2001 DeVille DHS / North Star motor losing power

DHSDaddy · #1 (**permalink**) 07-22-09, 06:58 PM

Greetings - I own a 2001 Cadillac DeVille DHS w/ 124K miles. I love this car but lately the motor seems to have been "emasculated" or lost its pwr. This is hard to describe - Up until 2-3 months ago the car has had extremely brisk acceleration. Ever since then car cruises / accelerates as if there is a 6 cyl. under the hood

. The caddy dealer (and my own mechanic) attempted to pull codes to ascertain the problem, but strangely the car is indicates all is operating normally - there are no codes indicated. The engine does not misfire, starts every time, and runs very smooth - there is no hint of anything astray - until I accelerate to any speed. Transmission is o.k. as well.

So there it is -if anyone has had this problem in the past I would be greatfull to find out what the "fix" is. I REALLY miss the stout power and the confidence that came with it.

submariner409 · #2 (**permalink**) 07-22-09, 07:10 PM

Air filter (WIX !), fuel filter, throttlebody cleaning.......?

Take the car out to a quiet straight stretch of road. Put the transmission in 2 and from a rolling stop, PUNCH IT ! Stick your right foot through the firewall and let the engine wind to redline in 1, the transmission will shift to 2, and just before 2 redline, flip your foot off the gas, let the engine pull the car back down to 20 mph, and do it again. Don't worry about the 2 redline - if you miss the foot flip the transmission will shift to 3: it will NOT let you break anything. Lots of crap and dirt out the tailpipe ? Go up to the Cadillac Technical Archive in the black bar and read the whole thing, particularly the article titled "Occasional full throttle is good for your engine" or equivalent.

**Ranger** · #3 (**permalink**) 07-22-09, 08:13 PM

Maybe a partially clogged CAT?

DHSDaddy · #4 (**permalink**) 07-22-09, 08:38 PM

Yes, I am aware of the "Occasional full throttle is good for your engine" mantra....this car (and thus motor) is not granny peddled. On the new jersey turnpike I usually cruise around 95-100mph for long miles at a time w/ the A/C blasting....and on occasion I leave red lights and let it rip through all 3 gears. No cobwebs in there....until now at least.

I'll try out your suggestion - hopefully that solves the problem. Thanks.

DHSDaddy · #5 (**permalink**) 07-22-09, 08:40 PM

Brand new CAT...about 1 yr ago from the caddy dealer in delaware.

askimbenim · #6 (**permalink**) 07-25-09, 12:02 PM

Hello,
I experienced with different customers engines I was working on, that leakages (regardless on intake or exhaust side) can lead to "loss of power" because new electronic controls relly heavily on perfect-no leakage environment to develop full power. I would recommend you to remove the top engine plastic cover, use some brake cleaner in idle on every spot where the intake manifold has screws, parts attached and also where the injectors are located etc. Just a little bit on idle. On idle you have the highest possible vacuum in the manifold. You will feel changes in speed if you detect leakages.
On the exhaust side, I would check the the gaskets between the cylinderhead -exh manifold until one foot behind the final o2 probe. that pipe has to be perfectly sealed. For example loose o2 sensors will detect lean mixture and the injection system will flood the engine...

But check also the Fuel pump, fuel pressure on idle and full load, fuel pressure regulator and the vacuum connection, airfilter, sparkplugs (how old are they and I recommend the ACDelco.). What oil? Check your serpentine belt for any damage and remove it. try to rorate the wheels which are driven by the belt and see if one has a higher drag.

Knock or detonation sensors, can detect wrong and retard the timing. Retarded timing = less power. If your car equipped with those sensors, check them, they need to be tightened with the right torque. very important...

Other thought is fuel. What fuel station and what grad are you using. Dont save 2 cents with no name fuel stations. Go to shell and put at least 89 grade.

How is your heat exchanger, if full of flies etc, try to clean it. but be carefull. check also the coolant level.

Hope you'll find the problem

submariner409 · #7 (**permalink**) 07-25-09, 12:29 PM

askimbenim is a German VW/Audi Tech who currently works for Caterpillar and is here studying for his Masters.

**Ranger** · #8 (**permalink**) 07-25-09, 01:06 PM

How did you know that Sub?

submariner409 · #9 (**permalink**) 07-25-09, 02:51 PM

Member Introductions. I go through it every day to see if we have someone new - it's good to have a new tech in the mix.

**Ranger** · #10 (**permalink**) 07-25-09, 03:39 PM

I must have missed that one. Yes, another resident tech is always a big help.

askimbenim · #11 (**permalink**) 07-25-09, 07:57 PM

Thank you so much guys.

Askimbenim

DHSDaddy · #12 (**permalink**) 07-26-09, 08:51 PM

Ok - thanks for ALL the great suggestions. Here's what I did - I removed the plastic "shield" that covers the engine (has the "Cadillac" symbol on the front), preparing to eventually get into cleaning the throttle body - which I thought was the easiest thing to do first. Low and behold I noticed the large circular clamp that keeps the big round hose (connects to the air cleaner) clamped to the front of the throttle bottle was extremely loose - loose enough to spin - and allow for an opening - and probably suck in additional air directly from the outside.

Thus I tightened the clamp to the point to where is now has a very firm hold on the throttle body opening.

Next I fired the car up, went for a ride and about 90% of the normal power from the engine was back, as well as the familiar muffled "growl" that comes along with that (is the intake noise or the mufflers?).

Why not 100% - I don't know. I still doesn't feel "totally" normal - but this beats the heck out of what it was - slow and lethargic 6 cyl type acceleration.

As a side note - I had this car at my local Cadillac dealer who tried to chase this issue down for me - with all their high tech tools and manuals and blah blah. After having the car for THREE whole days they gave up and called me to come get it back, as they were clueless. All I did was get frustrated and take a close look under the hood. Doesn't look good for caddy shop.

Hopefully I will be able to figure out where the other 10% or so is so I can get the car back to 100% normal again.

submariner409 · #13 (**permalink**) 07-27-09, 09:12 AM

When you change the air filter, remove that large convoluted hose first, then the MAF (note its orientation) and then the air filter cover. Use a WIX filter - more pleats, more surface area, less restriction.

The air ducting must be tight past the MAF or mixture and airflow signals get messed up.

Another test is to remove the engine cover again, start the car, and squirt a tad of choke cleaner or starter flid at the base of the rubber coupling between the throttlebody and the intake manifold - under the s/s hose clamp screw you can just see down in there. The connector "plenum" is prone to crack, giving vacuum leaks and possibly setting the engine light and O2 sensor lean codes. (The plenum clamp is #2 in the last drawing.)