Gary Lewis Posted December 10, 2023 Share Posted December 10, 2023 With the engine cold, both should read the same resistance value within the tolerance. That is a sanity check. After running it and shutting it off, once everything has heat soaked for a bit they should again read the same within the tolerance. Ok, that makes sense. So do a resistance test with the engine cold on pin 25 (ACT) and 37 (ECT) and there should be essentially the same resistance. Link to comment Share on other sites More sharing options...
85lebaront2 Posted December 10, 2023 Share Posted December 10, 2023 Ok, that makes sense. So do a resistance test with the engine cold on pin 25 (ACT) and 37 (ECT) and there should be essentially the same resistance. Yes, and hot, let it heat soak for 10-15 mins and check again. Measured from pins 25 and 37 to pin 46 sensor signal return. Link to comment Share on other sites More sharing options...
ReneH Posted December 10, 2023 Author Share Posted December 10, 2023 Yes, and hot, let it heat soak for 10-15 mins and check again. Measured from pins 25 and 37 to pin 46 sensor signal return. Ok, so I'll perform this test next weekend. Link to comment Share on other sites More sharing options...
ReneH Posted December 18, 2023 Author Share Posted December 18, 2023 Yes, and hot, let it heat soak for 10-15 mins and check again. Measured from pins 25 and 37 to pin 46 sensor signal return. Ok, I'm back... Much work and much to do at home while cruising straight to Christmas eve. Two days ago, while my bronco stand inside my workshop, it's was about 12 degrees Celsius, it won't start without pushing the pedal...I've disconnected the ACT...same thing...it won't start without pushing the pedal. Resistance of the ACT was the same as the CTS...so both seem not to be the problem. Currently I have the IAC or the TPS as suspect. The O2 sensor is very unlikely, cause it's not taken into account by the ECU at cold start. The MAP? Maybe...but why should it make problems only when the engine is cold? I'll be happy for some recommendations of possible suspects... Link to comment Share on other sites More sharing options...
ReneH Posted December 19, 2023 Author Share Posted December 19, 2023 Ok, I'm back... Much work and much to do at home while cruising straight to Christmas eve. Two days ago, while my bronco stand inside my workshop, it's was about 12 degrees Celsius, it won't start without pushing the pedal...I've disconnected the ACT...same thing...it won't start without pushing the pedal. Resistance of the ACT was the same as the CTS...so both seem not to be the problem. Currently I have the IAC or the TPS as suspect. The O2 sensor is very unlikely, cause it's not taken into account by the ECU at cold start. The MAP? Maybe...but why should it make problems only when the engine is cold? I'll be happy for some recommendations of possible suspects... Today the engine also wouldn't start without pressing the pedal at moderate temperatures above 12 degrees Celsius... Maybe I have miss-wired the IAC...I'm using the 90th IAC: rockauto.com I have added a diode in parallel, like shown here in the EEC documentation schematic...but this is from a 1984 truck...maybe this is a problem... As re-wiring all engine electronics, I may also have reversed the IAC cables (Pin 21 and pin 37/57)... Could this cause the described problem? Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 19, 2023 Share Posted December 19, 2023 Today the engine also wouldn't start without pressing the pedal at moderate temperatures above 12 degrees Celsius... Maybe I have miss-wired the IAC...I'm using the 90th IAC: rockauto.com I have added a diode in parallel, like shown here in the EEC documentation schematic...but this is from a 1984 truck...maybe this is a problem... As re-wiring all engine electronics, I may also have reversed the IAC cables (Pin 21 and pin 37/57)... Could this cause the described problem? Rene - I’m out and can’t study this right now, but have tagged Bill. He’s better at this than I, but I’ll check in when I get back. Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 20, 2023 Share Posted December 20, 2023 Today the engine also wouldn't start without pressing the pedal at moderate temperatures above 12 degrees Celsius... Maybe I have miss-wired the IAC...I'm using the 90th IAC: rockauto.com I have added a diode in parallel, like shown here in the EEC documentation schematic...but this is from a 1984 truck...maybe this is a problem... As re-wiring all engine electronics, I may also have reversed the IAC cables (Pin 21 and pin 37/57)... Could this cause the described problem? I'm confused. I see Ckt 67 on pin 22 as one side of the ISC, and Ckt 264 as the other side of the ISC. But I cannot find the pin # for Ckt 264. What am I doing wrong? Link to comment Share on other sites More sharing options...
85lebaront2 Posted December 20, 2023 Share Posted December 20, 2023 I'm confused. I see Ckt 67 on pin 22 as one side of the ISC, and Ckt 264 as the other side of the ISC. But I cannot find the pin # for Ckt 264. What am I doing wrong? Gary, I show circuit 67 as being on pin #21 for 1988-1990 5.8L then from 1991-1995 and 1996 over 8500 lbs, it changes to circuit 264. The other side of the ISC is circuit 361 12V power from the EEC power relay. This is still the power source from 1988-1995. I will be gone most of tomorrow so will not be able to contribute till later in the afternoon/evening. Link to comment Share on other sites More sharing options...
ReneH Posted December 20, 2023 Author Share Posted December 20, 2023 I'm confused. I see Ckt 67 on pin 22 as one side of the ISC, and Ckt 264 as the other side of the ISC. But I cannot find the pin # for Ckt 264. What am I doing wrong? I think my connection to the ECU on pin 21 is correct, cause I'm using the 1989. I've found this post on FSB: ISSUE: A rough idle created when the air bypass valve (idle air control) is replaced may be caused by a revision made to the valve's wiring harness. Vehicles built before the 1989 model year had a diode in the air bypass valve's wiring harness. The new replacement valves have a "D" marking on the plastic portion of the solenoid, above the connector cap, Figure 1. They have a diode in the air bypass valve. On the air bypass valve used on vehicles built before the 1989 model year, the positive and negative leads are not important to the valve's operation. However, the polarity on the new replacement air bypass valve is important because, if the wiring harness is reversed, the valve will not work. ACTION: Reverse the wires in the air bypass valve connector and retest the valve. Refer to the EFI Engine Application Chart for engines using these air bypass valves. FSB As I've added the external diode and connected the wires as shown for the 1986 circuit, but I'm using the 1994 IAC, that SHOUD have an internal diode and, as it seems, a reverse polarity... Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 20, 2023 Share Posted December 20, 2023 I think my connection to the ECU on pin 21 is correct, cause I'm using the 1989. I've found this post on FSB: ISSUE: A rough idle created when the air bypass valve (idle air control) is replaced may be caused by a revision made to the valve's wiring harness. Vehicles built before the 1989 model year had a diode in the air bypass valve's wiring harness. The new replacement valves have a "D" marking on the plastic portion of the solenoid, above the connector cap, Figure 1. They have a diode in the air bypass valve. On the air bypass valve used on vehicles built before the 1989 model year, the positive and negative leads are not important to the valve's operation. However, the polarity on the new replacement air bypass valve is important because, if the wiring harness is reversed, the valve will not work. ACTION: Reverse the wires in the air bypass valve connector and retest the valve. Refer to the EFI Engine Application Chart for engines using these air bypass valves. FSB As I've added the external diode and connected the wires as shown for the 1986 circuit, but I'm using the 1994 IAC, that SHOUD have an internal diode and, as it seems, a reverse polarity... Bill - I see what you are saying and agree. My problem was that I forgot that the IAC/ISC only has one connection to the ECU. So yes, the circuits are as you are saying. Rene - Are you thinking you may have the diodes in opposing each other? That would cause real problems. Below is the 1996 EVTM entry showing the IAC and diode for 5.8L under 8500. Link to comment Share on other sites More sharing options...
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