Author Topic: LT40 voltage drop engine bog alternator belt squeak (Read 746 times)

jovol · « **on:** January 10, 2019, 09:09:24 PM »

So my LT40 runs well, once it's going. However, running the hydraulics, or anything that draws high current like raising the sawhead, makes the engine bog down when its at idle. I put a volt meter on the alternator while I ran the loader, and I saw it drop from 14.4V with no load to 12.4V with the load. I have the Kohler 28HP gas. Should the engine bog like that? Should the voltage drop? And most annoyingly, what's with this *DanG squeak?! It only squeaks when the engine bogs down like this, doesn't squeak under no low or at high rpms. The previous owner but a new alternator belt on before selling it.

Here's a video of it bogging: IMG_8019.MOV - Google Drive

Another oddity: when returning to idle from running the saw, the engine RPMs go real low, borderline stall sometimes, then after 5-10sec it finds the normal idle. The only code it shows is the oxygen sensor is shorted, not sure if that would cause this.

Magicman · « **Reply #1 on:** January 10, 2019, 09:31:01 PM »

My engine idles at 1500 rpm which keeps the voltage in the required 14.6 range.

Again, I have no experience with your engine, but that voltage requirement is probably standard. Your battery should equalize any momentary engine speed drop until the governor kicks in.

carhartted · « **Reply #2 on:** January 11, 2019, 03:20:15 AM »

My lt40 with an Onan will bog down while using the hydraulics at idle, especially when it's cold. This spring I plan on putting a second battery on the frame to help with the voltage drop.

Are your cable connections and contact strip clean? I added larger battery cables, it seemed to help a little.

ladylake · « **Reply #3 on:** January 11, 2019, 05:46:12 AM »

The voltage is going to drop with a load applied, just normal. You might want to turn up your idle speed a little. Yes using the hydraulic take a lot of amps and you will hear the engine work with a load applied. Squeaking, either belt is too loose, or its shot, or the pulleys can wear so they don't grip the belt good, are your sure the belt is wide enough for the pulleys. Steve

Chuck White · « **Reply #4 on:** January 11, 2019, 06:53:44 AM »

I agree with Steve, I believe the squeak is from the drive belt!

Adjust drive belt tension and the squeak will likely go away!

mike_belben · « **Reply #5 on:** January 11, 2019, 07:01:04 AM »

Definitely belt. I have a lot of digital LCD gauges in my old road truck since i drive it cross country. Every time the headlights and heater draw it down below normal volts has been the belts.

If the belt is in good condition and tight but still slips try belt dressing. If its got a terrible squeak u cant solve, carefully hold a piece of barsoap or wax under the belt and into the pulley groove. Hold it with pliers and dont loose your hand.

Magicman · « **Reply #6 on:** January 11, 2019, 07:48:08 AM »

I installed this digital voltmeter that constantly shows my battery voltage (14.6) being supplied by the alternator even at idle speed. Three things are a must; (1) the alternator must be capable of supplying the voltage, (2) the idle speed must be high enough to constantly produce that voltage, and (3) there can be no alternator belt slippage. As Steve mentioned above, a worn pulley is just as bad as a worn belt. The belt grips the sides of the pulley, not the bottom. If you are running on the bottom you either have a worn pulley or the wrong belt.

Ben Cut-wright · « **Reply #7 on:** January 11, 2019, 07:58:21 AM »

Quote from: jovol on January 10, 2019, 09:09:24 PM

So my LT40 runs well, once it's going.

What does "once it's going" mean?

However, running the hydraulics, or anything that draws high current like raising the sawhead, makes the engine bog down when its at idle. I put a volt meter on the alternator while I ran the loader, and I saw it drop from 14.4V with no load to 12.4V with the load. I have the Kohler 28HP gas. Should the engine bog like that? Should the voltage drop? And most annoyingly, what's with this *DanG squeak?! It only squeaks when the engine bogs down like this, doesn't squeak under no low or at high rpms. The previous owner but a new alternator belt on before selling it.

The alternator is the primary source of electrical energy when the engine is running. At idle that engine is producing MUCH lower HP than at max RPMs. These conditions exert extreme stress on the belt when operating the hydraulics. IF the new belt was replaced because of such stress it most likely is stretched and/or glazed. I made provision to rev-up the engine to a 'fast idle' on my LT40 any time I am operating the hydraulics.

Here's a video of it bogging: IMG_8019.MOV - Google Drive

Another oddity: when returning to idle from running the saw, the engine RPMs go real low, borderline stall sometimes, then after 5-10sec it finds the normal idle. The only code it shows is the oxygen sensor is shorted, not sure if that would cause this.

The "only code" you have is a very pertinent fault code. Shorted sensors can create many control module problems. My advise is to get any such faults repaired before operating the machine.

BenTN · « **Reply #8 on:** January 11, 2019, 09:01:03 AM »

I would check belt tension and air cleaner.

CCCLLC · « **Reply #9 on:** January 11, 2019, 01:02:44 PM »

What is the exact alternator belt size for the Onan 24. The A33 (4L350) seems long. Alternator is moved all the way out to tighten this belt. Is "A" the right belt? Sorry for hijacking the earlier thread. Thanks

sparks · « **Reply #10 on:** January 11, 2019, 04:39:43 PM »

2volt drop in voltage when running the hydraulics is normal. Since the engine want to drop RPM drop very low going back to idle your issue may be in the electronics of the engine. Raising the head only pulls about 40 amps and that is not enough to bog the engine.
May have to get Kohler to scope the engine when you create the problem.

donbj · « **Reply #11 on:** January 12, 2019, 11:34:31 PM »

I would check the condition of your battery, and definitely tighten or replace your alternator belt. I have the 24hp Onan on my LT40HD and have no issues with bogging when using hydraulics. I have a good deep cycle marine battery. I have had the alternator belt squeal before but just tightened it. The battery should have enough reserve to handle hydraulics without overloading the alternator. If your battery isn't up to snuff you are putting the hyd load onto the alternator.

POSTON WIDEHEAD · « **Reply #12 on:** January 13, 2019, 07:09:00 PM »

You're gonna have to get a Kohler Tech. who has the software and a laptop to hook up to your engine and diagnose whats going on. You will not be able to fix it yourself without the software.
My Kohler engine did this and the TPS went out. Replaced it and after that other things started going wrong.....the engine got worse over time.
This went on over a year and I finally traded and got a diesel.

Good Luck.

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