member
I had a thread over in clubgp too, but I wanted to ask over here and see if anyone has any insight.


Randomally my car runs like complete ass, but it's ONLY on less than a half tank, and only when I've been driving in lots of stop and go traffic or hitting lots of stop lights. Also it seems to happen when it's hot outside.

Car has 167k miles, and since January i've replace the MAF and the crank position sensor as well as replaced the factory catalytic converter. Car didn't seem to have any issues in the cooler months, but now that it's warmed up to over 90* it's starting to act up again.

I'll either be driving along or I'll try to take off from a stop and the car has ZERO power. And if I try to accelerate more than 1500 RPMs or so it complete falls on its face, and almost dies. I have to continually pump the gas pedal to keep it from totally dieing on me, or if I just keep it floored, the Boost gauge goes all the way over and it sounds like it's choking to suck in air. One time it smelled like something had gotten so hot that it was starting to bake the insulation under the carpet or something.

Sometimes I'll just pull over and let it sit for a few minutes and once I start it up again it's fine. But if I end up back in traffic or at a stop light it'll start acting the same way again.

But I've found that if it does it, and I pull in and fill up with gas, the problem completely goes away regardless of how I drive it or how much traffic I'm stuck in.

So i'm pretty sure it's fuel related, just wondering if anyone had any definate answers so I'm not just throwing money at it replacing parts if I don't need to.

Thanks,
--Marcus
 


Well, the first thing I would do is check the fuel pressure. You might have a clogged fuel filter, a weak fuel pump, or a bad fuel pump resistor. What I’m thinking is that you have marginal fuel pressure, and when your tank is full the pressure head on your pump is greater therefore it is able to operate at a higher discharge pressure. And at low fuel levels the pump can’t keep up with demand (or is plain failing), this is just a theory. Good luck.
 
My guess is water in the gas tank, because it is warmer now condensation and build up ten times faster in the tank. WHen you fill if full the condensation will mix with the gas and cause to run fine because the consentration is of water and gas is low. But when your cars gets under a half tank more condensation will build up. Go to your auto parts store and get some sort of product that will help get the water out and stop the build up.
 
what year is the car? stock pump ect ect

it could be the venturi that has failed if ur a pree 00 gtp
 
Also have a check engine light on now...has 2 codes in the computer

po300 for a Random Multiple Cylinder Misfire

and

po420 for Catalyst System Efficiency Below Threshold (Bank 1)

and last week while driving around when the car was acting up, it gave me code

po131 - Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)

So it seems like whatever it's doing either has to do with the O2 sensors or it's effecting them in some way. And I just replaced the catalytic converter so what are the odds it's already bad?
 


was the cat brand new or like a junkyard replacement?
an o2 sensor could probably do that, if it's getting sporadic voltage then it could be giving sporadic readings to the computer causing random fuel adjustments.

also, this is kind of a longshot, but have you ever heard of vapor lock?
 
Poil336 said:
also, this is kind of a longshot, but have you ever heard of vapor lock?
Click to expand...

That is another reason I would like to know how much pressure he is running. A simple fuel pressure reading at key on and at idle would go miles for troubleshooting. Hint hint!:th_shakinghead2:
 
What would cause it to be getting vapor lock though? Thought that wasn't really a problem on fuel injected cars.

I don't have a fuel pressure gauge to check the pressure. Also, the schrader valve has been taken out of the fuel rail and capped off with an -AN fitting. Used to run a wet nitrous system and tossed the little valve out a long time ago.

Not sure if it makes a difference in getting a reading though
 
that's what i've read, but i figured you're in texas, this is happening when the gases have time to expand, seems like it could have been it. i'm not really sure, just kinda speculating
 
Start with some Mythel Hydrate ( think thats how you spell it?) That will get rid of any water in the fule. and ya, fule filter, is a good place to try... good luck!
 


Hook up a fuel pressure gauge and watch it while you drive. I think you will find that fuel pressure drops to zero when it acts up. I Had the same problem happen to me, it ennded up being a clogged fuel filter. It did take some investigating to find the problem though, but you have to WATCH the fuel pressure.
 
Replaced the fuel filter and did some Seafoam on it in the last few days. Was going to put a new fuel pump in it too but the pump I bought from Rockauto has different connectors for the wires so I decided to stick with the stock pump for now instead of having to cut and splice my factory fuel pump harness.

The fuel pump always comes on when I turn the key anyways so I'm thinking it's still working just fine if it always comes on.

Anyways, was driving today to go pick up my kids and was sitting at a stop light when as soon as the gas gauge got to a half tank, the car started sputtering and acting like it was getting choked for fuel and then died.

I left the car off while sitting there waiting for the light to change, and turned the key on and off to let the fuel pump cycle about 4 or 5 times. Once the light turned green, I started the car and it drove fine but I went ahead and stopped at the next gas station and filled up the tank.

Car drove fine for another ten miles or so of stop and go driving until about 3 lights from getting my son and it started to not want to accelerate any past 2k rpms. You could ease on the gas and it would drive ok, but if you tried to give it enough gas to get over 2k rpms, the car just falls flat on its face, but once you let off the gas, it will resume like normal.

I'm starting to think it's possibly something maybe in the PCM or something electronic and not so much fuel pump related.

How can I tell if my PCM is messed up?
 
99gtxws6 said:
Also have a check engine light on now...has 2 codes in the computer

po300 for a Random Multiple Cylinder Misfire

and

po420 for Catalyst System Efficiency Below Threshold (Bank 1)

and last week while driving around when the car was acting up, it gave me code

po131 - Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)

So it seems like whatever it's doing either has to do with the O2 sensors or it's effecting them in some way. And I just replaced the catalytic converter so what are the odds it's already bad?
Click to expand...

going out on a long shot here...but here it is.

i think your fuel pumps the problem. the 02 sensor low voltage means that your leaning out, which can also cause the random misfire and the catalyst below efficiency code. like i said im going on a long shot, but i do know that low voltage on an 02 sensor like say 200mv is lean and say 900mv is rich. maybe someone else can help you more.
 
kfish said:
going out on a long shot here...but here it is.

i think your fuel pumps the problem. the 02 sensor low voltage means that your leaning out, which can also cause the random misfire and the catalyst below efficiency code. like i said im going on a long shot, but i do know that low voltage on an 02 sensor like say 200mv is lean and say 900mv is rich. maybe someone else can help you more.
Click to expand...


I guess I'm going to go ahead and put this new fuel pump in. It's starting to have problems now no matter how much gas I've got in it. But it only does it after I've been in traffic a while and it's hot outside still. Kinda weird.

Like, for about a mile til I get to work, there's construction and traffic backs up, so I'm constantly stopping and accelerating and once I do that for a few minutes, the car starts acting like it's running out of gas. Sometimes it'll die but I can always cycle the pump 3 or 4 times and it'll start again.

Well Friday it died and I'd turn the key back and forth probably 10 times and the pump would never cycle on. Just let it sit for about 5 mins on the side of the road, tried it again, and the pump cycled back on, car started back up, and I drove the rest of the way to work.

So hopefully the new fuel pump will do the trick, just hate having to cut and splice the different plug into the stock harness.
 
Swapped the fuel pumps and the problem has seemed to have gone away. I've run it under a 1/4 tank many times while in traffic and hitting stop lights and it's not had a problem yet.
 


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