Updated 9/18/03 - Please Refresh Your Browser

    
Proper State of Tune for the GM Tbi Engines

We all think our engine is in the proper state of tune, but the real question to ask yourself is," Is it?" When was the last time you:

   Checked the compression?    

  It's easy ! It involves the same procedure as replacing spark plugs. If you haven't done this - go do it! A worn engine will not be able to be brought back in proper tune and cannot be cured by replacing a sensor, adding injector cleaner to the gas tank, or by adding a performance part. Compression gauges are usually cheap - about $20 or so - and will come with instructions on how to perform the tests and how to read the gauge.

   Replaced you fuel filter?

      More often than not we see them clog up between 15k-20k miles .  Yours may be fine - then again, it may not be! Because of the shear amount of times we've seen this happen we religiously change them every 15-20k miles - that is if they don't clog up sooner!

   Replaced or even checked your Spark Plugs?

       READ THE FOLLOWING WORDS - Always purchase and install the recommended factory AC Delco spark plugs. Again, we can't tell you how many drivability  problems or lack of power symptoms we see because of  aftermarket replacements and expensive "Go Go gadget" split or multi electrode spark plugs. This is definitely a place where you can save your money! Why do we say this? Proper heat range is 5 billion times (exaggeration) more important than anything else a spark plug offers!

   Checked or replaced your spark plug wires?

      We praised AC Delco with plugs, but their ignition wires are a slightly different story. Although their  (AC Delco) wires are decent quality when new, they tend to start having problems after a few years of use.  We've seen them last anywhere from 20K miles to an average of about 40,000 or so miles. What do we like? MSD and Accell 300+.  Do not get any generic 'that's all we carry - yeh their fine" auto parts store wires!!!  If in doubt, get the AC Delco's - they are good out of the box.  We don't care to remember how many times we've seen brand new wires from other manufacturers causing major drivability problems.   Oh, and if you are using an MSD, Crane, Jacobs, or etc. ignition system - high quality wires become even more important! Remember,  electricity takes the path of least resistance.  The more energy an ignition system has, the larger the chance the electricity finds an easier path to take than to the spark plugs!

   Checked or replaced the distributor cap and rotor?

           As with wires, AC Delco's cap and rotor are good out of the box but will usually only last 20k - 30k miles or so. The center electrode in the cap and the rotor wear out quickly.  Why? This is where the electricity is forced to jump a small gap to get to the next component and only where spark energy is present EVERY time any of the spark plugs 'fire.' Think about it, this part of the ignition (coil wire too) gets used 6 times more on a V6 and 8 times more on a V8 than any spark plug or spark plug wire. If an aftermarket ignition box with higher voltage and/or multiple 'strikes' is used with stock components the wear will happen much faster if not almost immediately!    Also remember, anywhere there is an air gap there is high resistance - the spark jumping these gaps has more energy than elsewhere is the system, thus more wear. This is why spark plugs, distributor cap, and rotor wear quickly. What do we recommend - Accell or MSD matched cap and rotor. If not available in your area, get the AC Delco - just remember to check/change it more often!  READ these words - NO AFTERMARKET DISCOUNT PARTS HERE!!!

   Checked your timing?

       Go buy a timing gun or at least borrow one. The timing can change over time so make sure to check it! Here, we are interested in the base timing since the computer takes care of the initial and advance duties. The computer will not know if the timing is off or set differently for it has no way to check this.  It always assumes  that the base timing is set where it is supposed to be - usually 0 with the computer/distributor timing wire disconnected. For full size trucks , this timing wire  is typically a tan wire with black stripe located near to or just to the right of the relay cover on the firewall. For '94's plus, many are under the glove box in the dash. Get a manual (Haynes is fine) to find out exactly where yours is. Okay, now we are assuming you have checked the timing and it is now exactly at 0 degrees with the wire disconnected. Re-connect it and see if the timing jumps advanced.  Here we are concerned, not in the advanced reading because it is computer controlled, but just in the fact it advances.  If it stays at 0 degrees you have a problem! We've seen this a good amount of times and it usually ends up being the distributor itself. Disconnect the - battery terminal for a few minutes to clear any codes that may have been set during this process.

   Checked for air leaks in the exhaust ?

        Yes, this is a big deal! Any air entering the exhaust before the 02 sensor will cause the 02 sensor to 'read' the extra air in the exhaust system, and therefore the computer will see this and believe that the engine is running too lean. It will add extra fuel to try to compensate for this false 'lean' reading by the 02 sensor. Fix those leaks now!!!

   Checked for vacuum leaks?

        A small (or large for that matter) vacuum leak can play havoc by changing the intake manifolds vacuum level. The MAP sensor reads the intake's vacuum level and relays this info to the computer.  The GM tbi computer relies more on the MAP sensor's information  than any other sensor in the system! It is read and adjusted for at all driving levels - Open loop, Closed loop, and even WOT! Fix those leaks now!!!  Tip: other than the obvious vacuum hoses and connections  Check the throttle body base gasket and intake manifold gaskets - these are very normal areas for vacuum leaks.

Okay I think you are starting to get the point now. Check all items associated with normal engine maintenance. If you can't remember when you replaced 'such and such' REPLACE IT! If you don't know or can't remember which manufacturer is better for which part - GET THE AC DELCO PART!!!