Fix It: Rebuilding a carburetor

It's been a rough couple of months and after over a year of picking up the slack for the Formula, the El Camino is starting to show the strain.  It started with the brakes getting a little noisy, then 3 of 4 tires developed sidewall bulges.  From there we had battery, alternator and wiring issues.  Most recently I went on the hunt for the cause of some poor performance issues that led me to a bad vacuum advance unit that was doing little more than providing a huge vacuum leak through a ruptured internal diaphragm.

On the bright side it's provided excellent material for my videos over the past few months...

It was successful completion of that last project that provided the catalyst for the latest round of underhood gymnastics.  While we may have succeeded in restoring additional timing to the engine when it needed it via the new advance unit we uncovered other problems with the ignition system.  Problems that led to ripping it apart down to the spark plugs to chase down a mysterious misfire that was cropping up under part throttle loads.  

Add in a tired carburetor assembled in desperation from the best bits of 2 used examples and things get even more interesting.  When that carburetor stops responding to the input of the go pedal we have to address it.  Issues with the fuel system were also making it harder to diagnosis our mysterious misfire.  If the carb is starving the engine for fuel, it could be causing a lean misfire but now we're straying dangerously close to grasping at straws.  We need a baseline.

Time for a rebuild.

That's the thing about classic cars.  No matter how much money you put into them, the more you drive the more work you have to do.

We want to continue driving and to do that we need to fix what's broke.  We can't if we're trying to herd too many cats.

Once we straighten out the fuel system we'll have a better idea of where our misfire problem is coming from.  It's a process of elimination and honestly something that should have been done a long time ago.

Below is the first of 2 videos documenting the process of rebuilding the Carter AFB carburetor currently living on top of my El Camino's engine. 

YouTube Automotive Treasure Trove

For a lot of you the weather is still very much "Winter" so you're probably not out and about or turning wrenches on your baby too often.  So what to do?

Well, if you're like me you find some favorite automotive videos on YouTube and maybe even subscribe.  Oh and don't forget the companion channel to this blog...Gearhead Garden Channel

One thing to remember about HOWTO videos on YouTube though.  Use the information at your own risk.  Don't take anyone's word as gospel and research from more than one source.  Anybody can post a video on YouTube even if they're a complete idiot!

This first example of a channel I follow comes from Scotty Kilmer.  I like Scotty, he reminds me of my step-dad and his information is usually pretty good.  He's a mechanic with almost 5 decades of experience under his belt that he's more than willing to share on his YouTube channel.  Along with videos like this, he also does a weekly Q&A show on his channel where he answers questions about car repair.  In this video he talks about the different grades of gasoline and when to use them.

This next example comes from a specialty automotive supply company called Eastwood.  I've known about Eastwood for 20 years and purchased specialty tools and products that I couldn't find anywhere else.   Their videos usually cover some procedure using their products.  The devil's in the details and Eastwood is a good place to go to deal with them.  There's a lot of good information that's helpful when you're trying to restore a classic.  This video features a project  79 Camaro Z28 and a primer on paint and finish techniques by TV's Keven Tetz.

The last Video is from a channel called Ramblin' Around.  It's basically a talented DIY Car guy named Jordan who details among other things the trials, tribulations and triumphs of putting an '87 Trans Am back together.  Lots of interesting stuff here.  This guy bleeds 50 weight but isn't full of himself.  It's the quiet guys who do the real work which is why I like his channel.  

So that's it.  I figure if I don't have any new content for you at least I can turn you on to someone who does.  Stay tuned though.  I still have the 95 Formula and will eventually get enough money and time to get it to pass emissions.  Expect a few videos and some writeups when that happens.  

You can be sure I'll detail those adventures here.

Formula Vs. Smog Check: Testing Fuel Pressure and the MAP sensor

On this page are a couple of videos showing you the results of my Fuel Pressure Leak-down test and how to test a MAP sensor on an LT1 V8.  These are two important tests when you've got an emissions problem especially if the car is running rich.  

The fuel rail will bleed off some pressure over time but not all of it in a few minutes!  Anything more than a couple of PSI drop after a few hours means there's a leak in the system somewhere.  

It's important to mention that if at all possible, you really want to isolate the individual components of the fuel system when troubleshooting.  If you're testing the fuel rail and you don't know the condition of the fuel pressure regulator, for example, then ideally you'd want to block off any return lines to the tank so you don't confuse a bad fuel pressure regulator with say a stuck check ball in the fuel pump. 

If that's not possible then you're only going to get a general idea that there's a problem.  In which case you'll have to take into account other factors.  In my case I know the Fuel Pressure regulator is good ( brand new ) so I'm fairly confident that any pressure loss seen at the rail is going to be isolated to a component of that rail.  Note that all of this testing is done with the engine off.  With the engine running other factors like the Fuel Pump, Injector pulse time and engine vacuum come into play which can mask a basic fuel pressure problem.  

Incidentally, you won't see it in the video but the way to isolate the fuel system to check for what part is causing you the headaches involves either pinching off the return lines or installing a shutoff valve.  I don't have the valve and I'm not about to start pinching anything made of plastic that's been baking under the hood of a car for 20 years.   So I didn't do that test but a rich mixture is more likely to be a fuel injector than a check ball in a fuel pump at the back of the car.  I was more interested in seeing if there was a drop in pressure in general.  

Once I can afford a new set of Injector O-rings I'll be pulling the injectors out, priming the rail and seeing which one(s) are leaking.

As for the MAP sensor testing, well, it's always the first thing blamed right behind the O2 sensor when an engine is running to rich or lean.  That makes sense since those sensors as well as the MAF (Mass Air Flow) provide critical data to the engine's PCM to adjust the mixture rate.  There are others like the Coolant Temperature sensor, Throttle Position Sensor and others but basic emissions troubleshooting will have us starting at the MAP sensor since it's usually the easiest one to access and check.  

The MAP sensor's job is basically to read engine vacuum and send a signal back to the PCM.  With an LT1 the PCM takes that vacuum value and compares it with the Air flow data from the MAF to see if the two values complement each other.  That allows the PCM to make more minute adjustments to the fuel mixture for performance and emissions.  It's also a sanity check for each sensor since the failure of one can be compensated for by the other.  Either one can provide enough data to allow the engine to continue to run but not as efficiently.

Some cars only have a MAP sensor but LT1's are a bit of a wild animal when it comes to tailpipe emissions. Getting the engine into emissions compliance takes a lot more data points than your average grocery-getter especially with high compression that lends itself to problems with NOx and CO issues.

So if you ever wondered why there's so many wires under your hood, now you know....

For me this is all kind of a reference exercise but for  you it might be instructional.  Enjoy!


Fuel Pressure testing...

Checking the Manifold Absolute Pressure Sensor (MAP)