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As I look at what I just typed in the Subject line, it occurs to me that the title is at least double redundant: "D-Jet", "MPS", and "Trouble" are actually all the same word, right?
Hey... ya gotta keep a sense of humor about these things!
Seriously folks - I have problems. The photo below shows the diaphram I just removed from the MPS on my 142E race car. As hard as you may find this to believe, yes... those are cracks you see in the metal. One long circumferential crack running along the inner edge of the clamped area from right to left in the pic, trailing into the diaphram outermost pleat at the left end. And just for good measure, at about 1/4 the right-to-left distance of the circumferential crack is an intersecting crack, at right angles to the main one, also ending in the outer pleat.
How discovered - On the last few engine runs (in shop at home), a new problem began to crop up... at idle, the engine would run fine for a few seconds at 1000-1100 rpm, then die out completely until getting down to about 600 rpm, at which point it would (usually) pick back up and run again for a few seconds. Also, it became increasingly difficult to accelerate the engine from idle to higher speeds, with much blipping and coaxing of the throttle necesssary. Once up to speed, the engine would sound okay, at least given the no-load nature of an in-shop run. At this point, (for apparent intuitive reasons I don't fully understand), I went straight for the juglar... vacuum test of the MPS. Hmmm... not good. Won't even pull a real vacuum with a hand pump, never mind hold one.
Confirmation: Walked over to my 73 1800ES and removed the MPS (different p/n - an 054 vs the 015 on the 142E). Installed the 054 temporarily on the 142 and cranked it up. Uh-huh... idle is back to normal and throttle pick up results in immediate acceleration to neighborhood glass-shattering rpm levels.
So, we tore down the heretofore apparently unmolested 015 and took a look, finding the cracks pictured below.
Questions:
1 - What I wrote in the "Confirmation" paragraph notwithstanding, I would like to know if everyone agrees that the cracked diaphram could cause the symptoms I described? I read somewhere that this failure usually results in over-rich conditions, but that was clearly NOT the case here... it is more like all fuel is temporarily being shut off. Again, keep in mind I was not driving the car, these are in-shop runs only.
2 - I know, I know, but I have to ask... has anyone had any luck repairing one of these diaphrams, meaning the repair lasts more than a few full-throttle cycles? I was thinking maybe three stop-drills and silicone?
3 - Can I assume the rebuilt units sold by Scandcar and possibly others, have proven themselves to be decently reliable (relative to "new" ones)?
4 - In any case, given the nature of the application (race car), what is to keep me from (at least temporarily) using the 054 MPS and "tuning" full throttle mixture via fuel pressure, as I do now (or did) with the 015? EGT guages are installed on cylinders 1 & 2, fuel pressure is adjusted (usually between 37-41 psi) while underway, altering A/F ratio to result in a target EGT of 1450 degrees F at the end of the straights. And if this doesn't do the trick, I can always tweak the 054 MPS. (Somewhat surprisingly, the 1800ES MPS has already been tampered with, as the adjustment screw is duly unsealed. I say surprisingly, because I've owned the car since 1979 and I know I haven't monkeyed with it.)
One last thought - keep in mind that I have little or no reason to care about engine response or driveability at anything much below 4800 rpm.
All comments are welcome, thanks in advance.
Gary L
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1971 142E ITB racer, 1973 1800ES, 2002 S60 T5
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