1996 Buick Century V6 dying after ~10 minutes, fuel filter & ignition coil replaced, at my wit's end

Okay, here’s the background. I’m about at my wit’s end, so I’m hoping maybe one of the car guys here will have some ideas. I have a 1996 Buick Century Custom with a 3100 V6 SFI Engine. The engine was replaced a bit over a week ago, because the old one had developed a constant misfire that wasn’t cured and the shop was suggesting $3k+ for a head job and teardown in the hopes that would solve the problem. The new engine was a reconditioned used motor, with 50k miles on it and a 1 year, unlimited mileage warranty.

I picked up the car on Friday and it was running fine, no problems, and I drove it home. On Saturday afternoon I got in the car and the check engine light was on, with the P0113 and P1406 (IAT Sensor Circuit High and EGR Valve Pintle Position Sensor, respectively) codes.

When I was driving to the parts store on Sunday to try and pick up a repair manual and new IAT sensor, the car totally died out – stopped accelerating at all. I could put my foot to the floor and get nothing, and then the engine died entirely and the battery and oil pressure lights came on. If I tried starting it right back up, it would start and immediately die again. If I left it to sit for 10-15 minutes, it would restart and run a while, but then die again.

Had my family mechanic looking at it yesterday, and we replaced an ignition coil (this car has the distributorless ignition) that didn’t seem to be firing from both sides and the fuel filter which hadn’t been done in years and was pretty full of crud. Neither fixed it.

Finally he found what we thought was it, the wire connector to the ignition coil assembly (the purple & yellow, 2-pin plug that goes in to the base where the coils are) seemed to be shorting, because if we pushed on or wiggled it at all, the car would immediately die.

So, today I replaced that connector (got a new connector, cut off the old one, and spliced the new on in) but am still having the same problem. The car will start and run perfectly fine for about 10 minutes, and then die. Makes no difference if the car is idling or if it’s driving under power, it still dies out.

The fuel pump seems to be working (can hear it kicking in when I turn the car on, and the car does run fine for the 10 minutes or so). The fuel filter has been replaced, the EGR valve has been replaced, the Intake Air Temperature Sensor has been replaced, and the Ignition Coil that tested bad has been replaced. The spark plugs and wires are all new.

The shop that replaced the engine is about 30 miles away, so getting it towed back up there is a costly proposition, and their answer is “If it ran fine for 3 days before it started dying, it probably wasn’t anything we screwed up, and all we did was swapped the motor, we didn’t change out anything else on your car, so if it’s ignition/electrical/fuel/whatever, it’s not our problem.” I’m at my wits end, so if anyone has some ideas I’d love to hear them.

There are two other things to check for this type of stalling problem. Either the ignition module is defective or the crankshaft position sensor is defective. Since the engine that was installed had all the orginal components it could be that one of these components are defective on that engine. If you still have access to the engine that was removed from the vehicle, remove those components from that engine and replace them on the new engine to see if that fixes the problem.


The fuel pump could still be the problem. The IAT should not cause the engine to randomly die and while an EGR fault could cause the engine to run rough or die at idle it should not cause the engine to die at speed. It could cause a surge at speed though.

I’m afraid that I’m going to be of little or no help on this one due to an engine swap, a who knows who did what scenario, and in my humble opinion; maybe a shaky shop.
They were wanting 3 grand for a teardown, cylinder head job, and they “hope” the misfire would be cured? That’s a pretty ludicrous way of going about things.

I mention the pump because long term running of a fuel pump with a clogged filter can seriously shorten the life of the pump.
You might try connecting a fuel pressure gauge to it and see what happens when the engine dies. I might also add that if the pressure goes to zero and the engine dies this does not necessarily mean the pump is bad. There could be a pump control issue.

There should be a test plug somewhere (small wire with a tiny connector) for the fuel pump. (Maybe near the passenger side firewall?)
When the engine dies run a jumper wire from the battery positive terminal to the plug and the pump should run. If it continues to run fine like that this means there’s a control issue rather than a pump issue. Hope some of that helps anyway.

Does it still die immediately if you pull on the wire with the replaced end? I would check the condition and connections of all battery cables and terminals. Test for spark at any of the plugs when it won’t run. An old cheap neon timing light is great for this. Are you getting any codes now?

Hi everyone, sorry, forgot to write back with the updates once I got the thing fixed. I appreciate all of the thoughts and suggestions. As it turned out, tester was spot on. The ignition control module was shot, and one of the ignition coils was bad as well (best guess, either the coil fried and took out the ICM, or the ICM fried and took out the coil, but there was a nice big burned hole where one of the connection pins for that coil went). Once the bad coil and the ignition control module were replaced the car started running fine again.


Tester is the man… Actually everyone gave you good advice. But we are severely limited doing diagnostics this way. If we were all actually there hanging out trying to fix the vehicle…Some small things may point us in the right direction…I mean I have actually correctly diagnosed some cars just by smell and sound believe it or not…I am sure these guys have similar stories. Glad you got it fixed AND THANK YOU FOR UPDATING US ON WHAT IT WAS…we give so much advice and never get an update or anything…thats annoying Y’know?

Yeah, I know it’s a bit of a longshot trying to do diagnosis via website with just relayed information, but I figured if nothing else it might give me some suggestions for what to check next and give me an idea if it was DIY-able or time to get ready to write a big check. As for updating you guys, I’d forgotten I’d posted here or I would’ve done it sooner. I know how annoying it can get to put ideas and suggestions out there and have no idea whether or not they helped, etc., and I really didn’t want to be one of those people who forget to say thanks!

Unfortunately now that I’ve gotten all that fixed a new (well, actually, I guess semi-old) problem cropped back up – that P1406 code is back again. Since I did a good bit of work to the car since this last post I went ahead and started a new topic for it this afternoon, but if anybody from here has any thoughts on it I’d certainly still appreciate them again! Beyond the ICM and coil that I mentioned above, I’ve also replaced my catalytic converter, as it was pretty well shot from running with the old engine misfiring as badly as it had been, and a couple of my fuel injectors which weren’t firing well, and performance-wise the car seems to be running fine now, just got that pesky check engine light again, which poses issues for passing my emissions next year.