[knifeboy2]

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.

 

[Dirt Dog]

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.

 

[Rio_Grande]

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...

 

[OlllllllOCJ]

Re: Engine stumbling when blower motor turned on

In reply to:

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.

In reply to:

Damn 4 passive chipmunks..

[/ QUOTE ]

But those chipmunks play nicely together and don't annoy anyone but the driver.

 

[517]

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.

 

[knifeboy2]

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.

 

[RRich]

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.

 

[LEVE]

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.

 

[Grapehead]

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.

 

[CJ7Taz]

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, I'm 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 it's shorted, it's trying to draw current from the battery too.

 

[knifeboy2]

Re: Engine stumbling when blower motor turned on

Ok, so now that I'm back near my Jeep I tested a few more things. With the engine off the blower motor starts up fine with no delay or stalling of the blower motor. With the engine running if I turn the blower motor on one of the two lower settings the engine will keep going like nothin is wrong. The engine still dies with the blower is on high. Also the engine will die if I have the headlights on, windshield wipers on high, AND the blower motor on the lowest setting all at the same time. Any one or two of those together has no affect, but all 3 will do it.

This leads me to believe it has something to do with the charging system most likely the alternator. What could be causing this? My guess is the draw is too much for the alternator and is putting such a drag on it stalls the engine. Does this sound about right? Is the alternator easily fixable to a very shadetree mechanic or is it something that should just be replaced (the whole alternator)? I really need this done by Sunday so the sooner the advice the better.

 

[CJ7Taz]

Re: Engine stumbling when blower motor turned on

It's been well over two weeks since you started this thread. If you've been driving it even occasionally in that time and haven't had dead battery problems, the alternator is doing it's job.

You most likely have a bad connection somewhere in a major supply circuit and/or the body ground. As I remember, you rewired that Jeep after a fire behind the dash using a Painless harness. It wouldn't be the first time a wire didn't get stripped or crimped properly in a connector. Check their connections and yours. See if any of the connections, or wires, are getting hot.

 

[Rio_Grande]

Re: Engine stumbling when blower motor turned on

This may be a stupid question but how are your batery cables?? I have changed a alternator and starter only to find my Batery wires were coroded up.

 

[knifeboy2]

Re: Engine stumbling when blower motor turned on

I haven't driven the Jeep at all since I posted the question. I couldn't get it driveable so I had to leave it at my dads house for those 2 weeks until I could get back to work on it which is this weekend. So I don't know if I've got battery issues other than I know it isn't losing a charge just by sitting. It starts up fine with no problems. I suppose the battery cables might be the culprit, but wouldn't that affect starting the Jeep?

And I did rewire the Jeep after the fire behind the dash using a Centech harness. The heater used to work fine. Recently I had pulled the passenger side fender off and a few wires off and thought I had them all. I went back and double checked but I'm gonna triple check tommorow one more time. I'll keep updating you if ya'lll keep throwing ideas at me.

 

[jdoggmoney]

Re: Engine stumbling when blower motor turned on

Sounds like your alternator is charging and there doesn't seem to be a draw over time. If it's sitting over time and starts fine, it has plenty of juice to run the ignition.

Check the connections and what type of voltage your using to power your ignition.

If you have a factory (or close to it) alternator, it could be that your powering your ignition system with a circuit that was meant not to be shared. Or you've tapped into the ignition circuitry to run the accessories.

Either way, it sounds like your using up the voltage in your ignition circuit, and it's not able to access battery voltage to make up for the large draw.

Have you had your alternator checked yet? Have you been able to or had someone else watch the headlights as the engine dies? Do they dim or go out? I have heard of alternators that charge fine under light loads, but give up under heavy use, but even if this was the case, your battery should be able to run things. Keep at it.

 

[4659]

Re: Engine stumbling when blower motor turned on

I would check the voltage on the coil (+) terminal and see how low it it dropping. Normally the heater is on a seperate circuit than the ignition but if you rewired it and the blower motor and the ignition are sharing the same circuit then you could be dropping the voltage to the coil to low. THis will cause it stumble in in some cases completely stall out.

THe GM blower motor does draw considerable current when running on high. Those resistors that control the speed limit the current the motor can draw so at lower speeds the engine can operate properly.

On my CJ the circuit the blower motor runs on drops to around 12 volts but the ignition still has 14 volts. At the coil mine drops to 9 volts because of a ballast resistor.

If your still running a balast resistor in your circuit then lets say the blower motor drops the voltage from 12 votls at idle to 10 volts. In that case the voltage on your coil could be as low as 4-5 volts. Not anywere enough to keep the coil firing.

So keep you circuits seperate. Use a heave gauge (10 Gauge or better) wire to feed your ignition all the way from the battery.

 

[RRich]

Re: Engine stumbling when blower motor turned on

Check the voltage at the coil as mentioned - with and without the blower on high.

Then check the voltage at your ignition switch - I'd bet it does the same - drops when the blower's on.

I suspect you have the wires backwards to the ignition - the one with the ignition resistor is the one feeding the ignition switch (+), and the other one (I) feeds everything else.
Should be the other way around.

The battery should always feed the switch (+) directly, no resistor. The (I) terminal then feeds everything else, heater, gauges etc - then a SEPARATE wire with the resistor feeds the coil from the same (I) terminal.
Probably a matter of a simple wire swap.

 

[RRich]

Re: Engine stumbling when blower motor turned on

Check the voltage at the coil as mentioned - with and without the blower on high.

Then check the voltage at your ignition switch - I'd bet it does the same - drops when the blower's on.

I suspect you have the wires backwards to the ignition - the one with the ignition resistor is the one feeding the ignition switch (+), and the other one (I) feeds everything else.
Should be the other way around.

The battery should always feed the switch (+) directly, no resistor. The (I) terminal then feeds everything else, heater, gauges etc - then a SEPARATE wire with the resistor feeds the coil from the same (I) terminal.
Probably a matter of a simple wire swap.

 

[Caver Dave]

Re: Engine stumbling when blower motor turned on

FWIW, my old blower had serious bearing/brush issues and would do the same thing (only 2 speeds though). I replaced it with a single speed and the problem "went away". Highly possible you simply got a bad motor...

 

[knifeboy2]

Re: Engine stumbling when blower motor turned on

Just FYI, this setup worked fine for a few months until I pulled the passenger side fender off to put a new header in. Since then its been throwing problems at me and this is the only non-easy fix I've had so far. (The problems were stuff like wires came loose). The motor and ignition worked in harmony well. I didn't change any of the circuits from the original setup of the new wiring harness. I have a Jacobs ignition so I don't kniow if that changes any of my test procedures. I'll be heading out to start work on it again today in a bit so hopefully I can give more updates.