6E MAF misfiring at particular MPH range?

[dyeager535]

Bored, can't work on the setup, but wondering if anyone has seen something like this, and has any ideas? ("Misfire" probably a bit misleading, sorry)

Between 35-45MPH, the engine starts bucking like there is no tomorrow. Definitely feels like fueling issue. This is under heavy throttle, normal operating temp. Light acceleration the problem isn't quite as bad, but there is definitely a sag in this range even at light throttle. I have seen no evidence when disabling PE that the motor is running lean here if I am gentle on acceleration.

I've extensively worked on getting BLM's close to 128 under "normal" conditions, however without a wideband I'm a bit handicapped on this problem since it's under heavy throttle when it should be going rich/open loop.

I've messed with AE fairly extensively, and PE a bit. What I can't figure out is why there is an issue in the same MPH range....I can be in 3rd or 4th gear (2368/1393RPM's respectively) and the problem still happens between those MPH's. Since everything is based on load and RPM, there is no reason I can figure as to how or why it could be MPH related. Over or under that speed range, it doesn't exhibit the same behavior. At 65MPH in 4th I'm turning right around 2200RPM, which is the same RPM range as 35-45 in 3rd and I have no problem with it breaking up at 65MPH, so again it doesn't seem to be RPM related.

The pickup coil and module are both new within the year (cheap parts store pieces, but had to use what I could get) but I keep going back to the MPH correlation, which doesn't point to ignition. The speedometer is driven off the DRAC/VSS, and I don't see any problems with speed display. The datalogs don't show any error in speed reporting.

No datalogs so far, since the '165 is so poor at keeping the stream going I normally make changes by feel when it comes to AE/PE. '7727 is coming, I swear. After I rewire my daughters Power Wheels. :)

[RobertISaar]

No datalogs so far

i would recommend this change... could be the ECM detecting knock or "knock" and it pulling and re-integrating timing. that can certainly cause bucking in high load, low RPM situations.

[dyeager535]

Yeah, I just hate dealing with this stupid '165 and datalogging...driving down the road and it locks up, have to shut down the truck, leave it off for about ten seconds, then restart everything.

It's funny, I'm going backwards here, I have datalogging capability but have grown frustrated trying to use it. :( The '7727 is going to be a breath of fresh air.

I know sometimes there are problems with knock sensors being overly sensitive, is there any possibility (just thinking out loud here) that there could be a harmonic issue with the drivetrain that could be strong enough to hit the knock sensor? This thing rides like a brick on the road for the most part.

[RobertISaar]

that has actually happened MANY times on the TGO boards, so it really wouldn't be surprising.

[brianko]

I concur, having just spent several hours with a $6E calibration that exhibits false knock at all RPM ranges. However, even with the KR, I wasn't getting the "bucking" you were getting. I didn't mess with AE though, just PE. What's the WB doing when it starts "bucking"?

[dyeager535]

That's part of my problem, no WB. But since it does it at light/moderate throttle (just not so bad) I SHOULD be able to get a rough idea whats happening via the NBO2. INT/BLM, O2, and knock counts should give me an idea.

The good thing is that it's such a narrow range I can make changes and test for improvement. Bad thing is, it competes with my million other projects for my time.

Really need to work it out though, causes serious problems trying to pass or pull steep hills in town.

I HAVEN'T been seeing knock since the fueling seems(ed) to be pretty good, but I need to re-visit that. I have this nagging thought in the back of my head that maybe the antifreeze that disappears fairly slowly is getting into the cylinders. Pressure testing the coolant system showed no leaks, but these are poorly machined Vortecs (I suspect they were factory rejects) and with their propensity for cracking, I just wonder if there is a minute crack that doesn't leak but under very specific conditions. I don't smell it, I don't see it, testing doesn't show that it is leaking, it just isn't there anymore.

[Dewayne_S]

Ok, I struggled for 4 or 5 years trying to tune my 6E Camaro WITHOUT a wide band. Back then the prices were too high for me to buy one so I just kept on fighting it. After I broke down and purchased a WB-o2 I quickly learned why everyone kept tell me to get one. Get a Wide Band o2

Concerning knock sensors, they are a pain as well. Mine would pick up false knock from ANYTHING. I now run without a knock sensor hooked up at all.(it's my car, I can unhook it if I like) This may not be a good idea but I'm comfortable with my engine and ability to to read plugs, plus i have been running this way for a few years now without any issues due to detonation.

You can't successfully tune just by changing what you think the problem is. You have to datalog and see what the ECM is seeing and how it is responding to the information.

Lean cruise, make sure it is disabled. At least until you get these issues sorted out.

The '7165 ECM is aggravating as heck when it comes to the datastream. That is the biggest and really the only issue I have with my setup.

I always wanted to put TPI in a truck, I bet that thing will be fun once you get the bugs out.

[EagleMark]

There's a few things I can think of that would do this.

1. It's a transplant in a truck right? Where is the O2 sensor now compared to when it was stock? How far a difference? Convert it to percent and adjust Integrator Delay Vs. Airflow
2. Proportional Gains vs O2 Error need to be reduced 25% to 50% depending on cam. Is this $6E? I think it's "O2 Error Reduction Gain Vs. Airflow"

Easy way to see if it is the O2 sensor feedback causing the issue is run Open Loop and see if it's still there.

3. Reset INT w/ BLM change Checked and test. Without a wideband your fueling may not be as correct as you think, espeically with the data stream issues.

Better yet... I just looked through the $6E XDF and with horrible data.... find another ECM...

[dyeager535]

Now you see why I have the '7727 stuff Mark!

It is a transplant, and the O2 is WAY back (3-4 feet?) in the stream...long tube headers dual all the way back, and the O2 is on the "extension" side of the collector. At least it's heated. I don't know where it was on the F-bodies, but I assume in the manifold right at the head. I had thought of your previous posts in adjusting the int. delay due to this, but haven't done so. I hate spending more time on the MAF setup when my intent is to dump it.

I know the WBO2 is coming, I've got some things that are competing for funds. It just can't happen right now. I would think someone really smart would have been able to create a free program to control one from a laptop. That would cut cost down even further. Maybe someone already has and I missed it? That would make them even more affordable.

Once I started really playing with fueling and timing I was able to get away from knock...stock PROM with the Vortec heads and higher compression in a truck with tall gears/tires (3.42/33's) it pinged ALL the time. I wouldn't doubt it if the KS saved my rear more than a couple of times back then. In my case the thing sits so long, bad gas is a fact of life...KS helps there for sure. I now try to park it as close to empty as I can so a fillup dilutes the bad stuff really well, but at 31 gallons and little use, pretty hard to park it near empty.

I've got EGR, AIR, and Highway mode disabled. I'm not messing with highway mode until I can get my oil temps logging.

I completely understand it's not right to tune by feel. In the case of AE, at 60MPH I can modify it and if it stops bogging, I'm at least better off than I was. Even if it's not right, it's better.

It actually felt really strong with the stock prom and injectors, but it was very, very lean of course. Once I got the current (SVO) injectors figured out in the PROM, and have been spending more time trying to learn everything, how it runs has gotten much better. When running right, it is fun in the truck. Once I get past that 35-45MPH "block" in third, it pulls VERY hard up to 65MPH+. But there are a lot of "small" issues that make driving it less than enjoyable. Driving and tuning is very difficult. I mentioned it before, the early MAF's just seem a real pain compared to MAP. You get everything to 128's through the MAF tables, but throttle response, acceleration, deceleration, startup, open loop, all of it still needs massive amounts of work, where it seems with MAP, once you get VE figured out the rest of the stuff is at least interrelated enough to the VE tables that you are somewhat close.

I intend to log/monitor the KS to see if maybe that's whats happening in this case. It's very plausible, although so far I've not seen that this KS is ridiculously sensitive. With it being so consistent, it's not like I can't pin it down. I'll see what I can do to log it and really spend the time to analyze whats going on.