Hey guys I’m new to this website but I have read a ton of stuff on here and it’s been a great help so that’s why I’ve joined. Anyways my 78 280z has been running fine for a while, I have all new fuel injectors, fuel pump, and afm. My fuel pump relay was bad so I wired up a switch to the wires where the fuel pump relay normally connects to and it’s worked fine. Recently however it has been idling horribly at around 500 rpm, but when I flip the fuel pump switch to off it jumps right back up to 1000rpm and idles fine until it dies from fuel starvation. It will also occasionally die out in addition to not accelerating sometimes. I’ll be driving and suddenly the power will not exactly cut out but not change if that makes sense. It’ll hold steady but stop reving and accelerating. It also blows darkish white smoke out of the exhaust when I rev it.

I know it’s a lot of info but I can’t figure this out if anyone has had a similar problem or a solution please let me know!

54 minutes ago, Jack Pearcy said:

I tried all of the above and no liquid, just the smell of gas, I also just turned the car on with the fuel pump turned off and it’s been idling smooth as silk for about 5 minutes straight and still going strong with the fuel pump turned off, it’s not even smoking 

impossible. The pump is running.

2 hours ago, Dave WM said:

impossible. The pump is running.

That’s what I thought but the switch was off and when I went under the car the pump wasn’t running but the car was, I can’t explain it, normally the car just dies out pretty quickly with the pump off but it ran for about 8-10 minutes before I turned it off. Honestly I can’t explain how it happened unless there’s another way to turn the pump on other than the fuel pump relay.

I suggest If you have not already you read the EFI section of the factory service manual. It has extensive trouble shooting and information on exactly how the EFI system works. Read is several times if need be until you have a through grasp of how the system works. Coming here for answers when you state the fuel pump is OFF and the car runs for 8-10 minutes is a waste of time.

On 6/15/2019 at 2:11 PM, Jack Pearcy said:

It will also occasionally die out in addition to not accelerating sometimes. I’ll be driving and suddenly the power will not exactly cut out but not change if that makes sense. It’ll hold steady but stop reving and accelerating. It also blows darkish white smoke out of the exhaust when I rev it.

I've seen people report the engine running with the pump off before.  If you have elastic rubber lines they can hold some pressure.  Idle doesn't use much fuel.  If it's running rich, then it will slowly go from rich to lean as fuel pressure drops.  There's an assumption that fuel pressure will be zero if the pump's not running (no offense Dave), but that might not be the case.  A gauge reading would tell more.

The pump not running results suggest that the FPR is not the reason for the rich running.  Could be a bad ECU or a stuck AFM.  The other part of your first post, above, is kind of typical of either of those.

8 to 10 minutes? with the pump off sounds impossible to me. the hoses are maybe a couple feet total, I just cant see them expanding enough to maintain any kind of pressure for more than a few seconds, even at idle. However I could be wrong but just cant see it happening for 8-10 min of idle. And if they are expanding enough, then I suggest a fire extinguisher be at the ready, really should have one on hand, but in this case, replacing the hoses would be 1st thing.

agree with needing a fuel pressure gauge as a 1st step.

 

Edited June 19, 20195 yr by Dave WM

I agree.  I had actually written something about how his 8 to 10 minutes might actually be 3 -4 in real time.

On the other hand though, there are other possible causes for that.  A ballooned fuel supply line maybe.  Once it expands and the pump check valve closes, it's a small reservoir of fuel.  So it might be true but it's a sign of a bigger problem, a line about to explode.  He should really examine his fuel lines, front to back.

for fun I am going to try turning power off to my pump on my test stand. It has several feet of rubber tubing. If nothing else should be interesting to see what happens.

Any way back to the OP issue, I would look at the FSM and check the CTS to see if its gone high resistance. Always the 1st and easy thing to check.

 

Pretty sure car with triple carbs won't run for 8-10 mins with the fuel pump off, and the carbs of course have quite big reservoirs.
Any chance this car has got two fuel pumps?

5 hours ago, jonbill said:

Pretty sure car with triple carbs won't run for 8-10 mins with the fuel pump off, and the carbs of course have quite big reservoirs.
Any chance this car has got two fuel pumps?

My car's a 280z, so it has EFI instead of carbs

8 hours ago, Dave WM said:

for fun I am going to try turning power off to my pump on my test stand. It has several feet of rubber tubing. If nothing else should be interesting to see what happens.

Any way back to the OP issue, I would look at the FSM and check the CTS to see if its gone high resistance. Always the 1st and easy thing to check.

 

Here's the thing, I'm not saying I can explain how or why this happened, I am saying that it did and the point of me posting that my car ran w/o the fuel pump on wasn't to impress you guys it was to voice my confusion as to how that's possible and maybe shed some light on the problem as it is most certainly a symptom.

22 hours ago, Zed Head said:

I've seen people report the engine running with the pump off before.  If you have elastic rubber lines they can hold some pressure.  Idle doesn't use much fuel.  If it's running rich, then it will slowly go from rich to lean as fuel pressure drops.  There's an assumption that fuel pressure will be zero if the pump's not running (no offense Dave), but that might not be the case.  A gauge reading would tell more.

The pump not running results suggest that the FPR is not the reason for the rich running.  Could be a bad ECU or a stuck AFM.  The other part of your first post, above, is kind of typical of either of those.

The AFM is brand new I bought it because the old one was crap, one thing that I have seen is that there is a fuel pump control relay alongside a fuel pump relay. Could that possibly be controlling the pump at idle and me flipping the switch on the fuel pump relay is messing up the power to the fuel pump? Just a thought.

Another thing to note is that I went under the car and checked the fuel pump while the car was running with the switch in the off position, and the pump didn't appear to be running. It was making no sound and when I grabbed it to feel if it was running I felt no vibration or hum other than that of the engine. This was also only a one time deal, every other time I would turn the fuel pump relay off with the engine running the car would die from fuel starvation. Still no idea how this happened but I don't think it was from a swelling fuel line. All of the fuel lines were rotted when I bought the car so I replaced all of them along with the fuel filter in the engine bay.