1986 F150 5.0 hard to start,will not idle

Okay guys, here's one of many questions I'm sure I'll have down the road:

My 1986 F150, is hard to start, and  won't idle at all.  I have timing spot on at 10* BTDC ( with SPOUT disconnected). To get it to start each time I have to give it a couple shots of starting fluid. As long as I hold pedal down it'll run. Let off and it dies.

                                        On a hunch, I pulled off the vacuum line going to the fuel pressure regulator, the hose nipple on the regulator as well as end of the vacuum line was wet with gas.    Did I find the culprit, would the pressure regulator cause the problems I described? There are no other vacuum leaks, all ignition parts have been replaced.

Hi Jeff!
I would say definitely A cause, if not THE cause, but you seem to have covered all your bases.  

The FPR isn't seeing the vacuum it should with the throttle body closed and it's getting raw/rich fuel connected to that vacuum line.

Replacing that regulator is a given.

ArdWrknTrk wrote

Hi Jeff!
I would say definitely A cause, if not THE cause, but you seem to have covered all your bases.  

The FPR isn't seeing the vacuum it should with the throttle body closed and it's getting raw/rich fuel connected to that vacuum line.

Replacing that regulator is a given.

Would also explain it going from 1/2 tank of gas to 1/8th tank of gas only idling it for three 10-15 min periods in last 10 days

You seemed to say that it WON'T idle...

I'm sure your plugs look like they're covered in Vanta Black but should clean up driving ~50 or so miles with proper mixture.

Probably want to replace that vacuum line while you're at it.
Not a lot of $ and sitting full of fuel isn't good for most rubber.

ArdWrknTrk wrote

You seemed to say that it WON'T idle...

I'm sure your plugs look like they're covered in Vanta Black but should clean up driving ~50 or so miles with proper mixture.

Probably want to replace that vacuum line while you're at it.
Not a lot of $ and sitting full of fuel isn't good for most rubber.

It would idle, but not the best. That bad regulator dumping all that excess fuel wasn't helping matters any.
My truck  still has the color coded plastic vacuum lines on it. Been thinking of eliminating those in favor of rubber line

If the lines aren't brittle and crumbling to dust I'd say best to leave them alone.
Many of us would be envious of functional factory vacuum lines.
I think the only one I still have is the one from the cowl splitter to the HVAC controls in the cab.

ArdWrknTrk wrote

If the lines aren't brittle and crumbling to dust I'd say best to leave them alone.
Many of us would be envious of functional factory vacuum lines.
I think the only one I still have is the one from the cowl splitter to the HVAC controls in the cab.

They are all in rather good shape yet, I could at least blow that particular one out with compressed air to get the gas that may be in it out of the line.

Put on a new fuel pressure regulator, Then started it. It fired right off, checked fuel pressure and it is just as the specs say it should be. It idles smooth in park at about 900 rpm. Still, when putting in gear it'll die off.

But when restarting now it'll fire right back up, and idle back @ 900 in park. Timing is spot on @ 10*. Could it be, that the computer still hasn't re-learned its memory settings since the battery  has been disconnected since 2019? Longest period I've had it idling at any one time is 10-15 min. No vacuum leaks externally.

Note: Before I replaced a bad TFI module, it would idle in gear.

That's great news!
Congratulations  

Perhaps the torque converter simply needs some exercise? Four years is a long time.
Though I'll admit that I don't know all the in's and outs of the AOD.

I would definitely try driving it around the block as is and observe how it behaves.
When you change many things at once you can never be sure which changed what.

ArdWrknTrk wrote

That's great news!
Congratulations  

Perhaps the torque converter simply needs some exercise? Four years is a long time.
Though I'll admit that I don't know all the in's and outs of the AOD.

I would definitely try driving it around the block as is and observe how it behaves.
When you change many things at once you can never be sure which changed what.

Not really sure myself, I do know the trans was good, as it was being driven daily before it was parked. The fluid was a good red color with no debris in pan. I put new filter and fluid in too. Would idle in gear, before I had to repair the misc issues with the ignition, and the fuel pump relay/pressure regulator.

                                                           Can't really drive around the block yet, as I have to bleed and inspect the brakes after replacing the master cylinder. I could possibly try at least moving it back and forth. It's certainly possible, the computer does not have a baseline idle speed learned

Functional brakes are definitely prerequisite for driving on the road.
I wasn't aware they were full of air.  

Is it idling higher now than when you changed the TFT module?

ArdWrknTrk wrote

Functional brakes are definitely prerequisite for driving on the road.
I wasn't aware they were full of air.  

Is it idling higher now than when you changed the TFT module?

I think so. The question that needs solving,  is why it would idle in gear before the module replacement, but now it won't. 

In case you need it Gary has the EFI idle speed adjustment information here....

ArdWrknTrk wrote

In case you need it Gary has the EFI idle speed adjustment information here....

Heck I didn't know it could be adjusted. Would replacing the TFI module cause it to need adjusting? I sure wouldn't have thought so

Here is photo of the screw on my throttle body for reference

I don't know that replacing the module would upset the balance.
I only know that the computer is looking for a certain voltage from the TPS and can make adjustments to the IAC.

Judging from the spring coils that stop screw is wound in pretty tight right now.
I'm just a shadetree mechanic but I'd be checking voltage from the throttle position sensor and see if backing off that screw brings the idle down to where the convertor doesn't load the engine enough to stall it.

I wish I were better at troubleshooting these very early EFI systems.
There's a lot of members here that are far more knowledgeable.
Hopefully someone will chime in with suggestions and/or procedures that can help you!  

I'm kinda thinking, that  maybe the TPS may be shot, judging from how far that screw is turned in, the computer thinks the throttle blades are open further than they really are, which would be the reason, that putting it in gear kills the engine

The computer has no idea of how far the throttle stop is turned in.
But I imagine the blades are more open than they ought to be.

The TPS has its own calibration procedure.
I can go look for the TPS test procedure, but if someone has screwed with it there's no telling what it reads now compared to what it should.
That would definitely cause the ECU to be making some spurious calculations.

Jeff, Jim, the 1985/86 5.0L EFI system is not like the 1987 up systems, The idle stop screw setting is very touchy on these. The EGR system starts to function just off idle (Matt's drove both of us nuts). In the right front corner behind the battery is a set of solenoid valves:

Two of them are for the EGR valve, the other two are for the Thermactor system. If the TPS voltage is too high, the EGR pair will chatter and the EGR valve will try to open, which kills the idle, followed by closing where it will pick up again.

The idle may be raised to get around this. One item we did discover, aftermarket sensors do not always react the same as OEM Ford ones, he had a Standard TPS and could not get the closed throttle voltage low enough. A Motorcraft one solved the problem.

ArdWrknTrk wrote

The computer has no idea of how far the throttle stop is turned in.
But I imagine the blades are more open than they ought to be.

The TPS has its own calibration procedure.
I can go look for the TPS test procedure, but if someone has screwed with it there's no telling what it reads now compared to what it should.
That would definitely cause the ECU to be making some spurious calculations.

I did find a TPS test procedure in my Haynes manual, but I have no clue which is the signal return wire, VREF wire or TPS Signal wire. All I see is a green wire, an orange wire, and a black wire come out of the TPS.  BUT, since that idle stop screw is obviously been messed with, I would wonder if testing the TPS voltage would show anything.
                                                  I do think something is fishy with the TPS,  as this morning it fired right off and had a decent idle, but several hours later I started it again, it idled, but poorer than it did before.

You're looking for exactly 1V (+/- 0.05V) between black and green.
Here's a ten year old quote from Bill

"on the 1985-86 EFI 302, the TPS voltage is critical. These computers work on absolute voltage, unlike the later ones that work on difference from start value. Archion learned the hard way on his 86 F-150. An aftermarket TPS was nominally in spec at 1.08v at closed throttle. His EGR vent solenoid sounded like a machine gun and the truck wouldn't idle worth a damn it also acted strange even driving. The spec to set the TPS voltage on these is measured between the dark green with light green strip wire and the black with white stripe wire. Orange with white stripe to black with white stripe should be 5.0v.

Set voltage is 0.95 to 1.05v, if you cannot get that and have it idle, or you end up backing the screw out until it doesn't touch and still can't get there, the TPS is probably bad. Unfortunately, the only ones that work correctly on these are Motorcraft ones."