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.

[Aurora40]

Can you datalog the car while it is doing this?

[bradslt5]

i agree with the above post that would help in figuring your problem alot

[Paul Workman]

Originally Posted by Aurora40

Can you datalog the car while it is doing this?

Yes...Now that I relocated my missing scanner jumper! I'll do that next time out.

P.

[GrayZ]

Paul,
although I'm no mechanic, which many here will
freely agree and comment upon. I do retain a bit of knowledge
of things that have happened to me before. albeit, not all.
with that pretense in mind, My car, 1990, #0074 had some similiar
problems as you have described, Upon acceleration, it would sometimes,
fall flat on her face, fart, then, pick right back up, It didn't matter whether hot or cold. and she did it when she wanted.
a few months of this, and, upon arriving in Bowling Green for the gathering a few years ago, I was explaining my problems, to anyone that would listen, standing around my open clam shell. Gordon Killibrew and a host of others, were looking and talking about stuff.
Gordon told me he thought it was the map sensor hose, collapsing upon
acceleration, He said, if the hose was soft, and pliable, that would be one of my problems, he was right, and the next morning, at the Museum,
I went to his tent, and he cut me a piece of new hose, showed How to replace it. He also said he the air cleaner needed to be replaced.
I had dyno'd the car the day before, and after the new map hose and
the air cleaner, it dyno'd and extra 22 hp. Holy mother of pearl, i was suprised, and delighted, and the hesitation was history.
Of course you probably already know, but the map sensor hose, is located right in the back in the middle of your plenum, there is an aluminum bracket, that you take off to get to it. Here's hoping it is something as simple as that.

Paul, give me a call.

[Tyler Townsley]

You have the thought process down but the specific steps could use some work.

1. Compression check.
2. Run the car, park it and look at the plugs they should be uniform in appearance if not then chase fuel/spark on that cyl.
3.Take a good known plug and one cyl at a time unplug the wire, plug in the plug, lay it on the plenum and start the car. The spark should be the same on every cyl if not then you know which coil pack/wire to chase for problems.
4. There is a DIS checker and should you suspect the dis of falling apart I can lend it to you. You need some kind of a scope to look at the signals to verify its falling apart.
5. If you pull the plenum then you can check the injectors by pulling fuel rail up, crank the car and look at the spray pattern.
6. If you have a suspect cyl you can eliminate spark with step 2 and check fuel by swaping injectors from cyl to cyl, this requires pulling the plenum but you get pretty good at in with practice.
7. Listen for the vacuum pump at the left front of the car. You should hear it cycle for a couple of seconds when the key is first turned on the go quiet for at least 5-10 minutes. Both failing to pull the vacuum, on start and an continuly cycling pump signal problems that will cause what you describe.



Let us know what you find.

Tyle

[kenthompson]

Only thing I can add to the knowledge here:

My 90 had a huge stumble @ 2500-3000 until I changed the O2 sensors.

[Paul Workman]

Originally Posted by Tyler Townsley

You have the thought process down but the specific steps could use some work.

1. Compression check.
2. Run the car, park it and look at the plugs they should be uniform in appearance if not then chase fuel/spark on that cyl.
3.Take a good known plug and one cyl at a time unplug the wire, plug in the plug, lay it on the plenum and start the car. The spark should be the same on every cyl if not then you know which coil pack/wire to chase for problems.
4. There is a DIS checker and should you suspect the dis of falling apart I can lend it to you. You need some kind of a scope to look at the signals to verify its falling apart.
5. If you pull the plenum then you can check the injectors by pulling fuel rail up, crank the car and look at the spray pattern.
6. If you have a suspect cyl you can eliminate spark with step 2 and check fuel by swaping injectors from cyl to cyl, this requires pulling the plenum but you get pretty good at in with practice.
7. Listen for the vacuum pump at the left front of the car. You should hear it cycle for a couple of seconds when the key is first turned on the go quiet for at least 5-10 minutes. Both failing to pull the vacuum, on start and an continuly cycling pump signal problems that will cause what you describe.



Let us know what you find.

Tyle

Tyler, yours is the kind of testing that is guided by the intuition gained by experience...the kind I'm always interested in!

Well...

1. Compression check: Good point. I'll check it.
2. Plugs: All plugs are uniform in appearance; no plug varies in appearance from the others to anything significant.
3. Coil pack: Ah-HA!
4. DIS: I hope it doesn't come to that (gotta round up an "O" scope somewhere (ebay?) to do that). But, if I have to take ya up on that, I deeply appreciate the offer to use your test equipment, "fer sher".
5. Injector function: I guess I would have to latch the secondary relays to observe those injectors at the same time (not to mention doing it in a well ventilated area!)
6. Swapping injectors: Good, logical procedure. Thx.
7. Vacume pump: I'll check the actuator vacume for leaks and check the pump as well (same tool).

Many thanks for your insight and suggestions. Even if it turns out to be something else, I appreciate the help with "specific steps" in view of the symptoms I have.

Truth be known, this "little" annoyance I'm experiencing is giving me a reason to spend hours researching the LT5's operation - what makes it tick. This way I can be really dangerous!!
P.

[Paul Workman]

Originally Posted by ITLGO2

Paul,
although I'm no mechanic, which many here will
freely agree and comment upon. I do retain a bit of knowledge
of things that have happened to me before. albeit, not all.
with that pretense in mind, My car, 1990, #0074 had some similiar
problems as you have described, Upon acceleration, it would sometimes,
fall flat on her face, fart, then, pick right back up, It didn't matter whether hot or cold. and she did it when she wanted.
a few months of this, and, upon arriving in Bowling Green for the gathering a few years ago, I was explaining my problems, to anyone that would listen, standing around my open clam shell. Gordon Killibrew and a host of others, were looking and talking about stuff.
Gordon told me he thought it was the map sensor hose, collapsing upon
acceleration, He said, if the hose was soft, and pliable, that would be one of my problems, he was right, and the next morning, at the Museum,
I went to his tent, and he cut me a piece of new hose, showed How to replace it. He also said he the air cleaner needed to be replaced.
I had dyno'd the car the day before, and after the new map hose and
the air cleaner, it dyno'd and extra 22 hp. Holy mother of pearl, i was suprised, and delighted, and the hesitation was history.
Of course you probably already know, but the map sensor hose, is located right in the back in the middle of your plenum, there is an aluminum bracket, that you take off to get to it. Here's hoping it is something as simple as that.

Hmmm.... I didn't consider the MAP hose being "soft"; loose fitting, yes, but not collapsing. But, then the air pressure in the plenum increases (becomes less negative) at WOT, so if the MAP hose is collapsing to external pressure, it would have to be doing it at idle when plenum pressure is at it's lowest (I would think?). Assuming that to be the case (collapsed at idle or low speed), a collapsed hose might well impede pressure changes to the MAP resulting in grievous signal error to the PCM, I would guess.

Easy enough and cheap enough to replace it, so I'll put it on the list when I pull the plenum.

Thx for that!

P.