Stumble Sensation in Ovedrive

[kens96]

Just had the plugs and wire changed out. The needed it from what was left on the plugs. the Eldo is driviing better but I'm still getting that feeling like a fish tugging on a line when in overdrive. The dealer scanned and there are no more misses, he also tried an ignition control module and it made no difference. I'm startng to lean towards a solenoid in the transmission or even a bad motor/ tranny mount.

Any thoughts?

[med]

Just had the plugs and wire changed out. The needed it from what was left on the plugs. the Eldo is driviing better but I'm still getting that feeling like a fish tugging on a line when in overdrive. The dealer scanned and there are no more misses, he also tried an ignition control module and it made no difference. I'm startng to lean towards a solenoid in the transmission or even a bad motor/ tranny mount.

Any thoughts?

I get pretty much the same thing after everthing is warmed up. It's between overdrive and a lower gear sometimes (like when I'm on cruise and she's taking on a hill and needs to kick down). It feels like a bad tranny/motor mount, TC clutch, or solenoid. I don't get it unless I have a lot of miles driven and car is completely warmed up --> never have it in the city only the highway. It's a slight bucking (two or three times). I hope someone can chime in on this as my car is pretty old and I think a lot of mounts could stand to be changed - but then again I don't like fixing something that wasn't broke in the first place.

[BodybyFisher]

Ken, I am out now, but I have wanted to look to see if we (OBD2ers) can do a snap shot to record what is going on at the time of the issue, Ill let you know what I find out.

This only happens in overdrive? Does it happen all the time can you recreate it?

[kens96]

All I have to do is try to maintain a steady speed around 40MPH or higher and or set the cruise control and it doesn't take long before you feel the "tug". It is random, but happens enough where you can show someone what it is doing. Doesn't happen under acceleration and I only feel it in fourth gear. Don't see a change or jump in RPM or in MPH when it happens. There are no codes !!!

Something else I noticed tonight is that when the car is coming to a stop with the brakes on it feels like the engine is settling back into the cradle. a mild clunk through the floorboard.That's why I asked if it could be an engine mount. My guess is leaning towards a stuck solenoid not letting the car go into neutral or a coasting situation or a mount that is letting the engine settle or bump when there is no load on it. To note I replaced the front mount 3 years ago and replaced the torque struts last week.

Thanks in advance for the help.

[BodybyFisher]

Ken, I just wrote Autotap an email. I believe that my Autotap diagnostic reader provides enhanced GM parameters and that it can return the following TCC details,

TCC Apply Time

TCC Duty Cycle

TCC Mode

TCC Pressure Commanded

TCC PWM Duty Cycle

TCC Ramp Off Time

TCC Slip

TCC Slip Speed

TCS Circuit History

TCS Circuit Status

If I can determine that the Autotap can provide that information, I will talk to you about sending my Autotap to you for you to record the parameters when the stumble occurs. This might highlight what is responsible for this stumble.

I am also going to look into how the SNAPSHOT works and whether it will provide any useful information. It is sounding like a momentary drop out of lock up, if it is electrical it might be evident.

Do check your engine mounts, maybe your engine is shifting, when lockup occurs. By the way, how often will this stumble occur, more than once when you exceed 41?

This will take a few days I have an email into Autotap asking them if I have the GM enhanced parameters now that I upgraded to their version 3.1 and how I get the parameters.

Check this list of enhanced parameters that the autotap is capable of reading

<a href="http://www.autotap.com/enhanced_parameters_gm.asp" target="_blank">http://www.autotap.com/enhanced_parameters_gm.asp</a>

One more thing, as you know when you tap your brake, the tranny will come out of OD, this could also be a bad switch. This is just a guess, because I don't know if a bad TCC off switch actuated by the brake pedal would set a code. But this is something to think about. I need to look at the manual to see if contacts are opening or closing when you tap your brake relative to the TCC.

[BodybyFisher]

Check this article link out

Autotap will provide this informaton also

Fuel Trim Cell

Fuel Trim Cell Bank 1

Fuel Trim Cell Bank 2

Fuel Trim Index

Short Term Fuel Trim Bank 1

Short Term Fuel Trim Bank 1

Short Term Fuel Trim Bank 2

Short Term Fuel Trim Bank 2

<a href="http://en.allexperts.com/q/Pontiac-Repair-...-grand-prix.htm" target="_blank">http://en.allexperts.com/q/Pontiac-Repair-...-grand-prix.htm</a>

[kens96]

Thanks Mike,

I will try tapping on the brake to see what the effect is and to see if I can get a code. To answer your, question it does this throughout the steady state driving at random. It is just an insantaneous tug that you feel while the car is maintianing a steady speed. I had the tranny rebuilt 35K ago and replaced the TCC Module about 2 years ago. I left a message with the tranny shop to call me Monday. They have an excellent reputation and I've brought all my cars to them for tranny service. They might have the scanner to pull the codes and will be able to check the engine mounts. That Auto Tap looks like a great tool. Should look at adding it to the toolbox.

[kens96]

Tried tapping the brake when it "bites" in fourth gear. Then I tried driving with the cruise on in third gerar and I got a more pronounced "chuggle." Starting to lean towards fuel delivery. or breaking down electronics. Cleaned the throttle body and I'm going to road ttest now.

Think it might be a trip to the Caddy Dealer for a full scan.

Thoughts?

[Jan Olsson]

Tried tapping the brake when it "bites" in fourth gear. Then I tried driving with the cruise on in third gerar and I got a more pronounced "chuggle." Starting to lean towards fuel delivery. or breaking down electronics. Cleaned the throttle body and I'm going to road ttest now.

Think it might be a trip to the Caddy Dealer for a full scan.

Thoughts?

Have you cleaned the EGR system? Have you changed and or cleaned something recently and not disconnected the battery? It takes longer for the electronics to relearn if you don't disconnect the battery after a job that requires relearning? Hmm, do you have the badyears on?

Had the same sensation with my -93 STS. A good cleaning of the EGR solved part of the problem. The other half of the problem was that my spark wires was "loose" on the spark plug ends. Not a snug fit..

This is slightly off topic but you might get helped anyway..

On my -02 STS I was convinced that my halfshafts were shot because the vibrations would vary in speed but it was only the dreaded 75 mph shake (and in other speeds too)

The funny thing about my OEM badyears was that they sometimes felt smooth as silk and sometimes the whole car would shake, the steering wheel would wander from left to right, the rear suspension would fish-tale like if the shocks were shot (propably due to the suspension trying to soften out the shakes), the shift quality stinked (hunting for gears etc etc)

and it seemed like the engine had a chuggle...

New Michelin Primacy HP solved that. I DID want to get them road force balanced but there are only a few shops here in Sweden with that eguipment. Luckily an ordinary dynamic balancing cured 95% of all shakes. It still feels a little in some speeds and temperatures but I can live with that. Not worser than any Volvo I have had anyway

[navion]

My '94 SLS had the same symptoms. Part of it was traced to corrosion in the high tension terminals in the coil packs.

Apparently, the corrosion was just enough to cause an intermittent miss on one or more cylinders.

On my car the problem was most pronounced at 50 to 55 MPH. It would lessen with a slight application of throttle or a slight decrease of throttle. But if you tried to hold a steady speed, then it became more pronounced.

Chasing this chronic problem made me prematurely bald!

I finally talked to an ex Caddy mechanic who told me about the coil pack corrosion problem. After cleaning the terminals, the problem was greatly reduced, but not eliminated completely.

The ex Caddy mech suggested that the rest of the problem could be bad wires. I suppose that it is possible, The wires were about 18 months old. But before I replaced them, I traded it off for a '03 SLS.

Britt

[kens96]

Just came back after cleaning the throttle body and it is running much better! Still get a little chuggle in 3rd like there is water in the gas and don't feel anything in 4th anymore.

I did disconnect the MAF to clean the TB so I wonder if that tripped the computer. I ran the engine and fogged the TB with cleaner while goosing the throttle to keep it running with the MAF disconnected. Did get a check engine and service emmission code. Cleared them and nothing has come back.

We just started receiving gas at Shell with up to 10% ethanol. Could that contribute to the issue? Put some Prestone system cleaner in the tank and I'm now leaning toward running it for awhile to see what happens.

Should I disconnect the battery after a wire and plug change? Does the PC retain info from the old plugs and wires?

No "Badyears" on the car wearing Michelin Destiny. Got tired of replacing the higher rated tires every 3 years.

[kens96]

Disconnected the battery to clear the computer. Added a can of Prestone Fuel treatment. Drove it to work today and it is much better but still giving me an occasional tug. I'm waiting for the tranny place to call me and will see where we go next.

[BodybyFisher]

Just came back after cleaning the throttle body and it is running much better! Still get a little chuggle in 3rd like there is water in the gas and don't feel anything in 4th anymore.

I did disconnect the MAF to clean the TB so I wonder if that tripped the computer. I ran the engine and fogged the TB with cleaner while goosing the throttle to keep it running with the MAF disconnected. Did get a check engine and service emmission code. Cleared them and nothing has come back.

We just started receiving gas at Shell with up to 10% ethanol. Could that contribute to the issue? Put some Prestone system cleaner in the tank and I'm now leaning toward running it for awhile to see what happens.

Should I disconnect the battery after a wire and plug change? Does the PC retain info from the old plugs and wires?

No "Badyears" on the car wearing Michelin Destiny. Got tired of replacing the higher rated tires every 3 years.

I am surprised that cleaning the TB would improve this. I am not sure how cleaning the TB, which regulates air would improved a lean condition, I would think that cleaning the throttle body would make a lean condition worse. If it were seriously lean, you would set a code.

Did you look at the coils and clean the terminals? The plugs and wires were replaced, so the thought of oil pooling in the plug port causing a misfire is out.

Mike D is having a similar problem and he has blamed it on a CAM lobe.

I wonder if you have a valve that is caked with carbon that is interfering with flow. Have you done the WOT procedure to clean out the combustion chambers and the valves? The WOT procedure is not just WOTs it involves heavy deceleration in second gear creating a high vacuum condtion that sucks carbon out. When you do a WOT is your exhaust throwing out heavy smoke/dirt?

Do you hear any valve train ticks? Could you have a lifter that is not filling up?

[kens96]

Have done the WOT (that's why I was asking about the motor mounts ) Exhaust is clean now. I will try to clean the terminals. I am guessing you mean the clip on connectors that go to the coil pack holder. No valve train ticks..engine is solid and idles and runs strong. Still hard to tell if it is electrical or mechanical. Any chance a flakey FPR would give me these symptons? How hard is it to replace? Also, Would the ethanol give me these symptoms? It reminds me of havinq water in the tank like when I lived up on Long Island and kept dry gas in the trunk for every fill up.

[lothos]

Any chance a flakey FPR would give me these symptons? How hard is it to replace?

The FPR is really easy to change. If you follow the fuel rail around to the end, there's a black cap covering a valve that looks like an oversized tire pressure stem. Take the cap off, use some paper towels, and press the needle to relieve pressure. Gas will spray out. The FPR is on the other side of the rail, by the firewall, and is held on with a clamp. Mine looks like an "A" shaped bracket that slides out, but I think the newer design has a C looking clamp. Take the clamp off and it comes right off. Make sure you get the old O rings out. Stick the new one on, and clamp it back up.

Mine was 60 bucks but I think the FPR for the 1996 is around 45 from RockAuto.com. There's also a seal kit to replace the insides but I opted to get the updated FPR instead of replacing the seals on my 1st design FPR.

I believe the FPR can cause stumbling, and that's why I'm replacing mine. Although it hasn't happened for a while, my STS completely fell on it's face twice when I tried giving it gas.

[BodybyFisher]

So you have done the procedure where you decelerate from 70 down to 40 in second gear? (ten times a session?).

I am going to post the Autotap export that I ran yesterday. I was able to record about 60 different parameters and play them back and export it to an Excel spread sheet. You can not believe how much I was able to monitor and record. I am curious how this info would help diagnosing these types of problems

[navion]

Have done the WOT (that's why I was asking about the motor mounts ) Exhaust is clean now. I will try to clean the terminals. I am guessing you mean the clip on connectors that go to the coil pack holder. No valve train ticks..engine is solid and idles and runs strong. Still hard to tell if it is electrical or mechanical. Any chance a flakey FPR would give me these symptons? How hard is it to replace? Also, Would the ethanol give me these symptoms? It reminds me of havinq water in the tank like when I lived up on Long Island and kept dry gas in the trunk for every fill up.

Actually, the high tension (High voltage) terminals where the spark plug wires connect to the coil packs is where we found the corrosion in mine. You need to clean down inside the receptacle. You can use a pencil & a small piece of Scotch Brite. Be sure to blow the residue out with clean air when finished.

Britt

[kens96]

I haven't done the deceleration 10 times, only 2x up to 70 and 2 down to 40mph at a time. Don't see any trailing smoke after the second time.

What do you think about the ethanol concern? Real or will the engine PCM compensate for it?

[BodybyFisher]

I haven't done the deceleration 10 times, only 2x up to 70 and 2 down to 40mph at a time. Don't see any trailing smoke after the second time.

What do you think about the ethanol concern? Real or will the engine PCM compensate for it?

I don't think the ethanol is causing this, we all would be complaining.

[navion]

Mike,

What year did the switch to "Coil On Plug" take place?

Britt

[MIke D]

2000 or 2001....

[kens96]

Dropped the car at the tranny place today just to make sure that it is or is not the transmission. Will know later today what they find. I suspect they will say it is okay but needs new fluid with 35K on the rebuild.

Maybe getting ultra sensitive. Notice a hesitation from a dead stop gets better when the car is warm but its still there. Had the fuel rail recall done about 2 years ago. Found out they don't replace the FPR when they do the recall. Last week we smelled raw fuel sitting at a light but blamed it on the car in front of us. No change in idle when this happened. Haven't smelled it again. Any chance I have a flakey FPR?

[BodybyFisher]

Dropped the car at the tranny place today just to make sure that it is or is not the transmission. Will know later today what they find. I suspect they will say it is okay but needs new fluid with 35K on the rebuild.

Maybe getting ultra sensitive. Notice a hesitation from a dead stop gets better when the car is warm but its still there. Had the fuel rail recall done about 2 years ago. Found out they don't replace the FPR when they do the recall. Last week we smelled raw fuel sitting at a light but blamed it on the car in front of us. No change in idle when this happened. Haven't smelled it again. Any chance I have a flakey FPR?

I would think that a bad fuel pressure regulator would create problems before 41 mph, at 41 mph the engine fuel demand decreases. If anything, I would look at the fuel pump performance, but again, why after 41 mph is your problem occuring?

See what comes out of this inspection today from your tranny shop, maybe its is something mechanical

[kens96]

Thanks Mike,

That's why I was asking about ther hesitation from a stop. Kind of bogs down through the first few MPH under load and then picks up. If it were an older car I would say it feels like the points gap was off or a float was stuck in the low position. Remember those days... repairs were easier to diagnose.

[navion]

Thanks Mike,

That's why I was asking about ther hesitation from a stop. Kind of bogs down through the first few MPH under load and then picks up. If it were an older car I would say it feels like the points gap was off or a float was stuck in the low position. Remember those days... repairs were easier to diagnose.

I'll add a bad accelerator pump to the list of causes in the days of carburetors.

Thinking along those lines leads me to ask about the fuel filter. Has it been changed lately? Even if it has, you may have gotten a bad tank of gas or fueled when a tank was just filled, thus stirring up the sediment & pumping it into your tank.

Britt