: 1998 Deville Tune-Up confusion

10-01-05, 03:40 PM
Okay, I got new plugs 41-950's. I plan to do the wires next weekend, but wanted to get new plugs going first. Now, I cannot find the gap for these. Not on the underhood sticker(s) and not in the manual. However, the manual lists the correct plugs as the AC 41-900's. :confused: I'm assuming the 41-950's are the replacements? So what is the correct gap? .050? Also, so you all use dielectric grease on your wire boots too? I have on all my vehicles, but haven't seen anything on this board regarding it. BTW, I have done searches on here but found nothing regarding my year vehicle. Thanks all! V.

I forgot: Is it easier to remove the plgs when warm/hot or cold? Thanks.

10-01-05, 04:39 PM
A/C 41-950's superceedes the 41-900's

Gap is .050

No grease. You'll notice the OEM wires are prelubed and there is a note on the box to indicate so.

Remove them cold and save your skin.

10-01-05, 05:35 PM
Thanks! I changed the plugs. Not bad at all. Anyone else cringe when remove plugs for the first time? I did. Luckily all was good. Normal wear, could of lasted the other 30000 miles. Decided to clean the throttle body; good Lord was it dirty!! The whole intake was filthy with oil sludge crud. Wondering why. Previous owner babied it too much? I sprayed quite a bit of throttle clear thru it, quickly assembled the air flow sensor and revved it pretty good. Hopefully cleaning a little bit of that crap out. Idles better now. Will replace wires tomorrow.

"Why the hell did I go through 15 vehicles before buying a Cadillac?? - idiot!!:helpless:
Thanks all for the great advice and help on this forum!! V.

10-01-05, 06:16 PM
The oily deposits you saw in the intake are normal. I gasped when I saw it for the first time as well. It is residue from the PCV gasses that settle when the engine is shut down. Cleaning it is a waste of time. What needs to be cleaned is the throttle plate and the TB bore. In particular, the mating surface where the plate meets the bore when in the closed (idle) position.

10-01-05, 07:13 PM
Thanks Ranger. I appreciate your help! V.

10-01-05, 10:40 PM
After the tune up and TB cleaning, you might want to disconnect the battery for about 60 seconds to clear out the learned values for idle, etc. Technically, it should pick up on the changes fairly quickly, but I feel reasonably confident that my car idled better after I did the disconnect. All it can hurt is clearing out your radio presets and resetting the clock. Might be worth a try.

I agree 100% with Ranger. Don't worry about the stuff inside the intake. It's normal and won't hurt anything. If it smells like gas, it could be a leaking FPR, but if you aren't having any hot restart problems, don't worry about it. Just drive it and enjoy.

11-30-08, 11:49 AM

I have a 1998 Deville, Northstar with 77K miles - babied.

The car 'immediately' starts when cold, but after it warms up it takes several turns to get the car to start . . .

I had new plugs put in at 50K miles.

Also, how does one clean the throttle body plate & TB bore?

The car idles around 625, but feels a little rough.

I've cleaned the throttle body, put in a new ERG, air filter, fuel filter and added Seafoam to clean the fuel system, disconnected the battery for 2 hours, but still the above problems persist?

Comments please!

In advance, thanks . . .

11-30-08, 12:45 PM
Hard hot starts are usually indicative of a leaky FPR. Check the Tech Tips section for a tutorial on checking it. It's very easy.

Cleaning the TB is basic. Block the throttle plate open, spray with TB cleaner and then scrub with a toothbrush and wipe with a rag til clean.

11-30-08, 01:09 PM

i found the url:

Checked on the FPR parts, does my 1998 Deville Northstar take a nylon or stainless steel FPR ?


11-30-08, 01:32 PM
The FPR itself is steel. The fuel rail is another story. You'll have to take a look, but I believe the '98 is nylon.

11-30-08, 01:40 PM
Ranger - thx . . .

11-30-08, 06:16 PM

My 98 Deville with the Northstar has 77K miles, with the original FPR.

If the FPR does not leak, is there still a chance the FPR is bad?

How often should these FPR be replaced?

Again, the car starts immediately when cold, but after it's warmed up, much harder to start, and while it idles around 625, it may go to 700, then back to 650 then 600, then 625.

Does this still sound like a FPR problem?

In advance, thanks . . .

11-30-08, 06:57 PM

Could my problems be an engine temperature sensor, since, it immediately starts when it's cold, but difficult to start when it's warmed up?

Where is the engine temp sensor located?

In advance, thanks . . .

11-30-08, 07:44 PM
FPR only gets changed when it leaks. If it doesn't leak, it's good. Hard hot starts are usually indicative of a leaky FPR or injector(s). I would doubt if the ECT sensor is the culprit. Have you pulled the DTC's? Have you checked the fuel pressure when the problem is present?

12-01-08, 11:32 AM

I have not performed any of the tests trying to identify and isolate the problem.

With your last comments, I will begin the testing . . .

Again, thank you for your ongoing suggestions . . .

12-01-08, 11:37 AM

What are the DTC's, I could not find the definition of a DTC performing a search on this forum?

12-01-08, 11:46 AM
DTC = Diagnostic Trouble Codes

See the sticky in the Tech Tips section on how to pull codes.

12-01-08, 02:17 PM

I checked the FPR, and 'indeed' it was leaking through the vacuum side. I just replaced it with a new one, the car started. Now I have disconnected the battery for 1-2 hours, will then reconnect, and drive it around to see if it resolves the problem of hard starting when warm/hot, again the car always started immeditiately when it was cold.

Since there 'was' gas leaking into the vacuum side of the FPR, where did that gas go to, did it go back into the air intake or where did the gas go, and what problems would occur?

Again, in advance thanks . ..

12-01-08, 04:29 PM
The gas was drawn into the intake manifold via the vacuum line then burned, so you where running rich. That raw gas in the intake acts like a choke on a carbureted engine. It assists in cold starting, but hinders a hot start. You should see a marked difference in hot starts as well as an improvement in your fuel mileage.

12-01-08, 04:37 PM

Great explanation, thanks for your prompt and courtious replies . . .

I will post the results after I run the car for a week or so.

Again, THX!

12-03-08, 11:14 AM

Drove the car about 40 miles, and restarted (5) times during the 40 mile errand run. The Deville, did 'not' hesitate starting after warm-up, so your assessment was "RIGHT" one - well done!

Replacing the FPR is a cleaner and easier job than changing a flat . . .

While the car seems to running fine NOW - Do you have other easy checks and fixes that I should consider with a car that has 78K miles one it?

I've changed the air filter, fuel filter, now the FPR, EGR, and (1) of the heated Oxigen 2 sensors.

I have no DTC's, nor is the service engine light on.

Again, thanks . . . well done!

12-03-08, 12:14 PM
Clean the TB and keep up with the coolant changes.

12-03-08, 02:34 PM

It appears that all Northstar engines because of their iron block and aluminum head develop head gaskets leaks - is this why you recommend changing the coolant frequently?

I spoke with Bar products and Cadillac called them into their factories years ago trying to remedy the problem, as the Northstars were leaking from the head gaskets before they were delivered to the dealers, and Cadillac told all their dealers to 'immediately' add 6 Bars Radiator sealant tablets to each northstar engine.

Most well known after market service centers (excluding Cadillac / GM) were not aware that they had to add Bars radiator tablets after each radiator flush / coolant, and many of these northstar engines developed cracked head gaskets.

It is still recommened to add Bars Radiator tablets after each coolant flush / refill?

Do wish to further comment on this ?

12-03-08, 03:35 PM
Northstar engines are all aluminum. No Northstar has an iron block. .......and all Northstars do not develop head gasket problems. Scheduled coolant change is part of any engine's normal maintenance.

The Bar's tablets (3) were originally installed at the factory to seal nuisance leaks and casting porosities and the head gasket problem due to pulled bolts never entered that picture. If your car was originally delivered with the GM Cooling System Supplement (Bar's Tablets) installed, then the sticker on the radiator sight shield will so state.

When the servicing GM dealer enters the individual vehicle VIN the service information will state the need or lack thereof for the Coolant Supplement. Large chain service centers typically do not complete various services to OEM specifications. That's the nature of the beast. If you have a GM/Helm factory Service Manual for your vehicle, then the cooling system maintenance section will state whether or not your engine gets the supplement as part of normal service.

Supplement use was all but discontinued by sometime in 2002. If you like, you can add it as recommended by GM: 3 crushed tablets in the lower radiator hose. 6 tablets is/was overkill.

Bar's products will not seal head gasket/exhaust gas leaks.

12-03-08, 04:50 PM
submariner . ..

I have had great success with Bars Head Gasket 'FIx' - it's a new product, 28 fl oz's of which you remove 28 oz from the coolant system, put the Bars Head Gasket 'FIx into the coolant system, run at idle for 15min with the heater on high.

Prior to using it, my 1998 DeVille with 75K miles on would burn 6 cups of coolant every 300 miles. Since I used the Bars Head Gasket 'FIx', I have gone over 2K miles (4 months) without it using 1 oz of coolant.

For me it worked like a champ.

12-03-08, 08:41 PM
Glad to hear that you have discovered the Holy Grail.

Bar's "Head gasket FIx", even on the label information, bears no resemblance to the OP questions concerning the Bar's tablets used by GM and others. The HDC 60 tablets and G12BC powder are the GM-recommended product.

It will be most interesting to hear of your ongoing experience with the new product. If the stuff has truly repaired a lifted/corroded head gasket failure in permanent fashion, then CF and GM owe Bar's a great debt of gratitude.

The old adage "run the heater on high" holds no water in today's constant-flow heater cores as opposed to the older heater flow control valve systems. Yes, that's a necessary caveat in Bar's instructions, but it is not germane. TAANSTAFL

(I notice that one of the ingredients in Bar's Head Gasket FIX is sodium silicate......the old "water glass" of chemistry classes of long ago. The stuff literally dries (from a small puddle) into a thin pancake of glass-like material that will cut the snot out of a finger if picked up carelessly.) Sodium silicate can be painted on fiberglass heat tape insulation weave in order to strengthen the surface of the wrap..........

12-03-08, 09:11 PM
Sub beat me to it, but I couldn't have said it better.

12-04-08, 11:57 AM
I'll keep you updated . . .

THX for all of your help . . .

This is a great forum - trying to keep our overpriced northstar engines running -

12-10-08, 12:06 PM

It's now been a week with the new FPR - and no doubt the car is running smoother, and the hard start when running at normal temps appears to be remedied.

Ranger - Great diagnosis . . .