: Losing Compression

01-25-13, 05:33 PM
I have a 2004 deville that has under 70,000 miles on the Northstar engine. This car is truly a car for Church on Sunday. The problem is the car began to stall. I took it to the shop and was advised it is losing compression. The car was tuned and I was advised that if the compression continues to drop, then I needed to replace the engine. What replace the engine that has less than 70,000 miles what a bummer. My thoughts (being a woman) is clearing the fuel line would help maybe clear some of the gunk that might have accumulated due to lack of driving. I put some fuel and carb cleaner to help remove gunk but it continues to stall, any suggestions, I truly need help. I feel like repairs guys are trying to take advantage of me due to my gender. Please help.

01-26-13, 12:54 AM

I feel like repairs guys are trying to take advantage of me due to my gender.

First, go to the DTC Sticky at the top of the forum page and pull the DTCs. Post them AND their definitions (from the OBDII link).

You are NOT loosing compression. That's almost unheard of.

Don't put anymore snake oil in the gas tank, cooling system or crankcase. :tisk:

Give us a little more info on this stalling problem. Cold engine or at operating temperature? At idle, during acceleration, while driving or on coast down approaching a stop?

Find another shop. This one is either dishonest or incompetent.

01-26-13, 11:18 AM
Ranger is 100% correct.....

Manic Mechanic
01-27-13, 10:23 AM
Not so fast, I just fixed one a few months ago that had lost compression due to "Aunt Sally goes to church" style driving causing the rings to accumulate combustion residues and stick in place, thereby losing their ability to seal in compression. These engines need occasional heavy throttle operation to stay clean, sort of like a self cleaning oven, it won't stay clean if you never heat it all the way up.

You guys have a sticky at the top of this forum labeled "Northstar Ring Cleaning Procedure" that features the Technical Service Bulletin (T.S.B.) that GM put out to identify this problem and how to best attempt to repair it. I used it to find success in repairing my customers 2000 DeVille DTS that was saved from the low compression grave and still running good.

Ms. Pewash I suggest you read these two posts and also print out the GM T.S.B. then take it to your Auto Technician and ask them to evaluate the prospect of performing the procedure on your car. The stalling needs to be further described as Ranger asked to help pin down the cause. It is likely as stated that it isn't related to low compression because the engine would be idling very rough for a while before it got to the point of stalling. If it has been tell us about that also. But if your "repair guys" are actually really competent and did a compression check as part of a normal tune up, as I do, and are telling you the truth then you may have a problem that can be fixed before it's too late by performing the prescribed procedure as I did. I'll look up the two posts and put a link to them here.

GM TSB, stuck at the top of this forum:

Post I made describing the episode I had identifying and repairing lost compression:


01-27-13, 11:18 AM
I like your posts Vernon. I was with Ranger 100% when I originally read the OP. It seems we all know about the slow driving ring sticking issue, but it just comes up so rarely that it still slips by everybody. The thought of a 70k mile engine losing compression sounds like BS, but we have to remember this is the Northstar. Doh. Good catch Vernon.

01-27-13, 01:38 PM
You are correct on the rings getting gunked and stuck....very common and I should have added that.

The oil separating cathchcan system prevents this:

That piston was hurt by the tuner going to lean and disabling the knock sensors, but it shows the varnish/gunk build up on the ring lands & rings.


Manic Mechanic
01-27-13, 10:24 PM
Thanks guys. I also appreciate the technical aptitude of this forum. Probably the best automotive tech for a particular brand I've ever come across and I've been on a bunch.


02-06-13, 02:51 PM
Should she try the WOT procedure? :sneaky:

02-06-13, 03:19 PM
Should she try the WOT procedure? :sneaky:

Post #4.

The OP joined on 01-25-13, has the one post, and hasn't been back since. Her last login was the time of the post, so she never came back to look for a reply.

02-06-13, 10:23 PM
That's strange. :hmm: