Problem Resolved [was I'm Stumped], Runs briefly, then dies & won't restart |
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Problem Resolved [was I'm Stumped], Runs briefly, then dies & won't restart |
ThinAir |
Aug 2 2008, 04:04 PM
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#1
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Best friends Group: Members Posts: 2,543 Joined: 4-February 03 From: Flagstaff, AZ Member No.: 231 Region Association: Southwest Region |
Background: In preparation for last year's RRC I fixed the mounting on the MPS of my son's stock 1971 914-4. All seemed well until we went out for the Saturday morning run - we turned a corner and the engine suddenly died and was clearly flooded. It restarted quickly, but we had the same problem several times on that trip after that.
I assumed that I had disturbed something electrical on the passenger side of the engine and in digging around I discovered that the wire connecting the Cylinder Head Temp Sensor was corroded at its base (in fact it fell off in my hands). Ok, this is simple I said - so I bought and installed a new CHT. Current Problem: The engine will start, but runs for only about 30 seconds before it dies. At that point it will not restart, but it smells of fuel as if it is flooded. I've checked for spark and I have spark. I've disconnected, cleaned and reconnected every electrical connection on the engine & relay board that I can find - including every relay on the board. The only connections that I have not checked are the connector where the FI harness connects to the brain. Does anyone have any ideas on what could cause this and where to look next? |
ThinAir |
Aug 2 2008, 04:56 PM
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#2
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Best friends Group: Members Posts: 2,543 Joined: 4-February 03 From: Flagstaff, AZ Member No.: 231 Region Association: Southwest Region |
Well... the mystery deepens!
Right after posting I went out, removed the air-cleaner snorkel and sprayed some starting fluid into the throttle, then cranked and cranked with the accelerator pedal to the floor and eventually it started. Once it started there was a big puddle of fuel on the driveway behind the exhaust. Although I was able to get it restarted again on several occasions, I just couldn't keep it running sooo... I removed the air cleaner and checked the paper filter. It looks pretty gross and there is some oil in the bottom of the air cleaner body so I left the filter out and put the the assembly back onto the snorkel. As soon as I would get the filter assembly within 1/2 inch of the snorkel the engine would stall. Opening the idle bypass sort of took care of this situation, but seemed strange since this has been fine for thousands of miles. Because I had noticed some oil-smoke coming from the crankcase ventilator hose I decided to remove the oil filler cap and discovered that if I left the cap off I could keep the engine idling even with the air cleaner assembly installed, but as soon as I put the cap back on the engine would die. Further experimentation shows that if I remove the electrical connector from the MPS I can still get it started with the accelerator to the floor, but the engine won't idle and won't rev smoothly. So at this point I'm thinking that I've got a bad MPS. Does this sound reasonable? |
swl |
Aug 3 2008, 06:43 AM
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#3
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Senior Member Group: Members Posts: 1,409 Joined: 7-August 05 From: Kingston,On,Canada Member No.: 4,550 Region Association: Canada |
Further experimentation shows that if I remove the electrical connector from the MPS I can still get it started with the accelerator to the floor, but the engine won't idle and won't rev smoothly. OK this is really bugging me. With the MPS electically disconnected how the heck is the engine running. My experience with a broken wire to the MPS resulted in none of the injectors working. After reading Brad Ander's stuff I convinced myself that the MPS was doing pulse shaping in the final drivers for the injectors. Break that cct and there is no pulse for the injector. If that is true then where is the gas coming from? The only other source of gas is the cold start valve but it would not be operating because the electrical cct doesn't kick in until it is bloody cold. Maybe Mike is onto something - maybe that valve is stuck open. I can't for the life of me figure out how that would happen but the gas has to be coming from somewhere. |
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