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Old 12-12-2011, 09:10 AM
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Gas pedal is going down beyond my control - EFI, 200R4

Hi. I have a strangest problem, that i couldnt figure out.

I upgraded my carb to Edelbrock EFI 3500 long time ago, and now changed tranny to 200-r4. Now, when i apply a little bit more throttle when start moving on high load (i.e. start driving uphill, or trying to climb to pavement), the throttle pedal is sucked down beyond my control as it scary-ghost movies, and released after the load is improved (i.e. car starts moving). In the mean time, i should not to crash, or brake.

My observations:

1) This happens only in 1st gear when start moving, and never happened before the tranny swap
2) The return spring of EFI is very stiff. And recently, transmission has TV cable, applying parallel force with return spring.
3) Somehow, it feels like the throttle cannot overcome the desire of engine vacuum at high loads, which prevents closing of throttle.

Does anyone has creative ideas or did you suffer with something that strange?

Thanks,
Yavuz - '55 Chevy V8

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Old 12-12-2011, 09:33 AM
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Quote:
Originally Posted by yaww
Hi. I have a strangest problem, that i couldnt figure out.

I upgraded my carb to Edelbrock EFI 3500 long time ago, and now changed tranny to 200-r4. Now, when i apply a little bit more throttle when start moving on high load (i.e. start driving uphill, or trying to climb to pavement), the throttle pedal is sucked down beyond my control as it scary-ghost movies, and released after the load is improved (i.e. car starts moving). In the mean time, i should not to crash, or brake.

My observations:

1) This happens only in 1st gear when start moving, and never happened before the tranny swap
2) The return spring of EFI is very stiff. And recently, transmission has TV cable, applying parallel force with return spring.
3) Somehow, it feels like the throttle cannot overcome the desire of engine vacuum at high loads, which prevents closing of throttle.

Does anyone has creative ideas or did you suffer with something that strange?

Thanks,
Yavuz - '55 Chevy V8
you said parallel... is it parallel but in an opposite direction?
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Old 12-12-2011, 09:43 AM
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I mean, the force of transmission TV cable(and spring in the tranny) is also in favor of returning the throttle to idle.
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Old 12-12-2011, 09:55 AM
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If you have a stock throttle linkage which would be a rod between the bracket on the firewall and the carb then look at the possibility of a broken motor mount on the drivers side. Common on old chevies.
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Old 12-12-2011, 10:01 AM
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Mmmm. Different angle of view, i will for sure check, thanks. But i have a flexible linkage, i modified it during EFI conversion:
http://www.yaptik.biz/private/EFI/gaz/gaz.htm
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Old 12-12-2011, 10:19 AM
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Is your linkage going "over center" to where the spring pulls it open?
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Old 12-12-2011, 10:41 AM
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Looked at your pic. Still just a factory type linkage. The flex part just replaces the solid part. If you can't find a new mount right away build a limiter to keep the motor from lifting up on the drivers side. A short piece of chain bolted to the head and onto the frame will work.
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Old 12-12-2011, 11:04 AM
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So do you mean that the head of my motor moves up, when i full-throttle at the start-up, and this is leading to more un-controllable throttle? While i installed the 200-R4; motor had two pair of mounts. One at front, the other at rear holding also manual transmission. After the swap, the rear mounts are omitted. Now there is front motor mount, and rear transmission cross member mount, so nothing left in the middle, where engine connects to tranny. But how can engine move that much while its fixed to transmission?
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Old 12-12-2011, 11:16 AM
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He's saying the left (driver's side) mount may be broken, the "in between" fused rubber separated from the top or bottom steel part. Hard to see sometimes. You have two mounts in front and one rear cross member mount. Have someone apply the brake, and in gear give it some throttle, see if torque is lifting the left side of the motor, which in turn could be pulling your throttle linkage open.
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Old 12-12-2011, 11:16 AM
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"But how can engine move that much while its fixed to transmission?"

I do not know what engine you have, or the first gear ratio of your transmission. Lets say it is a Chevy 350, and the transmission has a 3 to 1 ratio in first gear.
If your engine is capable of 350 FT-LBS of torque, when in first gear, the engine and transmission is twisting opposite the rotation of the engine with over a thousand foot pounds of torque.
The actual first gear ratio is most likely wrong. Your engine may have a different amount of torque. Your torque converter will also be multiplying the torque applied to the motor mounts.
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Old 12-12-2011, 11:25 AM
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Quote:
Originally Posted by DanielC
"But how can engine move that much while its fixed to transmission?"

I do not know what engine you have, or the first gear ratio of your transmission. Lets say it is a Chevy 350, and the transmission has a 3 to 1 ratio in first gear.
If your engine is capable of 350 FT-LBS of torque, when in first gear, the engine and transmission is twisting opposite the rotation of the engine with over a thousand foot pounds of torque.
The actual first gear ratio is most likely wrong. Your engine may have a different amount of torque. Your torque converter will also be multiplying the torque applied to the motor mounts.
Additionally,

the transmission moves with the engine. The tailshaft mount on a trans provides very little resistance against rotation, especially when it is worn. If you have worn engine mounts you prob have worn trans mounts and the entire assembly shifts when you accelerate or decelerate.

Some people think the trans holds the engine, take an engine out and look at how easily the trans flops around, worn engine mounts means your trans is ALSO moving- not good for either of them.
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Old 12-12-2011, 11:29 AM
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Sounds like you have the original type front motor mounts combined with a mount at the back of the tranny if I read it right. That's not a good way to support it. You need to side mount the motor or put in the original side mounts on the tranny. You can leave the support at the back. Certainly sounds like you're getting a bunch of torque twisting causing your throttle problem. Try a limit chain to see if it helps.
I had the same problem on my 56 chev until I put the side mounts back on the tranny.
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Old 12-12-2011, 12:59 PM
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I am scared just reading this!

If you only have a front and rear mount there is very little torque roll resistance so most likely, as mentioned, they engine and tranny are torque rolling horribly.

From what I am gathering the old transmission mounts were ears on the bellhousing that sat on rubber pads or something and the front is a single point mount. With this setup the torque roll is controlled with the transmission mounts. With a traditional automatic setup you would have the engine two-point-side-mounted and the transmission with one mount. From what you are saying you have catostrophically combined two mounting systems.

If this is right, IMHO, you absolutley must fix this before you drive it any more. It is very possible for either or both mounts to rip in half and the engine to lay over and hang at wide open throttle. This would get a little hairy.

The only correct solution would be to mount the engine at two points, one on each side.
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Old 12-12-2011, 03:58 PM
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Appreciate ur comments.

Sure i have left and right front motor mounts but 15 yo, time to replace. Maybe new 2,72 gear ratio torn them. I have 265 v8 stock engine.
BUT do i need a third support near converter? Yes, stock config had bellhouse support but newer models have only front motor mounts and rear crossmember mount, isnt it?
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Old 12-12-2011, 04:31 PM
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Its now clearer after some surfing. Seems that front motor mounts doesnt prevent twisting. I need either side motor mounts or side transmission support.
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