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Offline Wittsend

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LA-3 Premium Fuel Switch
« on: March 09, 2014, 04:35:04 PM »
After years of just trying to get my '88, T/C engined (LA-3), T-5, Pinto to run well (and finally succeeding) I'm venturing into refining it.

Yesterday I hooked up the "Premium Fuel Switch" (yes, I retained the '88 wire harness). Here is what is happening:

1.  The Premium light comes on, I can hear the relay click, but I'm not seeing any difference on the boost gauge when accelerating.

2.   A check (key on/engine off) shows 11 volts at the boost control valve - whether the switch is set to "Regular" or "Premium."  Meaning the switch setting does not change anything (at least not with key on/engine off) the voltage stays at 11 volts.  This seems odd.  What voltage/signal activates the Boost Control Valve?

3.   I ohmed the Boost Control Valve and was getting 70 ohms.  Thus I assume the electric internals are functional.

As to the boost readings; when I swapped over the engine/trans I adapted the T/C tach/boost gauge to the left instrument pod.  Curiosity got me to see if the gauge was adjustable. It was, and I immediately re-set it to the "0" marking.  The following is my experience.

A. When driving I can see the boost gauge drop below "0" (vacuum) unless I get on the throttle.    I drove the T/C for 10 years before it became a donor and don't recall the boost gauge acting like a vacuum gauge. Logically it would make sense that it does, but I just don't recall.

B. Regardless of the Premium fuel switch setting I'm getting 10 Pounds boost.  I'm also hearing a mild "wooosh" of air I don't recall hearing in the well padded T/C.  Is this typical?  Is it the wastegate? Or might I have a possible leak (looked, didn't see anything obvious)?

  One more thing to throw out there.  I retained the '88 exhaust system, though after the CAT I ran a single (not dual) exhaust through 2-1/4" pipe and a Dynomax muffler. Is it possible that the exhaust is restricting boost?

C. What were the factory boost levels for Regular and Premium?  I've heard a whole bunch of different numbers.

 I'm not looking for all out power.  I'd like to retain the "Regular/Premium."  Boosting beyond factory and 3" exhaust is not where I'm going.  But, if I'm limited my power simply because I can't get the "Premium" switch to do anything, then yes, I'd like to sort that out.  While I'd call the power level "swift" It doesn't seem any faster than the 1,000 pound heavier T/C. And, my recollection was there is a noticeable difference in power with the Premium switch activated in the T/C.

Update: I just grabbed the wastegate actuator and the rod isn't moving at all. I'm going to investigate this more.

Thanks, Tom

Offline 65ShelbyClone

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Re: LA-3 Premium Fuel Switch
« Reply #1 on: April 25, 2014, 01:50:13 AM »
1.   A check (key on/engine off) shows 11 volts at the boost control valve - whether the switch is set to "Regular" or "Premium."  Meaning the switch setting does not change anything (at least not with key on/engine off) the voltage stays at 11 volts.  This seems odd.  What voltage/signal activates the Boost Control Valve?

2.   I ohmed the Boost Control Valve and was getting 70 ohms.  Thus I assume the electric internals are functional.

3. When driving I can see the boost gauge drop below "0" (vacuum) unless I get on the throttle.    I drove the T/C for 10 years before it became a donor and don't recall the boost gauge acting like a vacuum gauge. Logically it would make sense that it does, but I just don't recall.

4. Regardless of the Premium fuel switch setting I'm getting 10 Pounds boost.  I'm also hearing a mild "wooosh" of air I don't recall hearing in the well padded T/C.  Is this typical?  Is it the wastegate? Or might I have a possible leak (looked, didn't see anything obvious)?

5. Is it possible that the exhaust is restricting boost?

6. What were the factory boost levels for Regular and Premium?  I've heard a whole bunch of different numbers.

7.) Update: I just grabbed the wastegate actuator and the rod isn't moving at all. I'm going to investigate this more.

1.) The BCS will at least click open/shut with a 9v battery in my experience.

2.) That sounds about right. The '87-88 cars have a BCS with higher resistance windings so it didn't require a driver box like the earlier cars.

3.) I don't think the factory gauges were ever plumbed into a manifold vacuum source; only a boost source.

4.) Hard to tell what the "whoosh" is without hearing it.

5.) Not likely.

6.) 10psi on "regular" and 14-15psi on "premium" depending on year.

7.) If the wastgate actuator was stuck shut, boost would spike extremely high. If it was stuck open, the engine would have trouble building it.
'72 Runabout - 2.3T, T5, MegaSquirt-II, 8", 5-lugs, big brakes.
'68 Mustang - Built roller 302, Toploader, 9", etc.

Offline Wittsend

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Re: LA-3 Premium Fuel Switch
« Reply #2 on: April 26, 2014, 06:52:28 PM »
Thanks for the comments.  I should have updated this post.  About a week later I realized I had routed the hoses incorrectly. When no one answered I assumed it had fallen into obscurity.   I had run the large hose that was for the speed control to ??? (can't remember).  I did make another post relating to this error as it was based on a readily available diagram on Google images. http://www.fordpinto.com/it%27s-all-about-the-turbo/turbo-boost-%28lose%29/msg145810/#msg145810   Anyway, removing it and capping the ends solved the problem.