OK, I have been told may things on how/ when the secondary injectors come into play. If anyone can shed light on these conditions that would be appreciated. Just trying to understand this part of the fuel system a bit better.


Thanks

 

they come on 3,644 rpm when the vaccum is less than 200mmhg

 

The secondaries come on when both the revs and the load (airflow) are high enough. They don't come on before 3800rpm, but will come on later than that under low load.

When they come on, all four injectors are pulsed together at half the pulsewidth the primaries were firing at just before the transition, so there is no change in AFR.

 

factory training manual... 3,644 rpm.

 

Dunno what you're reading but the 86 TM says 3688rpm and 90mmHg...

Since what you actually see on the tach at the time is really more relevant, most people (including me) prefer to call it 3800rpm.

 

 

I was told at one time that the TPS had something to do with this also (at WOT the Secondaries would come on also), apparently this is not the case.

So if I understand correctly if you are crusing at over 3,688 rpm (lets say 4000 rpm) and you have little to no load (lets say 4 inHg) then only the primaries are on. If you punch the throttle at that point (now boost ramps up to 7 psi) then the secondaries come on as soon as you sense over 0 inHg vac?

Thanks for all the info, this has been really informative. I am trying to understand the hesitaition that I feel when I boost the car at this rpm threshold. I was told to change the TPS but did not understand why. I know it can be gorunding, etc but understanding how something works initiialy is always the best route when troubleshooting.

 

There's a little test out of the non turo section of the series four manual that you might try to help diagnose your problem.

It goes like this: If you take the vacuum hose off the boost sensor and plug it so you don't have a vacuum leak, the boost sensor now sees atmosphreic pressure. With this conditon, each and every time you go over 3800 (grrrrrrr) rpm, the secondarys will come online. No other conditoin required. Even very light throttle. Even in your driveway. Over 3800 rpm (grrrrrr) and they come online.

And you seem to have the *how it works* down pat in your last post. With everyting connected up as on a normal car, you can drive with light pedal up into the 6000 plus rpm range without the secondarys coming online.

Or you can stomp the pedal at 1000 rpm and the secondarys won't come online until the tach hits 3800 (grrrrrrr) rpm.

 

Interesting. Would this negate the 3800rpm (grrrrr? lol) hesitation?

 

Got me. The transition still happens at 3800 (grr).

I had fun a few minutes ago. A fellow has a thread wondering about how he put a timing light on the engine and rev'd it up and the timing advanced like he knew it would, but then started retarding.

So I have a RTEK2.0 and I can look at timing, so I started my engine in the driveway, and rev'd my engine up to six grand. The timing advance as we all know it will and around six grand it read about 32 degrees BTDC. I did notice at some point the timing fell maybe five degrees, say from 35 down to 32 degrees.

So anyway, I decided it might be a boost sensor twitch, so I disconnected the vacuum line from the boost sensor, then rev'd the engine. Well around 3500 rpm the engine started to cycle up/down. That was the secondarys coming online doing that. I could push it into the higher rpms though.

This was during a somewhat slow rev up the band, that's why at 3500 rpm I got the up/down rpms when the secondarys came online.

 

Hmmm, make your car have the 3800 rpm hesitation and then do the boost sensor thing and see if it hesitates. If that makes sense...

 

oops, you are right.
i was the one that printscrned that picture and i got it wrong....

 

Funny thing was I was told the TPS had something to do with when the secondaries come on. I have also seen this indicated to others that are having hesitation problems at 3800 rpm, "Replace the TPS and it may go away". I guess that statement is totally false then or maybe that relates to a different condition, any thoughts?

 

I've never heard anybody say that...

The TPS has bothing to do with secondary injector operation.