Low fuel pressure? Fuel pump not working correctly?

Tiny
SYEDASAD555
  • MEMBER
  • 2003 TOYOTA COROLLA
  • 115 MILES
I got a diagnosis done on my Toyota Corolla 2003 and found that in one of the cylinders, "Fuel mixture system lean bank 1".
Probable cause
1. Low fuel pressure
2. Faulty MAF/VAF sensor
3. Cylinder misfire condition
4. Faulty H02s/af sensor
5. Large vaccum leak

How could this be set right?
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Wednesday, December 29th, 2010 AT 9:18 PM

31 Replies

Tiny
MERLIN2021
  • EXPERT
With over 100,000 miles any of the above things could be true! Testing with a scan tool that reads live sensor data can help eliminate good parts and show weak parts. All have normal operating ranges and a scan tool is needed, however, the most common is the o2 sensor, it's designed for 100,000 miles and you are above that. Vacuum leak is the other biggie. et a can of spray Throttle body cleaner, spray the vac lines and manifold area, when the idle changes, you've found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!

These guides will help walk us through the repairs.

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

and

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please run down these guides and report back.
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Wednesday, December 29th, 2010 AT 9:24 PM
Tiny
ALLEN SAYERS
  • MEMBER
  • 1998 TOYOTA COROLLA
  • 1.8L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 205,000 MILES
When ignition is in crank position fuel pump will not kick on. When key is turned onto the run position pump will pump fuel for couple seconds. Checked fuses and relays all seem to be good. Any suggestions? Thanks.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
PATENTED_REPAIR_PRO
  • EXPERT
I see the fuel pump is fed from two relays with one relay feeding the other. The circuit opening relay in the driver side j/b behind left kick panel is fed from the efi or f-htr relay in the engine room j/b located left front under hood.
It is fed from the ignition fuse in the instrument panel junction block, located left side of dash.
So, remove that circuit opening relay and test the spots in the empty socket for voltage. The same one that has voltage for the first two seconds when the key is first turned to run will be the same one that has to be hot when cranking the engine over. If it is not, make sure that ignition fuse is hot with the key on start.
If on the other hand the circuit opening relay spot is hot with the key on start, then the problem has to be with grounding that circuit opening relay and that is done by the ecm, most likely from a signal from the crankshaft position sensor telling the computer that the engine is turning over. So if that is the case first try seeing if there are any trouble codes stored in the ECM or just try a new crankshaft position sensor.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
ALLEN SAYERS
  • MEMBER
Thank you, I will check ignition fuse. I have checked both relays and the EFI fuse. I also tried running power straight to the fuel pump, and it will run, but still no start. Would this possibly be a symptom of a crankshaft position sensor? Only trouble code stored was an EVAP trouble code but it has been in the ECM for couple years. Thanks for your help!
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
PATENTED_REPAIR_PRO
  • EXPERT
It is possible a faulty crankshaft position sensor would also cause a no spark. Does your scan tool read cranking rpm's, if so see if you get a cranking rpm of around 100 rpm or so, if not then you should suspect a faulty crankshaft position sensor.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
ALLEN SAYERS
  • MEMBER
I have a good spark, just no fuel pump during crank.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
STEVE W.
  • EXPERT
Normally you will not have the pump on during cranking. The system should turn the pump on for about two seconds as soon as the key is turned on. Then when you crank the engine the pump will not turn on until the ECM receives a signal that the rpm's are increasing from cranking speed.
If you have bypassed that and the pump was running but the car still did not start you will want to check the actual fuel pressure in the system. Spec is 44-50 psi. A bad regulator or worn pump may drop the pressure enough that it will not run.
A way you could test quick would be to shoot some engine starting fluid into the intake. If it tries to run then you have a pump or injector issue.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
JUN841NC
  • MEMBER
  • 1995 TOYOTA COROLLA
  • 1.6L
  • 4 CYL
  • 2WD
  • 336,875 MILES
What is the possible causes for burnt fuel wires? Recently had to remove pump because I thought it was faulty just to find out that the wires (positive red and negative black) connected from the pump to the outlet power supply has burnt out. Removed those wires and plug and tested the pump outside of the tank and it worked. Please help. Is this normal or very dangerous?
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
ALLEN SAYERS
  • MEMBER
I should not have said pump runs during crank. I meant the only time pump runs is after cranking. Have tried the starting fluid, car will run a few seconds. Have changed fuel pump but not regulator. My scan tool does not read cranking rpm's. But when the pump is powered straight from battery, should the car start?
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
STEVE W.
  • EXPERT
It is somewhat normal, but not a good thing. What usually happens is that the fuel pump starts to fail and draws a bit more current. That in turn causes more heat in the wiring and connectors. Then after a short while the heat causes thermal cycling around the connector and air an moisture get in. The resulting corrosion creates resistance in the connector. That creates more heat and the cycle progressively gets worse until the metal in the connectors starts to get weaker from the constant cycling and the connector gets looser, then either the pump fails or the wiring gives up. When I do a fuel pump I always check the connections to see if they have any heat damage. I also replace the pump unless it was just replaced with a good unit. In this case I would replace the wiring pigtail and then test the current draw of the pump, Common pumps like yours draw about 4-6 amps if they are okay, Higher and I would replace the pump.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
STEVE W.
  • EXPERT
Not if it is not creating enough pressure or the injectors are not being activated.

Easy way to test that is to pull a connector off an injector and hook a test light up and see if it flashes during cranking.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
JUN841NC
  • MEMBER
Thanks for the input. I changed the pump about 6 months ago. What causes my pump to go that fast every year? I change it about twice. Also I tested it and it was pumping fine, is it necessary for pump replacement? I put about 3 or 4,000 kilometers on it for the 6 months.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
ALLEN SAYERS
  • MEMBER
I checked injectors with test light. One side of the plug lights up when key is turned onto run position and during crank, but dosent flash during crank.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
STEVE W.
  • EXPERT
If this is the first time you noticed the bad wiring it's possible the connector has been failing for a while and finally got bad enough to melt the wiring. I would check all of the wiring that feeds the pump to be sure there isn't another area that is failing. Then there is the issue of the pumps themselves, I don't have much luck with many of the aftermarket pumps when it comes to longevity so I try to get OEM if possible. Another thing is that you don't want to run the pump in low fuel often, the pump uses the fuel going through it for cooling and running the tank down low many times can cause the pump to get warm and cause problems.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
STEVE W.
  • EXPERT
Did you connect the test light across the connector or connect it to ground and probed each wire? You need to connect it in place of the injector. One side will have power with the key on, the other side will be switched to ground through the computer.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
ALLEN SAYERS
  • MEMBER
Not sure on how to connect it in place of injector. I just stuck test light in both sides of plug and connected test light wire to ground on battery.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
STEVE W.
  • EXPERT
That is what I thought. Easiest way would be to connect the test light to the battery positive post. Then gently probe the connector pin that did not light up when you tested. Now crank the engine. The light should flash if you have injector pulse.

Or go to a parts store that has loaner tools and borrow a set of Noid lights. Select the proper one and plug it in. It will flash if you have injector pulses.

While you are there you could also borrow a fuel pressure gauge and verify that as well.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
ALLEN SAYERS
  • MEMBER
I bought a fuel pressure gauge just to be sure, theres not pressure cause pumps not kicking on
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
STEVE W.
  • EXPERT
Does it come on when you first turn the key to on? If not check the relay as indicated above.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)
Tiny
CHADSTER28
  • MEMBER
  • 1994 TOYOTA COROLLA
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
I recently got this car after it had been sitting for awhile. I did a complete tune up. I noticed though that the fuel guage did not work. I have been putting fuel cleaner in the system to clean it out. The fuel sending unit seems to be working now, but im wondering if I have a problem with my fuel pump?

At low speeds from 30 and under the car has been hesitating, and even stalling. I drove the car, over 500 miles to see if I could burn out all the junk that was in the gas tank, and I was fine most of the way until I got off an exit near the end of the trip and it started hesitating uphill and then eventually stalling.

It does not happen at high speeds, but at the light, or low speed and even trying to go up hill, the engine stalls and dies or acts erractic, yet it doesnt die all the time or happen everytime im at low speed!

So I have already replaced the fuel filter, and have been using fuel cleaner, but even if I was able to travel a long distance is the problem still the fuel pump?

I say the fuel pump because I know that the fuel pump and fuel sending unit are together, and as I mentioned earlier, the fuel sending unit had been having problems.

So is it the fuel pump or am I missing something else? What else could it be? Fyi, it has a new battery, spark plugs, spark plug wires, hoses, air filter, fuel filter.
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Thursday, October 15th, 2020 AT 11:43 AM (Merged)

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