I don't know if you consider me an older poster, but I'm still having the same problem after a year or two. As I said, it only happens when it'* quite hot outside, and I've already tried a tranny cooler to remedy the situation. It doesn't surge quite as often as it used to, but it'* still an annoyance on long summer drives.

Hopefully macho_mike chimes in here again... he'* having his tranny redone after dealing with this problem for a long time. I also hope the new member Bill was referring to can be of some help. Bottom line: I want my car to run properly, and I'm sick of it being an embarrassment whenever I'm carrying passengers.

Hello

Today changed
Air filter, fuel filter, oil (nothing to do with it) and PCV valve.
Nothing changed in the tranny, still shuddering after 45 minutes on a long hill.
Tomorrow is spark plugs, although I don't think this will fix it.

Should I clean my MAF and TPS. How would I clean these?? Heard some scary post that said you could ruin these.
Someone said you can adjust the TPS but I wouldn't know how to do that.

Tranny cooler and flush would be next on the list, but winter is coming to good old Calgary soon so the problem will go away

I can't believe GM doesn't know what the problem is... more then likely they know but they don't want to recall it.

CHCPMAN

This will be very long.

I have read through most of this and tried to add comments and suggestions to everyone’* questions.

To start off though, I first need to TRY to stress how very important it is on these cars that the secondary ignition system is in perfect operating condition! IT’* REALY, REALY, REALY IMPORTANT FOR THIS PARTICULAR PROBLEM!!! I’ll explain more latter.

The secondary ignition consists of spark plugs, spark plug wires and the three ignition coil packs or one big coil pack on the older models. If the vehicle has more than 80,000 miles and none of these parts have been changed already, then that would be the first place to start….plugs and wires anyways. The coil packs are rather spendy to just replace for the sake of tune-up, but I have seen many mechanics do it with my own eyes.



For inspection of spark plugs….
Remove all plugs and check the gap, if it is beyond specification then you need to replace them. Clean the porcelain tower of the plug (where the wire goes) with a clean rag and some gasoline, then examine that area very carefully for cracks or carbon tracking. You may need (or should use) a magnifying glass for this as the cracks can be very small but will still cause a problem none the less.

Also check the color of the plug tip to determine the condition of the fuel mixture. That’* a whole other story that I’m not going to get into but you can find a wealth of info on the net about “reading plugs”.



For inspection of plug wires….
Spay water on the wires with the engine running and look and listen for sparks/arks, this is easier to do at night in a dark quiet area…the sparks are more visible and audible. If you see/hear any then they need to be replaced. Remove all wires and label them or do one at a time if you want to. Inspect both boot ends for rust, corrosion, stretched out terminals, black terminals, cracked boots, white spots, flaking, melted spots and carbon tracking. Inspect the length of the wire for white spots, rubbed spots, melted spots and cracks.

Ohm check the wires just to make sure one is not open, but you will not likely find anything here because of the nature of the wire. A plug wire is constructed with a carbon core and not a metal core like all of the other wires in your car. A carbon core wire has high resistance even when new. I believe the rule of thumb is about 1,000 ohms per foot of wire, or 1k ohms per foot. Like I said, this is a test that can be done but it is also a test that will not always find a bad wire….this test simply can not check for “real world” problems.



For inspection of coil packs….
Spay water on the coils with the engine running and look and listen for sparks/arks, this is easier to do at night in a dark quiet area…the sparks are more visible and audible. If you see/hear any then they need to be replaced. Remove the wires from the coils and inspect the towers of the coils for rust, corrosion, erosion, black towers, cracks, carbon tracking and white spots. Ohm test the coils from one tower to the mating tower on that coil, then check the other two the same way. They should all check very similar, if any of the three are far apart then I would personally recommend replacing all of them simply because when one fails the other two are not far behind.



Carbon tracking….
Basically this looks like white OR black lines that can take any shape or direction. It’* like lightning, it can go in a straight line if it wants to or it can make many random turns on its path to ground. Remember, electricity is lazy, it will take the path of least resistance but a straight line is seldom the path of least resistance for electricity.



Well I think that about covers the basic checks for the secondary ignition system so lets move on to WHY this is such an important system to closely examine for this particular problem….overdrive shudder/stumble…incase you forgot after reading all of this.

A random and/or intermittent misfire caused by the secondary ignition on these cars actually happens IN ALL THE GEARS! 1, 2, 3 and OD! The reason it is usually associated with OD only (and 3 rd sometimes) is because that is when most people “feel” it. In OD and 3 rd gear the TCC is engaged depending on many factors that I don’t care to get into right now. The point is that when the TCC engages, you essentially turned your automatic transmission into a manual. The converter locks up to a 1 to 1 ratio. Meaning there is no slip (or very little anyways). Before the lock up takes place the converter ABSORBS these intermittent misfires very effectively. Once it locks however, you FEEL everything the engine feels.



The transmissions in these cars are actually very strong and dependable units. I personally have not seen one cause or contribute to a 3 rd or OD shudder/stumble. I can’t say for sure, 100%, that this is not a transmission problem but I simply have not seen any personally. The thing about these transmissions is that the TCC solenoid is either “ON or OFF”. There is no in between. If it was faulty, it should either be stuck on or off in most cases. A solenoid does not generally “stick” half way through its travel.

The PCS (Pressure Control Solenoid), however, is a VARIABLE solenoid. It is what is referred to as a Pulse Width Modulated solenoid or a PWM solenoid. It receives a pulse of power or ground from the PCM to control its position. The WIDTH of the pulse determines how long it stays open and how far open it says. Make sense? Probably not, but try to stay with me.

If the torque converter clutch (torque converter) itself were bad it would most likely fail all the time or at least get worse over time. If the torque converter clutch solenoid were bad it SHOULD either stick on or off and not in between or “flutter/shudder/stumble”. If the PCS were to go bad it COULD cause fluctuating pressure to the torque converter clutch which could result in a shudder/flutter/stumble at highway speeds.

So, I would say a better place to be looking for the cure to this is in the secondary ignition first and if that turns up nothing, then look towards the Pressure Control Solenoid.



Now as for those who replaced “ALL” the ignition parts on there car with no cure…..Will you kindly define the meaning of the word “all”?

Does that mean plugs and wires but not coils? Or coils and plugs but not wires? Or coils and wires but not plugs?

Also, those who took there car to a shop, maybe even a dealer….Did it ever occur to you that they THOUGHT it was a bad transmission or solenoid and sold you a new one? Then after the mechanic test drove it he realized that it did not fix the problem so he brought it back to find a corroded plug wire….so he cleaned the wire with a small brush, pinched the terminal tighter and coated it with di-electric grease to ensure good connection for a year or two?

Did that ever cross your mind?

Not saying it happens…..but I’m not saying it doesn’t either.

Great post Thanks

Well it did cross my mind... however GM installed a new transmission under warranty so I wasn't going to say anything.

Now that I would have to pay, I'm thinking alot more about it.

Again thanks for the info.

I will check the other parts of the ignition system

chcpman

Thanks for that writeup 1fatcat. I haven't been on here much this summer so I haven't gotten to know you, but you seem very knowledgable and helpful when it comes to technical issues. I'll give you a little bit of rundown on my car'* story.

I noticed a slight "surge" or "chuggle" over a year ago when the summer months started to set in. I immediately thought of ignition problems and promptly changed my spark plugs. This didn't affect the symptoms at all, so I changed plug wires as well. This also failed to cure the problem, so I moved on to coils. After 3 brand new MSD 8224s and no relief from the surging, I started to suspect the PCM was going bad. I got a junkyard PCM, which quickly got reprogrammed to an INTENSE Standard PCM, and the problem seemed to go away for a while. However, I now attribute that to a lowering of the outside air temp during the change of the seasons. Somewhere in this timeframe I also cleaned my MAF really well with some QD Electronics Cleaner. As you can expect, this still didn't help.

At this point my mind started to mull over the possibility that the transmission (or at least one of its components) was acting up and causing my problems. My "surging" has never seemed like an ignition issue. Ignition misfires are often quick, jumpy changes in RPM that fluctuate two or three times every second. My "surges" are long changes in the RPM that fluctuate about once every second. It seems like the lulls in engine speed are too slow to be a simple misfire. I firmly believe this issue is TC-related. Not only do I believe it is a fault of the TC or a related component, but I believe it is directly related to some kind of heat build-up. Here'* why:

This spring I went for a very aggressive drive while the air temperature was still in the 50s. I had experienced no surging up to this point in the year, and I did some long runs of WOT acceleration and held speeds in excess of 100mph. After about 10 minutes of this driving I decided to call it quits and head home. I got on the main highway and accelerated lightly up a moderate grade, and suddenly the car started surging like crazy. It freaked me out because I thought I had broken something, but to my surprise the surging subsided after cruising down the road for 20 minutes. The rest of the ride was glassy smooth.

During this run my engine temperature stayed in the normal range, but I would suspect that my tranny temp was highly elevated from all the abuse. I need a good scantool to monitor tranny temps, but that'* beside the point. The high heat seemed to directly cause the surging condition. My suspicions were further confirmed later in the summer when ambient air temps were in the 70s and 80s. I was regularly experiencing surging during long drives and on long hills, so I installed a tranny cooler. I figured that if heat was the problem the surging would either go away or have a reduced effect.

Lo and behold, the tranny cooler made an instant difference. The surging went away completely. In the course of an afternoon, without touching any of the ignition components, the car wasn't affected by heat or hard driving anymore. I believe this is an obvious illustration (at least in my case) where the problem has nothing to do with the ignition system. Changing the temperature of the tranny fluid would have made no difference if the problem was a misfire. The problem was solved by adding auxilliary cooling.

In the few months since then, just as macho_mike predicted, the surging has returned. However, it has only been a problem during the 90-100 degree heat we've been having here in the Midwest. There is something about high tranny temps that make the car surge, so maybe somebody can figure out exactly what'* going on. Yes, I need to get either a tranny temp gauge or a scantool to pinpoint the temps where the surging begins. But please, can someone with extensive technical knowledge analyze my case and conjecture as to what'* going on? I think I've proven beyond a reasonable doubt that we can eliminate the ignition system as the culprit. Or maybe it'* tied into the TPS readings and the inputs from some other temperature sensors. One thing is for sure: it'* not my plugs, wires, or coils. The tranny cooler did something good, but the problem isn't gone. I don't want another "Band-Aid" fix!

Thanks.

1fatcat, again..great write up and I think as we've heard some of it before it will help with most. What is your take on the lack of a secondary tranny cooler on the 65'*? Clearly elevated tranny temps are bad.

Ben.. Good info as well.

Bill, I'm not sure if you were referring to my tranny as a 65, but for the record I have the 4T-60E Light Duty. I don't know if that makes a difference to your diagnosis or not.

Now I'm getting lost.

You put in a tranny cooler, this solved the problem. Then a few months later the problem returned. If the cooler solved the problem was the outside average temperature cooler then when you started seeing the surging again?

When you put in a tranny cooler is it completly removed from the engine coolant? RIght now the tranny cooler and the rad are the same device, basically this should means that the lowest the tranny temperature can get is what temp the engine is running at. If the cooler is removed from the engine coolant system then theoretically the temperature could move lower then the engine coolant temperatue. Perhaps you can get it to cold and have other problems. I guess another obvious question is how much tranny fluid is being pumped around the cooler. You can have the biggest monster cooler but with a small tranny fluid flow your not going to get any cooling effect.
Perhaps there is a tranny cooler that would have it'* own fan and temp switch that would attempt to keep the fluid at a uniform temperature.
Just rambling along trying to see is any of this makes sense to a guru...

We must be getting close to this problem everything seems to be heat realated. Either higher then normal temperatures effecting the fluid viscosity thereby causing some leakage or a device that when it gets to hot in the tranny leaks fluid past and causes problems.
If it was the latter then cooling the fluid down might help.

Exactly what was stated earlier we need to see what temperature the tranny fluid gets to on hot driving days.

New plugs and wires today, also cleaned every sensor on or near the throttle body. Also ripped my rubber boot connecting the throttle body to the air inlet scoop. Now that is a pain. Small tear not a real problem.

Now to go out and test... not holding out to much hope.

CHCPMAN

You're partially right. The radiator contains the stock "tranny cooler" in the sense that it'* a 3-core radiator. There are different sections of it for the engine coolant, A/C refrigerant, and transmission fluid. The tranny is not limited to the same temperatures as the engine coolant because it flows separately from the engine coolant and isn't run through the engine block. The transmission usually runs at a significantly lower temperature than the engine coolant. If your tranny temps are getting up to 180-200 degrees Fahrenheit, you've got big problems.

The tranny seems to get too hot, and thus wears something out that gradually makes the car surge more and more. That'* why the surging comes back in really hot temperatures, even with an auxilliary tranny cooler. Some ambient air temps are so hot that the cooler can't even do enough to keep the TC from surging.

We just need to figure out which part of the tranny is so vulnerable to heat and FIX it :?

That is not how it works. The condenser coil for the AC is completely seperate from the engine cooling system. If you look closely, you'll see the condenser coil is mounted in front of the radiator.

The transmission oil circulates inside the passenger side tank of the radiator. It is both cooled and heated by the engine coolant depending on the season. Typically, a 4T65E will run around 185* in summer which is well within its' design range, though 175* may offer longer life.

Cheers,