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88 DeVille engine noise


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1988 DeVille, 4.5L engine noise

On cold starting, the motor runs perfect, smooth, quiet, excellent throttle response. After reaching closed loop, it continues to run the same. But after, 10-15 minutes of driving, or after shutting it off, and restarting, it starts a slight “chauga-chauga” sound. Almost like a rod knock, but, I believe the block is tight. Even when making this noise, it still runs very good. At ¾ to 4/4 throttle, it disappears.

Here are the ECM data parameters after the cha-cha starts, KOER, in drive, parking and main brake applied:

P.O.1 Throttle position -0.6

P.O.2 Map 31

P.O.3 Computed baro. 102

P.O.4 Coolant temp. 94

P.O.5 Mat 91

P.O.6 Injector pulse width 1.2- 1.3

P.O.7 Oxygen sensor .67 - .69

P.O.8 Spark Advance 12

P.O.9 Ignition cycle counter 36

P.1.0 Battery voltage 12.8

P.1.1 Engine rpm 6000 - 6300

P.1.2 Car speed 0

P.1.3 Oxygen sensor cross cts. 28 - 36

P.1.4 Fuel integrator 121

P.1.5 Transmission temp. 75

P.1.6 E-Cell 1

P.1.7 ECM prom id 850

Anyone have an idea where I should start looking for the cause of the noise.


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6000+ rpm??? Was it idling very fast? :) The ECM receives a speed signal from the distributor. Assuming the reported RPM is invalid, there could be a temperature sensitive problem in the ECM hardware, distributor pick-up coil or module.


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