: Loud Pop



Yaemish
01-20-04, 02:33 PM
When I go to start my car up, and stop turning the keey before the engine actually starts, I hear a loud pop come from the engine and right out the exhaust. Is this the begining of a problem?

tstach
01-20-04, 05:20 PM
Are you sure it's not coming from one or more of your speakers. Occasionally, I get a loug pop that comes from what sounds like the sub in the rear deck. This happens right when I put the key in the ignition and before it's turned. I've also had it pop when I take the key out. Haven't seen any codes, so I'm not too concerned.

Yaemish
01-20-04, 09:58 PM
It definately comes right out the exhaust. It only happens when I stop turning the key before the car is started.

BeelzeBob
01-20-04, 11:25 PM
Any clue as to what year Northstar..??

With the 93-99 engines the direct fire ignition system can cause a backfire into the intake if the key is released prematurely and the engine rocks back...the crank sensors are still reading the crank and read it still turning even though it is turning backwards....so it can deliver a spark even though the engine rocks back. When this happens, with the waste spark type of system, spark is delivered to a "non-firing cylinder". If the intake valve is open when this occurs it can flash back to the intake and cause an "over pressurization incident" that opens the overpressurization valve in the intake to prevent damage to the intake due to the sudden pressure build up. That is likely the pop you are hearing. It really causes no harm to anything.

Another cause for a "backfire" similar to this is if there are any misrouted spark plug cables or other high voltage lines near the ignition system, coil pack or crank sensor leads. The high voltage can cause noise on the ignition pickup lines possibly causing the direct fire coil pack to deliver spark to a random cylinder. Nothing bad comes of this except the noise you hear.

Most of the time this situation is very random and rare as it depends on a perfect set of cirumstances ... including a homogeneous, combustable mixture in the intake manifold. Usually there is not a combustable mixture in the intake...unless there is a source of fuel seeping into the intake such as from a leaking or dripping injector or a weeping fuel pressure regulator.

Bottom line, if this has just started, check the fuel pressure regulator for leaking past the diaphragm. Pull the vacuum line off the fuel pressure regulator while the engine is idling and look at the vacuum nipple on the FPR for any presence of fuel leaking out of the FPR. There should be none. Even with no fuel obviously leaking from the FPR vac nipple if there is any smell of fuel I would replace the FPR and see if that helps.

It also helps to hold the key until the engine starts.... Since you seem to be experiencing a lot of early releases of the key it kind of implies that the engine is not starting very quickly....another sign of possible FPR leakage as a rich mixture in the manifold from the FPR leaking would cause a longer than normal crank and no start on a short crank.

Yaemish
01-21-04, 06:31 PM
Its a 96, the engine starts just as quickly as my 99 N*, I just sometimes let it go early becuase my last car was only a quick turn and it was on.