Tag Archives: Engine

bus trouble, Engine, learning, School Bus, school bus RV, Skoolie

Replacing the IPR *or* No more Hot Start Fail!

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So, I finally got to replace the IPR (Injector Pressure Regulator), in hopes of tackling the very frustrating Hot Start Fail problem that I’ve been dealing with on the bus’ T444E engine.  The IPR is attached to the base of the high pressure oil pump, between the valve covers and kind of under the fuel filter/water separator, and lots and lots of wires and air ducting.

In doing my research on changing this part, I found that I’d have to be prepared for some oil leakage from the high pressure pump’s reservoir, and that I’d need a deep socket to get the regulator itself out.  I had a chuck pad I could use (they’re really absorbent) and was able to slide it in under the old IPR to catch the escaping oil – though no quantity had been specified, just that I should “have a bunch of paper towels ready”.  I hoped I was ready.

The IPR is a solenoid valve, and the electromagnet comes off the stem that houses the moving bit to control oil flow.  So, to take the piece off, you first have to remove the holding nut, a spacer, and the electromagnet from the stem, which can then be unscrewed.
All in this very small place.

But it can be done, and relatively quickly, it turns out.  The electromagnet has an electrical connection for controlling it, and that just has two clips on either side, then slides out and can be woven back around some pipes and wires to keep it out of the way.  The upper portion of the plug is wider than the lower, so you can’t plug it in the wrong way – an important detail for putting everything back together and doing it by feel.

The next thing is to take off the 3/4″ nut that holds the electromagnet and spacer onto the stem.  This is a very thin metal nut, so it doesn’t take much to get it off, but if your 3/4″ wrench is long (like mine), be prepared to make a bunch of very tiny pulls to get it finger-loose.

Once the nut is off, the electromagnet and spacer should come right off.  I ended up having to unscrew the spacer for a bit along the threads for the holding nut before it broke loose enough to slide.  And a little wiggling was necessary to get the electromagnet to slide, but it came more easily than the spacer once I got it wiggling.

It was then time to get the deep socket.  In doing my research, I had taken the new IPR I had apart and fitted the stem to a large (shallow) socket that I had to find that it was a 1 1/8″ size.  Our local Autozone had a deep socket in stock for $8, so that wasn’t bad at all to get the right tool.  However, the stem is so long that you need every bit of space in the deep socket (I wasn’t sure that the ratchet end would sit in the socket securely), and it turned out that the deep socket’s center hole wasn’t a full 1/2″ in diameter, so it wouldn’t fit the stem up into it.  And of course, that would mean that the socket wouldn’t engage the points.  Luckily, I was able to use a 1/2″ drill and get the hole open so that it would work.

Then there was just the matter of getting the socket onto the stem, which involved some wiggling, moving of wire harnesses this way and that, and then, once on, doing some more of it it get the ratchet down to engage it.  For this, I ended up using the 3/8″ ratchet with a 1/2″ adapter on it to be able to get a better pull, as well as to get a spacer between the socket and ratchet that was long enough, but not too long, to work around hard engine elements.

The stem broke loose fairly easily, and with some wiggling and shifting, it came out!  I could see that the chuck pad had collected some oil, but couldn’t see how much at that point.  But the important step of removal was now complete.

I transferred the protective red plastic cap from the new stem to the old one, and set about reversing the process to install the new IPR.  The only real difference was that as I was tightening the new stem in place, I slid the chuck pad back away from the high pressure oil pump, so it wouldn’t have a chance of getting caught and messing up the seal.  Once the stem was nice and snug, and the electromagnet, spacer and holding nut were on and secure, I plugged the control wire back in.

In cleaning up, I checked out the chuck pad.  It looks like there might have been about 4-6 oz of oil that drained out when the stem came out of the pump.  I don’t know if that’s typical, but it’s my best estimate.

Once all the bits were stowed away, I started up the bus.  It cranked without starting at first, but knowing that it would have to pull enough oil to the high pressure pump before it would start, I kept it cranking, and then it caught.  It ran rather ragged for the first half-minute, then smoothed out pretty well.

The new IPR is more responsive than the old one, but some of that could be  in the fact that part of the seal on the bottom of the old IPR was missing!  I’m wondering if that, coupled with either less viscous hot oil, or perhaps some dynamic of the metal being heated was what was causing the hot start fail.

At any rate, a quick test-drive, then attempted restart of the engine proves that the engine now starts up fine when hot.  It also seems a bit more responsive to the accelerator pedal, so I have to get used to starting off in second all over again.

bus trouble, Engine, learning, school bus RV, Skoolie

Hot Start Fail

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So, we had a nice day, and I decided to take the bus out for a test-drive.  Well, a test-start, really.  I figured that I should try and document what was going on, as I had read the last  service paperwork (where they couldn’t replicate the problem after it got towed) more closely while cleaning up on the bus.  The way it reads, they were looking for a hard start, but proved that the bus would repeatedly start when it was cold, and wouldn’t quit once running, which wasn’t the problem.

So, I videoed the cold start before a quick trip, and the attempt to start it hot that failed.  (Caution, it’s a bit jumpy at parts, as I had a webcam that I was holding in my hand to take pictures at times.)

This really shows the difference, and how the engine started/didn’t and how it sounded, mostly for my own reference, and to possibly take into the dealership to show them.

But in putting it together and watching it after I had uploaded it, I noticed how low the oil pressure was (I had been looking at the temperature, not the oil pressure).  While I had asked the mechanics at the dealership if the pressure was too low before, and they assured me that it was fine, this looks really low.  And since one of the things about that sort of non-start is the IPR (Injector Pressure Regulator) failing, so the injectors don’t get enough oil to function, that could be it.

Unfortunately, there’s also a possibility that it’s the whole High Pressure Oil Pump, which isn’t thrilling.  So, the next thing is to replace the IPR, and see what that does.

 

 

 

Electrics, Engine, learning

Swapping out IDMs and back again …

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So, in my previous post, I talked about the bus not starting when the engine was hot (coolant temperature around 180 degrees), and I think the blame lies with the IDM (Injector Driver Module).  As such, I ordered one from Shop Injectors and went to replace it.

Searching on the internet, I had the vaguest of ideas where the IDM was in the 1995 T444E engine compartment, so I remembered to take pictures while I undertook the replacement.

The IDM in its natural habitat.

The IDM is located on the firewall above the engine, almost right up by the hood.  It is covered with a metal plate where some relays and positive cables are installed. The positive cables connect here and they’re live(!) so be careful about them touching anything.

Air Intake Sensor on the back of the intake line.

The cover is only held on by one screw, underneath the cover, so the easiest thing to do is remove the air intake line from the filter.  There’s a sensor just to port of the IDM case cover, so remember to unplug it before trying to move the intake.

Air Intake Line removed/swung out of the way.

As my bus has air brakes, the feed line for the compressor also comes off this air intake line, so rather than fully removing it, I just swung it back off to the driver’s side and out of the way.

Lower intake covered for safety!

Remember to cover up the lower end of the air intake so you don’t end up feeding gunk or spare screws and bits into the  turbo!

When removing the single screw holding the casing on (#3 phillips), be careful to try and catch the clip that the screw threads into.  Mine ended up on the transmission, but it could end up finding a place to hide there that would make your day miserable.

Casing removed and clipped to the radiator supports.

Once the screw is out, the top just needs to be lifted slightly, and the angles on the back of the top of the casing will come right off the back plate.  The two angles on the outer ends fit behind the plate, while the middle one rests in front of it, making it fairly secure.  I didn’t need to remove/unplug any of the wiring from the casing, as I was able to swing it also toward the driver’s side and hook the angles over the radiator supports.

The IDM, mounted on the firewall behind the engine, with the cover off.

The next step was to remove the plug from the IDM.  This requires a 10mm wrench or ratchet.  Given the voltages that this unit puts out, they don’t trust it to just clips, and the bolt is fairly long.

The IDM Plug that makes it all happen.

Once the bolt is loose there is one clip that you have to undo, but then the plug just slides out.  When I looked at mine, I saw some corrosion on the plug and the prongs of the IDM.  They are fairly easy to clean up with a pipe cleaner (since none of my files fit into the holes).

The back plate without the IDM in place. The bottom two screws dont need to come out.

All that remains after that is to undo the screws that hold the IDM to the back plate.  The top two need to come all the way out, and again have those clips that the screws fasten into.  The bottom two only have to be loosened up, as the IDM has grooves that they fit into, making the process (and that of inserting the new module in place) really painless.

Putting the new module in is as simple as reversing the process, making sure to snug but not over-tighten the bolt that holds the plug onto the IDM.

Unfortunately, after all that, the new IDM that I installed didn’t do anything!  The engine just spun when I tried to start it.  Swapping the old (now cleaned of corrosion) IDM back in, then engine started just like it always did (at least when it was cold).  I went back and forth between the old and new IDMs, and the new one just didn’t work.

I’ll now have to road-test the old module and see if it was a corrosion issue, and send the new IDM back to the company to have it tested.  The guy who I’d been in contact with before about the delivery was very helpful, so I don’t expect a problem.  But at least I now know how to make the change if I still have problems.