View Full Version : Cold Start Backfire from 97 N*?

01-01-06, 01:43 AM
I am getting ready to go to Florida to see my parents, and my mom has a 97 Deville 275hp N* and she is complaining that when she starts the car cold start, it backfires on start.

The car has around 90K on it, very little ever done to it (other than a new fuel pump last year though)

I don't have a N* and will be traveling to go there to do a full tune up.

What do I need to do and what do I need to bring? My dad has a FSM and some tools, but not a lot of specialized ones. Anything that I don't bring will likely have to be bought, so I want to avoid that as much as I can.

I notice some people change the EGR, FPR and Fuel Filter along with plugs/wires. I don't know if the fuel filter was replaced yet when the tank pump was. Is all that Cadillac recommended 100K service? This is lkely what I will be doing to it.

Anything else I should keep an eye out for? The car is rarely run hard, and with the head gasket issues I have seen, I am hesitant to run it hard either. Is this good or bad to do??


01-01-06, 03:46 AM
Cleaning the EGR is a good idea and not too hard. It shouldn't need to be changed. The FPR check is a quick check. The fuel filter usually doesn't cause any problems, but is another simple job.

If none of those have been done in some time, go ahead and knock them out. I am sure you are well aware of cooling system maintenance for aluminum engines. You might want to hook Mom's up.

Backfiring when the engine is cold is usually a symptom of a lean condition at start up.

Where at in Florida are you heading?

01-01-06, 10:47 AM
Palm Bay, we hope to be arriving next Sat sometime. Bringing the whole army, so we will be driving the Suburban (wife and I and 4 kids), this should be an interesting trip!

I had a 4.9L for a while, only think I did on it for cooling system is flush it once, and ended up with a plugged heater core anyway, so I had to flush it separately.

Just flush and add the coolant pellets? 5 is it?

She would have told me if there was a SES light, so I am assuming none. The last time I got cold start backfire was due to weak spark. I won't have a whole lot of time there, so I hope it just needs plugs. A sticking PCV might be a factor.

Is the heater core easy to flush on the N* Devilles?

01-01-06, 11:30 AM
On startup, ignition isn't turned on for a revolution (or two?), so any fuel vapors have a chance to evacuate. If there's still fuel in the intake, there's a possibility of a backfire. In my case, it would backfire on startup 90% of the time if I left it parked for an hour, maybe 75% if I left it overnight... Cause was leaking injectors. Only had 67,000 miles so now I'm highly suspicious of northstar injectors all the time. At any rate, I just picked up some 24# injectors off ebay for $50 and swapped them in. Never backfired since.

Another possibility is the FPR. The easiest way to test for all of this is to put a pressure gauge on the fuel rail, and see if it holds pressure, or if it just starts leaking down. Mine leaked down to 0 in about 60 seconds. With new injectors, it's up to 20+ minutes before it even moves 5psi.

01-01-06, 12:52 PM
A flush of the cooling system isn't recommended in most cases. However, if it needs to be done, try your best to get as much of the tap water out as possible. This can be done by leaving the bottom of the system open and attaching an air source, shopvac exhaust for instance, to the filler neck to purge the water out. There are minerals in tap water that you don't want left behind in your system. Drop the tabs in the bottom hose, then refill with 50/50 mix. Whichever comes out, Dexcool or green, put the same back in. Her 97 should have Dex.

01-01-06, 04:08 PM
It might be worth getting bottled water, even the reverse osmosis type and using that to flush. It would be pretty close to distilled and not too expensive if you get it from the "bring your own bottle" machines.

01-01-06, 04:16 PM
What size injectors are in the n*?

01-01-06, 06:39 PM

01-01-06, 11:57 PM
What about the heater core? Does it often plug up like the 4.9L cars do?