92 LINCOLN 4.6 L. MIL light on/off and running rough intermittantly

yugot2me

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OK here's the story:

A nice, 1992 LINCOLN TOWN CAR, 4.6 LITRE V8, with the EEC-IV engine control system that I recently recently purchased from estate that purrs like a kitten ...except when my wife drives it...no lie. I drive it 5 miles to work and back home and nary a problem. My wife gets in it and drives 18-20 miles to work and back and it starts with MIL the light on and off (on for 60-90 seconds and off then back on etc.) and running rough as can be.

Continuous memory codes are being set. KOEO passes good, have not ran KOER as manual says to address continuous codes first.

I cleared all codes yesterday and she took it to work and sure enough it started acting up. Here are the freshly set codes. (Same codes were present when I cleared them)

172 - HEGO lean left side
176 - HEGO lean right side
542 - Fuel pump secondary circuit failure detected

Now by my reading of the schematics it would appear that the EEC-IV is detecting a open between it's tap-in point in the circuit (just prior to the inertia cutoff switch) and ground. This also includes the fuel pump motor. I suspect if the circuit opens between the monitor point and ground it detects the voltage rise to applied potential and sets a code. (detects the loss of voltage drop across the pump = no current flow)

My assumption at this point is something, wire, inertia switch, fuel pump, bad ground etc. is intermittently opening up causing fuel pump cut out, momentary loss in pressure and fuel starvation both sides. Thus the lean HEGO codes.(It has a new fuel filter on it so I kind of am ruling out plugged filter for the lean codes)

Maybe heat related, vibration, etc?


Now my question is is there any "known common" problems in this circuit area such as inertia switches failing over time, common symptom of fuel pump on last legs, etc. No use reinventing the wheel here, if there is a known problem area or common point of failure hers I would just as soon go there first.


I have all the manuals and am a Electronics Tech by trade (not automotive, industrial machines) so I can use the test equipment and hunt stuff down albeit intermittent's are a pain in the Anus... and crawling around shaking wires doing wiggle tests is a real pain.

I just wanted to pick the brains of some of you guys who have worked on and/or owned these models of cars and get some input. Nothing like experience.

I also noted that per the diagnostic test flow chart, a passenger side HEGO harness shorted to power can set a steady 542 code, although I don't think that would result in a lean HEGO code on both sides.

Any input would be valued.

BoB
 

crunch

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The engine is running lean.
Fuel pressure,mass air flow sensor vacuum leaks first thing.
And check the pcv valve to intake hoses real close.
If bad ford has a replacement set for them.
The have a bad habit of colasping and getting soft back there on intake.
I would not worry about the fuel pump code very much.
I see it a lot on some of them with no problems.
On the fuel pump code go a fuel pump relay and clear code and see if it returns.
 

ironhead

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If you have access to a labscope with a low amps probe, you can check the power lead to the fuel pump and watch the wave form. If you see any mis-shapen waves, you have a pump on it`s way out.
Guy
 

yugot2me

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Well after looking at all the wiring that was accessable for the fuel pump and reseating the grounds with no resolution to the problem I decided to re-visit the vacuum issue. While all the plumbing looked good on the visual inspection and no leaks detected I decided to pull the connections on the PCV hose assembly and check them out up close and personal. What I found was that both of the rubber connections that attach at the manifold had cracks in them on th bottom side. These cracks were acting somewhat like a "duckbill" valve they were closed and relativly sealed at low vacuum but flared open at higher vac. levels leaning out the mix.

Replacement of the two rubber couplers resolved the issue.

As to the fuel pump code 542, in my research I found that the fuel pump kicks out when rpms drop to 120. I believe this message was a "anomally" being seen as a fault by the PCM as the car "stumbled" at idle due to vac leak.

Regardless I have drove it 300 miles since the fix with no stumbles, stalling or codes.

Thanks for the responses
 
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