Symptoms - So I was telling the guy ... the check engine light on my truck started coming on about 10 minutes after starting (a little less if it was already hot). Also, gas mileage was down to about 13 mpg around town and it smelled like it was running rich. I scanned Dejanews (like I tell everyone who asks me a question to do) and saw several mentions of the fuel pressure regulator. As it turns out, that was precisely my problem, but I also changed the Exhaust Gas Oxygen sensor for good measure - my truck had 96K miles at this point. What follows is a step-by-step procedure to diagnose and change the fuel pressure regulator.
Diagnosis - Since the check engine light started this adventure, the first thing I did was read the stored code with an Engine Code Reader (I borrowed one, but they are about $40 at Advance Auto Parts). My engine was storing code 173 - Heated Exhaust Gas Oxygen sensor (Bank #1) reading rich. Note that a '92 has only one oxygen sensor so Bank #1 has no real meaning. As I stated, at this point my truck had 96K miles on it so I went ahead and changed the sensor. Let me say that it helps to have long arms when changing this item.
At this point I was fairly certain that my fuel pressure regulator had failed but I also didn't want to spend a lot of money on parts (or special tools) that I might not really need so I still had some checking to do. The best way to check the operation of the regulator is to get a fuel pressure gage (about $35 at Advance) and read the fuel pressure at the test port on the fuel rail (right next to the regulator itself). The regulator/fuel rail are bolted on the passenger's side intake manifold near the oil fill tube. Check the various service manuals for the proper numbers, but in general you should see about 30-35 psi at idle. Since I was feeling especially frugal and a new regulator costs only $70 at Advance, I decided to use plan B to check the regulator.
| Plan B involves pulling two vacuum lines off the octopus at the back of the
driver's side intake manifold. While you are at the octopus, check to see
that the cap on the port pointing at the firewall is in good condition.
Sometimes, this cap will crack or blow off - if so replace it before going
further. Next, pull the two lines which attach to the octopus with the
angled (90 degree) connectors. One leads to the fuel pressure regulator and
the other to the air intake but you can't tell which one is which at the
octopus. So, pull them both and check for raw fuel in the vacuum lines.
Direct them into a glass jar, wear eye protection, and have a friend turn
the ignition switch to the ON position - DO NOT START THE ENGINE. If
you get fuel spilling into the jar or if fuel was in the lines to begin
with, your fuel pressure regulator has failed. Even if no fuel shows up in
the vacuum lines, it is still possible that your fuel pressure regulator
has become stuck (This is what had happened to my truck). Also, since you
are in the general area, pull the PCV valve out of the valve cover and
shake it to make sure it rattles. If it doesn't rattle, replace it first
before making any other changes.
Now I was even more certain that it had to be the fuel pressure regulator that was causing my problems so I decided to go ahead and replace it. For my truck - a '92 XLT - no special tools are required. So now we get to the real procedure.
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Procedure - First, depressurize the fuel system. Open the fuse box on top of the passenger side wheel housing and locate the fuel pump relay fuse. Start the engine and then pull that fuse and let the engine run until it dies. Crank the engine a few more times just to make sure the fuel system is depressurized.
To make your life easier (unless you have hands the size of a five year old) you'll need to get a few hoses out of the way. First I removed the air hose from the air filter to the throttle body. Then, I drained about a quart of coolant out of the radiator and disconnected/removed the radiator hose which feeds the water pump. Finally, I used some bungee to lift the A/C hose out of the way a little bit. Having done this, the fuel pressure regulator is out in the open, ready to change.
The fuel pressure regulator is attached to the fuel rail with two 8mm bolts. To remove these, I used a 1/4in drive ratchet with a short (2in) extension and a swivel. To get to the bolt closest to the firewall I slipped the extension and swivel underneath the wiring harness that runs through this area. After removing the 8mm bolts I then used a 17mm open end wrench to disconnect the fuel line that enters the top of the regulator. Once this is free, you can wiggle the regulator out of the fuel rail and disconnect the vacuum line. At this point fuel will probably spill onto the exhaust manifold so a cool engine, eye protection, and a fully charged fire extinguisher are all good to excellent ideas.
Closure - Then I installed the new regulator, reconnected all the hoses, poured the coolant I saved back into the radiator, reinstalled the fuel pump relay fuse, flooded the fuel rail area with some water to dilute any spilled fuel, re-pressurized the fuel system by turning the key to the ON position a few times, and started it up. It took me about an hour to complete the change - which incudes going to the local auto parts store to buy a new regulator in the middle of this procedure. Now my truck runs peppier, no check engine light, and all is right in my world - at least for the time being.
When my 92 Sport displayed the exact symptoms listed, replacing the fuel pressure regulator fixed the problem. What's interesting is that the dealer wanted $151.00 for the part, Napa wanted $113 for it, and Autozone wanted $73.00 for it. I bought the Napa/Echlin (distributed by Dana), and the return fuel line would not go on. I took it back and got the Autozone, manufactured by Sorenson, and the return line went on just like OEM.
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