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Discussion Starter · #1 ·
Recently I've noticed my Shadow lose power but only on weird occasions. Under full throttle, it will suddenly cut from full to reduced power (feels like about half) and occasionally on the highway I will just lose power completely and the car coasts until I pump the pedal enough that power kicks back on and I can accelerate back up to speed. This weekend I noticed it happens more often on the highway going 80-85 compared to 65-70 so I'm suspecting something in the fuel system. However, the fuel pump, fuel pump relay, injectors, and fuel filter have all been replaced within the last few months. The only thing I can think of is the fuel pressure regulator (17 year old stock). Any ideas?

its a 93 Shadow ES 3.0 pretty much all stock
 

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Auto or manual trans.
Was problem present before replacing fuel system components?

New does not always = good.
Has fuel pressure been verified to be correct under the problem condition.

Any fault codes set in the engine controller or trans controller if an auto trans?
Restricted air intake
Restricted exhaust
Collapsed vacuum line to Map or FPR
 

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Discussion Starter · #3 ·
its a 5 speed and if i remember correct it was having the same problem before the parts were replaced but it happened a lot less with the new parts. no engine codes, and i havent tested fuel pressure because i dont have a tester and the fuel system doesnt have a service port -_- ill check the vacuum lines but the way the power instantly cuts in and out leads me to believe fuel pressure is dropping off or a bad wire is turning off the injectors or something. but I would think if it were a wire it would cut in and out when i hit bumps but it doesnt
 

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There is no service valve on a 3.0L.
You need an adapter that has the service valve built in to connect the gauge and goes between the fuel supply line and fuel rail.
It would be part of any Master Fuel Injection Pressure Tester Kit.

An engine is nothing more than an air pump.
It brings air in and exhausts air out.
Fuel and ignition are add ons to make the engine run.
If the exhaust is restricted you cannot get the air out so in turn you cannot get more air in, when that happens you lose power.
If it is restricted enough the car will not run.
It would be the same as you breathing, if you inhale and do not exhale you can no longer bring fresh air in.
 

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Discussion Starter · #8 ·
An engine is nothing more than an air pump.
It brings air in and exhausts air out.
Fuel and ignition are add ons to make the engine run.
If the exhaust is restricted you cannot get the air out so in turn you cannot get more air in, when that happens you lose power.
If it is restricted enough the car will not run.
It would be the same as you breathing, if you inhale and do not exhale you can no longer bring fresh air in.
I understand that, I just don't understand how an exhaust restriction could cause power to INSTANTLY cut in and out.


I had problems with the speed sensor a while back but I just had to pull out the connector and clean it out, haven't replaced it. But again, I don't understand what this could have to do with it
 

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Got a loose engine ground anywhere?
 

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I understand that, I just don't understand how an exhaust restriction could cause power to INSTANTLY cut in and out.


I had problems with the speed sensor a while back but I just had to pull out the connector and clean it out, haven't replaced it. But again, I don't understand what this could have to do with it
exhaust can INSTANTLY have a restriction in it if the cat convertor substrate is loose and rattling around inside, it then can turn restricting the exhaust flow and then return to normal allowing exhaust to flow, thats how exhaust can INSTANTLY have/become a restriction. as for the speed sensor, it registers how fast the car is going to the ecu,if it INTERMITTENTLY drops the signal to the ecu it can cause a lack of power because the ecu no longer knows how fast the car is going.
 

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Discussion Starter · #11 ·
huh, learn something everyday. My cat definitely could be messed up. Its got 230k and I've beat the piss out of it for the last 30k. Once I get back to school I'll check out the fuel pressure, exhaust backpressure, cat temp, & engine grounds. Surely one of those will pinpoint it. Thanks for the input
 

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I have seen baffles in mufflers do the same thing.
Also, I have seen Cats fall apart and the pieces get lodged in the muffler.

As odd as it sounds way back in the day we had a Ford Pickup(carburated) with similar issues and it turned out to be a dead bee in the tank and when it sucked up against the sock the truck would lose power, when the power loss occured pump suction died, the bee fell away and the truck would have power again until...

We also had a customer when I was at Jeep that bought a used Cherokee and a week later was complaining that he was losing power at 45 mph.
Turns out he placed a spare qt of oil under the hood and placed it on the L/S inner fender 3-4" from the air intake snorkel on the air box.
As airflow and engine vacuum increased it sucked the bottle right up against the air intake blocking all air flow.
It was so bad it caused the hard plastic airbox to collapse.

Ford also used to use a double walled front pipe and the inner section would collapse creating an exhaust restriction.

The point is never assume something is ok.
Verifying basics are correct takes away all of the guesswork.
 

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Discussion Starter · #13 ·
I've figured out a little more about the problem. When the power cuts away on the highway, I can press in the clutch, hold the throttle steady, and the rpms stay constant for some reason. Vacuum at idle is 20", just put a ported 52mm TB recently. Haven't been able to check fuel pressure, but I did test compression and it was fine. Another weird thing I noticed is, when the power cuts, if I press the clutch and close throttle, it just idles normally. WOT also works just fine, problem only happens inbetween, which leads me to believe problem only happens when ECU is in closed loop. Also did a cooling system test in class and then the temp got up to 195F (using infrared thermometer), when the thermostat should open, coolant temp read just over 2/3 on the gauge. However whenever I'm driving temp gauge never goes over 1/3 unless I'm sitting idling for a while. So I'm thinking I should replace the thermostat, coolant temp sensor, O2s, and maybe spark plugs (looked kinda gray & burnt)?
 

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What does your vacuum gauge do when it hits its power loss?
 

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You are going to need to...
1)Verify fuel pressure @ idle/after long run time/during the problem condition
2)Check exhaust backpressure
3)Connect the vehicle to an oscilloscope and watch coil oscillations and KV requirements under load.

Being in an auto class you should be able to do all of this.
 

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I'd be interested to know how it reads when it has it's issue
 

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Discussion Starter · #18 ·
Don't really have time to do these tests in class, I'm pretty much on my own and on a small budget. Can anyone recommend some guages I could install and see what happens when power drops? Probably need to install fuel pressure, oil pressure, and vac/boost. Anyone recommend a gauge set preferably <$75?
 

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Auto Class is the only place you may have access to a scope.

Will they allow you to borrow tools such as the exhaust backpressure adapter?
It screws into the exhaust where the O2 sensor is and you connect a vacuum/boost gauge and read backpressure.
If not you can remove the O2 sensor(leave it connected electrically and drive the vehicle under the problem condition to see if the issue goes away.
Just be careful since the car will be loud and exhaust will be flowing underhood.

To check fuel pressure either buy/borrow a fuel pressure gauge with a long enough hose so you can tape the gauge to the windshield and watch pressure under all conditions.
You will also need a vacuum/pressure gauge to watch as rail pressure and vac/pressure are directly related.

It is usually cheaper to buy the needed tools that you will have forever as opposed to guessing and throwing parts at the issue.
 
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