EVAPORATIVE EMISSION PROBLEMS

Posted by Matthew Schroeder from Rotary Performance.com

P0441 / P0442 / P0443 / P0446 / P0455 / P0456: Code are all related to the evaporation emission system. The system periodically test that the fuel system sealed from the outside world. This system consist of an air pump and pressure transducer assembly that pressurizes the fuel tank and a Purge Solenoid that vents the pressure into the intake when the test is completed. It takes a few drive cycles for the computer to be satisfied that everything is OK. So, there is a delay before the system shows that all emission systems are ready as far as the emission testing is concerned.There are not too many places in the system that are problematic. I'll discuss them in order of how often we encounter them here at Rotary Performance.

First, the purge solenoid. The plumbing and electrical connections are pretty trouble free, but the solenoids themselves do fail. The resistance between the two terminals should be around 30 ohms. Above 40 ohms or so, the computer detects that they are faulty. This solenoid is in plain sight near the oil filler neck.

Second, there are air leaks in the system. Sometimes you get small, medium, or large evap. leak codes from the computer. The classic problem is the gas cap. The cap has a check-valve in it and should allow air to flow into the tank through the cap, but air should not be allowed to escape. Also, the o-ring can fail to seal. Beyond that, the next most common place for evaporation emission leaks is from the threaded rings that hold the fuel pump and level sending units in the fuel tank. When they fail, they will have cracks on their sides. This allows them to stretch and keeps them from compressing the o-ring seals enough to seal the covers to the tank. Of note, there is a level sending unit under each tank. Sometimes, these are simply not tightened sufficiently. An easy test is to fill the tank completely and look for fuel leakage on top of the tank.

Rotary Performance.com

GAS SMELL AND FUEL LEAKS...

Posted by Matthew Schroeder from Rotary Performance.com

The RX-8 is known for fuel leaks. Fortunately, it is almost always has to do with the fuel pump.
Unfortunately, when the leak is from the top cover for the fuel pump it comes as an entire fuel pump assembly.  You need to determine if the pump cover is leaking around the large seal that holds it to the tank, or if the pump-outlet -tube is cracked.
With the left rear seat base, and the metal inspection cover removed, you will likely see and smell gas. If it is a cracked outlet tube, there will be a hairline crack down it's length. It typically appears on the bottom side of the tube and will be visible with the fuel line still attached. A small mirror can help you see it. If you don't see it, start the engine and look for it dripping. It should be really obvious. If not, the problem lies with the seal between the tank, and the tank cover. Often, when the fuel pump is replaced, the big plastic nut that holds it down will not be adequately tightened. Sometimes, that plastic nut will crack on it's side when it gets old. A careful inspection should reveal your troubles.

RotaryPerformance.com

Nikki Carburetors

Posted by Matthew Schroeder from Rotary Performance.com

The Nikki carb that came on the 1979-1985 12A powered RX-7 is pretty reliable and performs well in most circumstances. With regular driving and periodic fuel filter changes, they are pretty trouble free. The introduction of E-10 Ethanol gasoline in many parts of the U.S. has however presented problems. These break down into two categories: Mixture and Maintenance.

All carburetors mix a quantity of fuel proportionately to a quantity of air. E-10 gasoline has less specific energy than the fuel that was sold when the cars were new. Since the carburetor does not know this, the result is a lean mixture. This can create running and performance issues that often manifest themselves as either starting and idling trouble, or a lack of smoothness or surging at cruise. The cure is changes to enrich the fuel mixture in the idle (or slow) circuit and often in the main circuit as well. While you can sometimes smooth out the idle pretty well with the mixture screw on the side of the carb, it is usually still a bit lean at idle, and does little to help leanness at cruise. The best answer is to resize the pilot jets. This type of work is best done with a dynometer and feedback from an air/fuel ratio gauge. When done correctly, the carburetor will work smoothly at cruise and the idle will be set with the mixture screw somewhere between 1 and 2 1/2 turns out. When tuning any carburetor, one must take into account each circuit and the transitions between them. "Seat of the pants" tuning is a poor way to get the desired results.

The second problem that we often encounter (which can exhibit many of the same symptoms above) stems from maintenance and driving habits. Many 1st generation RX7's are not driven frequently. This causes modern fuels to 'skunk.' When diagnosing running problems, we consider gasoline that is more than 3-months old to be suspect since ethanol enriched gasoline both absorbs moisture and degrades quickly. We advise that you drive your cars enough to burn through a tank of fuel at least every 3 months. Also, poor maintenance of fuel filters and gas tanks that are rusty can allow foreign matter to clog jets and passages inside the carburetor. The take away is this: Before modifying a carburetor that was working fine, you need to verify that it is clean and functioning properly first! Also, remember that it is very common for mechanics to mistake ignition problems for carburetor troubles.

At some point in your quest for rotary performance, you Nikki carburetor will become a performance bottleneck. There are aftermarket carburetors and intake manifold kits available for the RX-7, but they all have their drawbacks. We now offer modification services which increase the flow by about 65 CFM and still allows for proper idling and vacuum secondary control. This is a service that is done to your carburetor and tuned on our dyno for your engine. Give us a call or email us for more information on this or any other parts or services you may need. 

Rotary Performance.com