Frequently Asked Questions


Frequently Asked Questions - Howell EFI

Today, Howell EFI offers a wide variety of products for an amazing number of applications. While the instructions included with each kit should fully explain the installation, we understand there may be a few things that can cause confusion with these complex products – both during in the ordering process and installation. Currently Howell EFI offers wide-ranging GM-style EFI conversions for many applications and harness conversions for any GM V6 and V8 engine from 1985 to present. Here are some answers to some commonly asked questions by our customers. We will periodically update this page with more questions and answers. If you have a question not addressed here, please feel free to email us at


I am installing an LS3 crate engine in my ’72 Camaro. My friend says that if I make the camshaft swap I am thinking about, I will need to increase the size of my fuel injectors. Is that correct? And if I change my fuel injectors, what will I need to tell your tech line when ordering my Howell EFI conversion kit.

First off, the camshaft change will probably NOT require a fuel injector swap. Check with the camshaft manufacturer to be certain but that is rarely the case from our experience. What will require a fuel injector upsizing is a power adder installation like supercharging, turbocharging or Nitrous Oxide Injection. We do not offer fuel injectors so the power adder company will recommend the size of the new fuel injector required. If you do change the injectors, we will want to know the type and number of Oxygen Sensors that you will be using to make sure our harness is correct for your application. It would also be important for you to know if the new power adder/larger fuel injector application is emissions compliant – that information is always valuable to the vehicle owner. Also, investing in a Wide Band Air/Fuel Ratio Meter is a great thing to make sure your vehicle is operating as efficiently as possible.


I have just completed the wiring harness installation adding Throttle Body Fuel injection to my Camaro. I turn the key and the ignition will not fire. What could be wrong?

With these TBI conversions, you must run a tachometer to make the system complete. We have folks who never thought they needed a tachometer but if the white wire in the wiring harness loom does not see a tachometer signal, the ignition will not fire – it is as simple as that.


Where is the best place to mount my computer module? I have a friend who believes that mounting it in the trunk is a mistake, as it will delay the signal going to the engine systems. Is this correct?

First of all, today’s computer modules are high quality and installing them even under hood is not an issue as they are completely weather proof – the factory mounted all ’93-’97 LT1 and ’98 and newer LS engine computers in this location. Many of our Tuned Port and TBI users choose to mount their computers in the interior cabin and under the seats but that choice is up to them. If they want to mount the module in the trunk, there are no ill effects with regards to signal strength. In fact, if they let us know when they order their harness, we will make the wiring loom long enough to reach any trunk-mounted location.


If I change the wiring harness in my car and install fuel injection in place to carburetion, will my engine pass the emissions requirements for my state?

Howell EFI was the first fuel injection conversion company ever to offer California Air Resources Board certification for their products. Beginning in 1998, Howell EFI started working with the CARB to make certain that their systems met these regulations so that their customers would to stay within compliance with all 50 state’s emissions laws. Howell EFI goes to great pains to make certain their customers have the most complete and well-engineered EFI conversion systems available.


I installed the system in my Jeep and the Check Engine Light remains on after I turn the ignition key to on. What’s the problem?

This is one of our most common issues that we hear about on our tech lines and an easy one to fix. Usually the problem is that the battery system is the issue. You must have a 12-volt negative ground power source, which includes a power on ignition switch mode while the engine is engaging the starter motor. This is especially important with Jeep conversions where the original system many times did not use this power source or key mode.


Can you make adjustments to my computer module even if I am not purchasing a conversion kit for my vehicle? I am looking for a reputable company to make the changes to the computer system based on my set of specs and I like your reputation for these modifications. Do you offer this service?

The quick answer here is yes. We can do computer adjustments to any of the vehicle systems we work with which means any GM V6 or V8-powered car from 1985 to new. If an owner is looking for changes to a heavily modified car where things like high end supercharging, high lift camshafts or nitrous are installed, they would be better served to work with a local tuner who has a dyno and computer re-programming services and can work directly with their entire application.


Can I use an engine scanner to diagnose my vehicle after I have installed my Howell EFI kit?

Yes, just as you would do with an unmodified vehicle, using a vehicle trouble code scanner will allow you to determine if your system is running correctly and to learn of the codes that may plague a system. The scanner connection port can be mounted near the driver’s foot well as is the case with OE port placement.


I own a repair shop and have had a number of vehicles that have had engine fires. When this happens there is usually significant damage to the wiring harness. Since we seem to do a lot of these repairs, what is the range of car and truck wiring harness applications that you offer?

First off, we do not offer factory replacement wiring harnesses but we can make one-off harnesses for any of the applications we service (’85 to new V6 and V8 General Motors vehicle). So if your customer is looking for an “up level” wiring harness that delivers more total vehicle component control, we would be more than happy to create the harness to meet their needs.