99Sc1

[Caelan]

What could be wrong with this car? Help!

Details are:
Well maintainted '99 SC1 automatic with 106K km (66K miles) shudders strongly and misfires on cylinder #1 at low speed and especially at idle. By disengaging the trans. into neutral, it calms somewhat. Just tuned and replaced plugs, ignition wires, air filter, PVC without improvement. Bosch Platinum plugs were carbon fouled after 10K. Cylinder #1 plug especially fouled. Electrical appears fully functional. The car does not surge or shudder once it gets going. Shop cannot figure out what is causing this malfunction but discovered that the intake manifold gasket is leaking at right rear of engine. Would replacing this gasket remedy the problems? I have already spend $$$ on trying to fix this and do not want to waste anymore? Opinions? Does anyone else have experience with this problem? Other than this the car is in excellent condition and functions properly.

[travelair]

That's a tough one. An intake leak shouldn't cause those symptoms because air is air and the engine generally doesn't care where it comes from. It sounds like an ignition problem. My #1 spark plug hole fills up with oil and will eventually ground out the electrode. When it starts missing at idle I know it's time to clean the plugs. Check everything ignition related and be sure nothing is grounding. An old trick is to run the engine at night and look for sparks in the engine compartment. Good luck.

On second thought, a leaking intake gasket might allow coolant into the engine. Are you having to add coolant frequently? How often and how much oil do you have to add? Does the oil on the dipstick read high or appear milky?

[sierrap615]

i have heard of this several times before, replace the intake gasket. also, platium plugs are great, on paper. they don't work well in the real word. use standard plugs. NGK brand tend to work best for saturns.

Originally Posted by travelair

An intake leak shouldn't cause those symptoms because air is air and the engine generally doesn't care where it comes from.

this is a case of unmetered air. the engine is getting air the computer doesn't know about, so it can't add more fuel for the extra air.

[Caelan]

I took out the platinum plugs and put in ACDelco ones instead. I was not aware of the platinum problems. The service station told me that this engine does not appreciate plat. plugs. If it's getting unmetered air, wouldn't it be running lean instead of rich? The removed plugs had very dense carbon deposits.

[sierrap615]

Originally Posted by Caelan

If it's getting unmetered air, wouldn't it be running lean instead of rich? The removed plugs had very dense carbon deposits.

yes and no, the unmetered air itself would cause it to run lean, or in this case just cylinder 1. the computer doesn't know this air is going into the engine from the MAP sensor input, but it does see the unmetered air leaving the engine from the O2 sensor, the computer sees extra air to burn, so it adds more fuel. now the engine is running rich but the computer thinks it is running lean.

[Caelan]

Ignition system was tested and is functioning normally. The coolant is full and doesnt appear cloudy. Oil consumption is nil.

[sierrap615]

intake gasket, no doubt in my mind.

[Caelan]

Originally Posted by Caelan

I took out the platinum plugs and put in ACDelco ones instead. I was not aware of the platinum problems. The service station told me that this engine does not appreciate plat. plugs. If it's getting unmetered air, wouldn't it be running lean instead of rich? The removed plugs had very dense carbon deposits.

I am going to get a second opinion on the leaking gasket, just to make sure this is the problem. The garage I was using seemed very....disinterested. I think I agree, sierrap615, that the unmetered air is likely the problem and the engine is compensating by adding too much fuel which would explain the fouling of the plugs. I think the idle might be too low also as it shudders only at idle (750rpm) with the trans engaged. Shifting to neutral or park reduces the shudder drastically and the noise completely while increasing the idle about 250-300rpm. Sensor?
The 'service engine soon' warning light is on about 80% of the time.

I like this car and it has a lot of life left in it so you can imagine my frustration. Thankfully, it runs normally (or appears to) at speeds over 10 km/h (6 mph) or so. The garage want $275 to repair the gasket which seems quite high to me.

[sunny1]

Originally Posted by Caelan

I am going to get a second opinion on the leaking gasket, just to make sure this is the problem. The garage I was using seemed very....disinterested. I think I agree, sierrap615, that the unmetered air is likely the problem and the engine is compensating by adding too much fuel which would explain the fouling of the plugs. I think the idle might be too low also as it shudders only at idle (750rpm) with the trans engaged. Shifting to neutral or park reduces the shudder drastically and the noise completely while increasing the idle about 250-300rpm. Sensor?
The 'service engine soon' warning light is on about 80% of the time.

I like this car and it has a lot of life left in it so you can imagine my frustration. Thankfully, it runs normally (or appears to) at speeds over 10 km/h (6 mph) or so. The garage want $275 to repair the gasket which seems quite high to me.

Hey I know Im a girl and all but.... I have a friend with a 99 saturn sl1 that has 80k miles on it having the same problem... the mechanic is also a friend of mine and had me look on here for a fix... I printed this out and gave it to him and he replaced the gasket among other things and we are still having the same problem... Did this fix your car??? Does anyone have any further suggestions??? Could the computer be telling the number one cylinder to fire at the wrong time???? Not sure what else to do??? Please help!! Tia.... Tina

[sunny1]

Please help asap please..... tia

[sunny1]

Originally Posted by sunny1

Please help asap please..... tia

ok problem fixed.. Im not a mechanic so I dont understand how this helped but it turned out to be the number one injector!!! Yeah...