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skib

82 Turbo cutting out, Im stuck.

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skib    118

13581959_10208404043276486_3351890997338

Stock 82 turbo, has been a daily as long as Iv owned it and always runs great.

Started cutting out and running progressively worse over the course of a few days.
Fires up and idles perfectly, but wont really rev past 1500rpm.

I can get it to go higher but its when the boost gauge hits 0 or positive pressure its cutting out,
not getting enough fuel and will pop out the intake.


The timing is set to 20deg on the dot, brand new CHTS, O2 sensor, plugs, cap, rotor, coil, fuel pump, AFM is cleaned and wiper arm set on fresh carbon, all my electrical plugs are either brand new or cleaned, I can hear all the injectors firing ect.

 

Have done all the FSM EFI related tests and now Im starting to get stumped.

Iv even tried moving the AFM gear rich 4 teeth as a test just to see what would happen... no change.
(I normally hate touching that because it tends to just be a band aid fix for some other issue)

When I have the air box off and rev it to where it starts to cut out and have a friend push the flapper open a little more with a screw driver it goes away and revs strong like it always has....


... Really not sure what to look at next, Iv never had an issue like this with any of my L28et cars.

 

Edited by skib

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you said:

"When I have the air box off and rev it to where it starts to cut out and have a friend push the flapper open a little more with a screw driver it goes away and revs strong like it always has...."

 

what flapper do you mean?  the throttle body valve?  that circle that blocks the throttle body  and turns to open up when you press the gas pedal?   sorry if you know what I'm talking about but are talking about something else (you seem to know what you are talking about, so i might be misunderstanding what you're talking about).

 

If opening it more seems to be helping a whole lot, then I'd start looking at that.  for example, does the throttle plate open all the way if you press the pedal (for that one you'll need someone to press the pedal all the way in while you look, and you shouldn't be able to force it open any more than it opens on it's own)?  if so, then i'd check if the TPS is well hooked/attached to the throttle plate;  it might think that the plate is not fully open and tell the ECU to send less gas that it needs...  

 

if pressing the pedal does not fully open it, then i'd all the elements between the pedal and the throttle plate.  you might need to adjust something or another for wear or stretch.  

 

all that said, a throttle plate that does not fully open would not produce the symptoms you mention (unless there is an issue in the connection with the tps, like I said), they'd just make is like you haven't pressed the pedal all the way. I'd still check it, but...

 

if you meant that you only open it a little bit more and it solves the issue, then it could be that for some reason, your engine is getting too much gas/too little air (my car runs insanely rich, i'm working on that, and when it's too rich, it'll just bog down.. same as if too lean..  it's just creating misfires, one way or the other).  does the exhaust smell rich?

 

have you checked your fuel pressure?  a new pump might be overpowering the stock regulator, if it was old and tired to begin with. it might even leak into the intake, although that would create issues at idle.  an easy way to test the regulator is to unplug it's vacuum line and smell it.  if it smells like gas, it's done for.  if not, then plug it back, start the car, unplug it and either blow in it and suck (really hard) to see if that changes way the engine runs.  it's rudimentary, but shows you that it works (not necessarily well)....  

 

let us know.

Edited by supernova_6969

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skib    118

 

 

what flapper do you mean?  the throttle body valve?  that circle that blocks the throttle body  and turns to open up when you press the gas pedal?   sorry if you know what I'm talking about but are talking about something else (you seem to know what you are talking about, so i might be misunderstanding what you're talking about).

 

The "flapper" inside of the air flow meter.

By pushing it farther open Im telling the computer its getting more air than it is to get it to add more fuel,

confirming my suspicion at the time its cutting out because of a lean condition. (I dont have a wideband yet)

 

In the time preceding and during the issue starting nothing was changed. Everything functioned perfectly. TPS is good and tests correct per FSM test.

 

Tested it with a reman AFM and brand new harness connector, no real difference.

Fuel pressure tests show ~31psi at idle with vacuum plugged into FPR.

Pressure and engine cut out at 0 on the boost gauge same as before with fuel pressure stopping dead at 38psi 

 

 

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skib    118

I've expended quite a bit of work on engines that just needed new plugs, cap and rotor.  Did you try a basic tune-up?

 

Yes..... Its all in the original post.... 

Iv built enough stuff that if all it needed was a tune up I wouldn't be posting.

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so, yeah, you do know what you are talking about;  I'm the one who completely misunderstood what you were talking about re: the flapper. 

 

I just watched your video, and I was wondering if it was me, or if the car sounds like it's struggling the whole time?  It might be me or the sound recording, but it sounds like it runs rough the whole way, and worse so when you get close to WOT....

 

Is the AFM output testing included in the tests you did as per the FSM? 

I know you tried to change the AFM settings (moving the teeth so it to thinks it's got more air coming in) and it didn't help all that much.... I find it weird that when you fool it into thinking that it's getting more air by setting up the mechanism differently, there is no change, but when you fool it manually by physically opening it more (which in the end should be exactly the same thing as jumping some teeth I guess), then it works..    have you been able to see if there is a significant difference in how much each technique is changing the AFM output?  maybe the teeth changing thing gives it too much or too little, and the screwdriver forcing it open gives it just enough....  

 

one thing you can do I guess is to see if, when you do the screwdriver but push it all the way open and see if it makes it soooooo rich that it stalls the car out, or at least start smelling very rich (that can be done at idle, I suppose). that could validate that the AFM is working (not necessarily well though).

 

another option (I don't think so, but...) is that you might have the right amount gas going in, but that for some reason (I wouldn't know what) you engine has a problem that makes it want more, want to run rich.  When you do the test with the screwdriver thing, does the exhaust smell like it's too rich (provided that the person holding the screwdriver is holding the flap up JUST ENOUGH to make it run well, not all the way up)?

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skib    118

 

I just watched your video, and I was wondering if it was me, or if the car sounds like it's struggling the whole time?  It might be me or the sound recording, but it sounds like it runs rough the whole way, and worse so when you get close to WOT....

 

 

 

That's just my shitty phone, it fires right up and idles no problem even after not being touched all week.

It doesn't even hit WOT or get close. Where it cuts is when its hitting atmospheric pressure (0 on the gauge) where the FPR should be adding more fuel being a 1:1 ratio. Its stopping dead at 38PSI where it should be able to hit at least 45PSI under full boost.

 

And its running a re-manufactured AFM now with new harness plug, the physical AFM tests,changes where on the other one.

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mmm...

 

on my car, I only hit 0 psi (aftermarket gauge, and on the Megasquirt reading, which has it's own pressure sensor) when I am at WOT.   anything less than WOT has at least some vacuum.   at least when i'm driving, I've never WOT while the car is standing still, I've had it drilled in me that you shouldn't rev without load if you can help it..  

 

 

do you happen to have a vacuum gauge around that you could use and compare that reading with your car's gauge's reading? 

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NewZed    56

How about a holed FPR diaphragm?  At intake vacuum a small amount of extra fuel gets pulled in to the intake manifold.  At any boost level at all intake air gets pushed through the diaphragm, replacing fuel with air in the fuel rail.  Instant lean condition.  Plus only the FPR spring is controlling fuel pressure as the air leaks past the diaphragm so pressure control stops.  Fuel is much more viscous than air so the difference between the two leaks would be large.

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skib    118

Thats a good theory, and I just swapped over another FPR off a buddies running car to check mine and it still does the same thing.

 

The thing that drives me nuts about it is it will fire and idle perfect, and I can drive it if Im easy on the throttle and keep it out of boost.
But, the second it goes into atmospheric/positive pressure it cuts, even with the known good regulator on there.

So far the only test that has made a note worthy difference is when you hit the cut and manually push the AFM door open farther
tricking the system into feeding more fuel does it stop cutting and revs freely. 

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NewZed    56

Pushing the AFM vane makes the injectors stay open longer, so more fuel at the low pressure.  So it does seem like a fuel supply problem.  

 

Have you tried pinching the fuel return line to verify that fuel pressure can actually go higher than 38 psi?  You could pinch and rev and should get the same effect as opening the vane.  Or pressurize the FPR reference (vacuum) hose to increase fuel pressure.  Could be the problem is that fuel pressure just isn't rising when the intake manifold pressure does.

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skib    118

Man, what a pain.

 

I finally tracked down the culprit.... a bad connection at the ECU pin connector.

If I wiggle the wires on the middle plug it will either rev and drive hard under boost like normal... or kill the car lol

Anyone know how to unpin the connector wires? Iv unpinned plenty of plugs but these are extra small and proving to be a challenge to remove. 

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