Stock ’87 L98 (cold start injector disconnected) using mostly stock ’89 bin (things turned off/on, but no “tuning”), it stumbles off idle when you first roll into the throttle right after it is first started the first time that day, and is usually gone after less then a minute of driving (by the time I try it and come back it’s gone till I park the car for at least a few hours, making it very difficult to test).

For that matter, is there anything that different between the ’87 and 89 TPI’s? The only thing that I can come up with is that they had slightly different cams, but I would expect that they would be very similar otherwise, but the tables in the bins are very different especially the spark table is completely different, the ’87 has a lot more timing everywhere, almost as much as the ARAP.

 

You don't give your engine a min or two to warm up?.

If not then just add a little cold engine enrichment, if it's just light throttle. If when tipping into it enough to be using AE, then add some in the coolant vs AE table.

 

Start the car, give it a few seconds for the idle to stabilize, put seatbelt on, fidgit with radio and go… If I really cared about this heap I probably would give it a little more.

The thing is that it’s really right off idle, as in as soon as you touch the pedal. If you give it a little more it’s fine, if you’re rolling down the street at 1500rpm it’s fine, but slow down to idle and move the pedal it stumbles.

I’ll try a little cold enrichment, but was hoping someone came out with “they all do that when you try the newer bin because…” Seems like I’m running across all sorts of little issues doing something that shouldn’t have any issues.

 

I had the same thing, and I think it's from GM cheating on the calibration. The AUJM calibration and ARAP have only 9% cold (open loop) enrichment in the cold regions like 50-90 degrees or something like that, and it has 13 or more % once the engine warms up. My stock calibration also had a BLF at idle of 108 and in the free rev range. So, when cold, a BLF of 128 was used, and 9% enrichment. But, when you recalibrate to get a 128 when warm, and then only have 9% enrichment cold, it's 20% leaner than it used to be, and now there's a stumble at first tip in when cold. SO, I've added lots more Open Loop enrichment, and it's fine, and also use an idle BLF that's a little lower than 128. I've also disabled EGR, because for some reason, mine dumps in way too much EGR too quick, which means it was probably installed with the wrong washer, or the spring is too weak from use.

Cold warm up can easily be 11.9-13.0:1 A/F and run fine, and not do any harm, and make it much more drivable (just be careful to measure that with the AIR pump disabled). Economy doesn't suffer much either, because it warms up pretty quickly. It won't foul plugs or anything either, so if someone says it will, they're wrong.

 

BLF? Sorry, prom noob here… even did a search and only got this thread…

So about how much did you enrich it? (yea, I didn’t get a chance to play with it today… spent some time welding and cutting on another project instead)…

How was all this supposed to work with the stock ’89 L98’s? I would assume that that stumble wasn’t considered acceptable…

heh, mine was disabled by the previous owner… looked like he let the egr vacuum line fall into the alternator fan butchering the hardline… I just turned it off in the prom since I didn’t really see the point on spending time and effort on something that I didn’t really need.

I take it that you’re suggesting measuring it using a WBO2 or something? You can’t even tell rich or lean with a NBO2 before it heats up and the stumble is gone after about 30 seconds or so, well before the O2 starts doing anything.

 

BLF is the Block Learn Factor (long term fuel trim for 16 different load and RPM points). 128 = exactly normal = no fuel trim. Less than 128 means the closed loop had to remove fuel to obtain stoichiometric (14.7:1 Air Fuel ratio).

I enriched mine (in the Open Loop AFR% Change vs. Coolant Temp (Tuner Pro RT using AUJM calibration and ECU 6Ev011)) in a more gradual way, without the dip at 90° to 133°, but at 154° only having about 10%, and 26% at 24°. I also raised the sensitivity of Acceleration Enrichment vs Delta LV8 to that of ARAP.

That has rid me of my first tip in stumble, and improved cold drivability quite a bit. I think GM was just brute forcing it to pass the emissions drive cycle, or raise the CAFE a bit.

Good Luck.

 

Well, that worked stunningly badly… I tried it a couple of days ago and it didn’t work at all. The cold stumble ended up REALLY bad, and now it didn’t entirely go away (still stumbled when warm), didn’t want to idle… there basically wasn’t any engine response below about 1800rpm and/or below maybe 40% throttle, and then all of a sudden it would take off.

For now I just went back one chip and haven’t had time to play with it anymore… I’m wondering if it might be getting too much cold enrichment.

Funny, on another note having highway mode turned on seems to save about 2-2.5mpg in around town driving…

 

Oops. sorry for the trouble. Have you changed the MAF tables at all? It is really hard to have too much fuel when cold, but if that tip in is triggering accel enrich too easily (accel triggers with a small TPS movement), it could easily overdo it. What are your Block Learn Factors at idle and free rev when warm? Have you recalibrated the chip to achieve 128 there? That's what I did, and then added the enrichment. What bin are you using as a base? Arap? AUJM? What have you done to the bin? Seriously though, I'm telling you pretty much exactly what I did, and I had previously had the same very first tip in stumble, but I haven't been there to see your car do this, so I can't say what's what. Did you happen to change the wrong table? What software are you using? Details are what I'm looking for here.
Later,

 

hey, I’m not blaming you… you’re not here and you didn’t see what happened first hand, and I appreciate the effort. I’m just reporting back what happened

Not yet, but I need to, I’ll explain further down.

Yea, I figured the same thing… wasn’t expecting if I got it a little rich that I’d have any problems. I basically smoothed out the afr % change vs coolant temp like you suggested and raised the sensitivity of Acceleration Enrichment vs Delta LV8 about 5-10% (was in a hurry to get somewhere so I didn’t take the time to take compare the ARAP). I’m thinking that it was the accel enrichement since it was not only cold start related anymore.

Didn’t get that far… I needed to go somewhere and decided that I’d burn the chip, pop it in and see how it does on the way… since I didn’t have a laptop and since it was running hideously I popped the previous chip in for the ride home and on the way the water pump let go, ending the experimenting for a little bit. Last night I replaced the water pump and pulled the intake/fuel rails to swap in some 36pph injectors “since I was under the hood anyway” in preparation for some future experimenting. It’s still disassembled…

FWIW, the reason that I was saying that I need to mess with the MAF tables is based on my previous experience at the track previous to me getting into tuning at all. I modified the FPR to be adjustable and found that the car actually ran fastest with the fuel at 53-54psi (with both the stock ’87 chip and the matching hypertech chip, what was included with the car when I bought it), which obviously causes the car to run rich enough under other driving that the back bumper is covered with black soot all the time.

Stock ’87 L98 cold start injector disconnected
Started with an '89 AUJM $6E
- Set the fan turn on temps to be in the high 170’s and the turn off 167* (doesn’t make a difference, they stay on all the time right now).
- Disable EGR if MAT < X to 304.25* (bought the car without the EGR plubing so I don’t want it turning on and setting a code or reacting to something that isn’t there)
- VATS disabled
- I’ve tried both the ac pressure switch NO flag set and not (I was hoping that one way or the other it would override that there is no AC pressure switch connected, which I’m assuming is why the fan is always on)
- the 2 changes that you suggested are the only change between the previous chip and the chip that didn’t play nice.
- I’ve also tried setting the injector constants to 24.5 (roughly the flow of the 22pph injectors at 54psi), but it actually runs the same either way.
I’m using TunerPro, and no, I wouldn’t rule out that I did something stupid but for the most part a lot of this is pretty straight forward. I have posted a few questions in the last week or so (since I started burning chips), but it turns out that the rest of the issues that I was having were due to a problem with the memcal that I was using (some of the pins were not making contact with the chip, but the CE light wasn’t coming on either making me thing that I was having a different problem). That problem is fixed.