Surge at takeoff

[theophile]

'02 V8 sport. Have had it 2 months, and I'm still not sure this is an issue and not simply the way the car is supposed to drive, but here goes anyway. I've noticed what strikes me as an odd behavior when accelerating from a stop. Basically, it feels like the car wants to lunge forward when I give it nominal throttle. At first I just chalked it up to what happens when you go from an inline 4 to a V8--more power. But I haven't "adjusted" yet and I'm starting to think it's not behaving properly.

If I just put it in D5 and let off the brake, it will of course begin moving forward. If I give it gas very slowly and gradually, it feels like there's almost a "dead spot" in the initial travel, where there's no effect, then it gets to the "magic spot" where it lunges forward, and I instinctively back off the accelerator to compensate, before slowly opening it up again. In day-to-day driving, it's become my habit to take off that way--surge forward then immediately let off the gas.

All that said, the force is not as dramatic as the description might make it seem. It's a very slight sensation, but still somehow "not quite right." I don't seem to have any issues at any other speeds or at any shift points, and the car idles smoothly, so I'm hoping it's not an ignition issue.

Now, all that leads to this...

Last week the CEL came on, and the code was P0402 (excessive EGR flow). It stayed on a couple days then the light went out (though the code isn't cleared). I got this code several years ago in a '96 Taurus and couldn't get it to go away until I had replaced the EGR valve and gasket, the DPFE sensor, and the IACV. So I wondered whether this could be related to the "surge" issue. That is, maybe something is amiss in the intake system and that is the root cause of both issues.

My instinct is to take a peek into the TB and maybe spray a bunch of carburetor cleaner into it to see if that helps, but I know these cars are more electronic than any car I've ever owned, and I don't want to screw anything up.

Hoping you folks who know these cars better than I do at this point might have some insight. TIA!

 

[ReMiXeDg]

'02 V8 sport. Have had it 2 months, and I'm still not sure this is an issue and not simply the way the car is supposed to drive, but here goes anyway. I've noticed what strikes me as an odd behavior when accelerating from a stop. Basically, it feels like the car wants to lunge forward when I give it nominal throttle. At first I just chalked it up to what happens when you go from an inline 4 to a V8--more power. But I haven't "adjusted" yet and I'm starting to think it's not behaving properly.

If I just put it in D5 and let off the brake, it will of course begin moving forward. If I give it gas very slowly and gradually, it feels like there's almost a "dead spot" in the initial travel, where there's no effect, then it gets to the "magic spot" where it lunges forward, and I instinctively back off the accelerator to compensate, before slowly opening it up again. In day-to-day driving, it's become my habit to take off that way--surge forward then immediately let off the gas.

All that said, the force is not as dramatic as the description might make it seem. It's a very slight sensation, but still somehow "not quite right." I don't seem to have any issues at any other speeds or at any shift points, and the car idles smoothly, so I'm hoping it's not an ignition issue.

Now, all that leads to this...

Last week the CEL came on, and the code was P0402 (excessive EGR flow). It stayed on a couple days then the light went out (though the code isn't cleared). I got this code several years ago in a '96 Taurus and couldn't get it to go away until I had replaced the EGR valve and gasket, the DPFE sensor, and the IACV. So I wondered whether this could be related to the "surge" issue. That is, maybe something is amiss in the intake system and that is the root cause of both issues.

My instinct is to take a peek into the TB and maybe spray a bunch of carburetor cleaner into it to see if that helps, but I know these cars are more electronic than any car I've ever owned, and I don't want to screw anything up.

Hoping you folks who know these cars better than I do at this point might have some insight. TIA!

first i would like to subscribe to this thread.

secound i had the same code for the egr i got it cleaned and everything then a cat clogged p0405 code coming up cleared the computer its gone now after 100 miles

is it normal for what he's talking about because i think I'm experiencing the same thing but with a ls v6 2002.

 

[joegr]

Are you sure you aren't just feeling the transmission shift?
BTW, the transmission will learn your driving style and come to expect you to lift the throttle every time at that shift. (It'll just make the "issue" worse.)

 

[Telco]

Don't use carb cleaner in there, use throttle body cleaner or electrical component cleaner instead. Carb cleaner can work its way through the seals and eat the electronics attached to the throttle body. You can clean the mass airflow sensor as well, when you do only touch the sensor with the spray. Don't wipe on it because they are delicate.

I could also see you having an off-idle dead spot on the throttle position sensor (assuming the LS engineers didn't come up with a different way of that too) that would make the computer think you were gassing it. This might not show up at any time other than initial takeoff since aside from taking off from a dead stop you wouldn't be expecting power from 0 throttle. When you are moving and go from 0 to whatever, the car is already moving so no lunge.

However, before exploring what might be wrong you should correct what you know is wrong. Excessive EGR flow tells me the EGR is not closing off properly. It may just need cleaning, it may need replacing. If you choose to clean, only move the pintle in and out, don't try doing any twisting on it because that can damage the pintle. If you replace it, replace it with a stock Motorcraft piece and not a generic unit. The generics are one size fit none, and will likely either not fix the problem or cause other problems. I've tried a couple of the generic ones that you have to select a washer to match the car, and wound up returning them to get a factory EGR which would then fix the problem.

 

[joegr]

All very good points. The TPS on the LS is more or less normal. I would add that the excessive flow code could be because of a bad DPFE indicating a higher flow than there really is. It seems like (with Ford anyway) the DPFE is more often the problem than the EGR. On gen II, the DPFE and the EGR valve are all the same assembly anyway. I don't know if that's true for the gen I.

 

[theophile]

Great stuff everyone. Thanks!

This is almost certainly not at a shift point, unless it's supposed to shift into 2nd at ~2 MPH.

Looks like I'm going to clean the TB, the MAF sensor, and the EGR with throttle body cleaner, and replace the DPFE sensor, and see what that does. I could be wrong, but it almost looks as if the LS had the same DPFE sensor as my old Taurus!

 

[theophile]

Yep, they do use the same DPFE sensor, apparently along with every other car Ford has made in recent memory. Which means it's also the part Ford redesigned because the inlet and outlet were too close together if I recall correctly.

 

[FDR]

Great stuff everyone. Thanks!

This is almost certainly not at a shift point, unless it's supposed to shift into 2nd at ~2 MPH.

How about shift to first. I don't know about regular D5, but in the sport's SST on the first gen, 1st is locked out when stopped. It was some EPA garbage about 2nd gear starts. When you hit the gas hard enough from a stop, it will quickly downshift to 1st, resulting in a surge feeling. I don't know if that applies to drive, but I'll check it out later today. I also have an 02 V8 sport.

You could test it to see if its the same feeling. When stopped, put the car in SST. Then hit downshift. It won't shift yet, but the computer will shift into 1st when you hit the gas hard enough (~60%). Do a couple starts like that. The only major difference will be that it will stay in 1st and may buck a little when you lift off as the drivetrain lurches into deceleration. D5 may not need as much throttle to downshift (if it even does that).

I'm sorry if I point you in the wrong direction or if I'm wrong about how D5 may work, but this is an easy way to figure out if you're experiencing a problem or just another "feature"

 

[LS4me]

How about shift to first. I don't know about regular D5, but in the sport's SST on the first gen, 1st is locked out when stopped. It was some EPA garbage about 2nd gear starts. When you hit the gas hard enough from a stop, it will quickly downshift to 1st, resulting in a surge feeling. I don't know if that applies to drive, but I'll check it out later today. I also have an 02 V8 sport.

You could test it to see if its the same feeling. When stopped, put the car in SST. Then hit downshift. It won't shift yet, but the computer will shift into 1st when you hit the gas hard enough (~60%). Do a couple starts like that. The only major difference will be that it will stay in 1st and may buck a little when you lift off as the drivetrain lurches into deceleration. D5 may not need as much throttle to downshift (if it even does that).

I'm sorry if I point you in the wrong direction or if I'm wrong about how D5 may work, but this is an easy way to figure out if you're experiencing a problem or just another "feature"

Doesn't apply to D4 or D5. It's only in SST mode to avoid the Gas Guzzler Tax. The 2nd gens didn't have to run the same mileage regime.

 

[FDR]

Doesn't apply to D4 or D5. It's only in SST mode to avoid the Gas Guzzler Tax. The 2nd gens didn't have to run the same mileage regime.

Alright, I didn't think it applied to drive, but I figured it was easy enough to check if no one else got back to the guy