99 Deville Shudders At Take Off

[bschelle]

My 99 Deville shudders when I take off. It doesn't do it if I feather the gas but if I give it a litle more pedal it shudders. It only does it for a few seconds and then it clears up. FSM says it is probably the inner tri-pot joints. I haven't got under it to look yet but was wondering if it is a tough job. Any other suggestions would be appreciated.

[KHE]

I wouldn't suspect the axles - I'd be looking at the secondary ignition components. Spark plugs are a prime candidate if you have over 100,000 miles on the car (mine had less than 100K). I had a similar issue a couple of years back - the car acted like there was water in the gas or it was starving for fuel on acceleration. It turned out that 4 of the 8 plugs were missing the platinum pad on the ground electrode. A new set of plugs cured the problem.

[bschelle]

I wouldn't suspect the axles - I'd be looking at the secondary ignition components. Spark plugs are a prime candidate if you have over 100,000 miles on the car (mine had less than 100K). I had a similar issue a couple of years back - the car acted like there was water in the gas or it was starving for fuel on acceleration. It turned out that 4 of the 8 plugs were missing the platinum pad on the ground electrode. A new set of plugs cured the problem.

This isn't a miss. I can feel the vibration. I have about 40,000 on this set of plugs.

[bschelle]

New plugs made no difference. Replaced the engine struts (dog bones) and it helped a little. Next is a front motor mount. Ever replace one? What are the shortcuts? FSM says to remove fans and lift up the engine to do it.

[Caddynut]

could it be a transmission problem? My damned '04 Explorer does the same thing and I know those have transmission problems.

[bschelle]

could it be a transmission problem? My damned '04 Explorer does the same thing and I know those have transmission problems.

Jeeez, I hope not!

[Cadillac Jim]

could it be a transmission problem? My damned '04 Explorer does the same thing and I know those have transmission problems.

Unlikely. The 4T80E doesn't seem to have many internal problems. The only things I have seen posted here are the TCC, solenoids, and electrical problems like the speed sensor, and most of those are resolved by servicing electrical parts and speed sensors. One guy with 220,000 miles on his car recently asked about remanufactured transmissions, but he didn't say why. Have you had the transmission serviced (not flushed) every 30,000 miles or so?

My money is on plug wires, with plugs a close second. After that, I think the coils might be worth checking for resistance and output. It conceivably could be crank or cam sensors. Do you have any OBD II codes to report?

[bschelle]

could it be a transmission problem? My damned '04 Explorer does the same thing and I know those have transmission problems.

Unlikely. The 4T80E doesn't seem to have many internal problems. The only things I have seen posted here are the TCC, solenoids, and electrical problems like the speed sensor, and most of those are resolved by servicing electrical parts and speed sensors. One guy with 220,000 miles on his car recently asked about remanufactured transmissions, but he didn't say why. Have you had the transmission serviced (not flushed) every 30,000 miles or so?

My money is on plug wires, with plugs a close second. After that, I think the coils might be worth checking for resistance and output. It conceivably could be crank or cam sensors. Do you have any OBD II codes to report?

It's not throwing any codes other then P0741. I changed the plugs without any effect, but when I changed the dog bone mounts I am able to accelerate heavier but it still makes the noise. It doesn't feel or sound like a engine miss to me, but I am not an expierienced mechanic either.

[BodybyFisher]

Explain "shudders" in more detail, I am wondering if its related to the P0741 code

[98deville]

spark plugs maybe

[bschelle]

The best way I can describe it is it reminds of my 67 Nova when it would bottom out and the drive shaft would rub on the body but not as severe. If I take off real slow it doesn't do it. I can't make it do it over about 20 mph. The P0741 has been on for about 45,000 miles.

[BodybyFisher]

The best way I can describe it is it reminds of my 67 Nova when it would bottom out and the drive shaft would rub on the body but not as severe. If I take off real slow it doesn't do it. I can't make it do it over about 20 mph. The P0741 has been on for about 45,000 miles.

So I gather that you are sure this is not ignition related. It seems you feel its mechanical, ie engine mounts or something grounding out mechanically. Its odd however that you can't make it happen above 20 mph.

I have been wanting to say, check your ignition wires.

Try having a helper (that you trust) raise the RPM in drive with the brakes on HARD while you look under the hood to see if something is shifting..

[bschelle]

It's fixed!! My brother suggested I adjust the top engine struts and that might help. It didn't. I finally replaced the front engine mount and the noise and vibration are gone. When I tried adjusting the struts it stressed the exhaust and the pipe broke just behind the converter. It was a rusty joint to begin with and I am sure it was about to go sooner or later. I tried removing the mount from the bottom but I couldn't get it out. I then removed the right cooling fan and loosened the left one and I got it out from the top. As for the pipe I used an adapter to connect the two pieces back together. Hopefully I won't have to do this for another 140,000 miles. Now I have a constant noise from what I think is the drivers side front wheel. It changes pitch as the speed increases. I am starting a new thread with that problem.

[BodybyFisher]

It's fixed!! My brother suggested I adjust the top engine struts and that might help. It didn't. I finally replaced the front engine mount and the noise and vibration are gone. When I tried adjusting the struts it stressed the exhaust and the pipe broke just behind the converter. It was a rusty joint to begin with and I am sure it was about to go sooner or later. I tried removing the mount from the bottom but I couldn't get it out. I then removed the right cooling fan and loosened the left one and I got it out from the top. As for the pipe I used an adapter to connect the two pieces back together. Hopefully I won't have to do this for another 140,000 miles. Now I have a constant noise from what I think is the drivers side front wheel. It changes pitch as the speed increases. I am starting a new thread with that problem.

What was wrong with the mount did it separate? I have a thump on take off, I was curious what you found, Thanks, Mike

[bschelle]

It was dry rotted and the fluid was gone but still in one piece. I didn't have a thump at take off, it was a repeating rapping like sound. I think it was the exhaust banging on the two small supports bars that are right under the exhaust after the converter and just after the resonator.