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1991 Cadillac Sedan deVille
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Discussion Starter #1
My 1991 Cadillac DeVille has a knocking sound (from the engine area) on light acceleration when the engine is hot. One would swear it was a rod knock. It does not do it when the engine is cold, nor on heavy acceleration, only at lower rpms accelerating. At only 61k miles, surely it is nothing serious. I have been told by a couple of people here that it could be the EGR vacuum solenoid. Is there anyway to test it, or should I just shell out the $45.00 for a new one? It is my understanding that it is easy to replaced, but I haven't looked for it yet, or read about it in the FSM.

Thanks!
 

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White Diamond '03 DHS (with DTS floor shift)
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It IS easy to replace and I am sure the FSM has a test procedure, but I don't know what it is.

Being an OBD1 car, I'm sure it can be tested with the overrides function of the onboard diagnostics.
 

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1991 Cadillac Brougham D'Elegance 5.7 Litre, 1994 DeVille
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yes you can override it in diagnostics, you can also pull the vacuum line off it and plug the end. It sounds like you are describing pinging, what grade of fuel are you running?
 

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1991 Cadillac Sedan deVille
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Discussion Starter #4
Thanks.

I only run premium gas in it. It does not sound like a ping, to be honest it sounds like a rod knock, but if it were a rod, I would think it would do it at all RPMS, or worse at higher RPMS? It only does it on light acceleration when the engine is hot.

It did not do it when I test drove the car. It seemed to have started after I had my mechanic install new fuel injectors (which at the time he also replaced the EGR valve). Not sure if that issue is connected or not, but the car was running extremely rich (had several bad fuel injectors and was run a bit like that) and had "gassy smelling" oil when I got it back - which I have since changed and it has good 10w-30 clean oil now. I have put 2000 miles on it since. I hope the engine isn't ruined.
 

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1985 Sedan DeVille
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Way I tested mine was with a $15 vacuum gauge, hooked to the solenoid and tied to the wiper arm. When solenoid activates, vacuum gauge jumps up. When solenoid discharges, vacuum gauge falls to zero.
 

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1992 DeVille
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Check the hose system for the EGR system. I'll bet the hose coming off the throttle body is cracked. The valve or solenoid could be at fault too
 

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It can be controlled through the OBD system, as previously mentioned.

You should also be able to jump the ground as well. The solenoid is ground-side controlled. 5V is always supplied to the solenoid - the ground is switched to energize the solenoid.
 

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1991 Cadillac Sedan deVille
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Just remember, that the solenoid is energized to stay closed, and de-energized to open. Like others said, check the vacuum connections to and from the solenoid.

So, you're saying you don't hear "marbles in a tin can" type of sound, but a knock? If it's a knocking sound it could be fuel related (running too lean). How is your oxygen sensor? Did your mechanic check it when he replaced the injectors and EGR valve? A O2 sensor that's gotten lazy will make the engine run lean when hot (because of closed loop), and you may get a knock from it. To check the O2 sensor activity enter diagnostics (Off + Warmer), after 7.0 press Lo, wait for the display to change, then navigate to P.1.6 (o2 sensor cross-counts). Drive the car while observing the display - the counts should go in the 20s upon acceleration, and when cruising or idling should hit 0 occasionally, but not stay there most of the time.
 

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1991 Cadillac Sedan deVille
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Discussion Starter #10
Thanks so much for all of the replies.

Check the hose system for the EGR system. I'll bet the hose coming off the throttle body is cracked. The valve or solenoid could be at fault too
Hmm... there is a hose that is running off of the back of the throttle body area, I cant remember if it is running off of the air cleaner assembly, or the throttle body itself, but it looks like that hose is running down to the valve cover on the back. It does have tape on it up where it connects to the back of the throttle body, as if it was cracked. Is that it? If so, would that cause a knock? Not sure where I could get a replacement hose.

Just remember, that the solenoid is energized to stay closed, and de-energized to open. Like others said, check the vacuum connections to and from the solenoid.

So, you're saying you don't hear "marbles in a tin can" type of sound, but a knock? If it's a knocking sound it could be fuel related (running too lean). How is your oxygen sensor? Did your mechanic check it when he replaced the injectors and EGR valve? A O2 sensor that's gotten lazy will make the engine run lean when hot (because of closed loop), and you may get a knock from it. To check the O2 sensor activity enter diagnostics (Off + Warmer), after 7.0 press Lo, wait for the display to change, then navigate to P.1.6 (o2 sensor cross-counts). Drive the car while observing the display - the counts should go in the 20s upon acceleration, and when cruising or idling should hit 0 occasionally, but not stay there most of the time.
Nope, it is definitely not like a marbles in a can sound, I know that sound you mention though. I have no idea about the 02 sensor. I was assuming it was ok since there are no service engine lights on and the car only has 60k miles, but I guess that don't mean anything? I have no idea if my mechanic checked it or not. It seems like it didn't start though until I had him put in the new injectors and EGR valve. If it is too "lean" is there anything I can do? I know it sure don't get good gas mileage as if it was lean. I only average about 19-20 mpg, 80% highway driving, but on my dash when I am on the freeway, it seems to get around 25-26 on the highway on average, but guzzles gas I guess on what little city driving I do in it. Before the new injectors though I was getting about 6 mpg!

That hose mentioned by dch is cracked/taped up, so wondering if I should check that out.

I also have a new problem, there is wetness below my water pump, I THINK it is coolant, but the coolant level is full. I guess the water pump is failing at 60k. This poor old car. lol.
 

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1991 Cadillac Sedan deVille
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Cracked hoses need to get replaced. Just because it's taped it doesn't mean its vacuum sealed. Go to your parts store and get a couple of feet of vacuum hoses so you can replace anything needing a replacement (all vacuum hoses at this age are suspects).

If it is too "lean" is there anything I can do?

You can start by inspecting and replacing bad vacuum connections. Then observe the oxygen sensor's cross-counts as I described in my previous comment. See if you have an active sensor or a lazy one. If you find that you need a replacement go only with AC Delco; I'll tell you why. I replaced my AC Delco o2 sensor about two years ago (previous owners had that one installed not that long ago), because I thought the ground connection seemed to be no good (
strap over the o2 sensor body). I installed a Bosch Premium sensor and everything seemed to be good. Well, when I was chasing some drivability issues of my own I decided to swap the old AC Delco sensor in there. Results - the Bosch sensor would rarely exceed 5 cross-counts and very frequently would stay at 0 when idling. The AC Delco sensor rarely goes to 0 cross-counts at idle and I can frequently see numbers as high as 25-30 cross-counts at acceleration. If you think about it that makes for a lot of activity, considering cross-counts are registered per second - meaning 25-30 swings between rich/lean conditions in a second.

I know it sure don't get good gas mileage as if it was lean.

I would actually expect worse mileage with a lean running condition. Anytime your engine doesn't develop it's full potential power you're going to work it harder - waste more gas. When your engine is running better you don't have to mash the gas pedal as much to obtain the same acceleration/cruising speed. Ideally, if you could improve the power output of the engine without adding any more weight you will gain fuel efficiency as well (again less load on the engine to deliver the same results).

there is wetness below my water pump

You'd have to inspect if it is the water pump or some of the hoses around there. There is a bypass metal line that runs around the same area, that some members have had problems with. The pipe would rust out and develop holes for coolant to seep through. Otherwise, a lot of people say these water pumps are not a good design to begin with, and so they frequently fail. I know mine was replaced at around 50K miles from the previous owner, and I replaced it around 100K mi.
 

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Discussion Starter #12
Thanks. Well the photo of that hose in question is below. I looked in the FSM yesterday and it mentioned what it was called, but I already forgot. lol. It runs to the rear valve cover.

I don't think it was mentioned above, but if the o2 sensor was bad (or lazy) would my service engine soon light be on? I checked my MPG computer today and I am averaging 18.0 mpg and that was right on with my own calculation by using the trip computer/gallons to refill, so that thing is pretty accurate. That MPG is about 75% highway driving at 65 mph.

Another thing is that when I turn my car off when the engine is hot, I noticed a noise, like a "robot" was operating. One day I had the hood up and was running the car, shut it off and heard it again and it is coming from the cylinder thing in the pic below. I think it is the TPS? Anyway, it will make a whirring noise for about 5 seconds and that arm will move back and forth. Also it seems like when the engine is hot and started, the rpms kick up and then go down. Is that normal? Today it did that and I was too quick to put in in drive and it jerked the car. I thought I would ruin my transmission. I guess it is ok though.

*I did have a nice surprise though. I didn't think that my driver window worked... today I pressed the down button and it didn't click like the others do or even like the driver window does when you press the switch to go up... I pressed it harder and viola, the window went down quickly and went up quickly. I guess the switch is going out, or something. Still I will use it until it completely breaks. lol.

Now, here is that taped up hose. I don't think this would cause the engine to knock though?





Here is that thing that sometimes goes wild when I shut the car off...

 

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Another thing is that when I turn my car off when the engine is hot, I noticed a noise, like a "robot" was operating. One day I had the hood up and was running the car, shut it off and heard it again and it is coming from the cylinder thing in the pic below. I think it is the TPS?
That's the ISC (Idle Speed Control) motor.
 

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Yeah that taped off hose is part of the positive crankcase ventilation (PCV) system. I'd replace it. And ranger is right, that's your ISC ratcheting.

It is sweeping to reset the idle position so when you fire the car up it will idle in the right range.

If it ratchets for a long time or really loud it can be a sign of failure or being out of calibration. Ratmonster just posted about an issue that might be related to this and I gave him this link. It's about me going thru the whole system to calibrate everything.


http://www.cadillacforums.com/forums/showthread.php?t=620194
 

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Yes the ISC moves after you shut the car off usually in and out for a few seconds. Before even thinking about adjusting it or anything else go through the service manuals and follow the procedures for the problem you have (that knock rattle?) . Most of this other stuff should never need to be adjusted unless someone else has already messed with it before.
 

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Yeah broughams right. And from what you wrote it doesn't seem to be a major issue. When my isc failed I could let off the gas and the car was still pulling and I'd shift into neutral and the rpms would spike to like 2500 and stay there it was nuts.

Like brougham said fix the egr stuff and maybe whatever you're noticing might be a side effect that's cured.

Stone a few birds with one stone.

For what it's worth my tps was going bad and I was having some rough acceleration from dead stops. None had messed with the system but after replacing I never threw another intermittent Tps code again.

Also, have you checked for codes recently?? Check and post them and the definitions if you haven't.
 

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Check all of your vacuum hoses. Since you just had the EGR valve replaced i would check it to see if it is the correct type. Do you still have the old EGR? There are 2 different types used on the Deville depending on year. One is the " positive backpressure EGR" the second type is the " negative backpressure EGR". If they are switched then your EGR valve will not operate correctly. They both look the same but the computer is calibrated differently. I just went through this when the part number in the parts store was incorrect. The old one should have a marking on it indicating what type it is.Also you can check the FSM in the EGR diagnostic section and it should tell you which system you have.
 

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You should have a positive back-pressure EGR valve. Verify that's what your mechanic installed.

Regarding the o2 sensor, you'll most likely get a code for it when it gets really bad. It is easy for you to check its activity while operating the car. I posted the procedure earlier in this thread.

Regarding the PCV hose, it can stay like that. The only place you can find one is at a junk yard, and most of them will crack when you try to remove them. As long as it's taped good it's fine. If it's not taped up some amount of dirt will be entering your engine, because it will draw some unfiltered air through the cracks.
 

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Discussion Starter #19 (Edited)
They all look ok. I think I still have the old EGR. I am not sure how to tell the difference. I am not a DIY'er, which is why I trusted my mechanic to do the work.

With all of that said, I went ahead and replaced the EGR vacuum solenoid today and no surprise that it did not stop my engine knock noise. I didn't think I would get that lucky. I have already removed it and I am going to take it back tomorrow and get my $47.00 back and put a for sale sign in the car. A 60k mile car should not have an engine knock. I am finished with it.

*The only thing is that my old solenoid had most of that foam thing on one of the ends deteriorated away. I am not sure if I should just leave the new one on there or not. I am already going to be losing about $400 on the car... so $447 isn't going to make much of a difference?

Thanks for all of the replies.

Check all of your vacuum hoses. Since you just had the EGR valve replaced i would check it to see if it is the correct type. Do you still have the old EGR? There are 2 different types used on the Deville depending on year. One is the " positive backpressure EGR" the second type is the " negative backpressure EGR". If they are switched then your EGR valve will not operate correctly. They both look the same but the computer is calibrated differently. I just went through this when the part number in the parts store was incorrect. The old one should have a marking on it indicating what type it is.Also you can check the FSM in the EGR diagnostic section and it should tell you which system you have.
You should have a positive back-pressure EGR valve. Verify that's what your mechanic installed.

Regarding the o2 sensor, you'll most likely get a code for it when it gets really bad. It is easy for you to check its activity while operating the car. I posted the procedure earlier in this thread.

Regarding the PCV hose, it can stay like that. The only place you can find one is at a junk yard, and most of them will crack when you try to remove them. As long as it's taped good it's fine. If it's not taped up some amount of dirt will be entering your engine, because it will draw some unfiltered air through the cracks.
 
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