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I will first start by saying any and all replies are greatly appreciated as i’m at my whits end and have even stumped several friends with this.
I’ll first go over why i did what i did, bought the 2005 buick rendezvous(fwd) with just under 120k miles, everything was great. car ran smooth, did get lower gas mileage(14-16ish compaired to 18-19 in town from other owners), but i thought it was due to some clogged up injectors. Problems started to arise. it had a very hard start as though it was choked out, i began investigating.
So far I replaced:
Thermostat(twice because of head gasket repair in a bottle…)
Water pump that was leaking through bearing/shaft
PCV(cheap and easy, why not)
Fuel Pressure Regulator(could smell gas in engine compartment but couldn’t track it down)
Fuel Injectors(had rough start, thought it was then leaking injector flooding cylinder after car sat for a few hours)
Spark plugs and wires
Cleaned MAF with maf cleaner
Radiator cap for good measure
Fuel filter(though it looked new)
Ran fuel injector cleaner through systemThen i noticed milky substance in oil after about 2 months so i took engine apart.
Replaced Head gasket(took heads to machine shop that resurfaced and checked valves)
exhaust manifold gaskets
rear exhaust manifold from junkyard as mine had a small crack
Lower intake manifold gaskets
Upper intake manifold gaskets
Throttle body gasketafter i put it back together started it up and it would start and rev up slightly(maybe 1500-2k) and die, sometimes accompanied by a backfire/sputter into intake(did take off brake booster hose and verified a backfire with flames shooting out of port on upper intake manifold.) If i tried to rev up engine it would rev up for a very short period to maybe 3500 -4k rpms and die out almost always with a backfire at that point, and if i hold my foot on the gas it will still rev up to about 4k rpm’s and almost die out(foot still floored) and hover at between 600-1000 rpm’s. My first thought was i didn’t plug in my spark plug wires correctly, so i verified and tested, no avail, checked again as i was sure that was what was wrong, nothing out of place. Then a thought crossed my mind that i switched intake/exhaust pushrods so i took LIM off, verified, short on intake long on exhaust, checked for cracks in intake, cleaned up old gasket material from install, reassembled and fired up, same thing.
Did a compression test at this point
[b]Cylinder 1:108
Cylinder 2:105
Cylinder 3:108
Cylinder 4:109
Cylinder 5:108
Cylinder 6:110[/b]Sidenote!!! I Know you may be thinking these are low, i just bought a cheap compression tester from harbor freight and if you read the reviews some people will say all values read low.
looked at plugs, none were fouled or covered with fuel, my next thought was coil packs possibly damaged from removal, possibly getting banged around in engine compartment, so i took old wires i still had lying around and removed:
cylinder 5 – still had backfire
cylinders 5 and 2 – (they share coil pack.) still backfire
cylinder 2 – backfire
cylinder 3 – backfire
cylinders 3 and 6 – (they share coil pack.) backfire
cylinder 6 – backfire
cylinder 4 – backfire
cylinders 4 and 1 – (they share coil pack.) backfire
cylinder 1 – backfireOne of my friends said well it sounds like a restricted exhaust, i told him well it shouldn’t backfire into the intake, but it was worth a shot anyways, as i said i replaced exhaust manifold gaskets and the rear exhaust manifold, doing so you could plainly see, as if it were even possible, that there was no restriction but i unbolted the exhaust from the manifold to the cat, sounded like a damn motocross 2 stroke but no change in behavior.
I then thought it could be the Crank position sensor(b on this vehicle as it directly connects to coil pack.) I wasn’t sure how this vehicle reacted with it unplugged though i thought it wouldn’t start, unplugged it and of course no start, but the funny thing was up until that point i wasn’t sure if it was mechanical or electrical, but when i unplugged it the engine had no restriction, it wasn’t fighting itself. to be honest minus it not running the engine sounded beautiful. i still replaced the crank sensor(3x though for some reason manual says 7x, very hard frustrating job, have to lift up vehicle, remove exhaust completely(cat side) and then feel around with fingers as you can’t visually see it) but had no affect.
I found online a reference to felpro gaskets coming in two different sizes for the 3.4 so i took apart again, verified everything was correct, and compaired old gaskets to new gaskets, though the new fel pro’s left a little more of the intake/head ports through the inside of the gasket, they still make a great seal, i lined the alignment pegs/pins up properly everything still looks perfect, i recheck torque on rocker bolts, and at this point after putting back together with no different result than the first time i start up after initial repairs, am out of ideas.
Both my father and father in law think its a timing issue but it can’t be as the engine ran fine though it had an obvious head or intake gasket leak and it had a hard start which after removing the heads was because it was a head leak on cylinder 6 with coolant in chamber causing the hard start. why i say it can’t be timing is because i never touched any of the components, the timing cover doesn’t require removal to replace head gaskets. i didn’t even mess with the harmonic balancer besides to slip off the serpentine belt
final sidenotes: i referenced multiple sources that all gave the same information(alldata, internet, and a gm service and parts operations online manual) i followed every torque spec, even ones for valve covers which i find rediculous that you’d really need to torque them at all, just tighten up. and mind you, the car drove into my garage over a month ago before the headgasket repair.
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Update, when I unplug my maf sensor engine runs, but at 3k rpms. When I plug it in after its running it will die within about 5 seconds. When I shut it off or it dies I can still hear it whistle at about 1k rpms or less
maybe replace your MAF sensor? that would be where i would go next since that seems to stall it out when you plug it in. these newer cars nowa days with all theses high tech electronics can really throw you for a loop. i have a vehicle that had some corrosion on the battery terminals and you would have thought there was a huge electrical issue but all i had to do was clean the terminals and the post and put some of that red spray shit on and i haven’t had a problem since, but i swear you would have thought that vehicle was in dire straights
Went to junkyard pulled a maf sensor off a 2004 malibu with a bad transmission, went home plugged in same problem, cleaned out with maf cleaner $9 a can at oreilly’s still same issue, I’m starting to think I have a huge vacuum leak somehow though I’ve checked everywhere. When I get home I’m going to check for a crack near where the throttle body connects to intake. Not sure what else to look at
[i]First off, you need to determine whether it is backfiring out the exhaust or back up through the carb. We usually refer to an exhaust backfire as a “backfire”, and backfiring through the carb/intake as “spitting” or “coughing”.
“Backfiring” is usually caused by a spark plug “sparking” when it isn’t its turn and the exhaust valve is open. If your air/fuel mixture is too rich and you have unburned fuel in the exhaust system, cross firing from one spark plug wire to another can occur if they are touching each other and when this happens while the exhaust valve is open, it will ignite the rich / unburned mixture in the exhaust manifold and tail pipes and result in a big bang.
Having timing that is too late (retarded) can cause this same thing sometimes if your engine is running too rich. When the exhaust valve opens, the mixture isn’t done burning so it ignites the unburned fuel in the exhaust system and causes a loud bang.
Back firing can also be cause by a cracked distributor cap, or one that has carbon tracking inside which causes cross firing between the terminals inside, which in turn, sends spark to a spark plug that isn’t ready for it yet.
As with backfiring, coughing or spitting can also be caused by a bad ignition system, such as cross firing, which sends a spark to a cylinder that has the intake valve open. When that plug sparks out of turn, it lights the fuel in the cylinder and the pressure has to go somewhere… so if the intake valve is open, it goes right back up through the intake manifold and out the carb with a “spit” and sometimes even a flame.
When and how it backfires or spits will give you an indication for where to look.[/i]
It is spitting then, I’ve seen flames shoot out the upper intake plenum’s brake booster vacuum port that I had removed trying to figure out what was going on. The spitting isn’t occuring that I’ve noticed when the maf is unplugged, infact at high rpms 3k is what it revs naturally to atm it seems to run fine no sounds no whistling no spitting, only way I can get the idle to drop is plugging in the maf and it basically immediately kills it, as its dropping rpms down to 0, guessing here but at around 1k rpms or so you can hear it whistle just milliseconds before it dies.
So to anyone reading I finally found the cause. The throttle body gasket that I replaced didn’t get put on right and was blocking half the throttle. Straightened it up and it purrs like a kitten minus the bellowing smoke from handling the exhaust. Thanks for all the help everyone!!! Now I need to replace the heater core next!
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