Q&A / Tech

Ask Away! with Jeff Smith: Troubleshooting and Tuning a FAST EZ-EFI Fuel Injection System


I recently bought an EZ-EFI throttle body fuel injection system from FAST for my ’70 Buick Skylark. I installed it according to the instructions and it started and ran pretty good for the first few days. I’ve noticed now that the engine runs very rich and it’s starting to load up the spark plugs. I’ve not changed any of the settings yet it runs a lot richer than before. My idle air-fuel ratio is 13.0, the cruise setting is 13.5, and wide open throttle is 12.5. I don’t understand why the engine seems to run much richer than these settings. You have any ideas?



This is an EZ-EFI throttle body on a big-block Chevy we did a couple of years ago that worked out very well. Attending to the details will make a big difference in how the system works.

Jeff Smith: We’ve installed several of these new-generation, self-learning fuel injection systems and they seem to work very well. But there are a couple of areas where it is essential that the initial installation be performed properly and then attention to details can make all the difference. Let’s see if we can focus in on your problem.

The first thing to emphasize is that the main power and ground wires are in fact connected directly to the battery. All EFI systems operate on electrical signals from sensors that normally operate on a 0-5-volt scale. This leaves very little room for error with regard to proper grounds. So it is essential that the main power and ground leads go directly to the battery. This allows the battery also to operate like a giant voltage spike suppressor which allows the electronic side of the system to operate normally. Don’t be afraid to lengthen either or both power and ground leads if that what it takes to plumb them directly to the battery.

The next item to try is to run back through the initial calibration process again. This essentially purges the computer’s memory of the previous tuning changes. This means starting with engine displacement, idle rpm, rev limit, fuel pressure, and resetting the throttle position sensor (TPS) calibration. Then set your idle, cruise, and WOT settings the same as before. Once all this is complete, the engine should run as it did when you first installed the system. Drive the car for a couple of days and make sure to shut the engine off and restart it several times during the test. You may notice that the engine begins to run rich again after several cycles of running and then shutting the engine off. If the over-rich condition returns, I think what you may be experiencing is a very common problem where there is a leak in the exhaust system that is causing the over-rich air-fuel ratio problem.

If you’ve ever driven a car with an exhaust leak, you can often hear a very audible tick-tick-tick from the exhaust. The tick you hear is the result of an exhaust pressure spike that travels down the exhaust pipe, finally exiting after the muffler. When that pressure spike hits the atmosphere, it sends a reverse or low-pressure pulse back up the pipe and back to the engine. This low-pressure spike will pull in outside air as it passes through the leak area. Think of it like a siphon pulling fresh air in from the outside. Unfortunately, this can cause problems with a self-learning EFI system.

All of the self-adapting EFI systems use a wide-band oxygens sensor placed roughly at the header collector, downstream in the exhaust system. The sensor reads the exhaust gas and the engine control unit – the computer (ECU) uses the information as feedback to the tune. As their name implies, these wide-band sensors (WBOS) operate over a much wider area of air-fuel ratio from very rich at 10:1 to very lean at 20:1. All WBOS operate the same way. They do not actually measure the ratio of air to fuel. Instead, they are calibrated to sense the amount of free oxygen in the exhaust system. The ideally-balanced chemical air and fuel ratio for any fuel is called the stoichiometric ratio. For gasoline, this ratio is 14.7:1. With lean air-fuel ratios such as 15.8:1, there is more free oxygen in the exhaust because there is minimal fuel to complete combustion. This is called an excess-air ratio. An air-fuel ratio of 12:1 for example would be considered an excess-fuel ratio and contain very little free oxygen because there is more fuel available to use more air to combust the fuel.

The reason it’s important to know how a WBOS works is because there are several conditions that can fool an oxygen sensor into thinking that the engine is running lean. The first situation is actual misfire. Often, an engine might create a misfire that you may not necessarily feel as a hesitation. This happens quite often under high load at WOT. When this misfire occurs, that unburned fuel and free oxygen travel out the exhaust where the WBOS reads the free oxygen. This is then interpreted that the engine is running too lean and needs more fuel.

If, as may be the case with your car, you either have an engine misfire or – more likely – a leak in the exhaust system, this higher oxygen content in the exhaust will quickly fool the WBOS into reporting to the ECU that the engine is running lean. This adds fuel to the engine. What makes matters worse is that most (if not all) self-learning EFI systems store the new air-fuel ratio tune to the ECU when the engine is shut down. Then the process starts all over again because the leak in the exhaust system is still fooling the WBOS, each time the engine is operated and then shut down, the new, richer self-learning table is added to the existing tune. This is the downward spiral that makes the engine run richer every time it is started and run.

So it could be the solution to your problem is to check the exhaust system very carefully. Two logical places for air to enter the exhaust system is the gasket between the header and the head and the other at the collector flange where there is often a gasket that can easily allow fresh air into the exhaust. This can occur even if there is no audible tick or leak in the system. If the header gasket shows black exhaust tracks past the gasket, it’s likely that it is also allowing outside air into the exhaust. Another possible leak path is the WBOS mounting bung itself. Make sure that this fitting is fully welded into place with no pinholes that could allow air very near the WBOS itself. Another possible leak path could be any place where two exhaust pipes are welded together. This is a very common place for leaks to occur. Look for these holes at the top of the pipe where it is most difficult to weld when the pipes are in the car.

A great way to check for exhaust leaks is to pump smoke into the system. There are several commercial smoke generators on the market designed for this kind of testing, but we have also seen some ingenious home-built smoke leak detectors built with liter soda bottles that can do the job. Eliminating even a very minor leak or crack in an exhaust system will make a huge difference in improving the performance of your fuel injection system.

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  1. I solved all my Fast EZ EFI problems by removing the whole thing and tossing it in the trash. Fast could use a tech rep like you, because they are no help at all.

  2. JACK DAVIS says:

    I have a 1946 Chevy PU with a 383 stoker engine from Summit. FAST ez injection installed and from the get go never ran right. Come to find out the computer went belly up and whatever was programmed in the next day was back to factory. New computer installed and for a few days was good. No back to the old problems, stalls immediately after starting. Time and time again. Worst when cold. Sometimes I wonder if I will get back home if I am out and about. No fun.

  3. Ron rolens says:

    Fast tech support sucks they know nothing about what they or selling my 10 year old son knows more then they do

  4. I agree the fast tech team sucks, absolutely worthless , their own parts they sold me to upgrade my distributor hei factory to one of their 4 pin modules that’s suppose to give a clean tach signal. Well what do you know the car wouldn’t even start. It was running very rich I upgraded to a peritronix cap and high voltage Coil and then recapped plugs to 55 and then ran car back through the programming stage and it’s been no issues since . Actuall running very good

  5. Bruce Horton says:

    I have the ez efi 2.0 on my 96 Roadmaster wagon with a pretty healthy 455, I absolutely hate it , it will show 15.9 air/ fuel ratio and be loading up so bad your eyes water, And hardly ever starts without 30 seconds of cranking, backfiring, cranking. And I’m getting 5 mpg less than when I was running my 1000 Holley with 88 jets square. Worst money I have ever spent. Never Again.

  6. Rona;ld Nekula says:

    I too am having issues with my EZ 2.0 system. Out of the box it ran great. I don’t drive it much an might have put 200 miles on it in a year and a half. First time I had issues, tech gave me the same run around they give everyone. I rewired and replaced. After reading several threads I changed the MAP sensor and corrected the problem. I have driven it maybe 50 miles since that time and is giving me fits again. Tech support has been non existent for the past week. Thing runs but idles funky and studders when accelerating. Not sure where to go from here because there are no errors showing this time. All I know to do is start replacing sensors. Is there anyone with good knowledge on troubleshooting this system?.

    • Guy Bennett says:

      I had similar issues with running rich and studdering on acceleration. Was also throwing 02 censor code. I was so frustrated with it I handed it off to a tech that tried everything and just because he had tried everything else he switched out the plug wires and put later model wires off a fuel injected engine. They have a coating that stops the rf noise that interfere with the system. Sounds crazy but it worked. We chased it for the better part of a year. I havent run down the road yet because of the weather in Ohio but it runs smooth idles nice and no more codes and the green learning light comes on which we couldn’t get before. All the parameters are correcting as they should. Try it . It’s an inexpensive option that might just work.
      Good luck!

  7. HI have you had it out after replacing the wires? If so how is it running?

  8. Dave Vandehei says:

    i feel like i was misleadright from the minute i read the add. I called fast and ask if it would work on my 550 hp pontiac 428 . They said it would. I wish i remembered to write down the guys name when i called six months later and the first thing they said was that system wont work on that. i tried everything from credit twards one that will work to ill see you in court. they hung up on me

  9. Daniel Wilson says:

    I’ve read some very interesting topics that On All Cylinders has presented for the readers enjoyment but never quite understood why nobody took the time to comment. Just look at all of the negative comments from so many VERY unsatisfied owners of the FAST EFI System. WOW !!!

    I’m a big fan of the truth. Especially if it concerns a product that I have been seriously considering purchasing for my extensively modified 351 Cleveland engine project. I’m sure that many are satisfied with this EFI system but considering the total number of people that read this forum and the surprising number of negative comments, my old school Holley is working to my total satisfaction.

    From a technical standpoint, I can’t justify the cost of an EFI throttle body injection system that introduces fuel into an engine at the exact same location as a carburetor does. While the fuel might be better atomized and metered to suit the engines requirements at any given time, it is still subjected to the well known inconsistencies and distribution problems associated with intake manifold designs. Most intake designs are at best a compromise between low and high rpm performance. Maybe with one exception but everyone can’t run a tunnel ram on the street.

    Since fuel delivered by means of throttle body injection or carburetors is at the mercy of plenum and runner compromise, a better way would be to switch to one of the newer intake manifolds available with a boss cast into each individual runner at the heads intake port. The boss can be tapped for nitrous oxide injection but for my money, fuel injectors installed at each port will provided more consistent and reliable results when retrofitting a Classic V-8 for improved performance with the bonus of greater efficiency by using a modern EFI system. All aftermarket EFI systems are NOT created equal but they ARE all equally expensive. It’s best to do a little research before spending thousand$. You don’t want to end up crying on a blog about a product that sucks and the big name manufacturer greets your calls by hanging up. And the beat goes on…..

    • Amen, you are so right!! I’ve haved/have nothing but problems from day one since installing this EZ 1.0 w/new hand held ;i.e. new EFI Fuel tank, new 3/8 metal feed and return fuel lines plus new MSD 6A. I been three years and no smiles here!!!

  10. Robert Dixon says:

    I just bought the EZEFI. Still waiting for delivery. For the last couple of days I’ve been reading up on it( should’ve done that first) and it doesn’t sound like it’s going to work for me. The only thing the salesman said is as long as you have min 9-10 inches of vac it will work. That’s where I’m at so I figured it would be ok. Since then I’ve read it doesn’t work well with manual transmissions or any kind of road racing. Or cams that are cut on a 110 lobe separation. I fall in all those categories. I hate to return it without even trying it but if m to believe what everyone says it just won’t work on my car.
    I’m running a .030 over 455(462), 10.7:1CR, lightly ported Edelbrock RPM heads, a 232/241@.050/110 LSA Lunati Voodoo cam and a M20 Muncie 4speed trans.

    What’s your opinion, will it work?


    • Jeff Smith says:

      Robert – I will answer your question shortly –

    • jethro west says:

      dor yourself a favor………….do not install it! send it back now! I have a brand new X2 890 cranking amp battery………I get an error code, Battery….All connections are tight and new. I am pulling the piece of crap off my fj40 sbc and going with a carb. I have an MSD 8360. It had a vaccum advance…..I had to put a vaccum advance lockout kit on it……..It has run good for a year! I also installed an MSD on it ……All by the book………DONT BUY THIS POS!

    • I have been running this system on my .030 over 455 with edelbrock heads with a larger Lunati sold lift cam and 10.5:1 compression. The system has worked great for the 4 years it’s been on my car.
      Was a little hard at first to set up but works great.
      Set your idle up around 850 rpm IAC 15-20 and lean it out at idle with the hand held to compensate for the over lap in the cam.you may also have to play with your accel fuel,only move one point at a time it makes a big difference.

    • I have to say that I am completely done with this junk system. A year of my car not running. Tech support is absolutely ridiculous. The only reason I started getting return emails was by threatening them. First it was a bad RPM module, then I replaced my whole ignition system, then it was insufficient voltage to the handheld, then it was add this switch and relay into the system and it will work still nothing, then it all works again and drops the RPM signal again. And now the factory fuel rail is leaking fuel. Here is the funny part, the car ran after each one of these steps for exactly one day. The problems are all over the place with the system. I just this week emailed the tech support guy and told him to come out and get the system running himself or refund me all my costs plus the cost to convert back to carbs. I also informed him I would tell my story on every forum or site I could. So there it is. Return your system before you do anything and stick with carbs from a reputable company because FAST is junk.

    • Dear Robert I am using one on 383 with 234/ 238 @ .50 and have no problems. Just remember to tune correctly

  11. Need help with INJ DUTY error code on EZ-EFI, Car has been running but it will lose it mind in 24 hours. Fuel Pressure will not stay set at 43 psi it will jump to 60 psi after setting all night . Ready to put a Holley on it and be done.

  12. I was going to buy a FI Tec till a buddy had problems with his, so I figured I’d go with the FAST easy EFI 2.0 Well that was a big mistake. I’ve gone over and over my engine and exhaust to see if there is any leaks. I have both power and ground going to the battery. And today I’ve leaned it out beyond the suggested targets and I still watched my gas gauge drop. By the way I’m getting 25.9 liters per 100kmh. I shit you not from empty my tank holds 53 liters and I get 204 km out of a tank. Not just once but three times now. I can’t even give this paper wieght away. Oh and it’s just a normal 350 with a RV cam in a first gen toyota 4runner with a 700r4 and most are highway km.

  13. Using an EZ-EFI version 1 here since 2012 on my Cobra replica with a port injected SBF and T5. The performance has been perfect. Sorry to hear about all your woes.

  14. It seems I have some of the same problems others have with 9-10″ of vacumb being insufficient, my cam is 240-246 duration in a sbc 406, the engine is cold natured fouling plugs, then stalling when I put the car in gear, even warm idle issues persist along with hard starting at any temp, I also didn’t research the product before purchasing it. OOPS, now the realist in me surfaces. Why did I get better diagnostic info on it from threads online than comps tech dept? How much driving do i need to do before learning is complete? Why do the sales people not communicate the necessary info to their customers?(commission?). Why not put the ability to tune values in such a expensive product? If it wont work, who’s will? some threads say no self learning EFI will work with these large overlap cams. The carb only had warm up issues and sensitivity to our poor fuel. Does the carb need to go back on?

  15. JEFF DESIMONE says:


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