96 grand am stumbles while accelerating

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2.4L 4 cyl

So the other morning my wifes'mothers' car was in the driveway when I got home. It wouldnt stay running, so I swapped out the coil packs(her idea), didn't help. She doesnt believe in regular mantienance, so I put the old coil packs in and got new spark plugs, now it will idle fine. It idles funny but all pontiacw do imo, but at least now it will stay running.

The issue now is it stumbles on acceleration, if you feather the gas it will get up to 3-4k rpm but as soon as you tap the petal it bogs down. I'm thinking fuel filter, but it was rusted too bad to get off today so its soaking until tomorrow. (Love Ohio cars)

I got my OBDII scanner back and my wife ran the codes this evening, I'm at work, there were 3:
P0300, random misfire detected
P0141, o2 heater circuit: bank 1, sensor 2
P0440, evaporative emissions systems

I had her reset them and turn the key forward, no codes, as soon as it started up, random mifire detected code, I bet if it ran for 2-3 minutes the o2 code would pop up too.

So tomorrow I'm going to replace the fuel filter, would a bad o2 sensor make it misfire? What do you make of the evaporative emissions code? It's had this problem for awhile, at least a few months I know of, but now its to a point she wants to do something about it, its undriveable.


Oh, I listened to the injectors and they sound fine, I used pliers to pinch the vacuum hose on the fpr and no change in the idle, no fuel in the vacuum line when I pulled it off either, and without it attached there was no change in idle. Is the idle supposed to change when you pull the vacuum line off the fpr?

[FestYboy]

yeah... put the new coil pack back on. bet you have bad boots or weak coils from the crappy plugs.

the O2 won't cause a misfire directly, and in your case, you likely have a bad heater in your post cat o2 sensor (common issue).

the evap code is a leak, usually you'll see it at the vent solenoid for the carbon canister (spider webs), OR, a bad fuel cap (very common).

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I had the new coil packs in with the new plugs and it still does the same thing, so I swapped the old ones back in, they were just changed last year sometime so they're not 220k coils lol.. I scuffed up the contacts and wire brushed the springs. The boots look like they were replaced when the coils were put on last time, theyre just a piece of rubber with a spring in the middle. The coil cover thing? Was new last year too, and still looks brand new..I wire brushed the contacts even though they didn't need it.

The car won't rev past 4k at all(with new coils), its like a rev limiter kicks in, so I was thinking its not getting enough fuel?

When I asked her when the last time the spark plugs were changed she said she 'thought' last year, they're at least that old, she 'thinks' she got a new fuel filter 3 years ago...its pretty rusted.

I pulled about 50 nuts out of the air filter box, and blew a couple pounds of dust off the filter...I don't know how it was getting any air, it was that was bad.

[FestYboy]

in gear or in nutral? and that misfire; how long was she driving like that before you started working on it? i'm betting there's a cat that's about to clog shut on you rather soon.

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Auto tranny, its been in park the whole time, happens in gear too. If the fuel filter doesn't pan out ill disconnect the downpipe and see if it helps. I drove the car back in ..may? And it occasionally would stumble, especially with a load like slow speed uphill.

[FestYboy]

yeah there may be a rev limit in park/neutral and that would be set at 4k, but if it happens while driving as well, look at the cat.

[zoom zoom]

Ok, I got the fuel filter off today and blew it out, it was a little gunked up but I blew it out with an air hose so I think it's good...didn't change anything.

I completely disconnected the downpipe, and now it doesnt try to stall or drop rpm when you tap the gas from idle or a steady rpm like 3k. I reset the codes and none came back immediately, it idled for about 2-3 minutes and I built up rpms, when it hit 4k it's like a rev limiter kicked in and the random misfire code came back on.

I took the top end back off and did a dry compression test.. it read 180-190 across all 4 cylinders.

The car idles around 1000-1100 rpm, may or may not have anything to do with anything.


I started the car, let it idle for 20-30 seconds, and put it in gear, I did this a few times and it stalls in reverse and neutral as soon as it goes in gear unless you give it gas. It won't move without stalling.....this is without the downpipe connected, just an open exhaust manifold.

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Also, when I did the compression test, the spark plugs for cylinders 1&4 were white, #2&3 were both solid black like they haven't been firing.


The only thing I can think of that I haven't messed with on the ignition system is the crank position sensor and the cam sensor on the head. I pulled the timing chain cover back and from what I can tell its fine, theres a ton of oil in there though making me think the crank sensor is gummed up and needs replaced... I hope I don't have to go that far, but I've got 2 days off tomorrow and the day after, so if it needs done it needs done.

[Nerd Racing]

lit rag will fix it up pretty well.

I will never buy anything with gran in the title, unless its a grand national.

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Thinking about the spark plugs has me wondering which coils go with which plugs, maybe now that it can breathe its just one of the coils gone bad for 2&3? The cam sensor I referred to isnt really a cam sensor I think its the idi unit, but I'm not entirely sure what it does yet..still reading.

[Bert]

No offense, but there is a reason I love old carb vehicles that only have a single wire going from the ignition switch to the coil. No spark/no gas, and everything else is directly related. This business of trying to anticipate what manufacturers are doing with electronics is entirely non-intuitive (to me) and likely to everyone else or they wouldn't be relying 100% on made-in-China/Taiwan/India 'code readers' to tell them what's going on.

I'll tell you I was entirely un-impressed last spring when I discovered there is an electronic pickup within the distributor of EFI Festys that signals to the ECU that the distributor is turning (and therefore in 'computer programmer-speak', in every likelihood so is the engine) which then activates a signal to the ignition module to send high voltage current through the coil. Ought to be perfect for directing spark at such time that the distributor is turning. But no, when the dizzie pickup fails the computer does not recognize that the motor/dizzie is turning, even though it physically is!
So, ultimately you wind up at the side of the road with a completely dead car that turns fine but has no high voltage at the coil. And a replacement dizzie is about far from your mind as it gets under those circumstances because distributors are an age-old ingeniously simple device devised to distribute high voltage and not at all be secondarily enlisted to curtail it.
Stupid bastards, if might say so. Bastard is not a swear word (in my dictionary) but increasingly more likely an apt description of the illegitimate progeny of 2 computer nerds that believe they know how to engineer/operate engines)

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Book says 1&4/2&3 are paired, so I'm going to replace the coil again after I figure out which one.

A car is a car and this one is broke so it needs fixed, and somebody's got to do it, so it might as well be me. Could be because I'm young and dumb, and haven't lived 50 years of constantly being reminded I'm worthless, but all these fancy wires don't scare me as much as they probably should. Who knows, I might learn something in the process, instead of having someone else do it while I remain ignorant and talk about carbs like I have any clue about those either.

[Bert]

Hey zoom zoom this was not a snub of you, just me venting about the often needless electronic complexity of vehicles. Guaranteed the military doesn't run around in cars/trucks that have acres of gear dedicated to reduce emissions. Probably explains why surplus Hummers are not released to the general public and get chopped up instead.

You'll get your problem sorted out, just not by advice from me. Good luck.

[econoaddict]

Guaranteed the military doesn't run around in cars/trucks that have acres of gear dedicated to reduce emissions.

Spent 6 years as a mechanic in the military, every vehicle 1 ton and smaller had all the crap on it a civilian rig did plus all of the military add-ons, radios, satelite gear, weapon systems etc.....not even close to simple as most think.

[Bert]

Spent 6 years as a mechanic in the military, every vehicle 1 ton and smaller had all the crap on it a civilian rig did plus all of the military add-ons, radios, satelite gear, weapon systems etc.....not even close to simple as most think.

Is this for kept-at-home gear or does this also apply to war zones? If my life depended on rolling stock I would be the first to get rid of sensors and doo-dads that shut an engine down because it was not running quite right. Imagine a convoy grinding to a halt out in the sticks because the only gasoline they could get clogged all the Cats and blinded everyone with Check Engine lights.