OK, I have a 1991 RS with a 305TBI and a 700R4. Its probably coming up on 180k+ miles and though fairly well maintained but not rebuilt I know its nearing the end of its life. (which is why i have a stealth ram 355 in the works) But anyway on to my problem. On my way to work I started it up and all was normal until about 5 miles from my house it started bogging down and shuttering a lot. The oil pressure dropped to about 20 PSI and it felt kind of like running low on gas and sounded like a really clogged up exhaust tip. Well I just topped off the oil with Mobil1 high mileage 5w30 so its not low on oil. But i dont think id get an oil pressure drop with a clooged fuel system component or bad fuel pump. When I checked the oil to assure myself it was full I noticed a slight smell of gas. So that leads me to the question, Do you think its the rings or is it anything else one of you has run into? Either way I guess its time to start really workin on that 355.

 

It could be a number of things. I think you have an ignition problem caused by worn valve guides or bad rings, both of which could foul your plugs and give you an oil pressure drop, 20 psi is still not horrible oil pressure, and could be caused by the low rpms of your bogging engine.

 

I could see that but it usually runs around 40 PSI. Another thing i forgot was that the car did have that valve seal smoke at startup until i used that additive thats supposed to help lube them. Do you think that too could have something to do with it? I drove it around a little today and again it was fine for about five to ten miles before it started doing that again.

 

I think it sounds like worn valve guides that is causing excessive oil to drain into the cylinders and fouling the plugs, which in turn doesnt completely burn your fuel (which your computer could be dumping in more fuel to try to keep the RPMs up) Most people dont realize that the heads, (specifically valve seals and guides) ussually wears out before the cylinder rings do. Do a compression check and pressure check on your cylinders. but on a high mileage motor like that one, it could be multiple things

 

Sounds like either a coolant temperature or map sensor going bad causing the engine to flood out. This will wash down the cylinder walls and get fuel into your oil. If your rings were gone you wouldn't be able to see behind you because of all the oil smoke.

On worn engines bogging or even just heavy loads will cause the crank to move away from the oil holes in the bearings resulting in oil bypassing righ out the side of the bearings. I bet if you watch closely while you go from light to heavy load without the RPM's changing you'll see the oil pressure drop a bit. The amount of drop I get tells me how close I am to a spun bearing. Less than 5 psi is normal for an older engine or a loose bearing performance motor. More than 10 psi and your getting close to breakin somethin. The stock guage isn't accurate enough to use this method.