PontiacBonnevilleClub.com

So I've noticed an increasingly annoying issue with my Bonneville, and that is that it bogs when I hit the gas sometimes. It seems to be mainly limited to giving the car decent throttle from a roll, usually during a downshift. As it downshifts, it'll bog once or twice and finally go. It's also been bogging when starting too, as it'll start up and then bog down to almost cutting out and then kick back to life and run fine. Sometimes when I crank it, it'll crank and then just cut out before it even starts, but a second attempt always proves successful.

What's new (that hasn't made a difference)
-all 3 coils (Delcos)
-plugs/wires back in January
-fuel filter (Delco)
-LIM gaskets/UIM (APN kit, Prestone, etc)
-air filter (2ish months ago) (purolator)
-new upstream O2 sensor (maybe a week ago, and yes, it's a Delco).

No codes have come up for awhile and the torque converter hasn't been acting funky for awhile either. All gauges appear to read normal and temperature doesn't really seem to make any difference, though it MAY be more prevalent when warmer. The only codes that were present some time ago were a bad O2 sensor (hasn't come back since I put the new one in), and a P0742 (TCC stuck on condition, but that hasn't showed its face for a bit now either).

Could it be:
-bad fuel pump? (probably not though, as it sounds strong when it whirs to life and pressurizes the system and only does so for 2-3 seconds)
-vacuum leak? (I'm leaning towards this one)
-prematurely bad plugs (I'm pretty sure they're Autolites...don't remember)
-funky cat even? (I'm replacing that tomorrow morning with a Magnaflow direct-fit)
-bad fuel injectors?
-or a bad sensor (MAF, etc)

Scan it for KR, and look for a coolant leak around the heater hoses on the belt tensioner that's dousing the rear knock sensor connector. Mine has had a lot of these random massive power losses, and it's a knock sensor wiring issue with my car.

What's your fuel economy like? The other car that had this was getting 23 mpg highway, IIRC.

Yours sounds like it's losing crank sensor timing.

I don't have a scanner available to me to use, but I'll check for coolant leaks. For the record though, my coolant level remains constant and steady above the line and this problem is occasional, not constant. The other half of the time it drives like a champ.

Regarding fuel economy, I've never measured it yet, but it's not all that swell since my O/D is out, not to mention that most of my driving is around town and maybe some light highway driving, not to mention I'm hard on the gas a lot.

Well, new crank sensor hasn't made a lick of difference either. As before, the car bogs on startup once (the RPMs will surge down once before going back to normal idle speed), and the car feels like it's choking/bogging when I give it gas from speed to downshift usually. This seems more prevalent during hotter days. Most of the time the car drives pretty strong and has no issue in higher RPMS (so I can't imagine it's starving for fuel or air at all). I still think maybe a vacuum leak, but where are all the spots I should check for a leak? Bad ICM maybe?

Have you tried replacing the ignition module? I had issues with my '90 bonneville (bogging down/miss firing) and it took us weeks to diagnose the problem, but we finally landed on ignition module and after that it ran perfectly.

That's what I was referring to when I said ICM (ignition control module). I have not attempted replacing it yet though the coils are new. I've suspected it as one of several possibilities for awhile now, but haven't gotten around to checking it yet. It'll likely be the next thing I check into though.

Could it be a bad throttle position sensor? That might cause a bad bog since the throttle is letting in more air before the PCM gets the MAF signal saying to inject more fuel to compensate.

LeSabre in Buffalo wrote:Could it be a bad throttle position sensor? That might cause a bad bog since the throttle is letting in more air before the PCM gets the MAF signal saying to inject more fuel to compensate.

Based on how you put it, that sounds like it could be a possibility. I've considered that too but haven't bothered with it yet. My car has definitely had increasingly more difficulty starting lately, with it failing to start 2 times in a row before a successful 3rd attempt. But then other times, it'll start up virtually right away with a quick bog right after starting before idling normal.

EDIT: Oh, and it seems to be worse when it's hot out.

Sounds like a fuel pressure regulator. They're known for leaking with age. Hard starting is often a symptom. Pull off the little vacuum elbow on it and sniff for gas. If you smell ANY gas, replace the regulator since it'll be bad.

I think it may be your TPS.

Our 1993 Bonneville bogs as well. No power, bogging. When the check engine light is on. When it is off, it runs OK. We have a TPS code and it makes sense. We will be replacing it soon and I predict it will be good again. It does this on hot days, cold mornings it also jerks and whatnot, the idle drops. Sometimes it stalls when coasting in parking lots.

EDIT: We never have issues with starting. So maybe you should check out that regulator as well.