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Have 89 Deville 1G6CD5150K4284768 This vehicle runs well…

Have 89 Deville 1G6CD5150K4284768This vehicle...
Have 89 Deville 1G6CD5150K4284768This vehicle runs well until fan comes on - heavy load @ operating temp and low engine power under acceleration.
New plugs and wires, cap and rotor, fuel filter and fresh catalytic converter. Any suggestions on what to check/do would be greatly appreciated.The procedure for checking timing and anything other tests will help. I can run almost any test.Thanks, ***** *****
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Answered in 8 minutes by:
9/28/2017
George H.
George H., ASE Certified Technician
Category: Cadillac
Satisfied Customers: 19,282
Experience: ASE Master Tech 15+ Years
Verified
Hello I will help,
Since the problem comes up when you turn on a heavy electrical load I would suspect corroded grounds dropping the available voltage to the electronics.
Clean and tighten all the grounds at the battery and right strut tower and to the engine then see if the problem has changed.
Let me know what questions you have about this
Thanks
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Customer reply replied 9 months ago
I even applied a little dielectric. No change.

Next up is to measure voltage drops when it happens, case of computer to case of alternator, ground of fan to battery negative. case of alternator to negative battery etc. These tests must be done while it is happening.

Supply voltage to the computer and ground from computer to battery negative and alternator case.

If any harness is out of place or the high tension wires are where they could induce voltage into the harness move them apart.

It may boil down to the computer or the distributor.

In no case should any voltage drop exceed .5 volts. If it does you have a poor connection.

Have you done this type of troubleshooting before? Do you have a scope?

George H.
George H., ASE Certified Technician
Category: Cadillac
Satisfied Customers: 19,282
Experience: ASE Master Tech 15+ Years
Verified
George H. and 87 other Cadillac Specialists are ready to help you
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Customer reply replied 9 months ago
I have a parent/teacher conference to attend. So, I'll continue in the am. I like the direction we're going....Thanks

Great, I will be here most of the day tomorrow. With the fan as a trigger for the poor running either it is pulling down the voltage to the computer or the distributor or there is interference being induced into the signal wiring from the distributor to computer.

I will watch for your post tomorrow.

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