Bosch Design III Injector Upgrade

There is a better Bosch injector called a Design III.

The new injector improvements are

  • An all plastic body, which should transfer less heat to the fuel
  • Better atomization of the fuel, which should provide better gas mileage and more power

The injector on the left is the Design II and the injector on the right is the design III. (Design III is also missing the pental cap)

The height of the injectors are the same. If you measure from the bottom of the top O-ring to the top of the bottom O-ring it is the same. The EV1 connectors are the same so this is a direct replacement. Later Design III's come with an EV6 connector which would require an adapter plug.

The Design III's actually came stock on some 98-99 model Fords so there are plenty of used and new ones on the market.
Many vendors sell reconditioned ones for around a half to a third of the cost of new. Bosch claims less than 2% fail rate and that the injectors should be good for a million miles. Most injectors lose performance due to gas baking in the injector after the engine shuts down and the injector is no longer spraying fuel. Brand name gasoline has additives that helps to keep the injectors clean. Odds are that the smaller brands do not spend the pennies it cost for the fuel additives to help keep your injectors clean.

A few words on injectors
Most injectors, after properly cleaned, will flow very, very close to one another. It is not so important HOW much they flow but that each one flows the same. In our V8's we have a banks #1 and #2 along with O2 sensors for each bank. The O2 sensors read the exhaust gas in closed loop and makes corrections to the air fuel mixture. It reads the banks as a whole. It can not read the individual cylinders but instead it only sees the bank as a single source. So if you have one cylinder flowing high and one flowing low, the O2 sensor will see the combination and think that everything is fine. When actually it is not.

So you can see that we need the injectors to flow as even as possible. Most injector reconditioners will tell you things like their injectors are "blue printed and flow matched". They will also talk about 1% match or 2%. This all sounds good but is 2% better than 1%? Unless the guy has a bunch of injectors to match up there will probably be some difference between them. If you send YOUR injectors in to get cleaned, unless you have an electrically bad one, they are just going to get cleaned and sent back to you. You may or may not get documentation showing the numbers before the cleaning and after the cleaning. Besides, how will you check their work?

So what can you do if you have a couple of injectors that read low? Simple, just put your low ones on one bank and your high ones on the other bank. This way you will minimize the difference. So even though your entire set of 8 injectors may have a 6% difference, when you separate the highs and the lows you could end up with 3% on each. I also placed my lower ones closer to the O2 sensors. I figure this way the richer one has a longer time in the exhaust to burn, yeah like 4 inches longer exhaust. But hey I needed some reason for choosing an order. So if you send your injectors out or get some used ones to send off to get "Blue printed and Matched", I would make sure they will number the injectors and provide that information so you can decide on the placement. Course if they are truly within 1 or 2% it won't matter much. Ok enough of my personal thoughts on that, buy from whom ever you are most comfortable dealing with.

I bought mine from http://osidetiger.com and was very pleased with the service and quality of the injectors and attention to detail in everything they did.

Installing the injectors
Changing the injectors on the Bullitt is pretty straight forward, here is how I did mine.

I removed the fuel pump fuse from the fuse box under the hood, 20 amp #14 Try to start the car. It should not start.

Removed the schrader valve cap located on the front of the passenger side fuel rail. Depressed the valve to make sure there was no fuel pressure. There should not be any.

Next I removed everything that needed to come off so I could easily get to the injectors.

Disconnect or remove

Drivers side

  • Disconnect the battery, remember you are working with gas.
  • PCV breather hose from driver side rocker cover to air inlet
  • Fuel sensor, disconnect vacuum line and electrical connector
  • DPFE, disconnect vacuum line and electrical connector. I also removed the entire assembly.
  • Disconnect each injector connector

Passenger side

  • Disconnect MAF sensor
  • Disconnect IAT sensor
  • Disconnect IAC hose at air inlet
  • Remove air intake assembly
  • Disconnect TPS connector, just makes it easier
  • Disconnect IAC connector, just makes it easier
  • Disconnect each injector connector

I started with the drivers side.
There are two 8mm bolts that hold each fuel rail on. Remove the two bolts and pull up on the fuel rail. If needed you can place a screwdriver under the rail and leverage it against where the bolt fits the intake manifold. When the fuel rail pops, there is going to be some fuel that runs out from what was left in the rail.

The injectors may stay in the intake or some of them may stay with the fuel rail. I did not completely remove the fuel rail, just lifted it up enough to change the injectors.
NOTE: Make sure you have ALL THE O-RINGS. It is possible for the injector to come off and the O-ring to stay in the fuel rail or the intake manifold. You want to make sure you are not trying to insert an injector on top of another O-ring.

You will want to lubricate your O-rings with something so they slip into the fuel rail and intake easily. I just used ATF fluid.

Insert the injectors into the intake manifold. You will feel them pop in and go down about 1/4". After the four are in you can put the fuel rail back on top of the injectors. I started with the rear first and just inserted them enough so they would not come out and then worked towards the front. Once they are lined up, just push the fuel rail down and they will all pop in. Once the fuel rail tabs hit the intake manifold there is a tendency for the fuel rail to tilt toward the fender. Try to push straight down. I guess you could start the bolts before seating the fuel rail. Install the fuel rail bolts. Now that the fuel rail is in check the injectors and make sure they all look straight and everything looks even.

Do the same thing for the passenger side. There is a little less room to work on the passenger side, just take your time, it is not much worse than changing spark plugs.

After the fuel rails are down and tightened you can start hooking everything back up.
After everything is reconnected, start the car. May take two or three attempts to run.

I had been data logging the Bullitt before I changed my injectors and logged some after the injector change and I noticed immediately that my long term fuel trims were much improved. Also 4th gear acceleration at highway speeds was much improved.

Below are some pictures from the injector swap. Total time was about an hour, if you can change your plugs, then this is just as easy.

One last note on the 19lbs Bosch Design III injectors. You may see where people advertise them as 21 or 22 pounds for BMW's and what not. This is because they run at a higher fuel pressure so they will flow more. So don't freak out if you see people advertising them as something other than 19lbs.

Removing the fuel pump fuse

Removing the air inlet hose

Disconnecting the fuel pressure sensor

Removing the fuel rail on the drivers side

Removing the injector

Lubricating the injector O-rings

This is what the hole in the manifold looks like

Inserting the injector

Aligning the injectors on the drivers side

All the injectors in place

seating the fuel rail

Installing the fuel rail bolts

Installing the fuel injector connectors

Removing the fuel rail on the passenger side

After installing the injectors, aligning the injectors to the fuel rail

Aligning the fuel rail up on the passenger side

Injectors all in and everything connected back up

Install the fuel pump fuse

Special thanks to my wife for taking the pictures, again!

©2021 BULLITT Archive: Mustang and Mustang Bullitt are registered trademarks of the Ford Motor Company. All other trademarks are property of their respective owners