: CPS and spark plug question on 98 catera

01-15-09, 04:09 PM
This forum gives me a feeling that I finally find the correct place.

My 98 catera recently has a loud noise and shake in engine. Autozone electrical reader points out two and a random cylinder spark plug misfire(backfire?) and one Crankshaft Position Sensor error. I am planning to fix it myself, but the engine looks very complex. Currently, I try to replace the spark plugs but am crazy for how to remove the wires and tubes on the driver side in order to reach the three buried spark plug.

After reading the article in the forum, especially the one talking about Crankshaft position sensor replacement in the common question area, I begin to worry about my plan. I have several questions:

1) Could crankshaft position sensor error cause spark misfire? In other words, which one should I try to replace first?

2) Now I am lack of confidence to disassembly the stuffs covering the driver side spark plug, because I am completely loss on what they are, actually, I never did engine work before. It would be very nice if I can get a step-by-step instrument (idealy with pictures and photos) on how to replace the spark plug if anyone could help.

3) my radiater has been leaking for a while, I block it by tapes and super glue, and it seems OK now. I am wondering whether this coolent leaking could be the underlying reason for the engine problem?

Thanks for any comments!

01-15-09, 08:29 PM
:thehand:Absolutely replace the Crank Shaft Position Sensor first (CKP). So that you understand why I'll explain.
CKP sensor sends pulses to engine control module (ECM) as reluctor wheel teeth rotate past sensor. Besides using these pulses to synchronize ignition and fuel injector operation, ECM also times interval between each pulse and compares each new time interval with previous one to determine when an excessive change in crankshaft speed has occurred.

A misfire causes an unexpected change in crankshaft speed. A certain amount of acceleration/deceleration is expected between each firing stroke, but if crankshaft speed changes more than expected amount, ECM will interpret this as a misfire. ECM continuously calculates crankshaft position from CKP sensor signals.

This information is used to determine which cylinder is misfiring so ECM can increment appropriate misfire counter and set appropriate DTC, if necessary. If ECM is able to determine a specific cylinder is misfiring, DTC for that cylinder will set. If misfire is random and on multiple cylinders, DTC P0300 will set.

Further more I'd like to recommend that you have an auto tech take care of it for you.

01-16-09, 02:12 AM
Thank you very much for iiF3LiXii's comments!
The reason I want to do myself is to save money, as you may know, I regret a little for getting this second-hand cadillac. I will give my hand a try even I may still need to spend more money finally^_^
Based on your suggestion, I think I will order a CKP sensor and try to install it. Luckly, someone has done that in this forums.

By the way, could anyone give me a detailed step-by-step instruction on the spark plug replacement in case I have to do that? especially the steps to uncover the driver side spark plugs.