5.7 TBI Questions

[K.E. Towle]

Any answers to the following questions would be appreciated:

Situation: 5.7L w/700R4 trans, from 89 Chev pickup swapped into 84 G20 van
(305 removed), ECM #1227747, cal-pack ANLW.
Installed with freshly built long block from a not-so good rebuilder (too
late smart)

1. Engine went bad (exhaust valve stems mushroomed, broken lifter) after
30K miles. What would cause an observed excessive carbon build up on the
stem side of all the intake valves?

2. Does the presence or absence of catalytic converter(s) affect the proper
function of the O2 sensor?

3. The G20 van has a lower ratio (3.08:1) differential than the pickup
(3.42:1).  Any suggested changes to efi and/or ecm that I should be looking
into to get this combination to run better.

4. (This one should probably be on the ECM list) ECM is intermittently
setting code 34. I have installed a vacuum gauge and test light to monitor
when the ECM is 'testing' the EGR valve. What I'm seeing is low vacuum at
the throttle body port where the EGR vacuum is tapped off going to the
controlling solenoid valve. Obviously, the wider open the throttle, the
lower the vacuum. So, if the ECM 'tests' the EGR at a high steady speed,
the low vacuum isn't enough to have the EGR valve open. Therefore when the
ECM signals EGR valve to close, being closed already, there is no change in
the O2 reading and the ECM assumes a bad EGR and sets code 32. If the test
happens at a low, steady speed (I seem to recall 40MPH as a minimum), then
there is enough vacuum to have the EGR valve open, so it actually closes,
satisfying the ECM's test. What suggestions are out there to fix this
problem?

Thanks,
Karl
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