Any discussion of a cause of a1993 U300 rough idle?

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Any discussion of a cause of a1993 U300 rough idle?

September 23, 2020, 10:02:43 pm

This is a 1993 with a 6-94. Sometimes on start up the engine rpms fluctuate and the hyd fans cut in and out at the same time. I thought I had seen this discussed previously but not for this combination.

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #1 – September 24, 2020, 07:53:05 am

Ours does the RPM fluctuation sometimes when it's cold out, clears up quickly when all cylinders start firing.
Never noticed the fans acting up.

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #2 – September 24, 2020, 10:25:11 am

Our Detroits don't have a heated screen or glow plugs, etc to make starting easy. The block heater is installed in a non Detroit, non block location and is almost useless. The cold engine will start on one cylinder, then another, etc until all cylinders are firing. The colder it is and the higher the altitude, the longer it will take. Lots of white smoke at the same time. Since our engines are turbos, the compression ratio is two points lower which makes cold starting much harder.

Years ago, I posted a block temperature with the thermostat housing block heater running all night in freezing temperatures. The housing and crossover pipe were quite warm but the block was cold. This was with an IR gun.

Our bus had a non turbo 8-71 that started on the first quarter revolution even if fairly cold. Two points on the CR makes a huge difference.

After all cylinders are firing, I bring the idle up to 1000 rpm. This does away will all smoke and brings the air pressure up.

No, never was back there to see the fans operating on a cold startup.

If you want a fast cold start, move the "block" heater to it's normal location, under the AC compressor down low on the curb side or install a remote block heater, either electric or propane like some owners have.

All MCIs, Eagles, Prevosts, Wanderlodges, Bluebirds, etc. with Detroits 2 cycles have the block heater in the correct location. It's also a different part number. The only down side is that you have to drain the cooling system since the block heater is at the lowest point. But that is also why it works well there.

Pierce

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #3 – September 24, 2020, 05:15:00 pm

Thanks for the replies. This is after it gets started and is firing all cylinders. Each time the fans cut in and out the hyd pump belt tightens and loosens as the fans cycle in and out. Belt tensioner also jumps and some times the belt tries to climb off the pulley.

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #4 – September 24, 2020, 06:23:31 pm

Did you check to see if any codes were thrown with your code reader under the dash?

Sounds odd 'cause the 6v92TA Sillver with DDEC II should run smooth as glass at all RPMs.

Jerry

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #5 – September 24, 2020, 07:00:34 pm

There haven't been any codes in the past. This problem has been going on for several years. It seems like a result of the fans cycling on and throwing a momentary load on the hyd pump which throws a load on the engine causing a momentary rpm fluctuation. The whole series of events is fairly rhythmic . Above idle you can't feel or see it. At running temp it runs fine.

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #6 – September 24, 2020, 07:27:55 pm

Quote from: Cedric – September 24, 2020, 05:15:00 pm

Thanks for the replies. This is after it gets started and is firing all cylinders. Each time the fans cut in and out the hyd pump belt tightens and loosens as the fans cycle in and out. Belt tensioner also jumps and some times the belt tries to climb off the pulley.

As Jerry says, once the engine has started, 30 seconds later, it should be as smooth as glass at all RPMs. What year is this? You have the classic pulley alignment issue. Go to the search function on the forum and look up how to align the pulleys. You probably don't need a tensioner, just aligning the angle on all the pulley. I posted photos for exactly how to do it. If you have a 1993, it should have an 8 groove belt, an 8 groove crank pulley and an 8 groove pump pulley. The belt should ride all the way on the idler pulley but does not have to be exactly in the center. Use a Gates belt. I posted all the information on my post with the photo of the belt including the part number. Don't let anyone feed you the line that you can get by with a 6 groove belt.

Cedric, show your year, model and engine on your ID otherwise, I'm doing a lot of guessing.

Pierce

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #7 – September 25, 2020, 07:37:49 pm

Pierce, I sent that info to my profile. It's a 1993 U300W WTBI with a 6V92TA. I changed the tensioner a few years ago (bad bearing) and aligned it with the belt. As it was every time it jumped it sent the belt up 1 or 2 grooves and would chew the belt to pieces. Until I changed the tensioner and bracket I ran with a 4 groove belt so it could jump back and forth and not chew the belt. Used to take 2 belts to get from Maine to Florida. I don't think this is an engine issue. It seems more likely to be a fan controller issue and I'm not yet sure how that and the power steering work together. Sometimes it'll do it every initial start and then it be fine for a couple of starts. Sometimes if I cycle the engine on and off a few times it operates fine. I'm not chewing up belts now and I can live with it but it would be nice to make it work properly.
Cedric

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #8 – September 25, 2020, 11:48:25 pm

Cedric,

You have exactly the same engine, etc that we do. No, if you are running a 4 groove belt, something is very wrong. When we bought our U300 at 60K miles, the seller described how he lost a belt and had to wait hours for the tow truck driver to bring one that would work in the middle of the night. This happened several times to them.

On the way back to CA, it broke in the rain but I had purchased a couple extra so a quick change and we were going again. This was after the DDEC had gone to shutdown as the steering wheel blocks the warning light for me. It happened again in San Francisco, again going to partial and then full shutdown.

I decided to get to the bottom of the problem so called Tegas Bus and talked to the owner's son and then to Gates where I spoke to the engineering department. Both Tegas and Gates said there was a problem and I should have 8 ribs on the belt.

After taking a long look at it, I could see that before the belt failed, it would start to fray on the edge. This would progress until the belt came apart. Since I had a 6 rib belt as a spare, I watched it ride on one set of grooves on the crank pulley and a different set of grooves on the pump pulley. Watching it closely at idle, I could see the tensioner was jumping up and down about a quarter of an inche several times a second. On closer inspection, I could also see the belt was moving over on the idler pulley on the tensioner and jumping back several times a second causing the apparent length of the belt to constantly change and was the culprit causing the tensioner to jump up and down. I used a straight edge to see how the horizontal alignment was and determined it was OK. I had a angle indicator so put it on the crank pulley, the pump pulley, the tensioner mount and the face of the tensioner roller. All were exactly the same except for the tensioner roller. The tensioner back where it mounts on to the massive piece of steel was OK, just the roller was off by 3 degrees. I loosened it and found a washer of the correct thickness to go behind it almost at the top so all vertical angles were the same and it was still in horizontal alignment. Before that, I pulled the tensioner and oiled the bearings. If the pump pulley is off in the horizontal plane, it can be moved in or out on the shaft by loosening the bolts. Again, the idler roller angle measurement has to be on the face of the roller with the indicatior in exactly the vertical position and no other place.

The new Gates Green Stripe Fleet belt has gone over 50K miles now without a trace of wear and should last as long as I can drive it. It is the most important replaceable item on the coach as too many belt failures and high temperatures can ruin the engine even with the DDEC auto shutdown. One owner had his fail going into a tunnel in Zion as I remember. He was blocking traffic so used the override several times and overheated the engine so much that it warped the block and had to buy a new engine.

So, do your homework, put the right 8 rib belt on and if it not perfect, fix it so it rides exactly right without rubbing the edge of the belt. It should not overhang on the idler roller but ours does not ride exactly in the middle of the roller but still a little away from the edge of the roller. Our tensioner idler roller is very smooth now that the belt does not move from side to side. So many people have chased the jumping idler roller without success. Our tensioner is going toward 120,000 and is smooth as a glass. Both our ML320 and RAV4 have tensioners with well over 200,000 miles and working well.

Buy the Gates belt online as it's half price compared to NAPA or anywhere else. My previous post will have the correct belt number. Since it's the outside belt, you can fit a new one in as little as 7 seconds from having the belt in your hand to the time the engine is running. I practiced. Since we don't have an AC compressor, the hydraulic motor belt is the only belt on the engine and even then, it would be on the outside.

When the belt breaks, the temp goes up so fast that you would have to be really lucky to see it on the temp gauge. You also must have a least one spare as the broken belt will be a mile behind and without knowing the length, you are out of luck.

This is the fault of a poor engine accessory installation where not enough time was spend checking the alignment. Since this happens to most U300's with twin fan side radiator, I cannot find any other explanation.

Don't use the override. Did I say not to use the override?

The coach can be at any angle to check the alignment. The readings are what must be the same.

Pierce

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #9 – September 26, 2020, 12:32:26 am

Cedric,

The power steering pump is on the other end of the engine and internally driven. When you open the bed up and look down, the pump is close to the alternator.

Piece

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #10 – September 26, 2020, 08:45:31 pm

Pierce,
Thanks for all the info. I have lost that belt and had the engine shut down- in the pouring rain. (Did not and have not used the override). I had a spare , put it on and left. Several belts later, I figured out the tensioner alignment problem and have had an 8 groove belt on since. This present problem is different than the one you are describing. The tensioner is not jumping several times a second. It will jump, wait several seconds and jump again at regular intervals. It makes me think that whatever tells the fans to engage does so and then immediately tells the fans to disengage. Hence the jumping action. When the tensioner was at an angle to the belt and not centered on it, every jump would shove the belt forward and chew pieces off it causing eventual failure. It's been so long since I lost the belt that I forgot I still could steer okay after the belt departed. Thanks for that tip.
Cedric

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #11 – September 26, 2020, 09:18:42 pm

Do you know where the switch is located? It's on the right side and either could be faulty or you might have a wiring problem. Perhaps others may have experienced your problem and not only Detroit but it could also effect Cummins operators also.

How about your 8 rib belt length? Is the tensioner forcing the belt down so there is only a half inch or perhaps a little more clearance to the pulley? The higher percentage the belt wraps the pulley, the least amount any sudden load will effect it.

How about a light tachometer on the fans to see if the speed is changing when the tensioner jerks? They are pretty inexpensive.

Pierce

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #12 – September 28, 2020, 07:16:48 pm

I'm leaning towards it being the switch itself or the sensor in the coolant. I was hoping someone else had already been down this road.

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #13 – September 29, 2020, 01:53:17 pm

Ken,

Here is a photo.

Pierce

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #14 – October 02, 2020, 06:49:29 pm

Is that the one that might be suspect.

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #15 – October 02, 2020, 07:05:47 pm

Quote from: Cedric – October 02, 2020, 06:49:29 pm

Is that the one that might be suspect.

That would me my usual suspect. The dash temp gauge sender is on the other side. You can pull a wire off it and see if the dash temp gauge stops working.

I would gently bend the gray clip out a little on the connector and pull the connector straight out. Then clean the contacts on both male and female. While I. have never had your problem, several others have and my photo is the location they identify as the DDEC II temp sensor. It's not expensive, probably not more than $40 at the most.

Pierce

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #16 – October 02, 2020, 07:10:00 pm

Thanks for the info. I'll check it out and report back ASAP. Radiator is out right now for recore. Should be up and running next week.
Cedric

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #17 – November 13, 2020, 07:18:29 pm

Hi Pierce,
Well, I got the radiator back in checked the contacts and found them to be nice and clean. Loaded up and drove to Florida. Each morning until the engine get up to operating temp, the hyd pump cycled in and out and the fans moved a little. I'm not sure if the fans ever get up to rated speed because as the OAT got up to the 70s the engine temp ran around 200, in the 50s the engine temp stayed down around 185. (Have not checked the calibration of that gauge.) I tempted to remove all that hyd stuff and use electric fans.
Cedric

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #18 – November 13, 2020, 09:48:24 pm

I don't think you will be able to get away with electric fans without having another alternator. You might be able to use a front radiator utilizing the heater hose and then use electric fans at the back. Getting the fans right with a mount that sucks or pushes air efficiently is going to take some engineering. If it takes 60hp to run the hydraulics at high speed, getting half that much hp to run electric fans is going to be tough. Unless you are pretty savvy, converting to all fans where it's 100% reliable is going to give you headaches.

I would say to make sure your switch is working correctly to switch from low to high speed. You can purchase an inexpensive optical tachometer and see when the fans switch to high speed. Pull the grill and block off part of the radiator if you are having trouble building enough temperature while not moving. Switch or wiring could be faulty and randomly switching back and forth. Keep a log of temps, RPMs, etc.

Pierce

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #19 – November 14, 2020, 10:31:49 am

Cedric,

How about taking your smart phone and taking a video of the problem, the tensioner, etc and putting it on YouTube? It only takes a few minutes to upload it and then everyone could see what is going on. Lots of video tutorials if you have not done it before.

Everytime I look at all the hydraulic stuff, I feel like pulling my hair out so I know what your are going through.

Pierce

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #20 – November 15, 2020, 11:33:46 am

Hi Cedric,

Pierce and others were a big help in getting my hydraulic pump belt alignment in good shape ( Hydraulic Pump Belt Alignment - 6V92TA ).

I'm curious about the fan "cutting in and out". My basic understanding from working on the system is that there is is not an on/off condition, only a slow/fast condition that is controlled by a hydraulic solenoid. The PO of my coach removed the electric head on my solenoid so it would default to high speed setting at all times.

If your fan is cycling back and forth between high and low speeds, it could be a solenoid issue too. Perhaps a simple test would be to remove the wiring block head from the solenoid?

Either way, it sounds as if a belt alignment and new tensioner are in order.

Chip

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #21 – November 15, 2020, 11:52:30 am

Quote from: Chip7 – November 15, 2020, 11:33:46 am

Hi Cedric,

Pierce and others were a big help in getting my hydraulic pump belt alignment in good shape ( Hydraulic Pump Belt Alignment - 6V92TA ).

I'm curious about the fan "cutting in and out". My basic understanding from working on the system is that there is is not an on/off condition, only a slow/fast condition that is controlled by a hydraulic solenoid. The PO of my coach removed the electric head on my solenoid so it would default to high speed setting at all times.
If your fan is cycling back and forth between high and low speeds, it could be a solenoid issue too. Perhaps a simple test would be to remove the wiring block head from the solenoid?
Either way, it sounds as if a belt alignment and new tensioner are in order.
Chip

With the fan in the high speed position, a huge amount of energy is wasted and your fuel mileage has to suffer. The U300 is already slow off a stop sign because of the "no smoke" setting on the ECU and the power robbing high setting on the fan will make it worse, especially up at altitude. Perhaps a new "solenoid" is needed. You can always wire in a dash light with one of the extra wires that go from the engine compartment to the front so you can tell when it changes to high speed.

Pierce

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #22 – November 15, 2020, 05:51:40 pm

This sounds similar to a condition I experienced with my 6V92, I call it a galloup when the hydraulic pump causes a pulsing of the tensioner actually causing it to jump and snap the belt. I had a post on here a while back about this condition. you can hear and see the strain being placed on the engine and pump.

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #23 – November 15, 2020, 06:36:24 pm

Gerry,

I looked but could not find your old post. Sounds as if that may be the problem. What did you do to cure the pulsing? Pulsing is going to eventually cause failure of the other components.

Pierce

Re: Any discussion of a cause of a1993 U300 rough idle?

Reply #24 – November 15, 2020, 07:17:02 pm

I don't think the fan is changing speeds It acts more like every time the pump snaps in the fans spin a little. I think pulsing is a better description of the activity. Mileage was 7.5 from Maine to Virginia down 84 and 81. Pulleys are lined up and tensioner spins freely.
Cedric

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