So awhile ago I posted about my engine acting funny once reaching a certain speed. then after a while of not driving on the highway, i noticed that the engine did not act up the next time I had to drive on the highway. Its been a long time since ive taken my car up to highway speeds (over 55) since we take my wifes car when we drive anywhere. ..until yesterday

Yesterday I drove to meet my dad. My car acting just fine until i reached 70mph... and the engine started up again. Heres the details: The second I reached 70 (my rpms are at 3000) my engine starts to "pulse". the best way i can explain it is remember back to when you were in high school/college and you in the most boring class and kept nodding off. your head would begin to lower and then you shot back up in a split second... just like that!!! the time between the pulses is not consistant but it is consistant at that speed. I found out that this continued until i reach 80 and the pulsing started to stop. if i dropped below 70, nothing happened at all. but everytime, the second i reached 70 it started pulsing again.

also symptom: ONLY WHEN THE PULSING is happening... i noticed my temp gauge drop a little each time it pulses. I dont know why or how the two could be related but i need some ideas.

Has anyone experienced anything like this? Have any idea what wouold cause this? I just need some help. I'm worried that it could be somehow related to pressure in the block/head???

please help? and a "thank you" in advance

no one, huh...

please?

My friend had a problem like this, he changed the fuel pump and it stopped, don't know if there is anyway they are related though.

my car did something similar and it was the IAT sensor but then again as far as i know it would be at all speeds

yea thats one of the confusing things for me... its only at those particular speeds. i wonder if some of ..that cleaner stuff that i cant think of the name of at the moment, would help any if there is a clog of some sort?

Is your torque converter locking.

By the pulsing you described it sounds like your RPM is going up and down, yet you're holding the same speed. Sounds to me like your torque converter isn't locking, or rather staying locked when the PCM commands it to be. (Note, my Trailblazer does this same thing and I believe it to be the converter because it only does it at speeds it should lock in at). Or possibly the transmission is starting to slip out.

Maybe the problem isn't the engine, but rather the tranny. How long since it's got fresh fluid and filter?





www.gmscf.com

its been over a year ago since the tranny flush, but not a lot of miles as i only drive it to work and since ive been out of work for the past 6 months... if i had to ballpark it i say between 10-20k miles since the flush, but definately closer to the 10k side.

no ones mentioned the torque converter idea.... but shouldnt that lock more often than just at 70mph/3200 rpm range??

god i hope its not my tranny...

You can have an ignition problem too. Being at a certain speed can be related to the load on the engine. You don't feel it when you are getting up to speed because you don't spend enough time at the critical point.

I'd check the spark plugs and the cables. Putting new ones wouldn't be a bad idea if the other ones are old.


Gilles
2.3 Ho

i tried messin around a bit with the car.... put it in 2 and when im at abouot 40mph, the rpms are in the same place as eariler described and the engine does NOT act the same way. the only thing thave happens is the temp gauge drops when its around 3-3300 rpms....

so perhaps i have two things going on. something that causes my temp gauges to drop when it hit 3-3300rpms and another that happens when i get up to 70mph.

any more ideas on the seperate issues?

The temp dropping when you have this problem is what's really odd. Does it bob up and down quickly with the pulsing you mentioned before, or does the temperature just drop when it start to pulse?

I'm thinking it might possibly be a water pump issue. Do you notice any odd noises when it's happening? If the bearing in the water pump is bad, it's possible that at certain RPMs it's almost seizing up, causing the belt to drag. That's the only thing that I can think of that would cause both things simultaneously. I've never seen a water pump get quite that bad, but it's the only thing I can think of that might fit the issues.

i wouldnt say it drops to 0 instantly.... it goes down a bit and slowly back up. no strange noises (that i hear that i would call strange)

I would really check out your water pump. You should be able to tell if the bearing is really bad by taking the belt off and trying to wiggle the pulley on the pump. If it's got play in it, I'd try replacing it.

is there a how too for changing the belt on a 99 2200??