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Old 09-25-2007, 10:09 PM   #1
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Default Northstar 4.0 - Odd engine surge

Since L67Silouhette and I appear to be having the same issue, I figured it would be best to post in the specific forum pertaining to my drivetrain.

For the last little while, the car has had the oddest behaviour. It takes 2 or 3 cranks to get the car fired up when warm (ie 95F"ish"). When its cold it fires right up no problem.

Had the car in for some diagnostic work. The IAC was cleaned, as was the MAF and throttle body, no PCM codes evident and fuel pressure checks at the regulator yielded nothing out of the ordinary.

It doesn't seem to be a Northstar specific issue as it happens to all engines, but the typical culprits that cause these symptoms have been addressed and I'm still experiencing these issues.

Any ideas to bat around?
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Old 09-26-2007, 10:04 AM   #2
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Did they tell you what the fuel pressure was reading?
Did they try to pull codes? Even w/o a light..it could be setting a code.

How old are the plugs, wires etc?

If you start the car and mist it with a hose in the dark..do you see any sparking from the coil packs?

Rough idle?

Any coolant loss?
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Old 09-26-2007, 10:10 AM   #3
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Read L67'* thread. Your motor surges as well? That would suggest a vacuum leak. There are a few hoses on yours and pcv areas under your engine cover that could have deteriorated or come loose. I'd give them a check first.
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Old 09-26-2007, 10:33 AM   #4
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I'll check for vac leaks for sure, as its probably a good place to start.

Codes were pulled, no stored codes were found and when the IAC was cleaned, it was rescanned and again no codes.

The diffiicult start up, followed by a surge only when warm could be a result of the PCM holding things back until the engine reached desired oil pressure, but even when warm, the OP is sufficient. And if it was any of the associated electronics, codes would be thrown.

I'm still thinkin its the basics, air, fuel, spark and compression.

The wires/plugs were changed less then 40 000kms ago.
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Old 10-01-2007, 11:50 AM   #5
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Changed with what brands? Around here you can buy $10 wires and be lucky to get a year from them. Some I'd trust..some I would expect to change soon.

Another thought..check your pcv'* etc. Make sure both are working and check under your engine cover to ensure nothing is being pinched.
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Old 10-01-2007, 07:06 PM   #6
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GM DOHC motors can be very particular on the plug wires you use. What makes them susceptible to problems on these types of motors is the sleeve design. If it is a two piece design, sometimes the charge/spark can go through that joint, into the cylinder head and going to ground. You can tell of your plug wires are the issue by pulling them and noting any carbon tracking at the joint of any two pieces of the sleeve.

However, his surging has nothing to do with ignition. If he was having a misfire issue that was a count high enough to trip the count trigger in the PCM (one or two misfires randomly aren’t uncommon and can be normal at idle on some GM engines), will also trigger DTC P0300 “current misfire code” and then the corresponding cylinders it’* happening on. I.E. if it was cylinder three, you’d be seeing P0300 as well as P0303.

Since he’* not getting any DTC’*, it can’t be ignition. It’* either on the fuel side or in the EVAP/emissions system as noted above by searching for vacuum leaks.

Aside from checking hoses and vacuum lines, make sure any piece AFTER the MAF is secure and sealed. Even the tiniest crack between the TB and intake plenum that can allow unmetered air in can cause a surging issue. So make sure all gaskets between these pieces look ok, and that parts are torqued to the correct spec, effectively sealing and leaks.

Have you had an injector cycle test? You’ll need access to a TechII to do it. But you hook a fuel pressure gauge up to the end of the fuel rail, hook the TechII up, run an injector cycling test. What the TechII will do is run each injector at a set interval, sequentially, while you watch the pressure drop on the pressure gauge as each injector fires. Most fuel rails run in the 30 – 40 psi area (+/- some), so if each injector as it fires drops it 5 – 10 psi, that should be a normal pull. If some pull 30 psi or none at all, you’ve found your bum injector. Go about there remedying the situation.

Of course these PCM’* can be very tempermental too. Are you sure your EGR and Secondary A.I.R. system are working? Although if they weren’t, you’d be getting their DTC’* also, usually a P0410 or P0430. Otherwise, it could be a bad mapping in the PCM.

Have you tried an idle re-learn? Go to www.obdII.com or maybe it’* www.OBD-II.com, I can never remember. There you will get the entire process as well as driving procedure for the most effective “re-learn”. This process is akin to re-booting you home PC after it’* been running for a week or more. It clears all the bugs and cobwebs out and resets it back to the base programmed mapping.
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Old 10-01-2007, 09:05 PM   #7
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What I need is access to an OBD2 scan tool so I can see for myself. No one around here seems to have one

The performance of my car has not been hampered by this slight start up problem, and, recently even difficult start ups has been sporadic, further confusing the issue. :(
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Old 10-02-2007, 01:19 AM   #8
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Yea, some freeze frame data would be very beneficial when this happens.
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Old 10-09-2007, 11:30 PM   #9
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Does the Aurora have a reputation for ignition switch issues? The Intrigue does, I was having no-starts, hard starts, start-and-die situations, dying randomly while running, all sorts of weird stuff.

Then I got the hair brained idea to rip apart my dash and remove the ignition switch, cleaned up some contacts, reseated everything nice and tight...every single problem gone.
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Old 10-10-2007, 12:48 AM   #10
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No, however the 2nd gen has bad crankshaft position sensors.

The next pit stop on this most recent train wreck is the fuel pump.
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