Balking issue: More info...

[Paul Workman]

At the risk of sounding like I'm comiserating, I discovered yesterday that the balking & "stuttering" (we're talking a transmission lash-whacking jolt) will occur with the valet switch (full power) turned "off" as well as "on". Hmmmm...sez me. Here's some more info:

1. It seems overall operation tends to smooth out after it has been running (heat soaking?) for about 20 minutes. Up to then, even with the engine temp at the normal (mid-scale) range, the issues are most severe and prevailent. In fact, after about 20 minutes or a little more, with one exception (I'll cover shortly) it runs...well...like a BEAST.
2. After a few minutes of cool down to where the engine temp below operating temp, the bulk of the symptoms return and remain until the temp is back up to normal. (This characteristic is pretty consistant too, I should mention...)
3. The balking (intermittent) and such seems to be most prevailent with moderate pressure on the accelerator; let's say it happens over half of the time (unless it has been running for less than 20 minutes, in which case it is about 100% of the time). If I ease into it, or go WOT, the problem occurs less often, say 20-30% of the time. Also, the hard balk occurs just once, during acceleration trasition from light throttle to moderate (especially) or WOT.
4. Under WOT & when operating for less than 20 minutes (in spite of engine water temp in mid-scale), there is some scattered missing (stuttering) occuring - all the way to 7000 rpm. After about 20 minutes operating time or so, and or a couple runs up to 7k rpm, the missing disappears completely.
5. The balking will also occur with the "full power" switch "off".
6. New AC/Delco platinum plugs, gapped at .035
7. Injectors (told to me to be replace a year ago - costing "...about $80 something apeace") all read 12Ω (cold).
8. Static fuel pressure = 46-48#, w/ engine idling it = 43#
9. Plenum vacume at idle = unknown (but will be later today!!)
10. Idle rpm fluctuations noted, and sometimes stalling when at idle

Some thoughts I'm having include:

Fuel/air/spark...

Fuel system fault probability % estimates (swag!):

1. Filter(s): 5-10%. It runs strong after thurough warm up. So, a filter blockage I dismiss as fuel flow wouldn't change with engine temp. And, starvation would be most prevailent at WOT, which is NOT the case. (However, changing the filter is on the "to do" list!)
2. Fuel pump(s) failure or weakness: 10-?%. Estimated low for same reason filters are not suspected.
3. Injector(s): 40%?? They are suppose to have been changed a year ago, and they "ohm out" OKay - at least when cold. (I'll check 'em hot later today, perhaps). Injectors cannot be rulled out at this time, but I'm not sure that the symptoms of the problem warrant the expense of changing them out...yet(!).
4. Secondary injector relay(s): 5-10% rating. The problem with balking and some of the attendant "stuttering" occured with the valet switch in the "off" position. This (to me) pretty much eliminates the relays being a contributor...to the balking problem, at least.

Air:

1. Secondary throttle plates operation: Obviously they work some of the time, but transition smoothness and to what degree they open and when is unknown. But, as far as causing the primary problem at hand, that hard balk and attendant random stuttering, I rank it at 30-40% probability (low), but who knows??.
2. Leak somewhere: 50-60% chance. The characterisitics of the problem changes with temperature (i.e. expansion). This may or may not be the main cause, but certainly rated high(er) on my probability scale. This is bolstered too by posts reporting the bolts on the IH were "finger tight". And, when I re-torqued my own plenum, I found the torque to be from good to almost finger tight on a couple. A loose or leaking IH would (I think) possibly cause at least some of the problems.
3. MAP hose leak: 20-30%(?) chance. Can't rule it out because of the characteristics, but nothing was found on a perhaps cursory inspeciton and check using the propane gas test.
4. Faulty TPS: The characteristics are unknown, but certainly worth checking it out. (I'll do that too.) A faulty TPS or connection would feed false info to the ECM and mess up the throttle response. (until the MAP and the O2 lean signal is detected and corrected in closed loop operation??)

Spark/electrical:

1. Spark plugs: 0-5%. They were replaced w/o any change in the operational characteristics, specific or in general.
2. Coils: 50-60%: Just a guess, as yet untested, but certainly a consideration as operating temperature change could manifest itself in coil operation, especially if the coil winding insulation is breaking down (not un-common).
3. DIS module: Not tested. No way I'm aware of (for me/my test equipment) to assess probability accurately, but it cannot be eliminated from consideration, especially as it is electronic and subject to temperature fluctuations. Rating = ???
4. ECM: Low % at this time. However, there are some un-related anomolies with regard to the cooling fan operations which might point to the ECM as a possible source for some problems. It cannot be eliminated, but evidence so far does not support a valid conclusion at this time. (Asside: I see there are as many as 7 different scearios where the secondary fan, for example, is switched on or off. And, there are several scenarios for the primary fan as well. I appreciate the technological attempt to optimize fuel economy and reduce parasitic drag (alternator powering the fans), but it seems like the fan control is "over engineered"??...Just my silly opinion.)

Well, I hope I'm not boring the hell outta y'all. My training (electronics) forces me to go thru a "process" like this so that I can better isolate a problem and not "change stuff out until the problem goes away!!" What I lack is a 100% understanding of how all the components work in symphany and how to evaluate their function. I'm still on the steep side of the learning curve, hence my "thinking out loud" (or in this post, as it were).

That said, I'm trying to run down a source for coil packs. The best the local GM dealer would do was $80.xx ea. And, asside from the "16 hole" plenum gaskets, I'm looking for a better deal on plug wires too; a "package" for a plenum yank, if you will! (Jeffvette???)

What am I missing? Does any of this make sense? Or, should I just shaddap and go pull the damn plenum and leave y'all alone??

Maybe I'm just having too much fun. One thing does strike me tho... Among my varied past endeavors, technical training development is one of them. It occurs to me that perhaps someone like me (and others) could benefit by a series of short manuals; LT5 (or whatever) for "dummies". It could be in print and/or electronic format - even some movie clips - that would cover a variety of LT5 and ZR-1 topics. I envision a concept piece that would be repleat with photos and diagrams and some effort to gather the pertinant (and far flug!) scraps of information from the FSMs, and put it where someone could quickly grasp the what, where, how-to stuff in one place. I see it utilizing "subject matter experts" (SMEs) perhaps and especially from this board and other authorities to assure completeness and accuracy...Ya think that would be worth doing??

Thanks in advance for any thoughts (on any aspect of this windy post!)

P.