Car trouble

[KD5NRH]

1994 Sunbird LE 2.0L 4 cyl

Was running fine, did a good bit of freeway driving yesterday with no noticeable issues except the occasional random misfire at low RPM. Just enough to put it on my "tune up at some point" list, nowhere near "this is going to get nasty very soon" level. On the way home last night, I stopped for about an hour and a half to visit some friends, got back to the car, it started fine, ran pretty well, (cold weather and enough time to cool off, so a little rough was expected) and the "check oil" light came on. Checked the oil, and it was at the bottom of the "ok" range on the dipstick. Had some in the trunk, so I got it back up to the top of the range and took off again. Maybe five minutes of 30-45 MPH driving later, I went to get on the highway, and suddenly it got really rough with an obvious power loss. Roadside fiddling determined that pulling the #1 plug wire made no change whatsoever in the idle, so presumably #1 is just dragging now.

Got enough spark to shock the heck out of me when I pulled the wire, but again, no change at all in the rough idle. Pulling any other wire pretty much kills the engine, regardless of whether #1 is plugged in or not. Replaced the spark plug, then swapped them around to make sure I didn't just have a stroke of really bad luck and put DOA one in there. Some carbon fouling on all the plugs, but not bad considering they were probably in there for 60-100k miles before I got the car.
I can smell a little gas when I pull the plug out, but of course, no way to know for sure whether it's getting a good fuel/air mix that way.  Stuck a screwdriver as stethoscope on each of the injectors, but I can't tell any difference between the sound of them...or the sound I got from the screwdriver on the fuel rail itself for that matter.  Can't find a 12V check light to see if the module is firing the injector, but I may grab one when I limp it past WalMart on the way home.

This one is the one with a specific coil pack that's $500-700, so no way I'm going to change that as a troubleshooting step on a car that I only paid $500 for. I can go back to Craigslist and find another $500 beater that runs as well as it did for the last month, but if there's a $50-100 option, I'd like to keep it running for a couple months while I save up for something in better shape, and hopefully sell it to some other guy who just needs a beater to get around for a while. (With full disclosure of its remaining problems, of course. Sometimes "It gets down the road right now. No promises about tomorrow." is worth $350 to someone.)

[bedlamite]

Detcord.

[KD5NRH]

Detcord.

Believe me, if I had some, it would be used on whatever sick bastard came up with the layout for stuff in the engine compartment of this car.  Starter is on the back of the block, but not quite near enough to the bottom to be easily accessible from above or below, (fortunately it only needed the mounting bolts tightened when I was worried the solenoid was going out) and the coil pack and control module are above that, tucked under the fuel rail and intake.  The top radiator hose is just barely in the space where your extension needs to be when removing or installing the #1 plug, so you have to be extra careful not to crossthread it.  Nearly every hose or wire that you know leads to the part you need to find disappears under and/or behind the block.

[Hawkmoon]

Compression check. More than likely you have a valve that's not valving. If you don't have compression, fuel and spark don't accomplish much.

[RocketMan]

Are you sure it isn't bad spark plug wires?  You could be losing spark, arcing to the engine frame.

[KD5NRH]

Are you sure it isn't bad spark plug wires?  You could be losing spark, arcing to the engine frame.

Redneck test (put the plug in the wire and hold it against the block) showed spark at the plug.

[RocketMan]

Redneck test (put the plug in the wire and hold it against the block) showed spark at the plug.

Run the engine in the dark and look for sparks jumping from the sides of the cable with the cable routed and laid in the standoffs correctly.  Even at that, you probably wouldn't see anything arcing into the standoffs themselves.  If the cables are original, just replace them.  Might be a cheap fix.

[dogmush]

Hawk's right. Check compression.

What color is the spark when you redneck test it?  If it's decently hot it'll do something, even if it's not at full strength.

[KD5NRH]

Hawk's right. Check compression.

Noticed a little oil at the valve cover gasket, so that needs to be swapped out anyway.  Shows $6 for the basic FelPro, so if anybody local has a one in stock tomorrow, I'll just yank the cover and see what in looks like in there.

What color is the spark when you redneck test it?  If it's decently hot it'll do something, even if it's not at full strength.

Fairly white, bright enough to show well in full sun.

[KD5NRH]

Finally thought to do the paper test; paper held at the exhaust pops hard against the pipe in time with the miss, so almost certainly a stuck open exhaust valve.

This should be fun.  Hope somebody's got that valve cover gasket on hand.

ETA OReilly frickin' rocks.  None here, or the next town each way, (not that 30 miles on 3 cylinders and doing the work in their lot would be much fun) but then..."I can have it around 3:00 tomorrow afternoon."

My plans of going to the Dallas dance lesson are still shot, but at least I can get to it tomorrow instead of trying to shoehorn in some time next week.

[lupinus]

I'm going with squirrels.

[KD5NRH]

Well, removing the spark plug and shooting carb cleaner in, then cranking it with the plug loosely threaded (to encourage it through the exhaust valve but hopefully not cause too much trouble if the valve decided to slam shut with liquid still in the cylinder and hydrolock it) didn't get it. The gasket should be in soon, so we'll see how the simplest surgical option goes.

[charby]

Well, removing the spark plug and shooting carb cleaner in, then cranking it with the plug loosely threaded (to encourage it through the exhaust valve but hopefully not cause too much trouble if the valve decided to slam shut with liquid still in the cylinder and hydrolock it) didn't get it. The gasket should be in soon, so we'll see how the simplest surgical option goes.

That is a good way to blow the plug out the head.

[KD5NRH]

That is a good way to blow the plug out the head.

Not a full crank and run.  Just a few rounds worth of starter bumps to push the cleaner up through the valve.  I've sent plenty of blue towels across the yard blowing Sea Foam and Berryman's out after a piston soak, so I'm well aware of the force coming out the plug hole even just running the starter steady for a few seconds.

[KD5NRH]

Unnecessary complexity strikes again.

Can't move the fuel rail enough to pull injectors with the throttle body in the way. Can't get the TB out of the way sure to some stupid hose attached to the bottom of it with a hose clamp that's facing the wrong way so I can't get to the screw.

WTF happened to the TB just being a dead simple thing with air in on one side, air out on the other, and a butterfly valve to control the rate?  WTF does it need two hose and three electrical connections for?

[KD5NRH]

Unnecessary complexity strikes again.

Can't move the fuel rail enough to pull injectors with the throttle body in the way. Can't get the TB out of the way sure to some stupid hose attached to the bottom of it with a hose clamp that's facing the wrong way so I can't get to the screw.

WTF happened to the TB just being a dead simple thing with air in on one side, air out on the other, and a butterfly valve to control the rate?  WTF does it need two hoses (in addition to the air intake) and three electrical connections for?

[dogmush]

Throttle Position Sensor, Idle Air Control, the third is likely a trans control of some kind.

The two hoses are coolant lines to warm the throttle body a bit.  This prevents ice forming under certain circumstances and freezing your throttle open.  Pretty much all carbs and throttle bodies have some way to heat them built in to combat throttle blade icing.

ETA: I don't work on old pontiacs but it's usually best to unbolt the TB from the intake, then go for the hoses.  That little bit of movement makes them easier to get to.

[Brad Johnson]

Having free air spark and spark under compression aren't necessarily a 1:1 guarantee. You said the plugs were fouled and likely had 60-100k before you got the car. Change them all. Even if they aren't this specific problem they're still a problem in general. Wires too. Wires can break down in strange ways and cause odd misses even if they outwardly appear fine.

As others have said, compression test.

With the age and mileage I'd be less prone to think stuck valve and more likely be eyeballing injectors. If the compression test checks out, swap the injector from the dead cyclinder with one from a firing cyclinder. See if the prob follows the injector. Requires no parts and is relatvely simple so why not?

You'll be able to see valve actuation when you have the cover off to replace the gasket. I wouldn't spend a lot of time or effort on "stuck valve" diagnosis until then.

Brad

[never_retreat]

Does that thing have one coil pack per per plug? If so there might be just one dead one. You can try switching them around.

[Brad Johnson]

IIRC those years used an multifire coil pack. All the plugs fired from a single coil assembly.

Brad

[dogmush]

IIRC those years used an multifire coil pack. All the plugs fired from a single coil assembly.

Brad

The 2.0 did.  The 2.2L and the V6's used multiple twin coil packs.

[never_retreat]

IIRC those years used an multifire coil pack. All the plugs fired from a single coil assembly.

Brad

Tat was really straining my brain. I had a sun bird after high school if I can remember the car was 1990.

[Nick1911]

I'll echo what others have said... Start with a compression check.

That will tell you if the mechanical is, by and large, okay.  Especially after having a "Check oil" light (which I take to mean as GM's version of an oil pressure indicator lamp), you may have something internal going on.

[wmenorr67]

Where are the days one could be working on a car and not have to worry about all the extra BS wires and hoses in the way?  I can remember climbing up into the engine compartment of a truck, with a big block mind you, and still have room to move around and actually work.

[KD5NRH]

Throttle Position Sensor, Idle Air Control, the third is likely a trans control of some kind.

Yeah, and probably need to figure some way to spoof the IAC.  It's trying to idle up to 3k+ RPM sometimes.  Whatever idiot decided that RPM shouldn't be the "if this goes out of range, forget everything else and readjust" factor needs to be taken out, flogged, flayed, dipped in lemon juice, shot, drawn, quartered and the remains burned.

The two hoses are coolant lines to warm the throttle body a bit.  This prevents ice forming under certain circumstances and freezing your throttle open.  Pretty much all carbs and throttle bodies have some way to heat them built in to combat throttle blade icing.

Ah, yet another "feature" necessitated by fools who insist on living outside the habitable zone.

ETA: I don't work on old pontiacs but it's usually best to unbolt the TB from the intake, then go for the hoses.  That little bit of movement makes them easier to get to.

It was unbolted.  Problem is the hose clamp is turned around so the screw is completely inaccessible.

The 2.0 did.  The 2.2L and the V6's used multiple twin coil packs.

It's the 2.0, and that coil pack goes for $675 new, $200+ used.  Definitely be stripping that off if it dies on the side of the road.  Between that and the alternator, I could recover half my investment without any really heavy work.  If I can find something better soon, I'll borrow the boss's trailer, park this one on it, and strip everything that I feel like I can get more than scrap value from before hauling the remainder off to the scrapyard.  Might even turn a profit in the end.