: HARD loud knock @ acceleration. help

04-11-09, 04:20 PM
Hi, hopefully someone can send some advise my way.
what happend: knock at acceleration.
In parking lot, leaving a spot and heard loud knocking noise. thought the car needed oil, (even though the dash didn't call for it) put in oil, same noise.

2001 DTS, 97,000 miles, regular gas (always), Mobile 1 (always), no codes, no engine light. Had coil and plugs changed past summer. FIRST time hearing this noise today. does not loose power while driving. Carbon buildup???? do open throttle once in a while.

any suggestions??


04-11-09, 08:48 PM
One loud knock or constant knocking? Does it get quieter? Does it ever go away? Do you hear it at idle?

04-11-09, 10:48 PM


04-12-09, 09:52 AM
Turn off the CAPS LOCK.

Sounds a little lick cold carbon rap. That generally goes away after the cylinders get warmed up. When was the last time you gave it any WOT?

04-12-09, 09:10 PM
WOT yesterday after problem started.
the sound gave no indication or warning. Just happend all of a sudden. It has us baffled
& majorly discouraged at this point.
By the way, it's 92,000, not 97,000 miles.


04-12-09, 09:47 PM
Is the sound speed or RPM related?

Get a stethoscope or a piece of rubber hose and listen around. Does it sound like it's coming from the cam cover? That would be more of a tick tick. A hard loud knock sounds more like lower end (rod knock), but that is almost unheard of. Also CAREFULLY listen around the pulleys. Could be a bad pulley bearing.

04-12-09, 10:59 PM
I'll relay your info to my husband and we'll let you know what happends.


04-14-09, 06:24 PM
We posted over the weekend with a problem with the engine. a VERY loud noise coming from the engine when we accelerate. Not a tapping, a loud knock. almost like when kids put playing cards in their spokes. Continuous noise until the gas is released.
Just wondering how hard is it to determine what cylender has the problem. To get at this problem would the oil pan need to just be removed OR the whole engine???
Sound/problem gave us no indication there was a problem even begining, it just happend. Started the car up from a parking space and there it was.
ANY advice would be most helpful. trying to figure out if it something that we can do; husband is machanically inclinded.


04-14-09, 07:52 PM
There's a chance that this is actually a stuck EGR (Exhaust Gas Recirculation) valve. That piece of emissions equipment routes some exhaust gas back into the intake manifold in order to slow down the flame travel in the cylinders by diluting the fuel/air charge. If the EGR valve sticks open or partially so it causes a nasty spark knock under acceleration only which can sound as you describe. The valve itself is bolted to the intake manifold, has a pipe which comes from an exhaust manifold, and an operating mechanism which is either electric or vacuum controlled. Check, or have someone check, that system before you assume a rod knock, which is engine overhaul time.......

Update your User Profile with your car, model, engine, and year. It makes diagnosis easier.........

Mark C
04-14-09, 07:59 PM
If its really a rod knock, you can pull the spark plug wires one at a time. When you pull the wire on the cylinder with the bad bearing the knocking noise will decrease or disappear.

04-14-09, 08:20 PM
my car is a 2001 DTS, 92,000 miles, regular oil changes with Mobil 1, engine 4.9 32 valve Northstar.

04-14-09, 09:52 PM
OK, wait a minute. First off, a rod knock does not just appear out of the blue on the next start up. I think we can rule that out. Right guys?

Secondly, you have a 4.6 (Northstar). The 4.9 was its predecessor and was a conventional single cam overhead valve engine.

Thirdly, PLEASE do not start new threads. It makes it very hard to follow. I'll merge this one.

04-14-09, 10:40 PM
Sorry about the threads being all over the place, & thanks for grouping me together( kinda new at this).

Anyway! about the 4.9 engine, hmmm, that's what our hood says. did buy the car "almost" new, makes me wonder now! Husband knows we have a twin cam.
Thanks for the glimmer of hope thinking it may be a stuck ERG valve. Much better than a comlpete overhaul. We'll check on that tomorrow.
Like i said, out of the blue, only when gas is given and first at start up for those 2/3 seconds, AND yesterday when he started it up and drove it up and around the driveway it didn't make a sound till he was almost ready to park it.
Does an ERG valve un-stick itself?? and how does it get stuck in the first place?? Easy job? Hard job?

thanks guys!


04-14-09, 11:02 PM
OK P, if it is an '01, there is no way it is a 4.9. They where not even made after '96 I think. Not sure what you are looking at there.

No, the EGR will not unstick itself. It is a little bit of a PITA as the fuel rail is somewhat in the way and has to be lifted. That said, it's a lot easier than dropping the drivetrain. There is a tutorial in the Tech Tips section. The pintle valve gets carboned up and sticks open or closed, it should set a DTC if it is not operating properly.

I can assure you that it is not a rod knock. A rod knock will not go away after 2-3 seconds. That sounds more and more like cold carbon rap to me. Have you ruled out pulley bearings, tensioners, belts etc.?

04-14-09, 11:08 PM
If your car is a 2001, there's no way the engine is a 4.9.

EGR routes plain ol' exhaust gas back to the intake system. The EGR valve is susceptible to all sorts of nasty gunk and contamination from oil sludge and carbon buildup. If the car is well-used (not granny-driven) the EGR may never give a hiccup. Not saying that this is your problem, but it's the vastly easier and cheaper first step in an engine noise diagnosis.

Spend $20 or $45 to subscribe your car to www.alldatadiy.com for 1 or 3 years. In addition to the GM shop manuals you get every sort of diagnostic, recall, part, labor rate, electrical, who-knows-what info you can ever use, all right there in your keyboard.

AND, keying on Ranger's post, read the entire Cadillac Technical Archive up ^^^ in the black bar. Note the article "Occasional full-throttle is good for your engine".

04-15-09, 11:11 AM
Your correct. It's a 4.6. (can we attribute it to dyslexia??)

Doing the ERG valve now. let you know what happens!!

04-15-09, 11:30 AM
OK!! We have the EGR off. IF you shake it, should it make a noise, clicking/clanking??? As if you would shake a liquor jigger. well, ours makes a clicking noise, VERY similar to what we are hearing when the engine is on and gas is given. would cleaning it only take care of that problem??????

wiat to hear from you. Thanks!!

ps...a couple times when we pressed down on the spring loaded area, it did stick, other times, not.

04-15-09, 12:14 PM
The EGR valve should make no noise when shaken: that pintle works against a diaphragm and strong spring. Vacuum/electric signal pulls it open with the tapered pintle metering more or less exhaust gas into the intake manifold. As load comes off the engine, the opening signal decreases and spring pressure closes the pintle (tapered valve seat) Very uncommon, but the spring may be broken. If the pintle sticks, then you have heavy spark knock on acceleration.

www.rockauto.com, Luke in parts at Lindsay Cadillac over there --------->
or www.gmpartsdirect.com

04-15-09, 12:47 PM
I think Sub is right, but I think he will agree that EGRs are pretty reliable and I would not hesitate to get one from a junk yard, clean it up and use it. Probably would be a LOT cheaper.

04-15-09, 02:44 PM
I've posted my dealings already with the knock in the 4.6L. By chance other forum members (which we fully appreciate) thought it may have been the EGR valve. We cleaned that, put back in, and that was not the problem. It appeared to be in working condition, and noisy, but it wasn't stuck anymore. No codes are being given...we are stuck on this problem.
How hard it it to change this motor over??? Don't know what else to do. The sound is coming from the inside middle, lower half of the motor. The sound comes when gas is given. we are pretty much discouraged at this point.
some statistics: DTS, 92,000 miles. DID get low on oil pressure at one point several moths ago, no problem since then. No engine light, no codes.


04-15-09, 03:10 PM
Wait a minute. Low oil pressure. Tell us more. When? How long? Did it make any noise? Was it actually low pressure or just an indication problem?

BTW, I merged your thread again. If it is the same problem, keep it in the same thread so people can follow and advise.

04-15-09, 03:29 PM
Ok, concerning the low oil, it did get low, the car made it's melodical ding-ding, and i didn't let it go any further, got oil. No problem. that was about 2 months ago. we've always used the mobile 1 product 5w 30. We KNOW it uses oil like crazy. Actually went to the dealer the first month we had her. Told us it was normal. Read about it, and yes, normal.
That EGR valve made a racket when shook. IF you put some forse and gusto behind it, it sounded like the same noise when IN the car and working. Joe (husband and I thought, GEE! this is it.Then we placed it back and used some other words when the sound occured. The pintle seemed easy to push down. it was under tension, but not a forecable tension. pushed in on it with a toothpick and she went right down. It had slight resistance. The pintle actually moved while he shook it. It was loud! That's why we figured that was it. Put a motor behind it and that was the sound. BUT the sound is still present with it cleaned up.
the sound, like i said occurs when gas is given AND when you first turn her over.

04-15-09, 03:33 PM
You may have done some damage running it without oil pressure. Even 30 seconds without oil pressure can finish an engine. If a bearing started to wear, it will continue to wear. You may just be hearing the results now.

04-15-09, 03:37 PM
If it was actually low oil pressure, what did you do or have done to correct it?

04-15-09, 03:43 PM
Put oil in it right away. Just heard the chimes from the dash and put oil in. No oil ticking.

04-15-09, 08:43 PM
How much oil did it take? You didn't run it dry did you? You should have had a CHECK OIL LEVEL message at 2 qts low, still leaving 5.5 in the sump.

Mark C
04-15-09, 09:06 PM
Was the message CHECK OIL LEVEL, or LOW OIL PRESSURE STOP ENGINE? Two very different messages, one is just a warning, the other is very bad.

You should not be able to push the pintle on an EGR valve in with a toothpick. Your thumb or finger maybe

04-15-09, 10:31 PM
The oil level sensor could have been screwed- never rely on any type of sensor to maintain correct fluid levels. Especially engine oil. Check that dipstick at least every week if you drive it regularly.

04-15-09, 10:44 PM
"Check oil level" only. Never saw the other message on the dash. We've had the car for about 5 years and drove 70,000 miles with her. Had another Coupe DeVille 91, so we know about the cars. We put 310,000 on that car!!
We're always putting oil in the car. It doesn't leak, just drinks alot. No signs of smoke out the exhaust.
Ok, back to the EGR. It was a toothpick that easily, easily was used to push down that pintle. ??? We had another machanical guy look/hear the car and he said it COULD be coming from the top side rear middle, Or the middle underside. To him it may sound like a rod also. That EGR valve... when we had the car running it just sounded normal. no tell tale signs of anything wrong U N T I L you gas it. It's quite, nice hum to the motor, then when gas is applied, it's the God awful knock. The harder the gas, the harder the knock.
SHOULD a problematic EGR give some sort of code?? The car ran great all the way home when we first heard the knocking. We babied it home; made sure it wasn;t an oil problem, and gave it minimal gas for the ride back. It hasn't gotten any worse. The car has total power, not lacking in that department.
How to narrow down to a certain cylider?? would I remove the coil packs and remove the spring to each cyllinder to determine which cylider is making the noise? Or could the fuel injectors be unpluged to see if the noise diminishes? any recommendations?? Used the scope and couldn't tell where the noise was originating; head and oil pan areas. sound didn't get any louder. did not try it on the EGR valve though.
IF the EGR is stuck open or not operating properly what area would this knocking actually be heard???

04-16-09, 10:12 AM
OK Kim, first of, if it was oil level, you have no problem. There is a big difference between level and pressure. No oil pressure is fatal. Low oil level is nothing but advisory. When that message came on you still had 5 qts as I said before.

If the EGR is not operating correctly it should set a DTC as it is monitored. If it was stuck open the engine would not idle at all. If it is stuck closed, I believe the engine will knock under a load. I am not sure if the knock sensor would be able to compensate for that or not.

04-17-09, 01:14 PM
My original engine in my '97 ETC was replaced by the dealer due to "bearing knock" when pressing on the throttle pedal. When the noise persisted, it was discovered that the catalytic converter matrix had cracked and it was rattling around when I stepped on the gas. It did sound like a very heavy rapping, like a bearing. The cat was replaced and the rattles were gone for forever.

04-17-09, 09:18 PM
Hi Tateos,
Did the sound transfer from the cat to the engine?? what's strange with this is even with a stethescope, the sound seems to sound the same where ever you place it. Oil pan, heads, it doesn't get any louder when you reach a particular area.

04-17-09, 09:32 PM
Hi everyone,
Can you tell and describe what Spark Knock is?? are all 8 cylinders going to knock??? Is this the reason why the noise is all over the engine with a stethescope??

04-18-09, 08:41 AM
It's hard to describe a spark knock if you've never heard it, but yes, all 8 cylinders should knock.

04-18-09, 09:45 AM
Ah Ha ! If you're listening to a knock with a stethoscope, the car is probably sitting still in P with the hood open, idling, and knocking. Apperently this knock is not load dependent, so either something is very wrong with an ignition control module or you do, in fact, have internal mechanical problems.

I still don't like the description of the EGR valve characteristics. That pintle spring is not toothpick-collapsible..........

04-18-09, 11:26 AM
Spark knock sounds like throwing a handful of pebbles at a big iron pipe. The sound you hear is the distortion of the cylinder walls and important structural parts as they are punished by the intense explosions in the cylinders.

04-19-09, 11:27 PM
I think the big tipoff here is that it knocks for a few sec and goes away on a cold startup. That's a classic symptom of bearing knock. At cold startup, your bearings have a thin film of oil on them from last time it was run. For a second or two at, oil pressure picks up as the engine starts and the oil pump is driven. This is very obious if you have an oil pressure gauge on a vehicle. When pressure is up, the thick cold oil fills the void between the bearing and jounral and quiets the knock. After the oil warms and thins, the knock returns...

04-20-09, 10:14 PM
Hi guys.Just joined up today.Thrilled to be here.My 1995 STS,was making just about the same noise you described.I put it on my friends lift and found the exhaust pipe was touching a bracket just after the CAT.Sounded just like a rod bearing on hard acceleration inside the car .Bent bracket down1/4 inch.Noise gone. I hope thats it on yours .

04-21-09, 09:49 AM
Hmmm. Maybe would explain why the sound sounds like it's coming from down below.
We have an appointmant with an engine guy this afternoon. I'll let my husband know about this last post....I'd LOVE for that to be the problem!


04-21-09, 12:10 PM
Good luck and keep us posted.

04-23-09, 04:18 PM
Hi all,

Need a little information on online manuals. Which one(s) are the best for preforming an engine swap?? I looked into Mitchell1.com and alldatadiy.com. What would someone out there in Cadillacforums recommend??
The problem with the DTS seems to be a rod knock. It looks like we are going to do an engine change. (not happy about it but the car is in excellent condition and buying another is pretty much not on our "things to do" list.)

Thanks for your suggestions!


04-23-09, 10:17 PM
WOW! Sorry to hear that Kim. That is very rare. Please let use know what you find in the autopsy.

I have no experience with either, but I hear good things about Alldatadiy.

04-23-09, 11:10 PM
Thanks Ranger, we'll keep the forum posted. Tomorrow is decision day. As of right now, I think we're doing an engine job over the weekend. (this should be interesting!) I think www.alldatadiy is the one we're going to use. I emailed their site and got a positive reply back concerning engine information/replacement proceedure.


04-04-11, 08:55 PM
have 04 deville knocks on idle goes away with gas Spark Knock? unplugged egr no change in idle or noise any ideas Ruled out pullys

04-04-11, 09:46 PM
I answered this in your other post.

Multiple posts on the same problem get you less help as people can't keep track of what's going on.