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Running out of fuel at 9psi with a stock 280zx turbo?


Thumper

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I'm working on my friends 280zx turbo automatic. We are having the problem at high rpms above 4500rpm it will slowly lean the micture out. It will start at 11.5:1 and work its way up to 13.5:1 by 5700rpms. We put a new fuel pump, filter, and have varied no fuel pressure drop via fuel pressure gauge so its not a fuel supply problem. We put a new afm on and I loosened the spring inside of it so that is was running 9:1afr at 4000rpms and it still went to 13.5 by 5700rpms so its not the afm. The only thing I can think is the problem is the injectors are somehow clogged or the ecu has a problem.

 

The car is bone stock except intake and no exhaust. It has a greddy ebc that is turned off but it still raised the boost to 9psi instead of the stock 6psi. If we turn up the boost the problem happens earlier in the rpm range due to we are moving more air earlier. When the car is cruising or building boost the afr's seem to be ok so it only seems to be a problem at high rpms. What do you guys think is causing the car to run out of fuel? Thanks

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You need to increase the fuel pressure with an FMU or get larger injectors and tweak the AFM, or get larger injectors and a engine management system.

 

I have a really nice Begi FMU (probably the best) that I am willing to sell. PM if interested. With a Walbro fuel pump I ran 14psi boost with the FMU making 60psi of fuel under boost (stock injection). It was reliable and had more in it. I put down 265rwhp/300rwtq with it.

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The stock ECU is the problem - it simply cannot deal with increased boost pressures - it runs off preset figures in open loop type mode - so it doesn't add enough fuel for the boost you're running.

 

Anything over 5-7 psi and you simply start starving for fuel.

 

As someone suggest a RR FPR is one way to go, but an aftermarket ECU would add MUCH more driveability over the stock system.

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You need to increase the fuel pressure with an FMU or get larger injectors and tweak the AFM, or get larger injectors and a engine management system.

 

I have a really nice Begi FMU (probably the best) that I am willing to sell. PM if interested. With a Walbro fuel pump I ran 14psi boost with the FMU making 60psi of fuel under boost (stock injection). It was reliable and had more in it. I put down 265rwhp/300rwtq with it.

 

I ran 13 psi on my ghetto beast (stock 280zx) with just a intercooler upgrade and only ran out of fuel at 13psi so I know the stock injectors are suppose to handle more power than 9psi can put out.

 

The stock ECU is the problem - it simply cannot deal with increased boost pressures - it runs off preset figures in open loop type mode - so it doesn't add enough fuel for the boost you're running.

 

Anything over 5-7 psi and you simply start starving for fuel.

 

As someone suggest a RR FPR is one way to go' date=' but an aftermarket ECU would add MUCH more driveability over the stock system.[/quote']

 

I know the stock ecu system/ fuel system can run more boost I have done it and so has many people on this forum. And i'm trying to stay away from aftermarket ecu for my friend but I've installed atleast 6 of them and tuned ALOT more.

 

I know something is wrong in order for this to be happening. The stock fuel system and ecu can handle more power. Any other thoughts on what could be causing this? Thanks

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...if the injectors were clogged somehow wouldn't the car run lean all the time? or just at high rpms?

That's a tough call. It could go either way. Also, what are the odds that all the injectors are clogged evenly? Pretty low. Unfortunately, you can't tell if one injector is causing a lean reading or all of them are.

 

Is the regulator maintaining a constant fuel pressure differential under vacuum and load? Disconnect the regulator vacuuum line at idle and the FP gauge should jump up. Blow into the regulator with a bike pump or compressor at 10psi and the fuel pressure should go up by 10psi. A ruptured or sticky diaphram in the fuel pressure regulator will cause you to lean out under boost and run rich under vacuum.

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That's a tough call. It could go either way. Also, what are the odds that all the injectors are clogged evenly? Pretty low. Unfortunately, you can't tell if one injector is causing a lean reading or all of them are.

 

Is the regulator maintaining a constant fuel pressure differential under vacuum and load? Disconnect the regulator vacuuum line at idle and the FP gauge should jump up. Blow into the regulator with a bike pump or compressor at 10psi and the fuel pressure should go up by 10psi. A ruptured or sticky diaphram in the fuel pressure regulator will cause you to lean out under boost and run rich under vacuum.

 

The regulator is fuctioning correctly. It moves up 7psi when the vacuum is diconnected while engine is running. And it goes up 1psi for every 1 psi of boost. And it holds a vacuum when I put a vacuum pump on.

 

I'm going to try and get some more stock injectors and i'll take the fuel rail off and see the spray pattern of the ones i have currently.

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I had this same problem when I was running the stock system. Every once in a while I had to take the connections off the ECU clean them and plug em back in.. worked every time.. I would give that a shot Ted.. and if that doesnt work.. and I think you know what Im going to say next..... Megasquirt..heh.. :)

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