Time for a tune-up

[COBALT]

Howdy - it's time to give this '99 5.7liter tahoe a tune-up. Most of this is pretty self-explanatory, but I do have a couple of questions:

1. How do I check/adjust the ignition timing?
2. How do I service the fuel injectors?

I managed to pick myself up an ODBII scanner, so I can read the codes which is a plus, but I'm wondering once I replace the plugs, wires, distributor, ignition module, etc. what to do next...sensors, etc.?

[bwood]

There is no adjustment for ignition timing, it is all computer controlled. There is not timing pointer or a place to put one (just marks for lining up TDC), no timing wire to unhook, nothing. The only adjustment, and it is really not an adjustment, is the cam retard. The distributor doesn't have the ignition components in it like the older (95-eariler), just a cam sensor and rotor. The cam retard is suppose to be +/- 2 degrees from 0 @ 1000 rpms and you will need a scanner that will read live data not just codes. This is adjusted by twisting the dist, but when out of spec will throw a code P1345.

The injectors are located under the upper intake manifold as an assembly. There is no easy way to service them except some maybe a shop type injector flush service. It is actually a "block" of sorts with 8 injectors inside of it with a line and a small poppet valve at the end where it plugs into the intake runner. They are replaceable at about $80 a piece or you can go with the updated MPFI version that puts the injectors at the runners and eliminate the poppet as they are a weak spot in the orig injection set up.

During your tune up I would recommend using all AC parts even though they are a little higher and don't carry a LT warranty, just think how long they lasted.

You may also concider posting your questions in the 88-98 section as your 99 Tahoe actually falls into this bodystyle/engine family/drive train

[COBALT]

Very nice - thanks for the info. I'm venturing into some new territory with these new(er) ignition systems, and I just want to make sure I'm doing the right thing. I picked up an Accel kit as well as an AC Ignition Module and Coil. I'd go with all AC parts but my budget won't allow it right now...



As for fuel injectors - that'll have to wait unfortunately. Too expensive, and I had a hard time finding what you were describing.

I'll post a msg over on the other board to see what people think.

[bwood]

If you look at the upper intake, there is a large electrical connector, about 3"x4" just behind the throttle body. That is the top of the fuel injector assembly. The assembly is mounted to the lower intake and the electrical portion sticks up through the upper intake. Here is a pic of mine while I was swapping engines:

This is a shot from the rear with the upper intake on, the circle is the top of the injector assy/electrical connection:


This is a shot from the front w/o the upper intake with the injector assy installed:


Here are some other pics from the internet:


MPFI upgraded injector assembly:


This is what the original injector poppets look like. They are little valves that open with pressure and get their fuel supply from an injector at the other end of the tube.