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post #1 of (permalink) Old 01-25-2004, 04:27 PM Thread Starter
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Motor stumbles w/heater **FIXED**

It happens every time I turn the motor on High. On Low and Medium it stumbles slightly but not much.........but on High the engine almost dies and I need to give it gas or turn the motor off. But once its going the engine idles fine. I thought maybe it was a ground problem and gave it a direct ground from the fender under the starter solenoid. What can this be? Is it a grounding issue still? I'd really like to get it going.
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post #2 of (permalink) Old 01-25-2004, 05:20 PM
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Re: Engine stumbling when blower motor turned on

Check the blower fan circuit. Did someone tap into something they shouldn't have? Something that takes most of 12V do make the engine run right? Does it ever stay running when you turn it on high? If so what does the volt guage say? Did it do this before the blower motor swap? Or did it just start this, even after the swap?

OR


Did Rio Grande swap you engines? As we all know that the "blazer blower motor" swap takes more HP than his engine could put out. [img]images/graemlins/tongue.gif[/img] [img]images/graemlins/grin.gif[/img] [img]images/graemlins/grin.gif[/img] [img]images/graemlins/grin.gif[/img] [img]images/graemlins/grin.gif[/img] [img]images/graemlins/grin.gif[/img] [img]images/graemlins/grin.gif[/img] [img]images/graemlins/grin.gif[/img] [img]images/graemlins/grin.gif[/img] [img]images/graemlins/grin.gif[/img] [img]images/graemlins/bs.gif[/img]
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post #3 of (permalink) Old 01-25-2004, 07:29 PM
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Re: Engine stumbling when blower motor turned on

Hey how did I get drug into this??

But I would be supprised if my engine could do it..... Damn 4 passive chipmunks..

I bet dave is right on the wiring...
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post #4 of (permalink) Old 01-25-2004, 08:07 PM
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Re: Engine stumbling when blower motor turned on

</font><blockquote><font class="small">In reply to:</font><hr />
What can this be? Is it a grounding issue still?

[/ QUOTE ]

Not likely, more like a near dead short. There are resistors in the heater duct that are in line with the slower speeds of the blower motor. They look like a simple coil of wire but lower the voltage to the motor. When you flip the switch to High there is noting in line and it hooks the blower motor directly to battery voltage. If the motor has something dragging it down or the motor is about to smoke then you draw alot of current from the battery. Rev up the motor and the alternator pumps out some juice to overcome the load. Unless there is a short somewhere in the harness, your blower moter is the cause.

</font><blockquote><font class="small">In reply to:</font><hr />
Damn 4 passive chipmunks..


[/ QUOTE ]

But those chipmunks play nicely together and don't annoy anyone but the driver. [img]images/graemlins/shocked.gif[/img]
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post #5 of (permalink) Old 01-25-2004, 09:04 PM
 
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Re: Engine stumbling when blower motor turned on

Is your charging system or battery marginal? Either through a fault of the fan wiring or an insufficient output of the alternator, voltage is being pulled low enough to make the ignition spark marginal or intermittent.

Do the headlights do the same thing? (thinking of that as a test load). Check voltage with a digital meter. You should see 13.5-15 volts with the motor running if the alternator is working right.
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post #6 of (permalink) Old 01-26-2004, 02:08 AM Thread Starter
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Re: Engine stumbling when blower motor turned on

It didn't start until long after the blower motor upgrade so I doubt thats it. But when I pulled the fender off to get the headers in I bumped the ground wire and it had a poor ground. So sometimes while driving I'd hit a bump and it'd turn off....then I'd hit another bump and it would turn on.

But it always worked fine. Now that the temperatures have gotten much colder I decided to pull the heater box back out and fix the bad heater core and noticed the problem before I took the heater box out of the Jeep. I didn't have time to throw a voltage meter on it, and the one in the Jeep doesn't work. Throwing the headlights on doesn't affect the engine speed. Turning the fan on high will make it stumble.....and if the engine isn't warmed up it'll die.......but if warmed up it'll just stumble and keep going. I'm about 200 miles from my Jeep now sadly so I'll have to wait and fix this along with my leaky heater core.

I'll go through all the wiring......but I know I didn't splice anything into it (pretty new harness) and see if anything is out of place. Is it possibly the blower motor? If so I'd like to fix it while I've got the heater box out next time.
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post #7 of (permalink) Old 01-26-2004, 08:49 AM
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Re: Engine stumbling when blower motor turned on

It does sound like a bad ground. Somehow the blower and the ignition must be getting it's ground through the same body panels that aren't getting a good ground.

Strange things happen - like a '70 Mercury Cougar - the customer complained that his headlights shut off at night whenever he reached cruise speed.

Think about it - it's a head scratcher.

His "mechanic" had rebuilt his carburetor - he got the headlight door vacuum hose tied in to the distributor vacuum. When the ported spark vacuum for the distributor advance was enough, the headlight doors closed. The difficult thing was you can't see those doors while driving it.
My manager drove it home one night, noticed the headlights were still on, pointing to the ground. Would have made neat rock lights.

Put a voltmeter on the heater ground to the battery (-) to verify it.

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post #8 of (permalink) Old 01-26-2004, 09:07 AM
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Re: Engine stumbling when blower motor turned on

1. It could be a problem in the 12 volt supply line,
2. Or the ground return.
3. But it is sure that the blower motor circuit,
4. IS causing the ability of the alternator/battery to keep up.
5. Checking grounds don't always do much good.
6. Replacing and refurbishing grounds do.
7. Don't forget to look in often overlooked places,
8. Such as the:[*]Blower Motor Speed Switch[*]Dropping Resistors[*]Wiring Harness connectors[*]Tow halves of the fuse block
9. I still suggest that you NOT use the metal backing of the heater box,
10. To ground that motor.
11. Even if the tub and frame/engine/battery grounds are good,
12. That backplane connected to the firewall,
13. Can become compromised via corrosion.
14. I still favor tack welding a bolt/stud to the blower motor case,
15. And running a heavy, separate ground to it.
16. Then there's not a question that that ground is good.
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post #9 of (permalink) Old 01-26-2004, 10:21 AM
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Re: Engine stumbling when blower motor turned on

tim is on the right track i think.

do you have the stock blower motor, or have you upgraded to the chevy one?

bc i have the chevy one, and notice that when on high, it sucks a lot of current. i have a 6 cyl and dont notice a big difference, but i imagine a 4 cyl would take a big hit.
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post #10 of (permalink) Old 01-26-2004, 02:26 PM
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Re: Engine stumbling when blower motor turned on

Try turning on the blower without the engine running so you can hear it. Does it take a lot of time to come up to speed or does it ever even come up to speed.

That motor also acts as a generator. Once it gets turning it starts generating what is referred to as back EMF. Until it gets to turning, it draws a larger starting current. You could have a bearing going bad, dirt in the motor, the fan dragging, etc. all of which would cause it to draw high current.

No matter what you find on the heater blower, Iím thinking you have another problem. The engine should stay running even on low voltage so you may have a connection problem in the ignition circuit. Another thin that might cause this is a bad diode in the alternator. If itís shorted, itís trying to draw current from the battery too.
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