[T3] Temp sensor and MPS problems on new motor
Jim Adney
jadney at VWType3.org
Sat Feb 20 11:37:12 PST 2016
Jessica,
Okay, now I get that you're getting bucking and bad running at high
A/F, but this doesn't coincide well with the poor gas mileage, which
could also go along with low A/F. So what's really going on here?
Some thoughts:
Could unburned gas be causing your A/F sensor to indicate high when
it's really low? If so, this could mean that your problem is in the
ignition system somewhere. Double check your SP wires, connectors,
cap, rotor, etc. Look for arc tracks; swap cap & rotor, I know you've
already tried some of these. Just a thought.
If you've got a poor connection to one or more injectors, that can
make them inject less or even not at all. This will be intermittent
and temp dependent. For a '69 there are 2 things to check:
1) The grounds for the injectors went to screws into the heads in
'68-9. Those are heat-cycle failure prone unless you have Belleville
washers under the screw heads. I can supply those washers. I believe
you have one of Joe's repop harnesses, so he may have wired this to
put those grounds at the center of the case, where they do much
better. If so those will be fine. If not, you need the Bellevilles.
2) At some point in the Bosch injector production they changed the
thickness of the male connector prongs in the injectors. They made
them thinner. Replacement injectors will OFTEN make poor connections
with original connectors. If you have poor connections at any of
those connections, they will haunt you until you pull out the female
pins and squeeze them very slightly down. After squeezing, check each
pin for suitable fit ON its injector. Once again, if your replacement
harness was made by Joe, he probably fixed this, but he might have
missed one.
Finally, I believe you've checked the voltage available coming out of
your FI main power relay, but check also the 2 wires in the engine
compartment that bring that power to the FI harness. I've seen one of
those wires with badly frayed strands, and that can starve one part
of the FI system. (The 2 wires deliver power to 2 different parts of
the brain: One serves the low current control section. The other
supplies the much higher current injectors.)
Finally, I'd like to discourage you from misadjusting good components
in an attempt to "fix" a problem that none of us understands yet.
Something in your system is intermittent, and that's probably not in
the pressure sensor. Temp sensors have been known to become
intermittent as they temp cycle, but that's rare. Frankly, I suspect
the brain. Since you're using one that has one KNOWN fault, one might
wonder what caused that fault and what else might have happened at
the same time.
I look forward to looking at the brains you're sending me, but
ideally I'd like you to try a completely different one that I can
send back to you.
--
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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