Vacuum Diapham/ EFE?

[civicstomper]

Hey everybody. I was wondering if anyone had any information about the EFE (Early Fuel Evaporation) system a.k.a heat riser, manifold heat control valve, or vacuum diaphram in a TBI equipped truck? Its a 1987 K-5 Blazer 350TBI, and i have heard that the problem in my truck might be the EFE.

For anyone that hasnt had the pleasure of reading through my redundant and dumb questions in odd posts about my truck; it is having problems stalling out. I have narrowed it down to when I try to give it gas when it is idling/ going very slow. I have checked all the sensors/ new plugs/ wires/ fuel filter/ fuel pump/ fuel lines/ distributor cap/ rotor: all new. My friend says that he heard a dealer mention something called EFE in this year and later trucks? I am running out of options and any advice at all wold be greatly appreciated, thanks in advance /forums/images/graemlins/thumb.gif

By the way, I tried searching, but I couldnt find anything, let me know if this topic has already been covered.

-pete /forums/images/graemlins/k5.gif /forums/images/graemlins/truck.gif /forums/images/graemlins/usaflag.gif

 

[dyeager535]

If present on your truck, it will be on the passenger side, connected to the manifold. It joins the exhaust pipe to the manifold on that side.

When the engine is cold, the EFE "valve" should be shut, which blocks off the exhaust pipe on that side. That forces exhaust through the exhaust crossover in the intake and heads, heating the engine up faster. If it is malfunctioning or stuck, it can act as an exhaust restriction all the time.

If stuck, I'd expect power to get worse as RPM's increase.

 

[civicstomper]

Thats sounds a lot like what is happening on my truck. It does seem to get worse when I try to increase the RPMs when it is at about idle. I am going to see what there is to replacing this thing and how much it costs. I'll keep you updated, and Thanks for all the help! /forums/images/graemlins/thumb.gif
-pete /forums/images/graemlins/k5.gif /forums/images/graemlins/truck.gif /forums/images/graemlins/usaflag.gif

 

[dyeager535]

You can manually move the valve, or you should be able to, if it isn't frozen in place. Again, if present, you'll see the vacuum ine running to the EFE, where it hooks up should move easily.

Knowing GM, it should "fail" in the open position, and only on startup (cold engine) should the valve move to the "shut" position.

Personally I think EFE was a poorly designed/implemented device, since no one lets their vehicle sit long enough for it to open fully. I assume during the actual EPA certification testing though, it was allowed to warm up with no throttle input. I say, if no emissions testing, (or just sniffer) and it is faulty, gut it, or buy one of the "dummy" EFE spacers instead of replacing it.

 

[civicstomper]

Thats exactly what my Dad was telling me. The only thing is, I looked in my Hayes manual to see what it looked, and I dont remember seeing anything like that there. My Dad is thinking that maybe the previous owner removed it for some reason. When I get home from school (im a commuter), I will check and see if it is actually still there, and if it is, I will see if is stuck.

You mentioned a dummy EFE...is this pretty much just something to cover were the EFE was? If so, is there a different name for it, like if I go to Autozone or somewere like that to get one, what do I ask for? I will for it when I get home and let you know what I find.

I will keep you posted, and thanks again for all the advice /forums/images/graemlins/thumb.gif

-pete /forums/images/graemlins/k5.gif /forums/images/graemlins/truck.gif /forums/images/graemlins/usaflag.gif

 

[dyeager535]

With stock manifolds, you can't easily just remove EFE. The manifolds don't have anything but a flat surface to mate to, so you can't just bolt the exhaust pipe up to the manifold if EFE is removed.

Some cars didn't get EFE later on, the TBI trucks may not have received it in some cases either. If it's not there, then it can't be your problem. /forums/images/graemlins/smile.gif

Some late 60's Corvettes didn't have EFE (some 327's IIRC) so looking at Corvette catalogs will net you the "spacer" that they make. Some late 80's(?) Camaros also used a similar spacer.

 

[i8yrsuv]

When I was hooking the exhaust up the other day I found mine missing ??? Where is now ??? in the cat or the muffler??? If only I had a crystal ball or maybe call physic friends ?? /forums/images/graemlins/histerical.gif

 

[civicstomper]

nope, i guess thats not problem after all, I checked and I dont have one on my exhaust. I'm going to keep looking around for other ideas though. It still runs ok and everything, and as long as I'm not hurting it I guess its ok for now. I would still like to fix it someday though, so I will probably be back with some other odd TBI related questions, lol, Thanks anyways /forums/images/graemlins/thumb.gif
-pete /forums/images/graemlins/k5.gif /forums/images/graemlins/truck.gif /forums/images/graemlins/usaflag.gif