1987 Caprice issue

My 1987 Caprice has no power on the highway and struggles to get above 60 mph. Normal driving in town everything seems OK. Once it gets on the highway and in OD, power seems non-existant. Car also doesn't seem to downshift correctly. I have to slam the gas pedal to the floor before it will downshift a gear. This car has the 305 "H" code engine. I have had it several places and received different diagnosis at each place. One said the timeing chain had slipped. One said I got a tank of bad gas, even though I told him it has been going on for 6 months. Any suggestions? Thanks in advance.

My 1987 Caprice has no power on the highway and struggles to get above 60 mph. Normal driving in town everything seems OK. Once it gets on the highway and in OD, power seems non-existant. Car also doesn't seem to downshift correctly. I have to slam the gas pedal to the floor before it will downshift a gear. This car has the 305 "H" code engine. I have had it several places and received different diagnosis at each place. One said the timeing chain had slipped. One said I got a tank of bad gas, even though I told him it has been going on for 6 months. Any suggestions? Thanks in advance.

Does it produce a lot of heat while you're at speed? Almost, if not, on the verge of overheating? Do you ever smell a rotten egg or lit match (sulfur) smell? The power loss at speed is a big symptom of an exhaust restriction, usually a plugged catalytic converter. It could also be a timing issue (spark knock, ESC) or fuel delivery issue (carburetor, plugged air/fuel filter). My early money is on either the air filter or the cat. If your Service Eng. Soon light is lit, then by all means change the air filter.

First some answers to your questions. The car does run hot. I have replaced the radiator and water pump due to leaks on both. The carb is new and the air filter is a month old. The sulphur smell is not noticeable, if present at all. Sounds like it may be the cat/exhaust. Is there an easy way to tell if the cat is bad?

Forgot to mention that the check engine light does come on on the highway.

Forgot to mention that the check engine light does come on on the highway.

OK, do a quick check on the trouble code. You can do this by shunting pins A and B on the ALDL connector on driver side, under the dash and to the left of the steering column. Jumper the two pins together (you can use a paper clip if you wish) and turn the key ON, but DO NOT START the engine. The malfunction indicator lamp (MIL or Service Eng. Soon) will flash a series of flashes and pauses. You will see a flash-pause-flash-flash at first - this deciphers as Code 12 - this will repeat 3 times. Code 12 means the system is working properly, but is not receiving reference pulses from the distributor (because the engine's off). Next, you will see, in sequences of 3, whatever diagnostic trouble codes (DTCs) are saved in memory, incrementing until there are no more at which point the system will flash a Code 12 before repeating.

Pay no attention to the clicking you will hear from under the hood - this is the M/C solenoid on the carburetor being driven by the computer (you normally don't hear it because the engine is louder).

My guess is you will either see a Code 34 (flash-flash-flash-pause-flash-flash-flash-flash) or a Code 45 (flash-flash-flash-flash-pause-flash-flash-flash-flash-flash), meaning MAP sensor or running rich air/fuel mix. A catalytic restriction can sometimes show up as a Code 34 MAP sensor on these cars, because a restricted exhaust system will seriously drop engine vacuum (you can test for this with a vacuum gauge - should read around 15 in/hg at idle, rev engine and it will drop during revving, but should return to ~15 in/hg). A Code 45 can be either a plugged air filter (you said you changed it though) or a maladjusted/malfunctioning electric choke. Make sure the wire is firmly attached.

I'm betting on a plugged up cat. If the car has considerable mileage and the cat is original, you can't go wrong replacing it. I've also seen exhaust pipes collapse internally, some are double-walled and the internal sleeve folds in for some reason, but this is rare.

Have any of the mechanics given you an emissions readout on the car? Just curious, that would be one of the first things that they should have done.

Bob

Thanks everyone for the suggestions. In answer to the question about emissions, we don't have any where I live. I will check the code using the method described above. Thanks again.