Alternator causing a surge?

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Oct 26, 2010 | 10:36 AM

HdRider04

Thread Starter

Racer

Joined: Jan 2010

Posts: 347

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From: Deltona FL

Alternator causing a surge?

86 Stock motor
I am still having a surge problem at idle, I have checked/replaced all the common cause's. No codes.
I noticed last night when it surges the dash and lights are dimming a little bit, the Alt is showing 13.2 to 13.7 at highway speeds and between 12.5 and 13.1 at idle. Should I be seeing a steady output on the Alt?

Oct 26, 2010 | 11:56 AM

C4happy

Instructor

Joined: May 2008

Posts: 234

Likes: 1

From: Midland Texas

At low speeds you will have lower output, that is normal for the early style alternators
The PM alternators (Later style) you don't have this issue anymore, so as you motor idel incresses so will your output. I don't believe this is your problem it is just the result of your problem
Have you cleaned you IAC passage and TB?

Last edited by C4happy; Oct 26, 2010 at 12:04 PM. Reason: miss spelled words

Oct 26, 2010 | 12:47 PM

C4happy

Instructor

Joined: May 2008

Posts: 234

Likes: 1

From: Midland Texas

You can try disconnecting your Alt and see if your surge goes away.
It would test and see if your alt is causing the surge.

Oct 26, 2010 | 02:30 PM

c4cruiser

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Joined: Dec 1999

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From: Lacey WA RVN 68-69

NCM Sinkhole Donor

Those are pretty low voltages at idle but the volts while running are OK assuming the battery is in good condition and is fully charged. Use a digital voltmeter and take a reading at the battery terminals with the engine off and all lights off (close the doors making sure the interior lights are off and disconnect the underhood lights). A fully charged battery with the engine off and no current drain should read around 12.5 volts or slightly higher.

Start the engine and check voltage at the large post on the alternator where the red wire attaches. Even with a fully charged battery and at idle speed, you should see a constant 13.2 to 13.6 volts. Check voltage at the battery, should be about the same. Don't rely on the dash voltmeter here.

Oct 26, 2010 | 03:22 PM

AGENT 86

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Joined: Jan 2003

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From: Summerland B.C. Canada

Have you tried to set the minimum idle and then reset the TPS idle voltage ?

Oct 26, 2010 | 04:28 PM

HdRider04

Thread Starter

Racer

Joined: Jan 2010

Posts: 347

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From: Deltona FL

Quote:

Originally Posted by C4happy

Have you cleaned you IAC passage and TB?

Cleaned and replaced IAC, Cleaned and all new gaskets in TB (but maybe the bushings are worn?)

Quote:

Originally Posted by AGENT 86

Have you tried to set the minimum idle and then reset the TPS idle voltage ?

Yes and Yes

I'll unplug the Alt and see what happens.

Oct 26, 2010 | 07:34 PM

jfb

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Joined: Mar 2001

Posts: 54,124

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From: Cincinnati, Oh USA

Even at idle the alternator should put out 14.7 volts cold and this will drop to 13.7 volts at its operating temperature. The dash voltmeter will read 0.3 volts lower than this because it measures the voltage after the ign sw which has 0.3 volts drop. The voltage can drop more rapidly than the voltmeter can respond to, so if you see a sudden drop in voltage, this can cause weak spark and the ECM will attempt to compensate for this causing engine surge. Disconnecting the alternator is a good test, the voltage should remain constant with the alternator disconnected. Surging can have a number of causes and a good diagnostic tool to help find the cause is a scan tool.