90 5.0 complete overhaul erratic idle

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topless92

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I have a 90 bronco 5.0 aid trans completely overhauled engine runs great other than erratic idle has code 42 for running rich I checked no vacuum leaks hego ground strap is connected verified all wires from 02 sencor are good all way to ecm all sencors are new including injectors fuel tank pump and fuel rail pressure regulator I'm running out of ideas

 

miesk5

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Yo topless92,

Welcome!

I can see that you have a very good handle on troubleshooting.

Did you check for vacuum leaks in the HVAC circuit too?

I have a vacuum leak diagnosis here in post #20 @ http://broncozone.com/topic/23994-90-58l-getting-continuous-code-33-and-running-code-44/?p=125535

DTC 42; Engine Not At Normal Operating Temperature during Code Test.

O2 sensor voltage was stuck high for too long. (Rich).; "...Bad O2, or it's connector/wiring bad, Bad fuel pressure regulator, pull vac hose off, any gas in it or gas aroma means it's bad (ruptured diaphram); Leaking injectors, restriction in fuel return line or exhaust leak or clogged exhaust, lowering vacuum..."

DTC 41, 42, 85 OR THREE DIGIT CODES 171, 172, 173, 179, 181, 182, 183 & 565 are received , Check for proper HEGO Ground; in Catalytic Converter Diagnosis TSB 91-12-11 for 86-91 Bronco, F Series, & Econoline...see below wiring diagram;

by Ford via Stephen

...

Wiring Diagram in a 90 by Ford via Seattle FSB

1990-bronco-electronic-engine-control-244.jpg

Ground G101 (aka power ground) is @ G101 RH side of Radiator support

Ground G103 is @ LH rear side of engine near knock sensor. Is OK.

More locations in a 90 from 90 Bronco EVTM for future reference; "...G100 LH side of Radiator support; G101 RH side of Radiator support; G102 RH side of Radiator support; G103 LH rear side of engine near knock sensor; G104 LH rear side of engine compartment, near electronic engine control (EEC) module, on the left fender close to the firewall; G105 LH Side of engine; G106 RH fender apron, near voltage regulator; G107 RH fender apron, at starter relay; G108 RH fender apron, at voltage regulator; G109 RH fender apron; G201 LH rear side of I/P (looking at the diagram it is at the bottom of the driver's side dash assembly. Screwed to the bottom edge, just to the left of the steering column. It is the ground for the instrument cluster); G202 Behind RH cowl panel; G203 RH rear side of radiator support; G204 On steering column; G205 Behind Center of I/P (Dash); near speed control amplifier; G400 LH side of cargo area; near rear light assembly; G401 Below LH side of cargo area; near crossmember; G500 Inside driver's door; near left door speaker"

Source: by BroncoJoe19 (Joe) at Ford Bronco Zone Forums

...

EEC IV CONNECTOR PIN LEGEND

http://web.archive.org/web/20120118104425/http://www.oldfuelinjection.com/truckpinouts.html

&

Pin Diagram

http://web.archive.org/web/20120115055624im_/http://www.oldfuelinjection.com/images/eec05.gif

by Ryan M.

If the other HEGO grounds are good, the following areas may be at fault:

* Ignition Coil

* Distributor Cap

* Distributor Rotor

* Fouled Spark Plug, are they showing rich condition?

* Spark Plug Wires

* Air Filter

* Stuck Open Injector

* Fuel Contamination

* Manifold Leaks Intake/Exhaust

* Fuel Pressure

* Poor Power Ground

Although you inspected wiring from O2 to PCM, I will leave following in:

Look for Poor mating of the connector halves, especially if the locking tabs are broken, which occurs with our elderly Broncos.

Terminals backed out or not fully seated in the connector.

Damaged terminals or poor terminal to wire connections.

Corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring causing the conductor to corrode inside the insulation. Look for swollen and stiff sections of wire in the suspect circuits.

Wires that are broken inside the insulation.

Pinched, cut or chaffed wiring in the harness.

Look for unravelled or missing harness wrapping and loose harnesses where PO pulled harness from its straps, and/or clips.

Wiring that is damaged as a result of being in contact with exhaust components, such as the O2 sensors, CANP solenoid where it's hose is known to melt on exhaust manifold.

 
OP
OP
T

topless92

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Yes sir even completely capped off the intake except fuel pressure regulator and smoke tested found no leaks exhaust is new no cats just a y pipe is where the 02 sensor is located egr and smog system is deleated is there any way to make this thing idle right I'm not as worried about the code as I am this annoying idle also since I can't find any leaks and all wires test good could the ecm be the problem

 

miesk5

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Yo,

I have seen more owners than ever before reporting leaking capacitors in the ECMs.

Such as Capacitor Repair by seedpress @ http://broncozone.com/topic/20788-fuel-delivery-problem/

EEC IV Removal up to & include 91; " It's behind the drives side kick panel. To remove it first disconnect the battery and then get a 7/16" boxend wrench and unbolt the wiring harness from inside the engine bay. Then pull the plastic kick panel from inside the cab and remove the retainer clip keeping the EEC in the fender pocket. Remove it by lifting the rear slightly and wiggling it out of the pocket, the rubber gasket at the firewall will have a pretty good grip on the connector so it will take some persuasion to free. Apply some petrolium jelly to the outside of the connector on the replacement EEC to help ease it back in." by Conanski

I understand that you sealed off the intake mznifold for the smoke test, but did you inspect all the remaining vacuum operated components for leaks such as HVAC hose to check valve and so on next to the evaporator, MAP sensor & cruise control, if equipped?

 
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capacitors are a big problem in general when it comes to a vehicle 20+ years old. that being said, their are a lot of eecIV's still on the road with the original computers. it's something that could be a problem, but honestly it could be a bunch of things that could contribute to a condition that the computer interprets as rich. a weak or damaged oxygen sensor will output less voltage which in turn makes the computer think "i'm rich" until it calls b.s. and throws a code. likewise, an un-metered internal fuel leak can do the same thing e.g. blown out fuel pressure reg. diaphragm or stuck open injector.

i will say that if you disconnect an oxygen sensor, typically it does not make the vehicle idle as bad as you make it out to seem. i had an econoline with the EECIV 4.9L where the oxygen sensor was disconnected. it just got crap gas mileage. idled just fine. i think the code 42 is accurate in that the computer sees a rich condition (low switching voltage), and it's reporting it as it should. (if the oxygen sensor is original looking, i'd throw a new one in there after you solve the problem anyways as your mileage will improve)
 

There's a lot of things it could be. i like to start with the symptoms and go from there.

Does it idle better when cold or hot?

Does it generally idle slow or does it hunt up and down?

Is it intermittent? sometimes it's fine, sometimes it's not?

How fast does the code come back after a reset?

does it stall? if so when?

does it have a constant misfire on any paticular cylinder or does it miss across the board, sort of speak? (cylinder misfires will set rich codes, eg. spark problems)

 

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