Excessive throttle pedal resistance?????

[D. Showan]

I would like to do a search to find answers to this question because I'm sure it's been covered before but the search function seems to still be down. So I need to ask it here. What have people been finding is the cause of excessive resistance in moving the throttle? With the engine not running there is a definite hard spot midway through the travel. It is not nearly as pronounced with the engine running but it still seems to be quite hard. If this is normal I can sure see why the cables are known for breaking. Also full throttle at the pedal doesn't give full throttle at the engine and there doesn't seem to be any adjustments for that.



Any help would be appreciated

 

[Deezul1]

All the 12 valves will have a hard spot in the pedal travel when the engine is off but with it running it should disappear. Might be a frayed cable.

 

[Wade Hogg]

Could be the ball and socket rusted together. That was the trouble with mine.

 

[Jim Fulmer]

Mine was doing the same thing but it was more like hanging at part throttle going down the road, I have read there was a TSB on the item or something to do with it, but I didn't care! I bought a new cable changed it out and problem solved, he old cable was bad cause now it's smoother and doesn't hang.



Jim

 

[Dieselnerd]

I agree with the others. It's always smoother with the engine running. If you have hangups with it running it is probably the linkage or the cable. Although I imagine the P7100 could hang up, I've never seen it mentioned on this website.

 

[Dennis Garrett]

If your truck has an automatic, you're also pulling on the cable going down to the throttle valve. It might not pull freely when not running. Mine has the same tight spot, but not when running. If you have a Haynes manuel # 30041, throttle valve cable adjustment is detailed on pages 7B-4 & 5. They seem to think it's critical, & can lead to early transmission failute if not adjusted properly.

 

[Joe G.]

D. Showan,



Some of the trucks have a recall about the throttle linkage. If it applies to your truck you should have it done. The throttle cable and linkage are all replaced.



The adjustment for full throttle is the length of the throttle rod. There are a couple of lock nuts, one is left handed. The piece of the linkage rod that turns has a flat spot on it for a wrench. Kind of a PITA to do since there is very little room for your hands. If you have an automatic transmission this is also the adjustment for the TPS. Sometimes you get into a Catch 22 situation so that the TPS voltage is not right at full throttle.



Another cause of not getting full throttle and stiff pedal is installing the throttle rod backwards. This causes it to bind. The end parts of the rod should be parallel to the engine.



If the recall has not been done you may have some little almost invisable clips that hold the ends of the rod on the lever balls. If yours is this way you can feel a little wire end in the crease as the base of the ball end on the rod. If you take the rod off, pull on this little wire end to unwrap the clip from the ball end and pull it out. Awkward little devils.



The rod ends should be lubed with a little grease or a squirt of LPS#3.

 

[D. Showan]

Thanks for the responses.



I'm glad to know that the hard spot with the engine off is normal. I did have the cable and the links replaced under the recall. The full throttle adjustment is actually a little closer than I thought. Today I had another person push on the pedal hard so I could see what movement was left at the engine. The other day I had someone else (I won't say who) and they didn't push quite as hard. This linkage set up is a little strange. What I need is for the throttle cable itself to be just a little tighter. If I adjust the rod that goes to the pump any shorter I think my engine rpm will go up. If I adjust the TV cable so it is tight with full throttle at the pedal, I can then go out to the engine and full throttle it there and get a little more movement and the TV cable adjuster will click a few more times. I may shim the throttle cable at the grommet about 1/8" or so and see if that gives me full throttle by using the pedal. I think they design in just a little play at the end of full throttle so you can't actually pull on the cable real hard, the pedal hits the floor before the cable gets too tight.



Again, thanks for all the help. Dave S.

 

[Joe G.]

Dave,



You should have a little play, about 1/8" or so, at the TV lever on the trans at full throttle.



My throttle lever hits the high idle stop with only trottle rod adjustment. Yours should too. At that point your top RPM is no longer affected by linkage adjustment. The governor takes over from there. That's the reason for torque plates and governor spring kits. Shimming the cable won't do anything for you. The governor will shut down the fuel at it's set RPM regardless of how much you move the throttle.



There is an idle adjustment screw on the pump which should be the only linkage adjustment that affects the idle.

 

[D. Showan]

Joe G. , I thought the tv cable should be tight at full throttle, you are saying something different. I'm not saying you are wrong its just not what I thought was correct. I am also confused about why the last bit of lever movement at the pump would not give me a little more power. I thought that the governor didn't come into play until you reach the governed RPM, so if you try to get max power below Gov RPM the last bit of lever movement at the pump would deliver a little more fuel at RPM's below Gov. If I set it so the TV cable is tight when the throttle pedal is to the floor, the TV pressure is approx. 5psi. higher than when I set the TV cable tight when the throttle lever at the junction where the cables and rod meet is pushed to full throttle. I hope I'm making sense? How do you set the TV cable?

 

[Joe G.]

Take a look at the full throttle stop plate (torque plate). It has a shape. The governor has a follower that hits that shape at different places according to the RPM so it limits the fuel at lower RPM settings as well as the RPM limit. The governor is in play whenever you have the pedal to the metal regardless of RPM. That's the reason for all this different torque plate business.



I adjust the TV cable like Bill K. says. About 1/8th inch lever movement at WOT. I have noticed no slippage or shudder in my trans at all with that adjustment. Of course, I have a DTT VB and TC so I can get away with a #5 plate in my '95. It's shoved about half way forward from the stock position. Major smog alert if I step on it.

 

[D. Showan]

Now it makes more sense. Good explanation. I'm in the market for a fuel plate now that I have my transmission upgraded. I'm curious to see (feel) the difference a 250HP plate will make. Thanks Joe

 

[fest3er]

Originally posted by D. Showan

Thanks for the responses.



I'm glad to know that the hard spot with the engine off is normal. ...

I didn't see it mentioned here, so I'll do it.



The 'hard spot' you are noticing is the 'breakover' point. This is the point at which the system does not allow any additional fueling. It does no good to push the pedal beyond this point (at least when running; sometimes when starting in sub-zero temps, you may need to pass the breakover point to initially start. )



Actually, you will likely *lose* a bit of power if you push the pedal beyond the breakover point. That's one of the things I've noticed with mine. Pressing up to the point yields max available power. Going beyond causes a slight, but noticeable, power reduction. It's all in the mechanics of the pump.



The hard spot moves as conditions change. At low RPM, you'll encounter it sooner, until boost increases and the AFC allows more fuel. At higher RPMs and boost, you shouldn't see it 'til the pedal is almost to the wood.



Fest3er

 

[D. Showan]

Thanks Fest3er, Thats more great information. I learn something here every day I log on. I contribute when I can but I'm still doing way more learning than informing.