99 trailblazer fuel pump problem
 

Im looking for a bit of advice. I have a 99 s-10 trailblazer and I replaced the fuel sending unit about 10 months ago. I did buy a less expensive one online hoping to save money but I think it may have made a mistake. It quit on me.

in the past 2 months i have been getting the p0452 low pressure trouble code. I took it for a tune up and they couldnt get the fuel filter off so i have to take it back and get a line kit.. BUT in the meantime if im going up hills or have the tach above 2200 for more than 20 seconds the vehicle gets random multiple misfires runs like crap then goes back to normal after a few seconds and runs fine.

now here is the kicker! The pump quit working. I did a relay check and it was fine. I disconnected the plug from the tank and used my multimeter to check voltages When the key is first turned on im getting 12 v after a few seconds it drops to around 8.5v then of course the vehicle is not on so it eventually goes back to 0v. Are those the correct voltages?

In a nut shell the pump will not prime, vehicle will not start. and I am going to buy the expensive delphi sending unit this friday but first i would like a professional suggestion from you guys before I go and pay 400 for a new pump :) Am I heading in the right direction?

Neal

you cant buy the cheap parts, they never work for long and sometimes not at all, I would imagine your going to need a new fuel pump....but check around on here there is a particular brand that works well, I see alot of people changing out the fuel pump 2 or 3 times, thats gotta suck.
Have you checked your injector?

P0452 is not a fuel system pressure code, but an EVAP code. It means that the pressure in the EVAP system is reading low for one reason or another.

P0452 - Evaporative Emission Control System Pressure Sensor Low Input (Search FTW!)

If you are getting proper +12V & ground at the pump for the initial priming cycle and the pump is not working, then the pump is likely bad. You might be able to prolong the inevitable by hitting the bottom of the tank in the area of the pump, but that won't fix anything.

AC Delco or Delphi pumps only. All the rest are a problem waiting to happen again, IMHO.

Kyle Was Completly Right!!!
 

Kyle,

Once again you were right on the money!! The Airtex Fuel Pump (IE = POS) had a bad connection inside the fuel pump sending unit. I have attached a picture of a BAD AIRTEX FUEL PUMP that was purchased less than ten months ago! The internal grey wire had signs of damage and showed that it was burnt! Im highly P!$$#d off because of how dangerous this was! Im supprised my fuel tank never blew up! Once again Kyle you are awesome (Swartlkk) You have given me the best advice on 4 different issues I have worked on and THANK YOU VERY MUCH!!!.

Neal

I agree, Airtex pumps are junk but, keep in mind that high resistance causes wires to burn. The problem could be anywhere after that connection, including the pump motor, or any ground connection after the motor. Make sure you check the connections at the ground splice pack and the frame. If you don't fix the root cause, it will continue to take out pumps until you do.

Sorry captian, I disagree with your statement. The area where the wire burnt is where the resistance is. Resistance causes a voltage drop. Where there is a voltage drop there is electrical energy being converted to heat energy. (Heat) If the pump was drawing too much amperage, the entire wire would show heat damage. Since the damage is localized, I would say it was poor workmanship that caused a bad connection between the wire and the connector. Unfortunately, the pump motor was still required to do its work. In order for that to happen at a reduced voltage, the amperage had to go up (Ohm's law). The high amperage, low voltage condition is what kills motors. I am curious if the pump motor was actually damaged or if the bad wire connection finally burnt through. (Do you still have the pump Steelcityneal?)

As for an exploding fuel tank - the fire Tetrahedron requires fuel, air, and heat in the right conditions to create combustion. In a fuel tank, the amount of oxygen in a fuel tank is too low. The LEL and UEL of gasoline is 1.4 - 7.6%. (14:1 fuel ratio). It is almost impossible to get these conditions. If it were easy, we couldnt use the style of fuel sensor we do (Bare wire + wiper) or even the pump in tank design. All those Hollywood scenes you see in movie would be an everyday occurance! Exciting, but not good for business.

Not trying to stir the pot.

Yes kristoph I still have the pump. I also agree with you about the poor workmanship with the draw on the line and everything. I work in the electronics field and I know ecactly what you are talking about. I was explaining to my buddy yesterday that when you have stranded wire and you knick out a few strands it completly changes the integrity, tollerance, and electrical capicity of the wire. I do like the information you gave me on the air fuel ratio. Thank you. I strongly believe that it was poor worksmanship that caused that connection to fail. I didnt want to touch it because I am going to ask for a refund this week. But looking at up close its pretty much the theroy you gave.. high amps burnt up the connection which made severed the wire .

If they do not honor the warranty, I am curious if you would repair the bad connection and test the pump motor. If these pumps are failing due to a bad connection, then is it really a crappy pump? I want to know if the pump is actually ok!

I am glad you are educated in the electronics field. I read posts on here where people are trying to troublershoot problems without a wiring diagram, meter or even a test light. They dont understand basic electrical theory but get angry at you when you try to educate them that they need the correct info and tools to accurately troubleshoot electrical issues. Its refreshing to work with someone who also understands the technology. As for the air/fuel mixture stuff. I am have also been train in confined space work and rescue so I have to know about upper explosion limits and lower explosion limits. PLUS I am an officer for our local volunteer fire/rescue. I really truly hate Hollywood for trying to convince people that cars explode all the time.

Thanks for listening to me rant and rave. Its been a long stressful day with too much coffee. Let me know what happens with that pump!