91 F150 Ignition Timing Frozen --won't advance.
#1
11-22-2005, 02:34 PM
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91 F150 Ignition Timing Frozen --won't advance.
I've been working on this '91 F150 w/ 5.0L v8. First it was idleing at 1800-2000rpm. I found that the timing had been messed with so I adjusted it back down to 8 degrees or so and it idled great, BUT it wouldn't even rev up, let alone accelerate. I pulled the disty cap(there is no vacuum advance on this one) and it looks clean in there. I guess there's no mechanical advance because the rotor will not turn. The MAP sensor is new and TPS goes from .9V-4.55V so I think that is ok. With the timing light on the mark, you can rev it up and it will stay in about the same place no matter how high the rpm. It does twitch a little if you blip it, but not much. Oh, I had to re-advance the timing to get it to rev at all, causing a 1200rpm idle. The IAC is completely shut as it's doing this. There aren't any vac. leaks found. Any ideas?
#2
11-22-2005, 05:05 PM
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If you have the spout disconnected (and you do have the SPOUT disconnected, don't you?) when you set the timing, there will be no change in advance when you rev the engine. If it doesn't advance with the SPOUT plugged in, you most likely have a broken wire. Set the timing at 10° BTDC and see how it idles. That should be your baseline. If it's still too high, try cleaning the throttle body. They can accumulate crud and stick open just a hair, enough to raise the idle.
#3
11-22-2005, 07:41 PM
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I didn't have the SPOUT disconnected. I know what it looks like and does, but I did not see one under the hood. I didn't look super close anyway though. The truck is in good shape, I would doubt there is a broken wire, but anything is possible I guess.
What controls the advance under load anyway? The ecu? Or the SPOUT? I'm not real used to fords and they always seem to have these weird problems.
What controls the advance under load anyway? The ecu? Or the SPOUT? I'm not real used to fords and they always seem to have these weird problems.
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11-22-2005, 07:55 PM
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The ECU (actually PCM is the current term Powertrain Control Module) controls ignition advance in all situations. Pulling the SPOUT connector disables the ability of the PCM to adjust the timing. You have to set base timing with the SPOUT pulled; it's like disconnecting the vacuum advance on an old-style dizzy.
