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Stumble under load and random miss at idle L28ET


hwvigo

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my 83 stock L28et  has a stumble at idle, dose not want to take throttle under load, will not build boost till high rpm, and will only make 4 PSI .

I have verified all injectors are working, all cylinders are firing, I can not find any boost leaks on the stock Jpipe , I have cleaned all electrical connectors and grounds per instruction on http://atlanticz.ca/zclub/techtips/electricalconnections/index.html , and checked all grounds , car is running stock engine management system. The car takes throttle very well at idle but sounds like it had a random miss 

 

any help would be very much appreciated.

 

 

 The stumble under load can be heard here at 25-30 secs in to vid very clear. 

    

 

 

 

Just a short vid of the issues with the car and showing it taking throttle at idle  

Edited by hwvigo
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You'll want to go through the 1983 FSM and follow the trouble shooting guide. It will find 95% of most of the problems with the stock EFI system. Have you done the basic stuff like timing, new cap, rotor, wires, plugs, replaced old vacuum lines, compression and fuel pressure test, etc?

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That fuel pump waxing and waning bothers me a bit, I too am worried about fuel delivery. Long shot, but I'm guessing no AFR gauge?

 

My guess would be a lean spike when you tip into throttle.

 

As with most fuel related problems....

 

Fuel pressure?

 

Tank condition?

 

Does it happen more often with full tank vs half full tank vs empty tank?

 

Fuel pump condition? 

 

Fuel filter condition?

 

Fuel line condition?

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That fuel pump waxing and waning bothers me a bit, I too am worried about fuel delivery. Long shot, but I'm guessing no AFR gauge?

 

My guess would be a lean spike when you tip into throttle.

 

As with most fuel related problems....

 

Fuel pressure?

 

Tank condition?

 

Does it happen more often with full tank vs half full tank vs empty tank?

 

Fuel pump condition? 

 

Fuel filter condition?

 

Fuel line condition?

 

The fuel pump is very loud and you can hear it waver when the turn signals are used 

 

No AFR gauge

 

have not checked fuel pressure yet need to get a tester 

 

Tank no clue - plan on pulling it soon-

 

fullness dose not seam to matter 

 

Fuel pump I was told is newish not sure of specs 

 

Fuel filter is getting changed this weekend 

 

Hoses getting changed this weekend 

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I only watched from :30 to 1:30 but noticed that both stumbles were after you had just turned left.  Typical of fuel sloshing away from the pickup tube in the poorly baffled 280Z tanks and happens to everyone below about a quarter tank.  Probably worse in a 260Z tank designed for carbs.  If you have a hole in the pickup tube it can happen with even more fuel in the tank .

 

And the fuel pump noise rising and falling with the turn signals is just a voltage issue, with the low output of the alternator at idle.  Mine does the same and I have pretty good output.  You can make the same noise by turning your lights on and off or flicking the fan on and off.

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I just imagined with the swap he would be using the higher amperage zx alternator, but even that unit doesn't provide the best amperage.

 

My fuel pump does that on big dips or when I'm using the fuel it seems to quiet down a bit more, I imagine the pump is under less strain during those times.

 

I think it is one of things mentioned.

 

Small fuel lines depending on what was done may be providing insufficient fuel (this would show up with a fuel pressure gauge very easily)

 

I have heard some people have run the carb fuel pump on an FI motor and it runs, but poorly. I doubt that that is the case, but I would check the fuel pump asap.

 

The rusty tank can either be clogging the fuel filter, or as new zed says it can definitely be missing a piece out of the pickup tube or the pickup tube itself might have disinitegrated a bit. That means if the fuel moves away or exposes the hole or doesn't quite reach up high enough to seal the hole then you are going to loose fuel pressure. 

 

AFR gauge or fuel pressure gauge will be really helpful here, although I suspect it is one of those 3 things.

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Wild guess TPS should not be filled with oil and water! Guess I'm ordering a new one. Also changed fuel filter. And all lines to 3/8th no change in problem still have not pulled the pump or checked fuel pressure.post-19246-0-08328900-1434921269_thumb.jpgpost-19246-0-26325300-1434921362_thumb.jpgpost-19246-0-00496500-1434921426_thumb.jpg

Edited by hwvigo
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