Erratic Idle and bucking

[TheWeldingFords]

81-F150-Explorer wrote

I'm leaning toward more wiring faults somewhere, and/or weak windings or grounds to the fuel pump or pumps.

First I'd check the wiring going to the EEC from the fuel pump cutoff relay. Wires ZZ and YY in Gary's schematic.  

There should also be a connection through the fuel pump cutoff relay between wires ZZ, YY and the inertia switch wire 787 pink/black, or 37 Yellow wire when the cutoff relay is closed.

Make sure these wires are working correctly, or fix the problems, and work forward from there if needed.

I pulled the relay and tested voltage and continuity and I got ~10.5v when the key was on but I didn't get continuity, to verify I went into the cab and checked for continuity at the eec relay and that had continuity.

What would it mean if I have voltage but no continuity?

Is it maybe too much resistance or too low voltage?

[Gary Lewis]

I don't understand "voltage but no continuity".  Can you explain how you tested?

But if the pumps are running then it looks to me like the ECU isn't realizing that.  The way the schematic shows it the ECU is what pulls the relay in.  Saying it another way, the power comes in on ZZ and the ECU then grounds YY to pull the relay in.  So if the pumps are running then the relay must be coming it.  However, if the coil of your relay doesn't pull as much current as the Ford relay that may trick the ECU into thinking that there's no relay.

Can you put the Ford relay back for a test?

[TheWeldingFords]

I was testing across the coil for continuity and voltage (zz and yy in the diagram) coil is pulling in the relay but even with the relay unplugged it should still be getting continuity no matter what relay it is because the ecu should be completing the circuit.

I don't have a ford relay handy and they are crazy expensive for what they are.

maybe something is finding ground on its own but it isn't a very good one due to it being lower than the average 12.6v ( I'm not sure if the ecu is supposed to provide 12.6v or 10.5v im guessing its supposed to be 12.6v) I wasn't getting any resistance in the circuit.

[81-F150-Explorer]

Gary Lewis wrote

But if the pumps are running then it looks to me like the ECU isn't realizing that.  

I Agree.

The way the schematic shows it the ECU is what pulls the relay in.  Saying it another way, the power comes in on ZZ and the ECU then grounds YY to pull the relay in.  So if the pumps are running then the relay must be coming it.  However, if the coil of your relay doesn't pull as much current as the Ford relay that may trick the ECU into thinking that there's no relay.

Can you put the Ford relay back for a test?

Or trick the ECU into thinking the relay is bad.  There might be a hot wire bypassing the cutoff relay.

Normally the fuel pumps shouldn't run if that relay is bad, etc..

TheWeldingFords wrote

I was testing across the coil for continuity and voltage (zz and yy in the diagram) coil is pulling in the relay but even with the relay unplugged it should still be getting continuity no matter what relay it is because the ecu should be completing the circuit.

Yes but the resistance will be off and give a code 95. Why a bad ground, weak or dead pump can also give this code.

I don't have a ford relay handy and they are crazy expensive for what they are.

maybe something is finding ground on its own but it isn't a very good one due to it being lower than the average 12.6v ( I'm not sure if the ecu is supposed to provide 12.6v or 10.5v im guessing its supposed to be 12.6v) I wasn't getting any resistance in the circuit.

How did you bypass the Neutral safety switch?  

[TheWeldingFords]

I bypassed the neutral safety switch with a fuse at the connector instead of having a switch plugged in basically just jumping it, I can toss a normal toggle switch into it to try to rule it out.

[81-F150-Explorer]

TheWeldingFords wrote

I bypassed the neutral safety switch with a fuse at the connector instead of having a switch plugged in basically just jumping it, I can toss a normal toggle switch into it to try to rule it out.

Just jumping it shouldn't cause a problem.  

Just was curious how you did it.  

Didn't want to learn that you bypassed it using another 12v source from somewhere else is all. That could cause all sorts of weird problems.

[TheWeldingFords]

Yeah I pulled apart the broke switch to see it's just a arm that contacts and bridges a gap so I put a fuse in t as a safety precaution and wrapped it up to protect it.


I ohmed a Ford relay and my Bosch style relays and the Ford read 89-90 ohms and the Bosch style was 83 ohms

Would a 7 ohm difference really throw off the computer that bad?

[81-F150-Explorer]

It's a possibility that it might.

Do not know for sure, as I've never changed a relay with a different value.

What do you think Gary?

[Gary Lewis]

TheWeldingFords wrote

I was testing across the coil for continuity and voltage (zz and yy in the diagram) coil is pulling in the relay but even with the relay unplugged it should still be getting continuity no matter what relay it is because the ecu should be completing the circuit.

I don't have a ford relay handy and they are crazy expensive for what they are.

maybe something is finding ground on its own but it isn't a very good one due to it being lower than the average 12.6v ( I'm not sure if the ecu is supposed to provide 12.6v or 10.5v im guessing its supposed to be 12.6v) I wasn't getting any resistance in the circuit.

I'm not sure I understand, but I think I do.  I'm guessing that your meter has a continuity test setting and that's what you are using.  Or you have it in resistance mode.  In either case if you measure across ZZ and YY you shouldn't have continuity with the key off, and you might blow your meter with the key on.

The way the circuit is supposed to work is that with the key on ZZ provides battery voltage to the relay's coil, which might be 10.5v or 12.6v depending on the state of your battery.  And then the EEC provides essentially a ground on the YY connection to cause current to flow through the coil and pull the relay in.

And that mode of operation is pretty much standard with solid state electronics.  It is much easier for a transistor to "sink" current, meaning ground something, than to "source" current, meaning to provide power to a device.  So Ford provided power through ZZ from the EEC power relay and the EEC then takes that power to ground when it wants the pumps to run.

But it apparently is monitoring things somehow.  I just looked at the schematic again and the low side of the relay's coil is apparently connected to the EEC via Ckt 201 and Pin 17.  So maybe it is monitoring it that way?  And do you have the self-test connector plugged in?

[Gary Lewis]

I don't know.  But I do know for sure that changing out the Ford horn relay with a standard Bosch relay won't work.  Apparently the current draw through the coil on the horn relay has to be within a certain range or the speed control won't work, and a Bosch relay isn't within that range.

So while I wouldn't have thought that a 6 ohm change would cause a problem, I don't know that it won't.

Having said that, I doubt that getting that error code is where the problem lies.  Don't know where it lies, but since the engine runs well as it is warming up and starts having problems when it apparently goes into closed-loop mode I don't think it is the pump relay.

[TheWeldingFords]

Well just changed the fuel filter and it brought back it's power and not bucking anymore but the idle is still jumping, I'm gonna exchange the IACV to make sure it's not a faulty part

[ArdWrknTrk]

*AT the radiator support
C101 is the battery ground terminal pigtail connector.
The truck harness that runs up the passenger side fender turns across the radiator support and connects (almost) directly to the battery through C101....

The ECA controls the injector pulse through the ground side.
C101 (or lack of it) is often cited for "driveability" issues.

[81-F150-Explorer]

TheWeldingFords wrote

Well just changed the fuel filter and it brought back it's power and not bucking anymore but the idle is still jumping, I'm gonna exchange the IACV to make sure it's not a faulty part

Did that take care of Code 95?

unfortunately new parts are not always good parts.

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Also check that ground that ArdWknTrk mentioned.  

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Gary Lewis wrote

Having said that, I doubt that getting that error code is where the problem lies.  Don't know where it lies, but since the engine runs well as it is warming up and starts having problems when it apparently goes into closed-loop mode I don't think it is the pump relay.

I agree, but I think the EEC is being fooled into the Code 95 by the actual problem.  The EEC is just throwing Red Herrings etc...   He changed the fuel filter with good results.

[TheWeldingFords]

Yep spent about $500 this weekend just for it to need a $4 fuel filter

[TheWeldingFords]

It could also be the relay setup I have to switch polarity for the selector valve so I could keep the factory switch working

[Gary Lewis]

Well, I'm glad you got it fixed.  But sorry it took so much time, effort, and money to get a small problem like that fixed.

Are you still getting the 95 error?  I agree that is a red herring, but it puzzles me.  Did you answer about the self-test connector being in place?

[fords4life]

TheWeldingFords wrote

Yep spent about $500 this weekend just for it to need a $4 fuel filter

I completely understand this feeling and have done similar things in the past.

If you need it or want one to have around, I have a spare breakout box for our factory EFI trucks if you're interested.  Helps a ton with diagnosing electrical issues dive he runs inline with the PCM.