A. When it did start; Did it start quickly and idle perfectly OR did it stumble, miss, blubber and then finally idle smooth?

B. Did that mechanic wiggle or move any wiring before or while he was installing the fuel pressure gauge? [note: a 3406E is getting a little old, now and wiring looms can get worn thru, look very closely at areas where the loom touches ANYTHING; example, look at loom between ECM(computer) and as it goes under the cylinder head, it attaches to "ladder brackets" with plastic ties=they can rub there. The loom also goes behind air compressor and it can rub on water line/hose and/or fuel lines and have bare spots rubbed thru it there. They also get rubbed going up and over the front cover(in front of the 1st valve cover) on the "ladder bracket" there, too.]

C. The previous recommendation to reset the depth of the front rpm/timing sensor is a good idea, too.

D. Do you have a fuel hand priming pump on this engine? If not, I highly recommend installing one. It helps in troubleshooting along with filling/bleeding fuel filters, too.

E. You didn't give me a year or serial number, so I will tell you that the book spec for a 1999 engine 3406E (s/n 2WS prefix) says 78 psi fuel pressure at idle, and 93 psi fuel pressure at HIGH idle. {BIG note: There are two styles of transfer pump= early and late; early =all cast housing and has lower fuel pressure=probably only see 62-65 psi at idle WITH its old, original style "fuel return check valve". The late style= higher pressures and it has an aluminum end plate on it(=where the fittings attach to it), this style can use either an old, style "fuel return check valve" OR the newer, higher pressure "fuel return check valve". Special note: Just don't use an old pump, with the newer,high pressure "fuel return check valve". }

Either way 50 psi sounds a little low for idle, even with early style transfer pump and earlier, style fuel return valve, but IF engine started very quickly and sounded smooth immediately, then I would be looking at electrical condition as much as fuel pressure condition.(so if you had 35-50 psi cranking and no start and no smoke, that should tell you that fuel pressure isn't your main culprit, even though it is a little low: BUT you have now changed fuel filters, SO maybe it will improve; who knows?)

Now, The old style transfer pumps "can" suck air, when they are old and the lip-seals start to fail, but they don't actually leak fuel externally, either. Also, there high pressure relief valve,internally, can get stuck in one position and causes low fuel pressure while cranking, low fuel pressure at idle, but the extra high fuel pressure at high idle(MAX rpms). I need more fuel pressure readings to determine that.

Really need the answer to question #A first.

Sorry for the late response. I am working late this week. Don't get home till 10:00 pm (Pacific Time).

A. With your answer, My guess is that you probably aren't having an "air in the fuel" type of problem. That would really hurt your "cranking" fuel pressure.

B. Another "check" on the wiring, is that you can wiggle the loom around while the engine is idling and see if the engine "burps" or jumps/hesitates in RPMs. Wiggle it at the ECM, under the cylinder head, behind the air compressor, right at the RPM/timing sensor, right where the loom curves in front of the front valve cover, etc.

C. Did the adjustment seem to look any different, from when you first removed it? I know it is hard to tell, without measuring it beforehand, but sometimes a guy came visually see a little difference. What color was the tip? If it was black or white, I think I would replace it. If it was green tip, they have been pretty reliable, but they still can fail, too. The newest rpm/timing sensors are solid and non-adjustable.( I assume they are more powerful, to pick up the "reference teeth" for the signal to the ECM, thus no adjustment.)

D. Good, that you have a hand priming pump on the engine.

E. Thanks for the serial number. That engine will have a little lower fuel pressure than later engines and/or later transfer pumps. I still expect 60-65 psi at idle. CAT says anything below 35 psi , while running will cause misfire.

On what Bern said, about the OEM tach, if the tach is operated by its own (KW) sensor, then there should be a sensor(magnetic pick-up) in the lower area of the CAT rear engine bellhousing(points towards flywheel ring gear teeth). If you were to stand behind the engine, and look at the bellhousing, then the KW tach sensor would either be at the 5:00 o'clock position or the 7:00 o'clock position. The KW tach sensor will have two wires coming out of it. My guess is that KW still used their own sensor to operate their tach, back then, before they felt 100% comfortable using the CAT signal for their dash tach.

Also, as Bern said, there won't be any fault code IF, during cranking, the "RPM SIGNAL" isn't getting generated(bad sensor) or not getting back to the ECM(bad wiring), thus the ECM never tells the injectors to fire(doesn't know the engine is actually cranking).

Thanks for the additional info.

I assume the fuel filter base, that they believe is allowing air into the system, is the PRIMARY fuel filter base. (on the suction side of the system)

You could ask, if the Wagner CAT truck mechanics, also measured "fuel restriction" on the fuel supply system/hose. Those rubber bits are probably coming from the interior of your old, large fuel supply hoses. Also, look at your fuel tanks, have they rotated from the correct, original position(If the filler cap, on the tank, is almost straight up, vertical, then it has rotated) This rotation can cause the OEM fuel supply hoses to kink, causes fuel restriction and is really hard on the inner rubber of those hoses. We've seen lines bent tighter than 90 degrees, typically on log trucks or "heavy haulers", because they go thru some very "frame-twisting" environment/roads out in the woods/forest.

I could see the same twisting action going on with farm trucks, loaded, coming out of a field driveway, too.

If you can live without the truck, for one extra morning, then consider letting Wagner CAT keep the truck , overnight, WITH their sight glasses installed, so they can watch them during the next morning start-up(usually takes two people; one turns key,the other guy watches sight glasses closely at the immediately, critical cranking and first few seconds after start-up.) This helps to either "verify" an earlier repair, or prove to them that there is still a problem, that next morning. We would normally have a fuel pressure gauge hooked up also. I assume Denver CAT is very familiar with this.

Note: I have had as many as 6 sight glasses plumbed to one engine to find difficult, intermittent problems. We have tee fittings on our sight glasses(with quick disconnects) so restriction gauges can be quickly added to measure restriction on the fuel supply system.

Edit: I reread your post, I realize now, that you stated the rubber bits were coming from the fuel lines. Hopefully, they will get you fixed up and running.

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