Alky help...stalling

[RIPN6]

I finished the DIY kit as per the instructions on Steve Monroe's web site and took the car for a spin. It perfromed beyond my expectations as I had 0 KN at 22psi and 93 octane. However, the car would stumble and stall after a WOT run when lifting off the throttle. It continued to do this when at idle or coming to a stop. I then switched the pump off and did another pass which reulted in serious Knock but the stalling went away.

My conclusion is it's flooded with alky even after the pump is switched off, however I'm not an alky expert. Any suggestions as to what to look for? I'm running a smaller jet than what was recommended (.30 instead of .32) Any help is greatyly appreciated!

One more thing....I still have a 93/xylene mix in the tank and it was a little cold today. Could the xylene have an affect like this in cold weather?
Thanks RIPN

[SMC]

I'd check the "dead band" of your Hobbs switch- should be on at approx 12 psi & off by 10 psi. I've seen some that don't want to click back off till 5-6 psi, and end up spraying a bunch more alky after it is needed.

[RIPN6]

Thanks SMC I'll try to check it. I have it set to come on at 14psi but no idea where it shuts off. I thought it was the same. I assume you just use a volt meter and watch for the circuit to become "open" again (o volts)? That seems pretty hard seeing that boost drops so quick when lifting off the throttle. Is there an easier way or correct way of doing it?

If I bench test it and use a compressor to simulate boost, then bleed down slowly to get to the shut off point? Will that give a true reading of what it does on the car and lifting off the throttle?

Thanks for your help.
RIPN

[SMC]

I used to use a compressor to test & set each of our switches. What a PITA. Finally figured out that a cheapo plastic veterinary syringe will generate 25 psi! One of these with a tee & an old boost guage is perfect for setting pressure switches. Just listen for the clicks.

[HairDrier]

Did you rig a light to come on when the switch activates and sends power to the pump? This is a must. It would be easy to tell if the pump is staying on too long if you have a light rigged off the switch.

http://bobdittmar.tripod.com/blown87combobs1987buickgrandnational/id8.html

[RIPN6]

I never would have thought to use a veterinary syringe to set a pressure switch....great tip!

HairDrier..thanks for the link. I never knew there was a "power injection" light in the dash! I have a light just lying on the dash for now. I wanted to check the system out and make sure I would keep it before I hard wired it in the interior. Even with the light though, boost drops so fast lifting off the throttle that I can't tell what PSI the light is actually shutting off at.

I didn't get to bench check the pressure switch yet (doing that today), but I did do a little test on my way home from work yesterday. At WOT I used the in car switch to shut the pump down about a half second or second before I lifted off the throttle. This resulted in no stalling. I only did it once, but this tells me that SMC may be right about the switch hanging on to long.

The next question is...I know you can adjust them for turn on time but can they be adjusted for turn off time?

Thanks for all your help guys!! I really appreciate it!

[HairDrier]

Turn on time and turn off time should be the same

[SMC]

Turn on time and turn off time should be the same

Every pressure switch has a range between the ON point and the OFF point. This is known as a "dead band". A good switch will have a 1-3 psi dead band, a poor switch may have a 6-8 psi dead band. We test all our switches & reject any with a dead band over 3 psi. Sounds like you may have found the problem. Let me know if you need a good switch.

[1badTTA]

Every pressure switch has a range between the ON point and the OFF point. This is known as a "dead band". A good switch will have a 1-3 psi dead band, a poor switch may have a 6-8 psi dead band. We test all our switches & reject any with a dead band over 3 psi. Sounds like you may have found the problem. Let me know if you need a good switch.

It might be the switch, but since he is dropping boost almost instantly I have a feeling it really doesn't have anything to do with that. My guess is that he has a rather long line that is a larger diameter than he needs and also able to expand under pressure that is continueing to flow alky after the pump shuts off. Just think of a garden hose with a sprayer, leave the sprayer on and turn off the water and then see how much more water flows. HTH

[RIPN6]

It might be the switch, but since he is dropping boost almost instantly I have a feeling it really doesn't have anything to do with that. My guess is that he has a rather long line that is a larger diameter than he needs and also able to expand under pressure that is continueing to flow alky after the pump shuts off. Just think of a garden hose with a sprayer, leave the sprayer on and turn off the water and then see how much more water flows. HTH

I see your point TTA. From the NOS nozzle I'm running about 3 feet of SS Braided -3 NOS line to a barb fitting, and about 8 inches of 1/4" fuel hose (200psi fuel injection hose) to the pump. I don't think that expansion is a problem but I can see how additional alky goes through the nozzle even after the pump shuts off.

I wonder if putting a WOT throttle switch in addition to the pressure switch would help? Like the ones they use to activate NOS. This way when you lift off the throttle about a 1/16" it would cut the power to the pump quicker than the boost drop to shut off the pressure switch. Hmmmm.

Side note: I envy your TTA! It's too bad the LS1 style cars dont' have a Tbuick option. That body style with a whistleing V-6 would be awesome! :arco:

[RIPN6]

Forgot to mention that I tested the switch and it seems to be opening the circuit between 9 and 10 PSI. It's set to come on at 14 psi but even so, would the difference between 9/10 and 12/14 shut off be that much of a difference for stalling the motor?

BTW, thanks for the offer on a new switch SMC. Before I got to read your post I talked to a friend to order me a new one from NOS. If it seems to be crap to then I'll get a hold of you. I'll keep ya posted on what happens. Thanks

[1badTTA]

Forgot to mention that I tested the switch and it seems to be opening the circuit between 9 and 10 PSI. It's set to come on at 14 psi but even so, would the difference between 9/10 and 12/14 shut off be that much of a difference for stalling the motor?

BTW, thanks for the offer on a new switch SMC. Before I got to read your post I talked to a friend to order me a new one from NOS. If it seems to be crap to then I'll get a hold of you. I'll keep ya posted on what happens. Thanks
How long does it take for the boost to drop from 13psi to 9psi when you let off the throttle quickly?? I would guess about .02 seconds tops. How much Alky can it flow in .02 seconds?? Not enough to cause your stalling.

If you lowered the pressure and used a larger jet it would help reduce the amount of time that it is spraying after the pump stops.

[RIPN6]

Well, I think I have the problem whipped! I lowered the alky line a little between the pump and the nozzle to create a "trap" in the system. I also changed the switch to a new one that opened the circuit at 12 psi compared to 9-10 that the old one did.

As far as tuning...I dropped the fuel pressure from 50 (line off) to 45. I'm not sure what made the biggest difference, but the car is running much better now. I have to throw a race chip in and see how it reacts to the alky/boost.

Thanks for all your help!! I really appriciate it!
RIPN

[Bob Avellar]

Thats one reason I run a return line back to my tank (Nice shiny new aluminum one now). It allows bleeding down of the lines back to the tank rather than into the motor when you get off the throttle. I know some guys don't like it for simplicity sake but it works for me. For a daily driven street car I wouldn't do it any other way just for smoothness of drivabillity. Pump can supply way more than enough to pressurize the nozzles and bypass some back to the tank. I use a valve in the return line and adjust for best all around response. :arco:

[RIPN6]

Thats one reason I run a return line back to my tank (Nice shiny new aluminum one now). It allows bleeding down of the lines back to the tank rather than into the motor when you get off the throttle. I know some guys don't like it for simplicity sake but it works for me. For a daily driven street car I wouldn't do it any other way just for smoothness of drivabillity. Pump can supply way more than enough to pressurize the nozzles and bypass some back to the tank. I use a valve in the return line and adjust for best all around response. :arco:

Thanks for the info Bob!! If it's not too much trouble, could you email me a diagram and some info on how you ran the return line? I have a Stainless braided line from the pump to the NOS nozzle now. Any info and pics would be great!(even a rough hand sketch) If you don't mind sending the info, PM me and I"ll give you my email. Thanks again! :thrashi:
RIPN

[Bob Avellar]

http://home.comcast.net/~bavellar/
Try that link. A diagram is on the first alky page and check out some of the installation pics. I have a whole new setup now -much neater with AN fittingss, braided lines and a polished aluminum tank. I haven;t snapped any photos yet but I will try to do that.

[19gn87]

http://home.comcast.net/~bavellar/
I haven;t snapped any photos yet but I will try to do that.
Hope you're able to add to your site...nice, helpful idea for some of us.