1989 F150, 351, fuel injection

Problem - hard-start when hot. It acts like some giant has a grip on the crank, and the starter just will not rotate the crank.

I did a search of this forum and found several others have the same problem. Some of the suggested problems were over-heated starter, bad TFI, and bad TPS. Some solutions for starting were pumping the pedal or pressing it part-way down.

So - why would depressing the gas pedal allow the truck to start if the starter is hot and in a bind? That solution alone makes me think it's not a hot starter problem. Plus, I replaced the starter twice and the problem persists. Plus, I replaced the starter on a similar work truck and it still has the same problem. I also replaced the cables and cleaned the connections.

Jump-starting with a powerpack or another battery makes no difference, either.

Can I rule out the starter?

I replaced the TFI ysterday, took the truck out for a warm-up run, and it looks like the problem is still there.

Can it be the TPS? I replaced the TPS a month ago. I had the hard-start-when-hot problem before I replaced the TPS, and the problem seems to have changed a little. I wonder - do I need to adjust the TPS? Can it actually be adjusted? It looked, when I installed it, that it would only go on in one position, but I might be able to loosen the screws and rotate it a little. Will just a couple of degrees rotation of the TPS make that much of a difference?

 

BTW - here's a neat trick I found for replacing the TPS:

As you may have noticed, you can't put a Phillips screwdriver under the screws and remove them because there is very little room for fingers and tools, so you must remove the plenum to replace the TPS. That's bull, I said, so I came up with this trick.

First, remove the hoses that are between you and the TPS.

Second, take a big old hammer and a long screwdriver, and simply bust the old TPS to smithereens. It's plastic and will go without a whimper.

Then use some tiny (4" or 5" long) Vice-Grip pliers to turn out the Phillips head screws.

Install the new TPS using Allen screws and a shortened Allen wrench.

Turned a few-hour job into a few-minute job. Not real elegant, but it was real effective.

 

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The first thing I would do is check the timing. Disconnect the spout connector, and put a timing light on it to see if it's in spec. The timing number should be on a sticker under the hood somewhere.

 

Today I had a local shop check the timing. Service man said it was right on.

Also, after installing a new TFI yesterday, I took the old one and had it tested. The service man said the old one is in like-new condition.

 

When the engine is cold, start it up and quickly go around to the passenger side exhaust pipe and see if you feel or hear any small exhaust leaks. It could be puffing down on the starter making it hot.

 

I don't mind listening to opinions that the starter may be hot, but I'd really like to have some insight as to why, if the starter is hot, the engine will not start unless the pedal is depressed slightly.

Why would depressing the pedal overcome a hot starter issue?

I'll do that test in the morning. Should be plenty cool by then. Thanks, Franklin.

 

OK - no exhaust leaks.

Again, I'd like to hear some theories about why a hot starter issue can be overcome by depressing the gas pedal. Just doesn't make sense to me.

 

It sounds like we can rule out the hot starter issue.

You said in your first post that some people's solution was to depress the gas pedal partway...does this work for you?

I'm thinking that maybe, even though your timing is spot-on, you may have a carbon build-up that, when hot, is pre-igniting the mixture like when the timing is too far advanced.

Just theorizing here...it's a perplexing one, fer sure!

 

Thanks, Dan. I'll have that checked. I use mostly Shell and Chevron gasoline, and all the injectors are spotless, and working well. The plugs always come out the proper color when I check/change them, so I think carbon build-up is not the problem, but I will see if it can be checked.

And yes, depressing the pedal part way does the trick.

 

I have the SAME problem on a 91 F150. Ihave replaced the starter,starter solenoid,ignition switch, and the ignition coil. I dont remember if there was anything else but it sure has me and my mechanic scratchin our heads. It is odd though cause the truck starts and runs fine if I pop start it.

 

Changed the Intake Air Temperature sensor - that wasn't it.

I did find that pumping, rather than simply depressing, the gas pedal gives a quicker start.

Next test - replace the Throttle Position Sensor that I replaced a couple of months ago, since I keep getting codes that say the TPS is not within limits. Luckily for me I replaced the stock screws with socket head cap screws, so I do not have to remove the upper intake manifold to swap the TPS.

I find it hard to believe that, with hundreds and thousands of Ford users and techs in here that not one of you can come up with a valid, solid, reason for the "hard start when hot" problem.

To reiterate, none of these have had any effect on the problem:

Replace starter - nope.
Replace battery - nope.
Replace cables - nope.
Replace solenoid - nope.
Replace IAT sensor - nope.
Replace TPS - nope.
Replace spark plugs - nope.
Replace plug wires - nope.
Replace rotor/cap - nope.
Check timing - fine.
Fuel pressure - fine.

The engine starts properly when cold, runs properly when cold or hot, but just won't turn over when hot. Let it sit for an hour, and all is well again.

 

My 92 F150 302 has always had this same problem--it is necessary to crack the throttle slightly to start the engine when the engine is hot. Never a problem starting the engine when it is cold--and no throttle is necessary when the engine is cold.

 

when its hot take the gas cap off and see if it makes a suction pressure release sound if so u might have vapor lock?

 

Well, it's been over a week since I replaced a part and since then I have had no problems starting my engine when it's hot.

Thanks to all of you for your tips and hints. I learned a few things from some of you while looking for a solution.