'99 dt466e with air brakes, has constant low pressure alarm and slow pressure build.

[laegion]

I just bought this bus, it seems okay, but running a bit rough. I'm new to busses so I don't really know what to expect.
I looked up air brake tests before I drove it home. It was fine when I left on my 150 mile journey but about half way home the air pressure alarm started going constant, sometimes changing tone almost going off, then starting again. During all this the pressure stayed above 110 on the gauge. I tried the airbrake tests that are required for the certification and everything was fine with the tests of whether the brakes or tank hold pressure, except the test where you time how long it takes to get back up to full pressure. It seems to take around 3-5 minutes, however it does reach full pressure and stays around 110-120psi, seemed to work and stop properly but would still recharge slowly.
It didn't cause any scary problems so I drove it home. I'm just working on tearing the interior out and I won't be driving it for at least a year, but I figured it would be good to look into the issue. I've worked on a lot of cars but I'm not familiar with diesels specifically, and definitely not air brakes.
Is it possible the pressure sender for the compressor has gone bad and is leaking pressure? or am I way off? Any thoughts or suggestions?

Also, what would be things to look for if it's running fairly smooth but seems to lose power in the mid rpms and surge at idle when cold? boost leaks? worn charge pipes? needs oil changed and trans service? or is that just something that's normal with the power curve of a diesel?

[ewo1]

Originally Posted by laegion

I just bought this bus, it seems okay, but running a bit rough. I'm new to busses so I don't really know what to expect.
I looked up air brake tests before I drove it home. It was fine when I left on my 150 mile journey but about half way home the air pressure alarm started going constant, sometimes changing tone almost going off, then starting again. During all this the pressure stayed above 110 on the gauge. I tried the airbrake tests that are required for the certification and everything was fine with the tests of whether the brakes or tank hold pressure, except the test where you time how long it takes to get back up to full pressure. It seems to take around 3-5 minutes, however it does reach full pressure and stays around 110-120psi, seemed to work and stop properly but would still recharge slowly.
It didn't cause any scary problems so I drove it home. I'm just working on tearing the interior out and I won't be driving it for at least a year, but I figured it would be good to look into the issue. I've worked on a lot of cars but I'm not familiar with diesels specifically, and definitely not air brakes.
Is it possible the pressure sender for the compressor has gone bad and is leaking pressure? or am I way off? Any thoughts or suggestions?

Also, what would be things to look for if it's running fairly smooth but seems to lose power in the mid rpms and surge at idle when cold? boost leaks? worn charge pipes? needs oil changed and trans service? or is that just something that's normal with the power curve of a diesel?

First thing that needs to be done is a visual inspection of the entire system and a leak check to.

Chock ALL your wheels, both side of each wheel.
Start engine and buid up pressure.
Shut off engine, brakes engaged (locked), go under bus with a rag and a spray bottle full of soapy water.

Check all the components visually for wet spots (before spraying with soapy water), and the entire run of all the air lines.
With your rag, clean any dirt grime on all the connectors and then spray with soapy water. Anywhere you see bubbles forming, inspect further for an air leak, loose fitting or broken / worn out hose.

Make sure you also do this on the air compressor itself.

While your under there, after your done inspecting/testing, don't forget to drain the air tanks. Check and see if there is any oil coming out of the tanks and how much. when you open up the air tank valves, crack it open slightly, have a plastic soda bottle with the top cut open and try to catch the oil coming out. This will help you determine if you have alot or a little bit of oil in the system.

If anything at all, by going thru this process you will get a better view/understanding of what is down there under the bus and how to do a simple safety check when your under the bus greasing things up like u-joints !
Let us know what you find!

[ewo1]

Originally Posted by laegion

Also, what would be things to look for if it's running fairly smooth but seems to lose power in the mid rpms and surge at idle when cold? boost leaks? worn charge pipes? needs oil changed and trans service? or is that just something that's normal with the power curve of a diesel?

My wild guess would be dirty / worn injector ???

[laegion]

I can tell you a couple things already. The system has no noticeable leak-down when holding breaks, or while sitting after charged. I believe it auto empties the tanks but there is quite a bit of oil buildup on the outside of the air tank. The compressor itself looks very clean. I suspect that if I do have a leak it would be before whatever check valve keeps the air tank from leaking back into the compressor.
After the alarm started going constant I literally checked the guage every 30 seconds the last 80 miles of the drive and the tank never budged except when I used the brakes.
Thanks for the info. I'll try that. I wonder if I'll have to try it while the compressor is running to test that side of the system?
I can't do it yet however. I need to trace some lines and disconnect the one that went to the crossing arm at the source? I'm still not sure on that as I assume it shouldn't leak pressure unless it's activated? I would guess I would cap it off at some distribution block?

[laegion]

Originally Posted by ewo1

My wild guess would be dirty / worn injector ???

Would fuel treatment be a good first step or pulling and inspecting injectors and bench cleaning? I don't have anywhere to do it right now...but I'll be building a "workshop" into my build that will give me a place to do things like that.

[Simplicity]

Welcome. Where in Washington are you? I'm in Auburn.

Per your issue, EWO's suggested full inspection and bubble testing is a great start. Along with a rag, I'd use a small stiff brush to really clean the gunk from connection points.

You don't need to see large obvious bubbles for their to be a problematic air leak, so make sure you have a really bright light and can see all around your connectors and hoses. Using a small mirror will be helpful.

You may already know this, but if you don't it's good knowledge.

In general, you will have these components to your brakes:

Pedal and Treadle Valve
Air lines
Air heater - to evaporate any moisture in the system
Air tank(s):
Wet Tank collects whatever moisture gets passed the air heater
Primary tank is your largest tank and supplies the rear brakes which are your primary stopping power
Secondary tank supplies your front brakes.
Actual brakes - At this point you start to convert from air pressure to mechanical activation.

On your air gauge, you should have two needles, one for the primary and one for the secondary tank. Are both of them up in the same range, or is one lower?

Here's a good video:

https://www.youtube.com/watch?v=-R7J9BIjNEw

[laegion]

Most of the basics you mention where in the air brake test video I watched. I will be going over basically everything in this bus over the next few years as I work on my conversion and get all the mechanicals ready for trips. Thank you for the advice I looked at some of the components today, just slowly getting an idea of what and where everything is on the bus.
I can find the compressor, most of the air lines, the brake units, what seem to be some distribution points for various air accessories, and the main air tank. I'll take another look underneath and see where the secondary tank, air heater, and wet tank are sometime soon.

As for the needles; they seem to stay about 5-10 psi away from each other at all times. But both rise and fall together at all times. Maybe I have a faulty guage? They never seem to change position relative to each other. I can confirm the guage isn't why I think it's taking a long time to pressurize the system because I'm also waiting to hear the air purge from the compressor when the tanks reach ~120psi

Is the air compressor powered by engine oil/hydraulic? is that why oil in the tanks is a concern? or is it just lubricated by engine oil? I see what looks to be an oil line going to it from the the block but it has hose clamps so I assume it's not high pressure.

[Simplicity]

Originally Posted by laegion

I'll take another look underneath and see where the secondary tank, air heater, and wet tank are sometime soon.

The air tanks may be separate, yet more likely for your year it's one unit with internal chambers.

Sounds like you are on top of this. I think the bubble test will tell you what you want to know, i.e., is it a leak at a connection or a mechanical issue.

Per is the compressor, I'm not sure. I did a quick search and can't find anything definitive. I "think" it's likely part of the engine lubrication system. I'm thinking if there's oil in your tank, it's indicating there's possibly a leak in the compressor allowing oil to get into the lines.

Here's part of a post from Cadillackid in 2017 "For instance in the 444E you have oil running the injectors, the lube of the engine, extra oil required for the air compressor, the turbo, and even many 250+ amp alternators require an oil line."

I interpret this to mean the air compressor does use engine oil.

Hope this helps.

[o1marc]

Originally Posted by Simplicity

The air tanks may be separate, yet more likely for your year it's one unit with internal chambers.

Sounds like you are on top of this. I think the bubble test will tell you what you want to know, i.e., is it a leak at a connection or a mechanical issue.

Per is the compressor, I'm not sure. I did a quick search and can't find anything definitive. I "think" it's likely part of the engine lubrication system. I'm thinking if there's oil in your tank, it's indicating there's possibly a leak in the compressor allowing oil to get into the lines.

Here's part of a post from Cadillackid in 2017 "For instance in the 444E you have oil running the injectors, the lube of the engine, extra oil required for the air compressor, the turbo, and even many 250+ amp alternators require an oil line."

I interpret this to mean the air compressor does use engine oil.

Hope this helps.

Compressor is basically a 1 or 2 cylinder motor, rods and pistons that are lubricated by splashing oil in the bottom end.

[ewo1]

Originally Posted by laegion

As for the needles; they seem to stay about 5-10 psi away from each other at all times. But both rise and fall together at all times. Maybe I have a faulty guage? They never seem to change position relative to each other.

International dash clusters are a notorious problem child.

You could try opening up the cluster and setting them back together at zero but I don't think that will fix it.

Or....

just live with it.

Or...

you can eliminate those gauges and install new ones independent of the dash. All you got to do is remove the air line to the back of the gauges and attach to new gauges.

[laegion]

Originally Posted by ewo1

International dash clusters are a notorious problem child.

You could try opening up the cluster and setting them back together at zero but I don't think that will fix it.

Or....

just live with it.

Or...

you can eliminate those gauges and install new ones independent of the dash. All you got to do is remove the air line to the back of the gauges and attach to new gauges.

I will probably do a combination of replacing the critical guages like the air pressure with aftermarket and also I plan on doing some sort of tablet interface with the j1708 is what it looks like this bus has unless there is a 9-pin hiding somewhere.

[laegion]

Originally Posted by o1marc

Compressor is basically a 1 or 2 cylinder motor, rods and pistons that are lubricated by splashing oil in the bottom end.

It looks like mine also has the power steering pump attached to the same "crankshaft" driven off of a crank gear or sprocket.

[laegion]

I'm willing to bet my leak is on or near this distribution block where it looks like my pressure sender is mounted. It would be the most logical since the tanks themselves seem to hold pressure.

[laegion]

I need a darned service manual just to identify all the filters on this motor...so far I count 4.

[laegion]

Main tank, wet tank? and ??? or main tank, secondary and wet tank? plus random pic of my md3060. Kinda dirty. It does have a known oil pan leak.

[Truthseeker4449]

Originally Posted by laegion

I need a darned service manual just to identify all the filters on this motor...so far I count 4.

Let me see... I'm sorry this is going to be a bit wordy.

Your bus should have at least one fuel filter, more likely two with the second being a water separator. A water separator can be identified by the drain valve on the bottom of the filter. The filter on the driver side of the engine by the air compressor is a fuel filter. Take note of the primer bulb on top of the filter.

The oil filter is iirc the largest filter on this engine, being on the passenger side below and to the rear of the turbocharger.

In the same picture that shows your turbocharger, the filter mounted horizontally is going to be a coolant filter, it's mounted on or adjacent to the water pump.

The filter in the foreground of the same picture is a mystery to me, I've not seen a filter with what would appear to be air lines going into it. Try googling the part number on it.

Your third to last picture is your Air Drier, there is a filter element with a dissent inside that should be changed annually. On this model of drier, I believe it's an AD-9 but it may not be, it's also frequently recommended to change the purge valve at the same time.

The white object in the second to last picture may be a water separator, though I must admit it's a strange shape and it makes me doubt what it is.

The transmission has two filters towards the front of the pan. They are bolted in from the bottom. A service kit for the transmission will include both filters. The sump drain is at the rear of the pan, usually a 3/8" square drive. They do make deep and shallow pans and this may affect which service kit you require. Yours appears to be a 6" pan.

Take careful note of all the part numbers on the filters, you're going to need them to find replacements either like for like or cross reference the numbers to change brands.

The power steering pump is commonly driven off the back of the air compressor. Your reservoir may also have a filter inside of it, look for a nut on the top of the reservoir.

Identifying tanks can be tricky when they aren't labeled. Your only really solid way of proving of what they are is by tracing the lines. The wet tank will be connected to the air drier.

The distribution block you mentioned is in fact the governor for the air compressor. It tells the compressor when to engage (usually less than 100 psi) and disengage (about 120 psi) based on the air pressure in the primary and and secondary air tanks. It does not distribute air through the system, that happens at the tanks. The pressure switch mounted on it very well could be for your low air pressure warnings. The buildup time does seem excessive, unless you're doing this on empty tanks. Is that 3-5 minutes to raise pressure from 90 psi? Since the system holds pressure well, I think a worn out compressor or a large leak in the supply line from the compressor to the air drier (or even a leaky drier) is likely.

In regard to your poor running complaint, keep in mind that the DT466 and other engines with the HEUI fuel system are sensitive to oil quality. Before you start dumping additives and cleaners in the tank and crankcase, I would do an oil change and change the fuel filters with it. I would expect a boost leak to cause a loss of power at all speeds. I would not suspect a transmission problem at this time. A fault in the injection system is possible, including worn out injectors or a fault in the high pressure oil system for the injectors.

[Simplicity]

As TruthSeeker said, tracing your air lines is the most assured way of identifying the air lines. If you find the air purge valves, they generally are labeled and should be pretty easy to trace to the tank. If not, as I previously mentioned, the rear brakes use the primary (large) tank and the front the secondary tank. So, by default, trace one and the other will be, well, the other.

I'm kind of wondering about the gauge. Why the two indicator needles are always the same distance apart from each other. Yet, the fact that it takes 3-5 minutes to reach cut off, I do wonder if the compressor is failing. Especially if there's oil present after purging the tanks.

Per the rough running, I have a T444E, so HEUI and HPOP. While my engine seemed to be running well, after I changed my fuel and oil filter (spin on and internal), it really smoothed out. Much quieter.

I did add some Power Service fuel additive too, yet I'm not sure how much that helped. Side note, after finishing off the Power Service, I'm switching to Hot Shot. Watched a great YouTube additive comparison video and Hot Shot was overall the better additive.

If you do change your oil, maybe sending it off to be tested might be interesting.

Hope you find your issue and get it resolved.

[Brad_SwiftFur]

Air systems are pretty durable and reliable. Air pressure gauges rarely fail, since even on the IH buses, they are mechanical, not electronic (at least all the ones I've seen are.)
If you're showing over 60-80 PSI and getting a low air alarm, I would check/replace the pressure sensor which turns the alarm on/off at the 60 PSI range.

[laegion]

Originally Posted by Truthseeker4449

Let me see... I'm sorry this is going to be a bit wordy.

Wordy is fine as long as there is lots of good info like in your post.

The fuel filter was the only one I was absolutely sure of, since it says right on the filter what it is. The oil filter I suspected. I was not aware of these having coolant filters...that's a new one on me. I will have to check on the other filter, take a look at where the lines go and check the part number.

I'm thinking WIX filters? As I've heard they are the ones to go with on diesels? Any recommendations or ones to watch out for?

I wonder if any of these lines and components would be damaged by Engine degreaser??? I really want to get this stuff cleaned off so I can see better what's what and not get covered in grime just from looking around...

Yes, I'd noticed my transmission seems to have a deeper pan/sump than the short sump I've seen. I've looked up the transmission a bit more now, enough to know what it is and what the gear ratios are. Too bad it's not an MD3560 (being on the mountainous side of the country), but I can't really complain about an MD3060...

I don't see what I would call a "nut" on the top of the reservoir but there is a round knob that says "oil level" on it. I figured it was a dipstick; but I haven't tried pulling it out yet.

Yeah, that white bulb looking thing is strange. I will research further.
Maybe I can find a Field Service Manual for the '99 3800...

If that's the governor for the compressor and that is the low pressure sender than that seems even more likely to me that it could be my issue. Since it doesn't seem to effect anything other than charge time I suspect it's not in the brake system itself.
I'm not sure how the sender is constructed but I've run into other senders that sometimes when they go bad will leak whatever fluid/gas they are supposed to be monitoring. Or one of the fittings there could be loose, etc.

This is the video I watched about testing the air brake system.

https://www.youtube.com/watch?v=aACd...index=1&t=549s

Everything was great, it didn't drop any more than maybe 1-2 psi during any test. The two issues where the constant alarm/warning light and it took somewhere around 5 minutes actually to come back up from around 20psi to 120psi and the compressor purge. The gauge seemed to be basically on staying in between 100-120 psi during operation. Just recharging slowly compared to what he is saying..i.e. 45 seconds when revving at 1500rpm.

I will also say, the other bus identical to this one that I took a test ride in, charged very quickly after starting. I noticed this one being slower when we took it for a test but the alarm wasn't a problem at the time. I ended up going with this bus because there was far less oil all over the engine/transmission and it was shifting much better than the other one. So I suspected a transmission leak of some kind that was probably going on for some time.

That makes perfect sense about the oil quality on an engine like this. I mean it even makes a big difference on my subaru...so something that relies on oil and oil pressure so much....
An oil change, full filter changes, transmission service, coolant flush, u-joints, etc. etc. are all on the list of things before I drive this anywhere. I figured that would be necessary when buying something used like this. As I mentioned originally, this bus won't have to move anywhere for at least a year, maybe more. I've got time to get it all sorted out and learn the ins and outs of the systems on it.

Thank you for all the info!

[laegion]

Originally Posted by Simplicity

I'm kind of wondering about the gauge. Why the two indicator needles are always the same distance apart from each other. Yet, the fact that it takes 3-5 minutes to reach cut off, I do wonder if the compressor is failing. Especially if there's oil present after purging the tanks.


If you do change your oil, maybe sending it off to be tested might be interesting.

Hope you find your issue and get it resolved.

I'm thinking the gauge may just be worn out an the two needles are frozen to each other...they seem to read fairly accurately otherwise as I hear the purge when the gauge shows around 120 and after it goes below 100 it starts to charge and the gauge goes up.

Oil and fuel filter changes are definitely on the list before I drive this thing anywhere.

I've read about sending off oil samples for testing. I really should do that. Thanks for the reminder.

I will. I've got lots of time to get it all worked out. Thanks for the advice!