TPS idle switch questions

[deaner]

Hey all!

 

I've been reading about the FI system like crazy on a few different Z sites along with a couple Alfa and fiat sites but can't really find a definitive answer so I figured Id just ask.

 

Does the TPS idle switch add fuel on decel along with the fuel being turned back on at 2800rpm? I shaved my intake and deleted the bcdd(was bad) and this popping is annoying as heck! Plus my twice pipes are blued pretty bad I'm chalking it up to all the fireballs dancing all down the exhaust.

 

My thought was to either cut the idle switch wire or bend the tab so it doesn't do anything. I plan on putting the car on the dyno at work sometime this week to check afr's and get a good baseline for future mods and will try it out. With how hot the exhaust is getting and how well it runs/pulls, I'm thinking the backfiring is the problem.

 

Any insight or ideas would be great!!

 

Oh, car has...

Cold air

Homemade fuel rail with stock for

Msa header

Twice pipes

Shaved intake(egr delete, bcdd gone, cold start inj gone, etc)

 

Timing, fuel pressure and vacuum test will be done when I get her on the rollers. Cars idles perfect, pulls hard, doesn't stink, etc. The decel popping is just annoying me lol. Maybe this could be the fix?

[BluDestiny]

I believe the tps works like a switch, either on idle, or not on idle.

 

The Bcdd (Boost control decel device) is the main item that controls your decel in a stock efi car. It is normally attributed to giving a high idle if it leaks or is gunked up and stuck.

 

http://www.zdriver.com/forum/280zx-s130-forums-77/bcdd-block-off-34704/

 

Speaking of which what kind of car is it? what kind of engine management, if any, are you using?

[deaner]

Thanks for the reply BluDestiny! Sorry, its a 78. Stock efi, injectors etc.

 

I adjusted my tps yesterday and it cleared up a flat spot around 3000rpm. After playing with it and researching how this system works, that the idle enrichment switch, also worked with the bcdd on decel. I've kind of been thinking that that's why the bcdd was put there in the first place. To add air to the fuel that's being dumped in when the idle switch is closed, eliminating the decel popping.

 

I'm going to try and put her on the rollers today after work and try it out after I check timing and that good stuff. In theory I don't see why you couldn't run a switch inside the car to control the idle switch on cold starts. Then once the engines warm, turn it off so the enrichments not there when you let off the throttle.

[BluDestiny]

I've kind of been thinking that that's why the bcdd was put there in the first place. To add air to the fuel that's being dumped in when the idle switch is closed, eliminating the decel popping.

 

So you should probably find one that works..... I'm not sure if you mean that you're going to be getting one or not?

 

So you're talking about a cold start injector? Some thing adds fuel when the cars cold, but after it warms up it stops adding extra fuel?

 

I don't know about your weather, but I live in a very temperate climate and the only difference I noticed without my cold start is a low idle for about 30-60 sec before the temp guage started moving.

 

Honestly that shouldn't matter half the time since warmup is a very small portion of actually driving your car.

[deaner]

No, I really have no intention of putting any of that stuff back on. I think I may have worded some things wrong.

 

From what I've been looking at, maybe I'm wrong, but this is what I'm seeing.

 

TPS has 2 switches. Wot and idle. At idle there's an enrichment that helps with smooth idle. At wot there's more fuel added as well, for obvious reasons. The bcdd was a throttle bypass to lean out and hold the revs up for smoother shifts. I'm thinking that when you let off the throttle, the idle switch closes and the ecu starts richening the mixture thinking its at idle. With the bcdd, there's air there to keep everything from getting rich and making it pop and backfire. Take away the air leaning everything out on decel and now its dumping fuel into hot exhaust.

 

After playing with the tps last night, I figured out where on my peddle the switch opens but doesn't really open the throttle. On decel I'd try and hold it there. Seemed to work this morning on my way to work! Hopefully tonight I can check afr's to verify that everything's right on.