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505 Turbo Puzzler- Then Solution


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I recently spend six days figuring out a situation on the '87 turbo. On the seventh day, I had a beer. I'll give the solution at the end.

Last week, I left the house in the morning with the engine cold, I got about a half a block away, and experienced a bad "bucking" from the engine on acceleration. No power, until I stepped lightly on the gas, held it there, and then the power came back after a few long seconds. It didn't stall while it was happening. Whenever I came to a stop, same thing. It idled fine.

I had an important appointment to go to, so I kept driving. After it warmed up, the problem went away, and it ran fine. Next morning, same thing.

When I came home, I started troubleshooting. BTW, no detonation sensor signalling. It felt like it was an engine misfire, so I pulled the plugs, they looked fine. I was looking for maybe a wet plug or something, and it had new plugs about a month earlier. Compression fine. I checked the ignition components the best I could. I tried switching distributor caps, the coil, the module, no change. Checked all the plug wires, etc. Switched NTC sensors with an extra used one. Did pinout tests on the various injection components- checking out okay so far. I really didn't know if it was ignition or injection, and I knew that the field was wide open. I had reset everything about a month ago, TPS, timing, microswitch, mixture, etc.

Here's the solution:

The various components all checked out, except for the microswitch. It was sticking, where it would open, but then "click" only after a few seconds. I couldn't believe my eyes! After it was sufficiently warm, it didn't stick at all. The colder it was, the longer it stayed close.

I remembered what Joe G. said about the function of the microswitch, for it cuts the fuel on deceleration. After I switched out my extra one, the problem vanished.

I got really lucky on this one. A must-have tool for this engine is a multimeter.

-Bill

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aaaah yes, i think i've had the problem before.. with the microswitch closed, the engine won't rev above 1500 i believe.. I wonder if we can find a source for new aftermarket microswitches which will work for us turbo people.. hmmmm

glad it all worked out.

/august

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