: Help with Tune Up Northstar 4.6

06-28-11, 11:35 AM
I just acquired a 1998 Cadillac Eldorado with 125,000 miles. I would like to do a tune up on the car myself and had a couple questions. I have learned so far of the plugs and wires to purchase.

I just purchased the Plugs (AC Delco 41950) and wires set (AC Delco 748Q) from rockauto.com and a new air filter.

What else do i need to purchase to do a regular tune-up on the car?
Where on this site are the instructions of changing plugs and wires?

Thanks for your help

06-28-11, 12:48 PM
I'd change the oil, and have the coolant flushed.

From my Alldata:

Tune up Includes: Renew & Adjust Spark Plugs. Inspect Or Replace Distributor Cap, Rotor & Ignition Cables. Service Or Renew Air, Fuel Filter And PCV Valve. Adjust Ignition Timing And Check Advance. Make Necessary Fuel Adjustments, Service Battery.

Eight spark plugs are centrally located in each cylinder combustion chamber and can be accessed through holes at the top of both cylinder bank camshaft covers. The spark plugs have platinum pads welded to the electrodes. These pads extend the spark plug life to 160,000 kilometers (100,000 miles). Worn, cracked or dirty plugs may give satisfactory operation at idling speed, but under operating conditions they frequently fail. Faulty plugs are indicated in a number of ways: poor fuel economy, power loss, loss of speed, hesitation, shudder, medium throttle intake manifold backfire, hard starting and general poor engine performance.

Fouled plugs - may be indicated by black carbon deposits. The black deposits are usually the result of slow speed driving and short runs where sufficient engine operating temperature is seldom reached. Worn pistons, rings, faulty ignition, overrich fuel mixture or cold spark plugs may result in carbon deposits.

Excessive gap wear - on plugs of low mileage, usually indicates the engine is operating at high speeds or loads that are consistently greater than normal or that a plug which is too hot is being used. Electrode wear may also be the result of plug overheating, caused by combustion gases leaking past the threads, due to insufficient torquing of the spark plug. Excessively lean fuel mixture will also result in excessive electrode wear.

Broken insulators - are usually the result of improper installation or carelessness when regapping the plug. Broken upper insulators usually result from a poor fitting wrench or an outside blow. The cracked insulator may not show up right away, but will as soon as oil or moisture penetrates the crack. The crack is usually just below the crimped part of shell and may not be visible.

Broken lower insulators - usually result from carelessness when regapping and generally are visible. This type of break may result from the plug operating too "Hot", which may happen in periods of high speed operation or under heavy loads, When regapping a spark plug, always make the gap adjustment by bending the ground (side) electrode. Spark plugs with broken insulators should always be replaced.

Spark plug boots - cover the spark plug terminal and a portion of the plug insulator. These boots prevent flash-over which causes engine misfiring. Do not mistake corona discharge for flash-over or a shorted insulator. Corona is a steady blue light appearing around the insulator, just above the shell crimp. It is the visible evidence of high-tension field and has no effect on ignition performance. Usually it can be dust particles leaving a clear ring on the insulator just above the shell. This ring is sometimes mistakenly regarded as evidence that combustion gases have blown out between shell and insulator.

Gap settings for plugs is 0.050in
Torque is 11lbs ft

06-28-11, 06:19 PM
Hi...............and make sure the new plug wires are connected as shown.

You may find some oil on the plug insulators and/or outer shell - normal. The plug well O-rings tend to weep over time.

Torque the plugs to 13 ft/lb using a tad of anti-seize on the first 3 threads. The new plugs are pre-gapped to .050"

Look through Discussions: Item Specific, Cadillac Tech Tips for plug change work.

Also, read up on throttlebody cleaning. Use a WIX panel filter - don't get suckered into the "performance boutique" advertising - the performance is already built in and your $$ cannot buy a better air filter than a Fram, AC Delco, Parts Master, or WIX.

06-28-11, 09:11 PM
The rear plugs will be easier to access if you remove the strut tower brace (if you have one). Also remove the ICM and set it aside (leave the coils attached). Be advised, there is a hidden mounting bolt in the back that requires the Braille method to remove and replace. After that, it's pretty straight forward.