5.3 LM4 swap, no tach and idling issues
06-01-2017, 07:13 AM
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Staging Lane
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Join Date: Apr 2015
Location: Knoxville, TN
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5.3 LM4 swap, no tach and idling issues Background:
5.3l LM4 swap into a 86 BMW. The Engine, Harness, and ECM were all pulled from the same '03 Envoy XL. I converted the harness and ECM from DBW to DBC. Engine is stock other than a LS6 cam. DBC throttle body is supposedly from an '03 Express van (bought it from a JY). Engine is still running with MAF. I followed LT1-Swap to build my harness and add the necessary wiring for the IAC and TPS.
Issues:
1. No Tach Signal - I thought my aftermarket tach needed the signal boosted but HP tuners isn't seeing a tach signal either.
2. Starts fine then begins to run away - It appears as though the IAC is stuck in one position. No matter what count we put into HP tuner the IAC doesn't seem to move. I checked the connector and noticed I did have it wired backwards. Once corrected the engine was doing the same thing. I thought I fried the IAC so I installed a new one, no difference.
I can put my finger in the IAC port and control the idle and the engine seems to run great with a slight delay in throttle response but when I move my finger the RPM's take off. Continuity between the ECM and the connector is good so I don't believe it's a wire issue. Could it be bad pins in the ECM? Incorrect base tune?
5.3l LM4 swap into a 86 BMW. The Engine, Harness, and ECM were all pulled from the same '03 Envoy XL. I converted the harness and ECM from DBW to DBC. Engine is stock other than a LS6 cam. DBC throttle body is supposedly from an '03 Express van (bought it from a JY). Engine is still running with MAF. I followed LT1-Swap to build my harness and add the necessary wiring for the IAC and TPS.
Issues:
1. No Tach Signal - I thought my aftermarket tach needed the signal boosted but HP tuners isn't seeing a tach signal either.
2. Starts fine then begins to run away - It appears as though the IAC is stuck in one position. No matter what count we put into HP tuner the IAC doesn't seem to move. I checked the connector and noticed I did have it wired backwards. Once corrected the engine was doing the same thing. I thought I fried the IAC so I installed a new one, no difference.
I can put my finger in the IAC port and control the idle and the engine seems to run great with a slight delay in throttle response but when I move my finger the RPM's take off. Continuity between the ECM and the connector is good so I don't believe it's a wire issue. Could it be bad pins in the ECM? Incorrect base tune?
