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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!

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Have you done a compression test?

I think that's where I would start

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 Does the darkish white smoke dissipate or does it hang in the air? If it dissipates, it's likely steam. Oil smoke (bluish) tends to hang in the air for a while. That's why Charles recommends a compression test. You'll have more info when you pull the plugs.

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Could be running rich from too much fuel pressure. Idle going up to 1000 when you turn the pump off supports this and the dark exhaust could be fuel not oil. Is the fuel pump & fpr giving the right fuel pressure?

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Check the vacuum hose to the FPR for raw fuel.  Could be a hole in the diaphragm.

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18 hours ago, jonbill said:

Could be running rich from too much fuel pressure. Idle going up to 1000 when you turn the pump off supports this and the dark exhaust could be fuel not oil. Is the fuel pump & fpr giving the right fuel pressure?

That’s what I was thinking, I’ve heard I can adjust this with a screw on the back of the AFM

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12 hours ago, Zed Head said:

Check the vacuum hose to the FPR for raw fuel.  Could be a hole in the diaphragm.

I’ve been looking into the possibility of vacuum leaks since the car had been sitting for 13 years before I bought it and I replaced every hose that carries liquid but never touched any vacuum lines

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On 6/15/2019 at 8:56 PM, Mark Maras said:

 Does the darkish white smoke dissipate or does it hang in the air? If it dissipates, it's likely steam. Oil smoke (bluish) tends to hang in the air for a while. That's why Charles recommends a compression test. You'll have more info when you pull the plugs.

Smoke hangs around for a bit, doesn’t dissipate quickly like steam, I haven’t done a compression test yet but I’ll look into it

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On 6/15/2019 at 5:17 PM, Patcon said:

Have you done a compression test?

I think that's where I would start

Okay thanks!

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34 minutes ago, Jack Pearcy said:

I’ve been looking into the possibility of vacuum leaks since the car had been sitting for 13 years before I bought it and I replaced every hose that carries liquid but never touched any vacuum lines

It wouldn't be a vacuum leak, but you'd be sucking fuel straight through the FPR.  Vacuum on one side of the diaphragm, fuel on the other.  It's a flexible fabric that gets old and cracks.  A small crack can let a lot of unmetered fuel into the intake manifold.  Not uncommon.

image.png

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22 hours ago, Zed Head said:

It wouldn't be a vacuum leak, but you'd be sucking fuel straight through the FPR.  Vacuum on one side of the diaphragm, fuel on the other.  It's a flexible fabric that gets old and cracks.  A small crack can let a lot of unmetered fuel into the intake manifold.  Not uncommon.

image.png

I pulled the vacuum hose off while it was running and the idle cleared right up, I didn’t find any liquid fuel in the vacuum hose but it does smell strongly of gas

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Try turning the engine off then pulling the hose.  Just to see if it's wetter, the engine vacuum won't pull through the hose with the engine off so any leakage should still be there.  The fact that it runs better when you turn the pump off is a sign that it wants a leaner mixture though.  Seems like you need a new FPR.

Edit - if the FPR is leaking you might see some drops at the hose nipple for the vacuum source, on the FPR itself.   Run the fuel pump with the vacuum hose off.

Edited by Zed Head

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16 hours ago, Zed Head said:

Try turning the engine off then pulling the hose.  Just to see if it's wetter, the engine vacuum won't pull through the hose with the engine off so any leakage should still be there.  The fact that it runs better when you turn the pump off is a sign that it wants a leaner mixture though.  Seems like you need a new FPR.

Edit - if the FPR is leaking you might see some drops at the hose nipple for the vacuum source, on the FPR itself.   Run the fuel pump with the vacuum hose off.

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 

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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.

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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.

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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.

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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.

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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 by Dave WM

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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.

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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.

 

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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?

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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

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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.

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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.

Underhood Relays.png

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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.

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