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.