: Are Gremlins pinching my fuel line? ARGHHH!!

12-05-03, 07:28 PM
THE CAR: 1996 Seville STS 128K (mostly freeway)miles 3rd owner. Previous owner meticulosly(sp) maintained by the dealer. He even took it there to have a bulb replaced. This car is in beautifull condition.

THE PROBLEM: There has a very slight stumble noticable when the car is in Drive(or any other gear) with the foot on the brake, and not moving. Basically the car purrs but every once and a while if feels like the fuel line is pinched. You can see the rpm's drop like 250 or so for a blink of an eye. Also, usually if you start the car cold in the morning and put it into gear right away the problem really shows it self. The car chugs like its runing on 7 or 6 cylinders. A quick shift to neutral and a couple light reves and it goes away or at least back to the occasional stumble. This problem happens cold, warm and after being freeway driven. ALSO the car barley DIDN'T pass Californias stupid a** new smog test due to slightly high hydro carbons.

Every other aspect of driveablity seems perfect. Accelerates good, gets about 20ish MPG on the freway, shifts like budda, ect.

1. I have installed new double platnium plugs
2. Run a bottle of Red Line fuel system cleaner through a tankfull of gas
3. New air filter
4. Oil and filter channge(not that that would really change anything)
5. Tested the spark plug wires. They are totaly within spec AND have less resistance than the new set I bought(so I returned the new set)
6. Cleaned the EGR(actually it really didn't need it but had to try)
7. Installed a new fuel filter
8. I used a mechanics stethascope to listen to the fuel injectors for the clicking noise they are suppose to have. They all sounded like they were working.
9. New PCV valve

My next step is to try and get any engine codes. Maybe there is some code that was there before I purchased the car. However the check engine light has never come on with me. Is there a way to get the codes without buying the little OBD II computer. Maybe some trick with the DIC read out that my worthless Chiltons manual doesn't talk about?

If I don't have any engine codes my next step is check the fuel presure at the rails to see if the fuel pump is working properly. Though I suspect it is since the car preforms fine in all other aspects like acceleration. Then try cleaning the throtle body, then maybe start replacing injectors.

Any help or experience is appreciated.

fastseal75@hotmail.com :banghead: :banghead: :banghead:

12-05-03, 08:46 PM
I think you are on a good track..... You should be able to read the codes via the DIC.... Press OFF and WARMER is the protocol.... I cant remember if your model has the warmer button or whatever....

Fuel pressure would be my next thing id check... I think your supposed to check it before the fuel filter, but maybe im mistaken.....

GET A FSM FROM www.helminc.com

12-05-03, 10:54 PM
Cleaning the throttle body is an excellent idea. You might consider putting it on a scope if the problem is real consistent. That would eliminate the ignition system. I don't know what the chances of a weak coil or some other component are.

12-09-03, 09:48 PM
Hate to ask, but are you using any coolant? A headgasket starting to leak will exhibit syptoms like you described. I.e., the stumble hot or cold, and the elevated hydrocarbons.

Another problem could be partially blocked EGR channels under the intake manifold.


12-10-03, 01:07 PM
Did you try the new spark plug wires? It is possible you may have a dead cylinder. Plug wires are strange. They may appear to be fine, however, their insulating properties may have decayed to the point that one of the wires may be arcing to something other than the plug itself. I've had this problem with a previously-owned vehicle.

12-10-03, 03:53 PM
Hmmm very good ideas guys. I just cheked the coolant level. Right on the money. Since I purchased the car I have changed oil, and coolant and have been keeping a keen eye on both because of the North* tendancy to consume said fluids.

I think the sparkplug wire could be more of the right direction. I had that same thought as I was returning them. And come to think of it this stumbeling problem seemed to start after I was messing with all the wires. So maybe the unsulation on one of the wires is dry cracked and me moving/flexing them opened up a crack and is causing it to arc.

Any guesses as to why(lets say it is the wires) the problem seems most prevelant at start up and goes away with a couple light revs though?

Also the wires cost $80 at the local auto parts store. Actually an OK deal I think but anyone know of some aftermarket wires that are better, a little more expensive is ok because the stock ones are only like 6.5mm.


12-10-03, 03:57 PM
George, do you have any good links to threads about cleaning the EGR passages on a 1996 North*?


12-10-03, 07:05 PM
I am not, by any means, an expert on plug wires, however, I have read some input of other well-versed "posters" on this site, who have highly-recommended that the sensitive plug wires on the Northstars be replaced with ones that your local Cadillac dealer sells. Including the plugs as well.

Don't ask ME why. This is just something that I am keeping in the back of my head, for when I need to consider replacing the plugs and wires on my STS.

12-10-03, 11:23 PM
Someone posted a thread recently about strange problems from plug wires...plug wires that looked good I think. A scope will tell you if they're good or not but the scoping will cost you about as much as the new wires. I'd probably put them on and see.
I had a strange hesitation (just off idle) on a Dakota pickup that turned out to be a bad rotor. The rivet had loosened and the wiper and rotor were loose. It ran great except for that hesitation. (I know the N* doesn't have a rotor) Bad plug wires could give a similar effect.

12-11-03, 11:23 AM
Ok I am convinced to go get the plug wires, Now I just have to convince my wife :halo:
I will let you all know how it turned out.

12-11-03, 04:50 PM
I hate telling someone to spend money when I'm not pretty sure of the result but you changed so many other possible parts already and putting it on a scope is the next thing which will cost you about as much as the wires.

The only other possibility I can think of is see if a votech college has a class going that is willing to use your car. I signed up for "computer control diagnostics" at one of the community colleges here but I don't take it til the end of March. I know most of these let you use your own car to test.

12-11-03, 05:16 PM
HEYyyyyyyyyyyyyyyyyyyyy good thinkin! I will have to look into that at my local college.

12-20-03, 06:52 PM
George, do you have any good links to threads about cleaning the EGR passages on a 1996 North*?


George, do you have any good links to threads about cleaning the EGR passages on a 1996 North*?


Will , sorry for the late response.

I do not have any specific links to send you. The cleaning is very straight foreword, assuming that you have some basic mechanical skills and a few tools.

While you MAY be able to reuse the old gaskets I would advise getting new ones before starting the job, to avoid getting stuck waiting for new ones to be shipped to you.

There are a number of dealers online to order from:
I would only use GM OEM replacement gaskets on the Northstar engines!


You will be removing the intake manifold with the throttle body still attached. A person to assist is advised, it is not heavy but someone can help if there is still something connected when you lift off the intake manifold.

The following instructions may not include every last item to disconnect, but is intended to aid a person with reasonable mechanical skills.

Remember when working around the intake KEEP IT CLEAN! Loose debris falling in a port can destroy an engine when started.

Make sure there is no loose debris around the engine that could fall in after you remove the intake manifold.

Clear an area suitable for cleaning the manifold, a clean work bench is preferred.

If you have access to a digital camera, take a number of pictures of the vacuum lines and wire layout in the throttle body area.

Remove the air filter and rubber intake tube and set aside.

Carefully detach any wires or hoses that go to the intake or throttle body at their various connection points.

Remove the four bolts that go through the top of the intake cover and manifold, and lift off intake manifold.

The EGR runners will be exposed and obvious at this time.

Place clean rags in each intake port

Remove the ERG valve, if done carefully you can reuse the gasket.

The EGR buildup is usually kind of soft and can be easily scrapped out. If you can, use a shop vacuum when scrapping. You will be scrapping the heads, the phenolic spacers (if used) and the underside sealing area of the intake manifold.

Be sure to scrape out the hole that leads to the EGR valve.

I use spray brake cleaner to do a final wipe down on all sealing areas.

Remove the old gaskets and wipe the areas with spray brake cleaner, and place the new gaskets in their grooves.

Remove the rags from the intake ports!

Carefully lower the intake manifold back onto the engine. Before tightening the bolts look carefully to be assured that the manifold is setting down flat.

Replace the bolts and tighten down snugly, about twenty lbs. Do not over tighten; it will not help the seal and could strip the bolt holes.

Hook up all of the hose and wire connections using the photo images to verify the connections are correctly done.

The job is not as hard as the directions may make it seem, often it is harder to write directions then just do the job.

Good luck, George