Red0ktober

I think it's time I open a thread and beg for help. I think you guys are my best bet for TBI tuning. I've been reading here, doing my best to tune this thing on my own, but I'm just not making headway.

I'm dealing with a 2.8L to 3.4L swap in an Isuzu Trooper. Stock ECU is a 1228062 ($4E AKHS), but I also have a 1227747 ($42 APAB) on hand. Both are set up with ZIFs, and I have the moates goodies for logging and burning.

The engine:

• F-Body long block out of a '94 Firebird

• Intake and accessories from the Trooper (smog pump removed, intake bored to 1-11/16)

• DIS Swap

• Rebuilt 4.3L TB w/ 46# (ebay'd, injectors have no # stamped on top)

• Adjustable FPR (modifed stock), set at 13PSI

• 3/4 inch TBI spacer

• Crane Cams H-260-2 (specs here)

• Comp Cams Pushrods, Springs, 1.6 ratio "Magnum" Roller Rockers.

• 10" open element filter, standard parts store paper

The truck for the most part runs and drives fine, but the spark and fuel aren't tuned well given the vastly non-stock engine. I have what seems to be backfiring up the intake on certain engine conditions, most reproducible when going to WOT from idle. I'll do some test driving and logging tomorrow, maybe I can come up with something a little more specific.

I'm just not sure where I should be starting since the engine is configured so much differently than stock. As of today, the bin I'm running has had the BPW set such that the BLMs are showing near 128s with the stock fuel table. The BPW in the stock config is somewhat... wrong. When I do the math, the displacement solves as a 3.1L, not 2.8L it came from. The factory tune works that way, so I assume other values must be set to "correct" that and simply changing my BPW to reflect my actual cyl displacement and injector size isn't taking that into account.

I'm about to nod off here. Any thoughts thus far?

RBob

iTrader: (1)

Need more AE, can increase the MAP & TPS AE PW tables.

The BPC value doesn't affect the AE PW, only the steady state fueling PW calculation. Which is why the AE is now off.

Also, check that the fuel pressure is rock solid during the idle to WOT transition. This can be checked at a stand still by watching the fuel pressure gauge, then whacking and holding the throttle open.

Don't over-rev the engine, just hold the throttle open for a moment. If the fuel pressure drops even a half a psi, then the fuel delivery is inadequate.

RBob.

Red0ktober

How should I figure my changes, or guess and check? This is what I have:

Red0ktober

Wouldn't I need less AE? I adjusted my BPW down from 166 to 153.

Curious thing about the BPW on this chip. My engine was a 2.8L w/ 36# injectors. So hereis my math:

BPC = 1461.5 * (0.467 / 4.536) = 150.47

Ok, BUT, the chip has a stock BPW of 166. Given 36# injectors, that solves to a 3.1L (which was also available in TBI, used in some Isuzu trucks). When I checked the BLMs on a stock engine, they were right on 128. So the tune has been built around that incorrect BPW.

When I figure my BPW for my 3.4L with 46# injectors, I come up with 143 and with that my BLMs are off. With 152 though, my BLMs come pretty close.

RBob

iTrader: (1)

> Wouldn't I need less AE? I adjusted my BPW down from 166 to 153.

You mentioned that it is giving a lean pop through the intake on rapid opening of the TB. That means it needs more AE. Which could come from either increasing the AE PW, or from correcting a possible fuel delivery issue.

Recall in your original post you said nothing about which way the BPC was changed and what you were previously using for injectors.

At 11.6 psi, 3.4l, and 46#/hr, the BPC works out to 152, so you are in the ball park with that value. Yes, the fuel pressure gauge could be off by that much.


I thought that the 2.8l TBI injector were 33 #/hr. Which works out BPC wise.

RBob.

xch3no2

The engine told you it's going lean when AE is supposed to cover it.
With all the funk of a modified engine & reconfiguring bins,
don't forget to listen to the engine.
All of the essential math is a guide to get me in a ballpark to start tuning my unique combination.

Red0ktober

Ah, true enough. I didn't mention what I did with the BPW, sorry. It was late.

My gauge is and adapter are from CFM-Tech. The TBI and injectors are supposedly from a 4.3L (which I believe are 46#, right?) The injectors didn't have a stamp that I could see, but I have not pulled them from the throttle body. Most sites list the 2.8 injectors as 36#, but that's not to say that's what I had. My original throttle body (and engine) is in a friend of mines truck now. I might run over there and see what the part number on those injectors are.

According the the gauge when I installed a couple weeks ago, the unmodified FPR was putting out 10.5 PSI. I modified a spare FPR housing for adjustability and installed it on my TB. Also used a better looking diaphragm than was in there, but the same spring. Seems I had to crank the spring down pretty hard to get 13 PSI.

I logged a drive this morning, seems that my O2 is running at 1v under WOT, high MAP, High RPM. "Max RPM" on my cam is 4800 and it doesn't seem eager to pull past that. I think my FP and injectors are adequately sized. I did get some 55# injectors which have been flow tested and matched. Would there be any benefit to installing and tuning for those?

Thanks for the help, I'm eager to get this thing working proper.

Red0ktober

I'm just an amateur/hobby mechanic and don't always understand what it's saying to me. I'm trying to learn though!

Red0ktober

Any suggestion on what and how much I should change on my AE tables?

xch3no2

Divide new inj. flow into old flow, this represents a percentage of change for the AE pulsewidth that you can start with. ie. 85/65= .76 or a 24% diff

Me thinks your bin adaption might throw a curve in there.

Red0ktober

Yeah, about the only things original about this configuration are the heads. Diff bore, stroke, throttle bore, injectors...

If it's like RBob suggested, and my PSI is actually 11.6, maybe I can solve for the flow difference between flow at 11.6 PSI and 13 PSI.

That brings up another question. Are TBI injector flows rated at 13 PSI or 15 PSI?

Oh, just spotted another thing. My sig is out of date, I replaced the '81 Isuzu I-Mark with a much faster car. I better fix that.

Red0ktober

For reference, here are the 2.8L AE tables vs 4.3L.

The Delta MAP values are double on the 4.3, but Delta TPS much less.

Again, I have data, but still little idea what to do with it. I guess first I'll bump up the Delta MAP and see what happens...

xch3no2

Address TPS AE PW (& delta) for foot action, immediate sag on throttle hit.
MAP AE PW (& delta) for load, extended AE that gets you to PE.

Delta's address when & for how long, and therefore quantity of AE.
PW's just base quantity.

Red0ktober

I don't seem to be getting that lean popping anymore, I've only changed the Delta MAP so far. I'll experiment with the Delta TPS and see what that does.

Since my throttle size is disproportionate to my engine, maybe reducing the AE TPS will smooth the acceleration out a bit. It wants to lunge forward without much throttle, that will make things very interesting when I'm trying to drive this truck in the snow and ice, keeping the LSD planted and the truck straight.

Red0ktober

Here's my Frankenstein engine. I'm going to try to clean it somehow this next week:

xch3no2

Ooh my.

Sry I missed a Q
13psi will more closely represent stock flow than 15.
I think the best way to determine injector flow, for me, is to send them to somebody like Witchhunter for a clean & actual flow report.

Red0ktober

Is that about the not-so-clean state of my engine? It was a lot cleaner before a friend of mine got suck in a mud hole and I had to pull him out. That is some sort of clay that does not come off easily.

I know of witchhunter, I sent a set of 2.8 injectors to them a while back. I just emailed them a couple days ago to see if I could get a reprint of the results, I don't remember what they actually flowed. I could pull my spare set of 46# injectors and send them in too. I do have that set of 55# injectors that are flowtested, do you think it would be more trouble than it's worth to tune for them? Would be overkill for flow, but they'd just run at a lower duty cycle, right?

xch3no2

Ya..no 55's
I like the atomization of slightly higher pressures,
The spray gets "lazy" when you go to low on pressure.

PW can also go too low for the injectors to work right, don't do that.

Red0ktober

Lame. Want to buy some injectors?

Red0ktober

I've been working on this truck for literally four years since I swapped in the 3.4L (owned it for eight). It's been drivable for most of that time, but think this is the closest it's been to actually working properly.

I wish I would have stuck to the multiport. I figured out my issues after I had gotten frustrated and stripped out the wiring and disassembled a good portion of the engine. It was just easier to revert to TBI to get the truck back on the road before last winter. My multiport system may come back on a friends truck when he swaps to a 3.4, we'll see.

I think this week I'll chase some exhaust leaks and see if I can get this thing sounding better too.

Red0ktober

Should I be doing anything to reduce the popcorn in my exhaust on decel/coasting?