Auto Repair - Roadshow forum


Car engine Surge

Hey peeps, I'm new here. I have had some car trouble and figured this would be the best place to ask, since my dealership "can't replicate the problem" . So here goes

I drive a 2012 3.7l Ford mustang , it has about 99k miles on it. I'm having some RPM drops when accelerating. I doesn't happen when I floor it from a standstill. It only happens when I floor it once it's in second gear and the RPM drops at around 4000rpm , it drops by about 200rpm and then continues to accelerate fine.
This also happens when accelerating normally ,in 3rd gear at around 2200 rpm.
This effect is more noticeable after a cold start. Once it warms up instead of dropping a couple hundred rpm it (tachometer needle) freezes at 4000rpm and then moves up normally but it is still noticeable in 3rd gear . This is very annoying .
Yesterday I took it to the ford dealership and they charged me 95$ to run engine diagnostics with OBD just to tell me there are no error codes and hence nothing wrong with my car. When I asked the technician to come along with me for a drive (by then it was hot outside and the engine already warm from testing ) the effect wasn't as pronounced and the technician told me it's the torque converter locking up and that's why the RPM surges and that it's for efficiency . Doesn't sound right to me.

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All Answers

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no codes

In reply to: Car engine Surge

A fuel pump and it's fuel pressure isn't sensored. That could account for your problem without creating a code.

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Fuel pressure ,

In reply to: no codes

I too was thinking the same thing , that or a clogged fuel filter ? But I have no tools to check it...any advice? Because taking it to ford they're gonna ask me to pay another 100$ as they declared that nothings wrong the last time

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without proper tools and gauge

In reply to: Fuel pressure ,

It's difficult to impossible to test it.

"It only happens when I floor it once it's in second gear and the RPM drops at around 4000rpm , it drops by about 200rpm and then continues to accelerate fine."

that seems a high rpm for second gear. Used to call that a "flat spot". Instead of fuel pump, I'm thinking the onboard computer is set to expect certain shift range points and you are probably beyond that at 4000 and there's a momentary shift in the programming to compensate. This used to happen on older pre-sensor cars due to timing lag in the distributor, since they had springs that would only allow so much advance in timing.

I don't think you are going to find it. If you want to drive it like a racer, there are replacement computer modules that overcome that, but they aren't "street legal".

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Not just in 2nd gear

In reply to: without proper tools and gauge

it also happens in 3rd gear at 2200 rpm, initially i thought its up shifting to 4th but then i counted gears and it appears to be in the same gear (3rd). after the surge it continues to rev back up higher than 2500rpm before it shifts into 4th, all at the same throttle position.

"replacement computer module"? im confused,So are you suggesting i flash a different tune? or is it a fuel delivery fault as suggested before?

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No, not suggesting something illegal

In reply to: Not just in 2nd gear

And now with more information showing this happens at more than one shift point, it sounds similar to a problem older cars with transmission vacuum modulators aka transmission control modules of that time which controlled shift points in transmissions. Now it's all electronic, but there are still transmission shift control modules even on the newer cars.

[url=[Liter][]=3.7L]Here's some 'race' shifter controllers, just for an example.

In this video, pay attention to "shift solenoid".

Animated diagram of one in action.

Also, there's a class action suit that forced a recall on Ford Transmission Control Modules for Fiesta and Ford models, but I wouldn't be surprised if it should have extended to other models too.

For instance, I had to replace stepper motors in an 2004 Impala and 2005 LeSabre with no recall, yet they used the exact same stepper motors as in some Chevy trucks which did get the recall, but that also was due to a class action and limited to just those models. I was NOT happy. Cost me over $100 for each instrument cluster which I had to send into a repair place.

This transmission recall DOES apply to your car. Take advantage of it.

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In reply to: Not just in 2nd gear

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One more thing to consider

In reply to: Not just in 2nd gear

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Was the last video for a manual?

In reply to: One more thing to consider

I have watched all the videos you linked. Thanks. Also , i looked up any remaining recalls and there are none. Ive taken care of all of them.
My car is an automatic.
Also, the day i took it to ford and back it was much more responsive. its back to its old self again with the surge, did they reset something that made it better initially? and has the PCM relearn been bad? could it be a bad TPS?
Or should i just live with how it is ? Sad

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In reply to: Was the last video for a manual?

Hi; When you mentioned that it happens at the same RPM, I immediately thought of the TPS, also. With an ohmmeter, you can check for a 'dead spot' while sweeping the TPS. Very seldom set a DTC.
Good luck.

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I would take it to a certified transmission place

In reply to: Was the last video for a manual?

They possibly would be better for diagnosing the exact cause than even the dealer garage. There are other things that can cause it like the servos that operate the bands which go around the shift drums, etc.

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In reply to: I would take it to a certified transmission place

I took it to firestone . The mechanic there said it's missing a gear and that it could be a simple fix like flashing the computer or might need a transmission repair . He too suggested I take it to a transmission shop. I will do that in the next few days . Thanks for all the help guys.

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In reply to: Transmission

Can you give us an update on the car and what your transmission specialist said.

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