Restore of my 1986 Bronco XLT

[ReneH]

So, I've changed the ACT without noticeable effect...if I disconnect it, the engine starts much better, like before. I'll check my wiring to the ECU, but as far as I remember, I've checked it twice before connecting the sensors...

[Gary Lewis]

I'm struggling to understand why it would start better w/o the ACT unless you have the wrong ACT sensor.  Or if you have the ACT sensor connected to another input instead.  Like maybe MAP?

This is where the EEC-V shines as you can log all of the inputs and see how they are responding.  I don't think you can do that with EEC-IV.  

[ReneH]

Hi Gary,

Maybe, you can tag Bill, in case of the pinout. I use a 1989 351W ECU. In my excel list o have set the ATC to Pin no. 25. Looking at the 1989 pinout, 25 is ign. Gnd...ACT is pin 29...I'm a bit confused...

[Gary Lewis]

You can tag Bill yourself.  On the Assignment dropdown, below, just click the center one and assign it to 85lebaront2, like I've done.

But I'll bet he's going to point you to the documentation he provided on our page at Documentation/Electrical/ELECTRONIC ENGINE CONTROL (EEC).  There click the Pin Outs tab and then go to the bottom of the page and pick the EFI 5.8 tab.  And on there I see 25 being ignition ground and 29 being ACT.

[85lebaront2]

Rene' the 1985/86 truck EFI pinouts are different from the 1987 up ones.

[ReneH]

So, I currently check the excel list...everything seems to fit...

On the 1989, 5.8l tab, there is pin25 described with circuit 310, that means 310 is ACT...

Pin 29 is circuit 94: HEGO.

So, my pinout seems to be correct...

But this means, the problem caused elsewhere...

Some other ideas?

[Gary Lewis]

Rene - I see what you are saying.  Where the 1989 column intersects with the Pin 25 row it says that's Ckt 310.  And if you go over to the Circuit # column 310 is the ACT circuit.

Bill - Are we reading it correctly?

[85lebaront2]

Yes, but look one column over, 1990 it becomes circuit 743, ACT or Air Charge Temperature still the same function. If you look at the resistance charts I sent you the ECT and ACT are the same values for a given temperature.

[Gary Lewis]

So we are reading it correctly.  

And I see that ACT and ECT are the same resistance for the same temp, but does that mean Rene needs to do something?  Are you suggesting that he ensure that he didn't interchange them in the wiring?  Or, why did you mention it?

[85lebaront2]

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.

[Gary Lewis]

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.  

[85lebaront2]

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.

[ReneH]

Ok, so I'll perform this test next weekend.

[ReneH]

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...

[ReneH]

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?

[Gary Lewis]

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.

[Gary Lewis]

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?  

[85lebaront2]

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.

[ReneH]

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...

[Gary Lewis]

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.