Enclave SIDI Fuel Leak

SIDI   Spark Ignited Direct Injection

The wave of the future... SIDI delivers many benefits including better performance and lower emissions. This article will not cover the SIDI fuel system in depth, that will be done in an upcoming Knowledge Base article. Instead, today we will simply look at the procedure for replacing an SIDI fuel injector on a 2009 Buick Enclave. This is provided so as to give others an idea of what is coming down the pike and that it isn't really that complicated.

The vehicle came in smoking like crazy. There was no doubt that the exhaust system was heavily loaded down with raw fuel. The first thing to do will be to take a look at the stored DTCs. Let's have a look...

The document below is a flashpaper document. You can zoom in or out, scroll through it, print it, search it, etc...

Here is the injector control schematic...

An SIDI fuel system injects fuel directly into the combustion chamber. Unlike fuel systems that inject the fuel into the intake manifold, the SIDI system has only a small window of time in which to deliver the fuel. To accomplish this task, the ECM can control not just injector pulse width, but also the fuel pressure.

The SIDI fuel system consists of a normal fuel pump in the fuel tank that delivers about 60 psi to a high pressure mechanical pump driven by one of the cams. The high pressure pumps operation is quite simple, what ever fuel goes into the pump on a given compression cycle the higher the pressure goes out to the fuel rail.

To vary the fuel pressure to the fuel injectors, the ECM controls the amount of fuel entering into the high pressure pump through a PWM solenoid valve.

Now, how do we diagnose this fault... The possibilities are:

  • One or more fuel injectors have sealing issues with their pintle's
  • The control wiring is shorted
  • The ECM is holding one or more injectors open

Note from our schematic that the ECM controls not only the ground side of the circuit, but the power side also. The ECM can easily shut down an injector circuit if it sees a problem. As a side note, the ECM is stepping up the injector voltage, it is not system voltage.

So either there is an injector leaking or the ECM is at fault.

Currently GM has the fuel injectors on these engines on "restriction". This means, I have no option but to call TAC (GM's support) and give them the information and let them decide what they want to do. Once gaining parts authorization, they will give me a case number for the parts department to submit in order to get my parts. It was decided that the #5 fuel injector would be replaced.

It took about 3 weeks to get all of the needed parts.... By that time I had almost forgotten how to put the darn thing back together...

Here is what the engine (3600) looks like after removing the plastic beautification cover.

Now we remove outer paper covering and wires

Now lets remove the upper manifold...

Digging in deeper...

All SIDI piping with the yellow tags must NOT be reused. The yellow tags indicate high pressure lines. The fuel pressure sensor must also NOT be reused.

Let's remove the sensor, the piping, and the fuel rail... Notice carefully that on top of the fuel injector, sitting between the injector top and the fuel rail, is a heavy metal retainer that provides tension between the injector and the fuel rail insuring a good tight fit of the injector into the head. This cannot be reused but must be replaced after fuel rail removal.

The injector wiring is inside of that plastic channel. The channel also clips onto the lower portion of the injectors, making it difficult to remove the injector. I just clipped the ears off... And now out comes the fuel injector.

This engine only had 1,000 miles on it, so the injector came out quite easily. There is a special tool for removing them that may or may not be necessary once these get some serious miles on them. Remember, that seal on the end and the hole it fits in is exposed to combustion gases.

Now that the injector is out, we need to clean the channel it fits into with a special tool.

Now the new fuel injector must have a seal installed and this requires two special tools (only one shown in picture).

VERY IMPORTANT !!

The new seal is slipped on with a special sleeve (not shown) and then before the fitting tool above is used, you must pack the seal against the injector with your fingers. Failure to do this will cause the fitting tool above to cut and destroy the seal.

There are more seals and spacers involved than have been shown. These will be discussed properly in a future Knowledge Base article.

After the #5 fuel injector was replaced the engine ran fine. Evidently, the onboard diagnostic software properly identified the failure which is a testament to the engineers who designed the system.

It took almost 200 miles of driving however to get all the raw fuel burnt out of the exhaust system and eliminate the smoking.

  Copyright © 2008 Flatrater Diagnostics