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Alternator Noise (Screeching) when 3-Pin CONNECTED

Old 07-19-2011, 06:46 PM
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Join Date: Jun 2011
Location: lancaster, ca
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Exclamation Alternator Noise (Screeching) when 3-Pin CONNECTED

Hello all:

New to the forum...hope iím properly searching and posting here...did not find solution to my problem (on a repair for a friendís vehicle), so...

1993 Honda Accord 5-Door, 4-cyl. 2.2L, A/T

Original ISSUE:

Timing Belt Drive Pulley failure (two broken teeth) led to complete timing assembly failure during operation, leading to 6 bent valves.

Head machined (Surfacing/Valve Job). Head reinstalled using top-end gasket kit; Intake Plenum and exhaust components also resealed using included gaskets/o-rings/seals. Valves adjusted to spec. Timing assembly repaired, belts replaced. ALL work done to spec. (according to Haynes).

Engine starts and runs like new...

However, upon intial start, a very loud, steady screeching noise could be heard coming from the front of the engine. Belts were checked, readjusted and the car restarted. Noise continued.

Upon further inspection, the noise was isolated to the alternator. It was shown that unplugging the 3-Pin connector at the back of the alternator caused the noise to cease; when 3-Pin plugged back in, steady noise resumes. All tests of 3-Pin connector power/ground come up PASS.


- During first tries to restart, it was determined that the fuel pump was not getting steady ground and thus the car would not start/stay running without difficulty. It was found that a triple-wire ground beneath the thermostat housing was not secured. The ground was secured and the problem was corrected.

- 80AMP MAIN fuse (#15 to battery, at under hood fuse block) was replaced as it was discovered to have been damaged (blown and without a top glass). Fuse remains in working order, while alt. noise issue remains.

- TCU codes initially showed 1, 2, 7 & 8. after checking harness connections at unit and under hood, and tapping Solenoid Valves A & B under hood, the codes were cleared. Subsequent code checks came up NONE. (Transmission shifts into all available gears.)


- ECU & TCU Codes check. After some initial codes, results now consistently NONE.

- MAIN RELAY (under driverís dash) thoroughly inspected/tested. PASS.

- Charging System Check. System fails Haynes Step #11.1i.1 in Chapter 5 (Engine Electrical) on Page 5-7 (i.e. Ė test light is ON when between NEGATIVE battery post and disconnected NEGATIVE cable). Pulling fuses (Step #11.2) results in test light OFF when removing fuses #22 (Interior Light) & #24 Back Up (Radio) located in the under hood fuse block. This failure seems to suggest a drain (short) in the circuits, however, to me, this appears to be a non-issue.

- Checked all radio, lighter and center console electrical connections

- Thorough under hood harness connections check

- Fuse block checks (both, all fuses)

- Purchased new alternator and installed. Issue remains. However, at some point during this new part installation, the 80AMP MAIN fuse issue noted above was discovered, and during diagnosis of that issue, the noise ceased when fiddling with the damaged fuse, the new or original alternator installed. But after replacing the fuse and reinstalling the original alternator (which twice tested ďGoodĒ at Autozone), the noise returned as before.

- Starter was recently replaced; functions as designed


There is a loud, steady screeching sound coming from alternator when 3-Pin connector at rear is CONNECTED; noise ceases when 3-Pin connector DISCONNECTED. All primary visual, mechanical and electrical troubleshooting has been conducted with all results coming up PASS (except for Charging System Check concerns noted above); specifically, all tests of 3-Pin connector power/ground come up PASS.

It does not appear to be ECU or TCU related; fuse, power or ground related; belt adjustment related; or a faulty alternator (e.g. - bad bearings).

ANY thoughts? please keep in mind that i have done EVERYTHING by the book, have the car running like new, and know what iím doing (5th rebuild rodeo)...iíve explored the common...iím seeking to resolve what appears to be an extraordinary situation that will likely require the feedback of a highly adept Honda electrical guru.

That said, in the end, it will probably be something simple that is being overlooked...

I appreciate any help in advance...

Old 07-20-2011, 06:18 PM
poorman212's Avatar
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Join Date: May 2010
Location: Youngsville, NC
Posts: 11,819

Ok, nobody else jumped in....So the alt belt is new...correct. Even if new be sure there is not grease or oil on the ribs.

With the connector installed the alt is "working".....14.5 v, correct (yea it is making noise but working)?

So do we know if the alt is making the noise or the belt? Have you tried the "many" tricks for checking the belt (I know it was by the book).

You've pretty well got it down to the alt or the belt (when the plug is connected their is a load on the alt-trying to charge)......
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