QuestionMy mother-in-laws cadi has developed a sharp low knock at low to mid rpm's, under load, and only when engine is fully hot. The car has 78k on it, but was only driven a few times in the last couple of years ( her health issues ). I have changed the engine oil and transmission fluid/filter. The oil I actually drained and changed the filter twice. The first change I ran the engine for only ten minutes, then changed it again. I completely tuned it up, and had to replace the EGR valve. It passed the smog tests at 50% or less of the allowed parameters. Am I looking at a bad set of main or rod bearings? Or could it be a bad carbon deposit causing pre-ignition in one cylinder once the engine gets hot? Also, the transmission will not do a full throttle downshift from OD when hot, and the engine seems to be cut back by the ECM when you try to attemp the downshift. It works great before it gets hot. Thanks for your opinion on this issue.
AnswerWhat I would suggest that you do FIRST is to purchase 2 cans of TOP ENGINE CLEANER as it is most likely a carbon buildup on the pistons of which happens quite frequently on Cadillac engines.
1. Start and warm up the engine to normal operating temp and let it return to normal idle speed.
2. remove the air cleaner components so you have access to the throttle plate intake area.
3. With the engine running at idle, pour in enough cleaner to stall out the engine.
4. Do NOT restart the engine and just leave it set over night.
5. next morning, start the engine and let it purge out the cleaner and wait until you can get the engine to idle again and let it get up to normal operating temperature and then hold the idle speed up to about 1500 rpms and slowly pour in the remainder of the cleaner and let this purge thru the engine and let it get back to a normal idle speed.
6. see if this solves your problem.
7. if NOT, wait a few days and repeat the process using the second can of cleaner.
It is possible that the engine cut back and the no kick down may be caused by this possible carbon knock as the KNOCK SENSOR is hearing this knocking and is retarding the ignition timing of which can effect the transmission shift patterns.
I have also seen faulty crank shaft harmonic balancers make this same type noise if applicable to your vehicle.
Are you getting ANY CHECK ENGINE light(s) illumination on the dash ?.
Worse case would be a main bearing knock of which would not surprise me in the least.
Loss of power could also be caused by an exhaust restriction due to a partially restricted catalytic convertyer which is also very common.
Try it and let me know.
autohelp
