Hard starts when hot

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Hard starts when hot

mp470
After it warms up, even on shorter trips, it's hard to start. Cranks just fine, and wants to turn over but doesn't. It's not a slow crank but cranking just doesn't seem to result in anything. Cold starts perfectly with one crank. Something that heats up and is worn internally, but what? Starter, ICM, coil, efi components. Best way to test these? Would rather not fire the parts cannon at it since these are all expensive parts.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle
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Re: Hard starts when hot

ctubutis
I am guessing you're talking about a 1985/86 EFI 302, correct?

Sounds like the engine cranks just fine ("crank" and "turn over" are the same thing in my mind) but the engine doesn't want to start... does it EVER start when warm/hot? What do you do to get it to start?

My first thought is vapor lock in the fuel system.

Check for spark & fuel when the problem occurs.

This can also be a bad electrical connection in the ignition system (at the coil in particular) that doesn't pass enough energy when heated up.

It can be a lot of other things, too, easiest to diagnose it when the problem is actually occurring.
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Re: Hard starts when hot

Gary Lewis
Administrator
In reply to this post by mp470
Let's make sure we understand - "turn over" doesn't mean the engine rotating with the starter.  It means "run" or "fire".  Right?

Have you checked to see if the computer is trying to tell you something?

And there are steps for testing the EEC-IV systems in the Resources.
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/soon-to-be ZF5/3.55's & EEC-V MAF/SEFI
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Re: Hard starts when hot

mp470
In reply to this post by ctubutis
Yes it's a 1985 EFI. Usually I floor the gas pedal and it starts with a bad struggle after which I have to hold the gas partially down for a minute or two to keep it going otherwise it will stall out.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle
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Re: Hard starts when hot

mp470
In reply to this post by Gary Lewis
Yes, I mean running / firing. I've checked for codes - only KOEO though - and there are none.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle
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Re: Hard starts when hot

Gary Lewis
Administrator
Maybe you have a vacuum leak.  David/1986F150Six used the smoke test to find a leak on his.  And while his was carb'd I don't think that mattered.

I haven't seen it done, but my understanding is that he found a large hose going into the intake manifold or the base of the carb, blocked the top of the carb, and blew smoke from a cigar into the hose.  On the second puff smoke came out from somewhere it shouldn't, and he discovered a bad vacuum cap.
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/soon-to-be ZF5/3.55's & EEC-V MAF/SEFI
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Re: Hard starts when hot

mp470
A vacuum leak only when hot though? I suppose it's possible.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle
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Re: Hard starts when hot

Gary Lewis
Administrator
I'm thinking that the running engine can handle it, but it can't when trying to start.
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/soon-to-be ZF5/3.55's & EEC-V MAF/SEFI
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Re: Hard starts when hot

ctubutis
In reply to this post by mp470
mp470 wrote
Yes it's a 1985 EFI. Usually I floor the gas pedal and it starts with a bad struggle after which I have to hold the gas partially down for a minute or two to keep it going otherwise it will stall out.
You shouldn't need to touch the gas pedal when starting an EFI engine, something is wrong if you need to do that. And I'm guessing whatever is wrong/failing is now bad enough to cause this kind of behavior.

This could be a lot of things, or a combination of two or more things.

My approach has always been to first make the computer happy (KOEO/CM/KOER) and the real problems make themselves evident as you get the computer to give you 11's across the board.
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Re: Hard starts when hot

PetesPonies
In reply to this post by mp470
First, your engine is turning over. turning over has nothing to do with starting .  .other than if it is not turning over it won't start :) This is a common misuse of the tern "turning over'. You engine is spinning, it is turning over . .it's just not starting. You should not be using the gas pedal when starting a fuel injected engine. Typically heat related starting or even running issues, are electronic in nature.Heat causes extra resistance, can make small breaks in wiring grow to larger gaps, etc. When you turn your engine off, it heat soaks, meaning more heat is present to this components than were present when it was running. I would not suggest just buying parts to try, but if you can find a loaner coil, that is where I would start first, it's easy. Next would be the module inside the distributor.
Pete's Ponies
Mustang RUSToration & Performance

1982 F100 Flareside
1983 Bronco

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Re: Hard starts when hot

mp470
Helpful stuff, thanks.  I'm thinking electronic as well, just wasn't sure where to begin.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle
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Re: Hard starts when hot

LARIAT 85
In reply to this post by mp470
My wife's 2001 Ford Mustang was doing that, and the problem turned out to be a bad idle air control valve.  In order to start the engine, I had to give it gas as if it had a carburetor.

Lucille:  1985 Ford F150 XLT Lariat

*Colors:  Dark Canyon Red exterior, Canyon Red interior
*Engine: 5.0, CompCams 31-230-3, "Thumper" E7 heads, Edelbrock Performer intake, Autolite 4100 carburetor, DuraSpark II ignition, Thorley Tri-Y headers, Flowmaster dual exhaust, H-pipe.
*Drivetrain:  AOD transmission, 3.55 gears, 2wd.



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Re: Hard starts when hot

mp470
Thank you, that actually makes a lot of sense. I will try to simulate it by unplugging the valve.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle
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Re: Hard starts when hot

PetesPonies
In reply to this post by LARIAT 85
That is a port fuel injection engine. tThe IAC dithers to allow air in during idle . . when the throttle plate in the TB is totally shut.
Pete's Ponies
Mustang RUSToration & Performance

1982 F100 Flareside
1983 Bronco

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Re: Hard starts when hot

mp470
I knew that too, so I'm a bit red-faced on this one. Of course unplugging that valve recreated the issue exactly.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle
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Re: Hard starts when hot

mp470
Well I'm getting somewhere.  Went for a long drive.  Ground side lights up very dim on the connection to that valve.  Now to find where it grounds.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle
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Re: Hard starts when hot

Gary Lewis
Administrator
Here's some info:
http://www.garysgaragemahal.com/ground-wires.html
Pages 60 and following here - http://www.garysgaragemahal.com/electronic-engine-control.html
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/soon-to-be ZF5/3.55's & EEC-V MAF/SEFI
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Re: Hard starts when hot

mp470
Thanks Gary, looks like it's ground switched by the ECA.  I wonder if it's supposed to light up dim while not in operation.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle
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Re: Hard starts when hot

Gary Lewis
Administrator
Let's make sure my understanding of "lights up dim" is correct.  Your trouble light?  If so, probably yes.  Battery voltage is supplied to the various components and then the computer grounds them when it wants them to activate.  That creates a current flow and they do their thing.  So if you put a trouble light on the ground, or computer, side of any of the components then you will have voltage when the thing isn't activated.
Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/soon-to-be ZF5/3.55's & EEC-V MAF/SEFI
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Re: Hard starts when hot

mp470
Basically, it's a LED test light that lights up green for ground (hooked to battery +) and red for power (hooked to battery -).  Any other body ground lights up nice and bright green, while this IAC ground is very dim.  At least it was after that long drive.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle
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