Fuel Pump Probs Chevy Trailblzer

chevrolet
trailblazer

#1

I have a 2005 Chevrolet Trailblazer LT. Recently the gas gauge was stuck at empty and the cause was determine to be in the tank. In the process of fixing this problem, which required the tank to be taken off, the fuel pump was also replaced . Since that time the Trailblazer has intermittently had trouble starting. It seems to happen most when I have driven to work (20 min drive ) in the morning then try to start up around lunchtime. I usually have no problem first thing in the mornings or within a few hours of driving.

The problem starting consists of the engine turning over 5 or so times before starting with a struggle or sometimes after turning over multiple times not starting at all. After one failed attempt I can turn the key a second time and will start right up no problem. Through none of this am I holding the key and grinding on the engine to start.

I went back to the auto shop that replaced the fuel pump and they said it was not holding its prime , which seems to be the case and the pump was replaced with a non aftermarket part. Unfortunately the same issue is still occurring . They do not seem to be able to figure out what is going on.

Any help would be appreciated


#2

is that govt speak? non-aftermarket? you mean they put in a GM fuel pump on repair #2? i hope we dont start a discussion on who GM sources their pumps from. it is a delphi part? a bosch part? is it made for GM in mexico? or some other korean supplier? they check fuel pressure when truck has sat overnite? and they drive it for 1 hr and than check fuel pressure at the restart?


#3

I would suggest that running your old pump with bad fuel gauge may mean it ran almost dry and may have picked up debris from the bottom of the gas tank which is now lodged in your fuel injectors. The dirt keeps the injector open and less the pressure drop after the engine shuts off. As for “losing the prime” that is rubbish. The pump is submerged in fuel, how could that be possible?

Injector cleaner in the tank is unlikely to fix it so you need a mechanic that uses a fuel system cleaner that attached to the fuel test port and blasts cleaner through the injectors.


#4

I presume by “not holding prime” they meant the fuel pressure was leaking down as they truck sit parked, due to a faulty pump check valve. That’s a common thing here, but the symptom is usually that it won’t start on first start of the day, rather than when sitting a few hours. The rail fuel pressure has more time to leak down overnight to the point it won’t start right up during cranking under the fuel pump has had time to re-pressurize the fuel rail. There’s no need to guess about this though, a fuel pressure test would determine that straight away and is easy enough to do. You might need to leave your car overnight at the shop tho. But if that’s not it ?? … hmmm … I guess there’s two cases to consider

Case 1: The recent fuel system work is responsible for this symptom appearing. Clogged fuel filter, clogged fuel injector, sticking fuel injector, or some kind of evap system problem or vacuum building in tank preventing fuel delivery. Check for store codes, replace fuel filter, see if a tank of gas with some added fuel injector cleaner helps, replace the evap purge valve, see if it starts ok when the gas cap is loose.

Case 2: The recent fuel system work is a coincidence and unrelated to the symptom. Deferred maintenance, cam or crank position sensor on the fritz, ignition module on the fritz. First step is reading out the codes as above, next is to bring all engine routine maintenance up to date. Spark plugs, engine air filter, intake manifold vacuum measurement, idle rpm measurement, compression test, etc. If that all doesn’t solve it time to take it to a shop who has the GM/Chevy scan tool who can check the fuel trims etc.


#5

Perhaps “losing prime” was a bad use of terminology. Most in-tank pumps do have a check valve in them to prevent the fuel from receding back from the rail (to the point of equilibrium) when you turn it off. This problem is usually verified by repeatedly cycling the key from OFF to RUN without starting the engine. The fuel pump will run for 3-5 seconds each time and refill the fuel line/rail. Then when you try starting, it fires right up (versus multiple cranking sessions to accomplish the same thing).

Now I see George beat me to it…how did I miss that last post?? Old age creeping up…


#6

How quickly the line loses pressure, and ultimately fuel, is largely a function of whether there’s an injector leak too. If there is, and the check valve is leaking, it can drain quickly like a straw. If there’s absolutely no injector leak, AND the check valve is leaking, the pressure will dissipate and the fuel will remain in the line. Air must be able to get into the line for the fuel to run out. And it does not take much of a leak for that to happen.

It functions like a laboratory pipette, or a drinking straw. Keep your finger over the end and the fluid will remain in the pipette or straw. Lift it, and the fluid will run out.


#7

That’s true for designs not using a return line. Most, if not all, of the early systems used return lines to reduce the propensity for percolation. Fuel constantly cycling… That’s kind of where the check valve came into being. I have vehicles still using that design but I know some newer cars have figured out how to eliminate the return line and not suffer from heat soak issues.