Davyboy
Full Access Member
Okay I'm going to explain exactly what happened, then what I believe is the problem etc.
First What Happened:
I was driving on the highway, going 110 (KMH, about 70MPH I believe) and when I started to go up a hill, my truck (1994 yukon) shifted out of overdrive and the Tach needle rapidly began to bounce between 3000RPM and 3500RPM, and I lost pretty much all my power as the next second I looked at my speed which had dropped to about 90KMH (just about 55MPH). Now I tapped the brakes, and it shifted back into OD and there was no problem, slowly accelerated back up to highway speed and all was good until the next hill. Then once again same problem, only this time check engine light came on as I was nearing the top of the hill, this stayed on for about 20 seconds after I got it back into OD and sitting at a normal idle.
Needless to say after this I turned around (30 min into an hour and a half drive) and drove back home. I remembered that something similar had happened once or twice driving in the city (massively hard acceleration to the point of redline, (from when I just got the truck and was having fun going to a big vehicle from a small cavalier)). So I tried driving around, and it drives perfectly fine at RPM of less than 2500, but anything over 2500RPM the tach bounces and even though it seems to increase and the speed increases, the engine itself sounds as though it bogs at 2500RPM and doesn't sound like its revving higher. Now the reason I didn't pay attention to this, is because with mileage of 12MPG in the city, I don't like to drive the vehicle hard, and the way I accelerate it usually shifts at about 2100RPM, that and I havn't driven on the highway in probably almost a month and a half.
So that is my current situation.
With that being said, here were mine and travis's (not a forum member) assumptions of what could be wrong with it, and what had been done (without knowledge of this problem)
Ones not believed to be cause after discussion:
1. Clogged Air Filter (replaced 2 months ago)
2. Fouled Spark Plugs/Bad Ignition system (dismissed idea as if that were the case would be happening at all RPM and at idle)
3. Dirty Injectors (had run seafoam through engine and in fuel so shouldn't be the case)
Probable Causes
1. O2 sensor (have no idea when would have been replaced last)
2. MAP sensor (could also be dead)
3. MAF sensor (again could be a problem)
4. EGR valve (what I am believing is at least part of the cause) (have ran vehicle, disconnected vacuum line (nothing), plugged vacuum line (nothing), plugged where vacuum line connects (nothing)) by nothing I mean no change to engine at all.
Any recommendations, going to try driving with the vacuum line disconnected from the EGR valve tonight and see if that solves anything.
Any other recommendations for other possible causes, or solutions would be greatly appreciated.
First What Happened:
I was driving on the highway, going 110 (KMH, about 70MPH I believe) and when I started to go up a hill, my truck (1994 yukon) shifted out of overdrive and the Tach needle rapidly began to bounce between 3000RPM and 3500RPM, and I lost pretty much all my power as the next second I looked at my speed which had dropped to about 90KMH (just about 55MPH). Now I tapped the brakes, and it shifted back into OD and there was no problem, slowly accelerated back up to highway speed and all was good until the next hill. Then once again same problem, only this time check engine light came on as I was nearing the top of the hill, this stayed on for about 20 seconds after I got it back into OD and sitting at a normal idle.
Needless to say after this I turned around (30 min into an hour and a half drive) and drove back home. I remembered that something similar had happened once or twice driving in the city (massively hard acceleration to the point of redline, (from when I just got the truck and was having fun going to a big vehicle from a small cavalier)). So I tried driving around, and it drives perfectly fine at RPM of less than 2500, but anything over 2500RPM the tach bounces and even though it seems to increase and the speed increases, the engine itself sounds as though it bogs at 2500RPM and doesn't sound like its revving higher. Now the reason I didn't pay attention to this, is because with mileage of 12MPG in the city, I don't like to drive the vehicle hard, and the way I accelerate it usually shifts at about 2100RPM, that and I havn't driven on the highway in probably almost a month and a half.
So that is my current situation.
With that being said, here were mine and travis's (not a forum member) assumptions of what could be wrong with it, and what had been done (without knowledge of this problem)
Ones not believed to be cause after discussion:
1. Clogged Air Filter (replaced 2 months ago)
2. Fouled Spark Plugs/Bad Ignition system (dismissed idea as if that were the case would be happening at all RPM and at idle)
3. Dirty Injectors (had run seafoam through engine and in fuel so shouldn't be the case)
Probable Causes
1. O2 sensor (have no idea when would have been replaced last)
2. MAP sensor (could also be dead)
3. MAF sensor (again could be a problem)
4. EGR valve (what I am believing is at least part of the cause) (have ran vehicle, disconnected vacuum line (nothing), plugged vacuum line (nothing), plugged where vacuum line connects (nothing)) by nothing I mean no change to engine at all.
Any recommendations, going to try driving with the vacuum line disconnected from the EGR valve tonight and see if that solves anything.
Any other recommendations for other possible causes, or solutions would be greatly appreciated.
