Help with diagnosis.

[sr5luv]

Hey guys, I went through a pretty good search process already. but I want to get a more definitive answer before I go and spend money in all the wrong places.

My 85 has been lacking real bad in power. She also has what smells like a fuel leak.(although i cant find it) And compared to my 83, sounds like there is a vacuum leak in the P/R side of the engine. (Although I have checked all the lines) I know she has an exhaust leak where the header is attached to the downpipe. I found that out after my seafoam treatment. I have changed the spark plugs( 2/4 were really black and sooty.) And ive changed the fuel filter. But every time i put her under load. (going uphill, upshifting to soon, or even just plain driving) she will jerk and buck like a bad horse. Do you guys have any good answers for me? I'm thinking a fuel pump?

[dlb]

so there is a gas smell, an exhaust leak where the manifold meets the pipe, and it's bucking under load and at low revs. the exhaust leak is probably its own problem while the gas smell and bucking under load are possibly related, but not necessarily.

there are some simple fuel pump tests in the FSM so try those to start with. the fuel line from the tank to the pump could be plugged with crap too. just disconnect the line from the tank and the filter, get someone to hold a rag over one end, and blow compressed air into the other. check the rad and see what came out. you can also do the line between the filter and the pump but it should be clear since the filter should strain any big stuff before it gets downstream.

you should also check your timing with a timing light. base timing is 5* BTDC with the vacuum advance hoses disconnected and plugged. once you hook them up, the timing should advance to 13* BTDC. you should also remove the distributor cap and check for a small amount of spring-loaded counter clockwise play in the rotor. if there is none, the advance mechanism is gummed up and the distributor must be disassembled, the old grease cleaned out, new grease put in, and reassembled.

[Petros]

sounds like you have fuel starvation. first replace the fuel filter if you think the seafoam may have loosened enough gunk to plug it up, that is usually the cause.

Check your motor oil and see if it smells like fuel. if the fuel pump has a punctured diaphragm it will still pump, with diminished capacity, and weep fuel out the vent hole on the underside of the fuel pump. or worse, into to engine, thinning the motor oil. Check your motor oil, if it smells of gasoline and looks thin, DO NOT DRIVE IT. Change out the oil and replace the fuel pump.

[sr5luv]

thanks for the help guys. turned out it was a bad plug wire.

[keith]

Good that you found it, but if you haven't done the examination of the suggestions above, you may be overlooking opportunities to make further improvements. Timing is critical and as any car of this vintage or older, the weights that control the mechanical advance tend to stick. I would not grease them though, I would use an oil, I prefer a light viscosity synthetic oil for this.

The vacuum advance diaphragms dry rot and get holes in them too.

One thing not mentioned is to find the connector for checking the O2 sensor and check it. You should get a good sweep of voltage from about .2 to .7 volts every second or so at this connector. This will keep your A/F ratio closer to optimum for best power and fuel economy.