Intermittent cut out – BPT

[mattswabb]

My BPT Festiva runs great except for sometimes when I push the pedal down. Occasionally it will cut out, go, then cut out, etc.... I can move the gas pedal a bit and it stops. This doesn't happen all the time. Only now and then.

Here's what I have. Stock BPT, BP26 ecu, 3 wire tps and throttle body from a manual 91 escort gt, no knock sensor. The car harness has been converted to be the same as an escort gt.

In the garage I have a 4 wire tps from an auto BP protege. Should I be using this and wire it up?

[ScOrTGtC]

hmm.. do you have the stock vaf or the gtx vaf? if the gtx vaf .. if your using the gtx vaf, for safety reason the computer dumps alot of fuel in the motor. . cuz its in safe mode.. ( no signal at the tps and knock sensor..) try using a RX7 vaf.. but if your using a rx7 vaf its probably too tight or too loose ( flapper ) if GT same thing .. check flapper...

[mattswabb]

I'm using the escort gt VAF. Not sure what you mean too tight or loose. I have another should I try that?

[FazdaBoy4ever]

no i delt with your problem forever... tighten up the spring in your vaf. the ecu uses the vaf signal for the overboost control. If the flap opens up too far it will cut, so your spring is too loose and your hitting your boost cut. if your pushing more boost than stock turn it down dont touch the vaf, tightening the spring will lean you out... but if your at stock boost tighten the spring a click or two checking each time you adjust it to see if its still doing it.

[FazdaBoy4ever]

pop the black top off the vaf (its silicone sealed on) then tighten the spring.


www.nwerdt.com - i dont know if this site is still running if it is go to the how toos and there are some great pictures on how to tune an rx7 vane (same principal)

[FazdaBoy4ever]

http://www.nwerdt.com/how-to/mechanical/rx7vafswap.htm

[Lex]

It may be boost cut in which case it has to do with how much boost you're running and how tight or loose the VAF door is as FazdaBoy said. At what boost level does this happen?

[mattswabb]

It may be boost cut in which case it has to do with how much boost you're running and how tight or loose the VAF door is as FazdaBoy said. At what boost level does this happen?

This is happening at 10-12 psi. Boost is set at stock, I usually can get just over10 psi. I will try to tighten the spring tonight and see if that helps.

Which way do I turn to tighten?

[mattswabb]

I turned it 5 clicks total. 1 at a time then a test drive. No change. What is the screw adjuster for on the outside of the VAF. Should I mess with that? I've tried 2 different escort gt VAF's and 1 from a festiva. The festiva didn't have the screw adjuster. All did the same. It still cuts out after the turbo lag and before the boost approaches 10 psi. By feathering the gas pedal I can accelerate to 7000rpm. Once I get over 5000 (or so) rpm it doesn't do this.

Also I have this mounted with the plug facing straight up, is this OK?

Should I mess with this screw?

[thegreatelbobo]

Is the car throwing a code?

[mattswabb]

I don't think festivas throw codes. We don't have that luxury of a computer telling us what's wrong.

[mattswabb]

Does the way I have it mounted matter? Usually they are mounted with the flapper parallel to the ground and the plug coming out of the side. I have mine mounted with the flapper perpendicular to the ground and the electrical connection coming out of the top. You can kind of see it in the pic:

[Lex]

Well, do you have any boost leaks? Are you getting enough fuel?

The screw I believe is just an air bypass and doesn't matter in this case. Mounting it properly would probably help things since its a physical flap that is affected by gravity.

[mattswabb]

The fuel pump has been upgraded and no boost leaks. I was also thinking of the gravity issue of the flapper. I'll make another mounting bracket tonight and see if changing the position helps.

Thanks for all the suggestions so far. I'm going to a festiva meet this Saturday and really want it to run smoothly.

[Lex]

maybe just to be safe, run an EGT gauge or a wideband O2 ... the fuel pump is not the only reason you could be running lean.

Oh, one more thing - check your sparkplug gap and perhaps narrow it a little if you're getting misfire.