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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Stock 85 with tpi. Everything still hooked up and stock. Car runs great with one exception. On cruise at highway speeds, you can feel it ever so slightly pulsating? Not violent just enough to feel it. Not if related, but every so often the car will just die. Starts back up and runs fine. Electrical? Fuel related? Not sure where to start. Any help appreciated.
It could be a number of things. I don't know the conditions when it is stalling. I had a similar condition in a 3800 V6 ("fishbite" lightly jerking feel at cruise and occasional stall at idle) and it was very hard to track down. Turned out that it was the crankshaft position sensor becoming intermittent. In your case, the TPI equivalent is the pickup in the distributor. I would be inclined to start with ignition- could be pickup, module, or coil.
I would not start with fuel if it isn't showing other signs of running lean. The fuel pressure regulator ought to be keeping the rail up easily at light throttle and if it runs lean very much due to low fuel pressure, you should set a check engine light - lean code. You can put a fuel pressure gauge on the rail and verify the pressure if you want to be sure.
Another thing that can cause surging and stall at idle is EGR system.
Thanks for the help.
Any idea how to check the egr system?
does it make any difference that this car sat for 7+ years?
no codes are being thrown. I am thinking something with ignition as well. Already changed cap rotor and module. Will look at wires and plugs. They are the originals.
What conditions cause a stall? This may give additional clues. The problems may not be related.
Regarding ignition, it can't hurt to change plugs and wires. If they are original, they may be deteriorated, but they may also be ok. Worth ruling them out. If that doesn't do it, then consider the distributor pickup coil. It means pulling the distributor and disassembling it, you need to remove the lower gear to pull the shaft, replace the pickup, reassemble and reinstall and set timing. The pickup coil does have a magnet built in, sometimes the magnetism drops with age and sometimes the coil of wire in the pickup becomes intermittent.
Fuel. I passed off fuel at first, but I work to an old adage that I ran across long ago. "If you think you have an ignition problem, look at fuel. If you think you have a fuel problem, look at ignition." It is amazing how often the symptoms mimic each other. When you said the car sat for 7 years, that may have an influence. How was the car stored? Gas drained? Gas stabilized? You could have issues with injectors if they sat with stale fuel. They may work, but the spray pattern could be bad. There are many opinions on what to do with injectors - repair vs new. On my 1985 TPI, I sent them out to a service for them to be disassembled, cleaned, electrically tested, reassembled, and flow tested. They work very well now. Pressure at the rail ought to be 40.5 to 47 with the engine off and keyed up. It will be regulated down to about 37 at idle. If it is low, make sure you have a clean fuel filter.
Regarding EGR, the EGR valve has an internal valve that is sensitive to backpressure and it can become sticky or clogged with carbon deposits. The valve can not respond properly or hang and not close tight. I'll attach the service manual pages, test routines are complex.
Beyond that are still many possibilities. I'll also attach the troubleshooting chart from the service manual for surge.
Thank you for the assist. Today purchased plugs and wires. They are 35 years old anyway and will get to them.
tonight I have a fuel pressure gauges duct taped to my windshield. Will let you know the outcome. FYI. Fuel system was a mess when I pulled this car out of a barn. Already done 2 fuel filters, new injectors, new regulator Ended up cutting an access panel and changing fuel pump. If I had known the tank was going to be as bad as it was, I would have just pulled it out. But then I was already there. Cleaned out the tank as best I could. Will check fuel pressure tonight.
Got wires and plugs installed.
During the process I pulled the fuel filter.
significant rust came out of the fuel filter.
I think the issue has been identified!
time to change the tank. Bummer
thanks for your help
08-22-2020, 03:55 PM
