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Discussion Starter #1
My 2002 Vulcan is having issues with low power. Additionally, there is a persistent P0174 code that I have been unable to fix. I do not know for certain if the two issues are related. A while ago, I noticed that my car had reduced power when going up hills. At the time, this wasn't terribly noticeable except for some very steep hills (where typical traffic is under 35 mph anyway), so I chalked it up to engine age. Two weeks ago, my water pump rather suddenly went bad out of town (as in the bearings failed completely to the point where the belt couldn't run the alternator). As a result, the car got hot (never into the red area on the gauge, but pretty close). I replaced the water pump, but since then, the power issue has gotten noticeably worse, to the point where it struggles to maintain 40mph over some pretty typical highway hills (which means it's not really safe to drive).

I have done the following:
New water pump
New drive belt
New air filter
New fuel filter
New spark plugs (cylinder 5 was oily, others seemed okay for their age)
New-ish wires (replaced these separately about half a year ago)
Cleaned MAF sensor
New DPFE sensor
New PCV, elbow, and hose (old one was cracked, but replacement didn't seam to make a difference)
Carb cleaner test for other vacuum leaks (nothing noticeable)

In addition to the aforementioned P0174 code, I once found a P0305 (which was very intermittent and has not recurred since changing the spark plugs), and a P1401 (which hasn't returned since changing the DPFE sensor). I have never found a P0171 code, any of the EGR or catalytic converter codes, or any other code for that matter.

My bank 1 fuel trims seem normal (LTFT near zero, STFT +/- 5ish); my bank 2 fuel trims are very high (LTFT 20-25, STFT usually positive). My upstream O2 sensor readings seem okay (back and forth between 0.1ish and 0.9ish), downstream less certain (seem to stay in the 0.1 area; have had trouble figuring out what these readings should be on this car). The throttle position readings seem sensical (16% at idle, 100% at floored).

At this point, I'm hoping someone might have an idea for vacuum leak locations that would only affect one bank. Otherwise, I fear I may be getting into the "painful zone" (head gasket, catalytic converters, or actual engine internals - which are a complete and total mystery to this mechanically-inclined but non-car guy).

Thanks in advance!
 

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Might want to do a compression check to find out the health of the engine after overheat. Without the pump turning you can get hot spots in the engine which won't show on the overall temp gauge. There is a connection that I found pretty loose on my 2001 shown by the yellow arrow.
 

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Discussion Starter #6
They don't increase or decrease at 2500 from the idle trims?
Apparently I didn't do a very good job of noting my fuel trims the first time; just checked again and found:

725rpm (idle) - bank 1: 10% - bank 2: 30%
2500rpm - bank 1 : 0% - bank 2: 22%
 

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You have a nasty vacuum leak on bank 2 (front bank). Possible UIM / LIM gasket issue. Probably have a not so huge vac leak on bank 1 also.
 

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Discussion Starter #8
You have a nasty vacuum leak on bank 2 (front bank). Possible UIM / LIM gasket issue. Probably have a not so huge vac leak on bank 1 also.
Is there anything that would primarily affect bank 2 that I should look at before pulling the intake plenum to check/replace the gaskets? I've used soapy water and carb cleaner and found nothing.
 

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You might want to verify the spark plugs, wires, and coil on bank 2, again. Make sure that the spark is actually getting to the tip of the spark plug, and is not fouled out.

A cylinder that is not firing can cause a false lean code because of the unburned oxygen getting to the oxygen sensor.
 

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Also, I didn't see any mention of fuel injectors above.

Have you checked these to make sure that they are all working?

A clogged injector might be responsible for this, too.
 

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Discussion Starter #12
Also, I didn't see any mention of fuel injectors above.

Have you checked these to make sure that they are all working?

A clogged injector might be responsible for this, too.
I've done the "use a screwdriver as a stethoscope and check for clicking" shorthand test, but nothing more involved than that.
 

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If I were in your shoes, I would attack the problem like this:

Do a compression test on the bank 2 cylinders, and check the spark plugs, wires and coil to make sure they are performing as expected, and not arcing/grounding out, or having any carbon tracking issues.

If you find a cylinder that is significantly lower on compression, then the next step is to perform a leak down test to determine where the compression is going. This will determine whether you have a tough repair ahead, or a relatively easy one.

If the compression on all of the cylinders seems reasonable and you didn't find any issues with the spark, then that leaves fuel and air.

At this point, I'd pull the upper intake manifold and carefully test the fuel injectors.
(Unplug the coil, and remove any other potential ignition sources, to make sure you don't set yourself on fire!)

Inspect the UIM carefully making sure that there are no holes or cracks in it, and then reinstall it using new gaskets and seals.

If you made it this far, I would hope that you would have found and corrected your problem. I can't think of anything else that would manifest itself as you have described.
 
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Jim Beckett
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