Is it Possible that a bad diode in the alternator rectifier can put ou

miesk5 · Oct 18, 2009

yo!

Is it Possible that a bad diode in the alternator rectifier can put out a sq wave into the ABS sensor (also called the differential speed sensor or VSS) ckt & then be picked up by the PSOM/and or PCM resulting in numerouse PSOM, E4OD shifting or PCM problems?

I'm beginning to believe so after seeing the following waveforms;

Bad Diode Pattern Waveforms - Scroll down;

Diode Pattern Waveforms, Bad; "...This waveform was captured using the diode pattern test located in the engine tests menu. This particular alternator has a bad rectifier, causing an AC voltage to ride on top of the DC voltage signal. T

his AC voltage affected the pip and spout signals (Ford primary ignition signals) causing a no code driveability problem. The fix was to replace the alternator.

This waveform was captured using the diode pattern test located in the engine tests menu. This alternator, like the previous alternator, has a bad rectifier.

This is another example of how a bad rectifier can affect the diode pattern. The fix was to replace the alternator. This waveform was captured using the lab scope. This is a good example of how an alternator with a bad diode can affect other signals that the ECM looks at. In this case it is an IAC motor. When viewing waveforms that have a lot of hash always look at the alternator diode pattern as a possible cause..."

http://www.omitec.com/uploads/pics/_2346_20BADDIO_2.gif

Source: by omitec.com http://www.omitec.com/en/support/waveforms/

92pobronco · Oct 18, 2009

miesk5 said:
yo!Is it Possible that a bad diode in the alternator rectifier can put out a sq wave into the ABS sensor (also called the differential speed sensor or VSS) ckt & then be picked up by the PSOM/and or PCM resulting in numerouse PSOM, E4OD shifting or PCM problems?

I'm beginning to believe so after seeing the following waveforms;

Bad Diode Pattern Waveforms - Scroll down;

Diode Pattern Waveforms, Bad; "...This waveform was captured using the diode pattern test located in the engine tests menu. This particular alternator has a bad rectifier, causing an AC voltage to ride on top of the DC voltage signal. T

his AC voltage affected the pip and spout signals (Ford primary ignition signals) causing a no code driveability problem. The fix was to replace the alternator.

This waveform was captured using the diode pattern test located in the engine tests menu. This alternator, like the previous alternator, has a bad rectifier.

This is another example of how a bad rectifier can affect the diode pattern. The fix was to replace the alternator. This waveform was captured using the lab scope. This is a good example of how an alternator with a bad diode can affect other signals that the ECM looks at. In this case it is an IAC motor. When viewing waveforms that have a lot of hash always look at the alternator diode pattern as a possible cause..."

http://www.omitec.com/uploads/pics/_2346_20BADDIO_2.gif

Source: by omitec.com http://www.omitec.com/en/support/waveforms/

I have a memory flash with my check engine and no hard codes - It only flashes with a load on the engine and my foot on the gas - I changed what was a visually condemned TPS throttle position sensor - truck shifts a lot smoother and runs a lot better over all -But my alternator seems to be easily burdened by the easiest of tasks like heat blowing - wipers - headlight - dome light - its always a noticeable drag on the alternator but otherwise still performs as it should - I still have random harsh downshifts and fineky acceleration moments when the tranny is above 1st gear. The problems are not that obnoxious when the truck is driven with the least amount of acessories running but still happens never the less - I am intrigued by the question because I have always had a hunch that the alternator could be the source of random trouble code problems and an easy to move battery charge needle on the dash - (rebuilt transmission and new converter less than 6,000 miles ago - solid motor - could use a tune up which is coming soon, but stills per's like a kitten)

Otherwise im stumped

miesk5 · Oct 19, 2009

92pobronco said:
I have a memory flash with my check engine and no hard codes - It only flashes with a load on the engine and my foot on the gas - I changed what was a visually condemned TPS throttle position sensor - truck shifts a lot smoother and runs a lot better over all -But my alternator seems to be easily burdened by the easiest of tasks like heat blowing - wipers - headlight - dome light - its always a noticeable drag on the alternator but otherwise still performs as it should - I still have random harsh downshifts and fineky acceleration moments when the tranny is above 1st gear. The problems are not that obnoxious when the truck is driven with the least amount of acessories running but still happens never the less - I am intrigued by the question because I have always had a hunch that the alternator could be the source of random trouble code problems and an easy to move battery charge needle on the dash - (rebuilt transmission and new converter less than 6,000 miles ago - solid motor - could use a tune up which is coming soon, but stills per's like a kitten)

Otherwise im stumped

--

ok, post the Codes found here;

Remember to have engine @ Normal Operating Temperature before doing the KOER portion

All accessories (radio, lights, heater/ac/fan off, etc.) Off

Also, have battery checked; sounds from here, like a shorted cell, esp. if you have random no-starter turn-over or slow starter turn-over speeds

We discovered the bad diode possibility when troubleshooting a 95 Bronco; went thru all of the Pin-Point Troubleshooting, but nada.. The PSOM along w/Odometer were 100% operable, 4WABS was 100% with no amber ABS light (bulb was good).. Cruise was 100% as well, but E4OD was quirky. ETC., ETC.

Suggest you buy a Ford Bronco Electrical and Vacuum Troubleshooting Manual (EVTM), Powertrain Controls and Emission Diagnosis Manual (PCED), Service Manual CD from Steve83 or E Bay. He has is info in the For Sale section here.

miesk5 · Oct 20, 2009

I messed up in my reply, was thinking about the fellow who had a similar problem and that's why I poted up the Question. So. try the KOEO & KOER self tests one more time.

BroncoJoe19 · Oct 22, 2009

miesk5 said:
yo!Is it Possible that a bad diode in the alternator rectifier can put out a sq wave into the ABS sensor (also called the differential speed sensor or VSS) ckt & then be picked up by the PSOM/and or PCM resulting in numerouse PSOM, E4OD shifting or PCM problems?

I'm beginning to believe so after seeing the following waveforms;

I dont' know, but I imagine that if the problem occurs often enough, you could try disconnecting the alternator for a test drive, and just run on battery, unless that diode is in the power distribution box.

miesk5 · Oct 22, 2009

BroncoJoe19 said:
I dont' know, but I imagine that if the problem occurs often enough, you could try disconnecting the alternator for a test drive, and just run on battery, unless that diode is in the power distribution box.

--

Yo Joe!

Exactly!

That is what Mr Bell wrote in another MB; "...came across something alot like this recently. It turned out to be a bad diode in the alternator that put a rf signal into the speed sensor line. I unplugged the alternator electrical connector and it went away....Well I am a mechanic by trade and this was on a 2001 superduty that would die when it hit 1100rpm. I was doing my key on engine running selftest when the scanner could not complete it due to excessive vss. So i monitered my vss and when my target rpm was hit the pcm would have the speed limiter kick in and since there was no laod on the engine it would stall. Naturally I started unplugging stuff untill my interferance signal went away...."

Never did get the original DTC from him, but will contact him again; Note that Mr bell did use the Ford SD/F series Electrical and Vacuum Troubleshooting Manual (EVTM), Powertrain Controls and Emission Diagnosis Manual (PCED), Service Manual CD and went thru all pin point VSS DTC tests and found nothing wrong w.anything exc for the alt rect diode.

BroncoJoe19 · Oct 22, 2009

LOL... glad I could help.

You da master!

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Is it Possible that a bad diode in the alternator rectifier can put ou

miesk5

96 Bronco 5.0

92pobronco

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miesk5

96 Bronco 5.0

miesk5

96 Bronco 5.0

BroncoJoe19

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miesk5

96 Bronco 5.0

BroncoJoe19

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