I'm having an issue with fuel pressure dropping at WOT and am hoping that someone on here might have experienced something similar and can lend a hand with resolving this. So here's the background...

I have a 2003 Z06 that has the later model fuel system, meaning the pump in located on the top of tank. The engine is modified and makes roughly 475 hp... heads, cam, long tubes, ect. What is happening is under heavy load and typically higher rpms, the car will loose fuel pressure and fall hard on it's face. The pressure will drop rapidly from 59 to darn near 0, and when I let off the pedal, it'll quickly recover and be fine. When this first occurred, it would drop here and there, and if you stayed off the throttle it would behave normally. But over time this got progressively worse and eventually got to the point that it would do it at part throttle under a medium load. At this point I decided to go ahead and change the fuel pump, of which I used the factory pump since I was told by many that it was good for much more power than I was putting out. So after the pump swap, the car was back to it's old self and running like a champ. I drove it for roughly a month without issue, and then all the sudden it coughed under a WOT acceleration. I hoped it wasn't the fuel pressure dropping again, and possibly something like the traction control, but it got progressively worse just like what I described above and I was pretty sure it was the same problem again. I connected up my pressure gauge and sure enough it was dropping out exactly like it did before. So it became obvious to me that the pump was not the issue, but a symptom/resultant of something else that is the problem. I've googled this issue like cray and have yet to find anyone that has had a similar issue, so I'm really at my wits end with this. My next step is to look at the voltage being supplied to the pump, but since the issue was gone and progressively came back, that really doesn't sound like an electrical issue. To me it sounds more like a pump starvation due to capacity and or clogging up. But I will tell you that the left side tank was clean when that new pump was installed. Anyway... that's the story and I'm hoping that someone on here has experienced the same thing and can shed some light on this.

 

Following. I do not have much to offer on this but I think you should at least monitor the voltage to the pump. That way if the voltage is increasing and pressure isn't you would know it may be a clog or another bad pump??? Better to have too much data then not enough.


Chris

 

Thanks Chris!

Yeah I totally agree... it never hurts to have too much data. Although it doesn't sound like a typical electrical issue, this whole thing doesn't sound typical, so who knows what I'll find out.

Tim

 

I have seen where there was fuel pressure issues except when jacked up. It was a connection issue at the pump we finally diagnosed. Double check your connections and pins.

Also pull your dash DIC codes.


Mr. Sam

 

Pulled codes and nothing to be had there. Connections were checked the first go around with swapping the pump and all seemed good. Didn't check the actual pins though. If the voltage supplying the pump looks good, then a pin not contacting well (snug male to female fit) could still be a possibility.

Thanks "Mr. Sam" for your input !

 

There may be nothing wrong other then you may need a higher capacity fuel pump or a boost a pump. It could be starving for fuel and thus your fuel pressure drops off because of that. My 2 cents, good luck.

 

I thought the same about the capacity of my stock pump, but many have said that they have ran well over 500hp with the stock pump. It also wouldn't explain why it gets worse over time and actually right after if takes a hard hit at WOT, it'll start acting up at part throttle. I also think that when you reach the capacity of the pump, it won't drop off instantly, 59 to 10 in a second, but will fall of gradually as it can't keep up with the required flow. So it would run say 40 at the high end instead of 59 and slowly get there as you increase speed at WOT. That's my thoughts anyway.

Really the biggest thing that keeps throwing a curve ball at everything is that it cured itself with the new pump but then slowly came back to behaving just like the previous pump. Something is causing this problem over time and not at an instant. Point being that if the pump is insufficient, then it would have happened right away and not a month later after several WOT pulls to red-line and perfect fuel pressure and A/F. This is what keeps me shying away from something electrical as well.

Anyway... Thanks a bunch for your input!!!

 

A fuel line that is collapsing on itself maybe, have you changed your fuel filter, just trying to offer more things to think about which could be causing your problems.

 

The fuel filter is part of the pump assembly that's in the tank and is new. The lines are under pressure, so they won't collapse, but a kink in a line would cause a restriction and lower the pumps capacity. Both are things I've thought of, and are very good theories and I really appreciate your input... Thanks a bunch!

My plan for now is to go down the electrical path and monitor the voltage at the relay to make sure the pump is not losing supply voltage for some reason. I also plan to do the same at the pump connector to verify that the wiring from the relay to the pump is ok. I'm leaving town for the weekend, so I won't get to this joyous task until next week, but in the mean time I really would like to here more theories from the experts!

Tim

 

Did you check the fuel pump relay, since it would be difficult to check the voltage drop across the it at WOT, pull the relay, energize the coil and see what the resistance is across the contacts, should be close to zero, if not that is the culprit.

 

Yep swapped the relay out with another in the power box. As for looking at the voltage at WOT... I have HP tuners with analog inputs so I'm going to record the voltage on the cold and hot sides of the realy on the fly. I'm hoping to set that up tomorrow, but I'm up north getting my cottage ready for summer right now. Thanks for your input!!!

 

Friend of mine is having this same problem with a chevy block. Did you come up with a solution?