Symptoms of a bad fuel pump? - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

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post #1 of 13 (permalink) Old 05-02-2008, 10:24 AM Thread Starter
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Symptoms of a bad fuel pump?

  • i have a 1994 A4 z28 and i took my car to the dyno about a week ago and they couldnt get it over 4500RPM on it and it only dynoed at 217 rwhp (the car ran mid 13's back in november and nothing has changed) which didnt make sense....seemed to be cutting out real bad and i just replaced my opti and plugs about 5000 miles ago..the car seems to bog down real bad too when i first start it up and sounds like its poping and missing untill it shifts
ive made sure the cats arnt clogged, ive replaced the fuel filter and ive ran my OBD1 scanner and i keep getting a "Fuel lean malfunction" reading

heres a vid of how the car runs when its first started up


http://s34.photobucket.com/albums/d1...t=100_2220.flv


could it be my pump? i hooked up a pressure tester and im getting around 20psi and less when i drive the car

help!
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post #2 of 13 (permalink) Old 05-02-2008, 11:29 AM
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20 PSI is awfully low, should be more then double that.
check your fuel pressure regulator, if its ok, then it sure seems like your fuel pump crapped the bed.
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post #3 of 13 (permalink) Old 05-02-2008, 12:41 PM
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Quote:
Originally Posted by JesusKnievel View Post
  • the car seems to bog down real bad too when i first start it up and sounds like its poping and missing untill it shifts
My old firebird did exactly the same thing! It would also feel like a misfire when the car when into overdrive. I changed the fuel pump and it fixed all my problems, like he said also check the regulator and the filter. Also if you get a pump from autozone or anyplace, TEST it before you put it in! if you do it right and drop the tank you will be VERY pissed when you strap the tank back in a try to fire her up and you get no fuel. I had to tank my back and get a 2nd...I hate autozone....

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post #4 of 13 (permalink) Old 05-02-2008, 02:18 PM Thread Starter
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well im doing the old "hack the SH*T out of the trunk" square cut thing
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post #5 of 13 (permalink) Old 05-02-2008, 03:39 PM
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When my pump went bad, the symptom was a high-end stumble around 5000rpm. I hooked up a gauge and got 40ish at prime and idle but the pressure would drop to ~20 close to readline. Replaced the pump, and pressure was good to go again. I also did the trap door method.

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post #6 of 13 (permalink) Old 05-03-2008, 07:49 PM
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20psi ouch. That sounds like the pump, my car did the same thing it could only build about 24psi. I got a racetronix kit, and installed it using the trap door, solved the pressure issue. The trap door is the way to go, only a couple minutes of cutting. Good luck, hope it fixes your pressure!
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post #7 of 13 (permalink) Old 05-05-2008, 05:01 AM
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had this issue with both my roadmasters. the first one, I drove home 300 miles like that... it was a pain on the highway! It had a mean miss, and back fire. I swapped a bunch of parts before I put a fuel PSI gauge on it, and saw 20psi. car was much quicker after that.

2nd car, it ran really really slow at the dragstrip, stumbled off idle, and had good pressure(43) at idle. it just felt slow to me. replaced the fuel filter, and it gained 60hp. then a week later it died at the gas station, right after I put a full tank in. I got to a parking spot, and then it wouldn't start...

the trap door method scares me. I don't need a another exposed area to allow rust. Maybe dropping the tank of a B-body is that much easier?

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post #8 of 13 (permalink) Old 05-07-2008, 07:27 PM Thread Starter
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whats the probability of it being the fuel pump over the regulator? im buying a used one tonight out of a 95 z28 with 30K miles on it for 20$
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post #9 of 13 (permalink) Old 05-07-2008, 07:39 PM
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regulators dont go bad very often, fuel pumps seem to be common on these cars. Mine has 91k and i just replaced the fuel pump.
trap door method style and was done in under 2 hours taking my sweet time.

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post #10 of 13 (permalink) Old 05-07-2008, 07:40 PM
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Quote:
Originally Posted by JesusKnievel View Post
whats the probability of it being the fuel pump over the regulator? im buying a used one tonight out of a 95 z28 with 30K miles on it for 20$
More then likely the fuel pump at that low of a pressure. Although you can sometimes save money with used, I dont think this is one of those places you want to cheap out. Lot of work if the pump only lasts a little while again. Its like buying used underwear, you just dont
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post #11 of 13 (permalink) Old 05-07-2008, 09:39 PM Thread Starter
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well i checked again and my pressure was 19 at idle and 11 at around 5K..

hoping to swap the pump out tomorrow so i can run this b**ch Friday night
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post #12 of 13 (permalink) Old 05-07-2008, 11:37 PM
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Quote:
Originally Posted by DJ_Kovacs View Post
More then likely the fuel pump at that low of a pressure. Although you can sometimes save money with used, I dont think this is one of those places you want to cheap out. Lot of work if the pump only lasts a little while again. Its like buying used underwear, you just dont
u dont use hand me down undies?

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post #13 of 13 (permalink) Old 05-08-2008, 10:28 AM
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Quote:
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u dont use hand me down undies?
Hand me downs and buying used undies are two different things
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