intermittent loss of acceleration

[rhauptschein]

I have a problem related to intermittent loss of acceleration this weekend. There are times when hitting the gas pedal, car would take awhile before the acceleration would kick in. Coincidentally or not, prior to this, I was on a dirt road and when turning around k-turn, it felt like I hit a rock on the bottom of the car. I was able to drive 90 minutes back home and reach normal speeds of 60mph, but again, had this intermittent delay of acceleration. Local mechanic looked at bottom of car on rack but did not visibly anything obvious. Thoughts, suggestions ?

[pbierre]

When's the last time you put in spark plugs? How old are your coil packs? Air filter?

When you're parked, how fast can you build RPMs? If it's got a lag, I'd be viewing traces on engine diagnostics, looking for:
- low fuel pressure
- lag in Mass AirFlow signal
- lag in throttle position


If the low acceleration only occurs when driving, it could be a problem in drivetrain. Monitor your fuel mileage for any decrease.

[rhauptschein]

is loss or compromise of computer communication to the ECM possible here ?

[rhauptschein]

When's the last time you put in spark plugs? How old are your coil packs? Air filter?

When you're parked, how fast can you build RPMs? If it's got a lag, I'd be viewing traces on engine diagnostics, looking for:
- low fuel pressure
- lag in Mass AirFlow signal
- lag in throttle position


If the low acceleration only occurs when driving, it could be a problem in drivetrain. Monitor your fuel mileage for any decrease.

thanks, pbierre; do you think any, all, or none of your possibilities are related to that under the car hit I described in OP ?

[UCrazyKid]

Fuel line or fuel filter come to mind when I hear about things under the car getting hit and it resulting in engine hesitation.

[pbierre]

thanks, pbierre; do you think any, all, or none of your possibilities are related to that under the car hit I described in OP ?

How does the engine do in P or N? racing up the RPMs....any lag?

There's a possibility that the rock hit the drive train (angle gear, prop shaft, Haldex-rear-differential) and put it out of alignment. That's why I suggested evaluating the engine response
while parked in P, and if it's good, monitoring fuel mileage. If the drive-train got banged up/misaligned, you should be seeing a loss of gas mileage.

Another way to evaluate drive train is to put her in neutral (engine off), and jack up either rear wheel, then rotate it manually. It should turn without much resistance and no squeals/grinding. Then, evaluate the other rear wheel the same way.

If you think the front-end got whacked, do the same wheel-resistance tests on the fronts ( in N).

[pbierre]

is loss or compromise of computer communication to the ECM possible here ?

Those are detected and reported at the dashboard console with a Check Engine alert.