Accelerator Pedal Stuck Open on the Expressway!

[DadofThree]

I was fortunate that nothing happened to other people, me, or the car. I will say that I'm glad to have a relatively low horsepower/torque car. I have a stock 302 with a Russ Thompson pedal hooked by Mechanical Linkage to a Fitech (400hp version). There are two return springs on the Fitech, and the unit is fed by a stock mustang fuel pump. My gear ratio is 3.08.

Yesterday morning, I was on a 2 lane interstate. I'm in the left lane traveling 70mph-ish with a Prius in front of me and had a truck to my right. I'm giving the Prius plenty of room, and I'm in 4th gear. After passing the truck, the Prius moves over, and I have an open lane. Drop it to 3rd, the motor comes to life, Hammer Down, and I'm off like a bullet!

**Pause** What I just did will get me and you in trouble with our cars. Be Safe. **Un-Pause**

Shifting to 4th, I got stuck in neutral and my engine is jumping to extreme High Revving and popping/sputtering LOUDLY!! I never got it into 4th (in hindsight, thank goodness). I didn't look at the Tach. But instead, listening to the engine thinking that it's going to do harm to itself. I cut the key off, and am coasting. I start the engine back and it goes straight to its high rev with sputtering in full tow. Cut it off again and move to the right side shoulder rolling in neutral. Hazards on, and coasting as far as I can towards the next exit. Never touched the brakes.

While coasting, I try to start it again, and Nothing. It's not getting any gas. Momentarily, I think that I’ve lost my fuel pump, but that doesn’t make sense. I turn the key off and back on again to start. Still no start.

Now I'm still coasting on the shoulder, thinking to myself that this car sure does coast a long way. As I'm starting to slow, I question the sputtering and realize that what I heard was the sound like the pump starving while trying to provide the fuel to the engine. I've heard it before under heavy acceleration. I wonder if that’s the Rev limiter on the fiTech. I cannot remember if it even has one.

While still rolling, I’m thinking it out. The engine is stuck at high rpm, and the fuel system is starved....I wonder if my pedal is stuck to the floor??!

Now slowing down to what feels like 20-30 mph now, I put my foot where the accelerator pedal should be; and the pedal is not felt until I put my foot near the back wall. It's stuck!! Putting my toe behind the pedal, it pops back into its proper resting position.

Turn the key, engine starts up! Drop it into 2nd gear and smoothly accelerate into traffic. Hazards off, and I'm back up to the flow of traffic.

What the Heck!!??

Last Night, I get it home and I open up the DS footbox top access panel to see where my Mechanical Linkage is getting hung up. I suspect that after 16,000 miles maybe a wiring harness leg, or something may have shifted into a possible binding location that is interfering with the linkage arms. While the car is sitting in the garage, I press the accelerator pedal to the floor and again, it sticks in place. Searching out the bind, I cannot find one. It’s not interfering with anything. Nothing in the DS footbox, and nothing near the FiTech.

I press the throttle linkage back to where it should be at rest, and it roughly snaps into place. Taking off the air cleaner, I inspect the linkage closer. What I find is at full throttle, the linkage rubs against the throttle body and holds in place. Satisfied with my find, I bend the linkage slightly so that it moves away from the throttle body. I can now fit a flat head blade between the two and see the gap. So I test again, AND AGAIN THE LINKAGE STICKS TO WIDE OPEN THROTTLE! What the Heck????!!!!

There is nothing binding, and its sitting at full throttle with two weak return springs not pulling it back in place. Do I need to Lubricate the linkage? The throttle body linkage does have a couple of torsion springs in there. Maybe they do need a little lubrication. I end up getting some WD40 to test the theory, and spray the two torsion springs. The linkage still locks in place at full throttle, but it does feel a touch better. I decide to lubricate the rest of the throttle linkage generously, and start working the lever back and forth. It’s getting MUCH better! Now it doesn’t hold open any more. I continue to move the linkage back and forth for a couple more minutes, and the throttle body linkage is back to normal.

So, Is lubrication to the throttle linkage a common general maintenance or PM? Note to self that I need to get stronger return springs too.

I wanted to share this with you so that you’ll be aware of your linkage and what may happen to you too.

Happy driving everyone!

https://youtu.be/Y7seyIwUg_I

[cgundermann]

Yikes! Good to know, glad it didn’t end poorly!

Chris

[phileas_fogg]

Holy crap Dave! Glad you're safe.

I've got nothing to add as far as lubricating the throttle linkage, because I'm a noob.


John

[Olli]

You don't mention any details about the mechanical linkage. Did you buy it from someone or did you make your own? One thing that I always wondered about with the mechanical linkage is how would it handle engine torque ? How are your motor mounts? Is mechanical linkage better suited with solid mounts vs polyurethane or rubber? Is it possible when you downshifted and "put the hammer down" the engine torqued and you bent an arm? Could one of your arms be slightly bent and putting one or more of the heims in a near bind? Perhaps the lube has temporarily freed that up? But wouldn't the lube attract dirt and possible future bind? Heims can vary in quality as well.

Olli

[DadofThree]

You don't mention any details about the mechanical linkage. Did you buy it from someone or did you make your own? One thing that I always wondered about with the mechanical linkage is how would it handle engine torque ? How are your motor mounts? Is mechanical linkage better suited with solid mounts vs polyurethane or rubber? Is it possible when you downshifted and "put the hammer down" the engine torqued and you bent an arm? Could one of your arms be slightly bent and putting one or more of the heims in a near bind? Perhaps the lube has temporarily freed that up? But wouldn't the lube attract dirt and possible future bind? Heims can vary in quality as well.

Olli

That's a very interesting point. Thank you for that point of view. I hadn't considered that.

I made the mechanical linkage off of parts purchased from McMaster Carr. Looking at my shopping list, I had purchased 3/16" hardened SS Rod, 1/4" Super Corrosive Resistant SS Rod, and Oil embeded Ball Joints.

I'll inspect it later, but I'd be surprised if anything is bent. I realize that the WD40 isn't the best to lubricate for the long term. But to test a theory, it was the ticket. Stock 302 in the low 200's hp, with mid 200's ftlb of torque. Stock rubber motor mounts.

Mechanical Linkage Album

McMaster List for Mechanical Linkage by D. R., on Flickr

20170923_184751 by D. R., on Flickr

[NAZ]

You didn't mention if you have confirmed that the linkage is not going over-center. Depending on how your return springs are anchored and their angle they can become significantly less effective at WOT or in worse cases, actually hold the WOT position if they go over-center. These are basics that need to be checked upon initial installation. And as mentioned above, engine torquing can affect linkage angles so this has to also be taken into account when ensuring the linkage won't over-center. And the entire linkage system starting with the pedal needs to be checked for potential issues not just at the throttle body.

[Derald Rice]

Your situation is why I always recommend a kill switch that will shut off the fuel or the spark ( or both ).

Mine is located beside the ignition switch, and it is a off-on-off toggle, so moving it in either direction will shut it all down.

Glad that you were able to get it shut down with the ignition switch.

[Railroad]

As your throttle linkage goes to WOT, it seems to cam over. I would disconnect the long rod from the pedal side and check the movement on the TB and attached linkage. You should not have to lube the TB or linkage. Your secondary linkage is in need of attention. The rod connecting the primary and secondary do not look to be in a parallel plane with the fixed attachment points. One of the ends definitely needs a shim washer under it. You can disconnect the secondary and check for binding, without it.
While you have the pedal disconnected, depress it to the floor and check for binding or restriction.
I do not know if you have a throttle stop, but I recommend one. You can pull the bracket on the end of the primary throttle shaft loose or torque it out of shape if you press to WOT letting the linkage and throttle blades be your stop.
It would be more revealing if you video the movement slowly, with your hands out of the way, showing the linkage from different angles.
Maybe someone with the same set up can post some pics of theirs and sort out what is going on.
Lube is not the solution.

[DadofThree]

Thank you all for your good eye, and recommendations! I'll definitely explore this more, and not consider it fixed yet.

[brewha]

Wow you are lucky to have that happen on the highway and not around town.
I had the same experience on an older car but it was a cable throttle and it frooze in the WOT. That’s why I went with a mechanical linkage. Right after I read your post I went and checked my Fitech linkage. At the moment I have no issue but I hit with a little spray anyways.

I do use a double spring on my return and it pulls it close with a hard snap after release of the gas peddle.

C9DAD4D1-DD0D-480A-AAAA-87E67D041167.jpg

[Garry Bopp]

Dave,

I had an issue with my throttle pedal sticking at WOT, but found my Russ Thompson pedal was binding in the foot box and was able to make a minor adjustment to clear the foot box. BTW, this was with a cable linkage and the Mustang EFI.

Glad there was no damage to your motor. And yes, the FiTech does have a rev limiter (600 hp version). I’ve got mine set at 6,500.

Garry

[RJD]

I made the mechanical linkage off of parts purchased from McMaster Carr.

I have the same mechanical throttle linkage set up as you but added the double return spring. Like brewha, mine snaps back when the pedal is released.

1E2A8805-EE37-4639-9083-0ECB2F9BDFB0.jpg

[dwheeler]

Do not overlook that possibility that it might be getting snagged on the bottom of the air filter housing. (Happened to me)

[dwheeler]

That threaded rod sure looks like it is going to saw its way through those wires.

[AtlantaCobra]

Dave,

I had an issue with my throttle pedal sticking at WOT, but found my Russ Thompson pedal was binding in the foot box and was able to make a minor adjustment to clear the foot box. BTW, this was with a cable linkage and the Mustang EFI.

Glad there was no damage to your motor. And yes, the FiTech does have a rev limiter (600 hp version). I’ve got mine set at 6,500.

Garry

Garry - was it your old MKIII??

[CraigS]

Could also be a warped throttle plate or bent throttle plate shaft in the throttle body.

[GWL]

I believe it was mentioned once but consider a pedal stop inside the cockpit. You've not mentioned if you have one or not.

George

[Garry Bopp]

Greg,

No, it was with my present car.

Garry

[Avalanche325]

I had that happen on an 85hp Vega and that was scary enough. It would be really bad in a Cobra.

Definitely look at the cam-over thing.
Pedal stop is a must. If not you can bend the throttle plate shaft or wear the base plate rod holes.

I assume that is a mock-up picture with no locking hardware?

[SSNK4US]

I’m kind of on Railroads thought process. It looks like it gets tougher to turn your linkage somewhere around 3/4 ish to WOT. Binding secondary linkage? Have you taken off the heim joint from your linkage rod to your throttle body? That would totally eliminate pedal to throttle body binding. Take off your return springs too. It should be a nice pretty much fluid movement from idle to WOT and springs on the shafts you WD40’d should bring things back to idle. Also with the heim unhooked you can work that back and forth to see if anything from there to pedal is binding. Just looking at your video to me it looks like something just isn’t right the last 1/4 of movement. But you need to isolate the two.... linkage to pedal / throttle body by itself..... IMHO something is up with the built on the throttle body linkage hanging, binding or over centering. You can rule out air cleaner binding because your video shows it getting stuck and the only air cleaner component on there is the gasket lol just my 2¢
Good luck and keep us posted

Kurt

[davekp]

Looks to me like the return springs are pulling down at WOT, creating the overcenter condition.
Disconnect the springs and see if that cures it.

[phileas_fogg]

Looks to me like the return springs are pulling down at WOT, creating the overcenter condition.
Disconnect the springs and see if that cures it.

I agree.


John

[Papa]

Garry,

Jockey is having a sale on underwear in case you need some new garments. Just watching your video, a couple of things look like they need attention to my novice eye. First, the spring bracket looks like it has actually cut a groove into the TB. Could you flip it over to avoid contact? Second, the springs don't look like they are offering any pull in the closed position. Perhaps some shorter springs that provide a more constant resistance all the way through the range of motion could help? Last, the bearing in the joint at the TB looks rusted. Maybe a replacement is in order? Again, these are just things I thought of as I viewed the video. Glad you were able to safely get over and coast the car.

Dave