HELP: Momentary fuel pump relay power loss every few seconds at idle
11-16-2002, 03:24 AM
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HELP: Momentary fuel pump relay power loss every few seconds at idle
At idle, the fuel pump relay (the second of two relays contained in the DME relay) clicks off for half a second and then back on every few seconds or so. I have narrowed it down to the ground activation signal from pin 20 on the DME (which is connected to pin 85b on the DME relay). Under what conditions would the DME be trying to turn off the fuel pump (and oxygen sensor)? In other words, which sensors should I check on (or get checked)?
Thanks,
William Butler
1987 951
Thanks,
William Butler
1987 951
11-16-2002, 11:34 AM
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If only at Idle, I would check the power supply. lack of amps would cause a chattering relay. Lights and such stuff would cause an amp draw. radio with an amp would take away from the available amperage. voltage alone is not enough. voltage needs a good push. Maybe a tired fuel pump? needs to many amps to keep up with demand? HTH...
11-16-2002, 02:32 PM
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Speed sensor. One closest to the fire wall provides the continuing signal to keep the fuel pump contacts closed.
Check it for 1k ohm resistance across two of the pins; the center and one of the outer ones.
Check it for adjustment -- should be .8 mm from teeth on flywheel.
Could just be a loose connector to it.
Then it could be a bad DME rely or even the DME.
Check it for 1k ohm resistance across two of the pins; the center and one of the outer ones.
Check it for adjustment -- should be .8 mm from teeth on flywheel.
Could just be a loose connector to it.
Then it could be a bad DME rely or even the DME.
11-16-2002, 06:22 PM
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How about the AFS? (air flow sensor) Wouldn't cause the relay to disengage but would cause a change in fuel delivery if it was intermittent in it's signal.
11-17-2002, 03:42 PM
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[quote]Originally posted by trrbocharged:
<strong>I actually have an Autothority MAF Sensor, but it is a little old (1991). I am going to check it out tonight.</strong><hr></blockquote>
Ah! So I take it your DME has been chipped too?
<strong>I actually have an Autothority MAF Sensor, but it is a little old (1991). I am going to check it out tonight.</strong><hr></blockquote>
Ah! So I take it your DME has been chipped too?
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11-17-2002, 08:52 PM
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I got some replacement DME and KLR chips two weeks ago and returned them because they didn't solve the problem.
I used the DME/KLR test plan (WKD 453 920) to see what I could uncover, and the only thing that I noticed was that the magnitude of the speed sensor signal was a little low when measured with an oscilloscope.
I used the DME/KLR test plan (WKD 453 920) to see what I could uncover, and the only thing that I noticed was that the magnitude of the speed sensor signal was a little low when measured with an oscilloscope.
