I've been trying my hardest to make these injectors work because they are all I have. I've encountered the following situation:



RPM is showing between 1300 and 1500. This also occurs all the way down to about 1000 RPM. Pulse width is .8ms, MAP is bottomed out, and my AFR is showing pig rich. The problem here is my VE for this area is for the most part less then one. I cant take out any more fuel. It behaves the exact same way in Open Loop, for which the commanded AFR is right about 14.0.




Is it time to trade for some 68# or 65# injectors? Or is there still some possible way around this?



Is it possible my Zietronix WB is wrong?

 

Why is your TPS showing zero% Did you just let off gas?

I can run 80 lbs inj's at 19 lbs FP 350cid and I see A/F at light cruise at 15.0-16.0/1? I think spw msec is about 1.3-1.5 from recollection.

Is your WB calibrated? I assume so.

What is your fuel pressure?

 

This particular situation is downhill throttle lift, thats why I'm speeding up with no TPS. It's a little bit better on flat-ground throttle lifts, but it still does the same things. Clears up when you get down to about 15 MPH. Fuel pressure is stock at right around 11.5 to 12 PSI.

I didn't personally calibrate the WB, I was under the impression that the ZT-2 came pre-calibrated.

 

Thats normal for a throttle lift, the intake manifold actually gets fuel pulled from the walls by the higher than normal vacuum, causing a rich spike. You need to change the Decel Fuel Cut-0ff parameters and use DFCO there.

 

I'm aware of and notice the rich spike after the initial throttle lift. It goes down to 10 for about a second. This is after the rich spike levels off. I rolled down this hill at 50 mph for a solid 10 seconds and the rich condition is constant.

 

The VE values are very low in that area of the table. It may be that the injector bias table values are too high. To me that is the only place the 0.8 msec PW could be coming from. It would be this table: INJ - Injector Correction offset

For stock fuel pressure the values around 14.4 V should be in the 400 - 600 usec range (.4 - .6 msec).

RBob.

 

Injector offset is over 800 in that area. I did this because I was having trouble with low RPM low MAP surging, I figured the injectors were shutting off fuel because the PW was getting too small. I suppose I could put the INJ offset back and play with the prop gains to see if I can eliminate the low RPM surging that way and maybe fix this issue too.

 

The high offset values are where the PW is coming from. For the surging also check that the ECM isn't flipping between sync & async fueling. I believe that you disabled async, but just want to be sure that isn't an issue.

The 800 usec offset values are typically required for higher fuel pressues. It slows down the injector opening rate.

Note that when you lower the offset values the lower VE% areas of the VE table (by engine RPM & MAP) will be lean. Just need to expect this and do some learns.

RBob.

 

I still don't understand why recently sooo many people care about being rich at low MAP and closed throttle. USE DFCO!!!!!!!!!! Even with small injectors, it's a crap shoot whether or not the fueling will be close from day to day, or hour to hour, and whether it'll ignite or not. There's lots of EGR going on, the cylinder charge is very bad, and the compression pressure is tiny.

If it can idle in closed loop, don't worry about too big of an injector (until you start having to calibrate for a full emissions drive cycle, which will be never).

 

My point exactly. Get the WOT fuel where you need it and work the part-throttle fuel around it.

On a side note, pull some more spark advance and allow the ECM to enter DFCO.

 

The offset has me curious. How much fuel pressure can the TBI injectors handle before bad things happen (not opening, leaking, reliablity, etc)?

 

Hmm, trying to be polite, did any one pushing DFCO look at the engine RPM Darkside posted? 1350 to 1400 is where an engine will stall when using an auto in DFCO. The MPH was high enough at 52, but the engine RPM was low.

I understand that being at 11:1 at low manifold pressure isn't all that bad. But there still isn't something correct about the tune. Note the PW sticking at .8 msec and the low (1 - 2 %) VE values.

If the AFR was a little higher, say in the 12.5 to 13 range then it would be OK. There is little manifold pressure (20 KPa-) and very little air/fuel density in the chambers. So a tad rich helps keep the mix burning correctly.

RBob.

 

My 305 will not stall clear down to 800 rpm with the TCC engaged. I exit DFCO @ 850 rpm or if it rises above 25 KPA map, this is with my TPI.

 

This is true, running without TCC decel unlock is like a clutch car. At least in 2nd & 3rd , no overrun in 4th. But unless the cal is setup that way an engine stall may occur. And can still stall if the trans is shifted into neutral during this time. Same with a stick car and the clutch is dis-engaged.

I tend to try and keep calibration recommendations more generic. Better to be on the safe(r) side of a calibration.

RBob.

 

Did some more tweaking today. I put the Injector Offset back to 600usec and did some more WB VE Learns to get the tables back into shape. Took it out on the freeway and observed the following.

This is a high speed throttle lift. Don't ask me why TPS is 1, my foot is off the pedal. The injectors seem to have stopped flowing completely as the AFR gauge is maxed out lean. DFCO is NOT engaging, as you can see the PW is still at .8.



This is just a few seconds later. The RPM has dropped a bit. The MAP and the PW is exactly the same. Why are the injectors flowing here, but not above? Especially since the PW is equal both time?



If I add VE to the area's the injectors stop flowing they start flowing again but rich. If I take VE out of the rich areas the injectors stop flowing. If I add more injector offset I end up with the problem I originally posted here.


All I want for this car is to operate in closed loop like normal and be able to take my foot off the gas and decelerate to a stop with an AFR that lingers reasonably around 13, WITHOUT any surging and without any backfiring. It just doesn't seem like it's possible to lean these injectors out to the point I want to at such low MAPs.

 

enable open loop decel. in the option words, maybe

I'm dumb. you are in open loop