Thursday, October 8, 2015

Formula vs. Smog check: Feeling the (Fuel) Pressure!

You know the drill...

You get your registration renewal and in big block letters you see, "EMISSIONS TEST REQUIRED."

So you dutifully prepare to waste half a day sitting in your car inhaling exhaust fumes from the 30 other people ahead of you similarly afflicted. 

So it was with my Formula.

If you've kept up with this blog you already know the car's been an adventure having suffered more breakdowns in the 2 years I've had it than the last 5 cars I've owned combined.  Not that I'm surprised.  It's led a long life of commuting and road trips that have ticked off over 165,000 miles in its 20 years.

So things are gonna break.  I've been down this road before and the truth is that you're either in it for the long haul or destined to wave goodbye as it's dragged off to the scrap yard.

I was pondering the latter after suffering the indignity of the car failing almost every emissions standard except the gas cap.

Things are still tight and the last thing I needed was another dip into my wallet.  As it is I'm living on ramen noodles!

So armed with my failing report card I began my latest adventure.

The car failed on all the readings, CO, HC and NOx.  I've been suspecting the catalytic converter was failing but these readings went far beyond anything a single emissions component could cause.

The CO readings were slightly above the acceptable standard but HC was almost 2x.  HC means unburned fuel is leaving the exhaust pipe (rich.)  CO is also considered to be a condition of an overly rich fuel mixture but usually caused by weak spark not completely burning the fuel.  Remember we're dealing with chemistry here.  While CO and HC being high both indicate an engine being over-fueled (rich) they aren't the same thing.  

HC is unburned gasoline showing up in the exhaust stream.  It hasn't been chemically changed by the combustion process.  

CO is an overly rich condition as well but the difference is that it has been partially changed by the combustion process.  A weak ignition, compression loss in a cylinder, anything that interferes with the combustion process can cause this reading to go high.  

If HC is a raw steak, CO is that same steak but partially cooked.  Neither is edible.

I've had carbureted vehicles that ran lean but produced a high CO reading.  That seems contradictory but taken with the accompanying Low HC it made some sense.  The other component I failed to mention was that the reading only went high at high speed but was normal at idle.  That meant there was a problem with my ignition system not keeping up with the fuel being delivered.  

It's an example of the value of looking past initial readings and the importance of collecting all the information.  If I'd just taken the high CO at face value I'd be led to believe I had a fuel problem instead of an ignition problem.  Which ultimately turned out to be the case.

When computer controls get involved things get even more interesting.  The output from the O2, MAP, MAF and other sensors play an important role in keeping that ideal fuel ratio of 14.7 to 1.  Any failure of those measurements could effectively lie to the engine management computer and cause a response that makes it run inefficiently.  For example, a rich running engine with sensors telling it it's lean could literately flood the engine with even more fuel. 

HC and CO aside, however, the worst failure was the NOx readings.

It was almost 3x the standard.  NOx readings indicate how efficiently the engine is at using fuel.  High readings usually mean the engine is running too lean and heating up the combustion chamber.  But even a rich running engine (like mine) can make this reading go high if upstream sensors are getting bad information.  
It's kind of the canary in the coal mine since it's more of an overall indicator of the combustion process than just the HC or CO readings alone.  

Causes could be an overheating engine (which can happen from idling too long in that damned line) and/or a failing EGR ( Exhaust Gas Recirculation) valve.  The EGR is designed to force some spent exhaust back through the combustion chamber to cool it down thus removing the conditions for the gas to form.  If your EGR fails you lose that effect.

The other component that can affect NOx is the catalytic converter whose primary job is to clean up any leftover NOx before it leaves the tailpipe. 

So now we have some idea of the problem, time for the solution.

The Formula has always had a slightly rough idle which I attributed to mileage and age.  Thing is, with a completely new ignition system and no evidence of a compression problem on the cylinders, something else had to be in play.

Looking at the test results and noting that the car has been experiencing long starts intermittently it was time to dig deeper. 

I looked at the 2 most likely culprits that could cause both an excess of fuel and high combustion chamber temps.

That led me to checks for vacuum leaks (which can make high NOx worse) and fuel pressure.   I began by hooking up a fuel pressure gauge to the port on the fuel rail and watched the pressure over time.  What I noticed was a slow drop just barely noticeable but it was there.  

I then pulled the vacuum line off the fuel pressure regulator (FPR) and connected a vacuum pump to the fitting on the regulator.  It mimicked the result I saw with the Fuel pressure gauge, a slow bleed off but of vacuum not fuel.  The final test was to take a whiff of the vacuum line that connected to the regulator. 

Damning evidence, the telltale smell of gas where there should be none.  Gas fumes present in the FPR vacuum line indicate a ruptured internal diaphragm which compromises fuel metering and allows fuel into places it shouldn't be.

So I needed a new FPR.  That should help with the high HC readings but what about the NOx and CO?

The EGR valve on the Formula (and the FPR for that matter) is in an almost inaccessible area under the foot or so of bodywork that supports the windshield above.  Still I have my tricks and I was able to do some preliminary testing of the EGR valve itself.

Testing an EGR without the car running is pretty straightforward.  The first test is to try to move the internal EGR diaphragm assembly by hand.  If it moves freely then you know the EGR valve itself isn't frozen. 

This first test it passed.  On to the next test...

I connected my vacuum pump again and proceeded to give a few pumps. 

Nothing, absolutely nothing...

It was like attaching the vacuum pump to a straw which told me the internal diaphragm was ruptured.  Being a vacuum controlled valve no vacuum means it's broke.

The final test required the engine to be running.

With the engine idling I again moved the internal EGR assembly and the engine sputtered and died.  That's exactly what it should do and told me that the internal passages were clear enough to work with a properly functioning valve.

OK, so now I know I have 2 problems that are causing me all this grief with the emissions Nazis.  A bit of research and some shopping found me a deal on both parts ( thanks )

Thing is, even with a deal I was going to be out a C-note I couldn't really afford but I couldn't afford to be without the car either. 

Once more we fast forward to today and the first of my parts showed up.  The FPR.  I did a little more research to see how much of a pain it was going to be and if I was going to need more parts.

I made the decision that I had what I needed and if I didn't... Well, I was going to need more parts anyway so there was really nothing to lose. 

Instead of recounting the whole process of replacing the FPR I made a video.  I'll just touch on the major points you need to know.

Safety is always a primary concern so make sure you do the following before attempting the repair.

  • Disconnect the negative battery cable - Sparks and gas are meant for combustion chambers, not garages.
  • Depressurize the fuel system - A faceful of gasoline or worse spread all over the engine is not only annoying but dangerous.
  • The minute you open the fuel system gas is going to come out - make sure you've got rags or something handy to catch the fuel that's going to leak out the minute you pop off the fuel line and/or FPR

Once you've done all that keep the following in mind while you perform the repair...

  • Take your time - Better to do the job right the first time than wonder because you rushed through it.
  • Be organized - keep track of all the bits and pieces that you take off.  Nothing's worse than a 45 minute job taking 3 hours because you lost a screw you can't replace.
  • Follow directions - Use a manual or do some research on the Internet before you do anything.  You're not inventing the wheel here and chances are someone's done it before and wrote it down or posted it somewhere.
  • Use the right tools - For instance the retainer bolt for the fuel line clip that you must remove is a T-25 (Torx) the FPR retaining bolt is a T-27.  The T-25 kind of fits but you risk stripping the head of the bolt and ruining your day
  • Check your work - make sure you've got everything back where it needs to be.  #2 makes this a whole lot easier

So with that I'm going to close Part 1 and invite you to come along with me as I replace the FPR on my Formula in the video below.

Next time, we'll cover the EGR and see how that goes..

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