04 Seville idling problems

[im1coolcat]

I have a 04 Seville that I'm having idling problems. I just bought it thinking it would be an easy fix, but its turned into a nightmare. Drives down the road smooth just like a Cadillac should. First I went to auto zone and they used their little computer and it showed misfire in #7. I bought new plugs (ac delco) and no luck. Then I bought a coil for 7 and again no luck. I then took it to Meineke and paid 50.00 for them to put on their machine so I wasn't spending precious dollars trying to figure it out. They said it showed p0300, plus p0307, and other cylinders. It was bouncing around. Also showed a crank sensor A and B, so I replaced those (not fun), and still no luck, went back to them and they didn't even understand because the fuel was showing 0 which was perfect and it shouldn't be with the miss. They said the injectors showed fine and also no vacuum leaks. Anyone possibly got and ideas?? This is driving me crazy!!

[Cadillac Jim]

P0300 always shows when you have a miss count above a certain threshold over a particular period. The P030n that tells which cylinder won't display on the dashboard when you run the OBD codes.

You need to look at the miss counts and see what cylinders are steadily incrementing the miss counts at idle and under load to get a really good idea of what is happening.

One thing you might consider is clearing the codes and see what comes back. If you do not have the MIL (check engine) light on, the miss isn't consistent enough to cause a problem, but probably needs to be addressed as a tune-up issue.

If you are sure that the plug and coil are OK, be sure that the boot is clean and dry and that you aren't getting arcing in the plug well. Arcing is usually audible if it happens at idle when you can raise the hood in the garage and listen for it. Often you can see arcing in the dark - but some aurora around each plug as it fires may be normal.

Then, there's the possibility of a sticking injector.

After you clear the codes, run them from the A/C buttons (see the link in my signature block for a Caddyinfo page on instructions) and post all of them here.

[cdgrinci]

Maybe even a compression check; piston, valve, ring (hopefully not).

[im1coolcat]

Thanks for the info. I've cleared the codes several times but after I go two feet they come right back. I'm going to go ahead and have a creditable full diagnostic check and figure this out. Just bought the caddy, and love it (except for this issue).

[im1coolcat]

Just had it checked and the said low compression on cyl 1 and 7, so will need head work or another engine. Bad news.

[Cadillac Jim]

Northstars rarely have valve problems other than sticking valves, or carbon under a valve seat.

[Jan Olsson]

I had a burned exhaust valve on my -93 STS. I only know of Barry94 and myself to ever have had that problem here on this forum. It is, according to the guru, very uncommon. Usually there are deposits from babying the car around forever causing the burned valves when someone finally finds the accelerator. I always drive my cars hard and the Northstar engine absolutely loves it. To avoid such deposits to form and also to make the piston rings move freely you should regularly perform the WOT-procedure. Especially if your car hardly uses its full potential. Before I let the shop remove the heads I would perform some WOT-treatment.

This is what the guru says about the WOT-procedure.

Occasional Full-Throttle Acceleration Is Good For Your Engine

There are many advantages to occasional full throttle accelerations with a Northstar and any engine.

It keeps the carbon cleaned out of the combustion chamber. This is maybe a little more important with the Northstar than some other engines due to the tight squish volumes between the piston and the cylinder head. It's designed this way to promote good in-cylinder mixture motion (good combustion) but it has the down side of providing a ready place for carbon build-up to touch the piston - causing noise. Ever heard of the Northstar "cold carbon rap" problem?? Simply put you'll hear a rythmic, piston slap-like noise when the engine is cold. Very prominent and very annoying. Cause: excessive carbon build up causing the the piston to contact the carbon on the head - causing it to rock in the bore and "slap" Much more evident when the engine is cold and the pistons haven't expanded to full diameter yet. Simplest and easiest "fix" for this: A few good WOT (wide open throttle) accelerations to clear the carbon out. That is all it takes to eliminate the problem and prevent it from re-occurring.

Occasional WOT accelerations also help seat the rings to the ring lands and exercise the rings and keep them mobile and from becoming stuck in carbon in the ring lands. At high RPM and WOT the rings move around on the piston - they actually rotate on the piston and will polish away any carbon and seat themselves to the sides of the ring grooves. This is especially important on the 2000 and later Northstars which had hard anodized top ring lands on the pistons. Very hard and wear resistant - also harder to break-in and seat the rings to the sides of the ring-lands to promote the best possible seal. Many oil consumption complaints on the 2000 and later engines are related, to some extent, with the rings never seating to the sides of the ring-grooves due to lack of load as the engine was babied around forever. Even engines with rings stuck in the ring-grooves due to carbon build up can eventually be freed up with enough high RPM operation.

WOTs warm up the engine thoroughly and clean out the exhaust due to temperature in the exhaust and high flow rates blasting particles, rust and such out of the system.

Here is the WOT Procedure

{C}{C}Frequent WOT operation will not hurt the engine or the transmission. They're designed for that. The healthiest engines that I have seen at high miles are always the ones that are run the hardest. Rings are free on the pistons and sealing; no carbon buildup.

The exercise that I think works best for many things is to select manual 2nd gear on an isolated stretch of expressway. This takes the transmission shifting out of the question if you are worried about hurting it. Start at 55 MPH or so and go to WOT in 2nd gear and hold it until the RPM reaches near the normal shift point - i.e. 6500 for an L37 and 6000 for an LD8. Hold the throttle wide open until the engine reaches, say, 6200 for an STS and then just let completely off the throttle. Leave the transmission in 2nd so that the engine brakes the car and creates some pretty heavy over-run conditions at high vacuum levels. Let it slow until it is about 55 or so and then go to WOT again and repeat. This exercise really loads the rings, allows variable RPM operation at WOT for several seconds continuously, creates heavy over-run which tends to unload the rings and make them move and thus exercise them in the ring grooves and it will blow-out carbon and the exhaust - all without creating a spectical of yourself and attracting the attention of cops. You can do it on most any freeway and stay within the 70-75 MPH range allowable. Once a week like this will keep the engine cleaned out and healthy and is DEFINITELY recommended for the Northstar in particular.

The Northstar engine was designed/developed/validated to be run hard. It was expected that people would use the performance of the engine - which few people seem to do. The biggest single problem that many issues stem from is lack of use at full throttle by the owners. It just doesn't like to be babied around. The rings are low-tension by design for good high RPM operating characteristics and low friction/good power. They work best if "used" and kept free.

In every conversation with owners I have had, once the owner started doing the WOTs and using the power of the engine they report no more carbon rap, better oil economy, no "smoke" when they do light it up (keep the exhaust cleaned out. If you notice a "cloud" at WOT then you are not doing enough WOTs...) etc... A bit of judicious use of the other end of the throttle travel is a GOOD thing...

[barczy01]

I have seen a handful of burnt valves and broken valve springs. Coolcat where are you located? I would steer away from installing a used engine.

[im1coolcat]

I'm in Kansas. Trust me I'm looking around for any option but changing engines. Firestone diagnosed it with cylinder 1 with less than 10 lbs of compression, cylinder 7 they did not check compression but plug was good, coil good (swapped coil pack with another) and still the misfire. Jan, your post makes sense. I just bought this car, and from a older couple, so betting the car was babied and driven slow all the time. I love the car fully loaded and very clean. The cleanest car I've seen. Cadillac Jim, what would you think my options are at this point? At first I spent 60 bucks on new ac delco plugs, 46 on Meineke's machine that narrowed it down to crank sensor A and B that I paid 100 for parts (I youtubed how and did it myself), then spent 100 for Firestone to basically tell me its shot. Right now the check engine light is not blinking when I drive it, its staying on and you can feel it missing around 45 to 50 mph still. Before it would start blinking when I throttled and ran so Cadillac smooth you couldn't tell it had a misfire until you came to an idle.

[cdgrinci]

Since the engine 'may' be 'toast', and wait for others to chime in, you may want to perform the 'Italian tune-up' (in case your compression loss is due to extensive carbon build-up in and around rings/valves/etc. Some full throttle (in a safe place) in the lower gears with decelerations in the same lower gears might dislodge carbon deposits accrued. With #1 so low I'm thinking it might not just be carbon but, not a lot to lose, (at this point). Certainly wait for Texas Jim or one of the others with Northstar experience to confirm or refute my advice.

[Jan Olsson]

Since the engine 'may' be 'toast', and wait for others to chime in, you may want to perform the 'Italian tune-up' (in case your compression loss is due to extensive carbon build-up in and around rings/valves/etc. Some full throttle (in a safe place) in the lower gears with decelerations in the same lower gears might dislodge carbon deposits accrued. With #1 so low I'm thinking it might not just be carbon but, not a lot to lose, (at this point). Certainly wait for Texas Jim or one of the others with Northstar experience to confirm or refute my advice.

I agree. The WOT-prodedure wont hurt anything.

[rockfangd]

i recommend getting a second opinion on the low compression. I dont trust many shops. most are out to take your money. Take it to a dealer and have them do a proper compression test on each cylinder. I am kind of skeptical of 10 as a reading.

I advise against replacing the engine. Best thing to do is to repair your current engine

[Jan Olsson]

i recommend getting a second opinion on the low compression. I dont trust many shops. most are out to take your money. Take it to a dealer and have them do a proper compression test on each cylinder. I am kind of skeptical of 10 as a reading.

I advise against replacing the engine. Best thing to do is to repair your current Engine

I'm also kind of allergic against throwing parts at it instead of repairing what's wrong. Sure a replacement engine can solve the problem but then one has to think about that engines history. Was it well maintained, is it a complete rebuild or just another possible problem on the way?

Your engines history is of course also unknown. Service from a reputable shop makes it a keeper. If it is the valves there is some work involved. But if you don’t plan to make the work with the engine in the car there isn’t much extra work involved to repair the engine instead of replacing it. With the engine out the heads are easily removed and valves are easily replaced. If necessary an engine shop will have to machine the valve seats and stems or replace them.

I also like the thought of keeping the car with all original parts if possible but that’s just my personal preferences J

[im1coolcat]

Thanks for all the feedback. Definitely want to keep the original engine in it. Except for this issue the engine is strong. I have been thinking and think I will take it to a dealer and recheck.as soon as I find out I'll post.

[im1coolcat]

By the way I tried the WOT procedure, and no luck.

[Cadillac Jim]

A diagnosis of under 10 lbs compression is a red flag to me. That would mean a valve stuck open. On the intake, a "whoosh-whoosh" sound would be audible from the intake or exhaust, depending of which valve it is, during idle. A helper and an ear can tell the tale there.

[barczy01]

when you crank the engine over to start it, is it non rhythmic . Does the cranking go from slow to fast real quick? 10psi might have a broken valve spring possibly.