96 Deville 4.6 No start and backfire. Need Suggestions

[stenseltizm]

Any suggestions as to what this problem may be will be greatly appreciated.

I am looking at purchasing a 96 Deville with the Northstar 4.6L V8 110k. The car has some issues with the rear suspension so the owner parked it. It was said the car ran great before it was parked, just wore out the rear tires quickly and needed rear shocks. The car sat for 2+ years while they procrastinated and now it will not start. He called the mechanic that works at the dealer who sold him the car to come look at it. The car cranks, sometimes sputters, and will backfire with a flash seen at the top front of the engine near the pulleys. (this looks like a guarenteed intake leak as the throttle body is on the drivers side). The mechanic stated that it looked like the timing belt stretched and jumped a few teeth.

I pulled the #2 spark plug and did a comp test but only got 30psi. #7 had over 110psi but I didnt' look at it exactly. I assumed the mechanic was correct. Just to be certain I threw the comp tester in #4 and expected 30psi but instead the pressure was spiking upwards just like cylinder #7 did. Then I was reminded that I didn't imobilize the motor via spark or injectors and it backfired loudy, oops.

I didn't check the codes as I thought the built in system used the radio controls and this car has an aftermarket head unit installed. My reading here shows I was mistaken and it uses the heater controls? At any rate the owner says there are no codes showing.

I still assumed the mechanical timing was off until I researched here and found the northstar has a timing CHAIN. Is there any history of these chains stretching? Especially when the car has just been sitting? In my Acura the timing belt is known to stretch and eventually break but I've never had any experience with chains stretching or 'skipping teeth' Are there any guides that could possibly wear out and throw the timing off?

I'm starting to think the problem may be something simple such as a crank angle sensor or something of that matter as that would most certainly throw the injector and distributor timing off if it took a dump. Any history of these going bad?

Basically I am interested in purchasing this car if it seems the problem is sensor/small component related. I am not afraid to replace the intake and rear bushings to make the car nice again. I just am not prepaired to replace the engine or do valves/guides if the timing is way off. I just don't have the time or money to invest in that large of a project.

What kinds of tests or diagnostic procedures should I try to norrow down the root causes? I'm deffinately going to spend a few more hours diagnosing the car before I make an offer on it.

Thanks Guys.

[Cadillac Jim]

What may well have have happened is that a valve stuck a little so it doesn't close firmly. As you found, Northstars don't have timing belts. And, no, the timing chains are worth the life of the car.

If you saw fire out the front of the engine, it probably blew out the protection port that keeps the intake manifold from shattering when it backfires through the intake. Find it and put it back in by hand and you should be OK. Someone here who has seen that plug and knows more about it than I can help more.

[stenseltizm]

Thanks!

I've been talking this over with my father who also agrees a timing chain will not just 'go bad' from sitting idle for many years. I hadn't thought of sticking valves or other components though. I know the last car I bought had sat for only 1 year and it had very low compression in a few cylinders that cleaned right up with a touch of oil. Then after running a while the car had great compression all over.

BTW what should a healthy 1996 4.6L engine come in compression test wise?

And a protection port eh, not bad I assumed the intake was bound to be broken since I new it was not metal.

Any insight into the wierd rear tire alignment? Could it be the bushings they are talking about here: http://caddyinfo.ipbhost.com/index.php?showtopic=12526

[winterset]

Check the FPR (Fuel Pressure regulator) which is on the fuel rail. pull off the vaccum, and check for fuel. Also when you turn the key, listen for the fuel pump. press the off & warmer buttons on the climate to check for codes - there's a how-to on this board.

[Ranger]

Check the FPR (Fuel Pressure regulator) which is on the fuel rail. pull off the vaccum, and check for fuel.

Do this while at idle.

[BodybyFisher]

Definately check and post your codes, let us know if you don't know how, this is very important

[KHE]

There is a relief valve on the intake to prevent damage to the engine if it backfires. I doubt the manifold is damaged.

If the car sat for over two years, the first thing I'd suspect is rotten gasoline. Siphon/remove as much as you can and put some fresh gas in the tank and see if it starts.

[growe3]

Remember, a backfire is a symptom, not a cause.

Backfires are most commonly caused by spark while the intake valve is not yet closed. i.e., firing order wrong.

I know there other causes, but lets eliminate the easy ones first.

Verify that the spark plug wires are on correctly.

Remove the spark plug wire protective covers, and trace each spark plug wire, from the coil to the spark plug.

As for a bad valve, or a (2) plug wires out of position, that will not prevent the engine from starting, it would add some roughness though.

-George

[stenseltizm]

Thanks for the replies guys. It's pretty obvious that I'm not going to get any further diagnosing the engine without some more time with the car. So I'll assume it may need some major engine work for now. Anyone know what a compression test range should be?

Now my main concern is the rear tires balding oddly, any ideas? The outside corners were rounded off and the center tread was good. The owner said it needed rear shocks that were very expensive, and that it looked like the tires were pointing in further than normal. What are commen parts to fail in a DeVille that would cause this?

[BodybyFisher]

Thanks for the replies guys. It's pretty obvious that I'm not going to get any further diagnosing the engine without some more time with the car. So I'll assume it may need some major engine work for now. Anyone know what a compression test range should be?

Now my main concern is the rear tires balding oddly, any ideas? The outside corners were rounded off and the center tread was good. The owner said it needed rear shocks that were very expensive, and that it looked like the tires were pointing in further than normal. What are commen parts to fail in a DeVille that would cause this?

WHY would you assume that it needs major engine work? It might just be a bad FPR or a DTC code might turn up something

Bald on the outsides usually means that they were under inflated. You might just be in need of a good 4 wheel alignment.

[stenseltizm]

For budget reasons I don't want to offer too much assuming it's something minor. That 30psi has me a bit nervous so before I get more time with the car I'll assume it will cost a decent amount to fix. Then diagnose some more and see how it goes. My fiance purchased a car that 'ran great but won't start' It turned out to be the fpr. Changed that and the head gasket leaked. Pulled the head to find it was cracked etc etc. I don't want to drown myself and loose money.

Outside can be underinflated but the owner said it did it to the last two pair on the rear so I'm assuming it is not simply pressure. Maybe it is simply out of alignment.

[BodybyFisher]

For budget reasons I don't want to offer too much assuming it's something minor. That 30psi has me a bit nervous so before I get more time with the car I'll assume it will cost a decent amount to fix. Then diagnose some more and see how it goes. My fiance purchased a car that 'ran great but won't start' It turned out to be the fpr. Changed that and the head gasket leaked. Pulled the head to find it was cracked etc etc. I don't want to drown myself and loose money.

Outside can be underinflated but the owner said it did it to the last two pair on the rear so I'm assuming it is not simply pressure. Maybe it is simply out of alignment.

Oh I am sorry I forgot about the low compression, I understand. If it is backfiring into the intake, it might be an intake valve hanging up.

As someone mentioned there is a backfire safety on the intake manifold that sounds like it blew out on yours if you saw flames.

[Cadillac Jim]

I would bet that the low compression on that cylinder is related to the backfiring -- a stuck valve. An oil change and a drive to warm-up will likely fix it. I've never heard of a Northstar with burnt valves. That's very rare with aluminum heads. As far a rings are concerned, they can stick in a Northstar but I've never heard of one being pulled down and the original honing marks not still showing on the cylinder walls. The next thing down the line is a cracked piston, which can be caused by hydrolocking. That's very hard to cause in a Northstar but if you pour a liquid into the intake while any high-compression engine is running, or pour it in and then try to start it, it can happen. But, that doesn't happen from sitting for a long time with the battery dead.

[joeb]

what does the owner want for the car? its 12yrs old, been sitting for 2yrs. mechanic says it might need some top end parts/repair. did the owner and mechanic have a little talk about that repair cost? i am thinking the car might be in the <1k$ range. and you think thats a lot of money? if its a nice car, buy it and fix it or sell it to the next guy.

[stenseltizm]

what does the owner want for the car? its 12yrs old, been sitting for 2yrs. mechanic says it might need some top end parts/repair. did the owner and mechanic have a little talk about that repair cost? i am thinking the car might be in the <1k$ range. and you think thats a lot of money? if its a nice car, buy it and fix it or sell it to the next guy.

To bring this back from the dead (I hate when people never update what ever resulted from a thread) I had the same thoughts as you joeb, I was looking for insite so repairs cost didn't end up overtaking the value of the car. I talked the 'owner' down from $1000 to $600, sold my fiance's car to afford it and any repairs needed (money was tight at that moment), then was blessed with the birth of my first child. I contacted the 'owner' to modify our arrangements on purchasing the car only to find out it was in his wife's name and she was hell bent on making something of the car. I let myself be jerked around for a couple more weeks before showing some imiturity and telling the man where he could take his car. (I later apologized, people change their minds all the time)

Anyway I still ended up joining the ranks of a Cadillac owner by purchasing a 2003 Deville last saturday. It cost a lot more than the 96 but I have come to realize I do not have the time to spend wrenching to keep my family in a reliable and safe large car.

So thanks for your help and I'll still be around for insite to these cars.

[Texas Jim]

Congratulations on the 2003 DeVille.

Tell us more about it (color etc) and your (other) new baby.

Boy?? Girl??

[stenseltizm]

Thanks Jim,

I have a son about to turn 3 months on Valentines day (musta bought some nice flowers last year?) He's a long one consistantly around the 95th percentile each doctors visit for heigth of baby's his age. It really is the most amazing thing in the world and I can't believe I helped make him.

The car is pretty basic by Cadillac standards, though the standard options blow away any car I've owned. It's black with tan leather interior and 57k miles. Carfax confirmed it as a one owner car, and the maintenance records showed the thing was serviced at the dealer religiously. I planned on hiding it in a friends garage until this Friday night to debut with a big red bow Saturday morning (cheesy I know), but I couldn't wait and took my fiance with me to pick it up. It really floats down the road like a cloud with very nice power. The only issues so far are a check coolant DIC that seems to be tracked to a faulty sensor as the coolant level and temp haven't budged, and what seems to be an oil leak that I have yet to diagnose as to where it comes from. I plan on diagnosing both to the letter before going back to the dealer to have them fixed under warranty.

[Texas Jim]

Sounds very nice.

Glad you like it.

Yep, having a new little one around, is a wonder.

They are so much fun to play with and as they get a little older, teaching them how do do stuff.

Won't take long to teach him the difference between metric and SAE wrenches.

By you saying "UNDER WARRANTY"..I assume you Cadillac is CERTIFIED?

If so..that is great news. It means you won't be out any money, no matter what may happen.

One thing you may need to look at...if the coolant has not been changed...it is time to do that.