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I'm making progress, but still having problems with this 91 with LH 3.1
I bought this car with what PO described as "running problems" a month or so ago and have made a lot of progress with it - but still contending with a poor/stumbling idle. When I first start it in the morning it runs very rich. Runs great with throttle depressed - lots of power - but idles very poorly. At first I wasn't getting any lights at all from the OBD port - but I replaced the top of the unit with one from the junkyard and now I can retrieve and reset codes fine.
I don't get any error codes at all in socket 6. The only code that I keep getting in socket 2 is 212 so I replaced the o2 sensor (used a new bosch 13953 and spliced it to the existing harness). But the 212 code is still coming back with the new o2 sensor. I probed the connector on the new o2 sensor with a voltmeter and got a steady .5 reading - no swing at all. The other symptom I am having is an occasional bucking while cranking - like was described by Art B in another recent thread as caused by a Crank Position Sensor going bad. I plan to replace the CPS. The engine also seems to have a lot of pinging - especially under load.
I am beginning to suspect the 572 ecu is the cause of the problem. The PO had a spare one he had purchased in his attempts to fix it - but it is much worse than the original. It seems to just dump fuel and completely flood the engine. I have tried swapping the Ignition control unit too - but no difference.
So far I have found and corrected the following: (I'm actually really amazed that the engine started at all with all of these problems - although it ran very poorly).
The check engine bulb was burned out -replaced.
The car had an incorrect throttle body with incorrect throttle position switch (lh2.2 vintage) installed. These have been replaced with a correct lh3.1 TB/TPS and probing the TPS shows 4.8 v input with .9 - 3.9 variable output depending on throttle position.
The timing belt had been installed one tooth off - this has been corrected with new timing belt/tensioner installed.
The distributor was installed/rotated 90 degrees clockwise from the normal position, but the wires had also been rotated to correctly match - so it shouldn't have caused a problem - I have returned them both to the proer position nonetheless. Also replaced the wires with a known good set from one of my other cars.
The Idle Air Control valve has been swapped with another known good unit from one of my other cars - no change.
It was really bucking/attempting to stall whenever I would let off the throttle - I got a code 311 (no vehicle speed signal). I found two orange/red wires with mating black connectors disconnected at the top left corner of the passenger footwell - reconnected these wires and the bucking on decel stopped and code 311 has not come back.
PO had installed some Denso replacement injectors. I looked them up and they appeared to be the correct flow and resistance - but I changed them out for some original bosch yellow tops - didn't seem to make any difference.
Ive tried two different AMM's - no difference between them and resistance tests the same/good on both of them.
I've got another 572 ECU, EZK ICU, AMM, and TPS from a wrecked 240 with lh 3.1 coming - but I'm stumped by the recurring 212 code after replacing the o2 sensor.
Any suggestions are appreciated!
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