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Ask Jared D Your Own Question
Jared D
Jared D, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1349
Experience:  Shop Supervisor at County Fleet
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I have a 99 tahoe that lacks power going up a mountain and

Customer Question

i have a 99 tahoe that lacks power going up a mountain and then starts to miss but as soon as i top the hill it quits im thinking the fuel pump is week
Submitted: 1 year ago.
Category: Chevy
Expert:  Jared D replied 1 year ago.

Where do you want to start on this one?

Do you want to test fuel pressures?

Do you want to inspect the spark system to make sure it is strong enough?

Did you change the fuel pump harness when you changed the pump (they are notorious for going bad)?

What was the injector upgrade you performed?

Plugs and wires?

Expert:  Jared D replied 1 year ago.

Here area couple of areas to check (I am assuming you have a multi-meter and a basic scan tool):

1. Disconnect the Mass Air Flow (MAF) sensor and reset the fuel trims using the scanner and re-road test.

2. Re-road test and see if the power comes back and see if the fuel trims are 0 +- 10.

3. If the power comes back and fuel trims are OK, clean or replace the MAF sensor.

4. If no change, install a fuel pressure gauge and monitor fuel pressure under acceleration.

5. Pressure should be a minimum of 60 PSI under load or Wide Open Throttle (WOT).

6. If pressure does not achieve this, try blocking off the fuel return line and see if the pump is capable of 90-100 PSI.

7. Verify power and ground to the fuel pump, make sure it is not dropping out slowing the pump down.

Customer: replied 1 year ago.
jared im a pretty handy mechanic and i have done alot new plugs wires cap rotor and i took the old poppets out and put in the injectors got a full blown laptop dianostic scan tool i needed to set cam retard when i put the new intake gaskets new fuel pump and yes i did the harness also
Customer: replied 1 year ago.
what am i looking for for fuel trim is it a value or number or what or just reset it
Expert:  Jared D replied 1 year ago.

Fuel trims should be a value between -10 and 10. It ranges based on throttle position. If it's out of those ranges than something is adding too much fuel or air.

When you reset the fuel trims you are forcing it to pull new info into the long term fuel trim data.

Customer: replied 1 year ago.
ok ill do that dose just unplugging it reset it or do i need to do something else to it
Expert:  Jared D replied 1 year ago.

You can reset it with the scan tool or by disconnecting the battery for 30 minutes.

Customer: replied 1 year ago.
ok ill check it out and let you know thanks
Expert:  Jared D replied 1 year ago.

Sounds good.

Expert:  Jared D replied 1 year ago.

Please let me know if you need any additional information.

Expert:  Jared D replied 1 year ago.

I just wanted to see if you need more help. Please don't forget to rate.